Data from: The genetics of egg retention and fertilization success in Drosophila: one step closer to understanding the transition from facultative to obligate viviparity

Oviparous, facultative egg retention enables Drosophila females to withhold fertilized eggs in their reproductive tracts until circumstances favor oviposition. The propensity to retain fertilized eggs varies greatly between species, and is correlated with other reproductive traits, such as egg size and ovariole number. While previous studies have described the phenomenon, no study to date has characterized within-species variation or the genetic basis of the trait. Here, we develop a novel microscope-based method for measuring egg retention in Drosophila females and determine the range of phenotypic variation in mated female egg retention in a subset of 91 Drosophila Genetic Reference Panel (DGRP) lines. We inferred the genetic basis of egg retention using a genome-wide association study (GWAS). Further, the scoring of more than 95,000 stained, staged eggs enabled estimates of fertilization success for each line. We found evidence that ovary- and spermathecae-related genes as well as genes affecting olfactory behavior, male mating behavior, male-female attraction and sperm motility may play a crucial role in post-mating physiology. Based on our findings we also propose potential evolutionary routes towards obligate viviparity. In particular, we propose that the loss of fecundity incurred by viviparity could be offset by benefits arising from enhanced mate discrimination, resource specialization, or modified egg morphology.

兼性保卵作为卵生生物的特性之一，使得果蝇雌性个体能够将受精卵储存在生殖道内，直至环境适宜产卵。不同物种间的受精卵保卵倾向差异显著，且与卵大小、卵巢管数量等其他生殖性状存在相关性。尽管此前已有研究对该现象进行了描述，但截至目前尚无研究对该性状的种内变异以及遗传基础进行解析。在此，我们开发了一种基于显微镜的新型保卵检测方法，用于测定果蝇雌性的保卵情况，并对选取的91个果蝇遗传参考品系（Drosophila Genetic Reference Panel, DGRP）亚群的交配雌性保卵表型变异范围进行了测定。我们通过全基因组关联分析（Genome-Wide Association Study, GWAS）推断了保卵性状的遗传基础。此外，通过对超过95000枚经过染色、分期的虫卵进行评分，我们得以估算每个品系的受精成功率。我们发现，与卵巢、受精囊相关的基因，以及影响嗅觉行为、雄性交配行为、雌雄吸引以及精子活力的基因，可能在交配后生理过程中发挥关键作用。基于本研究结果，我们还提出了通向专性胎生的潜在演化路径。具体而言，我们提出，胎生所带来的繁殖力损失，可以通过增强配偶识别、资源特化或改变卵形态所带来的收益得到补偿。