Parental kinship coefficient but not paternal coloration predicts early offspring growth in lake char.

The 'good genes' hypotheses of sexual selection predict that females prefer males with strong ornaments because they are in good health and vigor and can afford the costs of the ornaments. A key assumption of this concept is that male health and vigor are useful predictors of genetic quality and hence offspring performance. We tested this prediction in wild-caught lake char (Salvelinus umbla) whose breeding coloration is known to reveal aspects of male health. We first reanalyzed results from sperm competition trials in which embryos of known parenthood had been raised singly in either a stress- or non-stress environment. Paternal coloration did not correlate with any measures of offspring performance. However, offspring growth was reduced with higher kinship coefficients between the parents. To test the robustness of these first observations, we collected a new sample of wild males and females, used their gametes in a full-factorial in vitro breeding experiment, and singly raised about 3000 embryos in either a stress- or non-stress environment (stress induced by microbes). Again, paternal coloration did not predict offspring performance, while offspring growth was reduced with higher kinship between the parents. We conclude that, in lake char, the genetic benefits of mate choice would be strongest if females could recognize and avoid genetically related males, while male breeding colors may be more relevant in intra-sexual selection.

Population genetics reveals divergent lineages and ongoing hybridization in a declining migratory fish species complex.

Deciphering the effects of historical and recent demographic processes responsible for the spatial patterns of genetic diversity and structure is a key objective in evolutionary and conservation biology. Using population genetic analyses, we investigated the demographic history, the contemporary genetic diversity and structure, and the occurrence of hybridization and introgression of two species of anadromous fish with contrasting life history strategies and which have undergone recent demographic declines, the allis shad (Alosa alosa) and the twaite shad (Alosa fallax). We genotyped 706 individuals from 20 rivers and 5 sites at sea in Southern Europe at thirteen microsatellite markers. Genetic structure between populations was lower for the nearly semelparous species A. alosa, which disperses greater distances compared to the iteroparous species, A. fallax. Individuals caught at sea were assigned at the river level for A. fallax and at the region level for A. alosa. Using an approximate Bayesian computation framework, we inferred that the most likely long term historical divergence scenario between both species and lineages involved historical separation followed by secondary contact accompanied by strong population size decline. Accordingly, we found evidence for contemporary hybridization and bidirectional introgression due to gene flow between both species and lineages. Moreover, our results support the existence of at least one distinct species in the Mediterrannean sea: A. agone in Golfe du Lion area, and another divergent lineage in Corsica. Overall, our results shed light on the interplay between historical and recent demographic processes and life history strategies in shaping population genetic diversity and structure of closely related species. The recent demographic decline of these species' populations and their hybridization should be carefully considered while implementing conservation programs.

Higher temperature exacerbates the impact of sediments on embryo performances in a salmonid.

In a warming climate, higher temperatures are likely to modulate positively or negatively the effect of other environmental factors on biota, although such interactions are poorly documented. Here, we explore under controlled conditions the combined effects of two common stressors in freshwater ecosystems, higher temperature and sediment load, on the embryonic development of arctic charr (Salvelinus alpinus L.). In the warm treatment, embryos had a lower survival, a longer incubation period and a smaller body size with a bigger yolk sac volume. Our data show a significant interaction between temperature and sediment load with temperature increasing dramatically the negative effects of sediment load on fitness-related traits. In the climate change context, these findings highlight the importance of taking into account different thermal scenarios when examining the effect of environmental or anthropogenic stressors.

Petromyzon marinus (Petromyzontidae), an unusual host for helminth parasites in western Europe.

The sea lamprey Petromyzon marinus, which is among the most phylogenetically ancient vertebrates, is a hematophagous ectoparasite that feeds on vertebrates and is considered vulnerable in Europe but is a pest in the North American Great Lakes. We conducted a literature review of helminth parasites of P. marinus and investigated postmetamorphic lampreys sampled in rivers and northeast Atlantic coastal waters (western France) during spawning migration. Based on the literature review, 16 helminth taxa have been recorded in P. marinus, among them 14 in North America but only 2 in Europe, with no species in common between these areas. Specific parasites are lacking, and helminth parasites recorded in P. marinus are mostly opportunistic and are trophically transmitted to fish hosts with both extremely low prevalence and mean intensity. Thus, P. marinus seems an unusual host that is probably infected through accidental ingestion of parasites by microphagous larvae (ammocoetes) and/or hematophagous postmetamorphs. Our field study supports this hypothesis, since only a single third-stage larva of Anisakis simplex sensu stricto was found in 2 postmetamorphic P. marinus among the 115 individuals dissected. This opportunistic, trophically transmitted, and cosmopolitan nematode species has never been recorded in North American sea lampreys and only once in Galician rivers (southern Europe). Infestation pathways of P. marinus by A. simplex are proposed vis-à-vis the feeding strategy of postmetamorphs and fish host species which potentially harbor anisakid larvae in their musculature. More generally, the complexity of biotic interactions is discussed considering P. marinus both as a host for helminth parasites and as a parasite for hosts such as fish and mammals, which are also potential predators of sea lamprey.