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).