Patterns and Limits of Phenotypic Plasticity in Guppies Across Ecological Contexts

Abstract

Phenotypic plasticity is an important adaptation for organisms that live under fluctuating environmental conditions. It can create trait variability, broaden the adaptive surface of organisms, and help population persistence. However, investment in phenotypic plasticity may require complex molecular and physiological demands, potentially leading to trade-offs. Under sexual selection, different strategies can lead to the same fitness outcomes, allowing for the diversification of phenotypic plasticity. However, cue reliability and developmental constraints may limit the evolution of specific periods that traits be plastic. Plasticity during early development allow traits to be more flexible, however it can also create mismatches between adult phenotype if environmental conditions change. While plasticity can be exhibited at different life stages, the extent to which animals rely more on plasticity before or after maturity is unknown. For my PhD, I used a series of laboratory experiments to test how different environmental conditions affect phenotypic plasticity in guppies (Poecilia reticulata), a species under strong sexual selection. For chapters 1 and 2, I explore the effects of early-life food restriction on guppy life-history traits under two temperatures. I found that guppies are able to maintain a compensatory growth response after diet restriction even under high temperatures. However, patterns of size and time at maturation were sex specific. My results also showed that the combined effect of high temperature and diet restriction early in life stunted male size, persisting up to eight months after treatment exposure. In chapter 3, I conducted an experiment focusing on the effects of social competition on developmental and sexual traits. I found that developing in a population of higher quality males did not affect either developmental or sexual traits in male guppies. Highlighting that socially cued anticipatory plasticity may not be adaptive for guppies. Finally, in chapter 4 I explored the behavioural plasticity responses of adult guppies to an immune challenge. Specifically, I focused on how an immune challenge affect the expression of behaviours that aid in the avoidance of predation. I found that an immune challenge did not affect anti-predatory responses, however fish showed pronounced sexual differences in behaviour. Taken altogether, my results show that environmental conditions during guppy development affect a limited group of traits, highlighting a possible resilience of guppies to maintain traits at an optimum level. Although the overall phenotypic response appears restricted, the functional significance of the affected traits indicates that developmental conditions can still have meaningful impacts on individual fitness and population dynamics. Show more