No. 45: May-Jun 1986
The Australian ant Myrmecia pilosula, called the "bulldog ant" because of its viciousness, carries all its genetic information in a single pair of chromosomes. (Males are haploid and have just one chromosome.) Although classified as a "primitive" ant, the bulldog ant exhibits complex social behavior and is obviously far from a simple biological entity. Biologists were therefore surprised to find all genetic instruction residing in a single chromosome pair. Social insects tend to have higher chromosome numbers. It is also interesting that Myrmecia pilosula, originally described as a single species, actually consists of several distinct sibling species with chromosome numbers (i.e., pairs) of 9, 10, 16, 24, 30, 3l, and 32. Yet, they all look pretty much alike.
(Crosland, Michael W.J., and Crozier, Ross H.; Myrmecia pilosula, an Ant with Only One Pair of Chromosomes," Science, 23l:1278, 1986.)
Comment. Chromosome number or the sheer quantity of genetic material seems poorly correlated with biological complexity.