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).