Ray broods have more than one father

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Scientists have shown for the first time that clutches of eggs from an egglaying marine ray can be fathered by multiple males.

Experts from the Department of Marine Benthic Ecology and Evolution at the University of Groningen in the Netherlands examined egg clutches in four wild-caught female Thornback rays and used a molecular technique to test their paternity.

By examining five highly variable parts of the genetic material, known as polymorphic satellite loci, the team were able to determine that each of the four clutches of eggs was sired by between four and six different males.

The results are the first to show in a ray, or any egglaying elasmobranch, that clutches of eggs can be fertilised by mulitple males - a biological process known as polyandry.

Thornback rays, Raja clavata, a marine species found around the British coast, are members of the skate family Rajidae, which are characterised by slow growth, late maturity, and low fecundity, producing around 140 eggs per year.

These traits are believed to make rays vulnerable to exploitation. It's not yet known whether the polyandry observed in Raja clavata is natural or has been triggered by the overexploitation of the species for food.

For more information see the paper: Chevolot M, Ellis JR, Rijnsdorp AD, Stam WT, Olsen JL (2007) - Multiple Paternity Analysis in the Thornback Ray Raja clavata L. J Hered. 2007 Sep 27.