Data from: Prepupal building behavior in Drosophila melanogaster and its evolution under resource and time constraints

Structures built by animals are a widespread and ecologically important ‘extended phenotype’. While its taxonomic diversity has been well described, factors affecting short-term evolution of building behavior within a species have received little experimental attention. Here we describe how, given the opportunity, wandering Drosophila melanogaster larvae often build long tunnels in agar substrates and embed their pupae within them. These embedded larvae are characterized by a longer egg-to-pupariation developmental time than larvae that pupate on the surface. Assuming that such building behaviors are likely to be energetically costly and/or time consuming, we hypothesized that they should evolve to be less pronounced under resource or time limitation. In accord with this prediction, larvae from populations evolved for 160 generations under a regime that combines larval malnutrition with limited developmental time dug shorter tunnels than larvae from control unselected populations. However, the proportion of larvae that embedded before pupation did not differ between the malnutrition-adapted and control populations, suggesting that tunnel length and likelihood of embedding before pupation are controlled by different genetic loci. The behaviors exhibited by wandering larvae of Drosophila melanogaster prior to pupation offer a model system to study evolution of animal building behaviors because the tunneling and embedding phenotypes are simple, facultative and highly variable.

动物构筑的结构是一类分布广泛且具有重要生态学意义的延伸表型（extended phenotype）。尽管其分类多样性已得到充分阐释，但物种内部构筑行为的短期演化影响因素却鲜有实验关注。本文报道，当具备适宜条件时，游荡期的黑腹果蝇（Drosophila melanogaster）幼虫常会在琼脂培养基（agar substrates）中构筑长隧道，并将蛹嵌入隧道内。相较于在培养基表面化蛹的幼虫，这类嵌入型幼虫的卵至化蛹发育时长更长。鉴于此类构筑行为大概率存在能量与/或时间成本，我们提出假说：在资源或时间受限的条件下，这类行为的表现程度应会减弱。实验结果与该预测相符：经结合幼虫营养匮乏与发育时间限制的选择方案演化160代的种群，其幼虫挖掘的隧道长度显著短于未经过选择的对照种群幼虫。不过，化蛹前发生嵌入行为的幼虫比例，在营养匮乏适应种群与对照种群间并无显著差异，这表明隧道长度与化蛹前嵌入概率受不同遗传位点调控。黑腹果蝇游荡期幼虫在化蛹前展现出的这类行为，为研究动物构筑行为的演化提供了理想模型系统——其隧道构筑与嵌入表型兼具简单性、兼性与高变异性。