Myrmedonota Cameron , 1920

Mathis, Kaitlyn A. & Eldredge, K. Taro, 2014, Descriptions of two new species of Myrmedonota Cameron (Staphylinidae: Aleocharinae) from Mexico with comments on the genus taxonomy and behavior, Zootaxa 3768 (1), pp. 95-100 : 96-97

Genus Myrmedonota Cameron, 1920

Diagnosis. The following character states in combination can diagnose Myrmedonota from other New World genera of Aleocharinae : (1) tarsal formula 4-5-5; (2) mesocoxae widely separated; (3) metaventral process much longer than mesoventral process, which extends little between the mesocoxae; (4) galea length greater than 7 times width at base, maxillae overall appearing extremely slender and elongate; (5) neck absent; (6) occipital suture complete to hypostoma; (7) pronotum with complete marginal line; (8) paramerite vellum much larger than condylite vellum; (9) paramerite vellum obscuring condylite vellum from outer view, condylite vellum small and fan-shaped; (9) apical lobe of paramere free and articulating with paramerite; (10) glossa bifid; (11) labial palpomere II and III subequal in length.

Comments on taxonomy. Myrmedonota taxonomy is quite chaotic. Elven et al. (2010) demonstrated that Myrmedonota and other New World genera formerly classified under Lomechusini are in fact a lineage within Athetini that has converged on similar morphologies ( Elven et al. 2010). Both Lomechusini and these pseudolomechusines are often symbiotic with ants and termites, one potential explanation for convergence may be adaptively rooted in symbiont ecology.

Since Elven et al. (2010), more formalized morphological characters that diagnose Lomechusini from pseudolomechusines are becoming apparent (Eldredge personal observation). It is turning out that most New World taxa fall under the currently outdated diagnostic umbrella of Lomechusini are pseudo-lomechusines, and belong to Athetini . This is in contrast to Lomechusini , which are predominantly distributed in the Old World. Therefore, superficially there appears to be a New World-Old World divide in distribution between pseudo-lomechusines and Lomechusini respectively. This is interesting in that it implies there have been two independent evolutionary histories with the lomechusine-morphotype; both have diversified in the context of social insect symbiosis and demonstrate potential for a comparative study of symbiosis.

Even with this enlightened perspective of a pseudo-lomechusine lineage, Myrmedonota as currently understood is plesiomorphic in overall body morphology, and many genera may in fact be lineages that have derived from Myrmedonota , rendering it paraphyletic. For example, the genus Termitognathus Borgmier, 1959 may be one such lineage, only diagnosable by morphologies derived from the pressures of living with termites.

To attest to the difficulties with distinguishing Myrmedonota from some other pseudo-lomechusine genera, Pace (1997, 2008a, 2008b, 2009) in a series of publications may have in fact described species of Myrmedonota under Apalonia Casey, 1906 ( Eldredge 2012) . Habitus and genitalic figures that accompany Pace’s descriptions support this hypothesis. In order to address issues concerning Myrmedonota taxonomy, the new species described below have been compared with Pace’s (1997, 2008a, 2008b, 2009) descriptions.

We bring up these issues on Myrmedonota taxonomy, even though much of the above is still speculative, because we think that Myrmedonota may be phylogenetically important. More apomorphic symbiont lineages may nest within Myrmedonota as we currently diagnose it, making the genus important in understanding the evolution of social insect symbiosis among pseudo-lomechusines. Additionally, this has implications if evolution of social insect symbiosis is to be studied comparatively between Lomechusini and pseudo-lomechusines. We suggest that new genera of pseudo-lomechusines be erected with caution, and urge the phylogeny reconstruction of this diverse clade.

Comments on behavior. Observations of Myrmedonota behavior have been accumulating for some time, although most are unpublished. From these, two interesting tendencies have come to light: (1) Myrmedonota swarm to ant colonies, especially during periods of colony agitation; (2) Myrmedonota mate by swarming, frequently in the presence of ants.

Myrmedonota are predators, and as ant symbionts either predators of ants (Eldredge personal observation, Mathis in preparation) or scavengers ( Kistner 2003). In Costa Rica, Eldredge has observed a Myrmedonota species fly into the midst of an agitated Pheidole Westwood, 1839 colony during nest excavation. Mathis (in preparation) has made detailed observations of aggregation and predation behavior of the two new species described below, but these will be presented subsequently.

Mating swarms of M. lewisi Maruyama et al. 2008 have been observed to occur on open ground with no apparent landmark (Eldredge personal observation, http://youtu.be/S3cdOavPZmc). Adults would fly above ground and periodically land, at which time they begin a searching behavior until the opposite sex is found. Upon locating a mate, a circular, almost ritualistic chase begins, followed by brief copulation. A white sheet placed on the ground did not elicit concentrated swarming around the sheet, but did allow easier observation of matings. Eldredge also observed mating swarms of a Myrmedonota species in Costa Rica, concentrated around the foraging column of an Eciton Latreille, 1804 species. The two new species described below have been observed mating in the presence of agitated Azteca sericeasur often while Pseudacteon phorid fly attacks took place (Mathis personal observation, http://youtu.be/1IwRT8EAp0Y). Adults appear to be attracted to a chemical compound present within the alarm pheromone of Azteca sericeasur (Mathis, in preparation). When the adults arrive to the location and find a mate, a chase begins, often resulting in a lengthy copulation.