Climatic stability and patterns of genomic diversity
Linear regression analyses revealed that population genetic diversity
was significantly correlated with habitat stability. The Chaco region,
representing the northernmost distribution limits of C. cactorum ,
is an open vegetation biome characterized by high endemicity and
diversity for both plant and animal species (Bonatelli et al., 2022;
Brusquetti, Netto, Baldo, & Haddad, 2019; Nores, 1994; Werneck, 2011).
Analyses of environmental habitat suitability between the present and
the LGM revealed relative habitat stability within the Chaco (Figure 4).
Consistent with this, nuclear genetic diversity in C. cactorumwas higher in the Chaco compared to southern regions, supporting the
hypothesis that areas characterized by a high climate stability over the
last glacial and interglacial periods tend to accumulate genetic
diversity (Barros et al., 2015; Carnaval et al., 2009, Hewitt, 2004;
Rocha et al., 2020). The higher effective population size for the
Central lineage, as estimated by coalescent demographic modeling, is in
line with the existence of Pleistocene refugia in Chaco. This region
also contains a higher number of Opuntia species than in any
other region in the sampled area (Varone et al., 2014). Such host plant
availability together with long-term habitat stability has likely
favoured the persistence of relatively large C. cactorumpopulations in this region. However, it cannot be discounted that large
effective population sizes may also be consistent with recent
demographic changes in the Chaco, favored by the introduction ofO. ficus-indica . The introduction of the novel host speciesO. ficus-indica expanded rearing resources for C. cactorumas a consequence of its use as a crop species over the last centuries.
Population growth of C. cactorum would have been further favored
as O. ficus-indica can support one more generation per year as
moths develop faster compared to development on native Opuntiaspecies (Varone et al., 2019).