Flóra Szabó

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1 INTRODUCTION Vertebrates exhibit an impressive diversity of reproductive modes, including variation in modes of parturition and nutrient provision to the developing offspring (Blackburn, 1999; Kupfer et al., 2016; Pyron & Burbrink 2013; Vági et al., 2019). In egg-laying (oviparous) species, the embryos develop mostly externally. This form of reproduction is common in chondrichthyes, teleosts, amphibians, reptiles, and birds.