Isotopic (Delta N-15) Relationship Of Pregnant Females And Their Embryos: Comparing Placental And Yolk-Sac Viviparous Elasmobranchs

Nitrogen stable isotopes ratios (delta N-15) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk-sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were N-15 enriched compared to the same tissues in the pregnant female, using the difference in delta N-15 (Delta delta N-15) between embryo and adult. Mean Delta delta N-15 was 2.17 parts per thousand in muscle, 4.39 parts per thousand in liver and 0.80 parts per thousand in blood. For P. glaucostigmus, embryo liver tissue was significantly N-15 enriched in comparison with liver of the pregnant female (Delta delta N-15 mean = 1.22 parts per thousand), whereas embryo muscle was N-15 depleted relative to the muscle of the pregnant female (Delta delta N-15 mean = -1.22 parts per thousand). Both species presented a significant positive linear relationship between Delta delta N-15 and embryo total length (L-T). The results indicated that embryos have different Delta delta N-15 depending on their reproductive strategy, tissue type analysed and embryo L-T.