Chacoan (North-West-Central lineages) and Pampean (East and South lineages) divergence
Genetic clustering analyses revealed three major lineages defined by geography: Central, East and South (Figure 2 and 3). Estimates from coalescent-based demographic modeling suggested that lineages began to diverge during the Late Quaternary, approximately 75 kya. The earliest divergence involved populations from the Chacoan biogeographic domain (hereafter “Chaco”), including populations from North, West and Central Argentina, and populations from the Pampean biogeographic region (hereafter “Pampa”) including South and East lineages (Figure 1 and 2). Prior to this split, habitats in the Chaco biome are believed to have become more like those of the Pampa biome, due to the regional contraction of subtropical and tropical biomes (Ortiz-Jaureguizar & Cladera, 2006). Subsequently, major geological changes and climatic shifts took place in the area leading to the geographical isolation of the Chacoan xeric woodlands from the typical grasslands of the Pampean region. Such changes included a topographic configuration promoted by the Andean and sub-Andean Piedmont and the uplift of the eastern orographic systems (the Pampean sierras) associated with the Peripampasic orogenic arc (Calatayud-Mascarell, Ferretti, Enguídanos, Arnedo, 2022; Crisci, Freire, Sancho & Katinas, 2001; Ortiz-Jaureguizar & Cladera, 2006; Speranza, Seijo, Grela & Solis, 2007). These tectonic events produced a rain-shadow effect that resulted in the extremely xeric conditions presently existing in this area. Additionally, climate change during the Quaternary, which included cold, dry glacial cycles alternating with warm, moist interglacial periods, also affected these regions causing expansion and contraction of many habitats (Ortiz-Jaureguizar & Cladera, 2006). This dynamic likely affected patterns of host species distributions and habitat suitability forC. cactorum , which is thought to have promoted the divergence between the Central lineage (Chaco) and East, South lineages (Pampean) (Figure 2 and 3).