Drivers of Diversification Across an Intercontinental Cryptic Species Complex within the Turtle Ant Adaptive Radiation
Open AccessAdaptive radiation is a key process in the generation of biodiversity, but can alternate sources of species production occur concurrently within a radiating lineage? This question is especially relevant in lineages that radiate across continents, where the potential for complex interactions is greater. My research investigates the evolutionary relationships within Cephalotes maculatus, a widespread, morphologically uniform species nested within the New World adaptive radiation of the turtle ants (Cephalotes). Turtle ants are found from the southern United States through Argentina, and new species formation in the group is driven partly by shifts between ecologically distinct biogeographic regions, ranging from dry desert to wet rainforest. I use a phylogenomic approach to examine whether nominal Cephalotes maculatus is a complex of radiating species, following the trend of the genus it is nested within, or if C. maculatus is a few minimally diverged, widespread species, contrasting with the rest of the genus. I constructed an ultraconserved elements-based phylogeny of C. maculatus from throughout its range. My phylogenomic data reveals a minimally diverged species complex with an intercontinental range but also reveals a sympatric, ecologically co-occurring cryptic species that diverged from nominal C. maculatus 10.5 mya. The C. maculatus phylogeny revealed two broad continent-scale lineages from: 1) South America and 2) Central America. Bootstrap support is high in the Central American clade, however lower support is observed across the South American clade, suggesting more complex processes in this region. In my second chapter, I generated a phylogeny of the pinelii species group to which C. maculatus belongs and then conducted divergence dating analyses and inferred biogeographic range across the species group. The pinelii species group arose at the end of the Oligocene in the Dry Diagonal biome of South America, coinciding with the origin of the Dry Diagonal. C. maculatus later arose in the Amazon region, spreading across diverse biomes from the Atlantic Forest in Argentina through Central America and into Mexico. In my third chapter, I phased alleles from my UCE sequence data and conducted multispecies coalescent-based analyses to investigate the poor support in the South American clade. These methods confirmed support for the Central American clade and strengthened support for a subset of the South American clade. Some taxa in the South American clade, however, remained poorly supported and differed in placement across the various analyses. Additionally, the former Trinidad & Tobago group moved into differing rogue placements, similar to the taxa with ambiguous placement in the former South American clade, suggesting complex gene flow patterns and the need for further population and network analyses to resolve the placement of these ambiguous taxa. Overall, these results show that even during the process of lineage wide evolutionary radiations, not all clades undergo the same pattern of rapid species proliferation.
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