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（facultative egg retention）这一卵生繁殖策略，可使果蝇（Drosophila）雌蝇将受精卵滞留在生殖道中，直至出现适宜产卵的环境条件。不同物种间的受精卵滞留倾向差异显著，且与卵大小、卵巢小管数等其他繁殖性状存在相关性。尽管已有研究对该现象进行了描述，但截至目前尚无研究阐明其种内变异规律及该性状的遗传基础。
本研究开发了一种基于显微镜的全新果蝇雌蝇保卵量检测方法，对91个果蝇遗传参考品系库（Drosophila Genetic Reference Panel, DGRP）亚群中交配后雌蝇的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，对超过95000枚经染色并分期的卵进行评分，使我们能够估算每个品系的受精成功率。
研究发现，与卵巢、受精囊相关的基因，以及调控嗅觉行为、雄蝇交配行为、雌雄吸引和精子活力的基因，可能在交配后生理过程中发挥关键作用。基于上述研究结果，我们还提出了通往专性胎生（obligate viviparity）的潜在演化路径：具体而言，胎生所带来的繁殖力损失，可通过增强配偶选择、资源特化或改造卵形态所带来的收益进行补偿。