‘Superbull’ males: what role do they play and what drives their appearance within the Doryteuthis gahi Patagonian Shelf population?

Cephalopod populations exhibit high variability in life history characteristics such as longevity and size-at-age. Here, we aim to understand how characteristics of a newly-described ‘super-bull’ male morph in Doryteuthis gahi populations (Patagonian shelf) arise and whether there is a selective advantage. At the population level it is speculated that super-bulls provide temporal and spatial connectivity, but individual benefit is less obvious. Age structure and reproductive potential of males was investigated to determine whether super-bulls could provide connectivity. Environmental variables affecting size-at-age were explored to ascertain whether morphological differences were primarily phenotypically driven. Super-bulls from the autumn spawning cohort were significantly older than the residual population, with added longevity potentially leading to spawning with the following cohort. A reduction in relative testis weight was apparent in super-bulls, but spermatophore production remained high. Generalised additive mixed models (GAMMs) indicated temperature, location and hatch year had significant effects on size-at-age. Weak correlations between warm El Niño southern oscillation (ENSO) phases and super-bull abundance were found. Results suggest super-bulls provide temporal connectivity and arise through phenotypic plasticity, likely providing connectivity as a side effect of body shape and size rather than a genetically selected advantage.