Can a threshold value be used to classify chondrichthyan reproductive modes: systematic review and validation using an oviparous species

The maternal-embryonic nutritional relationship in chondrichthyans has been poorly explored. Consequently, accurately discerning between their different reproductive modes is difficult; especially lecithotrophy and incipient histotrophy. This present study is the first to assess changes in mass thro...

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Bibliographic Details
Published in:PloS one 2012-12, Vol.7 (12), p.e50196-e50196
Main Authors: Frazer, Holly A, Ellis, Megan, Huveneers, Charlie
Format: Article
Language:English
Subjects:
Animals
Biology
Chondrichthyes
Earth Sciences
Eggs
Elasmobranchii
Elasmobranchii - classification
Embryogenesis
Embryonic development
Embryonic growth stage
Embryos
Endangered & extinct species
Female
Heterodontus portusjacksoni
Moisture content
Nutrition
Organic matter
Oviparity
Phylogenetics
Reproduction - physiology
Rounding
Scyliorhinus canicula
Sharks
Squatinidae
Studies
Validation Studies as Topic
Viviparity, Nonmammalian - physiology
Water content
Wildlife conservation
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Summary:The maternal-embryonic nutritional relationship in chondrichthyans has been poorly explored. Consequently, accurately discerning between their different reproductive modes is difficult; especially lecithotrophy and incipient histotrophy. This present study is the first to assess changes in mass throughout embryonic development of an oviparous chondrichthyan other than Scyliorhinus canicula. Heterodontus portusjacksoni egg cases were collected and used to quantify the gain or loss of wet mass, dry mass, water content, inorganic and organic matter from freshly deposited eggs (without macroscopically visible embryos) to near full-term embryos. A loss in organic mass of ~40% found from this study is approximately double the values previously obtained for S. canicula. This raises concerns for the validity of the current threshold value used to discern between lecithotrophic and matrotrophic species. Accordingly, 26 studies published in the primary literature between 1932 and 2012 addressing the maternal-embryonic nutritional relationship in sharks were reviewed. Values for changes in mass reported for over 20 different shark species were synthesised and recalculated, revealing multiple typographical, transcribing, calculation and rounding errors across many papers. These results suggest that the current threshold value of -20% established by previous studies is invalid and should be avoided to ascertain the reproductive mode of aplacental viviparous species.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0050196