Marchinko Kerry B, Schluter Dolph
Department of Zoology, 6270 University Boulevard, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Evolution. 2007 May;61(5):1084-90. doi: 10.1111/j.1558-5646.2007.00103.x.
Recent work has revealed the molecular mechanisms governing one of the most dramatic examples of parallel evolution in nature: the repeated loss of lateral plate armor in freshwater populations of threespine stickleback. Yet, the ecological mechanisms responsible for armor loss remain unclear. Using a balanced experimental design, we examined Heuts' (1947) hypothesis that selection due to differences in salinity indirectly drive the reduction of lateral plate armor in fresh water while maintaining armor in the sea. We measured two fitness-related traits, hatching success and juvenile growth rate, in offspring of reduced (low and partial) and complete lateral plate morphs from two polymorphic populations when raised in either fresh water or salt water. In contrast to Heuts' results, there was little difference among morphs in hatching success. However, salinity strongly influenced juvenile growth: offspring of reduced lateral plate morphs grew substantially faster (up to 65%) than offspring of completely plated morphs in fresh water, but there was little difference in salt water. We suggest that the parallel loss of lateral plates in fresh water has arisen through a correlated response to selection for faster growth during lateral plate development, but the effect of salinity on hatching success and juvenile growth rate cannot explain the predominance of completely plated morphs in marine populations.
三刺鱼淡水种群中侧板甲胄的反复丧失。然而，导致甲胄丧失的生态机制仍不明确。我们采用平衡实验设计，检验了休茨（1947年）的假说，即盐度差异导致的选择间接推动淡水环境中侧板甲胄的减少，同时使海洋环境中的甲胄得以保留。我们测量了来自两个多态种群的侧板形态减少（低侧板和部分侧板）和完整侧板形态的后代在淡水或盐水中饲养时与适应性相关的两个性状，即孵化成功率和幼鱼生长率。与休茨的结果相反，不同形态在孵化成功率上差异不大。然而，盐度对幼鱼生长有强烈影响：在淡水中，侧板形态减少的后代生长速度比完整侧板形态的后代快得多（高达65%），但在盐水中差异不大。我们认为，淡水环境中侧板的平行丧失是由于在侧板发育过程中对更快生长的选择产生的相关反应导致的，但盐度对孵化成功率和幼鱼生长率的影响无法解释海洋种群中完整侧板形态占主导地位的现象。
