Department of Biological Sciences, University of Illinois at Chicago, 845 West Taylor Street (MC066), Chicago, IL 60607, USA; Departamento de Ciencias Biológicas, Universidad de los Andes, Carrera 1°, no. 18A-12, Bogotá, Colombia; Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL 60605, USA; SELVA: Investigación para la Conservación en el Neotrópico, Diagonal 42A, no. 20-37, Bogotá, Colombia.
Department of Ecology and Evolution, University of Chicago, 1101 East 57(th) Street, Chicago, IL 60637, USA.
Curr Biol. 2020 Apr 6;30(7):1312-1321.e6. doi: 10.1016/j.cub.2020.01.064. Epub 2020 Mar 19.
Migratory animals move up to thousands of kilometers every year [1]. Losses of migration (i.e., migratory drop-offs) occur when individuals of a migratory species stop migrating and establish founder sedentary populations, a phenomenon documented in birds [2-5] and butterflies [6]. In theory, losses-and also gains-of migration might promote speciation if sedentary and migratory populations become reproductively isolated [7-9]. Because migratory and sedentary strategies involve alternative physiological, behavioral, and morphological traits [10-13], divergence along multiple axes of organismal function is expected to accompany switches in migratory behavior, potentially accelerating speciation. We present evidence of speciation driven by a migratory drop-off in the fork-tailed flycatcher (Tyrannus savana) resulting in reproductive isolation likely driven by changes in breeding schedules (allochronic speciation [13-15]) and geographic isolation of breeding grounds (allopatric speciation [16]). Phylogenetic analyses across New World flycatchers (Tyrannidae) showed that an association between speciation and drop-offs is also observable at a macroevolutionary scale. Loss of migration was significantly more frequent than its gain, and speciation rates of migratory and partially migratory lineages (i.e., species having both migratory and sedentary populations) exceeded those of sedentary lineages. Models of trait evolution indicated that partial migration is an intermediate step between migratory and sedentary states in this family. Given that partial migration is widespread across migratory animals (e.g., of all migratory birds, ca. 51% are partially migratory [5]), speciation via switches in migratory behavior might be an important yet overlooked mechanism of animal diversification.
迁徙动物每年移动多达数千公里[1]。当迁徙物种的个体停止迁徙并建立创始定居种群时，就会发生迁徙损失（即迁徙减少），鸟类[2-5]和蝴蝶[6]中都有记录。从理论上讲，如果定居和迁徙种群变得生殖隔离，迁徙的损失和获得都可能促进物种形成[7-9]。由于迁徙和定居策略涉及替代的生理、行为和形态特征[10-13]，因此，随着迁徙行为的转变，预计生物功能的多个轴线上会出现分歧，这可能会加速物种形成。我们提出了证据表明，叉尾蝇虎（Tyrannus savana）的迁徙减少导致了物种形成，这可能是由繁殖期（异步物种形成[13-15]）和繁殖地的地理隔离（异域物种形成[16]）的变化导致的生殖隔离。新世界蝇虎（Tyrannidae）的系统发育分析表明，在宏观进化尺度上，物种形成与迁徙减少之间也存在关联。迁徙的丧失比获得更为频繁，迁徙和部分迁徙谱系（即具有迁徙和定居种群的物种）的物种形成率超过了定居谱系。性状进化模型表明，部分迁徙是该科中迁徙和定居状态之间的中间步骤。鉴于部分迁徙在迁徙动物中很普遍（例如，所有迁徙鸟类中，约有 51%是部分迁徙[5]），通过迁徙行为的转变进行物种形成可能是动物多样化的一个重要但被忽视的机制。
