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

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 International Union for Conservation of Nature. Here we apply molecular markers to analyze its population structure and find that habitat fragmentation owing 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. Moreover, C. arnoldi displays similar levels of genetic diversity to its sister species Calotriton asper, from which it separated around 1.5 million years ago and which 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 timescale. We hypothesize that species in such conditions may evolve strategies (for example, special mating preferences) to mitigate the effects of small population sizes. However, it should be stressed that the influence of natural habitat fragmentation on an evolutionary timescale 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。若此类物种进一步被分割为遗传隔离的亚种群，其灭绝风险将进一步升高。尽管有研究显示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，而保护生物学领域往往忽略这些非负面的作用。蒙特塞尼溪螈（Calotriton arnoldi）是欧洲两栖动物中分布范围最小的物种之一（仅8平方千米），被国际自然保护联盟（International Union for Conservation of Nature，IUCN）列为极危物种。本研究借助分子标记分析其种群结构，发现自然屏障引发的栖息地碎片化使得种群被强烈区分为两个遗传分支，各采样位点间未检测到基因流。尽管所有种群的有效种群大小估值均较低，但研究发现种群内个体间的近交水平和亲缘关系程度均处于较低水平。此外，该螈与其姊妹种糙皮滑螈（Calotriton asper）的遗传多样性水平相当——二者约在150万年前分化，而糙皮滑螈的分布范围要大得多。本大规模研究表明，从进化时间尺度来看，自然栖息地碎片化并不会产生负面遗传效应，例如遗传多样性丧失和近交。我们推测，此类生境中的物种可能演化出了相应策略（例如特殊的择偶偏好）以缓解种群规模过小带来的影响。但需要强调的是，在制定保护策略时，不应将进化时间尺度下的自然栖息地碎片化影响，与人类活动造成的栖息地丧失或退化混为一谈。