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The functional significance of colour polymorphism in the European common wall lizard (Podarcis muralis)

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The functional significance of colour polymorphism in the European common wall lizard (Podarcis muralis)

dc.contributor.advisor	Font Bisier, Enrique
dc.contributor.advisor	Pérez i de Lanuza, Guillem
dc.contributor.author	Ábalos Álvarez, Javier
dc.contributor.other	Departament de Zoología	es_ES
dc.date.accessioned	2021-04-12T16:48:06Z
dc.date.available	2021-04-13T04:45:05Z
dc.date.issued	2021	es_ES
dc.date.submitted	23-04-2021	es_ES
dc.identifier.uri	https://hdl.handle.net/10550/78563
dc.description.abstract	Colour polymorphisms, the coexistence of two or more colour morphs of a species within a population, have long fascinated evolutionary biologists interested in the mechanisms generating and maintaining phenotypic variation in nature. The functional significance of colour polymorphisms (i.e. their adaptive value) is often linked to the selective mechanisms responsible for their maintenance over time. In lizards, the hypothesis that colour morphs may reflect alternative reproductive strategies involving differential sociosexual behaviour and/or alternative reproductive strategies has come to dominate the field. Wall lizards (family Lacertidae, genus Podarcis), with several geographically distant species that exhibit two or more alternative ventral colour morphs, have often been identified as a group in which alternative reproductive strategies and frequency-dependent selection likely underpin colour polymorphisms. However, several key aspects regarding the link between behaviour, fitness, and lacertid colour polymorphism remain overlooked or inadequately studied. In this thesis we tried to fill these gaps by experimentally addressing some of the most commonly assumed ideas about the functional significance of colour polymorphism in the European common wall lizard (Podarcis muralis, Laurenti 1768). In some populations of this species (e.g. eastern Pyrenees), adult lizards of both sexes may show up to three “pure” alternative colour morph (orange, white, yellow), and two mixed morphs consisting of a mosaic of differently-coloured scales (orange-white, yellow-orange). Although colour morphs are frequently thought to function as social signals mediating intraspecific interactions, morph categorization has been never assessed from the viewpoint of the intended receivers (i.e. conspecifics). Here, using a discrimination experiment and visual modelling, we found that lizards likely perceive the alternative colour morphs as chromatically distinct and show evidence of discriminating among them based on hue, rather than luminance. To evaluate the role of male coloration (including alternative colour morphs) in intra-sexual competition), we conducted lab-staged dyadic contests among size-matched males. We found lower fighting ability in lizards showing a smaller fraction of their outer ventral scales covered with dark melanin-based spots, and in lizards with orange ventral colour (which could result from the existence of a subordinate non-territorial strategy in this morph). However, our results in later studies (with a free-ranging population and ten experimental mesocosm enclosures), strongly refute the hypothesis that alternative socio-sexual behaviour or space use strategies characterize colour morphs when lizards interact under more natural conditions. In the free-ranging populations, colour morphs did not differ in inter-annual site-fidelity, home-range size, or male-female overlap. In the mesocosm enclosures, spatial dominance was the prime determinant of male fitness across colour morphs. In a later experiment, we conducted controlled matings among pure colour morphs and found no overall effect of female morph on clutch size or juvenile mass, and no effect of morph combination on offspring viability or prospective fitness. These results refute the existence of alternative reproductive strategies in female morphs and are also in disagreement with predictions from both correlational selection and heterosis. Lastly, by keeping the juveniles of known crosses in outdoor enclosures for a year, we studied the inheritance and ontogeny of P. muralis colour polymorphism. Specifically, our results confirmed that orange and yellow colour expression depends on two recessive alleles located at two separate autosomal loci and revealed that the whitish coloration exhibited by newborn lizards is likely perceived by conspecifics as a chromatically distinct colour different from any of the morph colours expressed by adult lizards. Overall, in this thesis we have hopefully presented compelling arguments to revise our perspective on the functional significance of lacertid colour polymorphisms, suggested promising lines of research for future work, and generally contributed to our understanding of the processes maintaining intra-specific variation in natural populations at large.	en_US
dc.description.abstract	Colour polymorphisms, the coexistence of two or more colour morphs of a species within a population, have long fascinated evolutionary biologists interested in the mechanisms generating and maintaining phenotypic variation in nature. The functional significance of colour polymorphisms (i.e. their adaptive value) is often linked to the selective mechanisms responsible for their maintenance over time. In lizards, the hypothesis that colour morphs may reflect alternative reproductive strategies involving differential sociosexual behaviour and/or alternative reproductive strategies has come to dominate the field. Wall lizards (family Lacertidae, genus Podarcis), with several geographically distant species that exhibit two or more alternative ventral colour morphs, have often been identified as a group in which alternative reproductive strategies and frequency-dependent selection likely underpin colour polymorphisms. However, several key aspects regarding the link between behaviour, fitness, and lacertid colour polymorphism remain overlooked or inadequately studied. In this thesis we tried to fill these gaps by experimentally addressing some of the most commonly assumed ideas about the functional significance of colour polymorphism in the European common wall lizard (Podarcis muralis, Laurenti 1768). In some populations of this species (e.g. eastern Pyrenees), adult lizards of both sexes may show up to three “pure” alternative colour morph (orange, white, yellow), and two mixed morphs consisting of a mosaic of differently-coloured scales (orange-white, yellow-orange). Although colour morphs are frequently thought to function as social signals mediating intraspecific interactions, morph categorization has been never assessed from the viewpoint of the intended receivers (i.e. conspecifics). Here, using a discrimination experiment and visual modelling, we found that lizards likely perceive the alternative colour morphs as chromatically distinct and show evidence of discriminating among them based on hue, rather than luminance. To evaluate the role of male coloration (including alternative colour morphs) in intra-sexual competition), we conducted lab-staged dyadic contests among size-matched males. We found lower fighting ability in lizards showing a smaller fraction of their outer ventral scales covered with dark melanin-based spots, and in lizards with orange ventral colour (which could result from the existence of a subordinate non-territorial strategy in this morph). However, our results in later studies (with a free-ranging population and ten experimental mesocosm enclosures), strongly refute the hypothesis that alternative socio-sexual behaviour or space use strategies characterize colour morphs when lizards interact under more natural conditions. In the free-ranging populations, colour morphs did not differ in inter-annual site-fidelity, home-range size, or male-female overlap. In the mesocosm enclosures, spatial dominance was the prime determinant of male fitness across colour morphs. In a later experiment, we conducted controlled matings among pure colour morphs and found no overall effect of female morph on clutch size or juvenile mass, and no effect of morph combination on offspring viability or prospective fitness. These results refute the existence of alternative reproductive strategies in female morphs and are also in disagreement with predictions from both correlational selection and heterosis. Lastly, by keeping the juveniles of known crosses in outdoor enclosures for a year, we studied the inheritance and ontogeny of P. muralis colour polymorphism. Specifically, our results confirmed that orange and yellow colour expression depends on two recessive alleles located at two separate autosomal loci and revealed that the whitish coloration exhibited by newborn lizards is likely perceived by conspecifics as a chromatically distinct colour different from any of the morph colours expressed by adult lizards. Overall, in this thesis we have hopefully presented compelling arguments to revise our perspective on the functional significance of lacertid colour polymorphisms, suggested promising lines of research for future work, and generally contributed to our understanding of the processes maintaining intra-specific variation in natural populations at large.	es_ES
dc.format.extent	302 p.	es_ES
dc.language.iso	en	es_ES
dc.subject	evolución	es_ES
dc.subject	comportamiento	es_ES
dc.subject	estrategias alternativas de reproducción	es_ES
dc.subject	lagartija roquera	es_ES
dc.subject	polimorfismo de color	es_ES
dc.subject	evolution	es_ES
dc.subject	behaviour	es_ES
dc.subject	alternative reproductive strategies	es_ES
dc.subject	wall lizard	es_ES
dc.subject	colour polymorphism	es_ES
dc.title	The functional significance of colour polymorphism in the European common wall lizard (Podarcis muralis)	es_ES
dc.type	doctoral thesis	es_ES
dc.subject.unesco	UNESCO::CIENCIAS DE LA VIDA	es_ES
dc.embargo.terms	0 days	es_ES