A single origin of extreme matrotrophy in African mabuyine skinks

Most mammals and approximately 20% of squamates (lizards and snakes) are viviparous, whereas all crocodilians, birds and turtles are oviparous. Viviparity evolved greater than 100 times in squamates, including multiple times in Mabuyinae (Reptilia: Scincidae), making this group ideal for studying the evolution of nutritional patterns associated with viviparity. Previous studies suggest that extreme matrotrophy, the support of virtually all of embryonic development by maternal nutrients, evolved as many as three times in Mabuyinae: in Neotropical Mabuyinae (63 species), Eumecia (2 species; Africa) and Trachylepis ivensii (Africa). However, no explicit phylogenetic hypotheses exist for understanding the evolution of extreme matrotrophy. Using multilocus DNA data, we inferred a species tree for Mabuyinae that implies that T. ivensii (here assigned to the resurrected genus Lubuya) is sister to Eumecia, suggesting that extreme matrotrophy evolved only once in African mabuyine skinks.多数哺乳类以及约20%的有鳞类（Squamata，蜥蜴与蛇）为胎生（viviparity），而所有鳄目动物（Crocodilia）、鸟类及龟类均为卵生（oviparity）。胎生在有鳞类中独立演化超过100次，其中石龙子亚科（Mabuyinae，爬行纲Reptilia：石龙子科Scincidae）内就曾多次演化出胎生，使得该类群成为研究与胎生相关的营养模式演化的理想研究对象。此前的研究表明，极端营养胎生（extreme matrotrophy，即胚胎发育所需的几乎全部营养均由母体提供）在石龙子亚科中至少演化了三次：分别见于新热带区石龙子类群（63种）、真石龙子属（Eumecia，2种，分布于非洲）以及伊文斯棱蜥（Trachylepis ivensii，非洲分布）。然而目前尚无用于阐释极端营养胎生演化过程的明确系统发育假说。本研究通过多位点DNA数据（multilocus DNA data）构建了石龙子亚科的物种树，结果显示伊文斯棱蜥（本文将其归入恢复命名的卢布亚石龙子属Lubuya）与真石龙子属构成姐妹群，这表明极端营养胎生在非洲石龙子类群中仅演化过一次。