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

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.在绝大多数有性生殖物种中，繁殖投入存在不对称性：雄性通常更多投入于求偶配对，而雌性则更多投入于后代生产。这使得雄性的择偶判别标准相较于雌性更为宽松。然而，当满足以下三项条件时，雄性也可能演化出择偶选择性：(a) 雌性的繁殖价值存在个体差异；(b) 雄性能够感知这种差异；(c) 与某一雌性交配会降低与其他雌性交配的可能性。上述条件在胎生谷鳉科（Goodeidae）鱼类中均可得到满足：该类群为墨西哥特有鱼类，雌性通常具有艳丽体色，雄性则以代价高昂的装饰结构与求偶表演作为获取交配机会的唯一途径。黑鳍谷鳉（Girardinichthys viviparus）的雄性虽拥有相对简约但代价高昂的求偶行为，其交配概率取决于一对一求偶互动的时长，因此雄性在向某一雌性求偶时，必然会错过与其他雌性交配的机会。我们针对雄性的求偶决策是否取决于雌性表型这一问题展开了评估。研究发现，雌性表型的三项指标与雄性的到访时长及雄性的展示频率呈显著正相关：腹部面积、色调（橙红色度）以及体型大小。鉴于雌性体型同时与繁殖力及后代存活率呈正相关，我们得出结论：黑鳍谷鳉雄性会评估雌性的潜在繁殖价值，并据此分配求偶投入。由于雄性的求偶投入同样受雌性体色影响，我们认为本研究结果或有助于解释该演化支中雌性性二态体色反复演化的现象。