Strong assortative mating by diet, color, size, and morphology but limited progress toward sympatric speciation in a classic example: Cameroon crater lake cichlids

Models predict that sympatric speciation depends on restrictive parameter ranges, such as sufficiently strong disruptive selection and assortative mating, but compelling examples in nature have rarely been used to test these predictions. I measured the strength of assortative mating within a species complex of Tilapia in Lake Ejagham, Cameroon, a celebrated example of incipient sympatric adaptive radiation. This species complex is in the earliest stages of speciation: morphological and ecological divergence are incomplete, species differ primarily in breeding coloration, and introgression is common. I captured 27 mated pairs in situ and measured the diet, color, size, and morphology of each individual. I found strong assortative mating by color, size, head depth, and dietary source of benthic or pelagic prey along two independent dimensions of assortment. Thus, Ejagham Tilapia showed strong assortative mating most conducive to sympatric speciation. Nonetheless, in contrast to a morpholo...模型预测，同域物种形成（sympatric speciation）依赖于严格的参数范围，例如足够强的分裂选择（disruptive selection）与选型交配（assortative mating），但自然界中确凿的实例极少被用于验证这些预测。我针对喀麦隆埃贾哈姆湖的罗非鱼（Tilapia）物种复合体开展了选型交配强度测定，该复合体是知名的初期同域适应性辐射（incipient sympatric adaptive radiation）研究范例。该物种复合体处于物种形成的最早阶段：形态与生态分化尚未完成，物种间主要差异在于繁殖体色，且基因渐渗（introgression）现象普遍。我于原位（in situ）捕获了27对交配个体，并测定了每只个体的食性、体色、体型及形态特征。研究发现，该复合体基于体色、体型、头高以及底栖（benthic）或浮游（pelagic）猎物的食性来源，存在显著的选型交配，且该交配偏好沿两个独立的交配维度发挥作用。综上，埃贾哈姆湖罗非鱼表现出的强选型交配，最有利于同域物种形成。然而，与一项形态学（morpholo）