Kerschbaumer M, Mitteroecker P, Sturmbauer C
Department of Zoology, Karl-Franzens-University Graz, Graz, Austria.
Department of Theoretical Biology, University of Vienna, Vienna, Austria.
Heredity (Edinb). 2014 Feb;112(2):89-98. doi: 10.1038/hdy.2013.78. Epub 2013 Sep 25.
Allopatric speciation often yields ecologically equivalent sister species, so that their secondary admixis enforces competition. The shores of Lake Tanganyika harbor about 120 distinct populations of the cichlid genus Tropheus, but only some are sympatric. When alone, Tropheus occupies a relatively broad depth zone, but in sympatry, fish segregate by depth. To assess the effects of competition, we studied the partial co-occurrence of Tropheus moorii 'Kaiser' and 'Kirschfleck' with Tropheus polli. A previous study demonstrated via standardized breeding experiments that some observed differences between Tropheus 'Kaiser' living alone and in sympatry with T. polli have a genetic basis despite large-scale phenotypic plasticity. Using geometric morphometrics and neutral genetic markers, we now investigated whether sympatric populations differ consistently in body shape from populations living alone and if the differences are adaptive. We found significant differences in mean shape between non-sympatric and sympatric populations, whereas all sympatric populations of both color morphs clustered together in shape space. Sympatric populations had a relatively smaller head, smaller eyes and a more anterior insertion of the pectoral fin than non-sympatric populations. Genetically, however, non-sympatric and sympatric 'Kaiser' populations clustered together to the exclusion of 'Kirschfleck'. Genetic distances, but not morphological distances, were correlated with geographic distances. Within- and between-population covariance matrices for T. moorii populations deviated from proportionality. It is thus likely that natural selection acts on both phenotypic plasticity and heritable traits and that both factors contribute to the observed shape differences. The consistency of the pattern in five populations suggests ecological character displacement.
异域物种形成常常产生生态上相当的姐妹物种，因此它们的二次混合会加剧竞争。坦噶尼喀湖的湖岸栖息着大约120个丽鱼科矛耙丽鱼属的不同种群，但只有一些是同域分布的。单独存在时，矛耙丽鱼占据相对较宽的深度区域，但在同域分布时，鱼类会按深度进行分隔。为了评估竞争的影响，我们研究了穆氏矛耙丽鱼“皇帝”和“樱桃斑”与波利矛耙丽鱼的部分同域共存情况。之前的一项研究通过标准化繁殖实验表明，尽管存在大规模的表型可塑性，但单独生活的穆氏矛耙丽鱼与和波利矛耙丽鱼同域生活的穆氏矛耙丽鱼之间观察到的一些差异具有遗传基础。现在，我们使用几何形态测量学和中性遗传标记，研究同域分布的种群与单独生活的种群在体型上是否始终存在差异，以及这些差异是否具有适应性。我们发现，非同域分布和同域分布的种群在平均形状上存在显著差异，而两种颜色形态的所有同域分布种群在形状空间中聚集在一起。同域分布的种群与非同域分布的种群相比，头部相对较小，眼睛较小，胸鳍的插入位置更靠前。然而，在基因方面，非同域分布和同域分布的“皇帝”种群聚集在一起，将“樱桃斑”排除在外。遗传距离而非形态距离与地理距离相关。穆氏矛耙丽鱼种群的种群内和种群间协方差矩阵偏离了比例关系。因此，自然选择可能作用于表型可塑性和可遗传性状，并且这两个因素都导致了观察到的形状差异。五个种群中这种模式的一致性表明存在生态位分化。
