Phylogeography and population genetics of black alder (Alnus glutinosa (L.) Gaertn.) in Ireland: putting it in a European context

Abstract

Black alder (Alnus glutinosa (L.) Gaertn.) is a widespread tree of European forests with a high potential for wood and biomass production. This study investigated the genetic origin and diversity in remnants of putative native alder forest stands in Ireland and compared it with other European populations to determine phylogeographic patterns. The efficiency of capture of the genetic diversity in a breeding population was also assessed. Data were obtained from chloroplast DNA (cpDNA) polymorphisms and from nuclear microsatellites. In silico PCR-RFLP was used to locate cpDNA sequence polymorphisms in order to develop flanking primers for high-resolution melting (HRM) analysis. The cpDNA polymorphism analysis detected two main haplotypes in Ireland. The same two are also found in Wales and England while only one is found in Scotland. The results suggest that Irish populations of alder have originated from at least two European glacial refugia. Black alder in Ireland exhibited no or very weak population differentiation using nuclear microsatellite markers, which is consistent for a wind-dispersed, outcrossing species. Based on the nuclear microsatellite data, a decline in population sizes is estimated to have occurred around a timeframe that coincides with a period of large-scale deforestation. The breeding population contained two haplotypes and showed a high level of genetic capture (86 % of microsatellite alleles) when compared with all samples combined. This study fills a gap in previous knowledge, provides an additional marker and an additional method for future studies. The characterisation of a breeding population provides valuable baseline data for a national alder tree improvement programme.