Finnerty and Block: Evolution of cytochrome b in the Scombroidei 



91 



Cytochrome b sequence strongly supports the 

 monophyly of the Istiophoridae. The extant members 

 of this family have experienced a long period of com- 

 mon ancestry as indicated by numerous istiophorid 

 synapomorphies (20 transitions and 35 trans- 

 versions, Fig. 8). The monophyly ofTetrapturus, and 

 within this genus, clades consisting of audax + 

 albidus and pfluegeri + angustirostris + belone, are 

 also supported. The number of substitutions sepa- 



rating Tetrapturus audax from T. albidus, and T. 

 angustirostris from T. belone and T. pfluegeri indi- 

 cates that these mitochondrial lineages share a recent 

 common ancestry (Table 3). The sequence differences 

 between these species (<0.5%) are small compared to 

 the maximum intraspecific sequence difference (1.8%) 

 detected among blue marlin, M. nigricans, over a simi- 

 lar region of cytochrome b (Finnerty and Block, 1992). 

 These data call into question the status of T. audax 



