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.
Bibliographical noteThis work was funded by the Falkland Islands Government. Thanks are due to FCT/MCTES for financial support to CESAM (UID/AMB/50017/2019) through national funds and ERDF
co-financing, under the Partnership Agreement for the PT2020 and Compete 2020 programs.
This work was funded by the Falkland Islands Government. The study was conducted using E.U. Copernicus Marine Service Information. We are grateful to the scientific observers from the Falkland Islands fisheries department for sample collection and to the director of fisheries, John Barton, for supporting this work.
- population dynamics
- reproductive biology
- population structure
- southwest Atlantic