Data from: No signs of inbreeding despite long term isolation and habitat fragmentation in the critically endangered Montseny brook newt

Endemic species with restricted geographic ranges potentially suffer the highest risk of extinction. If these species are further fragmented into genetically isolated subpopulations, the risk of extinction is elevated. Habitat fragmentation is generally considered to have negative effects on species survival, despite some evidence for neutral or even positive effects. Typically, non-negative effects are ignored by conservation biology. The Montseny brook newt (Calotriton arnoldi) has one of the smallest distribution ranges of any European amphibian (8 km2), and is considered critically endangered by the IUCN. Here, we apply molecular markers to analyze its population structure, and find that habitat fragmentation due to a natural barrier has resulted in strong genetic division of populations into two sectors, with no detectable migration between sites. Although effective population size estimates suggest low values for all populations, we found low levels of inbreeding and relatedness between individuals within populations. C. arnoldi displays similar levels of genetic diversity to its sister species C. asper, from which it separated around 1.5 million years ago and has a much larger distribution range. Our extensive study shows that natural habitat fragmentation does not result in negative genetic effects, such as the loss of genetic diversity and inbreeding on an evolutionary time scale. Species in such conditions may evolve strategies to mitigate the effects of small population sizes. However, it should be stressed that the influence of natural habitat fragmentation on an evolutionary time scale should not be conflated with anthropogenic habitat loss or degradation when considering conservation strategies.

地理分布受限的特有物种可能面临最高的灭绝风险。若这些物种进一步被分割为遗传上孤立的亚种群，其灭绝风险还会进一步升高。尽管有研究表明栖息地碎片化存在中性甚至积极的影响，但学界普遍认为其对物种生存具有负面效应，而保护生物学领域通常会忽略这些非负面的研究结果。蒙塞尼溪螈（Calotriton arnoldi）是欧洲两栖动物中分布范围最小的物种之一（仅8 km²），被国际自然保护联盟（IUCN）列为极危物种。本研究通过分子标记技术分析其种群结构，发现由天然屏障造成的栖息地碎片化，已导致种群在遗传上强烈分化为两个分支，各采样点间未检测到基因交流。尽管所有种群的有效种群大小估算值均偏低，但我们发现种群内个体间的近交程度和亲缘关系水平均较低。C. arnoldi的遗传多样性水平与其姐妹种C. asper相当，二者约在150万年前分化，而C. asper的分布范围要大得多。本项大规模研究表明，在进化时间尺度上，天然栖息地碎片化并不会引发遗传多样性丧失、近交衰退等负面遗传效应。处于此类环境中的物种，或许会演化出缓解种群规模过小所带来影响的策略。但需要强调的是，在制定保护策略时，不应将天然栖息地碎片化在进化时间尺度上的影响，与人类活动造成的栖息地丧失或退化混为一谈。