Berry R J
Department of Biology, University College London, U.K.
Philos Trans R Soc Lond B Biol Sci. 1996 Jun 29;351(1341):753-64. doi: 10.1098/rstb.1996.0070.
The reason for the distinctiveness of small mammals on islands has traditionally attracted some imaginative story-telling, usually invoking isolation (as a relict) followed by adaptation and/or random genetic changes. Studies of voles on Orkney, long-tailed field mice on the Hebrides and Shetland, and house mice on the Faroe archipelago show that the main factor in differentiating island races from their mainland ancestors is the chance genetic composition of the founding animals. Subsequent change has necessarily to be based on the genes and frequencies carried by this colonizing group. Probably most post-colonization change is adaptive, although possibly limited in extent both by the initial paucity of variation and by the conservative effect of intragenomic interactions. It is probably helpful to recognize that the 'founder effect' or principle commonly invoked in discussions about evolution on islands involves a founder 'event', followed by founder 'selection'. Island differentiation is not necessarily a precursor to speciation, although the wide occurrence of island endemics suggests that founder effects should not be rejected as a driving force initiating speciation. Notwithstanding, island forms provide a valuable 'laboratory' for testing new genetic combinations, a small proportion of which may prove evolutionarily exciting. Only more empirical studies will uncover their evolutionary importance.
岛屿上小型哺乳动物的独特性原因传统上引发了一些富有想象力的故事讲述，通常是援引隔离（作为一种残遗现象），随后是适应和/或随机的基因变化。对奥克尼群岛上的田鼠、赫布里底群岛和设得兰群岛上的长尾田鼠以及法罗群岛上的家鼠的研究表明，将岛屿种群与其大陆祖先区分开来的主要因素是奠基动物的偶然基因组成。随后的变化必然基于这个殖民群体所携带的基因和基因频率。尽管可能在程度上受到初始变异稀缺以及基因组内相互作用的保守效应的限制，但大多数殖民后的变化可能是适应性的。认识到在关于岛屿进化的讨论中通常援引的“奠基者效应”或原则涉及一个奠基者“事件”，随后是奠基者“选择”，这可能是有帮助的。岛屿分化不一定是物种形成的前奏，尽管岛屿特有物种的广泛存在表明奠基者效应不应被排除作为引发物种形成的驱动力。尽管如此，岛屿形态为测试新的基因组合提供了一个有价值的“实验室”，其中一小部分可能被证明在进化上令人兴奋。只有更多的实证研究才能揭示它们在进化上的重要性。
