Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises.

Gavin J Svenson,Henrique M Rodrigues,Sydney K Brannoch,Frank Wieland,James C O'Hanlon

doi:10.1038/srep37753

Abstract

Here we reconstruct the evolutionary shift towards floral simulation in orchid mantises and suggest female predatory selection as the likely driving force behind the development of extreme sexual size dimorphism. Through analysis of body size data and phylogenetic modelling of trait evolution, we recovered an ancestral shift towards sexual dimorphisms in both size and appearance in a lineage of flower-associated praying mantises. Sedentary female flower mantises dramatically increased in size prior to a transition from camouflaged, ambush predation to a floral simulation strategy, gaining access to, and visually attracting, a novel resource: large pollinating insects. Male flower mantises, however, remained small and mobile to facilitate mate-finding and reproductive success, consistent with ancestral male life strategy. Although moderate sexual size dimorphisms are common in many arthropod lineages, the predominant explanation is female size increase for increased fecundity. However, sex-dependent selective pressures acting outside of female fecundity have been suggested as mechanisms behind niche dimorphisms. Our hypothesised role of predatory selection acting on females to generate both extreme sexual size dimorphism coupled with niche dimorphism is novel among arthropods.

Highlights

(Westwood, 1832), appear to have unusually pronounced SSD8,12 (Fig. 1)
Using this camouflaged lineage of mantises, we demonstrate for the first time in an arthropod lineage that sex-dependent selective pressures acting on female predatory success rather than reproductive success drove extreme sexual size dimorphism (SSD) through female gigantism
We found that SSD was on average 1.7 times greater in THH taxa compared to HAO taxa (p = 5.4e−3; Supplementary Table S6), which was driven by small THH males (0.87 times smaller) and large a b

Summary

Introduction

(Westwood, 1832) (hereafter Theopropus), appear to have unusually pronounced SSD8,12 (Fig. 1). Hymenopus male and female nymphs were shown to be floral simulators, resembling flowers throughout post-embryonic development in order to attract and prey on insect pollinators[8,13]. To test for evolutionary rate shifts in sexually dimorphic features, we modelled trait evolution using the time-calibrated phylogeny to calculate the best set of evolutionary rate shifts given our data. Using this camouflaged lineage of mantises, we demonstrate for the first time in an arthropod lineage that sex-dependent selective pressures acting on female predatory success rather than reproductive success drove extreme SSD through female gigantism. Utilising a recent wealth of published behavioral studies and morphological observations, we hypothesise the likely evolutionary scenario that gave rise to the remarkable floral simulating orchid mantises based on patterns found

Methods

Results

Conclusion