Long distance dispersal and evolution of talitrids (Crustacea: Amphipoda: Talitridae) in the northeast Atlantic islands

Abstract

A lineal “island” theory is proposed to account for the dispersal of marine/estuarine, supralittoral talitrid populations, both to and from isolated shore “islands” on continental and true oceanic islands. Evolution may occur following dispersal to shores that are contiguous with ecologically open habitats, inclusive of sub-tropical forest litter and caves. Specific hypotheses of the lineal “island” theory are therefore: the conventional wrack hypothesis 1 – direct from marine supralittoral wrack to subtropical forest litter; the driftwood hypothesis 2(a) – direct from marine supralittoral driftwood to subtropical forest litter; the driftwood hypothesis 2(b) – direct from the marine supralittoral driftwood to caves opening on a marine supralittoral; and the driftwood hypothesis 2(c) – direct from the marine supralittoral driftwood via caves to subtropical forest litter. Circumstantial evidence supporting each hypothesis is presented using the ecology and distribution data of the talitrid fauna of the northeast Atlantic islands, north of 25°N and south of 40°N, including the Canaries, Madeira and the Azores archipelagos. The currently known talitrid fauna of all these islands includes 15 species: seven endemic, subtropical landhoppers, two synanthropically introduced landhoppers, three wrack generalists, one sand-burrowing specialist, one specialist cavehopper, and one specialist driftwood hopper. Based on distributional data from the northeastern Atantic islands, specialist driftwood hoppers have a long distance dispersal capability, which makes them potential colonizers of distant oceanic islands. Talitrids provide an excellent model of dispersal and speciation, whose evolutionary pathways can be solved by modern genetic methods.

Keywords:

• talitrid dispersal
• evolution
• driftwood hoppers
• Canaries
• Madeira
• Azores

Acknowledgements

I acknowledge Jan Stock and Ed Bousfield for interesting discussions on the biology of talitrids over the years, which have helped shape my views of talitrid evolution. Blythe Chang kindly prepared Figure 1. I also thank Derek Iles, Alastair Richardson, Laura Pavesi, Martin Thiel, John Valentine and two anonymous reviewers for improving an earlier version.