The effect of water on fitness and mating in seed beetles
Creators: name: Zhang, Zhuzhi
Publisher: name: The Australian National University
Year: 2021

description: How animals adapt to environmental stress has long been of concern. Studies looking at effects of resource limitation often focus on food. However, water is also essential for life and can be limited in the environment. Despite this, little is known about how water availability affects the life history and mating traits of animals. Here, I use the seed beetle, Callosobruchus maculatus, to explore how water availability affects oviposition preferences of mothers and the development of their offspring (Chapter 2). I also take an in depth look at how the water availability experienced by males and females during development affects mating interactions and the subsequent fitness outcomes of these interactions (Chapter 3). And finally, I look at the relative and interactive effects of water acquired during development and adulthood on male investment in reproduction throughout their adult life (Chapter 4). In chapter 2 I show that the moisture content of beans (on which females lay their eggs and in which offspring develop) does not affect oviposition preferences or offspring fitness. These results contrast with theoretical expectations, possible reasons for which are discussed. In chapter 3, I found that manipulating the availability of water to males and females during development affected their mating interactions and subsequent fitness as adults. Specifically, males reared in wet environments transferred larger ejaculates to females, but only when the female they mated with was reared in a dry environment. In this experiment I also found that females mated to males reared in dry environments laid more eggs than those mated to males from wet environments. And that eggs laid by females reared in dry conditions had greater survival when they had mated to males reared in dry than wet environments. These results shed light on how resource limitation mediates the fitness consequences of mating interactions and sexual conflict. Finally, in chapter 4, when manipulating water content during both development and adulthood, I found that greater water content of beans during development had no effect on male body weight at emergence nor their ejaculate weight, but did affect aspects of mating behavior. These effects contrasted with the effects of water during adulthood. Early in adulthood males with access to water lost more weight and had larger ejaculates than males without access to water, but later in life, access to water allowed males to maintain their body weight and prolong their lifespan but did not affect ejaculate size. These results improve our understanding of how water availability experienced at different life stages is allocated to key male fitness traits. When combined, the results from my three data chapters, demonstrate that although water acquired during both development and adulthood can increase the ability of males to invest in mating, the effects of water can differ depending on the trait measured, and the life-stage at which water was acquired. Further, the fitness consequences of such effects may depend on whether or not their mate has had access to water. In the final chapter of my thesis, I bring my results together and discuss their implications for evolutionary responses to stressful environments.