Data from: Evolutionary divergence in life history traits among populations of the Lake Malawi cichlid fish Astatotilapia calliptera

During the early stages of adaptive radiation, populations diverge in life history traits such as egg size and growth rates, in addition to eco-morphological and behavioral characteristics. However, there are few studies of life history divergence within ongoing adaptive radiations. Here, we studied Astatotilapia calliptera, a maternal mouthbrooding cichlid fish within the Lake Malawi haplochromine radiation. This species occupies a rich diversity of habitats, including the main body of Lake Malawi, as well as peripheral rivers and shallow lakes. We used common garden experiments to test for life history divergence among populations, focussing on clutch size, duration of incubation, egg mass, offspring size, and growth rates. In a first experiment, we found significant differences among populations in average clutch size and egg mass, and larger clutches were associated with smaller eggs. In a second experiment, we found significant differences among populations in brood size, duration of incubation, juvenile length when released, and growth rates. Larger broods were associated with smaller juveniles when released and shorter incubation times. Although juvenile growth rates differed between populations, these were not strongly related to initial size on release. Overall, differences in life history characters among populations were not predicted by major habitat classifications (Lake Malawi or peripheral habitats) or population genetic divergence (microsatellite-based FST). We suggest that the observed patterns are consistent with local selective forces driving the observed patterns of trait divergence. The results provide strong evidence of evolutionary divergence and covariance of life history traits among populations within a radiating cichlid species, highlighting opportunities for further work to identify the processes driving the observed divergence.

在适应性辐射（adaptive radiation）的早期阶段，种群不仅会在生态形态学与行为特征上产生分化，还会在卵大小、生长速率等生活史性状方面出现分歧。然而，针对正在进行的适应性辐射过程中种群生活史分化的研究仍较为匮乏。本研究以马拉维湖单倍型慈鲷辐射类群中的母口育型慈鲷饰鳍娇丽鱼（Astatotilapia calliptera）为研究对象，该物种栖息生境类型丰富多样，涵盖马拉维湖主体水域以及周边河流与浅水湖泊。我们通过同质园实验（common garden experiment）检测不同种群间的生活史分化，重点关注怀卵量、孵化时长、卵块质量、后代体型与生长速率等性状。在第一项实验中，我们发现不同种群的平均怀卵量与卵块质量均存在显著差异，且怀卵量越高的种群，其所产的卵个体越小。在第二项实验中，我们观测到不同种群的育幼规模、孵化时长、幼鱼释放时的体长以及生长速率均存在显著差异；育幼规模越大的种群，其释放的幼鱼个体越小，且孵化时长也越短。尽管不同种群的幼鱼生长速率存在差异，但该差异与幼鱼释放时的初始体型并无显著关联。总体而言，种群间生活史性状的差异无法通过主要生境类型分类（马拉维湖主体与周边生境）或种群遗传分化（基于微卫星microsatellite标记的FST值）进行预测。我们推测，本次观测到的性状分化模式符合局部选择压力驱动种群生活史分化的理论预期。本研究结果为正在辐射分化的慈鲷物种种群间生活史性状的进化分化与协变关系提供了强有力的证据，同时也为后续探究驱动该分化的具体过程指明了研究方向。