Isotopic (δ¹⁵N) relationship of pregnant females and their embryos: Comparing placental and yolk‐sac viviparous elasmobranchs

Abstract

Nitrogen stable isotopes ratios (δ 15 N) 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 15 N enriched compared to the same tissues in the pregnant female, using the difference in δ 15 N (Δδ 15 N) between embryo and adult. Mean Δδ 15 N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus, embryo liver tissue was significantly 15 N enriched in comparison with liver of the pregnant female (Δδ 15 N mean = 1.22‰), whereas embryo muscle was 15 N depleted relative to the muscle of the pregnant female (Δδ 15 N mean = −1.22‰). Both species presented a significant positive linear relationship between Δδ 15 N and embryo total length (L T). The results indicated that embryos have different Δδ 15 N depending on their reproductive strategy, tissue type analysed and embryo L T .