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The neonatal nutritional strategy of a viviparous elasmobranch with extremely low reproductive output

Bianca de Sousa Rangel*, Nigel Edward Hussey, Yuri Niella, Luiz Antonio Martinelli, Aline Dal’Olio Gomes, Renata Guimarães Moreira

*Corresponding author:

ABSTRACT: Throughout evolutionary history, elasmobranchs have developed diverse reproductive strategies. Little focused work, however, has addressed how neonatal nutritional state is affected by differing degrees of maternal investment associated with these markedly different reproductive strategies. To investigate the effect of maternal investment on the nutritional quality of pups during the early-life history of an extreme viviparous elasmobranch, quantitative biomarkers analysis including lipids, fatty acids and stable isotopes were conducted. Using the cownose ray, Rhinoptera bonasus (histotrophic viviparous) as a model, we found that pups were initially born in a positive nutritional state, enriched in physiologically important essential fatty acids and nitrogen and carbon stable isotopes values (δ15N and δ13C), a result of maternal intrauterine transfer. A systematic decrease in some fatty acids and δ15N values, as well as a decrease in cholesterol with growth, confirmed that these substrates were derived from maternal resources and used in initial metabolic processes following birth. An observed increase in condition factor, plasma essential fatty acids and triglycerides/cholesterol ratio with increasing young body identified a progression towards successful independent foraging with pups not displaying marked nutritional deficiency or fasting phases. Our multi tracer approach allowed the identification of two size classes of young rays (<50 cm and <70 cm disc width) that displayed distinct physiological states. Since prenatal maternal investment is critical for offspring condition and to promote successfully foraging post birth, understanding the trophic ecology and physiological state of pups during their first year are critical factors to guide management and conservation within nursery grounds.