Haga Eloísa B, Rossi Marcelo N
Department of Biological Sciences Laboratório de Ecologia Populacional (LEPOP) Federal University of São Paulo (Unifesp) Diadema São Paulo 09941-510 Brazil.
Ecol Evol. 2016 Sep 7;6(19):6892-6905. doi: 10.1002/ece3.2364. eCollection 2016 Oct.
Explaining large-scale patterns of variation in body size has been considered a central question in ecology and evolutionary biology because several life-history traits are directly linked to body size. For ectothermic organisms, little is known about what processes influence geographic variation in body size. Changes in body size and sexual size dimorphism (SSD) have been associated with environmental variables, particularly for Bruchinae insects, which feed exclusively on seeds during the larval stage. However, the effect of important seed traits on body size variation has rarely been investigated, and whether SSD varies substantially among populations within bruchine species is poorly known. Using the seed-feeding beetle infesting its host plant , we investigated whether specific seed traits (hardness, size, water content, carbon/nitrogen ratio, and phenolic content) were determinant in generating geographic variation in body size and SSD of . We also examined the relationships between body size and SSD with latitude and altitude. The body size of both sexes combined was not related to latitude, altitude, and any of the physical and chemical seed traits. However, the female body size tended to vary more in size than the males, generating significant variation in SSD in relation to latitude and altitude. The females were the larger sex at higher latitudes and at lower altitudes, precisely where seed water content was greater. Therefore, our results suggest that water content was the most important seed trait, most severely affecting the females, promoting geographic variation in SSD of .
解释体型的大规模变异模式一直被认为是生态学和进化生物学中的核心问题，因为几个生活史特征都与体型直接相关。对于变温生物而言，关于哪些过程影响体型的地理变异，我们所知甚少。体型和两性异形（SSD）的变化与环境变量有关，特别是对于豆象科昆虫，它们在幼虫阶段仅以种子为食。然而，重要种子特征对体型变异的影响很少被研究，而且在豆象科物种内不同种群间SSD是否有显著差异也鲜为人知。我们以寄生于其寄主植物上的食种子甲虫为研究对象，调查了特定种子特征（硬度、大小、含水量、碳/氮比和酚类含量）是否是导致该甲虫体型和SSD地理变异的决定因素。我们还研究了体型和SSD与纬度和海拔之间的关系。两性的体型总和与纬度、海拔以及任何物理和化学种子特征均无关联。然而，雌性体型的变化往往比雄性更大，从而导致SSD在纬度和海拔方面产生显著变异。在较高纬度和较低海拔地区，雌性为体型较大的性别，而这些地区恰恰种子含水量更高。因此，我们的研究结果表明，含水量是最重要的种子特征，对雌性影响最为严重，进而导致该甲虫SSD的地理变异。
