Tag Archives: dispersal

Long distance dispersal

The malacofauna of oceanic islands often shows a high endemism, but the origin of the fauna is many times obscure. Hendriks et al. (2019) have published a paper on Borneo land snails that is interesting in this context.

Schermafbeelding 2019-08-08 om 11.00.55
The abstract reads as follows:
Aim: Islands are often hotspots of endemism due to their isolation, making colonization a rare event and hence facilitating allopatric speciation. Dispersal usually occurs between nearby locations according to a stepping-stone model. We aimed to reconstruct colonization and speciation processes in an endemic-rich system of land- based islands that does not seem to follow the obvious stepping-stone model of dispersal.
Location: Five land- based habitat archipelagos of limestone outcrops in the floodplain of the Kinabatangan River in Sabah, Malaysian Borneo.
Methods: We studied the phylogeography of three species complexes of endemic land snails, using multiple genetic markers. We calculated genetic distances between populations, applied beast2 to reconstruct phylogenies for each taxon and subsequently reconstructed ancestral ranges using ‘bioGeoBEARS’.
Results: We found spatial- genetic structure among nearby locations to be highly pronounced for each taxon. Genetic correlation was present at small spatial scales only and disappeared at distances of 5 km and above. Most archipelagos have been colonized from within the region multiple times over the past three million years, in 78% of the cases as a result of long-distance dispersal (LDD) or dispersal from non-adjacent limestone outcrops. The flow of the main geographical feature within the region, the Kinabatangan River, did not play a role.
Main conclusions: Phylogeographic structure in these Bornean land snails has only partly been determined by small-scale dispersal, where it leads to isolation- by- distance, but mostly by LDD. Our results demonstrate that island endemic taxa only very locally follow a simple stepping-stone model, whilst dispersal to non-adjacent islands and especially LDD, is most important. This leads to the formation of highly localized, isolated “endemic populations” forming the onset of a complex radiation of endemic species.“.

Their results may be a helpful context when researching the malacofauna of Neotropical archipelagos like Juan Fernández, Galápagos, Cocos Islands, and even in the Caribbean.

Reference:
Hendriks, K.P. et al., 2019. Phylogeography of Bornean land snails suggests long-distance dispersal as a cause of endemism. – Journal of Biogeography, 46 (5):932-944. DOI: 10.1111/jbi.13546

Passive dispersal mechanisms

An interesting paper just appeared about passive snail dispersal mechanisms. Simonová et al. (2016) carried out an experiment with European forest snails and birds in an aviary to find out about survival rates of snails being eaten by birds or by being carried away by attachment to the bird’s body.

Their abstract is: “It is well known that land snails can be dispersed by birds, both by attachment to the body (ectozoochory) and by passing intact and alive through the bird’s digestive tract (endozoochory). Endozoochory has, however, only been recorded for very small species. We examined the possibility that larger species (up to c. 17 mm in maximum shell dimension) could survive passage through a bird’s digestive system. Live Alinda biplicataCochlodina laminata (both Clausiliidae) and Discus rotundatus (Discidae) were fed to 10 bird species (Corvidae, Turdidae, Sturnidae and Columbidae) in 14 experimental trials. Of 720 snails offered, 14 passed intact through the birds, of which nine were alive (eight clausiliids and one D. rotundatus); thus more than 1% of all snails offered survived ingestion. In an additional experiment, some A. biplicata and C. laminata remained attached to birds’ legs by pedal adhesion in simulated flight trials where the birds’ legs oscillated at the maximum rate achieved during flight”. It must be noted that faces were collected between 20 and 26h after offering the snails to the birds.

Simonova

These results are a pointer to the possibility of passive dispersal of these species. No doubt the same applies for species of snails and birds in other parts of the world. With regard to the Neotropical Realm, this mechanism could be a hypothesis in those cases where geology makes vicariance unlikely. However, for long-distance dispersal survival rates after prolonged times should be investigated. This as addition to the final conclusion of the paper: “More experiments with a wider range of snail and bird species are clearly desirable”.

Reference:
Simonová, J., Simon, O.P., Kapic, S., Nehasil, L. & Horsák, M., 2016. Medium-sized forest snails survive passage through birds’ digestive tract and adhere strongly to birds’ legs: more evidence for passive dispersal mechanisms. — Journal of Molluscan Studies (2016) 1–5. doi:10.1093/mollus/eyw005