FACTORS AFFECTING THE DISTRIBUTION OF GENETIC-VARIABILITY IN THE GUPPY, POECILIA-RETICULATA

Previous studies on Trinidadian guppies have shown an apparent associa tion of genetic variability, expressed as mean heterozygosity (H(o)) a t allozyme loci, with river order: fish from lowland sites exhibit hig her mean H(o) than their upland counterparts. Detailed genetic and beh avioural observations were undertaken in the present study by repeated sampling throughout two river courses to examine population heterogen eity. Results show that the predation regime mediated mating behaviour of upland and lowland populations in the wild is not as divergent as previous laboratory observations have suggested. Furthermore, genetic variation at the eight loci variable in Trinidian populations (P100 = 0.13-0.88, H(o)=0.03-0.23) appears to bear little association with pre dation regime, but is related to sub-structuring of populations by hab itat features and geographic isolation. We therefore conclude that the observed patterns of genetic variability arise primarily as a consequ ence of stochastic as opposed to deterministic factors.