A paper out this week in Zootaxa reminds us of the hazards of excessive reliance on the worker caste for ant taxonomy. Phil Ward and Seán Brady sequenced DNA from few genes from the enigmatic Amyrmex, a rarely-collected dolichoderine genus known only from males in South America. Except, it wasn’t a dolichoderine. Surprise! Genetically, this little guy is part of the doryline section (the army ants and relatives) in the Leptanilloidinae.
Where did we go wrong with Amyrmex? In my opinion, it’s in our dysfunctional dependence on workers. Worker specimens are the most abundant of the castes, of course. They dominate museum collections, and as a consequence ant taxonomy has been constructed almost exclusively on their morphology.
The convenience of a worker-based system carries a cost, however. Workers are highly reduced creatures, natural selection having favored the low-cost solution where body parts present in reproductive insects have been lost, fused, or stripped down to vestigial nubs. The little that remains can converge in form to fit the similar tasks that workers of all lineages perform. Taxonomists don’t cope particularly well with characters that no longer exist, and do even worse with convergent similarities.
Generations of myrmecologists placed such weight on the segmentation of the worker petiole that the subfamilies Dolichoderinae and Formicinae were considered to be sister taxa, as both share the derived ancestral state of a single constricted segment (most other ants have two constrictions, or a constriction and a half). But anyone familiar with the males from both groups should have suspected something amiss. Formicine males often bear a certain resemblance to workers- the antennae, for example, are geniculate- while Dolichoderine males are typically pleisiomorphic, looking much more poneromorph than formicine. Without a solid understanding of male characters and male variation, it’s all too easy to misplace male specimens.