Ecologic Novelty in Taxonomic Diversification: Evolution of Photosymbiosis in Planktic Foraminifera

生态学和形态多样化之间的关系目前存在很多争论。越来越多的研究表明，许多物种的形成是在生态没有任何变化的情况下发生的。这一范式表明，大多数物种形成是通过被动地建立扩散障碍而发生的。相比之下，诸如“适应带”之类的概念意味着，当分类群进化出“关键创新”时，许多物种形成就发生了，这些创新使它们能够攀登无人占据的替代高峰。从这个角度来看，多样化是一个由生态策略变化介导的主动过程。研究将侧重于光共生有孔虫中现存最大的类群——球芽素进化支的系统发育和生态学研究。该研究将使用稳定同位素方法推断已灭绝有孔虫中光共生的发生，然后将这些生态信息绘制到系统发育树上。如果结果表明共生是在球状球蛋白辐射开始之前或之后很久才获得的，或者如果光共生和非共生姐妹群体具有相似的进化历史，那么反驳关键创新假说应该是容易的。此外，可以通过比较新第三纪globigerinids中共生和非共生姐妹类群的辐射模式与光共生古新世morozovelliids的基本完整数据集来检验共生和分类多样化之间的任何联系。该结果可能为其他类群的光共生以及软体动物和其他无脊椎动物的化学共生的进化作用提供见解。

Norris 9505836 The relationship between ecologica and morphological diversification is currently much in debate. There is an increasing body of work that suggests that much speciation occurs in the absence of any change in ecology. This paradigm suggests that most speciation takes place by the passive erection of barriers to dispersal. In contrast, concepts such as "adaptive zone" imply that much speciation occurs when taxa evolve "key innovations" that permit them to scale unoccupied adative peaks. From this perspective, diversification is an active process mediated by changes in ecological strategies. Research will focus on phylogenetic and ecologic study of the globigerinid clade--the largest exant group of photosymbiotic foraminifera. The proposed study will use stable isotope methods to deduce the occurrence of photosymbiosis in extinct foraminifera and then map this ecological information onto a phylogenetic tree. It should be easy to disprove the key-innovation hypothesis if the results demonstrate that symbiosis was acquired long before or after the globigerinid radiation began or if photosymbiotic and non-symbiotic sister groups have similar evolutionary histories. Moreover, any linkage between symbiosis and taxonomic diversification can be tested by comparing patterns of radiation in symbiotic and non-symbiotic sister groups in Neogene globigerinids with a mostly complete data set for the photosymbiotic Paleocene morozovellids. The results may provide insights on the evolutionary role of photosymbiosis in other groups as well as chemosymbiosis in mollusc and other invertebrates.