The Role of Sex-specific Plasticity in Shaping Sexual Dimorphism in a Long-lived Vertebrate,the Snapping Turtle <Emphasis Type="Italic">Chelydra serpentina</Emphasis> |
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Authors: | Claudia Patricia Ceballos Nicole Valenzuela |
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Institution: | (1) Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 253 Bessey Hall, Ames, IA 50011, USA; |
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Abstract: | Sex-specific plasticity, the differential response that the genome of males and females may have to different environments,
is a mechanism that can affect the degree of sexual dimorphism. Two adaptive hypotheses have been proposed to explain how
sex-specific plasticity affects the evolution of sexual size dimorphism. The adaptive canalization hypothesis states that
the larger sex exhibits lesser plasticity compared to the smaller sex due to strong directional selection for a large body
size, which penalizes individuals attaining sub-optimal body sizes. The condition-dependence hypothesis states that the larger
sex exhibits greater plasticity than the smaller sex due to strong directional selection for a large body size favoring a
greater sensitivity as an opportunistic mechanism for growth enhancement under favorable conditions. While the relationship
between sex-specific plasticity and sexual dimorphism has been studied mainly in invertebrates, its role in long-lived vertebrates
has received little attention. In this study we tested the predictions derived from these two hypotheses by comparing the
plastic responses of body size and shape of males and females of the snapping turtle (Chelydra serpentina) raised under common garden conditions. Body size was plastic, sexually dimorphic, and the plasticity was also sex-specific,
with males exhibiting greater body size plasticity relative to females. Because snapping turtle males are larger than females,
sexual size dimorphism in this species appears to be driven by an increased plasticity of the larger sex over the smaller
sex as predicted by the condition-dependent hypothesis. However, male body size was enhanced under relatively limited resources,
in contrast to expectations from this model. Body shape was also plastic and sexually dimorphic, however no sex by environment
interaction was found in this case. Instead, plasticity of sexual shape dimorphism seems to evolve in parallel for males and
females as both sexes responded similarly to different environments. |
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