Genetic implications of mating structure in a Caribbean isolate.

Mating patterns in the population of St. Barthelemy French West Indies are examined to evaluate the expected genetic consequences of consanguinity avoidance and of failure to mate due to celibacy and emigration. Nearly 60% of all individuals reaching mating age on St. Barthelemy never contribute to the gene pool of succeeding generations. This greatly reduces the effective population size and therefore increases genetic drift or random inbreeding. The consequent loss of heterozygosity is partially countered by the fact that the individuals who fail to reproduce within the population tend to be more closely related to the population than are those who do reproduce. This nonrandom failure to mate results in nonrandom inbreeding which reduces total pedigree inbreeding. Total inbreeding is also reduced by consanguinity avoidance. However the effect of avoiding close consanguineous matings is to some extent reversed by an apparent preference for more distant relationships especially with 2nd cousins. Generally similar results are found for the related Northside French population of St. Thomas U.S. Virgin Islands. A recently developed mathematical model predicts the expected effects on heterozygosity of partial or complete avoidance of or preference for any combination of consanguineous matings and also takes into account nonrandom failures to mate. Applications of this model to these 2 populations suggest that under some circumstances nonrandomness in celibacy and emigration may have a greater influence on genotype distributions than does consanguinity avoidance. (authors)