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.

地理分布范围受限的特有物种（endemic species），往往面临最高的灭绝风险。若这类物种进一步分化为遗传隔离的亚种群，其灭绝风险还会进一步升高。尽管已有研究证实生境破碎化（habitat fragmentation）存在中性甚至积极的效应，但学界普遍认为其对物种生存具有负面影响，且这类非负面影响在保护生物学（conservation biology）研究中常被忽视。Montseny肋突螈（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（IUCN）列为极危（critically endangered）物种。本研究借助分子标记（molecular markers）技术分析该物种的种群结构（population structure），发现由天然屏障造成的生境破碎化，使其种群被强烈分化为两个遗传分支，各采样点间未检测到基因流（gene flow）。尽管所有种群的有效种群规模（effective population size）估算值均偏低，但我们发现种群内个体间的近交（inbreeding）水平和亲缘关联程度均较低。Montseny肋突螈的遗传多样性水平与其姊妹物种（sister species）糙肋突螈（Calotriton asper）相近——后者约于150万年前与其分化，且分布范围远大于前者。本项系统性研究表明，在演化时间尺度（evolutionary time scale）下，天然生境破碎化并不会引发诸如遗传多样性流失、个体近交升高等负面遗传效应。处于这类生境中的物种，或可演化出应对种群规模偏小问题的策略。但需要强调的是，在制定保护策略（conservation strategies）时，不应将演化时间尺度下天然生境破碎化的影响，与人为造成的生境丧失或生境退化（habitat loss or degradation）混为一谈。