Leips Jeff, Richardson Jean M L, Rodd F Helen, Travis Joseph
Department of Biological Science, Florida State University, Tallahassee, Florida 32306, USA.
Evolution. 2009 May;63(5):1341-7. doi: 10.1111/j.1558-5646.2009.00631.x.
Given a trade-off between offspring size and number and an advantage to large size in competition, theory predicts that the offspring size that maximizes maternal fitness will vary with the level of competition that offspring experience. Where the strength of competition varies, selection should favor females that can adjust their offspring size to match the offspring's expected competitive environment. We looked for such phenotypically plastic maternal effects in the least killifish, Heterandria formosa, a livebearing, matrotrophic species. Long-term field observations on this species have revealed that some populations experience relatively constant, low densities, whereas other populations experience more variable, higher densities. We compared sizes of offspring born to females exposed during brood development to either low or high experimental densities, keeping the per capita food ration constant. We examined plastic responses to density for females from one population that experiences high and variable densities and another that experiences low and less-variable densities. We found that, as predicted, female H. formosa produced larger offspring at the higher density. Unexpectedly, we found similar patterns of plasticity in response to density for females from both populations, suggesting that this response is evolutionarily conserved in this species.
鉴于后代大小与数量之间的权衡以及大型个体在竞争中的优势，理论预测，使母体适应性最大化的后代大小将随后代所经历的竞争水平而变化。在竞争强度不同的情况下，选择应有利于那些能够调整后代大小以匹配后代预期竞争环境的雌性。我们在细纹鳉鱼（Heterandria formosa）中寻找这种表型可塑性的母体效应，细纹鳉鱼是一种卵胎生、母性营养型物种。对该物种的长期野外观察表明，一些种群经历相对恒定、低密度的环境，而其他种群经历更具变化性、高密度的环境。我们比较了在育雏发育期间暴露于低或高实验密度下的雌性所产后代的大小，同时保持人均食物配给量不变。我们研究了来自一个经历高且变化密度的种群和另一个经历低且变化较小密度的种群的雌性对密度的可塑性反应。我们发现，正如预测的那样，细纹鳉鱼雌性在较高密度下产生更大的后代。出乎意料的是，我们发现两个种群的雌性对密度的可塑性反应模式相似，这表明这种反应在该物种中是进化保守的。
