Kambysellis M P, Ho K F, Craddock E M, Piano F, Parisi M, Cohen J
Department of Biology, New York University, New York 10003, USA.
Curr Biol. 1995 Oct 1;5(10):1129-39. doi: 10.1016/s0960-9822(95)00229-6.
The endemic Hawaiian drosophilids, a unique group that are remarkable for their diversity and rapid proliferation, provide a model for analysis of the process of insular speciation. Founder events and accompanying random drift, together with shifts in sexual selection, appear to explain the dramatic divergence in male morphology and mating behaviour among these flies, but these forces do not account for their spectacular ecological diversification into a wide array of breeding niches. Although recognized as contributing to the success of this group, the precise role of adaptive shifts has not been well defined.
To delineate the pattern of ecological diversification in the evolution of Hawaiian Drosophila, we generated a molecular phylogeny, using nucleotide sequences from the yolk protein gene Yp1, of 42 endemic Hawaiian and 5 continental species. By mapping ecological characters onto this phylogeny, we demonstrate that monophagy is the primitive condition, and that decaying leaves were the initial substrate for oviposition and larval development. Shifts to decaying stems, bark and tree fluxes followed in more derived species. By plotting female reproductive strategies, as reflected in ovarian developmental type, on the molecular tree, we also demonstrate a phylogenetic trend toward increasing fecundity. We find some statistical support for correlations between ecological shifts and shifts in female reproductive strategies.
Because of the short branches at the base of the phylogram, which lead to ecologically diverse lineages, we conclude that much of the adaptive radiation into alternate breeding substrates occurred rapidly, early in the group's evolution in Hawaii. Furthermore, we conclude that this ecological divergence and the correlated changes in ovarian patterns that adapt species to their ecological habitats were contributing factors in the major phyletic branching within the Hawaiian drosophilid fauna.
夏威夷特有的果蝇是一个独特的群体，以其多样性和快速繁殖而著称，为分析岛屿物种形成过程提供了一个模型。奠基者事件及随之而来的随机漂变，再加上性选择的变化，似乎可以解释这些果蝇在雄性形态和交配行为上的巨大差异，但这些因素并不能解释它们如何惊人地生态多样化，进入了各种各样的繁殖生态位。尽管适应性变化被认为对这个群体的成功有贡献，但其确切作用尚未得到很好的界定。
为了描绘夏威夷果蝇进化过程中的生态多样化模式，我们利用卵黄蛋白基因Yp1的核苷酸序列，构建了42种夏威夷特有果蝇和5种大陆果蝇的分子系统发育树。通过将生态特征映射到这个系统发育树上，我们证明单食性是原始状态，腐烂的叶子是产卵和幼虫发育的初始基质。在更进化的物种中，出现了向腐烂茎、树皮和树液的转变。通过在分子树上绘制反映卵巢发育类型的雌性生殖策略，我们还证明了繁殖力增加的系统发育趋势。我们发现一些统计证据支持生态变化与雌性生殖策略变化之间的相关性。
由于系统发育图基部的分支较短，这些分支导致了生态多样的谱系，我们得出结论，向替代繁殖基质的许多适应性辐射在该群体在夏威夷进化的早期迅速发生。此外，我们得出结论，这种生态分化以及使物种适应其生态栖息地的卵巢模式的相关变化，是夏威夷果蝇动物群主要系统发育分支的促成因素。
