Field estimates of survival do not reflect ratings of mimetic similarity in wasp-mimicking hover flies

Jennifer Lauren Easley,Christopher Hassall

doi:10.1007/s10682-013-9678-3

Abstract

The evolution of mimicry, and particularly the persistence of undefended Batesian mimetic forms that are imperfect copies of their defended models, remains a central question in evolutionary biology. Previous work has demonstrated that variation in mimetic fidelity in artificial prey can alter survival. However, no studies have validated the assumption that detailed laboratory-based measurements of mimetic fidelity are actually reflected in survival in natural field experiments. Here, we demonstrate that, in line with previous studies, the mimetic similarity of 77 hover fly (Diptera: Syrphidae) species to the common wasp Vespula alascensis is strongly related to the number of abdominal stripes exhibited by the flies. We then produce three artificial pastry baits: (1) a “model” which is chemically defended and has two stripes, (2) a one-stripe mimic, and (3) an unstriped mimic. Based on the ratings study, we predicted that the one-stripe mimic would exhibit survival intermediate between the unstriped mimic and the model. Baits were deployed in experiments each involving 81 baits (27 of each kind), at 3 sites, with experiments replicated 10 times at each site for a total deployment of 2,430 baits. Proportional hazards models show that both one-striped and model baits survived equally well and significantly better than the unstriped baits, suggesting categorical prey identification rather than the use of stripe number as a continuous trait, as was suggested by the laboratory study. These findings suggest that, while humans and avian predators can distinguish mimics from models in the laboratory using a range of traits, behaviour in the field may not reflect this ability. This absence of a link between continuous measures of mimetic fidelity and prey selection may contribute to the maintenance of imperfect mimicry, but more studies using near-natural experimental paradigms are needed to investigate the phenomenon further.

Highlights

Evolutionary biologists have described countless examples of exquisite adaptations, whether they be extreme sexual ornaments in male widowbirds (Andersson 1982), physiological adaptations to harsh environments in extremophiles (Rothschild and Mancinelli 2001), or unique life histories to exploit unusual niches such as the piophilid flies that live entirely within discarded moose antlers (Bonduriansky 1995)
This equates to a reduction in the hazard rate of 14.3% in the model, and 18.4% in the onestripe mimic relative to the unstriped mimic (Figure 3), but there was no significant difference in hazard between the model and the one-striped mimic
When we looked for evidence of learning over time, there were no obvious patterns in relative mortality over the course of the 10 experimental runs at each site (Figure 4)

Summary

Introduction

Evolutionary biologists have described countless examples of exquisite adaptations, whether they be extreme sexual ornaments in male widowbirds (Andersson 1982), physiological adaptations to harsh environments in extremophiles (Rothschild and Mancinelli 2001), or unique life histories to exploit unusual niches such as the piophilid flies that live entirely within discarded moose antlers (Bonduriansky 1995). Prey exhibit a remarkable array of anti-predator traits, which can be nullified through concomitant evolution (at a cost) by the predator (Tien and Ellner 2012). The weight of evidence suggests that prey are more likely to evolve traits in response to a predator than vice versa, and that those defensive traits show a greater degree of refinement than the offensive traits exhibited by predators (Abrams 2000). Anti-predator traits can be classified into four broad categories that act at different points along the predation event: (i) traits that reduce detection (e.g. the camouflage of moths against trees, Webster et al 2009), (ii) traits that reduce recognition (e.g. snake-mimicking caterpillars, Hossie and Sherratt 2012), (iii) traits that reduce capture (e.g. protean escape trajectories, Domenici et al 2011), and (iv) traits that reduce consumption (e.g. the death-feigning posture of some crickets, Honma et al 2006). L. and Hassall, C. (2014) Field estimates of survival do not reflect ratings of mimetic similarity in wasp-mimicking hover flies, Evolutionary Ecology. 28, 387-396

Methods

Results

Discussion

Conclusion