Towards a general perspective on life-history evolution and diversification in parasitoid wasps

In attempting to explain the marked interspecific variation evident in many components of life-history in parasitoid wasps, biologists have sought to identify general predictors of suites of ‘important’ life-history traits. Two predictors currently in general use are: (1) the parasitoid mode of larval development in relation to future host growth and development [no further host growth and development (= idiobiosis) versus continued host growth and development (= koinobiosis)]; and (2) the ovigeny index (the degree to which the lifetime potential complement of eggs is mature at the start of adult life in females). These have been postulated to share several life-history correlates, and an earlier comparative analysis showed the predictors to be associated. Two questions are thus posed: which life-history variables are actually common to both idio/koinobiosis and the ovigeny index, and which are responsible for the link between these two axes of life-history diversity? Through comparative analyses of a database of life-history traits for 133 parasitoid wasp species, four life-history correlates out of the 11 we investigated are shown to account for the association between the two predictors: the relative level of resource investment per egg (degree of yolk richness, which is lower in koinobionts), pre-adult lifespan (longer in koinobionts), female lifespan (shorter in koinobionts), and maximum egg load (larger in koinobionts). Our findings pave the way for full integration of the dichotomous hypothesis with the ovigeny index hypothesis, to provide a holistic perspective on parasitoid wasp life-history diversity and evolution.

为解释寄生蜂（parasitoid wasp）生活史诸多组分中显著的种间变异，生物学家一直致力于识别调控一系列"关键"生活史性状的通用预测因子。目前通用的两类预测因子分别为：（1）与寄主未来生长发育相关的幼虫发育模式[寄主不再继续生长发育（=抑寄主发育型，idiobiosis）vs 寄主持续生长发育（=保寄主发育型，koinobiosis）]；（2）产卵指数（ovigeny index），即雌性成虫羽化初期，其终身潜在产卵总量的成熟比例。此前研究已推测二者存在多项生活史相关关联，且早期比较分析亦证实这两类预测因子存在相关性。由此提出两个核心问题：一是抑/保寄主发育型与产卵指数二者共有的生活史变量究竟有哪些；二是哪些变量构成了这两大生活史多样性维度间的关联纽带。本研究通过对涵盖133种寄生蜂的生活史性状数据库开展比较分析，在我们所考察的11项生活史变量中，最终确认4项关联因子可解释两类预测因子间的相关性：单卵相对资源投入水平（卵黄丰富度，保寄主发育型寄生蜂的卵黄丰富度更低）、预成虫寿命（保寄主发育型寄生蜂的预成虫寿命更长）、雌性成虫寿命（保寄主发育型寄生蜂的雌性寿命更短）以及最大产卵量（保寄主发育型寄生蜂的最大产卵量更高）。本研究结果为抑/保寄主发育二分假说与产卵指数假说的全面整合铺平了道路，可为寄生蜂生活史多样性与演化研究提供整体性视角。