Evolution of stenophagy in spiders (Araneae): evidence based on the comparative analysis of spider diets

Stenophagy (narrow diet breadth) represents an extreme of trophic specialization in carnivores, but little is known about the forces driving its evolution. We used spiders, the most diversified group of terrestrial predators, to investigate whether stenophagy 1) promoted diversification, 2) was phylogenetically conserved and evolutionarily derived state, and 3) was determined either by geographical distribution and foraging guild. We utilized published data on the prey of almost 600 species. Six categories of stenophagy were found: myrmecophagy, araneophagy, lepidopterophagy, termitophagy, dipterophagy and crustaceophagy. We found that the species diversity of euryphagous genera and families was similar to stenophagous genera and families. At the family level, stenophagy evolved repeatedly and independently. Within families, the basal condition was oligophagy or euryphagy. Most types of stenophagy were clearly derived: myrmecophagy in Zodariidae; lepidopterophagy in Araneidae; dipterophagy in Theridiidae. In contrast, araneophagy was confined to basal and intermediate lineages, suggesting its ancestral condition. The diet breadth of species from the tropics and subtropics was less diverse than species from the temperate zone. Diet breadth was lower in cursorial spiders compared to web-building species. Thus, the evolution of stenophagy in spiders appears to be complex and governed by phylogeny as well as by ecological determinants.

狭食性（stenophagy）指食肉动物营养特化的极端形式，即食谱宽度狭窄，但目前对推动其演化的驱动因素仍知之甚少。本研究以陆地捕食类群中多样性最高的蜘蛛为研究对象，旨在探究狭食性是否具备以下特征：1）促进物种分化；2）具有系统发育保守性且属于演化衍生状态；3）由地理分布与觅食功能群共同决定。
本研究使用了已发表的近600个蜘蛛物种的猎物数据，共识别出6类狭食性类型：蚁食性（myrmecophagy）、蛛食性（araneophagy）、鳞翅目食性（lepidopterophagy）、白蚁食性（termitophagy）、双翅目食性（dipterophagy）以及甲壳类食性（crustaceophagy）。
研究发现，广食性（euryphagy）属与科的物种多样性，与狭食性类群并无显著差异。在科阶元层面，狭食性曾多次独立演化。在各科内部，祖先状态多为寡食性（oligophagy）或广食性。
多数狭食性类型均为明确的衍生状态：如蚁蛛科（Zodariidae）的蚁食性、园蛛科（Araneidae）的鳞翅目食性以及球蛛科（Theridiidae）的双翅目食性。与之相反，蛛食性仅分布于基部与中间演化支系中，提示其为祖先状态。
热带与亚热带地区蜘蛛物种的食谱宽度，相较于温带地区物种更为狭窄。游猎型蜘蛛的食谱宽度显著低于结网型蜘蛛。
综上，蜘蛛狭食性的演化过程较为复杂，同时受系统发育与生态因素共同调控。