Genetics and speciation in haplodiploid social insects

Effects of social structure and haplodiploidy on speciation in eusocial insects are examined. The seed harvester ants (Pogonomyrmex) are an ideal model system for studies in speciation for they can be sampled without harming the colonies, they remain in one location facilitating multiple sampling, and much is known about their natural history. In addition, they include two inquiline (living inside another species colony) ant species that lack a worker caste and live entirely dependent upon another Pogonomyrmex host colony. These species allow the direct testing of several hypotheses on their evolutionary origin. A molecular phylogeny of the genus Pogonomyrmex, based on sequence from the mtDNA cytochrome B gene, reveals a monophyletic origin of the inquilines, Pogonomyrmex anergismus and Pogonomyrmex colei, with a recent descendent from an eastern clade of one of their host species (P. barbatus). Implications for sympatric and allopatric speciation are discussed. A new method of presenting reproductive skew shows how polyandry and polygyny can lead to cheating through nonrandom. distributions of offspring among patrilines and matrilines. When two taxa diverge, but recontact before complete reproductive isolation, eusociality combined with haplodiploidy causes unexpected patterns of genetic variation in social insects. A detailed explanation of such a situation reveals how gene flow causes different castes to have different but constant allele frequencies over time. Finally, computer simulations show how haplodiploid genetic structure results in more rapid evolution of potential species isolating mechanisms than for diploid populations of the same effective number.