Stable isotope analysis reveals the importance of plant‐based diets for tropical ant‐mimicking spiders

Abstract

Ant‐mimicking spiders are a well‐known example of Batesian mimicry. Earlier studies have proposed that plant‐based diets (e.g. extrafloral nectar) are an important food source for ant‐mimicking spiders. However, it is still unclear whether the plant‐based diets are a main food source or supplementary energy source to the spiders. To examine the feeding habits, we measured stable nitrogen and carbon isotope ratios (δ15N and δ13C) of ant‐mimicking spiders (six species of Myrmarachne; one species of Agorius, Salticidae; and two species of Corinnidae) collected from a tropical rain forest in Malaysia and a dry evergreen forest in Thailand. We also investigated the isotopic signatures of several ant species sampled from the two forests for comparison. In general, the ant‐mimicking spiders had relatively low δ15N values, which were comparable to those of the nectar‐feeding and omnivorous ants. The δ15N values of the ant‐mimicking spiders differed significantly among the species: some species (e.g. Myrmarachne sp. H and Myrmarachne sp. 2) showed δ15N values similar to those of the nectar‐feeding ants, whereas the δ15N values of others (e.g. Myrmarachne maxillosa and Myrmarachne malayana) were close to those of the omnivorous ants. The δ13C values of the ant‐mimicking spiders did not differ significantly among the species, but tended to be similar to those of the nectar‐ and honeydew‐feeding ants rather than the predatory ants. These results indicate that plant‐based diets are important for the nutrition of ant‐mimicking spiders and suggest that the importance would differ among the ant‐mimicking spider species.

Constraints on the jumping and prey-capture abilities of ant-mimicking spiders (Salticidae, Salticinae, Myrmarachne)

“…However, our results suggest the possibility that Myrmarachne species changed their diets in nature or may have evolved specialized prey-capture behavior to compensate for the poor jumping ability. Although none of the field evidence indicated that Myrmarachne species have a specialized predation behavior, such as snatching prey from ants as observed in Menemerus jumping spiders 20 , our previous study using stable isotope analysis demonstrated that Myrmarachne species with slender body shapes, such as M. hashimotoi , had low δ 15 N values similar to those of nectar-feeding ants and arthropod herbivores, but not similar to those of predators, in the same study sites 21 . In contrast, the δ 15 N values of Myrmarachne species with broad body shapes, such as M. malayana and M. maxillosa , were similar to those of omnivorous ants and non-myrmecomorphic jumping spiders.…”

A new species of the genus <I>Agorius</I> (Araneae: Salticidae) from Sarawak, Borneo

“…Some spider species mimic ants in morphology or in chemical components on the body to feed on ants (Cushing 2012). Hyodo et al (2018) shows a result that δ 15 N values of A. hyodoi sp. nov. (as Agorius sp.…”

Intraguild predation is increased in areas of low prey diversity in a generalist predator community

“…Here, we address these questions using stable isotope analysis and DNA metabarcoding. Stable isotopes can be used to assess isotopic niche (Blüthgen et al, 2003; Hyodo et al, 2018; Newsome et al, 2007; Potapov et al, 2019). The heavier nitrogen isotope ( 15 N) is preferentially incorporated into tissues such that consumers have higher δ 15 N values than resources (Wada et al, 1991).…”