VARIATION OF REPRODUCTIVE SUCCESS IN A HAPLO-DIPLOID RED ALGA, GRACILARIA-VERRUCOSA - EFFECTS OF PARENTAL IDENTITIES AND CROSSING DISTANCE

The factors influencing reproductive success in a haplo-diploid marine alga, Gracilaria verrucosa, have been determined through single-male crosses in the laboratory. Crossing success was assessed by measuring its early components, fertility, and abortion rate. The effects of the male or female parent identity, of the male x female interaction, and of the geographical distance between mates were tested in crosses wit hin or between populations at different geographical scales. The ident ity of the female parent has a predominant effect on crossing success. Interparent distance has no effect in within-population crosses, this strongly suggests an absence of inbreeding depression, expected in a species where the haploid phase is individualized and isomorphic to th e diploid one. Crossing success tends to increase with distance betwee n mates in between-population crosses. This heterosis effect seems to indicate that the marine environment could allow genetic divergence be tween populations, even at short distances (about 100 m).