Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
BMC Evol Biol. 2011 Apr 1;11:85. doi: 10.1186/1471-2148-11-85.
Today many large mammals live in small, fragmented populations, but it is often unclear whether this subdivision is the result of long-term or recent events. Demographic modeling using genetic data can estimate changes in long-term population sizes while temporal sampling provides a way to compare genetic variation present today with that sampled in the past. In order to better understand the dynamics associated with the divergences of great ape populations, these analytical approaches were applied to western gorillas (Gorilla gorilla) and in particular to the isolated and Critically Endangered Cross River gorilla subspecies (G. g. diehli).
We used microsatellite genotypes from museum specimens and contemporary samples of Cross River gorillas to infer both the long-term and recent population history. We find that Cross River gorillas diverged from the ancestral western gorilla population ~17,800 years ago (95% HDI: 760, 63,245 years). However, gene flow ceased only ~420 years ago (95% HDI: 200, 16,256 years), followed by a bottleneck beginning ~320 years ago (95% HDI: 200, 2,825 years) that caused a 60-fold decrease in the effective population size of Cross River gorillas. Direct comparison of heterozygosity estimates from museum and contemporary samples suggests a loss of genetic variation over the last 100 years.
The composite history of western gorillas could plausibly be explained by climatic oscillations inducing environmental changes in western equatorial Africa that would have allowed gorilla populations to expand over time but ultimately isolate the Cross River gorillas, which thereafter exhibited a dramatic population size reduction. The recent decrease in the Cross River population is accordingly most likely attributable to increasing anthropogenic pressure over the last several hundred years. Isolation of diverging populations with prolonged concomitant gene flow, but not secondary admixture, appears to be a typical characteristic of the population histories of African great apes, including gorillas, chimpanzees and bonobos.
如今，许多大型哺乳动物生活在小而分散的种群中，但种群的细分究竟是长期还是近期的结果并不明确。利用遗传数据进行的种群动态建模可以估算长期的种群数量变化，而时间采样则提供了一种方法，可以将当前的遗传变异与过去采样的遗传变异进行比较。为了更好地理解与大型类人猿种群分歧相关的动态变化，本研究采用了这些分析方法，以西部低地大猩猩（Gorilla gorilla）为例，特别是对孤立且极度濒危的克罗斯河大猩猩亚种（G. g. diehli）进行了分析。
本研究利用来自博物馆标本和当代克罗斯河大猩猩样本的微卫星基因型推断了种群的长期和近期历史。研究发现，克罗斯河大猩猩与祖先西部低地大猩猩种群的分歧发生在约 17800 年前（95% HDI：760，63245 年前）。然而，基因流仅在约 420 年前停止（95% HDI：200，16256 年前），随后在约 320 年前（95% HDI：200，2825 年前）出现瓶颈，导致克罗斯河大猩猩的有效种群数量减少了 60 倍。对博物馆和当代样本的杂合度估计值进行直接比较表明，过去 100 年里遗传变异有所丧失。
西部低地大猩猩的综合历史可能可以用以下假说解释：气候波动导致西非赤道地区的环境变化，这使得大猩猩种群得以随时间扩张，但最终导致克罗斯河大猩猩种群隔离，此后其种群数量急剧减少。因此，过去几百年来，克罗斯河大猩猩种群数量的减少很可能归因于人为压力的增加。与其他非洲大型类人猿（包括大猩猩、黑猩猩和倭黑猩猩）一样，具有长期共同基因流但没有二次混合的分化种群的隔离似乎是其种群历史的一个典型特征。
