FISHERY BULLETIN: VOL. 81, NO. 2 



1. During the period when the eastern Pacific and 

 Atlantic Oceans were continuous, two species of 

 Scomberomorus were probably present, an ancestral 

 S. cavalla and an ancestral S. sierra. Both of these 

 were infested with species of Holobomolochus and 

 P. buccata. 



2. As the land mass of Central America separated 

 the Atlantic from the Pacific, the two ancestral forms 

 were divided into four populations. The Atlantic pop- 

 ulation of S. cavalla persisted while the Pacific pop- 

 ulation disappeared. The Pacific S. sierra population 

 persisted and gave rise to S. concolor, while the At- 

 lantic population subsequently divided into a south- 

 ern species, S. brasiliensis, and a northern species, S. 

 maculatus. The derivation of S. regalis was also prob- 

 ably from a sierra ancestor. The origin of pre-caval- 

 la and pre-sierra populations was probably derived 

 from the Indo-Pacific S. commerson line and the S. 

 tritor line, respectively (Fig. 4). 



FIGURE 4. — Tentative cladogram of the Scomberomorini. Numbers 

 refer to morphological characters from Collette and Russo (text 

 footnote 3). 



3. The population of ancestral S. sierra in the At- 

 lantic differentiated to produce ultimately the north- 

 ern coastal species S. maculatus and the southern 

 coastal species S. brasiliensis and insular S. rega- 

 lis. 



4. Some species of copepods differentiated as 

 either new host species were formed, or populations 

 of related hosts were isolated. 



5. An additional genus {Shiinoa) of parasitic cope- 

 pod became established on three of the Atlantic spe- 

 cies of Scomberomorus (brasiliensis, maculatus, and 

 regalis) after the formation of a land barrier separat- 

 ing the eastern Pacific from the Atlantic. The ab- 

 sence of Shiinoa on Scomberomorus cavalla may 



indicate that S. cavalla, derived from the S. commer- 

 son line, may have occupied the Atlantic prior to the 

 parasitization of scombrids by Shiinoa. The later 

 infestations of Shiinoa in the western Atlantic may 

 have been derived from Scomberomorus tritor and 

 consequently occur only on the three western Atlan- 

 tic species of Scomberomorus derived from the tri- 

 tor line. 



Based on the anatomy of Scomberomorus, the 

 American species belong to different species groups. 

 Scomberomorus cavalla is the western Atlantic re- 

 placement for S. commerson, which is widespread in 

 the Indo-West Pacific. The other five American 

 species, plus S. tritor from the eastern Atlantic, form 

 the S. regalis species group (Fig. 4), defined by the 

 presence of nasal denticles (Collette and Russo 

 manuscr. in prep. 3 ). These five American species 

 share a unique specialization of the fourth left epi- 

 branchial artery (Collette and Russo footnote 3), 

 which indicates that these species were derived from 

 an 5. tritor ancestor. This pattern of relationships is 

 fully compatible with that derived from the cope- 

 pod data. 



INDO-WEST PACIFIC SCOMBEROMORUS. - 

 There are 11 recognized species of Indo-West Paci- 

 fic Scomberomorus (Collette and Russo 1980; Figs. 3, 

 5, 6). Four genera of parasitic copepods are common 

 on Indo-West Pacific species of Scomberomorus (Ta- 

 ble 6): Unicolax, parasitic in the nasal sinuses; Shiinoa, 

 attached to the nasal lamellae; Pseudocycnoides , at- 



3 Bruce C. Collette and Joseph L. Russo. Systematics and mor- 

 phology of the Spanish mackerels (Scomberomorus). Manuscr. in 

 prep., 400 p. Systematics Laboratory, National Marine Fisheries 

 Service, NO AA, Smithsonian Institution , Washington , DC 20560. 



Table 6. — Infestation of Indo-West Pacific species of 

 Scomberomorus with parasitic copepods. Host species 

 arranged from most infested (most primitive'.') to least 

 infested (most specialized?). The eastern Atlantic & 

 tritor is included for comparison. 



^Unicolax, Pseudocycnoides. Shiinoa, Callous. 



236 



