Tuesday, June 19, 2012

Mimic Shark?

How bloody cool is this!

First record of potential Batesian mimicry in an elasmobranch: do juvenile zebra sharks mimic banded sea snakes?
Christine L. Dudgeon and William T. White


Various forms of mimicry have been recorded in a large number of marine fishes; however, there have been no records of mimicry for any elasmobranch species.

We propose that the distinctly banded neonates of the zebra shark (Stegostoma fasciatum) are Batesian mimics of banded sea snakes (Elapidae).
Observations of banded juveniles of S. fasciatum swimming close to the surface strongly resemble banded sea snakes in colour and body form as well as the undulatory swimming movements. Sea snakes are venomous and are known to defend themselves against predators. Although several shark species prey on them, most species appear to avoid sea snakes as prey items. Juvenile S. fasciatum possess a very long, single-lobed caudal fin that remarkably resembles the broad, paddle-like tail of sea snakes. This may be an adaptation enabling this species to mimic sea snakes, at least in the earliest life stages.
There is a need for empirical testing of the hypothesis that juvenile S. fasciatum is a true example of Batesian mimicry, but here we provide evidence that suggests this may be the first example of mimicry in an elasmobranch species.

Yes so far this is only a hypothesis!
But is it plausible?

The paper offers a variety of good reasons, and here's the picture from the paper that I find totally compelling.

Fig. 1. Colour pattern changes in Stegostoma fasciatum: (a) 40.5 cm total length (TL) newborn from Bahrain (photo: J. Randall); (b) 58 cm TL from Bahrain (photo: J. Randall); (c) ,220 cm TL adult from northern Australia (photo: CSIRO). (d) Newborn Stegostoma fasciatum swimming at the surface in shallow inshore, turbid waters off the Kimberley coastline of north-western Australia (photo: M. Pember); (e) a sea snake on the swimming on the surface in Shark Bay, north-western Australia (photo: W. White).

Wouldn't testing that hypothesis be the coolest Masters thesis, ever?
Here's a possible recipe, right from the paper.

Initially, it is necessary to isolate which of the banded sea snakes is/are the model species as well as which of the potential predators the deception is aimed towards.
It will then be possible to design experiments that test the behavioural and physiological responses of the predators to the model and mimic species as well as to target ecological and evolutionary data collection.
Whether juvenile zebra sharks are truly Batesian mimics of sea snakes and present the first example of mimicry in an elasmobranch remains to be proven; however, we believe that there is good evidence, as presented here, to support such a conclusion.

Any takers?
Fiji: we got the Shark and at least one Banded Sea Krait right here - and by the way, check out its tail: does it mimic the head?

Questions questions! :)

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