| 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 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 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 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.; 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. |
