RELATIONSHIPS BETWEEN ALLOZYMIC HETEROZYGOSITY, BODY SIZE, AND SURVIVAL TO NATURAL ANOXIC STRESS IN THE PALOURDE RUDITAPES-DECUSSATUS L (BIVALVIA, VENERIDAE)

Samples of the bivalve Ruditapes decussatus collected in the lagoon of Thau (France, Mediterranean) after a period of natural anoxia ("malai gue") that caused significant mortality were compared to other samples that had not experienced anoxia. Survival to malaigue was positively related to both shell length and heterozygosity at seven putative enzy me loci. Heterozygosity at locus Pgm-l was significantly higher in the sample of survivors than in the control; this was also observed in a sample of individuals monitored over a malaigue induced in artificial conditions. These results suggest that heterozygosity at locus Pgm-l c ould be directly involved in determining the physiological mechanism o f resistance to anoxic stress, but a genetic explanation involving the role of gametic disequilibrium is also discussed.