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.