Short communication Phylogenetics of the new world honey ants (genus Myrmecocystus) estimated from mitochondrial DNA sequences

1. IntroductionHoney pot workers that store immense amounts offood in the crop and are nearly immobilized due to theirhighly expanded gasters are known from a variety of antspecies in diﬀerent parts of the world, presumably asadaptations to regular food scarcity in arid habitats(H€olldobler and Wilson, 1990). Although these so calledrepletes are taxonomically fairly widespread, the phe-nomenon is most commonly associated with species ofthe New World honey ant genus Myrmecocystus, whoserepletes have a long lasting reputation as a delicacy withindigenous people. As repletism supposedly occurswithin all species of Myrmecocystus, it seems plausiblethat this key innovation promoted the diversiﬁcation ofhoney ants after formation of the North American de-serts. Accordingly, the distribution of the genus is cen-tered in arid parts of southwestern North America,including the Mohave, Sonoran, Great Basin, and Chi-huahuan Deserts.The genus Myrmecocystus seems to be most closelyrelated to Lasius (Snelling, 1976), and Bolton (1994)placed Myrmecocystus and the genera Acanthomyops,Euprenolepis, Lasius, Paratrechina, Prenolepis, Protre-china, Pseudolasius, and Teratomyrmex in the same tribeLasiini. Myrmecocystus can be distinguished from allNearcticgeneraofFormicinaebytheelongatedmaxillarypalpi, ofwhich thefourthsegmentisaslong as,orlongerthan,thecombinedlengthsofthetwofollowingsegments.Snelling (1976) subdivided the genus into three sub-genera: Myrmecocystus, Eremnocystus, and Endiodioc-tes.Thenominatesubgenuscontainsallthelightcolored,strictly nocturnal species, the subgenus Eremnocystuscontains small, uniformly dark colored species, and thesubgenus Endiodioctes contains species with a ferrugi-nous head and thorax and darker gaster. Snelling (1976)proposed that the earliest division within the genus wasthat between the line leading to the subgenus Myrmec-ocystus and that leading to Eremnocystus plus Endiodi-octes (maybe based on diurnal versus nocturnal habits)and that the second schism occurred when the Eremno-cystus line diverged from that of Endiodioctes.Based on external morphology and data from bothbehavior and distribution, Snelling (1976) recognized 27species and assembled most of them into species groups.In a supplement to his revision, Snelling (1982) de-scribed another two species. Johnson and Ward (2002)have recently listed four additional, hitherto unde-scribed species of Myrmecocystus in their treatment ofthe ants of Baja California, that appear to be endemic tothat region (M. sp. cf. ﬂaviceps; M. sp. cf. mendax;M. BCA-1; M. BCA-2). Fifteen of the 29 described species, including allsubgenera and seven of the eight species groups, arerepresented in this analysis as well as samples from thefour undescribed species from Baja California. A sampleof workers from Maricopa, Arizona, (referred to asM. sp. n. in this study) was determined to be M. ken-nedyi (Det. R.R. Snelling), but the alate queens aredistinctively diﬀerent (R.A. Johnson, pers. comm.). Wealso include this species in our phylogeny.This study is aimed at employing DNA sequence in-formation to elucidate the proper systematic placementof these undescribed Myrmecocystus species and toevaluate the systematic relationships within the genusthathavebeenproposedbySnelling(1976),mainlybasedon morphological data. A well supported phylogenetic