Biogeographic Hierarchical Levels and Parasite Speciation

The historical biogeography of freshwater fish helminth parasites is linked to speciation. It is well recognized and documented that bursts of speciation are often limited to certain periods of geological time (Eldredge & Gould 1972; Gould & Eldredge; 1977, Gould, 2002; Hoberg & Brooks, 2008) and is highly dependent on the space in which it occurs (Brooks & McLennan, 2002; Hoberg & Brooks, 2008; Lieberman, 2003; Vrba, 2005). This holds for freeliving organisms and parasites as well (Brooks & McLennan, 1993b; Hoberg & Brooks, 2008). Empirical evidence supports the contention that freshwater fish helminth parasites have mainly speciated allopatrically through two processes, vicariance and dispersal via host switching when the host has moved into novel areas, i.e. dispersal across pre-existing barriers (physical change sensu Vrba, 2005) (Brooks and McLennan, 1991, 1993b, 2002; Choudhury & Dick, 2001; Poulin, 1998). This suggests that the evolutionary biology of helminth parasites should have a strong biogeographical component, one that acts above the species level and to a lesser extent may have been driven by coevolutionary phenomena (Brooks and McLennan, 2002; Pérez-Ponce de León & Choudhury, 2005; Hoberg & Brooks, 2008). It is currently recognized that two processes, linked cyclically in time and space, have produced these patterns in parasite historical biogeography: taxon pulses (TP; Erwin, 1981; Hoberg & Brooks, 2008; 2010) and ecological fitting (EF; Janzen, 1985; Hoberg & Brooks, 2008, 2010).