In 2008 Jürgen Heinze penned “The Demise of the Standard Ant“, noting that the stereotyped ant nuclear family (one queen, one male, and lots of kids) was increasingly obscured by an accumulation of myrmecological data showing enormous variation among species in life history, that real ant colonies were often messy polygamous affairs, and that odd strategies like clonal reproduction were probably more common than previously thought.

Paratrechina longicornis, the black crazy ant

A study out today by Pearcy et al reveals that a common invasive ant, Paratrechina longicornis, is one of those oddballs:

from the abstract:

We discovered that the highly invasive longhorn crazy ant, Paratrechina longicornis, has evolved an unusual mode of reproduction whereby sib mating does not result in inbreeding. A population genetic study of P. longicornis revealed dramatic differences in allele frequencies between queens, males and workers. Mother–offspring analyses demonstrated that these allele frequency differences resulted from the fact that the three castes were all produced through different means. Workers developed through normal sexual reproduction between queens and males. However, queens were produced clonally and, thus, were genetically identical to their mothers. In contrast, males never inherited maternal alleles and were genetically identical to their fathers. The outcome of this system is that genetic inbreeding is impossible because queen and male genomes remain completely separate.

In other words, the DNA of males and queens are separate clonal lineages, while workers are hybrids between the two. This arrangement avoids the inbreeding problems associated with diploid males, possibly helping this species colonize new sites from small propagules.

What’s more, P. longicornis is not the only invasive ant with this reproductive quirk. Wasmannia auropunctata, the little fire ant, shares a similar system, suggesting that clonal reproductives and hybrid workers may be a more general strategy of invasive social insects.

For a better explanation than mine (as usual), Ed Yong has more.

Pearcy, M. et al 2011. Sib mating without inbreeding in the longhorn crazy ant. Proc. R. Soc. B, Published online before print February 2, 2011, doi:10.1098/rspb.2010.2562