Mating system and population genetic structure of the bulldog ant Myrmecia pavida (Hymenoptera: Formicidae)

Understanding the evolution of the alternative mating strategies of monandry and polyandry is a fundamental problem in evolutionary biology because of the cost-benefit trade-offs associated with mating for females. The problem is particularly intriguing in the social insects because queens in most species appear to be obligately monandrous (i.e., only a single male fathers their offspring), while those in a minority of species have evolved high, and sometimes extreme, polyandry. One group which may shed particular insight is the ant subfamily Myrmeciinae (Myrmecia and Nothomyrmecia). Here we examine the population and colony genetic structure of the bulldog ant Myrmecia pavida CLARK, 1951 by geno-typing offspring workers from 45 colonies. We find little evidence of geographic structuring or inbreeding in the population, indicating that the species outbreeds, most probably in mating swarms. We also find that queens of M. pavida show moderately high polyandry, with 84% having mated with between two and seven males, and an overall mean observed mating frequency of 3.8. This is significantly higher than previously reported for queens of Nothomyrmecia macrops, in which most females mate singly. This was similar to that of M. pyriformis, M. brevinoda, and M. pilosula, the three congenerics for which mating frequencies have recently been reported. The two genera in the Myrmeciinae therefore appear to show multiple transitions in mating frequency and further investigation of the subfamily may be highly informative for disentangling the forces driving the evolution of alternative mating strategies.