Do male fish prefer them big and colourful? Non-random male courtship effort in a viviparous fish with negligible paternal investment

Abstract

In the majority of sexual species, there are asymmetries in reproductive effort, with males typically investing more in securing matings and females investing more in producing offspring. This causes males to mate less discriminately than females. Yet males may also become choosy if the following conditions are met: (a) that females vary in their reproductive value, (b) that males can perceive this variation, and (c) that mating with one female reduces the possibility of mating with another. These conditions may be met in the livebearing Goodeidae, a clade of Mexican fish whose females are often brightly coloured and whose males display costly ornaments and courtship as the only means to obtain matings. Males of the black-finned goodeid (Girardinichthys viviparus) have relatively simple, yet costly courtship behaviour, with mating probability depending on the duration of one-to-one courtship episodes, thus by courting one female they must ignore others. We evaluated whether the decision to court a female depends on her phenotype. Three variables of female phenotype were positively linked to the duration of male visits and to the frequency of displays performed by males: belly area, hue (“orangeness”) and size. Since fecundity and offspring survival were also a positive function of female size, we conclude that male G. viviparus evaluate the potential female reproductive value and allocate their courtship effort accordingly. Since male courtship effort is also influenced by female colouration, we suggest that our findings may help explaining the recurrent evolution of sexually dimorphic female colouration in this clade. Amongst sexually reproducing species, females often invest heavily on offspring and mate only after selecting partners carefully, while males invest little on offspring but mate indiscriminately. In other cases, males carry the burden of raising offspring and are choosy. Thus, we see female mate choice in species with a bias towards maternal investment, and male mate choice in species with a bias towards paternal investment. Here we report male mate choice in a species with predominantly maternal investment; a viviparous fish whose females are choosy and whose males invest heavily on courtship. Males made longer visits to the wider bellied, and more orange-looking females, and larger (but not more orange) females produced more offspring which survived better, thus some attributes of females linked to their reproductive value influence how much time and effort males devote to court them.