Pemberton J M, Smith J A, Coulson T N, Marshall T C, Slate J, Paterson S, Albon S D, Clutton-Brock T H
Institute of Cell, Animal and Population Biology, University of Edinburgh, U.K.
Philos Trans R Soc Lond B Biol Sci. 1996 Jun 29;351(1341):745-52. doi: 10.1098/rstb.1996.0069.
Conventionally, small populations living on islands are expected to lose genetic variation by drift. Fluctuations in population size, combined with polygynous mating systems, are expected to contribute to the process by increasing sampling effects on genetic variation. However, in individually monitored populations of Red deer on Rum and Soay sheep on St. Kilda, which experience fluctuations in population size, two processes have been identified which mitigate loss of genetic variation. First, in a number of examples, population reductions are associated with selection. Selection may be in favour of heterozygotes, or, as we have documented in several cases, it may fluctuate in direction temporally. Second, in Soay sheep, in which mortality over population crashes is male-biased, ostensibly leading to low effective numbers of males, molecular studies show that there are systematic changes in the reproductive success of young males, and in variance in male success, that broaden genetic representation compared with expectation.
按照传统观点，生活在岛屿上的小种群预计会因遗传漂变而丧失遗传变异。种群数量的波动，再加上一夫多妻制的交配系统，预计会通过增加对遗传变异的抽样效应来推动这一过程。然而，在鲁姆岛上对马鹿个体进行监测的种群以及圣基尔达岛上对索艾羊个体进行监测的种群中，虽然经历了种群数量的波动，但已发现有两个过程可减轻遗传变异的丧失。首先，在许多实例中，种群数量减少与选择有关。选择可能有利于杂合子，或者，正如我们在几个案例中所记录的，选择方向可能随时间波动。其次，在索艾羊中，种群数量骤减时的死亡率存在雄性偏向，表面上导致雄性有效数量较低，但分子研究表明，年轻雄性的繁殖成功率以及雄性成功的方差存在系统性变化，与预期相比，这拓宽了遗传代表性。
