Differentiation in ant-eating spiders based on offensive and defensive exploitation of ants

Abstract

Ecological speciation via host-race has been documented in several herbivores and parasitoids. Analogous prey-race has recently been suggested to explain the diversity of specialised ant-eating spiders. Two sister species from the Iberian Peninsula, Zodarion alacre and Z. andalusiacum (Zodariidae), possess almost identical copulatory organs, but differ in body size and colouration. Zodarion spiders exploit different ant species offensively (as prey) and defensively (as mimetic models). Here we tested the hypothesis of prey-race diversification in these two species via offensive and defensive exploitation. We studied the diet of both species using metabarcoding, recorded their circadian activity in the field, investigated their mimetic similarity to ants, and modelled visual perception by potential predators. We found that both species feed on ants but Z. alacre hunted larger ant species than Z. andalusiacum. Their circadian activity was different too, with Z. alacre being active mainly during day while Z. andalusiacum mainly during night. Zodarion alacre appear to imitate Messor ants in movement, colouration, body shape, and size. Zodarion andalusiacum is similar to sand in colouration, moves less, and thus probably uses background matching. We conclude that divergent (offensive and defensive) exploitation of ants could have lead to diversification of the two ant-eating spiders.