Embryonic diapause in the elasmobranchs

WALTRICK, D.; SIMPFENDORFER, C.; AWRUCH C. A.

Adelaide

Congreso; Australian Society of fish Biology; 2012

Embryonic diapause is a term used to describe a temporary ceasing or retardation of development at any stage of embryogenesis. This reproductive strategy is observed in several species of invertebrates and vertebrates. Particularly, in elasmobranchs embryonic diapauses has been reported in, at least, 13 species of rays from three different families and one species of shark. Most of these elasmobranch species undergo obligate diapause, which happens in every gestation cycle. However, it is suspected that few species have the facultative type, which is dependent on external stimuli. The mechanisms controlling embryonic diapause among elasmobranch species are poorly understood. The physiological stimulus that trigger diapauses in elasmobranchs remains unknown, but possibly involve environmental cues and steroid hormones as in other vertebrate species. Possible hypothesis for species to have this form of reproductive strategy includes: (I) diapause results from segregation of sexes; and (II) the extension of gestation my allow parturition to occur in more favourable conditions (temperature, availability of food and/or other resources) and avoid newborns mortality. Even though embryonic diapause offers many advantages for the species, the occurrence of this reproductive strategy is not universal among species of the same group, closely related species do not always exhibit this strategy and hormonal control also differs from species to species, leading to believe that it has evolved independently within taxonomic groups.