Homozygosity and heterozygosity in three populations of Rivulus marmoratus

Rivulus marmoratus is a self-fertilizing hermaphroditic fish found in the t ropical Atlantic as populations of homozygous clones, with the exception of a single site in Belize where male fish are abundant and heterozygosity is the norm. The presence of male fish apparently leads to outcrossing and he terozygosity, but males have been found in limited numbers in other populat ions which are homozygous. DNA fingerprinting now reveals that the Belize p opulation has remained heterozygous, with a high proportion of males (20-25 %), for several years. In addition, two newly discovered populations with a lower percentage of males (1-2%) are reported from the Bahamas and Hondura s. One of these populations (Bahamas) consists of homozygous clones, while the other (Honduras) displays a limited proportion of heterozygosity. The H onduras population is only the second outcrossing population known in this species, and the limited heterozygosity seen here may reflect the lower pro portion of males.