Generation time and the stability of sex-determining alleles in oyster populations as deduced using a gene-based population dynamics model.
Crassostrea oysters are protandrous hermaphrodites. Sex is thought to be determined by a single gene with a dominant male allele M and a recessive protandrous allele F, such that FF animals are protandrous and MF animals are permanent males. We investigate the possibility that a reduction in generation time, brought about for example by disease, might jeopardize retention of the M allele. Simulations show that MF males have a significantly lessened lifetime fecundity when generation time declines. The allele frequency of the M allele declines and eventually the M allele is lost. The probability of loss is modulated by population abundance. As abundance increases, the probability of M allele loss declines. Simulations suggest that stabilization of the female-to-male ratio when generation time is long is the dominant function of the M allele. As generation time shortens, the raison d'être for the M allele also fades as mortality usurps the stabilizing role. Disease and exploitation have shortened oyster generation time: one consequence may be to jeopardize retention of the M allele. Two alternative genetic bases for protandry also provide stable sex ratios when generation time is long; an F-dominant protandric allele and protandry restricted to the MF heterozygote. In both cases, simulations show that FF individuals become rare in the population at high abundance and/or long generation time. Protandry restricted to the MF heterozygote maintains sex ratio stability over a wider range of generation times and abundances than the alternatives, suggesting that sex determination based on a male-dominant allele (MM/MF) may not be the optimal solution to the genetic basis for protandry in Crassostrea.
Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349, United States.
Eric N
EN
Powell
Center for Coastal Physical Oceanography, Old Dominion University, 4111 Monarch Way, Norfolk, VA 23529, United States.
John M
JM
Klinck
Center for Coastal Physical Oceanography, Old Dominion University, 4111 Monarch Way, Norfolk, VA 23529, United States.
Eileen E
EE
Hofmann
D000818:Animals; D005260:Female; D005787:Gene Frequency; D008297:Male; D008957:Models, Genetic; D010125:Ostreidae / Q000235:genetics*; D011156:Population Density; D011157:Population Dynamics; D019849:Sex Determination Processes / Q000235:genetics*; D012744:Sex Ratio