The Trinidadian guppy (Poecilia reticulata) is well known to biologists and home aquarium enthusiasts alike. Scientists have studied guppies for most of the twentieth century. Some of the most intensive recent research has been conducted by behavioral ecologists, who have found that the guppy mating system makes guppies especially useful in the study of sexual selection and mate choice. By observing guppy behavior in aquaria, researchers hope to obtain new insights into how selection operates in natural populations. Here Anne Houde summarizes and synthesizes the scientific work done to date, relates the empirical findings on guppies to current themes in sexual selection theory, and suggests new directions for future research. This book describes the sexual behavior of guppies and examines how mate choice by females leads to the evolution of the conspicuous colors and the courtship displays for which guppies are widely recognized. The author shows that female guppies prefer males with bright color patterns, especially those with orange spots, and that the mating preferences of females lead to sexual selection on both color patterns and courtship displays of males. Houde's work addresses a number of areas that are of interest in sexual selection, including the remarkable degree of plasticity and evolutionary lability of sexual behavior in guppies, geographic variation in mating preferences, possible mechanisms for the evolution of female mating preferences, and the role of sexual selection in speciation. In conclusion, the author explores the implications of her findings for behavioral ecologists who study sexual selection in other species.

In this thesis I report on a series of studies that addresses features of multiple mating and sexual selection in guppies (Poecilia reticulata) and birds in general. In chapter 3, I tested the genetic incompatibility hypothesis by asking whether female guppies can bias their use of sperm toward more compatible males. Despite the deleterious consequences of inbreeding, there was no evidence of inbreeding avoidance in pre-copulatory behaviors of females or males, or in sperm use by females. These results suggest that female guppies do not discriminate on the basis of genetic relatedness, against closely related males or their sperm and as such do not multiply mate to avoid the costs of inbreeding depression. In chapter 5, I examined several ecological and behavioural factors in relation to testes size; an index of the extent of extrapair mating. The results of this chapter suggest that traditional ecological and behavioral variables can account for a significant portion of the variation in sperm competition in birds. In chapter 2, I test the trade-up hypothesis which is a behavioural strategy that females could use to maximize the genetic benefits to their offspring. The hypothesis proposes that females should be more willing to accept a mate when the new male encountered is a superior genetic source than previous mates. I found that females responsiveness to second males was an increasing function of male ornamentation. Attractive second males also sired a greater proportion of the offspring. These results suggest that female guppies may utilize pre-copulatory mechanisms to maximize the genetic quality of their offspring. In chapter 4, I tested whether female guppies could potentially accrue direct benefits from mate choice by assessing whether the orange, carotenoid-based integument pigmentation of male guppies signals male functional fertility, that is, their ability to supply a large number of high quality sperm at copulation. Males with greater areas of carotenoid colouration had significantly larger sperm loads and more motile sperm relative to males with relatively little carotenoid colouration. However, I found no evidence that sperm traits were related to the intensity of carotenoid colouration.

The costs to females associated with polyandry are numerous. However, this mating strategy is very common in nature because mating with multiple males during the same reproductive cycle can also provide multiple benefits. Under such conditions, females can use different strategies to optimize the benefits of mate choice. Among these, the trade-up hypothesis is a model used to predict female mate choice when males are encountered sequentially: specifically, females mate with males of increased quality as they gain experience. These decisions are thought to be based on cues that indicate male quality to females. These cues, however, may well differ between populations as a result of adaptive divergence in response to different selective pressures. In this study, Trinidadian guppies were used to test the trade-up hypothesis and whether trade-up patterns differ among wild populations. Guppies from three populations were used to conduct within-population sequential ...