The role of phenotypic plasticity in the interpretation of ecological data

E. A. Morales''', F.R. Traino131 PCER, The Academy of Natural sciences of philadelphia, philadelphia, USA

^ ' ULRA, Universidad Mayor de San Simon, Coci-rabamba, BoLivia" Department of Ecology and Evolutionary Biology, The University of Connecticut,

Connecticut, USAmorales@acnatsci.org

Keywords: Algae, phenotypic plasticity, ecology, taxonomy

Abstract

Phenotypic plasticity is the capability of an individual to produce several phenotypes rnresponse to environmental changes In the algae, plasticity studies predate those inother groups with numerous examples at the morphological and physiological levels.Recent investigations elucidate the genetic and molecular mechanisms for piasticity, butvery little has been done regarding the influence of plasticity on other biological fields. Inbioindication, for example, plasticity could become a tool for the interpretation ofenvironmental impact through the phenotypes encountered in an environment ano,thus, plasticity could enhance the precision with which water quality is currentryevaluated. We present a view of how plasticity could be integrated into ecologicalanalyses based on a literature review complementary to our previously publishedrevtews.

1. lntroduction

When we want to initiate studies of the algal microflora present in a river, lake orestuary, or even simply enumerate these organisms, we most often use one of severarcommon keys. At that point, individuals who are just breaking into the field assume thateach of these identifications is accurate. But, with more experience we realize that thisis not so one sometimes has to employ an imperfect, and even deficient, taxonomy. Atpresent this is all the more troubling when we observe the many modifications proposedby extensive studies of relationships of organisms using molecular information Whenrelying strictly on non-molecular determinations, many investigators are unaware of thefact that one deals with the identification of palmelloid chlorophytes in one way, butmarine haptophytes or diatoms very differently Even in just these three groups, thespecies names used often have quite different meanings.

The causes of this taxonomic uncertainty are mostly historical and are usually related tothe sampling protocols, the laboratory culturing techniques and the limited resolutionprovided by the light microscope. Even today, only a few studies employ a samplingprotocol that spans several seasons and are spatially spread over the geographic

1150

Subiema 4: Innovaciones en pesouerias continentales v ecoloqia acudtica

extension of an aquatic system. As a result, only narrow windows in the life histories oforganisms are observed, which serve -in many cases- as the sole foundation for theerection of new taxa. Culturing of algae often takes place under standard conditions,which could hardly show the average behavior, physiology and or morphology of an

organism. Many results gathered under standard conditions have become thefoundation for physiological conclusions or even morphological assessments of taxa. ltls commonly accepted that if culture data are added to a protologue, the protologue is

then more robust, but if one set of conditions is all that is used, then supporting culturedata are clearly incomplete.

The development of the scanning (SEM) and transmission (TEM) electron microscopeshas had a profound influence on algal taxonomy and systematics. Many of thetaxonomic concepts developed with the aid of the light microscope have beendrastically modified with many groups split into many taxa. Some groups of algae havebeen only recently discovered mainly because light microscopy (LM) did not provide

sufficient resolution to resolve either the outline or cell structure of very small taxa. As aresult, many new classes and genera have appeared in the literature, and the numberof new species has skyrocketed in the last decade or so

The consequences of an uncertain taxonomy on ecological assessments are dramatic.Environmental impact studies using the algae currently employ a taxonomic system builton the morphological species concept, which might be summarized as "one morph - onetaxon". Such studies fail to recognize a species as plastic (i.e., an adjustable entity, a

genotype able to produce several environmentally induced phenotypes [morphs]), thusgiving a skewed view of the entities reacting to environmental change. lf each of themorphs is recognized as a separate species (as it often happens in the literature) thenthe whole spectrum of possible reactions of the underlying genotype will never be

recognized. Moreover, the notion of bioindicators is based on the premise that a speciesreaches its maximum abundance around an optimal environmental value, producing abell-shaped type of response. Within the plasticity framework, a single species is

actually capable of producing several abundance peaks, each represented by a morph.

Only recently, some ecological data have been found useful in developing a moremodern taxonomy of a limited number of algae But still, this does not represent a viable

solution, for the linkage of morphs with specific environmental conditions is only the

starting point in the recognition of plastic taxa.

The full spectrum of morphological variability of a given taxon can only be unraveled by

careful long-range monitoring, whether this in the field or the laboratory. Hence there

are strong arguments in favor of controlled laboratory studies that would make the

connection between the genotype and its responses to different and specific conditions.

In the following pages we further explore the relationship of plasticity and ecologythrough a review of recent literature.

I l5t

2. Discussion

The connection between plasticitv and ecoloqvPlasticity is a property of the genotype that arises from adaptation to changingenvironments, for a genotype reacts to its internal (within the cell or organismy and/orexternal (the habitat) medium, and then produces a modified phenotype (Fig. t) 11,2,31. Thus, any consideration of plasticity always has ecological implications at the level ofindividuals and their populations and communities. Publications on the effects ofplasticity on ecology are very revealing and affect the very foundation of population anocommunity ecology (see for example: werner and peacor [4], Bolker et al. [5], callawayet al [6]).

EHVIROHMEHT

PHENOTYPE

tr*"fI*Legend:A The environment indirectly affects the genotype through the phenotype, modifying the structure and/orrelationships among genes and their emerging propertiesB Schematic view of how alternative phenotypes are produced mediated by environmental influences

Fig. 1: The relationship between genotype, phenotype and environment

Classically, it was assumed that populations competed for resources by using the"tools" coded for by their genes and that these tools varied within very narrow limitsimparted by genetic variation. When evolution came into the picture, the tools werethought to change irreversibly over time due to selective pressures, includingcompetttion (in the latter case, the process is known as character displacement) Evenmodels such as those produced using the Lotka-Volterra equations assumed thatcompeting species had these fixed phenotypes [5, 7] Plasticity studies, however, reveal

1152

f-t-l

t

CHANGES Ih]

GEh]ETIC STRUCTURE

l,,,1Lrtstion, Trfl nsposition,Chrrrrrrosome rearrangernent,

Duplication, Conversion

t'-. --__- -

I

GE NOTYP E

CHANGES IN GENETICCORRELATIONS

Sub-tema 4: lnnovaciones en pesquerias continentales v ecoloq[a acudtica

that phenotypes can be modified reversibly maximizing their use of a resource andensuring their survival in the face of environmental change [4, 8]. For example, variousmacro and microalgae are able to alter their rates of growth and photosynthesisfollowing environmental, and presumably biological, cues [9, 10,'11, 12]. Unforlunately,results of the extrapolation of these studies to population and community levels remainto be seen (see Bell lTlfor a notable exception).

Plasticity is also related to conservation and biodiversity issues 113, 141. Plasticresponses of threatened species, their competitors, and their predators are vital piecesin the conservation puzzle and are necessary in order to apply a more accurateconservation program. Morales et al. [15] considered the effect of plasticity onbiodiversity stating that the number of species described within a genus could b6lowered, because many environmentally induced morphs are currently considered asseparate species, yet the number of forms and varieties could be increased as carefulresearch of the genetics and ecology of that genus is performed.

A great deal of investigations has been published on the topic of plasticity in predator-prey interactions. Prey is able to withstand grazing effects by detecting the presence ofpredator exudates and producing a phenotype incompatible with the food requirementsof the predator (e.9., changes in size and palaiability) A striking example is that ofspecies in the green algal genus Scenedesmus [16, 17,18], in which the formation oftetracellular colonies from unicellular individuals is triggered by predator excretions.Tetracellular morphs are less likely to be caught as prey, unless there is an even largergazet. When community level interactions are considered the web of causes andeffects between competitors and prey-predators become so complex that we canhypothesize only some outcomes of the multiple interactions Yet, consideration ofthese complex problems seems to be the only way to assess the true nature ofbiological communities and their ecology

Maintaining the link between theoretical and empirical plasticity studies is imperative,but even in the more traditional branches of ecology this link is still weak. Werner andPeacor [4] state that the causes for the divorce between theoreticians and empiricists isdue to the intricate fashion in which the theory is presented as well as a failure toextrapolate results from individuals to population and community scales. Indeed, thereare many examples of individual-scale plasticity experiments [9, 19, 20] and theoreticaltreatments have been growing steadily 115,21,22,231. Yet the absence of a unifiedfront is conspicuous. A holistic view would certainly change the way we view topicsfrom species concepts to aquaculture and conservation biology.

A:vrewlqrgegrcssAs stated above, three are the main historical reasons for uncedainty in the taxonomy ofalgae: sampling deficiencies, bias in culturing and limited power of traditionalmicroscopy tools. Sampling protocols must be expanded if life histories of organismsare to be observed in detail and the traditional view that biodiversity studies are to bebuilt on a single visit to an aquatic system is faulty Elucidating life histories is importantin an ecological context since they show the different phases of an organism and how

153

each of them is affected by the environment. Also, the more details of the ecology of ataxon are known, the more accurate the paleo-conditions of a lake (for example) can beassessed 124,251, improving the predictive power of multivariate and other models usedto study ecosystem change. Life histories are to be assessed by careful fieldobservations and controlled laboratory experimentation, especially the latter will yieldthe plastic capabilities of species and the ecological conditions that trigger them Thusfar, we have been slow to recognize certain aspects of algal plasticity, in part becausethe field had to develop adequate culture media. The latter, at times, was a slowerprocess than we might have expected, but progress occurred over approximately 150years (Table 1).

Table 1: Interest in balanced culture media and phenotypic plasticity overtimeCULTURES PLASTICITY

. The late 7800s. The first microalgal cultures, i e 'The late 7800s. Morphological variability wasChtorella and some cyanobacteria, were weeds. recognized for but a few taxa Many disagreed withThese tolerant organisms grew under the Cooke [26]: " .lhese lower algae, howeverconditions imposed. Mediaformulations were beautiful and interesting as microscopical objectscrude, with essential trace elements sometimes were not autonomous; many seemed fo pass rnloprovided only as contaminants of major elements each other by intermediate forms" Field datalllumination was in a north window and/or bv Support was yet to come. The choice was to:incandescent bulbs, with accompanying heat ' keep using past species names, orGrowing conditions were rudimentary, not natural . apply conclusions broadly,

Summary: Culture conditions were not adequate Summary: With no clear picture available, repoftsfor handling several research problems. of plastic responses were ignored.

'Period from 1900 to about 7950- Use of typical . The period from 1900 to c. 1950- Chodat [27]media enabled researchers to continue making published on plasticity in culture, while othersobservations in the laboratory year round, as well questioned reliability A morph might dominateas to exchange material Buffering was achieved because of the limited battery of signals presentedwith use of monobasic and dibasic phosphates, but in a culture study Axenic cultures appeared Someprovided 1000X more P than naturelSpiking of criticized any laboratory generated data, favoringmediacontinued,withtotal saltlevel oftenoverone environmental data Wewerejustbeginningtogram/L; unknowingly, trace impurities were part of appreciate the complexities of nature; precisethe package As reagent grade chemicals became replication of a lab event was not completelyavailable, each essential element was determined, understood. After 1926, examination of plasticityand added to media Some continued to use older fell outof fashion forthree oecaqesrecipes which worked for selected organisms!

Summary: Precision accompanies use of a modern Summary: Most worked comforlably either in themedium formulation laboratory or field, with little understanding of a

different approach.. The late 20th century: ldeally the organism in . The late 20th century: Data derived from cultureculture duplicates nature. However, only replication studies quickly accumulated, with the result thatof the dynamic conditions in nature, physical, many conflicts were resolved More examples ofchemical and biological flux, step by step, will lead plasticity surfaced and were confirmed, especiallyto this goal. Cyclic changes in the assemblage of coupling field studies with culturing. With someorganisms and developmental stages take place macroalgae, adjustments to photoperiod andLaboratory studies opted for siandard conditions- a temperature triggered alternate life history stagesspecific medium, temperature & illumination Focus (Wynne [30]) In addition, we continued to debateonmaintainingthisstandard atall times restricts thevalueof axeniccultures,foralgaegrowintheus Current laboratory media are complete and presence of other organisms in nature. Clearlybalanced, a base from which investiqations miqht experimentation with xenic cultures has value

1154

sub-tema 4: lnnovaciones en pesquerias conlinentales v ecoloqia acu6tica

be expanded The first media had ammoniumnitrate (NH4N03), potassium dibasic phosphate(KrHPO4), magnesium sulphate (MgSOo THrO),and ferric chloride (FeC13) plus distilled water. Nowseveral formulations are available, providing allknown required elements, buffer action andchelated trace elements. Chu [28] and Rodhe [29]devised useful /owsalts media which supoortedfewer cells- lower carrying capacity-, but was morein tune with nature. When needed, a high cellconcentration was maintained bv increasino N andP levels

especially when we know precisely what non-photosynthetic organisms are present and theirabundance. Many obstacles remain, but numerouscarefully controlled experiments have documentedextensive plasticity in sufficient organisms tosuggest the value of incorporation of this topic intoour knowledge of each organism, whether theapproach be physiological, morphological,molecular or systematic Universal acceptance ofplasticity by taxonomists is currently lagging

Summary: We learn about an organism's potential Summary: Knowledge of algal plasticity, regutated'by mimicking thoroughly natufglyglg@V. tV g"r"

"rti"r, i

Continued use of TEM and SEM will give a better picture of morphological changes atthe ultrastructural level, which would lead to better identification keys and a morereliable taxonomy. lt is frequently the case that once the ultrastructure has beenelucidated, going back to LM results in the recognition of some ultrastructural featuresth,at are diagnostic. lt is very important to continue the use of the LM (at magnificationsof 1000X or more) in routine ecological assessments since this practice keeps costs lowand enables more researchers to do this type of investigations. Unfortunately, privateand public funding agencies are not always willing to fund extended sampling, evenlimited culturing and/or ultrastructural studies Thus awareness of the importjnce ofbiodiversity studies must be raised in the eyes of such agencies

In recent years, molecular studies have proved to be extremely useful in the study ofplasticity and they might make the task much easier than expected The numbei ofstudies linking plasticity to biodiversity is steadily increasing [13, 31]. One of the mostremarkable connections between plasticity and biodiversity has been accomplishedthrough experiments in Chlamydomonas [7, 32, 33]. As noted by several authors [33,34, 351, several genotypes of a plastic population are favored by natural selection inunstable environments. This is because directional selection is unlikely to operate onany one genotype since none of the genotypes is able to reach maximum fitness underall environmental circumstances Hence, plasticity and local population regulation leadto a negative frequency-dependent selection of the genotypes, thus maintainingdiversity. The implication of this interpretation is widespread even at the communitvlevel [32, 36].

3. Conclusions

By considering plasticity along with other processes we get closer to the view oforganisms as functional and evolving entities, not static and immutable organisms [15,21, 221 From a taxonomic standpoint, consideration of plasticity leads u! to a morenatural classification system, while simultaneously presenting a holistic view oforganisms interacting with their biotic and abiotic media Plasticity is then a unifying

concept that links genetics, organism biology, biodiversity and ecology giving us a morecomplete and accurate view of nature.

References

tll M. Pigliucci. How organisms respond to environmental changes: from phenotypesto molecules (and vice versa). Tree, 17, 168-173, 1996.

l2l M. Pigliucci. Phenotypic plasticity. Beyond Nature and Nurture The JohnsHopkins University Press, Baltimore, USA, 2001.

t3l C. Schlichting, M. Pigliucci. Phenotypic Evolution: A Reaction Norm Perspective.SrnauerAssociafes, Sunderland, Massachusetts USA. 1998.

t4l E Werner, S. Peacor. A review of trait-mediated indirect interactions in ecologicalcommunities. Ecol., 84, 1083-11 00, 2003

tsl B. Bolker, M. Holyoak, V. Kiivan, L. Rowe, O. Schmitz. Connecting theoretical andempiricalstudies of trait-mediated interactions Ecol., 84,1101-1114,2003.

t6l R. Callaway, S. Pennings, C. Richards. Phenotypic plasticity and interactionsamong plants. Ecology, 84, 1115-1128, 2003.

l7l G. Bell The ecology and genetics of fitness in Chlamydomonas lll. Genotype-by-environment interaction within strain s Evolution, 45, 668-679, 1 991 .

t8l J Grime, J. Crick, J. Rincon. The ecological significance of plasticity. In: D.Jennings and J Trewavas. (Eds ) Plasticity in Plants p 5-29 Symposia of theSociety for Experimental Biology, 40, England, 1986.

tgl L Collado-Vides, D. Robledo. Morphology and photosynthesis of Caulerpa(Chlorophyta) in relation to growth form. J. of Phycology, 34,325-330, 1999.

tl0l C Payri, S. Marotorena, C. Bizeau, M. Rodiere. Photoacclimation in the tropicalcoralline alga Hydrolithon onkodes (Rhodophyta, Corallinaceae) from a frenchPolynesian reef J. of Phycology, 37,223-234,2001.

l11l R. Smith, l-. Stapleford, R. Ridings. The acclimated response of growth,photosynthesis, composition, and carbon balance to temperature in thepsychrophilic ice diatom Nitzschia seriata. J. of Phycology, 30,8-16 1994

t12l E Tang, R. Tremblay, W Vincet. Cyanobacterial dominance of polar freshwaterecosystems: are high-latitude mat-formers adapted to low temperature? J ofPhycology, 33, 171-1 81, 1997.

t13l C. Bertrand, E. Franquet, S. Fayolle, A. Cazaubon. Une nouvelle approche de labiodiversite: plasticit6 morphologique chez une diatom6e d'eau douce. Comptesrendus Biologies, 326, 107 -120, 2003.

[14] E. Morales, F. Trainor. Las algas: conceptos criticos en la evaluacion de sudiversidad. In. R Primack, R. Rozzi, P. Feisinger, R. Dizo and F. Massardo(Eds.) Fundamentos de Conservacion Biologica Perspectivas Latinoamericanas,77-80, Fondo de Cultura Economica, M6xico, 2001.

t15l E. Morales, F. Trainor, C. Schlichting. Phenotypic plasticity in the algae: ecologicaand evolutionary implications. Consf ancea, 83,2002.

l16l M. LUrling. Effect of grazing-associated infochemicals on growth andmorphological development in Scenedesmus acutus (Chlorophyceae). J. ofPhycology, 34, 578-586, 1 998.

1 156

S u b 4e m a 4 : I n nov a c i on e s e n pe s-g u p!! BSGpn !j0 e n !A! BE v e co lo q i a a c u 6ti ca

t17) M. LUrling. Grazer-induced coenobial formation in clonal cultures of Scenedemusobliquus (Chlorococcales, Chlorophyceae). J. of Phycology, 35,19-23, 1999.

[18] M. LUrling, E. Van Donk. Grazer-induced colony formationin Scenedesmusacutus (Chlorophyceae): Ecomorph expression at different temperatures. J. ofPhycology, 35, 1120-11 26, 1 999.

[19] P. Egan, F. Trainor. The Scenedesmus unicell: lts importance to the speciesconcept in the genus. Canadian Journal of Botany, 68, 1864-1872,1990.

120) H. Hurka. Environmental control of the morphology of the reef alga Turbinariaornata (Turn.)J. Ag. (Sargassaceae) studied by means of statistical populationanalysis. Osterr. Bot. 2., 120,369-389, 1972.

t21l E. Morales, F. Trainor. Phenotypic plasticity: its importance in developing a newalgal concept. The case for Scenedesmus. Algae, 12, 147-157, 1997.

l22l E. Morales, F. Trainor. Phenotypic plasticity in Scenedesmus: lmplications foralgal taxonomy and ecology. Gayana Botanica, 56, 11-20, 1999.

l23l J. Raven. Plasticity in algae. In: D. Jennings and J. Trewavas (Eds.). Plasticity inPlants. Symposia of the Society for Experimental Biology, 40, 347-372, 1986.

l24l S. Hausmann, A Lotter. Morphologicalvariation within the diatom taxon Cyclotellacomensis and its importance for quantitative temperature reconstructions.Freshwater Biology, 46, 1323-1333, 200'1.

l25l S. Kilham, P. Kilham. Melosira granulata (Ehr.) Ralfs: morphology and ecology ofa cosmopolitan freshwater diatom. Verh. lnternat. Verein. Limnol., 19,2716-27211975.

126l M. Cooke. Introduction to Fresh-water algae. Kegan Paul, Trench, Trubner & Co,London,1890.

I27l R. Chodat. Scenedesmus. Etude de g6netique, de syst6matique experimentale etd' hyd robiolo gie. Revue H yd ro bi olog i e, 3, 7 1 -258, 1 926.

l28l S Chu. The influence of the mineral composition of the medium on the growth ofplanktonic algae l. Methods and culture media J. of Ecology, 30,284-325,1942.

l29l W Rhode. Evironmental requirements of freshwater plankton algae. Symbol. BotUpsa/iensls, 1 0, 5-145, 1948.

t30l M. Wynne Life history and systematic studies of some Pacific North AmericanPhaeophyceae (brown algae). Univ. CA Publications in Botany,50, 1-88, 1969.

t31l J Blomster, C Maggs M. Stanhope. Extensive intraspecific morphologicalvariation in Enteromorpha muscordes (Chlorophyta) revealed by molecularanalysis. J. of Phycology, 35,575-586, 1999

l32l G. Bell. The ecology and genetics of fitness in Chlamydomonas ll. The propertiesof mixtures of strains. Proc of the Royal Soc. of London, 240, 323-350, 1990b.

t33l G. Bell The ecology and genetics of fitness in Chlamydomonas V. Therelationship between genetic correlation and environmental variance. Evolution,46 561-566. 1992.

t34l G. Bell. Two theories of sex and variation. Experientia, 41, 1235-1245, 1985t35l J. Maynard Smith Genetic polymorphism in a varied environmenl. American

Naturalist, 1 04, 487 -490, 1 970.

136l G Bell The ecology and genetics of fitness in Chlamydomonas l. Genotype-by-environment interaction among pure strains. Proc. of the Royal Society of London,240. 295-32'1. 1990a.

It57

Congreso Internacional sobre Desarrollo, MedioAmbiente y Recursos Naturales: Sostenibilidad aM0ltiples Niveles y Escalas

International Congress on Development,Environment and Natural Resources. Multi-level andM u lti-scale Sustai nabil ity

Volumen ll / Volume ll11-l3julio / JulY 2007Cochabamba, Bolivia

Editado por I Edited bY:

Jan Feyen, Luis F. Aguirre, Monica Moraes R.

Publicacion de la / Publication of theUniversidad Mayor de San Simon

Volumen ll/ Volume llTitulo/Title: "Congreso Internacional sobre Desarrollo, Medio Ambiente y Recursos Naturales:

sostenibilidad a multiples niveles y escalas"/ "lnternational Congress on Development,

Environment and Natural Resources: Multi-level and Multi-scale Sustainability"

Tef ./fax: 4 234244Casilla 1167

Edicion/Edition: Jan Feyen, Luis F Aguirre, Monica Moraes R'

Disefro tapas/Cover designe: Mauricio Rojas

Disefro interior/ General layout: Jan Feyen' Margareta Camps

D.L.2-1-1269-07

AfiolYear:2007

lmpresi6n: Talleres Gr6ficos "Kipus", lelf . 4237448, Cochabamba

Printed in Bolivia