Brendan F. Wringe

Inter-population ovarian fluid variation differentially modulates sperm motility in Atlantic cod Gadus morhua

This study tested the hypothesis that the effects of Atlantic cod Gadus morhua ovarian fluid on sperm motility variables are population specific. Sperm from a northern G. morhua population were activated in the presence of ovarian fluid from either northern or southern G. morhua at different concentrations. Ovarian fluid acted as a filter, in some cases reducing sperm swimming performance compared with seawater. Fluid from females foreign in population (southern) to the males (northern) had a greater inhibiting effect than those from the native population. Follow-up analysis indicated that the ovarian fluids had lower Ca(2+) concentration in northern than southern G. morhua, which could be the causative mechanism. If widespread, such cryptic female choice could reduce the incidence of intraspecific hybridization among diverged populations and contribute to reproductive isolation.

A novel sperm adaptation to evolutionary constraints on reproduction: Pre-ejaculatory sperm activation in the beach spawning capelin (Osmeridae)

Abstract Reproduction of external fertilizing vertebrates is typically constrained to either fresh or salt water, not both. For all studied amphibians and fishes, this constraint includes immotile sperm that are activated after ejaculation only by the specific chemistry of the fertilizing medium in which the species evolved (fresh, brackish, or salt water). No amphibians can reproduce in the sea. Although diadromous fishes may migrate between salt and fresh water, they are shackled to their natal environment for spawning in part because of sperm activation. Here, we report for the first time among all documented external fertilizing vertebrates, that in the absence of any external media, sperm are motile at ejaculation in a marine spawning fish (Osmeridae, capelin, Mallotus villosus). To illuminate why, we evaluated sperm behavior at different salinities in M. villosus as well as the related freshwater spawning anadromous rainbow smelt (Osmerus mordax). Surprisingly, sperm performance was superior in fresh water for both species. M. villosus spend their entire life at sea but our results show that their sperm are deactivated by sea water, suggesting a freshwater ancestry. By circumventing constraining water chemistry, we interpret the unique pre‐ejaculatory sperm activation in this species as a novel adaptation that enables fertilization in the marine environment. These findings also contribute to understanding the persistence of anadromy, despite great energetic costs to adult fishes.

In search of a “cultured fish phenotype”: a systematic review, meta-analysis and vote-counting analysis

The notion that cultured fishes develop a morphology that differs from their wild conspecifics has become nearly axiomatic. A commonly supervened corollary is that exposure to culture causes predictable and consistent morphological changes that together form a common “cultured phenotype”. While this is often asserted, it has not been formally tested. We conducted a systematic review of the literature based on PRISMA best practice protocols and identified 65 papers, composed of 106 studies that compared the morphology of 39 species of cultured fish to their wild conspecifics. From this we conducted a meta-analysis of quantitative, and vote-counting analysis of qualitative differences in 16 external morphological features and condition factor. Our results confirm that aspects of a general “cultured phenotype” exist. The meta-analysis analysis revealed that cultured fish had shorter heads, upper jaws and fins, and the vote-counting analysis was suggestive of this as well. The vote-counting analysis showed that across all studies cultured fish had greater body depth and condition factor than wild fish, but this was not supported by the meta-analysis. In addition to matching those required to develop the “cultured phenotype”, the detected morphological changes are consistent with experimentally observed plastic responses to conditions typical of the cultured environment. This is discussed, as is how the observed changes may be influenced or reinforced by intentional and unintentional selection.