Hybridization and restricted gene flow between native and introduced stocks of Alpine whitefish (Coregonus sp.) across multiple environments

Abstract

Translocations of Baltic whitefish (Coregonus sp.) into Austrian Alpine lakes have created ‘artificial hybrid zones’, threatening the genetic integrity of native lineages. We evaluate the genetic structure of Coregonus in Austrian lakes and characterize hybridization and introgression between native and introduced lineages. Fifteen populations (N= 747) were assessed for allelic variation at eight microsatellite loci and a reduced set (N= 253) for variation across two mtDNA genes (cyt b and NADH-3). Bayesian approaches were used to estimate individual admixture proportions (q-values) and classify genotypes as native, introduced or hybrids. q-value distributions varied among populations highlighting differential hybridization and introgression histories. Many lakes revealed a clear distinction between native and introduced genotypes despite hybridization, whereas some locations revealed hybrid swarms. Genetic structure among lakes was congruent with morphological divergence and novelty raising speculation of multiple taxa, including a population south of the Alps, outside the putative native range of Coregonus. Although statistically congruent with inferences based on nuclear markers, mitochondrial haplotype data was not diagnostic with respect to native and non-native lineages, supporting that the Alpine region was colonized post-glacially by an admixture of mtDNA lineages, which coalesce >1 Ma. Mechanisms promoting or eroding lineage isolation are discussed, as well as a high potential to conserve native Alpine lineages despite the extensive historical use of introduced Baltic stocks.

Climate, Demography, and Zoogeography Predict Introgression Thresholds in Salmonid Hybrid Zones in Rocky Mountain Streams

“…First, perhaps introduced stocks of rainbow trout have lower fitness than native populations, have been unable to spread as extensively, and have already reached their environmentally mediated distribution. A number of freshwater taxa have shown surprising resistance to introgression despite intense propagule pressure [75,76], a result which has often been attributed to lower fitness in the introduced forms. Such reduced fitness may also characterize hatchery-derived populations of salmonids [77], although it generally applies to captively reared fish, not naturalized populations [78].…”

Comparative phylogeography and demographic history of European shads (Alosa alosa and A. fallax) inferred from mitochondrial DNA

“…Whether natural or anthropogenically induced, changing environmental conditions have long been thought to play a major role in increasing rates of hybridization in fishes [45]. Several recent freshwater fish studies [46,47] underscore the importance of broader ecological degradation leading to increased hybridization rates, a situation which easily applies to the UK and Portuguese rivers where high levels of hybridization are documented. Nevertheless, shads represent a very unique case of introgressive hybridization among European fishes, something that needs to be further addressed using also nuclear markers.…”

Rearing Larvae of Different Strains of Coregonus lavaretus under Cold Water Conditions: Comparison of a Special Cold-Water Line with a Standard Agglomerated Microdiet

“…In winter 2011/2012 eggs of European whitefish (Coregonus lavaretus), from an existing breeding line originating from whitefish of the southern Baltic region (sometimes designated Coregonus maraena) and reared since the 19 th century in carp-pond aquaculture in Bohemia and northern Austria (Susta, 1888;Winkler et al, 2011) and bred in our own hatchery in the fourth generation were stripped and artificially fertilized. The offspring of these fish is thereafter called strain 1.…”