Biology Reference
In-Depth Information
Figure 9.7. Extant geographic relationships of the scombrid fishes Scomberomorus spp.
and Grammatorcynus spp. and their copepod and monogenean parasite species.
Numbers indicate species of fish/species of copepods/species of monogeneans
(in parantheses: only endemic species). Note the primary center of richness in the
tropical western Pacific, and a secondary center in the tropical western Atlantic, as
well as the effective barrier to historical dispersal represented by the eastern Pacific.
Reprinted from Rohde, and Hayward (
2000
), with permission from Elsevier.
some parasites from fish in high-diversity regions, which markedly
increased the relative species richness of parasites of these fish, whereas
acquisitions in the opposite direction were very rare. Considering the
relative species richness of individual fish species, the trend is even clearer:
the fish species with the greatest number of ectoparasite species has five
times more parasite species than the poorest ones, and even when fish of
similar size and geographical (latitudinal) ranges are compared, species
richness differs by a factor of more than two. This can only be explained
by historical events. In other words, there is no evidence that parasite
species numbers are, in some way, determined by different carrying
capacities of fish species for parasites, or by environmental factors.
A word of caution is necessary, however. Many ectoparasites of fishes
have a high degree of host specificity, which probably makes historical
events particularly important. Many endoparasites are less specific and may
be acquired more easily after host migration into new habitats. This was
shown for endoparasites of the rainbow trout, Oncorhynchus mykiss,andthe
brown trout, Salmo trutta. Populations introduced into new habitats had no
fewer parasite species than those in the original locations, and diversity was
even perhaps slightly greater (Poulin and Mouillot
2003
).
In summary, historical events, such as the erection and disappearance of
barriers, are important in determining richness of marine fish/parasite
