Conservation genetics of two threatened frogs from the Mambilla highlands, Nigeria

Amphibians are the vertebrate group with the highest number of species threatened with extinction, and habitat loss and fragmentation are considered to be among the leading causes of their declines and extinctions. Little is known of the population biology of amphibian species inhabiting montane forests in Central and West Africa, where anthropogenic activities such as farming and cattle raising are major threats to native biodiversity. We used Amplified Fragment Length Polymorphisms (AFLPs) to assess the population genetic structure of two poorly known species, Cardioglossa schioetzi and Leptodactylodon bicolor (both in the Arthroleptidae), in and around Ngel Nyaki Forest Reserve on the Mambilla Plateau in eastern Nigeria. The landscape comprises continuous forest on steep slopes and small riparian forest fragments in a grassland matrix. While increased fragmentation is well documented for these and other forests in the mountains of Cameroon and Nigeria over the past century, there are no previous assessments of the impact of forest fragmentation on montane amphibian populations in this region. Our estimates of genetic diversity are similar across populations within each species with levels of heterozygosity values consistent with local population declines. Except for a pair of populations (C. schioetzi) we did not observe genetic differentiation between forest and riparian forest fragment populations, nor across sites within continuous forest (L. bicolor). Our results demonstrate recent gene flow between forest fragments and the adjacent protected forests and suggest that small forest corridors connecting these may lessen the genetic consequences of at least 30 years of intense and severe fragmentation in Ngel Nyaki.

两栖动物是受灭绝威胁物种数量最多的脊椎动物类群，栖息地丧失与片段化被认为是其种群衰退及灭绝的主要诱因之一。栖息于中非和西非山地森林的两栖物种种群生物学特征鲜为人知，而该区域的农业耕作、畜牧养殖等人为活动是本土生物多样性面临的主要威胁。本研究利用扩增片段长度多态性（Amplified Fragment Length Polymorphisms, AFLPs），对尼日利亚东部曼比拉高原恩格尔尼亚基森林保护区及其周边区域的两种鲜为人知的两栖物种——*Cardioglossa schioetzi*与*Leptodactylodon bicolor*（均隶属于节蛙科（Arthroleptidae））的种群遗传结构进行了评估。该区域的景观由陡坡上的连续森林与草原基质中的小型河岸森林片段组成。尽管过去一个世纪以来，喀麦隆与尼日利亚山地的此类森林及其他森林的片段化程度加剧已有充分文献记录，但此前尚无针对该区域森林片段化对山地两栖动物种群影响的评估研究。两个物种种群的遗传多样性估算结果均较为相似，且杂合度水平与当地种群衰退的情况相符。除一对*C. schioetzi*种群外，本研究未观测到连续森林种群与河岸森林片段种群间的遗传分化；对于*L. bicolor*而言，连续森林内不同采样点间亦无遗传分化。本研究结果证实，森林片段与邻近的保护森林间存在近期基因交流，这表明连接这些区域的小型森林廊道或许能够缓解恩格尔尼亚基地区至少30年来高强度、严重的森林片段化所带来的遗传层面负面影响。