LEGACY OF ICE AGES IN TEMPERATE SOUTH AMERICA: THE ROLE OF HYBRIDIZATION SHAPING GENETIC SIGNATURES IN COLD-TOLERANT NOTHOFAGUS

PREMOLI, ANDREA, MATHIASEN, PAULA, ACOSTA, MARIA

Congreso; VIII Southern Connection Congress; 2016

Scenarios of survival in glacial refugia during cooling were put forward in dominant tree species of temperate ecosystems. These were analyzed using ecological niche modeling, fossil records, and/or molecular data which provided evidence of multiple (probably small) refugia for cool-tolerant taxa and ofsingle (probably big) refugia for cool-sensitive species. Many studies have also suggested that during post glacial expansions from different tree refugia hybridization may occur as a result of secondary contact. However, the formation of hybrids maybe more complex than previously suggested. In particular, coldtolerant Nothofagus species of subgenus Nothofagus (Nothofagus antarctica and Nothofagus pumilio) for which multiple glacial refugia were suggested, share widespread chloroplast polymorphisms along their entire ranges. These were interpreted as wide-range chloroplast capture events as a result of hybridization/introgression cycles. Although they may produce hybrids at some locations, these two species are morphologically and ecologically distinct and can be clearly identifiable by means of nuclear ITS DNA sequences. We combined nuclear and chloroplast DNA in combination with dating methods to analyze thelocal hybridization dynamics between 20 sympatric populations of both species. While population pairs shared up to 100% of DNA sequences of the chloroplast, a smaller proportion were so for genetic variants of biparentally inherited markers. Dating methods yielded divergence times that encompass different iceages of Patagonia. Our results show that sympatric cold-tolerant Nothofagus have survived multiple glacial events and that populations of both species have responded locally by hybridization-ecological speciation cycles.