Navigating the mtDNAroad map out of the morphological maze: interpreting morphological variation in the diverseMonomorium rothsteini(Forel) complex (Hymenoptera:Formicidae)

Abstract

Monomorium is a large and diverse ant genus with speciose radiations in both the Afrotropical and Australian regions. According to the most recent taxonomic revision, many Australian species are characterised by very broad distributions and variable morphology, which suggests that some species may be unrecognised species complexes. With a continent-wide distribution and diverse yet overlapping morphology, M. rothsteini (Forel) is representative of the greater challenge that exists in Australian Monomorium systematics. Here we investigate species boundaries in M. rothsteini using a molecular phylogenetic framework to interpret the complex overlap of nine morphological characters (with 31 states) and examine biogeographic relationships among the lineages. Bayesian inference resolved 38 mtDNA lineages that were morphologically separable, at least from their sister lineage. Although the morphological characters were intermixed across the phylogeny, instances of inseparable morphology among sister clades was rare. Seventeen lineages exhibited complete morphological overlap with one or more other lineages and could not be separated by Principal Component Analysis based on 12 morphometric variables. Two-thirds of all lineages occurred sympatrically with one or more both genetically and morphologically divergent lineages. The two nuclear markers EF1αF2 and wingless were used to generate haplotype networks which were characterised by a star-like pattern indicative of a rapid and recent radiation. Several haplotypes for both nuclear gene regions were shared among individuals occurring in separate mtDNA clades which we were also unable to distinguish morphologically or that were occurring in sympatry, indicating possible introgression in both the mtDNA and nuclear genomes. Clear biogeographic affinities among samples within a lineage were detected but there was no overall pattern in the biogeographic relationships among the lineages. We conclude that M. rothsteini is a large species complex that has undergone a complex evolutionary history following aridification of the Australian continent, and discuss the implications of this conclusion for the systematics of Australian Monomorium more generally.

Some ‘ant’swers: Application of a layered barcode approach to problems in ant taxonomy

“…For the second part, we retrieved the CO1 data from the recent published work on the Monomorium rothsteini complex (Sparks et al . ). With a diverse yet cryptic morphology, M .…”

“…rothsteini lineages can be to some extent identified using combinations of morphological and molecular characters (Sparks et al . ). However, a considerable number of lineages could not been diagnosed due to lack of genetic support.…”

Diversity and biogeography of a species‐rich ant fauna of the Australian seasonal tropics

“…If species have been systematically “split” then this would inflate measures of both richness and apparent endemism. However, genetic data have consistently shown that this is not the case (Andersen et al ., ,b; Sparks et al ., ), and indeed indicated that the sorting has been highly conservative, with many taxa sorted as widespread morphospecies actually representing multiple biological species, often with very restricted distributions (Andersen, ). This suggests that the figure of 901 Top End species in the TERC collection is actually a substantial underestimate, and that the percentages of species shared with other geographic regions are overestimates.…”

“…The southwestern and southeastern regions, and central Arnhem Land, remain relatively poorly collected. All morphospecies sorting in the TERC collection has been conducted by the senior author, and genetic data have consistently supported its validity (Andersen et al ., ,b; Sparks et al ., ).…”

The Megadiverse Australian Ant Genus Melophorus: Using CO1 Barcoding to Assess Species Richness

“…However, the generalized morphology of most Melophorus species makes species delimitation extremely challenging, and so the reliability of the morphospecies sorting in the TERC collection requires validation. Integrated morphological, behavioural, and genetic analyses have consistently validated the sorting of morphospecies in the TERC collection from other highly diverse and taxonomically challenging Australian genera such as Monomorium [24][25][26] and Iridomyrmex [27]. Indeed, CO1 data from specimens from the M. aeneovirens group suggest that the sorting of Melophorus morphospecies in the TERC collection is in fact highly conservative [23].…”