Plasticity in the reproductive strategies of the Southern Ocean ommastrephid squid Todarodes filippovae : a morphometric, lipid and fatty acid approach

Squid are important trophic links and integral components of the marine ecosystem in the Southern Ocean. Moreover, their life histories have been shown to be extremely plastic thus enabling them to respond quickly to changes in the environment. As a result squid are able to survive and reproduce without the threat of population collapse or annihilation. An examination of female reproductive plasticity in the poorly understood ommastrephid species, Todarodes fifippovae, revealed both annual variation in condition and gonad investment. This was most likely due to differing oceanographic conditions between the years and seasons investigated. Furthermore, higher gonad investment in females caught in the winter was possibly due to the fact that spawning coincided with the forthcoming spring bloom. It is suggested that T. fifippovae may spawn in a number of slope and seamount regions across its distributional range. On the terminal versus multiple spawning continuum, results from this study suggested that T. filippovae was towards the multiple spawning end. However, some degree of plasticity was associated with this spawning strategy, with one autumn sample of mature females exhibiting a shift away from the multiple spawning end of the continuum. Female individuals of T. filippovae seemed to fuel maturation through the direct acquisition of food. Although there was evidence of a small trade off between digestive gland lipid and mantle lipid with maturation, there was no evidence that lipid in the digestive gland was being mobilised as a significant source of energy for oogenesis. Rather it appears that lipid in the digestive gland was excess to maternal nutritional requirements for egg development. The major differences in the relative levels and amounts of lipid classes and fatty acids between the immature and mature ovaries of females signified the important nutritional role of lipid for the young of this species. The role of lipid in the ovary and oviduct was structural rather that as an energy reserve, with maternal provisioning of DHA and EPA most likely critical for the growth and survival of the embryo and rhynchoteuthion. The fatty acid profile of the mature ovary and oviduct varied little temporally suggesting that the quality of the egg was conserved. However, seasonal differences in lipid content and lipid class may have reflected the reproductive plasticity of female individuals of T. filippovae in response to environmental conditions at time of capture.