Behavioural Processes, 19 (1989) 47- 56 47 Elsevier

F|DEUTY TO THE BREEDING SITE |N THE ALPINE NEWT TRITURUS ALPESTRIS

Pierre JOLY and Claude MIAUD URA CNRS 367 Eoologie des Eaux Douces, Universit6 Claude Bernard Lyon 1, 69622 Villeurbanne C6dex,France

( Accepted 27 February 1989 ) ABSTRACT

Joly, P., Miaud, C., 1989. Fidelity to the breeding site in the alpine newt Triturus alpesiris. Behav. Process., t 9 : 47-56.

In a context of several closed breeding sites (archipelago model), the great majority of alpine newts are sedentary, visiting the same site during two successive years. A homing experiment offered the animals a choice between two breeding sites, one from which they came and the other which was inhabited by another population. This experiment demonstrates the fidelity of a great majority of newts for their site of origin. Fidelity was stronger when sites were distant (150 m) than when nearer (25 m). The speed and the probability of return still varied according to both the distance and the nature of the environment of the release point. The performances were better when the animals were released in the wood than when released in the pasture, The mechanisms of orientation and navigation which should explain such results, as well as the genetic consequences of the fidelity, are examined and discussed.

Key-words: newt, breeding site, site fidelity, homing, philopatry, metapopulalion

INTRODUCTION

In species in which breeding involves grouping, fidelity to a particular breeding site reinforces the

demic structure and may act as an isolating mechanism. A familiar example is given by Salmonid fishes in

which the mechanisms supporfinr such a spatial structure have been extensively analyzed (review in Hasler

and Scholz 1983).

Th~ newt is also a suitable model for the study of such a problem. Terrestrial for most of lhe ye~.r,

newts gather during spring ;n aquatic sites for breeding. With regard to the surface of the home range,

breeding sites may be delined either as point-like in the case of a small pond or linear in the case of a r,,er or a

lake. A river is itself a mosaic of different ecological units, and only some of them are favourable to the life of a

given species (a pool were the current i~ low for example). Thus breeding sites often present precise

boundari,3s. All the breeders inhabiting one site may constitute a population in the case of a spatially isolated

pond, or a subpopulation in the case of a collection of neighbouring sites where mo,'ements from ore site to

another are frequent (melapopulation dynamics).

Unlike Salmonids, newts are semelparous, breeding several lime3 during their life span. In the cas9

of the alpine newt, the period ol sexual maturity is about three to six years (Smirina and Rocek 1976). =t may

be of about 10 to 12 years in the crested newt Tritums cristatus (Hagstr6m 1979) and at least of six years in

T vulgaris (Halliday and Verrel11988).

Fidelity '~o a breeding site was first demonsfraled in the western red-I:;u;;ied newt Taricha rivularis

by Twiffy (1959). This species reproduces in pools along the course ( f mountainous rivers. Adult newts are

0376-6357/89/$03.50 © 1989 Elsevier Scierlce Publishers B.V. (Biomedical Division)

highly sedentary, coming back every year to the same pool and remaining in that pool during all the bre~dmg

period (Packer 1963). Such sedentarity is actively maintained by orientation mechanisms which were

highlighted by homing experiments (Twitty 1959, Twitty et al. 1964) Returns to the site of origin were

observed for distances ot up to 8 km (covered in one year). These authors still did not give a precise

description of the spatial organization of the different populations. Such a description would make it possible

to estimate the possibilities ot choice offered to the displaced animals.

A river is a large target for a terrestrial newt. Both its linear shape and water current provide

directional information, in particular allowing polarity for an orientation guided by chemical cues. If the newt

enters the river below the site it is seeking, it can use odors transported by the current to move towards the

site. Im, ersely, the lack of site odors at the point of entry may lead to movement downstream (Packer 1963,

Twitty et al. 1967 a and b).

Unlike rivers, small ponds are isolated targets, and to reach such isolated targets the newts are

raced with a more complex situ3tion. Gill (1979) observed the return of a large part of a population Of the red-

spotted newt Notophthalmus viridescensto their pond of origin, one year after the transfer ot the population

to another pond ~ituated 400 m away. However the newts spent 3!1 the b,e~.ding season following their

transfer at the release site.

To demonstlate the fidelity of an individual to a site, such displacement experiments are conclusive.

Sedentarity may indeed result only in response to environmental gradients. If each site provides a physically

attractive basin, constituted for example by gradients ol odors or humidity, and if the terrestrial newt remains

in one of thes~ b3sins, it will return every year to the same site and fidelity will then be only apparent. Testing

the hypothesis ol fidelity involves giving the animals a choice between sites using the criterion that they are

inhabited by a population. The presence of a population is in fact proof that the pond is favourable for the

newt's life. In the present paper, we propose such an experimental design: the newts from two populations

which inhabit neighbouring sites are marked according to their origin and then released at the same point

between the sites, at equal distance from each of them.

STUDY SITES AND ~IETHODS

The ponds under study are situated in the plain of Bresse in Eastern France (ait 270 m). The landscape, is an alternation of woods, hedges and pastures. The experimental station is composed ol three ponds (A,B,C) which were dug 100 years ago in a pasture, near the edge ol a wood. Distances are of 25 m between A and B, an "~ ot 150 m between B and C (fig. 1).

Sedentary hehaviour: during two successive springs, the ponds were dip-netted monthly. The newts were marked according to their pond of origin by cutting one external digit (outermost digits are the least regenerative). Alter measuring ~ength (snout-vent, total, tail height) and mass, they were released in their respective ponds.

I-Inming e~.periment: this experiment took place on 4th April 1986, just after the waterward migration, l he newts were fished in the ponds, marked and then released at points situated at equal distance from the two ponds. For each pair ot ponds (A-B and B-C), two release sites were delined, on~ situated in the wood and the other in the pasture. Points 1 and 2, between A and B, corresponded ~o ~hc~ displacements

(about 30 m from ponds), while points 3 and 4, between B and C, corresponded to longer distances (about 100 m from ponds, see Fig. 1). The animals were transported in opaque boxes and released at dusk in rainy weather. The newts were placed under dead leaves and grass. Ponds were censured the following day and then 14, 25 and 51 days later.

Wood: : O : : : ~ ~ ® i: :' l

Fig. 1. Spatial distribution of release points 1, 2, 3 and 4 with regard to ponds A, B and C.

RESULTS

Sedentarlness

The majority of the newts were found in the same pond during two consecutive years (fig. 2). No

newts from pond C, which was the most isolated, were recaptured in another pond. But on the other hand, a

few newts changed between ponds A and B, which are closer to each other.

1986 A ~ 25m ~ B 150m C

1987 A B C

Fig. 2. Number of newts marked in 1986 and recaptured in 19~7 in differeJ}t, ponds A, B and C. ]he vertical arrows indicate the sedentary newts whereas the oblique ones indicate the translers from one pond to another.

Homing experiment

1) sffe fidelity: the proportion of recaptures varied from one situation to another, ~ut it always

exceeded 25%. Figure 3 clearly shows that the newts mostly returned to their pond of origin. In the case of a

long displacement, between B and C, no transfer from one site to the other was observed. In the case of the

short displacement between A and B, a few of the animals changed from c3e pond to the other and the same

proportion from A to B and vice-versa.

:~ ~ ! ~ :~ ~: ! - ~ i ! : : :i:i :ii: i .. i :: ~ ! i. ~ i:::: ~i: i:~ii: ,. ~:: i :i :ii-~ i ~ • ~:i.: ~i~:.'. ~i:

5

Fig. 3. Numbers of newts recaptured after being displaced. The pattern of each arrow cortes }onds to the pond of origin. The iatio indicates the number of newts recaptured comparP.d with the number of displaced newts .The arrow width is proportiona~ to that ratio and the pattern indicates the pond of origirte.

2) speed and proportion of returns: returns were more numerous (68%) and quicker in the case of

the short displacement with release in the wood (fig. 4). The majority o~ the animals returned to a site within

two we~k~ o, and ~ome were already in a pond the day following release.

In the other types of displacement, the newts mostly reached a pond after a 14- to 25 day period.

Some took still longer, Maximum proportions of rgturns ranged from 2~ to 43%. The newts released between

A and B (short displacement) but in the pasture presented the same pedormances as those subjected to

long displacement (between B and C). It seems that the nature of the surroundings of the release point

played an important role in the newt's ability to orientate its movements.

The disp!aced animals which reached a pond three weeks after release had a lower tail height ftlan

the residents (tab. 1). Tail height is largely influenced by prolactin (Vellano et aL 1970), a hormone that also

51

plays an important part in the physiological changes associated with entering the water, and the secretion of

which is inversely related to temperature (Mazzi 1970).

100 J Re~ease envi.n0nn~nt: e,wood; o, poslu~ 1 .I l:~mt~:c4-~e~ length: --.short :- -,l~g

o _ _ - - - - _ ~ 2 . 2 - . - - ~ 2

I./ -

1 14 25

DAYS AFTER RELEASE

-ig. 4. Temporal pattern ot returns to the breeding sites. Numbers correspond to the release points

TABLE 1. Comparison of tail heights between displaced and undisplaced newts 25 days after displacement.

MALES FEMALES displaced und isp laced displaced undisplaced

tail height (mm) 7,8 8,5 6,7 7,3 N 27 54 23 62

The displaced animals might !lave been subjected after release to higher temperature than

undisplaced ones because of the thezmal inertia ot water. Now because of the additional time spent on land

due to the long distance to be covered or to wandering alter confusion, the newts might have been exposed

to relatively high temperature. It is fher~;fore possible that certain animals did not return to a pond due to a fall

in hydrotropism, following a decrease in the prolactin level. But the decrease of tail height may also be

related to the lack of resources to maintain it. The experimental displacement involves a lot of energy being

required for returning to water while the physiological state prevents an efficient predatory behaviour on land.

DISCUSSION

Sedentadness ant:l fidelity

Our homing experiment shows clearly that sedentariness from one year to another in the alpine

newt is supported by fidelity to a particula- breeding site. In the eon;.ext of point-like aquatic sites, it confirms

the results obtained by Gill (1979) in the re,. spotted newt Notophthalmus viridescens.

The concept of fidelity is not restricted in Urodela to migratory species. Salamanders, usually

sedentary, return to their home range when displaced (Joly 1968, Gordon 1961, Rose 1966, Barthalmus and

Bellis 1969, Madison 1969, Madison and Shoop 1970, Forester 1979). The newts when under water may

also present fidelity to a particular zone of a pool or a pond (Packer 1962, Dolmen 1980).

Fidelity to a site involves:

1) the animal's attachement to a site. It can recognize it by using some elements of th6

environment. This affirmation supposes the memorization of such elements.

2) the animal's perception of these elements in the terrestrial environment.

Experimental results show that they are also perceived when the animal is displaced outside its usual home

range. In such a case, either navigation or orientation (in the case of an odor gradient) may allow the return.

Orientation and navigation

Salamanders return to their familiar life site over distances which are 10 to 100 times longer than the

s~ze of their home range: 30 m in Desmognathus fuscus (Barthalmus and Belli~ 1969), 90 m in Plethodon

ch]ereus (Kleeberger and Werner 1982) and 300 m in Salamandra salamandra (Joly 1968). In newts, the

distances which were succes.~tully covered in displacement experiments durin~ the waterward migration

were longer: 130 m for Ambystoma maculatum (Whitford and Vinegar 1966), 400 m in Notophthalmus

viridescens (Gill 1979) and up to 8 km (covered in more than 1 year) in Taricha rivularis (Twitfy 1959). It is very

probable in the lat~er case that the animals were released outside their hom~ range. The return to the site

may involve either navigation or orientation toward landmarks which can be perceived outside the tamitiar

environment.

The path followed by the newts when returning seems to be a straight line in the salamanders

Plethodon jordani (Madison and Shoop 1970} and Plethodon cinereus (Kleeberger and Werner 1982). In

the Ambystomatidae, the migration movement occurs by night and also follows a straight line. Individual were

observed to maintain the same direction during waterward and landward miarations and over a period of

several years (Shoop 1965, 1968, Shoop and Doty 1972, Douglas and Monroe 1961, Kleeberger and

Werner 1983). ~uch observations exclude the hypothesis of orientation mechanisms which would be of a

kinetic type, according to the classification of Fraenkel and Gunn (1961).

Among the sensory inputs which may be involved, oltaction plays a major role in both newts (Twltty

IS59, Grant et al. 1968, H~rshev a,~'t ~r~ct:t~r 1QTQ~ and salamanders (Madison 1969, Barthatmus and Be!lis

1972, Forester 1979). The chemical cues have still not been identilied. Twitty (1966), Madison (1969) and

Hershey and Forester (1979) suggost that vision does not play any role. Landreth ~nd Ferguson (1967)

however show in Taricha rivu/aris a synergy between orientation using chemical cues and a solar compass.

Such a compass might be based on an extraocular perception of polarized light (Taylor and Auburn 1978).

But these last results are controversial (Hershey and Forester 1979).

The use of the eadh's magnetic field is at present an attractive hypothesis. Phillips and Adler (1978)

and more recently Phillips (1986, 1987) demonstrated the perception ot the magnetic field 3nd its role in

orientation along short distances in the salamander Eurycea lucifuga and then in the case ol the return to the

breeding site in the newt Notophthalmus viridescens. The capacities of orientation seem to be maintained in

that species for a 20 km long experimental displacement.

It is in fact probable that navigation towards breeding sites is the result of an assemblage of several

perceptive mechanisms: magnetoreception might provide the general direction, maintained during both

waterward and landward movements with respect to the earth's magnetic lield. The efficiency ol such a

mechanism depends on the fact that the terrestrial home range is spatially restricted. We have no data on the

terrestrial home range in newts but we know that it is very restricted in salamanders (Joly 1968, Kleeberger

and Werner 1982). Olfaction might improve accuracy, particularly by pinpointing the precise direction of the

pond, using clinotactic mechanisms when the animal perceives a gradient ot aquatic odors (due to algae,

aquatic vegetation or specific moisturing).

Our data suggest that the nature of the environment modified the speed and the probability of

return movements. The pasture appeared to be less lovourable to movement than the wood. Whitford and

Vinegar (1966) made similar observations in Ambystoma macu/atum. Such a result may be explained

because it is probable that the terrestrial life of most of them took place in the wood.

The understanding of the orientative mechanisms would progre,,;s if:

1) the distances covered and the directions chosen by migratory newts were known.

Unfortunately, since it is extremely rare to fin(:: newts on land, data are scarce an0 ~:nreliable. Such distances

may be short, aboul 20 m in Triturus vulgaris (Dolmen 1981, Grifliths 1984). But they are observed to range

from 100 to 300 m in other species: at least 100 m in Triturus cristatus (Cooke 1986), 100 to 260 m in the

Ambystomatidae (Williams 1973, Douglas and Monroe 1981, Kleeb~.~rger and Wernel 1983), 100 m in

Hynobius nebulosus (Kusano and Miyashi~a 1984). Longer distances were described but seem exceptional:

1000 m in Triturus alpestris (Vilter and Vilter 1962) and 1600 m in Ambystoma jeffersoniar'um (Bishop

1941). The rarity of the observations is to be related to the probable underground character of the terrestrial

life ol most of the species. They are probably commensal with small mammals, and live in their burrows

(Douglas and Monroe 1981, Kleeberger and Werner 1983, Verrell 1985 and personal observations). The

burrows may indeed offer humid and temperate shelters where Iood like emthworms is easily available. Thus

although if it is probable that the alpine newt moves about 100 m away from the breeding site, the nature of

the terrestrial environment remains to be defined.

2) the geographical surroundings were described: it is indeed possible that ce~lain

elements of the landscape, such as wood edges, are used as olfactory or visual landmarks.

Attachment to a site

Mushinski (1976) showed how the selection of a habitat may be modilied by early experience of

different habitats. Such a mechanism might partially explain fide!ity to a site, mainly in the case where the sites

are very different.

But attachment to a particular site, which does not seem to be very different trcm the next one,

probably involves the memorization either of landmarks durin G the (first ?) migration or of a specific chemical

cue associated with the site. The period ol life when such memorization occurs has yet to be defined.

In the case of landmark memorization during migration (including the direction of the earth's

magnetic field or chemical cues), it may occur either during the first landward movement or the first waterward

movement. The latter occurs two years after the former. In the first case, the animal would be faithful to its

natal pond (philopatry) and in the second case to the pond in which it bred for the first time.

Assuming the memorization of a :.peci,'ic odor, this may take place during the larval stage or during

the first aquatic stage. The first case would determine fidelity to the native pond tphilopatry). Only long term

experiments on the development of site fidelity in hewts will bring answers to such a problem.

Site fidelity and population Isolation

The isolation of breeding populations would be reinforced only in the case of fidelity to the native

pond, and only if such a mechanism does not show gL;=at interindividual variability. Ralinaki (1974) and

Kalezic and Tucic (1984) suggest that fidelity to the breeoing site may be a factor responsible for the genetic

differences measured between populations in the alpine and the smooth newt respectively.

In the populations of Taricha rivu/aris in the same sites where Twitty and Packer demonstrated

fidelity ol adult newts, Hedgecock (1978) did not lind a signilicant difference in genetic distances between

dames. Gene llow was apparently sufficient to prevent genetic divergence. Gene flow may be due to erratic

behaviour of certain adults. Adults travel longer distances on I,~nd than do juveniles (Twitty et al. 1967c).

But one must point out ti;at:

1) the present techniques of genetic analysis may not accurately reflect such an

isolation.

2) Such an analysis should be repeated in other stations including several sites

simultaneously with an ethological study.

Fidelity to a site is probably associated with memorization of landmarks which increase the accuracy

of the migratory movement easier, and so positively contributes both to the energetic budget and to the

survival of the individual, by limiting the duration of a period of vulnerability. The mechanisms o! attachment to

a site, and those of juvenile dispersion constitute unsolved problems at the moment. Their solutions would

make it possible to evaluate the metapopulation concept (Gill 1978, Couvet et al. 1985).

This study was supported by an allocation of the MinistOre Fran~ais de I'Education

Natlonale.We thank Tim Halliday and an anonymous referee for their constructive criticisms. E,lglish has been

corrected by Glyn Thoiron.

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