Department of Entomology, Natural History Museum, London, UK.
Oecologia. 2011 Dec;167(4):1053-61. doi: 10.1007/s00442-011-2036-7. Epub 2011 Jun 9.
Trophic interactions can trigger the development of exaggerated specialized characters and promote morphological diversification. For example, acorn weevils (genus Curculio) present strikingly long rostrums, which are used by females to perforate oviposition holes through the seed coat. Species exhibiting longer rostrums are known to exploit larger acorns, and therefore rostrum length is thought to be subject to selection to match the preferred acorn type. However, rostrum length is strongly correlated with body size, and morphological divergence could result from either selection on rostrum length for optimal food exploitation or from other pressures acting on body size. We collected infested acorns at oak forests where the large Curculio elephas and the small-bodied Curculio glandium co-occur. There were no interspecific differences in adult female body size to rostrum length allometric relationships, and rostrum length is equally correlated with body size in either species. MtDNA-based species identification showed that C. glandium larvae were present within acorns of all sizes, whereas C. elephas larvae were restricted to acorns above a minimum size, irrespective of oak species. Hence, exploitation of large acorns can hardly have triggered rostrum enlargement, as the small sized C. glandium adults (with short rostrums) could perforate and oviposit in both small and large acorns. Rather, increased rostrum length is probably a by-product of the larger body sizes of individuals emerging from bigger acorns, which allow increased larval size and enhance larval survival likelihood. Summarizing, when exaggerated feeding traits co-vary with other body features, interspecific morphological variability may result from contrasting selective pressures acting on these correlated characters.
营养相互作用可以触发夸张的特化特征的发展，并促进形态多样化。例如，橡实象鼻虫（属 Curculio）具有明显长的喙，雌性用其在种子外壳上穿孔产卵。已知具有更长喙的物种可以利用更大的橡实，因此喙的长度被认为受到选择以适应首选的橡实类型。然而，喙的长度与体型强烈相关，形态的分歧可能是由于对最佳食物利用的喙长度的选择，也可能是由于对体型的其他压力。我们在橡树林中收集了受感染的橡实，那里大型 Curculio elephas 和小体型的 Curculio glandium 共存。在成年雌性体型与喙长的异速关系方面，没有种间差异，并且喙的长度在两种物种中都与体型同等相关。基于 mtDNA 的物种鉴定表明，C. glandium 的幼虫存在于各种大小的橡实中，而 C. elephas 的幼虫仅限于最小尺寸以上的橡实，而与橡树种类无关。因此，大橡实的利用几乎不可能引发喙的增大，因为体型较小的 C. glandium 成虫（喙较短）可以在小和大橡实上穿孔和产卵。相反，喙的长度增加可能是个体从更大的橡实中出现的更大体型的副产品，这允许增加幼虫的大小并提高幼虫的生存可能性。总之，当夸张的进食特征与其他身体特征共变时，种间形态的可变性可能是由于对这些相关特征的相反选择压力造成的。
