FISHERY BULLETIN: VOL. 72. NO. 1 



without intergradation between morii and so- 

 biiiia support the conclusion that both are valid 

 species that have evolved relatively recently. 

 Morphological-geographical patterns provide 

 inferential evidence that sympatry among sub- 

 sets of the four species have led to modifications 

 of secondary sexual features, presumably in 

 the course of developing premating barriers to 

 hybridization. Obvious examples of this emerge 

 from comparison of pairs of species which 

 have extensive contiguous boundaries: e.g., 

 plumata and plat y chela in the Atlantic and 

 pliimata and moni in the Indian and Pacific 

 Oceans. In each pair of species the chela on the 

 male fifth leg in the tropical congener is broad- 

 ened in contrast to the slender chela found in 

 plumata. In the females of each pair the hair 

 patches on the genital segment are either miss- 

 ing or reduced to one pair in the tropical species 

 while pluynata maintains two prominent pairs. 

 Another source of evidence lies in the geograph- 

 ical variations in the female fifth legs of plumata 

 which follows a pattern indicative of character 

 displacement. 



Geographical variation in the frequency of 

 morphs in plumata distinguishes Atlantic from 

 Indian and Pacific populations; relationships 

 with platychela in the Atlantic and morii and 

 sobri)ia elsewhere suggest the variation is the 

 result of character displacement. Three of the 

 four morphs in morii and sobriiia appear to be 

 extremely rare. 



7. Each species exhibits a distinctive geo- 

 graphic range independent of the other three. 

 Absence of conspicuous geographical variation 

 indicates sufficient transport and advection to 

 maintain panmixis within each species except 

 the Atlantic and Indian-Pacific populations of 

 plumata. 



8. Abundance of all four species is low de- 

 spite relatively frequent occurrence within the 

 limits of the distribution. These indications of 

 high-order predation are supported by examina- 

 tion of gut contents in sexually mature adults 

 in which the remains consisted primarily of 

 particles from small copepods. 



ACKNOWLEDGMENTS 



CONCLUSIONS 



1. The genus Pontelliua represented by four 

 species is epipelagic and occupies oceanic sec- 

 tors of the circumglobal warm-water belt. 



2. Three of the species occur chiefly in 

 eutrophic sectors of equatorial latitudes where 

 the layer above the thermocline is relatively 

 homogeneous; the distinctiveness of this layer 

 was noted by Wyrtki who refers to it as Tropical 

 Surface Water. One species, platychela, occupies 

 the tropical Atlantic; .^obriua is in the eastern 

 tropical Pacific; and morii is found in the tropi- 

 cal Indian and tropical Pacific Oceans. 



3. The fourth species, plumata s.str., occurs 

 most frequently in oceanic, oligotrophic regions 

 in tropical and subtropical latitudes. 



4. Morphological differences among the spe- 

 cies are subtle and restricted to secondary sexual 

 structures. 



5. The four species comprise a monophyletic 

 complex showing three basic derivatives, plu- 

 mata, platychela, and a third that underwent a 

 subsequent episode of speciation to produce 

 morii and sobrina. 



6. The female fifth leg is polymorphic and 

 represented by four phenotypes or morphs. 



116 



This research was supported by the National 

 Science Foundation Grants GB12412, GA31092, 

 GB32076 and by the Marine Life Research 

 Group of Scripps Institution of Oceanography. 

 We express our thanks to R. Scheltema of 

 Woods Hole Oceanographic Institution, Woods 

 Hole, Mass.. and to the Indian Ocean Biological 

 Centre at Cochin, India, who have provided 

 significant quantities of material from the At- 

 lantic and Indian Oceans, respectively. We owe 

 special debts of gratitude to E. W. Eager for 

 his advice on data analysis and to Gillian Mag- 

 gert who carried out much of the preliminary 

 sorting of samples and whose faithful camera 

 lucida renditions of various specimens of Pon- 

 telliua first called our attention to the existence 

 of the problem. 



LITERATURE CITED 



Alexander, R. D. 



1969. Comparative animal behavior and systematics. 

 In Systematic biology. Publ. No. 16^2. Natl. Acad. 

 Sci.. Wash.. D.C.p. 494-517. 

 Anderson, W. W., and J. W. Gehringer. 



1958. Physical oceanographic, biological, and chemi- 

 cal data. .South Atlantic Coast of the United States, 

 M/V Theodore N. GUI Cruise 5. U.S. Fish 

 Wild!. Serv., Spec. Sci. Rep. Fish. 248, 220 p. 



