AFLP diversity within and between populations of the Caribbean seagrass Thalassia testudinum (Hydrocharitaceae)

Abstract.

Genetic variation was assessed in the seagrass Thalassia testudinum from three regions of the Caribbean and north Atlantic using allozyme electrophoresis and amplified fragment length polymorphism (AFLP) analysis. Very low allozyme variability was detected among the 196 shoots analyzed from a range of sites in the San Blas region of Panama. AFLP markers detected high similarity (0.87) among the population samples surveyed from Bermuda and Panama across six AFLP primer pairs and over 260 banding positions. High levels of gene flow were detected between all the sites analyzed (N _m>1.7). Significantly complete genotypic similarity was observed between samples from Bermuda and Panama, indicating that long distance vegetative fragment dispersal is highly probable. Very low genetic differentiation between all sites, even Bermuda and Panama, some 2,700 km apart, agrees with other studies and is further evidence of a highly uniform gene pool in T. testudinum. High levels of genetic uniformity in T. testudinum may be related to long-term environmental change over its geographic range. While AFLP analysis proved useful in determining genetic variation in this seagrass, the application of co-dominant markers such as microsatellites will be more informative in determining the nature of genetic uniformity and its adaptive significance in T. testudinum.