Kolm N, Goodwin N B, Balshine S, Reynolds J D
Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, UK.
J Evol Biol. 2006 Jan;19(1):76-84. doi: 10.1111/j.1420-9101.2005.00987.x.
The negative relationship between offspring number and offspring size provides a classic example of the role of trade-offs in life history theory. However, the evolutionary transitions in egg size and clutch size that have produced this negative relationship are still largely unknown. Since body size may affect both of these traits, it would be helpful to understand how evolutionary changes in body size may have facilitated or constrained shifts in clutch and egg size. By using comparative methods with a database of life histories and a phylogeny of 222 genera of cichlid fishes, we investigated the order of evolutionary transitions in these traits in relation to each other. We found that the ancestral large-bodied cichlids first increased egg size, followed by a decrease in both body size and clutch size resulting in the common current combination of a small-bodied cichlid with a small clutch of large eggs. Furthermore, lineages that deviated from the negative relationship between clutch and egg size underwent different transitions in these traits according to their body size (large bodied genera have moved towards the large clutch/small egg end of the continuum and small bodied genera towards the small clutch/large egg end of the continuum) to reach the negative relationship between clutch size and egg size. Our results show that body size is highly important in shaping the negative relationship between clutch size and egg size.
后代数量与后代体型之间的负相关关系为生活史理论中权衡取舍的作用提供了一个经典例子。然而，产生这种负相关关系的卵大小和窝卵数的进化转变在很大程度上仍不为人知。由于体型可能会影响这两个性状，了解体型的进化变化如何促进或限制窝卵数和卵大小的转变将会有所帮助。通过使用具有生活史数据库和222个丽鱼科属系统发育关系的比较方法，我们研究了这些性状之间进化转变的顺序。我们发现，祖先体型较大的丽鱼科鱼类首先增大了卵的大小，随后体型和窝卵数均减小，从而形成了目前常见的小体型丽鱼科鱼类与一窝少量大卵的组合。此外，偏离窝卵数与卵大小负相关关系的谱系在这些性状上根据其体型经历了不同的转变（大体型属朝着连续统中大窝卵数/小卵一端变化，小体型属朝着连续统中小窝卵数/大卵一端变化），以达到窝卵数与卵大小之间的负相关关系。我们的结果表明，体型在塑造窝卵数与卵大小之间的负相关关系方面非常重要。
