Maternal care under large clutches with small eggs: The evolution of life history traits in shield bugs

We examined evolutionary associations between parental care and other life-history traits, female body size, egg size, clutch size, reproductive output and developmental period of eggs and hatchlings, in shield bugs using phylogenetic generalized least squares (PGLS) models in the phylolm package for R.Then, the pattern of evolutionary transitions among character states, parental care and egg size, clutch size or reproductive output, was examined using the Discrete dependent model implemented in BayesTraits.Our analyses revealed that female body size affected reproductive resource allocation. Contrary to the expectations of current theories, the acquisition of maternal care was associated with small eggs, large clutches, and large egg-resource allocation.There was a greater trade-off between egg size and clutch size in caring species than in non-caring species.Egg and hatchling developmental rates were not correlated with egg size, but were slower in caring species than in non-caring species.Analyses of evolutionary transitions suggest that the establishment of large clutches, small eggs and large egg-resource allocation preceded the evolution of maternal care.本研究以盾蝽（shield bugs）为研究对象，借助R语言phylolm工具包中的系统发育广义最小二乘法（phylogenetic generalized least squares, PGLS）模型，分析了亲代照料与其他生活史性状、雌虫体型、卵大小、窝卵数、繁殖产出以及卵与初孵幼体的发育时长之间的演化关联。随后，本研究利用BayesTraits软件中内置的离散依赖模型（Discrete dependent model），探究了亲代照料、卵大小、窝卵数或繁殖产出等性状状态间的演化转变模式。分析结果表明，雌虫体型会影响繁殖资源分配策略。与现有理论的预期相悖，母性照料的演化获得与小型卵、大窝卵数以及较高的卵资源分配显著相关。相较于不提供亲代照料的物种，提供照料的物种中，卵大小与窝卵数之间存在更强的权衡关系。卵与初孵幼体的发育速率与卵大小并无关联，但在提供亲代照料的物种中，其发育速率慢于不提供照料的物种。演化转变分析结果显示，大窝卵数、小型卵以及高卵资源分配的性状演化先于母性照料的起源。