98 



Fishery Bulletin 88|l). 1990 



Figure 5 



Examples of some most parsimonious cladograms of hakes {Merlur- 

 ciiis). All have 23 steps and a consistency index of 0.522. Abbrevia- 

 tion of species names: ALBl = albidus; ANGU = angustimanus; 

 AUST = aiistralis; BILI = bilinearis; CAPE = capensis; HUBB 

 = hubbsi; MERL = merlucciu.r, PARA = paradoxus; POLL = polli; 

 PROD = pradurtu.t; SENE = Keveiidlnisis. 



With currently available information, the tree in Fig- 

 ure 3 is considered to be the better hypothesis than the 

 other existing h>T30theses of hake phylogeny. Admit- 

 tedly, it has a high ratio of homoplasy (17/23 or 73.9%). 

 Such frequent homoplasy is somewhat undesirable in 

 a cladistic analysis. Nevertheless, using different sets 

 of characters (number of gill-rakers, vertebrae, and fin 

 rays), Inada (1981) identified five groups in his key to 

 the species of Merluccins, with four species {au^tralis, 

 bilinearis, hubbsi, polli) in two groups, two species 

 (gayi, senegalensis) in three groups, and one species 

 (capensis) in four groups. This repeated sharing of 

 many characters (high frequency of homoplasy) seems 

 to be the norm in Merluccius. 



Close examination of each of the 188 most parsi- 

 monious trees revealed that European hake M. merluc- 

 cius, Senegalese hake M. senegalensis, Benguelan hake 

 M. polli, shallow-water cape hake M. capensis, deep- 

 water cape hake M. paradoxus, Argentine hake M. 

 hubbsi, and New Zealand hake M. aiistralis are always 

 included in a monophyletic group. However, relation- 

 ships among the three eastern Pacific hakes— Chilean 

 hake M. gayi, Panamanian hake M. angtuitimanus, and 

 Pacific hake A/, prnductus—and the two western North 

 Atlantic species— silver hake Af. bilinearis and offshore 

 hake M. albidus are not as consistent. Some represen- 

 tative trees are reproduced in Figure 5 for comparison. 

 Offshore hake (ALBI, Fig. 5) appears to occupy the 

 most plesiomorphic node in almost all cases. This is an 



Figure 6 



Strict consensus tree of hakes showing information common to the 

 188 equally parsimonious trees. For abbreviation of species names, 

 see Figure 5. 



indication that offshore hake is the extant species 

 closest to the ancestral form. 



The strict consensus tree in Figure 6 was obtained 

 using the CONTREE algorithm contained in the PAUP 

 program. It summarizes the point of agreement in all 

 188 equally parsimonious trees. Remarkably, the mono- 

 phyletic relationships of the seven species of hakes 

 occurring off the coasts of Europe, Africa, and eastern 

 South America are also supported by this consensus 

 tree. 



Biogeography 



According to the principle of vicariance biogeography 

 (Nelson and Platnick 1981. Humphries and Parenti 

 1986), the pattern of spatial distribution attained by 

 the hakes can be deduced from the phylogenetic 

 hypothesis. The area summary cladogram in Figure 7 

 illustrates how the present pattern of hake distribution 

 was attained. According to the progression rule of Hen- 

 nig (1966), it implies that the ancestral hake, residing 

 in the western North Atlantic, diverged into two line- 

 ages. One gave rise to the modern offshore hake 

 (ALBI, Fig. 7), and the other formed the species A, 

 which is the ancestor of all the remaining extant hake 

 species. Species A vicariated into two populations: the 

 northern population (C, Fig. 7) whose descendants later 

 occupied the Pacific Ocean, and the southern popula- 

 tion (B, Fig. 7), whose descendants gave rise to all the 

 hakes in the western South Atlantic and entire eastern 

 Atlantic. 



I interpret the cladogram to mean that (1) hake 

 originated in the western North Atlantic, (2) migrated 

 southward and then eastward in the Atlantic, and 

 (3) entered the Pacific in two ways, over the submerged 



