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The evolution of territoriality in butterflies

Preface

In The descent of man, and selection in relation to sex (1871) Charles Darwin devoted a

chapter to butterflies and moths in order to build up a body of facts and cases to support the

theory of evolution through sexual selection. He gave plenty of examples of differences in

coloration between males and females, and explained this by intersexual selection via female

choice, but he also reflected on intrasexual selection through male-male conflicts:

“Although butterflies are such weak and fragile creatures, they are

pugnacious, and an Emperor butterfly has been captured with the tips

of its wings broken from a conflict with another male.” -Charles Darwin (1871)

Darwin was not only one of the first to describe male-male contests in butterflies, but was

also the first to give a possible explanation for the origin and maintenance of such peculiar

behaviour. In fact, Darwin refers to the naturalist Cuthbert Collingwood who described

frequent contests between butterfly males in Borneo, on a scientific voyage in 1866-1867.

Collingwood (1868) expresses his frustration over the troubles to capture unharmed

specimens as he writes:

“Another source of disappointment arose from the fact that not

infrequent, when one thought oneself fortunate in capturing a fine

insect, after carefully disentangling it from the net, its wings turned

out to be so torn and rubbed as to render it almost useless, except

indeed as a decoy. This circumstance is due, I imagine, partly to their

frequent battles with one another, in which they whirl round each

other with the greatest rapidity, and appear to be incited by the

greatest ferocity...” -Cuthbert Collingwood (1868)

Ever since Darwin‟s and Collingwood‟s time, researchers and naturalists have recorded and

studied interactions between males of butterflies. A noticeable part of their behaviour is also

that males often are exceptionally faithful to specific patches, which they frequently guard

from intruding males via aerial flight disputes, just like the ones described by Collingwood

(1868). But despite numerous publications and excellent field studies over decades, there are

a number of parts concerning the evolution of territorial behaviour in butterflies that have

never been thoroughly investigated. There are also parts of territorial behaviour in butterflies

that have received a lot of scientific attention, but that still puzzle researchers today. The aim

of this thesis is to investigate the parts of territorial behaviour in butterflies that are still

largely unknown, and thereby to shed new light on the questions that despite earlier studies,

remain unanswered.

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Territoriality and mating success

Resources are not expected to be randomly distributed in the environment (Parker 1974) and

selection will favour animals to search where the resources are concentrated. But what are the

resources? In vertebrates the defended resources are sites associated with reproduction or

areas that relate to both feeding and reproduction, i.e. a “home range” where both sexes

maintain all activities, including reproduction. In insects, a vast majority of the defended

resources relates to mating opportunities (Baker 1983). If receptive mates are patchily

distributed in the environment it will be favourable to search in areas where the probability of

encountering receptive mates is particularly high.

In butterflies, the way mates find each other can be divided into two categories: “perching”

and “patrolling” (Scott 1974; Wiklund 2003). Males of patrolling species spend most of their

time on the wing and actively search for receptive females. This strategy implies continuous

flight, stopping only for feeding or when weather conditions make it difficult to fly. In a

patrolling species the male typically detects females while he is flying, whereupon the male

approaches the female and courts her. In perching species, the male remains stationary and

applies a sit-and-wait tactic, resting at some vantage point, waiting for females to fly by. Here

the female is the active and mobile part and if the female flies into the visual field of a

perching male, the male will take off from the perching site and investigate the female. The

couple will eventually alight whereupon the male starts his courtship ritual. The areas used by

males as perching sites are often well defined and may correlate to some resource utilised by

females, such as larval host-plants (Baker 1972; Courtney & Parker 1985; Rosenberg &

Enquist 1991; Lederhouse et al. 1992) or female food resources (Suzuki 1976; Fischer &

Fiedler 2001). However, areas used as perching sites may also lack any obvious correlation to

female resources and consist of some topographical or physical structure such as gullies

(Cordero & Soberon 1990), elevations and hilltops (Shields 1967; Lederhouse 1982; Alcock

1987) or trees and bushes (Wickman 1985a). Whatever the perching site may be, it is always

expected to have a high flow of receptive females passing by.

Males of perching species are often exceptionally faithful to the perching sites and will

attempt to exclude other males from the area. Consequently, males of perching species are

often defined as territorial. The territories are thought to serve as a rendezvous place where

the sexes meet and are expected to be located in areas where the probability to encounter

females is particularly high. Consequently, territory residency is assumed to be correlated

with high mating success. However, there are few studies that give empirical support for such

a prediction (although see Wickman 1985b), and the consensus that territories are used as

rendezvous sites is largely based on circumstantial evidence. In paper I we wanted to

empirically test the hypothesis that territory residency in butterflies is correlated to high

mating success. This would shed new light on the evolution of territoriality in butterflies,

since higher mating success for territory owners implies a greater reproductive output and

selection for such behaviour.

We used the speckled wood butterfly (Pararge aegeria) as a model species (figure 1a). P.

aegeria is one of the most frequently used species for studies in butterflies. Over the last

decades it has become something of a model species in butterfly research and used in studies

on behaviour (e.g. Davies 1978; Wickman & Wiklund 1983; Shreeve 1984, 1986, 1987; Van

Dyck et al. 1997a,b; Stutt & Willmer 1998; Kemp & Wiklund 2004; Kemp et al. 2006a,b),

life history traits (e.g. Gotthard et al. 1994; Berger et al. 2008; Gotthard & Berger 2010) and

climate change effects on the distribution of animals (e.g. Hill et al. 1999). Males of P.

aegeria use a perching mate locating strategy and are found perching in large sunspots on the

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forest floor (figure 1b, Davies 1978; Wickman & Wiklund 1983). If a flying object enters the

sunspot area, occupied by a P. aegeria male, the resident male immediately takes off and

pursues the intruder to investigate what the intruding object might be. If the intruder is a

conspecific female, a flight pursuit follows. However, the nature of the flight pursuit is highly

dependent on the mating status of the female. If the female is already mated the flight pursuit

is ended after just a few seconds, often caused by the female doing a vertical drop into the

vegetation. If the female is receptive the flight pursuit will be significantly longer (Bergman,

M. unpublished). The female will conduct a rapid flight and the male will follow at a close

distance behind. The couple will eventually alight in the vegetation, whereupon the male

starts a courtship ritual. But if another male enters the sunspot area, the territory resident will

take off and the two will engage in a flight contest (figure 1c), where the winner gets sole

ownership of the sunspot and the loser leaves the area and has to search for a new suitable

sunspot (Davies 1978; Wickman &Wiklund 1983).

(a) (b)

Figure 1: (a) A male of the speckled wood butterfly (Pararge aegeria) on an oak leaf. (b) A typical habitat for

P. aegeria - a deciduous forest in Ransvik, Kullaberg. (c) Two P. aegeria males in a territorial contest over the

residency of a large sunspot. Photo (a) and (b) by Christer Wiklund. Photo (c) by Martin Bergman.

(c)

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There are surely several reasons why studies on mating success in butterflies are few, but it

often comes down to the difficulties to observe natural matings in field. Typically females

mate very soon after eclosion and a majority of the females in the wild are already mated

(Wiklund & Fagerström 1977; Wiklund 2003). Studies on mating success require individual

observation of unmated receptive females and, consequently, these studies require the release

of laboratory-reared females. Another difficulty with studies of natural mating in butterflies is

that in perching species mating does not necessarily occur in the territories (e.g. Bitzer &

Shaw 1983; Alcock & Gwynne 1988; Brown & Alcock 1990). When a perching male detects

a passing female the male flies up and investigates the passing female. The female response

for this is usually a rapid flight, with the male in close association to the female. This can be a

way for non-receptive females to avoid male courtship but can also be a way to test the male‟s

ability. However, non-receptive females might also respond to the inspecting male by doing a

vertical drop into the vegetation (Wiklund pers comm). In some species, such as Polygonia c-

album, Aglais urticae, Inachis io and Vanessa atalanta, the courtship phase is excessively

prolonged; the male follows the female for hours before mating is initiated (Wiklund pers

comm). Consequently, matings occur somewhere away from the perching sites and this makes

it virtually impossible to locate butterflies in copula. Thirdly, when a female and a male have

alighted and copulate they are usually very cryptic and hard to find in nature. For the reasons

mentioned above, the experiments here have been in large outdoor cages done using

laboratory-reared butterflies (figure 2). The cages have been located at Kronängen,

approximately 100 km south of Stockholm in central Sweden. The cages were semi-

cylindrical, tunnel shaped and covered with a plastic green tarpaulin (figure 2). In the

tarpaulin we had removed one large section (2 x 2 m) and several smaller sections (0.2 x 0.2

m) that created one large sunspot and a mosaic of smaller sunspots on the cage floor, this to

create an artificial forest habitat that P. aegeria is naturally flying in (figure 3).

Figure 2: The experimental cages located at Kronängen, approximately 100 km south of Stockholm. Photo

by Martin Bergman.

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The results from paper I showed that resident males had a higher mating success than non-

resident males; residents achieved approximately twice as many matings as non-residents

(figure 4). Territorial behaviour and defence of large sunspots are favoured through selection

and the behaviour is thereby maintained in the population.

Although it was clear that resident males of P. aegeria had a higher reproductive output, it

was not clear why. What is the possible mechanism that generates a mating success

asymmetry between residents and non-residents? One explanation could be female choice and

that females have a preference for male character traits that correlate to residency and the

ability to win territorial contests. During the experiments in paper I we recorded rejections of

courting males made by females and these data did not support the hypothesis that females

Figure 4: Mating success of resident

and non-resident males, respectively, in

127 mating trials during which a female

exercised mate choice between a

resident male that controlled a 2x2 m

sunspot territory and a non-resident

male without sunspot territory or with a

smaller sunspot. Values are given with

a 95% CI.

Figure 3: The cages were covered with a plastic green tarpaulin prepared with holes to create a mosaic of

sunspots on the cage floor. Photo by Martin Bergman.

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would have any preference for male character traits associated to residency; residents were

rejected as often as non-residents. Another possible mechanism behind the mating success

asymmetry could be that females actively search for areas where males can be found, i.e.

large sunspots. Neither did we find any indications that this would be the case; females landed

as often in small sunspots as in the large sunspot, where the resident male perched.

Furthermore, the results also showed that virtually all male-female interactions were initiated

by a perched male discovering a female passing by, and 63 % of the matings were preceded

by the female being discovered when entering the large sunspot. This pattern could only be

explained by female preference for large sunspot or that females are more likely to be

discovered and successfully pursued by the male after flying through such sunspot. Since the

former explanation did not have any empirical support in paper I, the latter explanation was

more likely to hold true and warranted empirical testing.

Perching or patrolling?

The ways to locate mates vary greatly between species, but there are also examples of animals

where the mate locating strategy varies within species (Krebs & Davies 1993; Andersson

1994). In species where the competition between males is strong and the ability to acquire

matings is limited, males that lose contests with dominant opponents have to adopt a

suboptimal strategy to acquire matings. Among insects subordinate males often adopt the role

of a satellite in the vicinity of a dominant male and acquire matings by intercepting females

on their way to a territory owner (Otte 1972; Cade 1980; Alcock 2005).

In butterflies, a perching mate locating strategy is often combined with territorial behaviour

and defence of the perching site. When suitable territories are in short supply, males will

frequently fail to gain a territory and these males are often described to adopt a patrolling

mate locating behaviour, as an alternative mate locating strategy (Davies 1978; Shreeve 1987;

Van Dyck et al. 1997a; Fischer & Fiedler 2001). However, it has not been clear whether

males that have lost a territorial contest, adopt a patrolling strategy in the sense of Scott

(1974), and become as mobile as a patrolling species and spend virtually all of their time on

the wing in long continuous flights, in search for females. It could also be that males that have

lost a territorial contest continue to search for a suitable territory and after losing a number of

contests, settle in a suboptimal territory.

Several studies have observed both perching and patrolling behaviour in the same population

of P. aegeria (see Davies 1978; Owen et al. 1986; Shreeve 1987; Jones and Lace 1992;Van

Dyck et al. 1997b; Jones et al. 1998; Stutt and Willmer 1998; Van Dyck & Matthysen 1998;

Merckx & Van Dyck 2005). However, the classification of P. aegeria males as patrollers is

often based on snapshots of male behaviour, with short observations of males in field. In

paper II we wanted to thoroughly study the mate locating behaviour in P. aegeria males and

test the hypothesis that males adopt both a perching and a patrolling mate locating strategy.

Since this requires long continuous observations we performed controlled experiments in

large outdoor cages. This allowed us to follow individual butterflies for longer periods. By

studying the behaviour of the same individual both before and after contests we could test if

non-resident males, i.e. loser of territorial contests, abandon a perching mate locating strategy

and instead adopt a patrolling strategy if suitable territories are in short supply.

The results from paper II showed that all males adopt a perching strategy when suitable

territories are present. When a male was alone in the experimental cage, which contained only

one large sunspot, the male spent approximately 90 % of the time perching in the large

sunspot. Although resident males took off and performed shorter scouting flights, they were

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locally stationary and spent virtually all their time in the same large sunspot, on the lookout

for females. To study what happens when there are more males than suitable territories we

introduced two males into the experimental cage and studied the behaviour of residents and

non-residents respectively. Upon introduction, the two males engaged in a territorial contest

over the sunspot territory. The winner became resident in the large sunspot and the male that

lost the contest became non-resident. The non-resident increased the proportion time spent

flying during a 20 minute period after the interaction (figure 5). From spending only 10 % of

the time in flight when territories are available, non-residents increased their activity to spend

approximately 60 % of their time in flight, immediately after a contest. However, after 20

minutes the non-resident gradually adopted a stationary and perching behaviour again (figure

5), but instead of perching in the large sunspot the non-resident alighted in a small sunspot.

Forty minutes after the contest the resident and non-resident invested the same amount of time

in flight activity, but with a vast difference in perching sites, while the resident perched in the

large sunspot the non-resident perched in a small sunspot.

Figure 5: Time spent in flight by prospective residents and nonresidents, during the first 60 min

period when only single males were present in the cage, and by residents and nonresidents during

the last 60 min when two males were present in the cage simultaneously. Each bar indicates the

mean ± SE for a 10 min interval.

From the results in paper II we can conclude that male P. aegeria invariably adopt a

perching mate locating strategy when suitable sunspot territories are available. When

territories are in short supply, males that fail to occupy large sunspots spend a short time in

extended flight in search for another suitable sunspot. If there are no suitable territory

sunspots available, the male eventually returns to a perching strategy, but instead of a

preferred large sunspot he alights in a smaller, suboptimal sunspot, making the best of a bad

job. Previous descriptions of male P. aegeria adopting a patrolling strategy are most likely

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based on too short observations and are thereby misleading. It is probable that earlier studies

have recorded the behaviour of males in the exodus flight, which follows a male‟s failure to

take over a sunspot territory from another male. Paper II underlines the importance of long

continuous observations to fully understand the mate locating behaviour in butterflies.

Vision

Paper I showed that resident males had a higher mating success than non-resident males.

Furthermore, from paper II we could conclude that non-resident males did not adopt a

patrolling mate locating strategy, but utilized smaller sunspots as perching sites when larger

sunspots were in short supply. The results from these two studies indicate that sunspot size

correlates with reproductive success; perching in a large sunspot generates a higher

reproductive output than perching in a small sunspot. The reason for this may be that large

sunspots, but not small ones, represent suitable rendezvous sites for the sexes to meet.

However, this implies that females prefer large sunspots rather than small sunspots and have a

behavioral preference for locating and visiting large sunspots. But data on female dispersal

from paper I did not support this hypothesis, females landed as often in large sunspots as in

small sunspots. The mechanism resulting in a mating success asymmetry may also be that

larger sunspots facilitate visual detection and flight pursuit of females passing by. In paper

III we aimed to test the visual ability of perching males. But first we conducted a field study

to confirm that our observations from the cage experiments, that male P. aegeria preferred

large sunspots over smaller sunspots as perching sites, is also true in their natural habitat. To

assess the characteristics of defended sunspots, we identified and measured sunspots that were

used as perching sites by male P. aegeria, in the deciduous forest of Ransvik in southern

Sweden. The characteristics of these sunspots were contrasted to sunspots that were not used

as perching sites in the same area. The measurements showed that sunspots used as perching

sites were significantly larger than sunspots not utilized by males. So now the question was:

does a large sunspot enhance the ability to visually detect and pursue a passing object?

To experimentally test the male visual system we used an apparatus (figure 6) that allowed us

to present a model butterfly to a perching male and that permitted us to control the pathway

and speed of the model, making the presentations highly repeatable. This kind of method was

used in some earlier, now classical papers, which investigated the visual abilities of perching

male butterflies (Magnus 1958; Tinbergen et al. 1972; Douwes 1975). These studies

demonstrated that the stimulus required eliciting an approach by a perching male does not

have to be very specific. Indeed, numerous field observation have described how perching

males in a variety of species respond to all kinds of flying objects, including heterospecific

butterflies (e.g. Davies 1978; Lederhouse 1982; Shreeve 1984; Alcock 1985; Alcock &

O‟Neill 1986; Alcock & Gwynne 1988; Rutowski 1992), other insects (Davies 1978;

Lederhouse 1982; Alcock & O‟Neill 1986; Alcock & Gwynne 1988; Rutowski 1992; Van

Dyck et al. 1997b), birds passing by (Meyer 1879; Proctor 1976; Lederhouse 1982; Bitzer &

Shaw 1983; Alcock & O‟Neill 1986) and pieces of wood thrown over the head of the

perching male (Alcock & Gwynne 1988; Kemp et al. 2006b). The experimental apparatus

was mounted so that the butterfly model travelled in three different trajectories when it passed

the perching male. The trajectories were selected so that the butterfly model was illuminated

for 2 meters or 1 meter when passing the male, or not illuminated at all, passing just outside

the sunspot. We also recorded the position of the perching male in the sunspot, to estimate the

distance to the passing model.

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The results from paper III showed that perching males are more successful in pursuing and

intercepting a passing model when the model is flown through the sunspot. The males were

also more efficient in pursuing and intercepting the model when the model was flown for a

longer distance through the sunspot (figure 7). These results are based on experiments with an

artificial butterfly model in a large cage, and so it might be relevant to address the issue of

how this applies to a natural situation. In our experimental setup we varied the trajectory of

the model and thereby the distance that the model was illuminated by the sun when it passed

the perching male. In nature the time that a passing female is sunlit is likely to increase with

the size of the sunspot used as perching site by a male. At a certain distance, when a female is

passing a male that perches in a small sunspot, the probability that the female will be sunlit at

all is small, and consequently the probability of a successful detection and pursuit by the male

is low. If the sunspot is larger, the female will be sunlit for a longer time and the pursuit and

interception of the female will be more successful.

Figure 7: The mean ± SE level of male response to the flying model when flown just outside, or 1

or 2 m through a sunspot in which a focal male was perched; the response levels were: (0) no

response, (1) male takes off from the ground but does not pursue the flying model, (2) male takes

off and pursues the flying model, and (3) male takes off, pursues and completes flight pursuit of

the flying model

Figure 6: Schematic diagram of the

model presentation apparatus as

viewed from the side. In the trials the

male would be sitting on the ground

while the butterfly model passing by.

The trajectory of the model was

adjusted so that the model was sunlit

for 1 meter or 2 meters when passing

the perching male, or not sunlit at all,

passing the perching male in the

shade, just outside the sunspot.

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Another possible reason why males perch in large sunspots may be that the ability to detect

and pursue a moving object is enhanced if the object is seen against the blue sky. It has been

suggested that perching male butterflies should choose their perching sites to optimize the

chance of visually detecting females against the blue sky (Rutowski 2000, 2003). During the

experiments in paper III we estimated if the perching male was able to view the butterfly

model against the blue sky as a background, behind the 2 x 2 meter hole made in the tarpaulin

covering the roof. The data showed no effect of the background the model was seen against;

males detected the model equally often when the model was seen against the blue sky as when

it was seen against the tarpaulin cage roof.

From paper III we can conclude that male P. aegeria adopt territories in sunspots larger the

average sunspot in nature and they do this because a large sunspot improves the ability to

pursue and intercept receptive females passing by. This explains the mechanism that underlies

the mating success asymmetry between residents and non-residents (paper I). Furthermore,

this also implies that there is a variation in territory quality in nature, which correlates to the

size of the sunspot.

Contest settlement in butterflies

Conflict over resources is a widespread phenomenon among animals and a prominent

component of animal mating systems (reviewed in Huntingford & Turner 1987). The

understanding of the evolution of animal conflict is now vast. But still some groups of

animals continue confusing researchers, because of the difficulties to predict outcome of

fights. Butterflies is such a group.

An essential part of animal conflict theory is that conflicts are solved due to an asymmetry in

fighting ability, or resource-holding potential (RHP, Parker 1974). The individual that

possesses the greatest RHP is expected to win a conflict with another individual. RHP is often

strongly correlated to physical or morphological traits and nature is full of beautiful examples

of traits meant to increase the fighting ability. Large body size, horns and antlers are all the

result of selection for fighting ability and skills to acquire matings. However, not all animals

that compete for mating opportunities via male-male conflicts show obvious morphological

adaptations. In territorial butterfly species, males compete over mating opportunities by

engaging in aerial flight contests, but seem to lack any obvious physical adaptations for

fighting. What decides RHP in butterflies has been in researchers‟ focus over the last decades

(reviewed in Kemp & Wiklund 2001).

Theoretical models suggests that conflicts can be settled due to the convention “resident wins,

intruder retreats” (Maynard Smith & Parker 1976; Maynard Smith 1982), where the resident

and intruder roles per se are used as arbitrary cues for a quick settlement of a contest, the so-

called uncorrelated-asymmetry hypothesis (cf. Kemp & Wiklund 2001). Intuitively, this

would of course be applicable to contest settlement in the seemingly weaponless group

butterflies. Thus, in the 70s Nick Davies (1978) conducted a now classical field study where

he tested the uncorrelated-asymmetry hypothesis by using males of the speckled wood

butterfly (Pararge aegeria). He found that resident males always won contests with intruder

males and interpreted the results as empirical support for the uncorrelated-asymmetry

hypothesis. A few years after Davies‟ study, Wickman & Wiklund (1983) conducted another

field study with P. aegeria as a model. In clear contradiction to Davies‟ (1978) results and in

clear contradiction to the uncorrelated-asymmetry hypothesis, they observed several

occasions when an original owner regained the ownership of the territory after a few minutes‟

absence. This kind of take-over of territories, where the resident is defeated by an intruder,

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has later been confirmed in P. aegeria (Kemp & Wiklund 2004) and recorded in other

butterfly species (Hernándes & Benson 1998; Kemp 2000). Kemp and Wiklund (2004)

argued that Davies‟ results were most likely explained by the experimental procedure used by

Davies (1978), where the individuals in the “intruder-role” were treated in a way that

negatively affected their motivational level to engage in a territorial fight. Even though

studies have shown that resident males do not always win contests with intruders (Wickman

& Wiklund 1983; Kemp & Wiklund 2004), there is a clear consensus that residents generally

are more likely to win contests (Kemp & Wiklund 2001).

Shortly after Davies (1978) published his study, it was challenged by Austad et al. (1979).

They argued that the resident males could actually be better able persist in a contest because

they achieve a higher body temperature when perching in a sunspot. This hypothesis was later

empirically tested in P. aegeria by Stutt and Willmer (1998) and they concluded that

individuals that were warmer could fly for a longer period and were therefore more likely to

win a contest. However, this hypothesis was later tested and ruled out by Kemp and Wiklund

(2004), since they found no differences in body temperature between residents and non-

residents. Kemp & Wiklund (2004) argued that Stutt and Willmer (1998) in resemblance with

Davies (1978) had handled their animals during the experiment in a way that affected their

motivation to fight in a negative way.

Several of the possible hypotheses for contest settlement in butterflies have been empirically

tested and often also rejected. But the most common, and perhaps the most intuitive,

mechanism for contest settlement is still that an asymmetry in morphology/physiology

decides who will win a contest. Several physical traits have been tested in butterflies but

without any real consensus in how morphology/physiology affects contest outcome. For

instance, in some species there is a positive correlation between body size and contest

outcome, where larger males are more successful in territorial contests (Rosenberg & Enquist

1991; Martínez-Lendech et al. 2007; Peixoto & Benson 2008) while in other species the

smaller males are the more successful ones (Hernándes & Benson 1998). However, there are

also several species where body size does not affect contest outcome (Lederhouse 1982;

Kemp 2000, 2005; Takeuchi 2006a,b; Paper I). Age has also been shown to influence the

outcome of territorial contests, with older males having higher contest persistence in some

species (Kemp 2002a, 2005) while younger males have an advantage in other species (Kemp

2003, 2005). Yet in some other species age has no or little effect on contest resolution (Kemp

et al. 2006a; Takeuchi 2006b; Paper I). The effect of fat reserves on contest outcome has also

been investigated but without any clear connection to contest settlement and individual RHP

(Kemp 2002b, 2005; Takeuchi 2006b; Martínez-Lendech et al. 2007). Neither does wing

morphology seem to be of importance for contest outcome in butterflies (Kemp 2002b; Kemp

et al. 2006b).

In paper IV we wanted to investigate a previously untested mechanism of contest settlement

in butterflies. Motivational asymmetries are known to influence outcome in animal contests

but has received surprisingly little attention in butterfly contest research. Theory suggests that

residents will win frequently because they stand to gain a higher pay off if they are successful,

due to the time and energy invested in establishing and defending the resource (cf. the ‟dear

enemy‟ phenomenon, Temeles 1994). Residents might also win more frequently due to an

information asymmetry, where the resident is better informed about the quality of the resource

than the intruder. The resident then places a greater subjective value on the contested area and

is prepared to fight harder for the resource than the intruder is (Enquist & Leimar 1987).

Kemp & Wiklund (2001) argued that the latter might be potentially relevant in butterflies.

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Resident males could conceivably assess the value of the contested area if there are reliable

indicators of the potential rate of encountering receptive females. Such indicators could be the

encounter frequencies of females or conspecific males (Kemp and Wiklund 2001).

To investigate the motivational asymmetry hypothesis we staged contests between males of P.

aegeria in the large outdoor cages at Kronängen. After the dominance relationship was

settled, with one male being the resident and the other male the non-resident, we removed the

resident male from the cage. The non-resident male was now allowed to either interact with a

female for 30 minutes, or spent 30 minutes alone in the cage. When we reintroduced the

resident male, after a 30 minute absence, we found that the non-resident males that had

interacted with a female for 30 minutes were now more motivated to persist in a territorial

contest and more likely to defeat the original resident, reverse the contest outcome, and now

become dominant (figure 8). By introducing females into the sunspot territory we

manipulated the value of the resource and affected the motivational level in the males to a

level that allowed them to defeat their previous superior opponent

When we removed the initial resident from the large sunspot the non-resident claimed the

sunspot territory within minutes. However, there was some interesting variation in the length

of time it took before the initial non-resident perched in the large sunspot. We found that in

the female encounter group, males that were particularly fast in taking over the vacant sunspot

territory were also more likely to later reverse the contest outcome. This might reflect a

variation in intrinsic motivation and we contend that this intrinsic motivation is reflected in

the eagerness to take over vacant territories.

In the experiments in paper IV not all trials in the female encounter group resulted in a

reversed contest outcome. This implies that other asymmetries, in addition to the female-

encounter-based motivation asymmetry tested here, influence contest outcome in butterflies.

Since there are no strong effects of asymmetry in intrinsic fighting ability based on

morphological/physiological factors, and since both males were naïve with no contest

experience, we contend that an intrinsic motivation state can have a profound influence on

contest outcome. In the trials where the contest outcome was not reversed, it is likely that the

asymmetry in intrinsic motivation was simply too big, and a 30 minute interaction with a

Figure 8: The outcome of contests between

males of P. aegeria during the second contest

period when the original winner had been

reintroduced, and after the original losers had

either interacted with a female during 30 min

(female encounter group) or been alone for 30

min (control group); „reversal‟ (open bars)

denotes that the male that lost the contest

during the first contest period reversed the

outcome and won the contest against the

original winner in the second contest period,

and „no reversal‟ (filled bars) denotes that the

same male won in both contest periods.

13

female was not enough to manipulate the motivation to the extent that it reached a reversal in

contest outcome (figure 9).

Figure 9: A model of male‟s motivation to persist in territorial contests. Each male has a given

level of intrinsic motivation. But the level of motivation can also be affected by extrinsic factors,

such as encounters with females, and become higher or lower than the intrinsic motivational level.

(a) When the trial ended in a reversed contest outcome the non-resident‟s motivation was

manipulated to be higher than the resident‟s intrinsic level of motivation. (b) When the trial ended

with the same outcome the asymmetry of intrinsic motivation was too big.

The results in paper IV are the first study to empirically show that motivational asymmetries

are an important component in contest settlement in butterflies. The role of motivation is a

new and interesting approach in the extended and puzzling research field of butterfly contests

and we contend that motivational asymmetries may be a key factor in other systems.

Female behavior

Mate locating behavior of males is very much dependent of the distribution of receptive

females. A mating system is really the interaction of male behavior and female behavior

(Wickman & Rutowski 1999). This is especially true in perching species, where the females

are the mobile part and the males remain stationary. Consequently, the areas utilized as

perching sites are ultimately decided by the dispersal of females. Although several authors

have stressed the importance of female behavior when studying mate locating behavior in

males (e.g. Rutowski 1991; Rutowski et al.1996; Wickman & Rutowski 1999, Kemp 2001;

Wiklund 2003), there are relatively few studies of female behavior in relation to male

territoriality. The reasons for this may be several, but one is the fact that most females in the

wild are already mated and studies of the behavior of receptive females require the release of

laboratory-reared animals.

Although there is a lack of empirical studies on female behavior, earlier publications have

indicated that females have sophisticated adaptations to optimize their reproductive success.

Researchers have observed and investigated courtship solicitation behavior, where virgin

females and females in need of a fresh spermatophore, actively pursue males or behave in a

highly conspicuous way (e.g. Rutowski 1980; Rutowski et al. 1981; Wiklund 1982; Wickman

1986, 1992; Wickman & Jansson 1997; Hiroki & Obara 1998; Daniels 2007). The theory of

sexual selection suggests that females are expected to behave in a way so as to minimize time

spent unmated, in order to maximize time for ovipositing. In paper V we wanted to test the

(a) (b)

14

hypothesis that virgin and mated females behave differently, with the prediction that virgin

females behave in a more conspicuous way, as a way to acquire matings. Furthermore, since

the adult life of a butterfly is highly time-limited, age is expected to have an effect on mate

locating behavior in females. As the cost of being choosy increases with increasing age, older

females are expected to be less choosy and more willing to mate. Therefore, in paper V we

also tested the effect of age, with the prediction that older females would behave more

conspicuously than young females. We conducted experiments in the cages at Kronängen

where we studied female behavior for 20 minutes in young and old, mated and virgin females.

The results from paper V showed that females behave in a way that is consistent with the

idea that females are selected to minimize time spent unmated; older virgin females are more

active and spend more time in flight, and make more individual flights than mated and young

virgin females, and so behave more conspicuously (figure 10).

But we also wanted to test what possible consequences a higher activity can have. The

prediction and the intuitive result would of course be that the increased activity of older virgin

females leads to a faster detection and mating by a male. To empirically test this we

introduced a male into the experimental cage and after he settled in the large sunspot we

introduced a female and recorded the time it took until the male detected her. As predicted,

males discovered virgin females faster than mated females (figure 11).

Figure 10: The percentage of

time spent flying by females of

the speckled wood butterfly,

Pararge aegeria, during a 20 min

trial. Values are given as mean ±

95% confidence intervals.

15

Figure 11: The difference between mated and virgin females in the probability of being detected

by a male. If the female remained undetected for 1800 s (30 min) the trial was ended.

If females in a territorial species adjust their behavior to minimize time spent unmated they

would be expected to search for areas where males can be found. In P. aegeria this would

mean a female preference to visit large sunspots. The results in paper V did not support this

prediction; virgin females did not alight more often than mated females in large sunspots.

Hence, females adjust their behavior only by an increased activity, but with the clear

consequence of a fast encounter with a male. From paper V it also stands clear that a vast

majority of male-female interactions are initiated by a female being detected and pursued by a

male perching in a large sunspot. This confirms the results from paper I, that residency

increases the probability of encountering a female. The results also confirm that the main

strategy for males to acquire matings is to perch (cf. paper II), since 90 % if the interactions

were initiated by a female being detected by a perching male.

The study in paper V is novel, since it demonstrates how females adjust their behavior in

accordance to both mating status and age, as a strategy to encounter mates. This study also

stresses the importance of the distribution and behavior of receptive females to fully

understand the mating system of a species.

16

Conclusions

Males are expected to search for females where they are likely to be found. Females of P.

aegeria fly in open forest habitats and visits sunspots on the forest floor for thermoregulatory

reasons. The predictability of female behavior encourages males to search in sunspots.

Indeed, males are found in sunspots on the forest floor, on the lookout for females visiting the

sunspot (paper I-V). However, males are only found in sunspots above a certain size as they

only perch in sunspots larger than the average sunspot on the forest floor (paper III). This

behavior is maintained by a mating success advantage, where using large sunspots instead of

small sunspots as perching areas generates a higher reproductive output (paper I). The mating

success asymmetry is not explained by female choice or by a female preference for large

sunspots per se (paper I, IV), but rather the large sunspot facilitates visual performance of

perching males and improves flight pursuit and interception of females (paper III).

Territorial contests between P. aegeria males are not settled due to an obvious

morphological/physiological asymmetry (paper I), as is common in many other animals.

Rather, variation in resource value and motivational asymmetries are important for settling

contests (paper V). Males of P. aegeria use a perching mate locating strategy. The

perching/patrolling dichotomy ultimately relates to how matings are initiated. Even though it

is most likely that some matings are initiated by a flying male detecting a female in flight, or

even that a flying male detects a resting female, there is no doubt that a vast majority of male-

female interactions (paper IV) and matings (paper I) are initiated by a perching male

detecting and intercepting a flying female. In addition, the fact that both resident males and

males that recently have lost a contest spend approximately 90 % of their time perching

(paper II), strongly indicates that this is the main way for finding females.

A keystone in the evolution of territoriality in butterflies is a predictable distribution of

receptive females. If the distribution of females is predictable, and the choice of perching site

affects mating success, selection will favor exclusion of other males from the area and

territoriality is likely to evolve. The quality of the perching site/territory is determined by the

physical features of the site, how it affects a male‟s ability to visually detect and pursue

receptive females. Since mate location in butterflies is almost exclusively based upon vision,

physical features of territories that facilitate visual detection of females should correlate with

territory quality in most perching species. But the quality of the perching site is also highly

affected by the rate of butterflies that enter the territory. The inflow of other butterflies clearly

affects the male‟s subjective assessment of the territory and creates an information asymmetry

between a resident and an intruder, and often the resident puts a higher subjective value on the

territory, based on his female encounter experiences. The physically based territory quality, in

the case of P. aegeria, the size of a sunspot, may also have an influence on the subjective

assessment and valuation of a territory and only further studies can evaluate how physical

traits of a territory affect mate motivation to persist in territorial contests. Female-induced

motivation is, however, not the only mechanism for contest settlement in butterflies, and a

physical territory quality induced motivation might be a part of the explanation. An individual

intrinsic motivational level might also be an important part in understanding contests in

butterflies. How variation of this intrinsic motivation is shaped and why it exists is an

attractive field for future research on territoriality in butterflies.

17

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22

Territorialitet hos dagfjärilar

Hos flera av Sveriges dagfjärilsarter är hanarna territoriella och etablerar revir på

bestämda utkiksplatser. Dessa ställen används som mötesplatser för honor och hanar,

och de skyddas från inkräktare genom intensiva reviruppgörelser där hanarna utmanar

varandra i flygdueller. Kunskapen om hur detta beteende har uppkommit och hur det

bibehålls har länge varit bristfällig. Likaså har kännedomen om hur revirstrider avgörs

och vilka egenskaper som utmärker en vinnare i fjärilsvärlden under lång tid varit

knaper. Här presenteras aktuell forskning om territoriellt beteende, parningsframgång

och revirstrider hos fjärilar. Studierna är utförda med kvickgräsfjäril Pararge aegeria

som modellart.

Att på ett effektivt sätt finna en partner är av största vikt för en dagfjäril. Med en livslängd

som fullvuxen fjäril på en till två veckor är tiden knapp. Hos dagfjärilar kan man identifiera

två huvudsakliga sätt på vilka hanarna finner honor. De kan antingen använda sig av en

patrullerande eller en stationär strategi (Scott 1974). Patrullerande hanar spenderar största

delen av sitt liv flygande och rör sig över stora områden i sin jakt på honor. En stationär hane

tillbringar istället största delen av sin tid med att sitta och vänta på att en hona ska flyga förbi.

Om hanen väljer en stationär eller patrullerande strategi är ofta artspecifikt. Dessutom väljer

närbesläktade arter ofta samma strategi. Alla svenska arter i familjen vitfjärilar (Pieridae) är

patrullerare, medan alla svenska arter i underfamiljen vinterpraktfjärilar (Nymphalinae) är

stationära. En stationär hane rör sig över ett begränsat område, och även om kortare

inspektionsrundor är vanliga återkommer han ofta till sin utkiksplats och fortsätter sitt

spanande efter honor. Skulle en annan hane närma sig en utkiksplats som redan är upptagen

flyger den sittande hanen upp, och de två inlåter sig i en revirstrid i luften. Vinnaren får

tillgång till utkiksplatsen, medan förloraren tvingas lämna området och söka vidare efter en

annan lämplig utkiksplats.

På vilka platser det är fördelaktigt för en hane att söka efter honor bestäms av honornas

beteende. Stationära hanar etablerar utkiksplatser där sannolikheten att träffa på honor är

särskilt hög. Det kan vara i nära anslutning till någon resurs som används av honan, t.ex.

nektarväxter där hon söker föda eller värdväxter där hon lägger sina ägg. Skogslevande

fjärilar behöver ofta uppsöka solfläckar för att värma sig, och för hanarna kan det därför vara

fördelaktigt att söka efter honor där.

Även om man länge antagit att de stationära hanarnas utkiksposter fungerar som mötesplatser

för könen, och att en bra utsiktsplats därför ökar innehavarens parningsframgång, har det

empiriska stödet för denna hypotes länge varit svagt. Det finns flera tänkbara anledningar till

detta, men en del av problemet är troligen de begränsningar som är förknippade med

fältstudier. Fjärilshonor parar sig kort efter att de kläcks ur puppan, vilket betyder att de flesta

honor man ser i fält redan är parade. Studier av parningar och parningsframgång kräver därför

att man använder uppfödda fjärilar, där man kan garantera att honorna är oparade. Ytterligare

en svårighet med att studera parningar hos just stationära arter är att de inte nödvändigtvis

sker inom territoriets gränser. När en hona kommer inom en stationär hanes synfält flyger

hanen upp. Därpå följer en mer eller mindre utdragen flygjakt, där honan flyger iväg med

hanen tätt efter. När de två sedan landar och parar sig, ofta en bit därifrån, är paret vanligtvis

mycket väl kamouflerat och svårt att upptäcka.

23

Av dessa anledningar genomförde vi beteendestudier under kontrollerade förhållanden i stora

utomhusburar med kvickgräsfjäril (Pararge aegeria, figur 1) som modellart. Burarna (4 x 8 x

15 m) täcktes av en pressning med ett stort hål (2 x 2 m) och flera mindre hål (0,2 x 0,2 m).

Syftet med hålen var att skapa ett artificiellt skogslandskap med en stor solfläck och en

mosaik av mindre solfläckar på burarnas gräsbeklädda botten. Vi placerade även ut ett antal

julgranar av plast för att ännu mer efterlikna en skogsmiljö. Hanar av kvickgräsfjäril etablerar

revir i stora solfläckar som bildas när solens ljus tränger igenom trädskiktet. Där sitter de

sedan och spanar efter honor som flyger förbi (figur 2).

Genom att låta två hanar göra upp om herraväldet över den enda stora solfläcken och sedan

introducera en hona i experimentburarna kunde vi konstatera att de hanar som vunnit strider

med andra hanar och innehade en stor solfläck fick majoriteten av parningarna (figur 3;

Bergman m.fl. 2007). Därmed kunde vi empiriskt styrka den sedan länge förmodade men

sällan testade hypotesen att utkiksplatser försvaras av hanarna för att de fungerar som

mötesplatser för könen. En hög parningsframgång för de hanar som framgångsrikt lyckats

försvara en solfläck gör att dessa hanars egenskaper blir bättre representerade i kommande

generationer, och därmed bibehålls det territoriella beteendet i populationen.

Det stod nu klart att de hanar som utnyttjar stora solfläckar som utkiksplatser, och som

framgångsrikt försvarar dem mot andra hanar, har hög parningsframgång. Däremot var det

fortfarande inte helt klarlagt vad som orsakar dessa skillnader i parningsframgång. Man kan

Figur 1: Hane av kvickgräsfjäril (Pararge aegeria) sittande

på ett eklöv. Foto: Christer Wiklund.

Figur 2: Hane av kvickgräsfjäril (Pararge aegeria) sittande

i en solfläck på spaning efter förbiflygande honor. Notera

även de slitna vingarna. Foto: Martin Bergman.

Figur 3: I ett experiment introducerades en

hona i en bur där två hanar var närvarande;

en dominant hane som kontrollerade ett

revir i en stor solfläck, och en hane utan

tillgång till revir. I 65 % av de totalt 127

fallen parade sig honan med hanen i den

stora solfläcken, och endast i 35 % av fallen

fick den revirlöse hanen parningen.

Punkterna indikerar sannolikheten att få en

parning för en hane med respektive utan

revir. Värdena är givna med ett

konfidensintervall på 95 %.

24

tänka sig att honornas val av partner skulle kunna generera en högre parningsframgång, dvs.

att honor av kvickgräsfjärilar skulle föredra dominanta hanar. Beteendestudier har dock visat

att sannolikheten att bli avvisad under uppvaktningen är lika stor för en dominant hane som

för en underordnad hane (Bergman m.fl. 2007). Man kan även tänka sig att honorna skulle ha

en preferens för stora solfläckar i sig, och att de därför oftare skulle besöka solfläckar som

utnyttjas av territoriella hanar. Emellertid visar beteendestudier även här att så inte är fallet

(Bergman m.fl. 2007; 2010), eftersom honorna lika ofta besöker stora solfläckar som mindre

solfläckar.

Om nu svaret inte ligger i honornas beteende borde det ligga hos hanarna och deras förmåga

att följa efter och framgångsrikt uppvakta honor som passerar. I ett ytterligare experiment

testade vi hanarnas förmåga att följa efter ett passerande objekt. Vi lät bygga en apparat för att

på ett repeterbart sätt kunna presentera en fjärilsattrapp för en hane som sitter i en solfläck.

Apparaten var konstruerad som en linbana mellan två aluminiumstolpar, där vi kunde

kontrollera fjärilsattrapens fart, höjd och riktning. Med denna apparat presenterade vi

fjärilsattrapper för olika hanar och varierade deras färdväg förbi hanarna. Stationära hanar är

ofta förvånansvärt ospecifika med vad de flyger an mot, och attrappen fungerade utmärkt för

att framkalla en naturlig rektion hos en stationär hane. I naturen kan stationära hanar ses flyga

an såväl mot andra fjärilsarter som mot andra insekter och till och med mot fåglar. Om man i

fält lokaliserar en stationär hane på sin utkiksplats kan man till och med ofta få honom att

flyga an mot en tallkotte eller en barkbit som man slänger över huvudet på honom. Det vi

fann i experimentet var att hanen har mycket lättare att följa efter attrappen när den flyger

genom solfläcken än när den flyger strax utanför. Vi såg även att ju längre attrappen var

solbelyst när den passerade hanen, desto lättare hade hanen att följa efter den (Bergman &

Wiklund 2009). Allt tyder alltså på att hanarna ökar sina chanser att följa efter en passerande

hona genom att sitta i en solfläck. Genom att föredra en stor solfläck framför en liten ökar

dessutom den sträcka under vilken honan är solbelyst när hon passerar, vilket ytterligare ökar

hanens möjligheter att komma ikapp och få kontakt med henne. Genom resultaten från dessa

experiment började bilden klarna. Hanarna utnyttjar solfläckar eftersom sannolikheten att

stöta på honor är större där, och de föredrar stora solfläckar framför små för att

ljusförhållandena i de stora solfläckarna gör det lättare för dem att följa efter honorna.

En annan fråga som länge har gäckat forskarna är hur revirstriderna avgörs. Vad är det som

bestämmer vem som vinner reviruppgörelser mellan fjärilar? Vanligtvis när djur slåss eller

mäter sig med varandra finns det fysiska anpassningar för detta – till exempel älgtjurens horn,

ekoxens käkar eller gorillahanens styrka – men fjärilar saknar sådana karaktärer och tycks inte

vara direkt anpassade för strid. Faktum är att under en revirstrid mellan två fjärilshanar har de

sällan kroppskontakt med varandra och kan därför inte skada sin motståndare. De två

kombattanterna tumlar runt i luften och jagar varandra tills en ger upp och flyger därifrån. Det

är helt enkelt den hane som är mest uthållig, och som är villig att duellera längst, som vinner

striden. I försöken att hitta fysiska karaktärer som är kopplade till slagsmålsframgång har man

testat kroppsvikt, kroppstemperatur, energireserver och vingstorlek, men inget av detta verkar

ha någon större inverkan på utgången av revirstriderna.

För att ytterligare utforska gåtan med revirstridernas utgång ville vi därför testa en tidigare

oprövad hypotes. Hos vissa andra djur vet man att skillnader i motivation kan påverka

utgången av strider. Om två individer gör upp om en resurs, och en av dem värderar resursen

högre än sin motståndare, kan detta resultera i en skillnad i hur motiverade de är att strida för

resursen. Om man, som hos fjärilar, har en revirägare och en utmanare borde hanen som

innehar reviret vara bättre informerad om dess kvalité. Då ett revir av hög kvalité

25

kännetecknas av en hög förekomst av honor borde just interaktionen med honor vara en signal

som skulle kunna öka en hanes motivation att kämpa för reviret. För att testa detta

genomförde vi experiment där vi lät två hanar göra upp om ett revir. Därefter avlägsnade vi

den vinnande hanen ur reviret och lät sedan den förlorande hanen antingen interagera med en

hona under 30 minuter eller vara ensam i reviret under 30 minuter. När vi sedan

återintroducerade den ursprungliga vinnarhanen kunde vi se att om förlorarhanen hade varit

ensam under 30 minuter återerövrade den ursprunglige vinnarhanen oftast sitt revir. Om

förlorarhanen däremot hade träffat en hona under 30 minuter vann han istället vanligtvis mot

sin tidigare överman (figur 4; Bergman m.fl. 2010). Genom att introducera honor i reviret

hade vi manipulerade dess kvalité. Från att ha varit av låg kvalité (utan honor) hade reviret

blivit högkvalitativt (med god tillgång på honor) och därmed värt att strida hårdare för.

Resultaten från dessa experiment tyder på att skillnader i motivation, och variation i hur

enskilda hanar värderar reviren, har stor betydelse för utgången av revirstrider.

I boken “The descent of man, and selection in relation to sex” (1871) ägnar Charles Darwin

ordningen Lepidoptera ett kapitel där han ger talrika exempel på hur skillnader i färg och form

mellan hanar och honor orsakas av intersexuell selektion genom honligt val. Darwin beskriver

också sin fascination över dagfjärilshanar inlåter sig i revirslagsmål. Han skriver:

“Although butterflies are such weak and fragile creatures, they are

pugnacious, and an Emperor butterfly has been captured with the tips

of its wings broken from a conflict with another male.”

Darwin använder detta som ett i en lång rad av exempel på intrasexuell selektion genom

konkurrens mellan hanar. Idag är det närmare ett och ett halvt sekel sedan Darwin som en av

de första vetenskapsmännen dokumenterade revirstrider mellan dagfjärilshanar. Även om

många frågor sedan dess har besvarats genom idogt empiriskt arbete av forskare världen över

har vissa gåtor kring territorialitet hos dagfjärilar till stor del förblivit ouppklarade. Den studie

som presenteras här är ett led i att kasta nytt ljus över hur detta intressanta och frapperande

beteende har uppkommit, och varför vi ser det hos dagfjärilar. Dock kvarstår, som vanligt

inom vetenskapen, fortfarande många intressanta frågor inom detta fascinerande område.

Figur 4: I detta försök fick två hanar göra upp

om ett revir, vartefter vi avlägsnade vinnaren

och lät förloraren antingen interagera med en

hona under 30 minuter eller vara ensam i 30

minuter. När vinnarhanen sedan

återintroducerades observerades utgången av

striderna. De svarta staplarna indikerar de fall

där den ursprungliga vinnaren tog tillbaka sitt

revir när han kom tillbaka, medan de vita

staplar betecknar fallen när den ursprungliga

förloraren vann. När förlorarhanen varit ensam

under 30 minuter segrade den ursprunglige

vinnarhanen i en majoritet av fallen, men hade

förlorarhanen istället träffat en hona vann han i

mer än hälften av fallen. Skillnaden mellan

grupperna är signifikant (Fischers exakta test:

p=0,0061).

26

Litteratur

Bergman M. & Wiklund C. 2009. Visual mate detection and mate flight pursuit in relation to

sunspot size in a woodland territorial butterfly. Animal Behaviour 78, 17–23.

Bergman M., Gotthard K., Berger D., Olofsson M., Kemp J.D. & Wiklund C. 2007. Mating

success of resident versus non-resident males in a territorial butterfly. Proceedings of

the Royal Society B 274, 1659–1665.

Bergman M., Olofsson M. & Wiklund C. 2010. Contest outcome in a territorial butterfly: the

role of motivation. Proceedings of the Royal Society B 277, 3027–3033.

Bergman M., Gotthard K. & Wiklund C. Mate acquisition by females in a butterfly – the

effects of mating status and age on female mate locating behaviour. Animal

Behaviour in press.

Darwin C. 1871. The descent of man and selection in relation to sex. Murray, London.

Scott J. A. 1974. Mate-locating behaviour of butterflies. The American Midland Naturalist 91,

103–117.

27

Acknowledgement

Den här doktorsavhandlingen är ett resultat av gott samarbete, stöd och hjälp från flera olika

personer. Jag ska här försöka ge mitt varmaste tack till er, en i taget.

Mitt främsta tack går till min handledare Christer Wiklund. Grunden till ett lyckat projekt

är en noggrann förberedelse. De studier vi har genomfört tillsammans har varit noga

genomtänkta och planerade, vilket har visat sig ge goda resultat i slutändan. Du har en

fingertoppskänsla för vad som är genomförbart och hur man bör gå tillväga, det är jag

tacksam för. Jag är även tacksam för ditt engagemang, deltagande och att du alltid har tid.

Även om du uppenbart har mycket att stå i har du alltid tid för en fråga, och skickar man ett

manus till dig kommer det i retur inom kort. Detta gör att man får saker gjorda och det är

sällan något som ligger och släpar efter. Det är även kul att vi båda har ett intresse i musik och

att vi tycks ha vissa gemensamma nämnare i skivhyllan. Man kan ju inte bara snacka

vetenskap hela tiden.

Ett stort tack går även till min biträdande handledare Karl Gotthard för hjälp med

planering av experiment, diverse statistikproblem och läsning av manus. Tack även för

medförfattarskap i två av avhandlingens papper. Kalle har även del i att jag fick in en fot här

på zootis, som handledare på mitt examensarbete. Det var genom mitt exjobb som jag insåg

att det här med ekologi och evolutionsbiologi är ju faktiskt väldigt kul och något jag vill

fortsätta jobba med. Det kan jag tacka dig för Kalle. Det är även roligt att xiphia-projektet har

hållit i sig, om dock lågintensivt.

En annan person som varit till stor hjälp under åren på zootis är Magne Friberg. Magne

har legat steget före som doktorand och därmed kunnat vägleda mig under

forskarutbildningen. Din passion och ditt intresse för vetenskap och biologi smittar av sig på

människorna omkring dig och du är en inspirationskälla. Tack även till David Berger för

medförfattarskap samt för goda stunder på zootislabbet och i fält. Tack till Martin Olofsson

för medförfattarskap och för hjälp med genomförande och planering av experiment. Det är

trevligt med lite sällskap i dedär burarna på Kronängen emellanåt. Tack till Helena

Larsdotter Mellström för sällskap under åren som gått, såväl på zootis som på diverse

konferenser. Tack Ullasa Kodandaramaiah för trevliga stunder på zootis, över en bit mat

eller på boulebanan i Stureby.

Johan Charlier träffade jag redan första dagen på grundutbildningen och har varit en god

vän sedan dess. Johan har del i att jag hamnade i Stockholm och jag har således honom att

tacka för mycket. Att vi fortfarande efter alla år är kollegor på samma institution är kul. Tack

även Anna Palmé för trevligt sällskap och för gott samarbete i den undervisning vi haft

tillsammans.

Det trevliga sällskapet på zootis har jag mycket mina rumskompisar Titti Bohlin och Lina

Söderlind att tacka för. Tack för skratten och diskussionerna. Diskussionerna har emellertid

förändrats en aning, från att ha handlat om rock‟n‟roll och vetenskap till att handla mest om

barn, dock fortfarande med litet inslag av vetenskap.

Tack till Anette Lorents, Berit Strand och Siw Gustafsson för hjälp med allt det där runt

ikring, förutom forskningen. Tack Minna Miettinen för att man alltid kan slå sig ner i

fåtöljen för en pratstund. Och såklart för hjälp med miljöarbetet och allt det där annat som

ingen annan kan hjälpa till med.

Tack till de doktorandkollegor som passerat genom åren, ingen nämnd, ingen glömd. Vi

har haft trevliga stunder i zootis korridorer, på blodbadet och andra konferenser världen över,

i undervisning och på lab.

Tack min familj för ert stöd och visat intresse genom åren.

Tack Veronica och Jack, för att ni finns i mitt liv.

Tack!