Date of Graduation

Fall 2017


Master of Science in Biology



Committee Chair

Chris M. Barnhart


freshwater mussel, reproduction, spermatozeugmata, temperature, fecundity, fertilization

Subject Categories

Biology | Life Sciences


Freshwater mussels, Order Unionoida, are diverse and widespread in North America but have suffered general decline and many extinctions in recent decades. The reproductive biology of Unionoida is complex and may be vulnerable to human impacts. Male mussels release aggregates of sperm called spermatozeugmata that drift downstream. Females obtain spermatozeugmata from the water and brood the fertilized eggs internally during development. Many aspects of general reproductive biology are poorly understood, including the mechanisms that coordinate spawning and the route by which sperm meet eggs in the female. The present study focuses on reproduction in the Deertoe (Truncilla truncata), which spawns in the spring. Adult individuals were collected from the Minnesota River watershed in early April 2016 and held at temperature below 10°C. Gonadal sex was reliably predictable from shell and gill morphology. Effects of temperature and chemical cues on spawning were examined. Both male and female Truncilla spawned within 24 hours after temperature reached 13°C. At lower temperatures, spawning could be delayed for at least one year. Sperm presence had no effect on the timing of male or female spawning. Spawning females invested about 2.5× more energy in gametes than males did. Female and male investments were 9.7 ± 6.2 and 4.0 ± 4.3 calories per gram whole body mass, respectively. Sperm activated and detached from spermatozeugmata in the presence of unfertilized eggs, suggesting that a chemical signal released by the eggs triggers sperm to disassociate from spermatozeugmata. Contact with female gills, however, did not trigger dissociation.


© Kendell R. Loyd

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