Relationships between heterozygosity, growth parameters and age in the common pandora Pagellus erythrinus (Sparidae) in the Gabes Gulf (Tunisia)
Résumé
The relationship between heterozygosity and age, as well as growth-related traits, was explored in the common pandora Pagellus erythrinus, a sparid fish subjected to commercial exploitation in the Mediterranean Sea. Allozyme electrophoresis was used to quantify the levels of heterozygosity of 238 adult fish from 3 to 7 yr old, aged by means of otoliths and captured in the Gabes Gulf, located along the south-eastern coast of Tunisia. Analyses were conducted by using individual single-locus and multi-locus heterozygosity and 4 growth-related parameters-standard length, total body weight, otolith length and otolith weight-as well as 2 measures of condition (condition factor and relative condition factor). For the 4 growth-related parameters and 2 condition parameters analyzed at 8 polymorphic loci, heterozygotes had higher average values than homozygotes in 36 out of 48 comparisons. However, since these 6 biometric parameters are highly correlated, this proportion should not be considered globally as strong evidence of a heterozygosity-fitness correlation (HFC). Interpreting these data on a per parameter basis, only otolith weight appeared significantly and positively correlated with multi-locus heterozygosity. Thus, although there was evidence for HFC, it appeared relatively weak for the growth para meters analyzed and may have arisen by chance. The results we obtained relative to survival are more convincing. Although cohorts did not appear genetically differentiated and the whole sample did not display any internal structure after a Bayesian analysis with the STRUCTURE software, multi-locus individual heterozygosity was significantly and positively correlated with fish age. This suggests better survival of heterozygotes and establishes the presence of a heterozygosity-fitness correlation in the Tunisian population of the common pandora.