Data from: Genetic rescue, the greater prairie chicken and the problem of conservation reliance in the Anthropocene

A central question in conservation is how best to manage biodiversity, despite human domination of global processes (= Anthropocene). Common responses (i.e. translocations, genetic rescue) forestall potential extirpations, yet have an uncertain duration. A textbook example is the greater prairie chicken (GRPC: Tympanuchus cupido pinnatus), where translocations (1992–1998) seemingly rescued genetically depauperate Illinois populations. We re-evaluated this situation after two decades by genotyping 21 microsatellite loci from 1831 shed feathers across six leks in two counties over 4 years (2010–2013). Low migration rates (less than 1%) established each county as demographically independent, but with declining-population estimates (4 year average N = 79). Leks were genetically similar and significantly bottlenecked, with low effective population sizes (average Ne = 13.1; 4 year Ne/N = 0.166). Genetic structure was defined by 12 significantly different family groups, with relatedness r = 0.31 > half-sib r = 0.25. Average heterozygosity, indicating short-term survival, did not differ among contemporary, pre- and post-translocated populations, whereas allelic diversity did. Our results, the natural history of GRPC (i.e. few leks, male dominance hierarchies) and its controlled immigration suggest demographic expansion rather than genetic rescue. Legal protection under the endangered species act (ESA) may enhance recovery, but could exacerbate political–economic concerns on how best to manage ‘conservation-reliant’ species, for which GRPC is now an exemplar.

保护生物学的核心议题之一，便是在人类主导全球生态过程的背景下（即人类世（Anthropocene）），如何最优地管理生物多样性。主流的保护干预手段（即个体迁地引入（translocations）与遗传拯救（genetic rescue））能够延缓潜在的种群灭绝风险，但此类手段的实施效果持续时长尚不明确。一个经典教科案例便是大草原松鸡（greater prairie chicken, GRPC：*Tympanuchus cupido pinnatus*）：1992至1998年间的个体迁地引入操作，曾被认为成功拯救了遗传多样性匮乏的伊利诺伊州种群。本研究时隔二十年重新评估了这一案例：于2010至2013年的四年间，针对美国两个县的6处求偶场（lek）的1831根脱落羽毛，对21个微卫星位点（microsatellite loci）进行了基因分型分析。研究测得种群迁移率极低（不足1%），证明两个县的种群在统计上彼此独立，但种群数量均呈下降趋势——四年间平均总种群规模N=79。各求偶场的遗传相似性较高，且均经历了显著的遗传瓶颈，有效种群大小（Ne）普遍偏低：四年间平均Ne=13.1，Ne与总种群规模N的比值为0.166。种群遗传结构由12个遗传差异显著的家族类群构成，平均亲缘系数r=0.31，高于半同胞（half-sib）的基准亲缘系数r=0.25。用于指示种群短期存活能力的平均杂合度（heterozygosity），在当代种群、迁地引入前种群与迁地引入后种群间无显著差异，但等位基因多样性（allelic diversity）则存在显著分化。结合本研究结果、大草原松鸡的自然生物学特性（即求偶场数量稀少、雄性个体存在等级支配关系）以及其受控的迁入模式，我们认为该种群的恢复更倾向于种群统计扩张，而非遗传拯救效应。根据美国《濒危物种法》（Endangered Species Act, ESA）获得的法律保护，或可助力种群恢复，但也可能加剧相关政治经济层面的争议——即如何最优地管理‘依赖保护物种’（conservation-reliant species），而大草原松鸡如今已成为这类物种的典型范例。