Data from: High gene flow across large geographic scales reduces extinction risk for a highly specialised coral feeding butterflyfish

The vulnerability of ecologically specialised species to environmental fluctuations has been well documented. However, population genetic structure can influence vulnerability to environmental change and recent studies have indicated that specialised species may have lower genetic diversity and greater population structuring compared to their generalist counterparts. To examine whether there were differences in population genetic structure between a dietary specialist (Chaetodon trifascialis) and a dietary generalist (C. lunulatus) we compared the demographic history and levels of gene flow of two related coral-feeding butterflyfishes. Using allele frequencies of >11 microsatellite loci and >350 bases of mitochondrial control region sequence our analyses of C. trifascialis and C. lunulatus from five locations across the Pacific Ocean revealed contrasting demographic histories and levels of genetic structure. Heterozygosity excess tests, neutrality tests and mismatch distributions were all highly significant in the dietary specialist C. trifascialis (all P<0.01), suggesting genetic bottlenecks have occurred in all locations. In contrast, we found little evidence of genetic bottlenecks for the dietary generalist C. lunulatus. High gene flow and low genetic structuring was detected among locations for C. trifascialis. Contrary to our expectations, a greater level of genetic structuring between locations was detected for C. lunulatus. These results suggest that dietary specialisation may affect demographic history through reductions in population size following resource declines, without affecting population structure through reductions in gene flow in the same way that habitat specialisation appears to. Although C. trifascialis is highly vulnerable to coral loss, the high gene flow detected here suggests populations will be able to recover from local declines through the migration of individuals.

生态特化物种对环境波动的脆弱性已有充分文献记载。然而，种群遗传结构可影响物种应对环境变化的脆弱性，近期研究表明，与广食性同类相比，特化物种的遗传多样性更低，种群结构分化程度更高。为探究食性特化物种三带蝴蝶鱼（Chaetodon trifascialis）与食性广化物种新月蝴蝶鱼（C. lunulatus）的种群遗传结构是否存在差异，我们对两种亲缘关系相近的珊瑚食性蝴蝶鱼的种群历史动态与基因流水平进行了比较。我们采集了太平洋5个采样点的样本，基于超过11个微卫星位点（microsatellite loci）的等位基因频率与超过350个碱基对的线粒体控制区序列（mitochondrial control region sequence）开展分析，结果显示二者的种群历史动态与遗传结构水平存在显著差异。针对食性特化的三带蝴蝶鱼，杂合子过剩检验、中性检验及错配分布分析均呈极显著差异（所有P<0.01），表明所有采样点的种群均曾经历遗传瓶颈事件。与之相反，食性广化的新月蝴蝶鱼几乎未表现出遗传瓶颈的相关证据。三带蝴蝶鱼的种群间基因流水平较高，遗传结构分化程度较低。但与我们的预期相悖的是，新月蝴蝶鱼的种群间遗传结构分化程度反而更高。上述结果表明，食性特化可能通过资源衰减后种群规模缩减影响种群历史动态，但并未像生境特化那样通过降低基因流来影响种群结构。尽管三带蝴蝶鱼对珊瑚礁退化的脆弱性极高，但本研究检测到的高基因流表明，其种群可通过个体迁移从局部种群衰减中恢复。