A review of the Pseudomyrmex ferrugineus and Pseudomyrmex goeldii species groups: acacia-ants and relatives (Hymenoptera: Formicidae)

Abstract

The Pseudomyrmex ferrugineus group contains the Mesoamerican acacia-ants, an assemblage of species that inhabit and protect swollen-thorn acacias (Vachellia spp.). Recent phylogenetic studies have confirmed the existence of two generalist (dead twig-inhabiting) species that are embedded within the P. ferrugineus group. They are described here as P. evitus sp. nov. (occurring from Mexico to Costa Rica) and P. feralis sp. nov. (Guatemala). The morphological definition of the P. ferrugineus group is revised to incorporate additional variability in the worker and queen castes. The previous diagnosis of the males, based largely on features of the genitalia, requires little revision. Closely related to the P. ferrugineus group is a clade of five predominantly South American species, here designated and diagnosed as the P. goeldii group. The five species, P. goeldii (Forel), P. laevifrons Ward, P. micans sp. nov., P. obtusus sp. nov., and P. parvulus sp. nov., are characterized and illustrated. P. laevifrons and P. micans are closely related and difficult to distinguish, possibly reflecting incomplete isolation. Keys are provided for the identification of the species in both groups.

The acacia ants revisited: convergent evolution and biogeographic context in an iconic ant/plant mutualism

“…Sister to this more inclusive group of (P. perboscii þ P. ferrugineus group) is a clade comprising (i) P. haytianus, an isolated species endemic to Hispaniola, and (ii) the Pseudomyrmex goeldii group, which is centred in South America (figure 1a). These more distantly related species are all generalist inhabitants of dead twigs [36].…”

“…the acacia ants nest only in Vachellia domatia; (ii) the workers are aggressive and sting much more readily than generalist twig-inhabiting species of Pseudomyrmex; (iii) the workers patrol the plants constantly; (iv) the ant colonies subsist on harvested Beltian bodies and extrafloral nectar, i.e. the workers are not generalist scavengers like most species of Pseudomyrmex; and (v) the workers have smaller eyes and more slender profemora than related non-mutualistic species [33,36].…”

“…Based on current taxonomic knowledge [13,[33][34][35][36], this represents a comprehensive sampling of the species of Pseudomyrmex that are related to the acacia ants. For eight of the 10 species of acacia ants, we sampled multiple populations, drawn from across the known range of the species [33].…”

Peer Review #2 of "Accessible molecular phylogenomics at no cost: obtaining 14 new mitogenomes for the ant subfamily Pseudomyrmecinae from public data (v0.1)"

“…One particular ant group that suffers from poor mitogenome sampling is the ant subfamily Pseudomyrmecinae that contains three genera: (i) the New-World genus Pseudomyrmex, consisting of ~137 species, most of which can be classified in one of the ten morphological species groups described (Ward 1989(Ward , 1993(Ward , 1999(Ward , 2017; (ii) the Paleotropical Tetraponera, with ~93 species; and (iii) the South American Myrcidris, that has only one species described, Myrcidris epicharis (Ward & Downie, 2005;Bolton, 2012;Ward, 2017).…”

“…In both trees, both the monophyletic status of the P. flavicornis group and the paraphyletic status of the P. viidus group confirms (i) previous observations based exclusively on morphology (Ward, 1989), (ii) phylogenies using both morphological characters and few nuclear markers (Ward & Downie, 2005), and (iii) our own observations regarding mitogenome size. Although the morphological division in species groups has not been formalized or regulated under nomenclatures (Ward, 2017), the work using a hybrid morphological/molecular approach of Ward & Downie, 2005 shows that only two out of nine groups defined at the time were paraphyletic: P. pallens and P. viidus groups. The corroboration of morphological studies by mitochondrial data analysis confirms the relevance of using morphological characters in determining relationships between clades, but also reinforces that molecular evidence can clarify and complement such studies, refining and improving the overall support of the phylogenies reconstructed.…”