Ho: Phytogeny and biogeography of Merluccius 



97 



Figure 2 



Cladogram showing hypothesized relationships of the merlucciid 

 genera. Character codes: 1 = V-shaped crest on skull present; 1' 

 = V-shaped crest on skull absent; 2 = foramen for trigemino-fascialis 

 nerve present; 3 = shape of anterior parasphenoid vertical; 4 = up- 

 per window on suspensorium closed; 5 = two dorsal fins; 5' = one 

 dorsal fin; 6 = one pseudospine in dorsal fin; 7 = two pseudospines 

 in dorsal fin; 8 = caudal fin tapering. 



Phylogeny 



An unusually large number of trees (cladograms) were 

 obtained, 188 in total, all with a consistency index of 

 0.522. The F value of these most parsimonious trees 

 ranges from 0.277 to 0.482. However, there is only one 

 tree with the lowest (best) F value, reproduced in Fig- 

 ure 3. Since the development of host specificity in 

 parasites is the result of coevolution between the host 

 and its parasite, an hypothesis of the host phylogeny 

 should also apply to the phylogeny of its specific 

 parasite. In other words, host-specific parasites can be 

 useful to corroborate host phylogeny. 



Brooks et al. (1986) suggested that the lower the 

 F-ratio ( = F value), the greater is the degree of his- 

 torical constraint on the data. In this regard, the tree 

 with the lowest F value (Fig. 3) should exhibit the 

 highest degree of congruence with the parasite data 

 set. To check this congruency, a parasite summary 

 cladogram needs to be constructed. Figure 4 is such 

 a cladogram, generated by replacing the hake species 

 on the cladogram with each of their respective sub- 

 species of Neobrachiella insidiosa, a host-specific 

 copepod parasite of hakes. Since Chondracanthus 

 palpifer WUson was recently found by Villalba and Fer- 

 nandez (1985) to parasitize not only Merluccius but also 

 another merlucciid (Macruronus magellanicus Lonn- 

 berg) in Chilean waters, it can no longer be treated as 

 aMer/McciMS-specific parasite as previously proposed. 

 Accordingly, only the three subspecies oi Neobrachiella 

 insidiosa are considered. 



Figure 3 



Cladogram showing hypothesized relationships among species of 

 Merluccius. For character codes 1-23, see Appendix 1. 



A i\ .:. i\ A A A A A A A A 



^ Pacilici 

 A l3geniIormis 

 A 'fsidt 



Figure 4 



Parasite summary cladogram showing relationships among sub- 

 species of Neobrachiella insidiosa inferred from hypothesized rela- 

 tionships among species of hake {Merluccius). Arrows indicate the 

 changes (evolution) of parasites. 



As in Figure 4, the result agrees, indicating that the 

 hake-specific Neobrachiella insidiosa had changed 

 (evolved) from A'^. insidiosa lageniformes (western 

 Atlantic form) to A'', insidiosa insidiosa (eastern Atlan- 

 tic form) on one hand, and from the western Atlantic 

 form (original form) to A'^. indisiosa pacifica (Pacific 

 form) on the other. This scheme of evolution for 

 Neobrachiella insidiosa contradicts the one proposed 

 by Kabata and Ho (1981) but, nevertheless, agrees with 

 the hake-parasite evolution proposed by Ho (1974). The 

 phylogenetic hypothesis predicts a Pacific form of N. 

 insidiosa, but it is yet to be found in M angustimanus. 

 The discovery of A'', insidiosa pacifica on the Panama- 

 nian hake would strongly support the cladogram shown 

 in Figure 3. 



