Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA; Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland.
Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA.
Curr Biol. 2024 Jul 8;34(13):2880-2892.e7. doi: 10.1016/j.cub.2024.05.042. Epub 2024 Jun 18.
The diversity of insect eggs is astounding but still largely unexplained. Here, we apply phylogenetic analyses to 208 species of stick and leaf insects, coupled with physiological measurements of metabolic rate and water loss on five species, to evaluate classes of factors that may drive egg morphological diversification: life history constraints, material costs, mechanical constraints, and ecological circumstances. We show support for all three classes, but egg size is primarily influenced by female body size and strongly trades off with egg number. Females that lay relatively fewer but larger eggs, which develop more slowly because of disproportionately low metabolic rates, also tend to bury or glue them in specific locations instead of simply dropping them from the foliage (ancestral state). This form of parental care then directly favors relatively elongated eggs, which may facilitate their placement and allow easier passage through the oviducts in slender species. In addition, flightless females display a higher reproductive output and consequently lay relatively more and larger eggs compared with flight-capable females. Surprisingly, local climatic conditions had only weak effects on egg traits. Overall, our results suggest that morphological diversification of stick insect eggs is driven by a complex web of causal relationships among traits, with dominant effects of resource allocation and oviposition strategies, and of mechanical constraints.
昆虫卵的多样性令人惊讶，但仍在很大程度上未得到解释。在这里，我们应用系统发育分析方法研究了 208 种竹节虫和叶虫，同时对其中 5 种进行了代谢率和水分损失的生理测量，以评估可能推动卵形态多样化的因素类别：生活史限制、物质成本、机械限制和生态环境。我们支持所有这三个类别，但卵的大小主要受雌体大小的影响，并与卵的数量呈强烈的权衡关系。产卵相对较少但较大的雌性，由于代谢率低得不成比例，其卵的发育速度较慢，它们也倾向于将卵埋在或粘在特定位置，而不是简单地从叶片上掉落（祖先状态）。这种形式的亲代抚育会直接有利于相对细长的卵，这可能会方便它们的放置，并使它们更容易通过细长物种的输卵管。此外，不会飞的雌性表现出更高的繁殖输出，因此与有飞行能力的雌性相比，产卵数量相对较多且卵较大。令人惊讶的是，当地的气候条件对卵特征的影响很小。总体而言，我们的研究结果表明，竹节虫卵形态的多样化是由特征之间复杂的因果关系网络驱动的，其中资源分配和产卵策略以及机械限制的主导作用。
