Experimental Zoology Chair Group, Department of Animal Sciences, Wageningen University & Research, Wageningen, The Netherlands.
PLoS One. 2018 Apr 16;13(4):e0195976. doi: 10.1371/journal.pone.0195976. eCollection 2018.
A live-bearing reproductive strategy can induce large morphological changes in the mother during pregnancy. The evolution of the placenta in swimming animals involves a shift in the timing of maternal provisioning from pre-fertilization (females supply their eggs with sufficient yolk reserves prior to fertilization) to post-fertilization (females provide all nutrients via a placenta during the pregnancy). It has been hypothesised that this shift, associated with the evolution of the placenta, should confer a morphological advantage to the females leading to a more slender body shape during the early stages of pregnancy. We tested this hypothesis by quantifying three-dimensional shape and volume changes during pregnancy and in full-grown virgin controls of two species within the live-bearing fish family Poeciliidae: Poeciliopsis gracilis (non-placental) and Poeciliopsis turneri (placental). We show that P. turneri is more slender than P. gracilis at the beginning of the interbrood interval and in virgins, and that these differences diminish towards the end of pregnancy. This study provides the first evidence for an adaptive morphological advantage of the placenta in live-bearing fish. A similar morphological benefit could drive the evolution of placentas in other live-bearing (swimming) animal lineages.
有性生殖策略会在怀孕过程中引起母体的巨大形态变化。游泳动物胎盘的进化涉及母体营养供应时间的转变，从受精前（雌性在受精前为卵子提供足够的卵黄储备）转变为受精后（雌性在怀孕期间通过胎盘提供所有营养）。有人假设，这种与胎盘进化相关的转变应该会给雌性带来形态上的优势，导致在怀孕的早期阶段体型更加苗条。我们通过量化两种非胎盘鱼类 Poeciliopsis gracilis 和胎盘鱼类 Poeciliopsis turneri 在怀孕和成熟处女对照期间的三维形状和体积变化，来验证这一假设。我们发现，在繁殖间隔的开始和处女期间，P. turneri 比 P. gracilis 更加苗条，而这些差异在怀孕后期会减小。这项研究首次为有性生殖鱼类胎盘的适应性形态优势提供了证据。类似的形态优势可能会推动其他有性生殖（游泳）动物谱系中胎盘的进化。
