Biology Reference
In-Depth Information
Figure 9.1. Phylogenetic tree and historical migration routes of Anguilla spp. modified
fromAoyama et al.(
2001
) and Tsukamoto et al.(
2002
). Note: likely origin of Anguilla
in the western Pacific. One explanation for the reduced diversity of eel parasites in the
Atlantic may be a loss of parasites during migration, although a temperature effect
(increased species richness at low latitudes) may also be an important factor. With the
permission of the authors.
particular of trematodes specific to European eels, compared with
A. reinhardti.MarcogieseandCone(
1998
)alsoconcludedthat
reduced diversity of parasites of Nova Scotia (Canada) and Europe
relative to diversity of Australian eels is due to the shorter time avail-
able for the acquisition of (particularly specialist) parasites in the
Atlantic. Nevertheless, the tropical/subtropical habitats in Australia
versus the cold-temperate ones in Canada and Europe may also play a
role, as pointed out by Kennedy (
1995
).
In summary, then, richness of parasite communities of Anguilla spp.
cannot be explained by the assumption that a limit to diversity has been
reached, determined by the number of species that can be accommo-
dated, and that this limit differs between regions; it can only be explained
in two ways, i.e., firstly by historical contingencies, and secondly by
temperature differences in the various regions. Concerning the first
point, species richness in Atlantic eels may have been reduced as the result
of very long distance dispersal over evolutionary time, and, given enough
evolutionary time, a greater diversity is likely to develop at least in
Atlantic eels, but possibly also in Indo-Pacific ones. Concerning the
second point, as pointed out by Kennedy (
1995
), differences in tempera-
ture may be important: a greater species pool in the tropics may have led
to an increase in the richness of eel parasites, at least of generalist species
(see Chapter
9
(Latitudinal diversity gradients)).
