Is the geographic variation in size of American eel Anguilla rostrata elvers due to genetic differentiation?

Elvers of the American eel Anguilla rostrata collected along the east coasts of North America and Haiti exhibited geographic variations in age and size at time of arrival at estuaries and in duration of glass eels as well as their growth rate, based on a previous otolith study. They were able to divide into two groups: the northern large size group and the southern small size group. Thus, this study aims to understand whether the geographic variation in size of elvers is due to genetic differentiation by using microsatellite DNA. A total of 216 elvers of A.rostrata, collected from 6 estuaries along the Atlantic coasts of Central and North America,were used for the microsatellite DNA (6 loci) analysis. The genetic analyses indicated that there were no geographical isolation in genetic structures between the northern and southern groups (FCT = -0.00101; P = 0.507), although there was a weak significant difference among sampling locations (FST = 0.00538; P < 0.05). The differences were patchy and did not correspond to the geographic difference in size of elvers. Integrating the preious otolith daily growth increment (ring) analyses and genetic data suggested that the geographic variation in size of the elver at estuarine arrival between these two groups was not due to genetic differentiation but to the distance of the estuaries from the spawning ground and latitudinal difference in coastal water temperatures.