Ahnesjö J, Forsman A
Department of Biology and Environmental Science, Kalmar University, Kalmar, Sweden.
J Evol Biol. 2003 Nov;16(6):1308-18. doi: 10.1046/j.1420-9101.2003.00610.x.
Theory posits that selection on functionally interrelated characters will promote physical and genetic integration resulting in evolution of favourable trait-value combinations. The pygmy grasshopper Tetrix undulata (Orthoptera: Tetrigidae) displays a genetically encoded polymorphism for colour pattern. Colour morphs differ in several traits, including behaviours, thermal biology and body size. To examine if these size differences may reflect phenotypic plasticity of growth and development in response to temperature we used a split brood-design and reared hatchlings from mothers belonging to different morphs in different thermal environments (warm or cold) until maturity. We found that time to maturity was longer in the cold compared with the warm treatment. In the warm (but not in the cold) treatment time to maturity also varied among individuals born to mothers belonging to different colour morphs. Although low temperature and long development time are normally accompanied by increased body size in ectotherms, our results revealed no difference in size at maturity between individuals reared in the two temperature treatments. There was also an increase (not a decrease) in adult body size with shortened time to maturity across families within each treatment. Taken together, this suggests that body size is canalized against environmental perturbations, and that early maturation does not necessarily trade off against a size-mediated decrease in fecundity. Heritability of body size was moderate in magnitude. Moreover, body size at maturity varied among individuals belonging to different morphs and was influenced also by maternal colour morph, suggesting that a genetic correlation exists between colour pattern and body size. These findings suggest that different characters have evolved in concert and that the various colour morphs represent different evolutionary strategies, i.e., alternative peaks in a multi-modal adaptive landscape.
理论认为，对功能上相互关联的性状进行选择将促进身体和基因整合，从而导致有利性状值组合的进化。侏儒蚱蜢Tetrix undulata（直翅目：蚱科）表现出一种由基因编码的体色多态性。体色变体在几个性状上存在差异，包括行为、热生物学和体型。为了检验这些体型差异是否可能反映了生长发育对温度的表型可塑性，我们采用了分窝设计，将来自不同体色变体的母亲所产的幼体在不同的热环境（温暖或寒冷）中饲养至成熟。我们发现，与温暖处理相比，寒冷环境下的成熟时间更长。在温暖处理中（但在寒冷处理中没有），不同体色变体母亲所产个体的成熟时间也有所不同。尽管在变温动物中，低温和较长的发育时间通常伴随着体型增大，但我们的结果显示，在两种温度处理下饲养的个体成熟时的体型没有差异。在每种处理中，随着成熟时间缩短，成年个体的体型也有所增加（而非减少）。综合来看，这表明体型对环境扰动具有缓冲作用，而且早熟并不一定会以体型介导的繁殖力下降为代价。体型的遗传力中等。此外，成熟时的体型在不同体色变体的个体之间存在差异，并且还受到母体体色变体的影响，这表明体色模式和体型之间存在遗传相关性。这些发现表明，不同的性状是协同进化的，各种体色变体代表了不同的进化策略，即在多峰适应景观中的替代峰值。
