Gamete compatibility, gamete trait variation and their effect on fertilization success in northwest Atlantic blue mussel (Mytilus edulis l. and Mytilus trossulus gould) hybrid zone

• Main Author: Liu, Guangxu
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2009
• Subjects: Canada; Northwest Atlantic
• Online Access: https://research.library.mun.ca/9174/; https://research.library.mun.ca/9174/1/Liu_Guangxu.pdf

Mytilus edulis and M. trossulus coexist and form a natural hybrid zone along the Atlantic Canada coast, which provides an excellent model to study marine invertebrate evolution, speciation and especially reproductive isolation barriers that maintain species integrity. Gamete traits and their role in determining fertilization success among M. edulis, M. trossulus and their hybrids were investigated in the present study. Sperm of all three genotypes (the term genotypes was used throughout the thesis to include M. edulis, M. trossulus and their hybrids) conducted circular movement in a two dimensional plane, which may represent a trait that increases fertilization success under sperm limitation on a small spatial scale. Neither egg water nor egg presence elicited sperm chemotaxis in our experimental set-up, which suggests that sperm chemotaxis may not be necessary for successful fertilization of marine invertebrate species with dense aggregations, synchronized broadcast spawning and high gamete output. Although no significant difference in gamete output was detected among the different genotypes, sperm velocity differed among M. edulis, M. trossulus and their hybrids, F₁ hybrids producing the slowest swimming sperm. Sperm of M. edulis had faster VAP (average path velocity) and angle change rate than those of M. trossulus . Most of the variation in sperm velocity was attributed to variation within individuals, which may be caused by differences in stage of maturity among individual sperm. Both sperm velocity and sperm half life (T₅₀) decreased as temperature increased. F₁ hybrids had the shortest sperm longevity and M. trossulus was least temperature sensitive, which may be an adaptation to a longer spawning period, resulting in exposure to higher temperature fluctuations. M. edulis produced larger eggs than M. trossulus and F₁ hybrids, providing a larger target for sperm-egg interaction. Both homospecific and heterospecific fertilization success differed among parental combinations and may be due to the combined ...