Evolutionary transitions among egg-laying, live-bearing and maternal inputs in sharks and rays
Abstract
Sharks and rays are thought to have a large number of independent origins of live-bearing. We examined evolutionary transitions to live-bearing and maternal input to embryos in this subclass by optimizing reproductive characters onto a composite phylogeny. Egg-laying (40 per cent of all species) is the likely ancestral reproductive mode for this clade, and there is evidence that live-bearing has evolved independently 9–10 times and maternal input 4–5 times. Most transitions (12–15) have been toward live-bearing with provisioning limited to yolk. These have occurred from egg-laying ancestors or live-bearing taxa that provide maternal input to embryos. Only 2–3 transitions have occurred in the other direction, i.e. away from yolk-only bearing. Egg-laying has evolved from live-bearing ancestors in skates, Rajidae (25 per cent of all species) and possibly in the zebra shark,Stegostoma fasciata. Thus, although there has been an overall trend toward the evolution of live-bearing in elesmobranchs, the evolution of additional maternal input has been extremely labile.
Keywords: Elasmobranch Oviparity Parental Care Phylogeny Reproduction Viviparity
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Selected References
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- Lund R. Viviparity and intrauterine feeding in a new holocephalan fish from the lower carboniferous of montana. Science. 1980 Aug 8;209(4457):697–699. doi: 10.1126/science.209.4457.697. [DOI] [PubMed] [Google Scholar]
- Martin A. P., Naylor G. J., Palumbi S. R. Rates of mitochondrial DNA evolution in sharks are slow compared with mammals. Nature. 1992 May 14;357(6374):153–155. doi: 10.1038/357153a0. [DOI] [PubMed] [Google Scholar]