Divergent warning patterns contribute to assortative mating between incipient Heliconius species.

Richard M Merrill,Nicola J Nadeau,Audrey Chia

doi:10.1002/ece3.996

Richard M Merrill, Nicola J Nadeau + Show 1 more

Open Access

https://doi.org/10.1002/ece3.996

Copy DOI

Abstract

Theoretical models suggest that traits under divergent ecological selection, which also contribute to assortative mating, will facilitate speciation with gene flow. Evidence for these so-called “magic traits” now exists across a range of taxa. However, their importance during speciation will depend on the extent to which they contribute to reproductive isolation. Addressing this requires experiments to determine the exact cues involved as well as estimates of assortative mating in the wild. Heliconius butterflies are well known for their diversity of bright warning color patterns, and their amenability to experimental manipulation has provided an excellent opportunity to test their role in reproductive isolation. Here, we reveal that divergent color patterns contribute to mate recognition between the incipient species Heliconius himera and H. erato, a taxon pair for which assortative mating by color pattern has been demonstrated among wild individuals: First, we demonstrate that males are more likely to attempt to mate conspecific females; second, we show that males are more likely to approach pinned females that share their own warning pattern. These data are valuable as these taxa likely represent the early stages of speciation, but unusually also allow comparisons with rates of interbreeding between divergent ecologically relevant phenotypes measured in the wild.

Highlights

Uncovering the mechanisms by which divergent mating behaviors evolve is a key to our understanding of animal diversity
The extent to which magic traits contribute to speciation remains unclear, and this will depend on the degree to which they contribute to reproductive isolation (Servedio et al 2011; see Haller et al 2012)
It has previously been shown that H. himera and H. erato mate assortatively both in the wild and the insectary (McMillan et al 1997; Mallet et al 1998a), it has not yet been demonstrated experimentally that warning patterns are used as mating cues. We address this gap and present evidence that divergent color patterns contribute to assortative mating between these incipient species: First, we demonstrate that males are more likely to attempt to mate conspecific females; second, we show that males are more likely to approach pinned females that share their own warning pattern

Summary

Introduction

Uncovering the mechanisms by which divergent mating behaviors evolve is a key to our understanding of animal diversity. To test whether color pattern acts as a mate recognition cue, dead mounted H. erato and H. himera females were presented to males during 1-h trials. Assortative mating between H. himera and H. erato has been previously demonstrated through an extensive series of insectary experiments (McMillan et al 1997), this study did not consider male and female behaviors seperately.

Results

Conclusion