Embryo development under context of hybridization and a review of regional patterns in hybrid frequency of Atlantic salmon and brown trout

Poulos, Steven (2019) Embryo development under context of hybridization and a review of regional patterns in hybrid frequency of Atlantic salmon and brown trout. Masters thesis, Memorial University of Newfoundland.

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Abstract

Reproductive isolating mechanisms that maintain the integrity of species sometimes fail, resulting in hybridization. Such isolating mechanisms occur pre- and post-gamete release, and influence nuances of sperm phenotype that may affect offspring development. Hybridization between congeneric Atlantic salmon and brown trout occurs in their native range of sympatry in Europe, and via human introductions of brown trout in North America. It is known in other hybrid systems that pre-zygotic post-copulatory isolation via cryptic female choice perhaps mediated by ovarian fluid can bias fertilization towards conspecific sperm. Anthropogenic hybridization of these species in the invaded range of North America is not well understood. This provides an opportunity to understand mechanisms of isolation between the species. Therefore, I explored 1) developmental characteristics of offspring sired from sperm exposed to conspecific and heterospecific ovarian fluid and 2) developmental characteristics of pure salmon, pure trout, and bidirectional hybrids in two fluctuating temperature regimes. Ovarian fluid had no effect on the development of offspring, however, hybridization did. Hatch success of hybrids was high, supporting previous work. Although effect sizes were small, hybridization generally caused earlier hatching for each female, and hybrids produced with salmon eggs suffered the fastest rate of mortality shortly after hatching relative to hybrids of trout eggs. This is important, for previous work reported hybrids produced from trout eggs die shortly after hatching.

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