Mode of maternal provisioning in the fish genus Phalloceros: a variation on the theme of matrotrophy

The placenta is a complex organ that shows high morphological diversity. Among fish, the first vertebrates that have evolved a placenta, the family Poeciliidae exhibits very diverse modes of maternal provisioning even among congeneric species. Here, we investigated the embryonic growth curve across seven recently-described species of the highly diverse genus Phalloceros (Eigenmann, 1907). We also investigated possible intraspecific differences and whether other female characteristics affected embryo mass. We found that embryo mass decreased until around stage 20 and then increased, resulting in 1.5 to 3-fold mass gain from fertilization to birth. Embryo mass changed non-linearly with stage of development and was affected by species identity (or locality) and female somatic dry mass.  This initial loss then gain of embryonic mass during development is unique among other Poeciliidae species and was conserved across populations and species, even though size at birth can vary. Other species...

胎盘是一类形态多样性极高的复杂器官。在已演化出胎盘的脊椎动物类群中，鱼类的花鳉科（Poeciliidae）即便在同属物种间，也展现出极为多样的母体营养供给模式。本研究针对物种多样性极高的异栉鳉属（Phalloceros，Eigenmann, 1907）的7个新近描述物种，探究了其胚胎生长曲线；同时还考察了种内可能存在的差异，以及其他雌性个体特征是否会对胚胎质量产生影响。研究结果显示，胚胎质量在发育至第20期左右时出现下降，随后逐渐升高，从受精至分娩的全过程中，胚胎质量可提升1.5至3倍。胚胎质量随发育阶段呈非线性变化，且受物种属性（或采样地点）以及雌性个体体细胞干重的影响。这种发育过程中胚胎质量先降后升的变化模式在花鳉科物种中实属特有，且在不同种群与物种间均保持保守，尽管不同个体的出生体型存在差异。其他物种……