Department of Zoology, Graduate School of Science, Kyoto University, Kyoto, Japan.
J Evol Biol. 2012 Sep;25(9):1835-42. doi: 10.1111/j.1420-9101.2012.02568.x. Epub 2012 Jul 25.
The body size of a univoltine carabid beetle Carabus tosanus on Shikoku Island, Japan, was clearly smaller in higher-altitude populations (subspecies), which possibly represents incipient speciation. To explore the determinants of altitudinal differences in body size in this species, we studied the degree of phenotypic plasticity by conducting rearing experiments at two constant temperatures and examined genetic differences through interpopulation crosses. At 15 °C, C. tosanus had a longer developmental period and a shorter adult body than at 20 °C. Nevertheless, variation in body size due to temperature effects (phenotypic plasticity) was small compared to the interpopulation differences, which suggests substantial genetic differences between populations (subspecies) at different altitudes. In F(1) offspring from crosses between a low-altitude (subspecies tosanus) and a high-altitude population (subspecies ishizuchianus), adult body length was affected by the genotypes of both parents, with an interaction effect of parental genotype and offspring sex. Further analyses revealed that adult body length was affected by sex-linked factors in addition to autosomal factors. These genetic differences in body size may have resulted from adaptations to different altitudes and may be important for the process of incipient speciation because body size differences could contribute to premating reproductive isolation.
日本四国岛单化型步甲 Carabus tosanus 的体型在高海拔种群（亚种）中明显较小，这可能代表着物种形成的初始阶段。为了探究该物种海拔体型差异的决定因素，我们在两个恒温下进行了饲养实验，以研究表型可塑性的程度，并通过种群间杂交检验了遗传差异。在 15°C 时，C. tosanus 的发育周期比 20°C 长，成虫体型比 20°C 小。然而，与种群间差异相比，温度效应（表型可塑性）引起的体型变化较小，这表明不同海拔种群（亚种）之间存在大量遗传差异。在来自低海拔种群（亚种 tosanus）和高海拔种群（亚种 ishizuchianus）的杂交 F1 后代中，成虫体长受双亲基因型的影响，并存在亲本品系与后代性别的互作效应。进一步的分析表明，除了常染色体因素外，成虫体长还受到性连锁因素的影响。这些体型上的遗传差异可能是对不同海拔的适应的结果，对于物种形成的初始阶段可能很重要，因为体型差异可能有助于交配前生殖隔离。
