Heritable variation of sex ratio in a polychaete worm

• Published in: Journal of evolutionary biology Vol. 9; no. 6; pp. 845 - 854
• Main Authors: Premoli, M. C., Sella, G., Berra, G. P.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-11-1996
• Subjects: Heritability of sex ratio; Ophryotrocha labronica; polychaete worm; sex determination; sex ratio
• ISSN: 1010-061X; 1420-9101
• DOI: 10.1046/j.1420-9101.1996.9060845.x

Ophryotrocha labronica is a gonochoristic polychaete worm whose sex determining mechanism and sex ratio control are supposed to be polygenic. From a lab population, whose sex ratio (i.e., proportion of males) was 0.5, the estimate of sex ratio heritability by offspring‐father regression was 0.54 ± 0.15 and by offspring‐mother regression was not significantly different from 0. Estimate of sex ratio repeatability between successive broods of a pair was 0.64 ± 0.33. Since female parents do not contribute in any way to the variability of sex ratio, sex ratio variation seems to be largely a paternal character. On the basis of these estimates we advance the hypothesis that in this species sex is determined by a multilocus genetic system, allowing the combined effects of a female major sex gene (which could give rise to a form of female heterogamety) and masculinizing modifiers. The hypothesis that the male sex has the least canalised sexual differentiation is supported by the observation that some old males developed oocytes.