Viability and fertility of hybrid New Zealand tree wētā Hemideina spp. (Orthoptera: Anostostomatidae)

Natasha E Mckean,Steven A Trewick,Melissa J Griffin,Mary Morgan-Richards,Eddy J Dowle

doi:10.3897/jor.27.14963

Abstract

Natural hybridization between species provides an opportunity to study the mechanisms that maintain independent lineages and may help us understand the process of speciation. The New Zealand tree wētā speciesHemideinathoracicaproduces F1hybrids where it lives in sympatry with two closely related species:HemideinacrassidensandHemideinatrewicki. This study looked at the viability and fertility of F1hybrid wētā betweenH.thoracicaandH.crassidensthat were collected from the wild and kept in captivity. The hybrids appeared to have normal viability from the late juvenile stage, with all male wētā maturing at a late instar. Male F1hybrids displayed normal mating behavior and one male produced offspring in captivity. In contrast to Haldane’s rule, female F1hybrids appeared to be infertile; they refused to mate and did not produce eggs. No evidence ofWolbachiainfection was identified in any of the three North IslandHemideinaspecies.

Highlights

Natural hybridization between species provides an opportunity to study the mechanisms that maintain independent lineages and may help us understand the process of speciation (Butlin 1987, Barton and Gale 1993)
There was no significant size difference between adult F1 hybrid females and adult females of the two parent species from the same location with ANOVA; F = 2.575, P = 0.09 (Fig. 2A), male F1 hybrids were significantly larger than males of either parent species (ANOVA; F = 8.969, P = 0.00049; Fig. 2B)
The size of H. thoracica × H. crassidens hybrids fell within the normal range expected for the parent species, and many hybrids were found as adults in the wild, we have no positive evidence of hybrid inviability or abnormal development

Summary

Introduction

Natural hybridization between species provides an opportunity to study the mechanisms that maintain independent lineages and may help us understand the process of speciation (Butlin 1987, Barton and Gale 1993). Low hybrid fitness arises through natural and sexual selection when an intermediate phenotype is a disadvantage (Svedin et al 2008). Unimodal hybrid zones are geographically constrained; with most individuals in the zone having mixed ancestry, and the width of the hybrid zone depending on hybrid disadvantage and dispersal of the species (Jiggins and Mallet 2000). If hybridization is more limited, a bimodal hybrid zone may result, where parental forms overlap and predominate with a few individuals of mixed ancestry amongst them. Bimodal hybrid zones are typically associated with assortative mating so, in tree weta, reproductive character displacement is a likely outcome that increases assortative mating (Dieckmann and Doebeli 1999, Jiggins and Mallet 2000). Sexual exclusion, where one species (often the males of that species) out-competes the other for mates, can limit fitness through reproductive interference (Gröning and Hochkirch 2008), as observed between the tetrigids: Tetrix ceperoi and Tetrix subulata (Hochkirch et al 2007)

Methods

Results

Conclusion