Liotta Melissa N, Abbott Jessica K, Morris Molly R, Rios-Cardenas Oscar
Department of Biological Sciences The Ohio Center for Ecological and Evolutionary Studies Ohio University Athens OH USA.
Department of Biology Lund University Lund Sweden.
Ecol Evol. 2021 Mar 20;11(9):3941-3955. doi: 10.1002/ece3.7288. eCollection 2021 May.
Alternative reproductive tactics (ARTs) have provided valuable insights into how sexual selection and life history trade-offs can lead to variation within a sex. However, the possibility that tactics may constrain evolution through intralocus tactical conflict (IATC) is rarely considered. In addition, when IATC has been considered, the focus has often been on the genetic correlations between the ARTs, while evidence that the ARTs have different optima for associated traits and that at least one of the tactics is not at its optimum is often missing. Here, we investigate selection on three traits associated with the ARTs in the swordtail fish ; body size, body shape, and the sexually selected trait for which these fishes were named, sword length (elongation of the caudal fin). All three traits are tactically dimorphic, with courter males being larger, deeper bodied and having longer swords, and the sneaker males being smaller, more fusiform and having shorter swords. Using measures of reproductive success in a wild population we calculated selection differentials, as well as linear and quadratic gradients. We demonstrated that the tactics have different optima and at least one of the tactics is not at its optimum for body size and sword length. Our results provide the first evidence of selection in the wild on the sword, an iconic trait for sexual selection. In addition, given the high probability that these traits are genetically correlated to some extent between the two tactics, our study suggests that IATC is constraining both body size and the sword from reaching their phenotypic optima. We discuss the importance of considering the role of IATC in the evolution of tactical dimorphism, how this conflict can be present despite tactical dimorphism, and how it is important to consider this conflict when explaining not only variation within a species but differences across species as well.
替代繁殖策略（ARTs）为性选择和生活史权衡如何导致同一性别内的变异提供了宝贵的见解。然而，很少有人考虑这些策略可能通过基因座内策略冲突（IATC）来限制进化的可能性。此外，当考虑到IATC时，重点往往放在ARTs之间的遗传相关性上，而关于ARTs对相关性状有不同最优值且至少有一种策略未达到其最优值的证据却常常缺失。在这里，我们研究了剑尾鱼中与ARTs相关的三个性状的选择情况；体型、身体形状以及这些鱼得名的性选择性状——剑长（尾鳍延长）。所有这三个性状在策略上都是二态的，求偶雄鱼体型更大、身体更深且剑更长，而偷腥雄鱼体型更小、更呈梭形且剑更短。我们利用野生种群中的繁殖成功率测量值计算了选择差异以及线性和二次梯度。我们证明了这些策略有不同的最优值，并且至少有一种策略在体型和剑长方面未达到其最优值。我们的结果首次提供了在野外对剑（性选择的标志性性状）进行选择的证据。此外，鉴于这两个策略中的这些性状在一定程度上很可能存在遗传相关性，我们的研究表明IATC正在限制体型和剑达到它们的表型最优值。我们讨论了考虑IATC在策略二态性进化中的作用的重要性，尽管存在策略二态性这种冲突如何可能存在，以及在解释物种内的变异以及物种间的差异时考虑这种冲突为何很重要。
