Phylogenomic species delimitation in the ants of the Temnothorax salvini group (Hymenoptera: Formicidae): an integrative approach

Abstract

The members of the Temnothorax salvini (Forel) species group are rarely collected, arboreally nesting ants of Central American forests. Previously thought to consist of two broadly dispersed species, recent collections have revealed a diversity of specimens that defy the two‐species salvini group concept, but these are difficult to distinguish from each other based solely on morphology. I contrast several model‐based approaches to species delimitation based on target‐enriched genomic data. With molecular data from thousands of ultraconserved elements (UCEs), mitochondrial genome sequences and morphometric data, I use an integrated approach to species delimitation within the salvini group. Morphometric data were analysed using cluster analysis of principal component analysis (PCA) output. I use several popular methods of molecular species delimitation, including bPTP, BPP and STACEY, using a novel approach to filtering UCE data based on posterior predictive checks of nucleotide substitution model adequacy. In addition, I use iBPP to integrate morphometric PCA data and filtered UCE data in a ‘total evidence’ analysis. I use geographical range data for an independent contrast to discriminate among competing species delimitation hypotheses. Furthermore, I investigate the evolutionary timescale and biogeographical history of the group and find that it arose roughly 13 Ma ago in habitats associated with present day mid‐to‐high elevations of the mountain complex spanning southern Mexico to northern Nicaragua. In addition, dispersal of the salvini group into the Southern Sierra Madre in Mexico, lowland habitats and the southern Central American cordilleras in Costa Rica and Panama subsequent to mountain building in southern Central America 5–8 Ma ago appears to follow a taxon‐cycle dynamic, with the lowland‐adapted T. aztecus representing the most recent expansion phase. I find that the salvini group, which previously contained two named species, is composed of nine, all of which are morphologically diagnosable a posteriori.

Taxonomic revision of theTemnothorax salviniclade (Hymenoptera: Formicidae), with a key to the clades of New WorldTemnothorax

“…Data for material examined follows the following standard format: [type status, if applicable]: [Country]: [primary administrative district]: [secondary administrative district, if applicable]: [locality], [geographical coordinates in decimal degrees ± error radius], [elevation in meters], [collection date, with range if applicable], [collector name & collection code], [habitat], [microhabitat], [number and caste of specimens on pin] (unique specimen identifier) [specimen repository]. In order to be consistent with Prebus (2021) , I discretized elevation into low (<1,000 m), mid (1,000–1,800 m), and high (>1,800 m) when describing elevational range.…”

“…Essentially, species boundaries are established if morphological and genetic disparity are maintained in sympatry in morphologically similar specimens. The genetic data for this study comes from Prebus (2017 , 2021) as well as a study in preparation. Still, I was not able to acquire genetic data for all species listed below; in these cases, species boundaries are more subjective, and based solely on my personal concept of how morphologically disparate populations of Temnothorax must become before they may be considered distinct species.…”

“…With ten species (eight described as new here), the salvini group is the second largest in the salvini clade. Up until a recent species delimitation study ( Prebus, 2021 ), this group was thought to contain two species, T. aztecus and T. salvini , but upon including specimens from across its considerable geographic range and morphological variability, this group was found to contain an additional seven species. Following publication of this study, an additional species was discovered that had been overlooked in collections ( T. terraztecus sp.…”

“…However, recent initiatives such as the Arthropods of La Selva project (ALAS), Leaf Litter Arthropods of Meso-America (LLAMA), and Ant Diversity of the Meso-American Corridor (ADMAC) have revealed a trove of undescribed Temnothorax species from the Neotropics, many of which are members of the salvini clade. Recently, Prebus (2021) used a combination of morphological and phylogenomic data to disentangle a particularly taxonomically difficult Mesoamerican species group, the salvini group, consisting of the previously described species T. salvini (Forel) and T. aztecus (Wheeler), and their undescribed close relatives. In addition to the seven undescribed species detected in Prebus (2021) , I describe an additional 28 species from other species groups in the clade, more than doubling the size of the salvini clade.…”

“…Recently, Prebus (2021) used a combination of morphological and phylogenomic data to disentangle a particularly taxonomically difficult Mesoamerican species group, the salvini group, consisting of the previously described species T. salvini (Forel) and T. aztecus (Wheeler), and their undescribed close relatives. In addition to the seven undescribed species detected in Prebus (2021) , I describe an additional 28 species from other species groups in the clade, more than doubling the size of the salvini clade. To facilitate the diagnosis of the salvini clade, as well as all other clades identified in Prebus (2017) , I have also provided a dichotomous key to all clades of Temnothorax in the Americas.…”