Molecular phylogenetics and diversification of trap-jaw ants in the genera Anochetus and Odontomachus (Hymenoptera: Formicidae)

Abstract

Ants in the genera Anochetus and Odontomachus belong to one of the largest clades in the subfamily Ponerinae, and are one of four lineages of ants possessing spring-loaded "trap-jaws." Here we present results from the first global species-level molecular phylogenetic analysis of these trap-jaw ants, reconstructed from one mitochondrial, one ribosomal RNA, and three nuclear protein-coding genes. Bayesian and likelihood analyses strongly support reciprocal monophyly for the genera Anochetus and Odontomachus. Additionally, we found strong support for seven trap-jaw ant clades (four in Anochetus and three in Odontomachus) mostly concordant with geographic distribution. Ambiguity remains concerning the closest living non-trap-jaw ant relative of the Anochetus+Odontomachus clade, but Bayes factor hypothesis testing strongly suggests that trap-jaw ants evolved from a short mandible ancestor. Ponerine trap-jaw ants originated in the early Eocene (52.5Mya) in either South America or Southeast Asia, where they have radiated rapidly in the last 30million years, and subsequently dispersed multiple times to Africa and Australia. These results will guide future taxonomic work on the group and act as a phylogenetic framework to study the macroevolution of extreme ant mouthpart specialization.

Mandible strike kinematics of the trap‐jaw ant genus Anochetus Mayr (Hymenoptera: Formicidae)

“…This relationship cannot be explained by relative differences in body size, as the body mass of A. horridus is intermediate between A. targionii and A. paripungens , and one‐fifth that of A. emarginatus . Other factors, such as similar head and mandible morphology, differing life‐history strategies, or evolutionary constraints (Larabee et al ., ), may partially explain differences in strike performance of A. horridus and A. emarginatus relative to other Anochetus species.…”

“…The confounding effect of shared evolutionary relatedness may also partially explain the strike performance patterns we observed. Anochetus horridus and A. emarginatus are closely related, both being members of the emarginatus species group (Larabee et al ., ). In contrast, A. targionii and A. paripungens originate from the phylogenetically and geographically distinct mayri and rectangularis species groups (distributed throughout the new and old world tropics, respectively; Larabee et al ., ).…”

“…Anochetus horridus and A. emarginatus are closely related, both being members of the emarginatus species group (Larabee et al ., ). In contrast, A. targionii and A. paripungens originate from the phylogenetically and geographically distinct mayri and rectangularis species groups (distributed throughout the new and old world tropics, respectively; Larabee et al ., ). The strong similarities in their strike performance suggest that morphology and body size are a large component of what determines strike performance in this genus.…”

“…We selected four species of Anochetus representative of the morphological, phylogenetic, and size diversity within the genus (Fig. ): two species, Anochetus horridus and Anochetus emarginatus, from the emarginatus species group (Brown, , ; clade F in Larabee et al ., ); one species, Anochetus targionii , from the mayri species group (Brown, ; Brown, ; clade F in Larabee et al ., ); and one species, Anochetus paripungens , from the rectangularis species group (Brown, , ; clade G in Larabee et al ., ). We compared the kinematics of Anochetus to two species of Odontomachus chosen to represent the large variation in size seen in this genus – Odontomachus chelifer (one of the largest; Fig.…”

“…In addition to quantifying interspecific variation within Anochetus , we compare their strike performance to two species of Odontomachus . While Odontomachus are generally larger than Anochetus , one of our species ( A. emarginatus ) is similar in size to smaller Odontomachus (Larabee et al ., ). We use these data to test the following hypotheses based on the scaling of body size with performance seen in Odontomachus : (1) Anochetus mandibles will achieve higher accelerations and velocities, and (2) Anochetus mandibles will generate less kinetic energy relative to larger species of Odontomachus .…”