Larval growth, juvenile size and heterozygosity in laboratory reared mussels, Mytilus edulis
M.A. Del Rio-Portilla, A.R. Beaumont-2000
Journal of Experimental Marine Biology and Ecology,
254 (1): 1-17
Abstract:
Studies with marine bivalve juveniles have shown a
positive correlation between growth and allozyme multi-locus heterozygosity
(MLH), and, in some cases, between larval growth and juvenile growth, but
there has been little research on the relationship between allozyme
heterozygosity and larval growth. Larvae of M. edulis from different mating
systems (half-sib families with a single female, or a single male parent, a
reciprocal cross of two males×two females and two mass matings of 13×13
and 8×17 females and males, respectively) were reared in the laboratory and
selected into fast and slow growing groups when about 10--30% were
undergoing metamorphosis. Offspring were reared to the juvenile stage
(>3.00 mm) and both groups of each mating were electrophoresed and
genotyped at up to 12 allozyme loci. There was generally good agreement with
Mendelian inheritance (half-sibs and reciprocal cross) or the
Hardy--Weinberg model (mass matings). Null alleles were detected at the Odh
and Lap loci but there was no evidence that null allele heterozygotes grew
slower than other genotypes. Over all cohorts, juveniles from the fast
growing larval group were not significantly larger, or smaller, than
juveniles from the slow growing group which suggests that larval growth rate
may be independent of juvenile growth rate. This observation agrees with
some, but not all, earlier studies and has commercial relevance. Tests of
heterozygosity and juvenile shell length indicated no association between
average heterozygosity across all allozyme loci and the size of juveniles in
any cohort regardless of the mating system used or their larval growth rate.
The association between MLH and juvenile growth in bivalves is seldom
detected in cohorts from a limited genetic background. The lack of an
association between heterozygosity and size might therefore be expected in
the half-sib and reciprocal cross cohorts, but not in the mass matings. The
results argue against any significant association between heterozygosity and
larval size in mussels.
(Departamento de
Acuicultura, Centro de Investigación Científica y de Educación Superior
de Ensenada, Km. 107 Carr. Tijuana--Ensenada, Ensenada, Baja California
22800, Mexico)