Mandible morphology reflects the type of male antagonism in the ant genus Cardiocondyla (Hymenoptera: Formicidae)

Christine V Schmidt,Jurgen Heinze

doi:10.14411/eje.2018.047

Abstract

The ant genus Cardiocondyla is characterized by wingless, ergatoid males, which in some species replace the typical winged male. Depending on species, ergatoid males engage in lethal fighting for access to sexual females, establish territories within their nests, or are mutually tolerant. Here we investigate, whether the morphology of ergatoid males and in particular the shape of their mandibles reflect phylogeny or male behaviour. In contrast to the worker mandible, which is relatively similar in shape in the ten species examined, mandibles of ergatoid males show a great variation in size and shape not only between the two clades of Cardiocondyla but also among species belonging to Cardiocondyla clade A. This diversity appears to reflect the diverse reproductive tactics of ergatoid males of different species, with extremely long, anteriorly oriented mandibles associated with indirect killing of adult competitors, while particularly short mandibles possibly constitute an adaptation to a tactic in which ergatoid males crush the cuticle of young rivals.

Highlights

The genus Cardiocondyla Emery is unusual among ants in having two different male phenotypes, winged males and ergatoid males
In contrast to the worker mandible, which is relatively similar in shape in the ten species examined, mandibles of ergatoid males show a great variation in size and shape between the two clades of Cardiocondyla and among species belonging to Cardiocondyla clade A
This diversity appears to reflect the diverse reproductive tactics of ergatoid males of different species, with extremely long, anteriorly oriented mandibles associated with indirect killing of adult competitors, while short mandibles possibly constitute an adaptation to a tactic in which ergatoid males crush the cuticle of young rivals

Summary

Introduction

The genus Cardiocondyla Emery is unusual among ants in having two different male phenotypes, winged males and ergatoid males. Winged males are typical of most ant species but occur in less than 25% of the species of Cardiocondyla examined (Heinze, 2017). Ergatoid males occur in all the species of Cardiocondyla examined They stay inside the maternal nest and locally mate with available female sexuals (Heinze, 2017). Their entirely non-dispersing life cycle is reflected in a superficially “worker-like” morphology: ergatoid males are wingless, have small eyes and lack ocelli. They may be relatively long-lived (up to one year; Yamauchi et al, 2006), and, in contrast to all other males of social Hymenoptera, are characterized by life-long spermatogenesis (Heinze & Hölldobler, 1993)

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