Ho; Phytogeny and biogeography of Merluccius 



99 



Figure 7 



Area summary cladogram of hakes (Merliicrius) with ancestral 

 species (A-H). For abbreviation of species names see Figure 5. 



Panamanian Isthmus and through the Drake Passage. 

 Assertion (1) agrees with the proposal of Ho (1974) con- 

 cluded from a work on host-specific copepod parasites 

 of hake, but it contradicts Inada (1981) and Kabata and 

 Ho (1981) who suggested otherwise. Assertion (3) is 

 roughly the same as those suggested by Inada (1981) 

 and Kabata and Ho (1981), differing only in the details. 

 However, the 2nd assertion is a new discovery; this 

 track has never been proposed. 



Inada (1981) speculated that hakes had migrated out 

 of the western Atlantic only once, when they dispersed 

 to the southern hemisphere during the Pliocene over 

 the submerged Panamanian Isthmus. He believed that 

 the hakes could not have migrated to the South Atlan- 

 tic along the coast of Brazil because the low salinity 

 in the estuarine area of the Amazon River would have 

 acted as a natural barrier to their -dispersal. However, 

 the Amazon River estuary was not an effective deter- 

 rent to hake dispersal in the early Tertiary. In work 

 on the coevolution between freshwater stingrays and 

 helminth parasites, Brooks et al. (1981) concluded that 

 the Amazon Basin became a separate eastward-flowing 

 entity in the Miocene. Moreover, Damuth and Kumar 

 (1975) reported that the Brazilian plate developed a 

 geosyncline downfold when the Andes began to fold 

 up in the Pliocene, and, as the result of this lowering 

 of the eastern side of the plate, the water from the land- 

 locked sea (of the Pre-Amazonas) started to flow 

 eastwards to the Atlantic. Therefore, during and 

 prior to the Miocene the salinity in this area could not 

 have been as low as it was in the Pliocene and the 

 ancestral hakes could have migrated to the South 

 Atlantic along the coast of Brazil. If true, migration 



pathways of hake would be different from those pro- 

 posed by Inada. 



Both the works of Inada (1981) and Kabata and Ho 

 (1981) indicated that European hake M. merluccius 

 occur in the region of the North Atlantic inhabited by 

 the original stock (Fig. 1). However, the phylogenetic 

 hypothesis (Fig. 3) implies that European hake is the 

 most derived species among the eastern Atlantic hakes, 

 and, consequently, could not be the one occupying the 

 original habitat (Hennig 1966, Wiley 1981). 



Before discussing further the biogeography of hake 

 inferred from the phylogenetic hypothesis given in Fig- 

 ure 7, some points about the nature of the movement 

 and range expansion of hake need to be explained. 



Hakes of the genus Merluccius are coastal inhabi- 

 tants occurring in the waters above the continental 

 shelf and slope. Most species exhibit a seasonal on- 

 shore-offshore bathymetric migration correlated with 

 water temperature. Adults and juveniles move inshore 

 during the spring. When winter cooling occurs on the 

 shelf, they migrate to warmer waters on the continen- 

 tal edge and slope (Grinols and Tillman 1970). Addi- 

 tionally, the silver hake and Pacific hake apparently 

 undertake a latitudinal migration (Bailey et al. 1982, 

 Leim and Scott 1966, Nelson 1969). During the fall they 

 move southward and then return to more northerly 

 waters during the late spring. Clearly, paleotempera- 

 ture changes in the ocean could be one of the factors 

 in altering the limits of the distribution of hake in the 

 past: they expanded onto the continental shelf or slope 

 of lower latitudes when there was a cooling trend, and 

 retreated to the waters of higher latitudes when the 

 cooling trend subsided. 



The copepod parasite Neohrachiella iyjsidivsd Ingeni- 

 formes has been recorded from widely separated 

 species of hake, e.g., the silver hake off the coast of 

 Florida and the New Zealand hake in the western South 

 Pacific (Kabata and Ho 1981). Since this parasite is 

 found mostly on the adult hake, rarely on juveniles and 

 never on the larvae, the dispersal of this parasite from 

 North America to New Zealand via the South Ameri- 

 can coast must have been effected by the adults. 

 Besides, this parasite belongs to the family Lernae- 

 opodidae which is noted for a brief stage of free-living 

 during development. It is logical to assume that adult 

 hakes, not larvae, are responsible for extending their 

 range. 



The offshore hake M. albidus, primarily an inhabi- 

 tant off the U.S. east coast and in the Gulf of Mexico 

 and Caribbean (Inada 1981), does not share its clade 

 with any extant hake (Fig. 7). The distributional ranges 

 of its ancestor must have waxed and waned like other 

 ancestral hakes with the changes of ocean temperature 

 and sea level. However, it is very likely that this 

 stock of hake stayed mostly in the Gulf of Mexico and 



