Legacy of ice ages in temperate South America: the role of hybridization shaping genetic signatures in cold-tolerant Nothofagus

PREMOLI A. C.; MATHIASEN P.; ACOSTA M. C.

Punta Arenas

Congreso; VIII Southern Connection Congress; 2016

Southern Connection

Scenariosof survival in glacial refugia during cooling were put forward in dominant treespecies of temperate ecosystems. These were analyzed using ecological nichemodeling, fossil records, and/or molecular data which provided evidence ofmultiple (probably small) refugia for cool-tolerant taxa and of single(probably big) refugia for cool-sensitive species. Many studies have alsosuggested that during post glacial expansions from different tree refugiahybridization may occur as a result of secondary contact. However, theformation of hybrids maybe more complex than previously suggested. Inparticular, coldtolerant Nothofagusspecies of subgenus Nothofagus (Nothofagusantarctica and Nothofagus pumilio) for which multiple glacial refugia weresuggested, share widespread chloroplast polymorphisms along their entireranges. These were interpreted as wide-range chloroplast capture events as aresult of hybridization/introgression cycles. Although they may produce hybridsat some locations, these two species are morphologically and ecologicallydistinct and can be clearly identifiable by means of nuclear ITS DNA sequences.We combined nuclear and chloroplast DNA in combination with dating methods toanalyze the local hybridization dynamics between 20 sympatric populations ofboth species. While population pairs shared up to 100% of DNA sequences of thechloroplast, a smaller proportion were so for genetic variants of biparentallyinherited markers. Dating methods yielded divergence times that encompassdifferent ice ages of Patagonia. Our results show that sympatric cold-tolerantNothofagushave survived multiple glacial events and that populations of bothspecies have responded locally by hybridization-ecological speciation cycles.