Sexual dimorphism in feeding apparatus and niche partitioning in juvenile jumbo squid Dosidicus gigas

ABSTRACT: In a wide range of sexually reproducing marine organisms, males and females coexist through niche separation to reduce intraspecific competition and maximize survival; however, sexual segregation in mesopelagic cephalopods is poorly understood. To evaluate ontogenetic differences in diet and habitat partitioning between juvenile female and male jumbo squid Dosidicus gigas, we determined age and maturity, quantified stable isotope ratios along gladii bulk tissue and individual amino acids (AAs), and analyzed morphometrics of feeding apparatuses. D. gigas of 24 to 33 cm gladius length (GL) were collected in the northern Humboldt Current. Results showed that females had larger feeding apparatuses than males and higher δ15N values in bulk tissue and trophic AAs, but relatively similar source-AA δ15N values at same GLs. These results indicate that females catch prey of higher trophic position at earlier maturing stages than males, but tend to share similar habitat. This behavior likely reduces intraspecific competition, promotes ontogeny of sexual niche partitioning, and maximizes energy intake. Our study reveals that sexual segregation in feeding habits occurs in juvenile D. gigas during ontogenesis in the northern Humboldt Current, a strategy that can help elucidate its complex population dynamics and adaptation to fluctuating environmental conditions.