Twins! Microsatellite analysis of two embryos within one egg case in oviparous elasmobranchs

Abstract

Elasmobranchs display various reproductive modes, which have been key to their evolutionary success. In recent decades there has been a rise in the number of reported cases of foetal abnormalities including fertilised, double-embryos held within one egg capsule, hereafter referred to as twins. Previously, the occurrences of twin egg cases have been reported in two batoid and one shark species. We report the first cases of twins in three species of oviparous elasmobranchs: the undulate ray (Raja undulata), the nursehound (Scyliorhinus stellaris), and the small-spotted catshark (Scyliorhinus canicula). We investigated the genetic relationships between the twins in S. stellaris, and S. canicula using microsatellite markers. Whilst the S. stellaris twins displayed the same genotypes, we found that the S. canicula twin individuals arose through heteropaternal superfecundation. This is the first reported incidence of such a paternity in elasmobranchs. The relationship between environmental change and reproductive strategy in elasmobranchs is unclear and further research is needed to determine its effect on the prevalence and mechanisms of formation of elasmobranch twins.

First evidence of multiple paternity and hybridisation in Australian sawsharks

“…Potential benefits of multiple paternity include avoiding inbreeding or genetically incompatible mates, increased fecundity, and creating genetically diverse offspring (Jennions and Petrie 2000;Neff and Pitcher 2005;Slatyer et al 2012). In elasmobranchs, multiple paternity has been documented in both viviparous (Rossouw et al 2016) and oviparous species (Chevolot et al 2007;Griffiths et al 2012;Hook et al 2019) and appears to be common within the group. Indeed, multiple paternity is believed to be the ancestral condition of all elasmobranchs (Lamarca et al 2020).…”