Which web to invade? Argyrodine kleptoparasites differentiate amongst architecturally different host webs.

Kleptoparasitism, the theft of resources from another organism, is a widespread foraging strategy amongst animals. Many Argyrodinae cobweb spiders (Theridiidae) are obligatory kleptoparasites that have abandoned web building, relying instead on webs of larger hosts (kleptotany). Theory predicts that kleptoparasites are not randomly distributed amongst host webs and prior studies indicate that web architecture (size and tenure) and prey availability impact kleptoparasite abundance and host choice. This study is the first to examine argyrodine biology in Madagascar and provides an insight into a multi-species endemic community of spider kleptoparasites and their in-situ distribution across contrasting host webs: Nephilingis (Nephilidae, large nocturnal orb weavers), Caripetella (Pisauridae, large nocturnal sheet web builders) and Anelosimus (Theridiidae, small cathemeral social spiders constructing 3D tangle webs). We found a striking diversity of nine kleptoparasite species in six genera that, remarkably, are not conspecific with the five species that were previously known from all of Madagascar. Kleptoparasite species composition and abundance varied across the three hosts: some appeared host-specific, while others are versatile. In general, argyrodine kleptoparasites evidently discriminate amongst hosts, but differ in the degree of host preference. At the community level, we speculate that species assembly into host webs involves a complex interplay between host preference and species competitive hierarchy. Future field research should investigate this system as a community of multiple interacting species to gain a more comprehensive understanding of the rules that may govern the assembly of diverse kleptoparasites into equally variable host webs.