Aging reduces reproductive success in mussels Mytilus edulis

The present study was aimed to determine whether reproductive success constantly increases with age in a relatively short-lived invertebrate with continuous growth – the bivalve mollusc Mytilus edulis or there is an age-related decline such as observed in species with finite growth (mammals, insects, nematodes, etc.). We studied the reproductive output and viability of the offspring during early embryogenesis in females of different sizes and ages, and used allometric approaches to correct for the effects of the body size and to discern pure age-specific effects on these reproductive traits. We have also determined contributions of females of different age and size classes to the total larval pool of a population. Both gonadosomatic index and individual fecundity significantly decreased in the course of aging if the size of the animals was accounted for. The proportion of normally developing embryos declined from almost 100% to 60% in females of 2–10-year-old. We suggest that animals with infinite growth and “slow aging”, such as molluscs, undergo senescence, the physiological manifestations of which can be masked by a more pronounced effect of continuously increasing size.