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. A maternal 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.

Managing cryptic biodiversity: Fine‐scale intralacustrine speciation along a benthic gradient in Alpine whitefish (Coregonusspp.)

“…Two interacting anthropogenic impacts may have had profound effects on shaping endemic Lake Lucerne whitefish diversity: (i) eutrophication and (ii) stocking, both of allochthonous and autochthonous whitefish. Given the relative evolutionary youth of the Alpine whitefish radiation as a whole, mating barriers between the constituent species will be largely based on behavioural and/or extrinsic pre-and postzygotic isolating mechanisms rather than intrinsic genomic incompatibilities (Eckmann, 2015;Vonlanthen et al, 2012;Woods et al, 2009). In some Swiss lakes, anthropogenic eutrophication has led to a complete collapse of whitefish diversity over the past 60 years due to an interaction between negative population growth and speciation reversal .…”

Impact of Fishing and Stocking Practices on Coregonid Diversity

“…Only in the late 1990s was this practice finally banned, with gamete collection of the two species now occurring on different dates. Hence, unwanted artificial hybridization could have easily occurred over several decades, and may have contributed to the observed decline in genetic diversity [88].…”

Does eutrophication-driven evolution change aquatic ecosystems?

“…Known ecologically relevant differences among species include body size, growth rate, diet and depth-habitat. Reproductive isolation among members of lake radiations is maintained by differences in spawning depth, spawning season, possibly mate choice ( [49,50]; B. Lundsgaard-Hansen 2012, unpublished data) and natural selection against intermediate phenotypes [51,52].…”