Socially Mediated Plasticity and Polymorphism: Integrating Theory and Experiment to Predict Alternative Phenotypes
Understanding the maintenance of phenotypic variation within populations has long been a puzzle in evolutionary biology. Many models ignore that fact that animals are not living alone; instead social factors have the potential to alter the development and fitness consequences of alternative phenotyp...
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| Format: | Others |
| Language: | English English |
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Florida State University
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| Online Access: | http://purl.flvc.org/fsu/fd/2019_Fall_Lange_fsu_0071E_15531 |
| Summary: | Understanding the maintenance of phenotypic variation within populations has long been a puzzle in evolutionary biology. Many models ignore that fact that animals are not living alone; instead social factors have the potential to alter the development and fitness consequences of alternative phenotypes to promote variation in many systems. Furthermore, while there is empirical evidence that individuals alter phenotypes in response to social cues, it is unclear under what conditions socially-cued plasticity will evolve and be adaptive. My dissertation research combines theory with developmental experiments in sailfin mollies (Poecilia latipinna) to understand if and how individuals alter phenotypes in response to social cues. The first chapter of my dissertation uses an individual-based modelling approach to determine if and when individuals should evolve a strategy that uses social cues during development to alter the expression of alternative phenotypes. We found that socially-cued plasticity evolves under limited conditions where selection acts on survival differences between alternative phenotypes and the expression of socially-cued plasticity is costly. Socially-cued plasticity was not adaptive when selection acted on fecundity. Because costs facilitated the evolution of adaptive socially-cued plasticity, our results suggest that socially-cued plasticity is a special case of plasticity where general models do not hold. Furthermore, we found that socially-cued plasticity is a self-limiting strategy; using social cues to alter phenotypes in adulthood was most likely to evolve when the majority of the population was not using socially-cued plasticity; this scenario allowed social cues to be reliable predictors of environmental conditions. In the second and third chapter of my dissertation, I used sailfin mollies to determine how species with alternative reproductive phenotypes (ARPs) alter their life history and mating behavior in response to social cues during development. Sailfin mollies are a livebearing fish that exhibit extensive variation in body size and correlated traits including age at maturity, morphology and mating behavior, both within and between populations. Together these traits make up a male's ARP. Smalls males mature quickly (50-60 days) and use their disproportionally longer intromittent organ in sneaking behavior. Large males take longer to mature (130-150 days) and use their disproportionally larger dorsal fins in courtship displays to entice female cooperation in mating. Intermediate-sized males, which are intermediate in morphology and time to maturity, switch between courting and thrusting depending on the social context. Previous studies have examined the role of abiotic environmental factors on male ARP in mollies, but found that these factors cannot account for the observed inter- and intra-population variation. Since mollies are gregarious and social environment has been shown to influence adult male behavior, we hypothesize that variability in social conditions can influence the relationships between genotype and phenotype to produce ARP variation. My second chapter describes an experimental study where we examined the relationship between genotype and phenotype by determining how the variation in social environment during development influenced sex-specific differences in life history phenotypes. We found that both variation in the social environment influences life history development in both males and females, but there were sex-specific differences in how social environment modulated the genotype-phenotype relationship. These results suggest that social environment is an important driver of life history differences in sailfin mollies. My final experiment tested the hypothesis that social environment during development affects male alternative mating behaviors. We found that courtship and sneaking behaviors were affected by variation in the social environment, but these effects manifested in complex interactions between experimental treatments. For example, the relationship between body size and courtship displays was affected by a genotype by social environment interaction, and there was a three-way interaction between genotype, developmental stage, and the male’s own body size. In addition,. These results implicated alternative reproductive morph, social environment during development, stage, and body size as non-independent factors in the expression of male ARPs. Results from my dissertation demonstrate that conditions for adaptive evolution of socially-cued plasticity are limited, but despite this, variation in social cues elicited substantial variation in life history and behavior, in ways not accounted for by current life history or sexual selection theory. These seemingly paradoxical results may be resolved by considering the natural history of mollies. Sailfin molly males of different ARPs have differences in survival and therefore results from the modelling chapter suggest mollies may be a system where socially-cued plasticity would evolve. To determine if the patterns observed in this dissertation are adaptive, or are accounted for by gene flow, by exposing animals to social environments they would not typically encounter in nature, or by other non-adaptive processes, future studies should assess mortality in different social environments and reproductive success to determine how social environment affects fitness. Taken together, my dissertation provides a better understanding of how phenotypic plasticity evolves and how social environment affects life history and mating behaviors. === A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === 2019 === November 7, 2019. === alternative reproductive phenotypes, life history, Poecilia latipinna, social environment, socially-cued anticipatory plasticity, theory === Includes bibliographical references. === Kimberly A. Hughes, Professor Directing Dissertation; Elaine Hull, University Representative; Joseph Travis, Committee Member; Emily DuVal, Committee Member; Don Levitan, Committee Member. |
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