Absence of intrinsic post-zygotic incompatibilities in artificial crosses between sympatric coregonid species from upper Lake Constance

Abstract

A full factorial crossing experiment with five females and five males of each of two coregonid species from upper Lake Constance was used to test for intrinsic post-zygotic incompatibilities during early ontogeny. Up until shortly before hatching, there was no difference in embryo mortality between homo and heterologous crosses. Amaternal effect on mortality was found in both species, but paternal effects and female–male interactions were absent. Thus, genetic incompatibility during early ontogeny does not appear to prevent introgressive hybridization, suggesting that genetic divergence between these species is maintained primarily by pre-zygotic barriers. The recent genetic homogenizations of coregonid species flocks in European alpine lakes may have been caused by a flattening of adaptive landscapes through eutrophication, but intensive stocking with larvae obtained in hatcheries from artificially fertilized eggs is also likely to be a contributing factor. To safeguard diversity among sympatric coregonids, it is important to re-establish ecological conditions conducive to species divergence and to revise traditional management strategies.