Data from: Dramatic niche shifts and morphological change in two insular bird species

Colonizations of islands are often associated with rapid morphological divergence. We present two previously unrecognized cases of dramatic morphological change and niche shifts in connection with colonization of tropical forest-covered islands. These evolutionary changes have concealed the fact that the passerine birds madanga, Madanga ruficollis, from Buru, Indonesia, and São Tomé shorttail, Amaurocichla bocagii, from São Tomé, Gulf of Guinea, are forest-adapted members of the family Motacillidae (pipits and wagtails). We show that Madanga has diverged mainly in plumage, which may be the result of selection for improved camouflage in its new arboreal niche, while selection pressures for other morphological changes have probably been weak owing to preadaptations for the novel niche. By contrast, we suggest that Amaurocichla's niche change has led to divergence in both structure and plumage.

岛屿拓殖事件往往与快速的形态分化紧密关联。本研究报道了两例此前未被认知的、与热带森林覆盖岛屿拓殖相关的剧烈形态变化与生态位转移事件。这些进化演变曾长期掩盖了一个分类学真相：来自印尼布鲁岛的马丹加（Madanga ruficollis）与几内亚湾圣多美岛的圣多美短尾莺（Amaurocichla bocagii），实则均为鹡鸰科（Motacillidae，即鹨与鹡鸰类群）的森林适应性类群。研究表明，马丹加主要在羽色上发生分化，这可能是其在全新树栖生态位中获得更佳伪装效果的选择结果；而由于其对新生态位已存在预适应，其他形态特征受到的选择压力或相对较弱。相比之下，本研究认为圣多美短尾莺的生态位转变同时导致了其形态结构与羽色的双重分化。