In a general review of the phenomenon of hyperostosis in fishes, including those of the allopatrically
distributed and externally nearly identical species Caranx hippos (Linnaeus) (Atlantic Ocean) and C.
The study of introgression patterns of different characters through hybrid zones between allopatrically
diverged taxa provides insight into dynamic evolutionary processes.
Yet, even if species form allopatrically
they may produce viable and fertile hybrids when they later become sympatric.
Previously, hybrid zones were considered temporary transition zones resulting from secondary contact of allopatrically
diverged species, but arguments have been raised in favor of both the stability of hybrid zones (Moore and Buchanan 1985; Barton and Hewitt 1989) and of the potential role of primary origin (McNeilly and Antonovics 1968; Endler 1977).
However, these barriers are unlikely to be absolute and in cases where closely related taxa replace each other allopatrically
, the failure to spread is likely to partly result from biotic interactions.
John River drainage) resulted from the secondary contact of two monophyletic groups of whitefish that evolved allopatrically
in the Atlantic and Acadian refugia [TABULAR DATA FOR TABLE 1 OMITTED] during the last glaciation events (Bernatchez and Dodson 1990a).
In accounting for this pattern, by hard criteria the current data cannot discriminate between scenarios of primary selective influence along an environmental gradient versus secondary contact between allopatrically