Department of Animal and Plant Sciences, The University of Sheffield, Sheffield, UK.
Heredity (Edinb). 2012 May;108(5):569-76. doi: 10.1038/hdy.2011.125. Epub 2011 Dec 21.
Insects with complex life-cycles should optimize age and size at maturity during larval development. When inhabiting seasonal environments, organisms have limited reproductive periods and face fundamental decisions: individuals that reach maturity late in season have to either reproduce at a small size or increase their growth rates. Increasing growth rates is costly in insects because of higher juvenile mortality, decreased adult survival or increased susceptibility to parasitism by bacteria and viruses via compromised immune function. Environmental changes such as seasonality can also alter the quantitative genetic architecture. Here, we explore the quantitative genetics of life history and immunity traits under two experimentally induced seasonal environments in the cricket Gryllus bimaculatus. Seasonality affected the life history but not the immune phenotypes. Individuals under decreasing day length developed slower and grew to a bigger size. We found ample additive genetic variance and heritability for components of immunity (haemocyte densities, proPhenoloxidase activity, resistance against Serratia marcescens), and for the life history traits, age and size at maturity. Despite genetic covariance among traits, the structure of G was inconsistent with genetically based trade-off between life history and immune traits (for example, a strong positive genetic correlation between growth rate and haemocyte density was estimated). However, conditional evolvabilities support the idea that genetic covariance structure limits the capacity of individual traits to evolve independently. We found no evidence for G × E interactions arising from the experimentally induced seasonality.
具有复杂生命周期的昆虫应该在幼虫发育过程中优化成熟时的年龄和大小。当栖息在季节性环境中时，生物的繁殖期有限，面临着基本的决策：在季节后期达到成熟的个体要么以较小的体型繁殖，要么增加生长速度。在昆虫中，增加生长速度是有代价的，因为这会导致更高的幼体死亡率、降低的成虫存活率，或通过削弱免疫功能而更容易受到细菌和病毒的寄生。环境变化，如季节性，也会改变数量遗传结构。在这里，我们在两种实验诱导的季节性环境中探索了蟋蟀 Gryllus bimaculatus 的生活史和免疫特征的数量遗传学。季节性影响了生活史，但不影响免疫表型。在日长减少的环境中，个体发育较慢，体型较大。我们发现，免疫特征（血细胞密度、原酚氧化酶活性、对粘质沙雷氏菌的抗性）和生活史特征（成熟时的年龄和大小）的组成部分有足够的加性遗传方差和遗传力。尽管各性状之间存在遗传协方差，但 G 的结构与生活史和免疫性状之间基于遗传的权衡不一致（例如，生长速度和血细胞密度之间的遗传相关性很强）。然而，条件可进化性支持了遗传协方差结构限制个体性状独立进化的能力的观点。我们没有发现实验诱导的季节性产生 G × E 相互作用的证据。
