Relationships among morphological traits, body weight, and gonadal development in juvenile Strongylocentrotus intermedius

Abstract

To investigate the effects of morphological traits and body weight on gonadal development in juvenile Strongylocentrotus intermedius, we performed correlation, path, histological, and sex-specific gene expression analyses. Live body weight (BW), test diameter (TD), test height (TH), gonadal development score (GDS), and sex-specific gene (EBR1 and bindin) expression levels were determined in six-, seven- and eight-month-old juveniles. Path correlation coefficients, correlation indices (R2), and coefficients of determination were then calculated, with GDS as the dependent variable and the other morphological traits (or BW) as independent variables. Our results indicated that TD, TH, and BW were positively correlated with GDS (P < 0.01) in S. intermedius at all of the ages tested; that TD was the most important indirect factor affecting the GDS of juvenile S. intermedius (R2 > 0.85); and that the indirect effect of TD on GDS was age-dependent. In addition, we found that juvenile S. intermedius with TDs greater than 10 mm were sex differentiated, because at this size reproductive cells (gametes) began to appear and sex-specific genes began to be differentially expressed. TD, TH, BW, and GDS did not differ significantly between males and females. Our results clarified the correlations between various morphological traits (or BW) and gonadal development in juvenile S. intermedius, and our models predicting GDS might be useful tools for S. intermedius aquaculture and for sex-control-based selective S. intermedius breeding programs.