Genetic and ecological aspects of the hybrid zone between the mussels Mytilus edulis and Mytilus trossulus in the northwest Atlantic

• Main Author: Miranda, Marcelo B. B.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2004
• Subjects: Newfoundland; Northwest Atlantic
• Online Access: https://research.library.mun.ca/11056/; https://research.library.mun.ca/11056/1/Miranda_MarceloBB.pdf

Two mussel species (Mytilus edulis and Mytilus trossulus) form a hybrid zone in the northwest Atlantic that is complex in its structure and dynamics. The study of Mytilus hybrid zones can reveal important aspects of marine evolution and speciation. A patchy distribution of M. edulis and M trossulus around Newfoundland suggests that differential adaptation to environmental conditions may be important in determining the species relative frequency and fitness. The observation that M. trossulus is less tolerant to warm temperatures than M. edulis implies that physiological differentiation may contribute to reproductive isolation since discrete biogeographic distributions help to maintain the genetic identity of the species. Differences in the microgeographic distribution of the species indicate that habitat specialization may also contribute to reproductive isolation. The presence of pure M. trossulus populations in five sites sampled in Labrador likely result in a great larval input from this species into the hybrid zone through the Labrador Current. Poorer adaptation to the environmental conditions of Newfoundland would then result in a higher mortality of M trossulus in the area. Evidence for differential survival was suggested by the observed decrease in the relative frequency of M. trossulus in the larger size classes at most sites in Newfoundland and by the greater mortality observed in field grow-out and temperature experiments. Differences in life-history strategies may also influence the observed frequency pattern since M. trossulus reproduces earlier, spawns smaller eggs and possibly has a shorter generation time than M. edulis. Gamete recognition and incompatibility are probably important isolating mechanisms between M. edulis and M. trossulus. Intrinsic postzygotic mortality likely represents an additional isolating mechanism. Reduced hybrid viability was observed mainly in the early stages of development, but higher mortality of hybrids also occurred at later stages. F1 hybrids and advanced backcrosses ...