Mapping the evolution of accurate Batesian mimicry of social wasps in hoverflies

Abstract

Hoverflies (Diptera: Syrphidae) provide an excellent opportunity to study the evolution of Batesian mimicry, where defenseless prey avoid predation by evolving to resemble defended "model" species. Although some hoverflies beautifully resemble their hymenopteran models, others seem to be poor mimics or are apparently nonmimetic. The reasons for this variation are still enigmatic despite decades of research. Here, we address this issue by mapping social-wasp mimicry across the phylogeny of Holarctic hoverflies. Using the "distance transform" technique, we calculate an objective measure of the abdominal pattern similarity between 167 hoverfly species and a widespread putative model, the social wasp, Vespula germanica. We find that good wasp mimicry has evolved several times, and may have also been lost, leading to the presence of nonmimics deep within clades of good mimics. Body size was positively correlated with similarity to the model, supporting previous findings that smaller species are often poorer mimics. Additionally, univoltine species were less accurate wasp mimics than multivoltine and bivoltine species. Hence, variation in the accuracy of Batesian mimics may reflect variation in the opportunity for selection caused by differences in prey value or signal perception (influenced by body size) and phenology or generation time (influenced by voltinism).

Body size in Batesian mimicry

“…In comparative analyses, body size and mimetic accuracy have shown a positive association in hoverflies (Penney et al 2012;Leavey et al 2021) and in spiders (Pekár 2022). This is consistent with the hypothesis that larger prey (at least in these taxa) are preferred by predators due to the higher nutritional reward, and hence under stronger selection (Penney et al 2012).…”

“…Several comparative analyses have already examined the relationship between size and mimetic accuracy, usually revealing weak positive associations (Penney et al 2012;Wilson et al 2013;Leavey et al 2021), but these studies calculate mimetic accuracy to one or a few model species. Although challenging, it would be very interesting to compare mimics to a wide range of potential sympatric models.…”

Influence of mimicry on extinction risk in Aculeata: a theoretical approach

“…The black-and-yelloc4w pattern and the black-orange-black pattern are two common colourations among Aculeata and Hymenoptera in general (Mora & Henson 2019, Boppré et al 2016). Wasps and bees colour patterns occur also in other taxa of insects including undefended species like flies of the family Syrphidae (Waldbauer 1970, Leavey et al 2021). Thus, the protection provided by mimetic interaction involving Aculeata could benefit a large number of species and limit their extinction risk.…”

YOLO object detection models can locate and classify broad groups of flower-visiting arthropods in images

“…Using YOLO for object detection provides us with the benefit of detecting several arthropods in a single image, which is one of the reasons we want to explicitly test how well this task is performed. Additionally, we expected that one of the more difficult classifications will be of Dipterans in the family Syrphidae (hoverflies), which have mimicry of bees and wasps (Hymenoptera) 28 . Thus, we performed a separate test to see how well our model differentiates this family of flies from Hymenoptera on 1000 annotated images of hoverflies.…”