Cridland Julie M, Hanna Giovanni, Fan Tiezheng, Begun David J
Department of Evolution and Ecology, University of California, Davis, CA 95616, USA.
Genome Biol Evol. 2025 Sep 2;17(9). doi: 10.1093/gbe/evaf161.
Identifying the factors determining the repeatability of adaptation is a long-standing problem in evolutionary biology. Addressing this problem requires both comparative analysis and an understanding of how genetic variation within species responds to natural selection. Latitudinal clines are a classic system for studying adaptation in many species, including Drosophila. Here we investigate male reproductive tract (testis and accessory gland [AG]) transcriptomes from Maine (USA) and Panama City (Panama) populations of three species that have recently colonized North America, a pair of close relatives, Drosophila melanogaster, Drosophila simulans, and a much more distantly related species, Drosophila hydei. We observed strong evidence of parallel gene expression adaptation in the AG, but little such evidence for the testis. This parallelism takes the form of genes that exhibit high vs. low latitude expression differentiation in multiple species, as well as between-species correlations of high vs. low latitude log fold changes. However, the degree of parallelism among these species is not related to their relatedness. More specifically, D. simulans, which is very closely related to D. melanogaster yet very distantly related to D. hydei, shows much stronger parallelism for latitudinal AG transcriptome differentiation with the latter than with the former. This, despite the reproductive biology of D. melanogaster and D. simulans, is very similar and highly diverged from that of D. hydei. These results suggest that despite a signal of adaptive parallelism among all three species, the underlying selection responses are not well predicted by relatedness or similar ecologies, suggestive of idiosyncratic processes operating simultaneously with deterministic ones.
确定决定适应性可重复性的因素是进化生物学中一个长期存在的问题。解决这个问题既需要比较分析，也需要了解物种内的遗传变异如何响应自然选择。纬度渐变群是研究包括果蝇在内的许多物种适应性的经典系统。在这里，我们研究了最近在北美定殖的三个物种（一对近亲果蝇黑腹果蝇、拟果蝇，以及一个亲缘关系更远的物种海德氏果蝇）来自美国缅因州和巴拿马城种群的雄性生殖道（睾丸和附腺[AG]）转录组。我们在附腺中观察到了平行基因表达适应性的有力证据，但在睾丸中几乎没有这样的证据。这种平行性表现为在多个物种中以及在高纬度与低纬度对数倍变化的物种间相关性中呈现高纬度与低纬度表达差异的基因。然而，这些物种之间的平行程度与其亲缘关系无关。更具体地说，拟果蝇与黑腹果蝇亲缘关系非常密切，但与海德氏果蝇亲缘关系非常远，它与海德氏果蝇在附腺转录组纬度分化上的平行性比与黑腹果蝇更强。尽管黑腹果蝇和拟果蝇的生殖生物学非常相似，且与海德氏果蝇的生殖生物学高度不同，但仍出现了这种情况。这些结果表明，尽管所有三个物种之间都有适应性平行的信号，但潜在的选择反应并不能很好地通过亲缘关系或相似生态来预测，这表明特异过程与确定性过程同时起作用。
