Molecular evidence for hybridization in Colias (Lepidoptera: Pieridae): are Colias hybrids really hybrids?

Heather E Dwyer,Marie Jasieniuk,Arthur M Shapiro,Miki Okada

doi:10.1002/ece3.1574

Abstract

Gene flow and hybridization among species dramatically affect our understanding of the species as a biological unit, species relationships, and species adaptations. In North American Colias eurytheme and Colias eriphyle, there has been historical debate over the extent of hybridization occurring and the identity of phenotypically intermediate individuals as genetic hybrids. This study assesses the population structure of these two species to measure the extent of hybridization and the genetic identity of phenotypic intermediates as hybrids. Amplified fragment length polymorphism (AFLP) marker analysis was performed on 378 specimens collected from northern California and Nevada. Population structure was inferred using a Bayesian/Markov chain Monte Carlo method, which probabilistically assigns individuals to genetic clusters. Three genetic clusters provided the best fit for the data. C. eurytheme individuals were primarily assigned to two closely related clusters, and C. eriphyle individuals were mostly assigned to a third, more distantly related cluster. There appeared to be significant hybridization between the two species. Individuals of intermediate phenotype (putative hybrids) were found to be genetically indistinguishable from C. eriphyle, indicating that previous work based on the assumption that these intermediate forms are hybrids may warrant reconsideration.

Highlights

Detection of gene flow between populations is a critical component of understanding a species’ population biology
Ecology and Evolution published by John Wiley & Sons Ltd
C. eriphyle has historically been considered a subspecies of Colias philodice, another close relative of C. eurytheme found throughout the eastern United States, and is often referred to as C. philodice in the literature (Wheat and Watt 2008)

Summary

Introduction

Detection of gene flow between populations is a critical component of understanding a species’ population biology. At a higher taxonomic level, interspecific gene flow can lead to sustained hybridization and introgression. In North American butterflies species Colias eurytheme (Fig. 1) and Colias eriphyle, there has been historical debate over the extent of hybridization occurring and the identity of phenotypically intermediate individuals as genetic hybrids. This study assesses the population structure of these two species to measure the extent of hybridization and the genetic identity of phenotypic intermediates as hybrids. Hybridization in the sulfur butterfly complex (Pieridae: Coliadinae), which includes Colias eurytheme (orange sulfur), Colias philodice (clouded sulfur), and Colias eriphyle (yellow sulfur), has long been recognized (Gerould 1943; Ae 1959; Taylor 1972). C. eurytheme and C. eriphyle are understood to be sister taxa; Colias philodice (the clouded sulfur) is the sister group to these two species (Pollock et al 1998; Wheat and Watt 2008)

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Discussion

Conclusion