Reticulate evolution: ancient introgression of the Adriatic brown trout mtDNA in softmouth trout Salmo obtusirostris (Teleostei: Salmonidae)

Abstract

Two populations of softmouth trout (Salmo obtusirostris) from the rivers Neretva (Bosnia and Herzegovina) and Jadro (Croatia), along with two neighbouring populations of brown trout (Salmo trutta) were analysed with a suite of genetic markers (two mtDNA genes, two nuclear genes, and nine microsatellites) as well as morphological characters. The Jadro softmouth trout were fixed for a brown trout mtDNA haplotype of the Adriatic lineage, which is 1.7% divergent from a previously described haplotype characteristic for the Neretva softmouth trout. All other genetic markers, as well as morphological analysis, supported the clear distinction of softmouth trout from the rivers Neretva and Jadro from brown trout in neighbouring populations, and thus a mtDNA capture event is assumed. Population specific microsatellite allele profiles, as well as a high number of private alleles for both populations of softmouth trout, support the hybridization between brown trout and the Jadro softmouth trout most likely being of ancient origin, thus leading to a reticulate evolutionary pattern of mtDNA in this taxon.