Female choice and the relatedness of mates in the guppy (Poecilia reticulata)

Abstract

Several studies suggest that females may offset the costs of genetic incompatibility by exercising pre-copulatory or post-copulatory mate choice to bias paternity toward more compatible males. One source of genetic incompatibility is the degree of relatedness among mates; unrelated males are expected to be genetically more compatible with a female than her relatives. To address this idea, we investigated the potential for inbreeding depression and paternity biasing mechanisms (pre- and post-copulatory) of inbreeding avoidance in the guppy, Poecilia reticulata. Inbreeding resulted in a reduction in offspring number and quality. Females mated to siblings gave birth to significantly fewer offspring compared to females mated to non-siblings and inbred male offspring took longer to reach sexual maturity. There was no evidence of inbreeding avoidance in pre-copulatory behaviors of females or males. Sexual responsiveness of females to courting males and the number of sexual behaviors males directed at females did not decrease as a function of the relatedness of the two individuals. We also tested whether female guppies can use post-copulatory mechanisms to bias sperm usage toward unrelated males by comparing the number of offspring produced by females mated to two of their siblings (SS), two males unrelated to the female (NN), or to one unrelated male and a sibling male (NS). We found that NS females produced a number of offspring not significantly different than what would be expected if fertilization success were halfway between completely outbreeding (NN) and completely inbreeding (SS) females. This suggests that there is no significant improvement in the number of offspring produced by females mating to both related and unrelated males, relative to that which would be expected if sperm from both males were used equally. Our results suggest that female guppies do not discriminate against closely related males or their sperm.

Cryptic female preference for genetically unrelated males is mediated by ovarian fluid in the guppy

“…First, there is ample evidence that inbreeding has deleterious fitness consequences in this species [35 -39]. Second, while female guppies show a pre-copulatory preference for unfamiliar males or males with a rare colour phenotype [40 -43], which indirectly reduces the risk of inbreeding, they are apparently unable to distinguish among related males when familiarity cues are controlled for [39,44,45]. Third, males can undermine female choice by means of gonopodial thrusting [46], a coercive mating tactic that allows males to forcibly inseminate females [47].…”

Evidence for inbreeding depression in a species with limited opportunity for maternal effects

“…2003), (2) There is little evidence of mate choice for unrelated males in Poeciliids (e.g., Pitcher et al. 2008; Ala-Honkola et al. 2010), but see (Kelley et al.…”

“…2014), so there is no immediate benefit of discriminating against a related male's sperm (e.g., Pitcher et al. 2008). In short, there is no obvious adaptive explanation why females would partially fertilize a clutch.…”

Social Recognition of Conspecifics

“…However, studies of adults of the cooperatively breeding African cichlid, N. pulcher, have failed to show either kin preference or kin avoidance (Striver et al 2008) despite the documented ability of juveniles to use relatedness during shoaling decisions (Le Vin et al 2010). Similarly, in the guppy there is at best only a marginal trend for mating partners to be unrelated (Pitcher et al 2008;Johnsson et al 2010) despite an increase in offspring number (Johnson et al 2010) and quality (Pitcher et al 2008) produced by unrelated partners. Perhaps kin-biased mate-choice decisions will only be found in populations where inbreeding depression is already present and there are considerable potential benefits to increasing heterozygosity and maintaining genetic variation.…”