Passow Courtney N, Arias-Rodriguez Lenin, Tobler Michael
Division of Biology, Kansas State University, Manhattan, Kansas, United States of America.
División Académica de Ciencias Biológicas, Universidad Juárez Autónoma de Tabasco, Villahermosa, Tabasco, México.
PLoS One. 2017 Oct 27;12(10):e0186935. doi: 10.1371/journal.pone.0186935. eCollection 2017.
Convergent evolution in organismal function can arise from nonconvergent changes in traits that contribute to that function. Theory predicts that low resource availability and high maintenance costs in extreme environments select for reductions in organismal energy demands, which could be attained through modifications of body size or metabolic rate. We tested for convergence in energy demands and underlying traits by investigating livebearing fish (genus Poecilia) that have repeatedly colonized toxic, hydrogen sulphide-rich springs. We quantified variation in body size and routine metabolism across replicated sulphidic and non-sulphidic populations in nature, modelled total organismal energy demands, and conducted a common-garden experiment to test whether population differences had a genetic basis. Sulphidic populations generally exhibited smaller body sizes and lower routine metabolic rates compared to non-sulphidic populations, which together caused significant reductions in total organismal energy demands in extremophile populations. Although both mechanisms contributed to variation in organismal energy demands, variance partitioning indicated reductions of body size overall had a greater effect than reductions of routine metabolism. Finally, population differences in routine metabolism documented in natural populations were maintained in common-garden reared individuals, indicating evolved differences. In combination with other studies, these results suggest that reductions in energy demands may represent a common theme in adaptation to physiochemical stressors. Selection for reduced energy demand may particularly affect body size, which has implications for life history evolution in extreme environments.
生物功能的趋同进化可能源于对该功能有贡献的性状的非趋同变化。理论预测，极端环境中低资源可用性和高维持成本会促使生物的能量需求降低，这可以通过改变体型或代谢率来实现。我们通过研究多次定殖于富含硫化氢的有毒泉水中的胎生鱼类（食蚊鱼属），来测试能量需求和潜在性状的趋同情况。我们对自然界中重复出现的含硫和不含硫种群的体型和常规代谢的变化进行了量化，对生物的总能量需求进行了建模，并进行了一项共同培养实验，以测试种群差异是否具有遗传基础。与不含硫的种群相比，含硫种群通常体型更小，常规代谢率更低，这共同导致极端嗜热种群的生物总能量需求显著降低。虽然这两种机制都导致了生物能量需求的变化，但方差分析表明，总体而言体型的减小比常规代谢的降低影响更大。最后，自然种群中记录的常规代谢的种群差异在共同培养的个体中得以维持，表明存在进化差异。结合其他研究，这些结果表明，能量需求的降低可能是适应物理化学应激源的一个共同主题。对降低能量需求的选择可能特别影响体型，这对极端环境中的生活史进化具有重要意义。
