‘Picking up signals’ in male genital morphospace and integrating phylogenomics to delimit Neotropical Nylanderia Emery species (Hymenoptera: Formicidae)

Genital morphology, a cornerstone in taxonomy that predates
Linnaeus's Systema Naturae, is vital for species delimitation.
However, the widely accepted paradigm that genitalia are taxonomically
informative lacks robust testing between closely related species, and
supporting evidence is often limited to taxonomic literature in which
genitalia are assumed a priori to be species-specific. The cosmopolitan
ant genus Nylanderia Emery includes 125 described species, with most in
the Neotropics still undescribed. Workers are often morphologically
cryptic, and males are rare in collections but required for morphological
delimitation. Using Ultraconserved Elements (UCEs) from 236 samples
including 50 Neotropical Nylanderia species, we reconstructed phylogeny as
a framework to compare genitalia (gonopods) of males collected alongside
workers. We used geometric morphometrics on images of slide mounted
genitalia from 14 morphospecies and nano-CT scans of Nylanderia fulva
(Mayr) and Nylanderia pubens (Forel) genital capsules and interpreted
results considering phylogeny under maximum likelihood and the
multispecies coalescent. We found strong morphological and molecular
support for two distantly related American clades, identifiable by gonopod
shape, with significant differences observed among most species. Three
previously reported COI clades of N. fulva were not supported as
monophyletic, nor were their gonopods significantly different. However, N.
pubens was supported as distinct by all phylogenetic and 3DGM results. Our
findings emphasize the importance of male genitalia for delimiting species
boundaries and revising Neotropical Nylanderia. Given their importance,
particularly in morphologically cryptic taxa, we recommend a greater focus
on linking male and worker phenotypes, which can be facilitated through
comprehensive nest series collection.