Several different analyses, including allele frequency
differences, amova and isolation by distance, revealed
weak large-scale geographical separation of L. setiferus
populations. The lack of substantial population structure
was not due to lack of polymorphism at the loci studied,
nor was it due to highly polymorphic loci obscuring
statistical analyses; there was no correlation between
heterozygosity and population differentiation. Large-scale
differentiation was far less pronounced than that detected
from mtDNA sequence data from white shrimp (A. Jackson,
pers. comm.). The different level of population structure
found with these two genetic markers stems probably from
the larger long-term effective population size measured by
nuclear DNA, slowing the appearance of the effects of
genetic drift by a factor of four.