Phylogenetic relationships among social parasites and their hosts in the ant tribe Tetramoriini (Hymenoptera: Formicidae)

Mathias Sanetra,Alfred Buschinger

doi:10.14411/eje.2000.017

Abstract

The phylogenetic relationships among Palaearctic species of the ant genus Tetramorium and its social parasites of the genera Strongylognathtus, Anergates and Teletomyrmex, were investigated electrophoretically at 21 presumptive enzyme loci. The data set comprising 33 species was analysed with distance (UPGMA, Neighbor-joining and least squares statistics) and parsimony methods (independent allele, minimum turnover and mutation coding) in order to rule out analysis-dependent effects. Several groupings were consistently resolved by all procedures. Observed branching patterns support the placement of the three parasite genera and their hosts into the Palaearctic species group of Tetramorium (tribe Tetramoriini). The genus Strongylognathus forms a monophyletic group in which the slave-makers of the S. huberi group constitute the sister group of the inquilines S. testaceus and S. karawajewi (S. testaceus group). Most species of the S. huberi group show very low genetic differentiation. However, little consensus has been found with regard to which Tetramorium species are the closest relatives of Strongylognathus.According to the electrophoretic data, social parasitism in Palaearctic tetramoriine ants has evolved independently at least twice. Though inquilinism once arose from slave-making ancestors in Strongylognathus, the extreme inquilines Anergates atratulus and Teleutomyrmex schneideri are clearly set apart from the Strongylognathus clade in phylogenetic analyses. Thus, extreme inquilinism cannot be regarded as the endpoint of a single parasitic lineage in the Tetramoriini. In these highly advanced inquilines, evolutionary rates at allozyme loci appear to be higher than those of their Tetramorium hosts. The results do not unambiguously reveal whether Anergates and Teleutomyrmex arose jointly or independently from Tetramorium ancestors. However, a combined analysis using all available evidence supports the former hypothesis. The finding that the Tetramorium parasites are not the closest relatives of their respective host species is discussed in relation to current theories for the evolution of social parasitism.

Highlights

Social parasites of the widespread ant genus Tetramo rium are predominantly Palaearctic in distribution (Bolton, 1976), the only exception being two inquilines known from the Afrotropical zoogeographical region (Bolton, 1980)
While slave making behaviour is characteristic for the members of the S. huberi group, in the S. testaceus group inquilinism has most likely evolved via degeneration of slave raiding (e.g. Wasmann, 1905; Kutter, 1969; Acosta & Martinez, 1982)
In the current study we focus on the evolution of social parasites in the myrmicine ant tribe Tetramoriini

Summary

Introduction

Social parasites of the widespread ant genus Tetramo rium are predominantly Palaearctic in distribution (Bolton, 1976), the only exception being two inquilines known from the Afrotropical zoogeographical region (Bolton, 1980). Teleutomyrmex, often called the “ultimate para site” (e.g. Holldobler & Wilson, 1990), displays the most outstanding adaptations ever recorded for ant social para sites With their highly specialized tarsal claws the flat tened Teleutomyrmex queens attach themselves to the much larger host queen, where they are efficiently tended and fed by the host workers (Kutter, 1950; Stumper, 1951; Collingwood, 1956). A clearly different strategy occurs in the workerless parasite Anergates atratulus since the infested nests are devoid of host queens (e.g. Wasmann, 1908; Wheeler, 1910) The occurrence of these varying degrees in socially parasitic behaviour raises the question of whether parasitism arose only once in the evolution of tetramoriine ants or whether it has had multiple origins. Possible transitions of different parasitic relations from one type to another would be interest ing to discover

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