Snail dispersal by birds

There have been some previous reports on snail dispersal suggested by means of birds (e.g. Gittenberger et al., 2006). Now Japanese biologists have studied the survival rate of snails digested by birds and found a surprising 15% for the micro-snail Tornatellides boeningi (Wada et al., 2011). In this case they explain the dispersal of this snail within an isolated island in the Ogawasama group in the western Pacific.

Schermafbeelding_2011-07-12_om
It may be noticed that the example of Wada et al. relates to micro-snails. If larger species are at stake, it would be more likely that only juveniles may be digested. Hence the rate of success during the establishing phase after a successful dispersal is expected to be lower than in the case of adults, as the juveniles first need to mature before they start to reproduce.

However, this is an interesting result as it could explain long distance dispersal and establishment (LDDE) events more easily. Of course this will be related to the migration route of birds, the speed of flying and the duration of the passage in the digestive channel of the birds. In the case described by Wada et al., the snails were evacuated 30-40 minutes after digestion, which makes the distance a bird can travel meanwhile rather limited. The alternative to explain longer distances seem to be attachment of egg capsules to bird legs.

It is all a matter of chance, but if time is long enough chances for such events are more than zero.

Update:
Cadée (1988, 2011) described estuarine species (Hydrobia ulvae) passing the digestive system of waterfowl. This is an operculate species, but the reported survival rate is similar to Tornatellides: 13-16%. 
Afbeelding_1_09-12-18
References:
Cadée, G.C., 1988. Levende wadslakjes in bergeend faeces. – Correspondentieblad Nederlandse Malacologische Vereniging 234/244: 443-444.
Cadée, G.C., 2011. Hydrobia as “Jonah in the whale”: shell repair after passing through the digestive tract of shelducks alive. – Palaois 26: 245-249.
Gittenberger, E., Groenenberg, D.S.J., Kokshoorn, B. & Preece, R.C., 2006. Molecular trails from hitch-hiking snails. – Nature 439: 409.
Wada, S., Kawakami, K. & Chiba, S., 2011. Snails can survive passage through a bird’s digestive system. – Journal of Biogeography (Early View; doi:10.1111/j.1365-2699.2011.02559.x).
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