East and South (Pampean) lineages divergence
East and South lineages were estimated to have diverged approximately 19 kya. Regional climate models suggest that this timing coincided with an increase in precipitation along the eastern foothills of the Andes (Cook & Vizy, 2006). The topographical features together with the Quaternary climatic evolution of the region maintained a fragmented distribution of host species from C. cactorum in the Pampa (Mourelle & Ezcurra, 1997). This would likely have limited dispersal of C. cactorum , restricting the East lineage to the more humid environments with deep fertile soils typical of the Pampa, and the South lineage to the drier grasslands of the northern border of the Patagonian steppe.
Climatic changes during the Quaternary promoted complex phylogeographic patterns in many southern South American arthropods, such as the grasshopper Dichroplus vittatus Bruner (Rosetti et al., 2022), the beetle Naupactus cervinus Boheman (Rodriguero et al., 2016), mygalomorph spiders (Calatayud-Mascarell et al., 2022), among other taxa (Bonatelli, Gehara, Carstens, Colli & Moraes, 2022). Similar phylogeographic consequences of climate change over the last 21,000 years have been recently documented for O. bonaerensis , one of the host species for C. cactorum (Köhler, Esser, Font, Souza-Chies & Majure, 2020). The concordance in the timing of intraspecific diversification within O. bonaerensis and C. cactorum is strongly suggestive of a fundamental role for Quaternary climate on the evolutionary history of the cactus-moth system. Intraspecific genetic differentiation in C. cactorum and its close relatives C. doddi and C. bucyrus also dates back to the late Quaternary (Poveda-Martínez et al., 2022). Diversification within C. bucyrus , a specialist on the columnar cactusTrichocereus atacamensis , is estimated to have initiated during the Marine Isotopic Stage 3 (~42 kya), an interstadial during the last glacial period. Divergence within C. doddi, which feeds upon Opuntia sulphurea, is estimated to have occurred very close to the end of the Pleistocene (~19 kya), coincident with estimates for the split between East and South lineages of C. cactorum (Poveda-Martínez et al., 2022).
Maps of environmental suitability estimated with ecological modeling suggested that the Chaco and northern Pampean regions harbored larger climatically suitable areas than other biogeographic regions such as the Yungas, Monte, Puna and Prepuna (Figure 1). Both C. doddi andC. bucyrus are found in the Prepuna and Monte regions whereC. cactorum is absent, supporting the idea that disparate environmental/habitat conditions and disjunct host plant distributions played a role in divergence within C. cactorum and its closely related species (Poveda-Martínez et al., 2022). These findings suggest that intraspecific diversification within this group of closely relatedCactoblastis species have been strongly influenced by shifts in the distribution of host species in response to Quaternary climate dynamics.