Dr. Urzua-Osorio, Angel

In marine invertebrates, the modes of development at early stages are related to the type and capacity of larval feeding to achieve growth. Therefore, studying the factors that determine larval feeding strategies can help to understand the diversity of life histories and evolution of marine invertebrates. The polychaete Boccardia wellingtonensis is a poecilogonous species that encapsulates and incubates its offspring. This species produces two types of larvae: (1) larvae that do not feed within the capsule and hatch as planktotrophic larvae (indirect development), and (2) adelphophagic larvae that feed on nurse eggs and other larvae inside the capsule to hatch as advanced larvae or juveniles (direct development). Otherwise, the larval types are indistinguishable at the same stage of development. The non-apparent morphological differences between both types of larvae suggest that other factors are influencing their feeding behavior. This work studied the potential role of the activity of 19 digestive enzymes on the different feeding capacities of planktotrophic and adelphophagic larvae of B. wellingtonensis. Also, differences in larval feeding structures and the larval capacity to feed from intracapsular fluid were evaluated by electron and fluorescence microscopy. Results showed that both types of larvae present similar feeding structures and had the capacity to ingest intracapsular fluid protein. Adelphophagic larvae showed overall the highest activities of digestive enzymes. Significant differences between larval types were observed in nine enzymes related to the use of internal and external nutritional sources. Given that larval feeding is closely related to larval development in species with encapsulation, this work supports that the study of the digestive enzymatic machinery of larvae may contribute to understanding the evolution of developmental modes.

Pleuroncodes monodon is an important fishery resource and key species from the Southeastern Pacific. During its prolonged reproductive period (from February to December), ovigerous females are exposed to seasonal variation in environmental factors (e.g. temperature and food availability), with higher levels of these environmental parameters during summer and lower in winter, and must adjust their biochemistry to ensure their own survival and that of their embryos. The aim of this study was to analyse seasonal changes in the biochemical composition of ovigerous females and their eggs. The data show that the content of lipids, proteins and organic matter in the hepatopancreases of females was significantly higher in winter than in summer. Similarly, the lipid content of the eggs was significantly higher in winter than in summer, yet the protein content of the eggs had the opposite pattern with greater values found in summer. Consistent with the ‘reproductive energetic model’, the initial and final energy produced by the hepatopancreas showed significant seasonal variations, whereas female investment in egg production (in absolute values) did not show significant seasonal differences. The seasonal differences observed in the biochemistry, organic matter and energy content of the female hepatopancreases may be related to the storage of energy for growth and reproduction. Furthermore, the seasonal variation in the content of lipids, proteins and energy in eggs is likely related to embryogenesis and larval hatching in function with environmental conditions. Seasonal variation in the biochemical composition of P. monodon has direct effects on the marine food web and also upon fisheries.

Environmental variables are pivotal factors for the condition of marine invertebrate species with a complex life cycle, influencing larval biochemical composition, and therefore, indirectly affecting later benthic stages. We herein explore the physiological responses of the fishery resource the red squat lobster (Pleuroncodes monodon) under contrasting environmental conditions of seawater surface temperature and planktonic food availability in the Humboldt Current System (HCS), through the analysis of larval condition and its consequences in the HCS. Larval condition was measured as dry weight, biochemical composition and fatty acids profile at hatching during ‘late summer’ (i.e. March) and ‘early winter’ (i.e. June). Larvae hatching from larger eggs produced in winter months showed a higher size, dry weight and a higher content of bioenergetic fuel (i.e. lipids and essential fatty acids) compared to those from larvae hatching in summer months. Temperature and food availability can to be key driving factors favouring an evolution of temporal variability in larval condition of the red squat lobster. These physiological adaptations provide an extension of the reproductive period of P. monodon, specifically planktonic larval development during ‘early winter’, characterized by a period with restricted food availability and lower temperatures than ‘late summer’.