100 120 UO 160 lao 200 220 240 260 20 30 40 SO 60 70 80 



SE United Stoles 

 W Flo.ido 

 Cent Amer.co 

 West Indiei 

 Venemelo 

 Med.lerraneon 

 Gul* of Cu-neo 

 Jopan 

 Austrol.a 



Philippine! 



P SINENSIS 

 Chino Coa-.t 



P CONSTRICTUS 

 E Pacific 



P ENSICULUS 

 E Pocific 



N.50 

 N=51 

 N.36 

 N.26 

 N^28 

 N-17 



N-22 

 N-IO 



FiGiTRE 188. — Lengths of two setae on leg 5 of four ispecies of Parahomoloch us by geographic area. Symbols as in figure 187. 

 The first line represents a single sample from Htrongylxtra titniiou from Sarasota, Fla. 



influence or the ecology of the host. And in Lervian- 

 fhropiis bel-ones and Paraboinolochus bellones, 

 intr.aspecific variation is clearly geographic. 



Relative Rates of Evolution 



An often cited axiom of modern parasitology' 

 asserts that because parasites evolve more slowly 

 than their hosts, information on the parasites will 

 assist in understanding the evolution of the hosts. 

 In other words, hosts that harbor closely related 

 parasites m.ay themselves be closely related. This 

 axiom is related to the question of host specificity. 

 Four worldwide species of copepods (Caligodes 

 laciniatii^, Lenianthf'opus helones, L. tylosuri, and 

 Colohomatus gaodingl) show little geographic 

 variation except in total length. The four world- 

 wide species of needlefishes show varying amounts 

 of geographic viiriation (Collette and Parin, 

 1970) . This variation is weakest in Ahlennes Jiians. 

 Tylosiu'u.s crocodilus has at least two subspecies, 

 one restricted to the eastern Pacific. T. acus has 

 five subspecies: western Atlantic, Mediterraneaji, 

 Gulf of Guinea, Indo-West Pacific, and eastern 

 Pacific. PlatyieJane argcdiis has seven subspecies: 

 western Atlantic, Annobon-Fernando Poo, Ascen- 

 sion-St. Helena, Cape Verdes, Red Sea, Indo- 

 West Pacific, and eastern Pacific. Thus, the four 

 worldwide species of needlefishes appear to be 

 more highly differentiated than are the four world- 

 wide species of copepods. It must be remembered, 

 though, that studies of geographic variation have 



not been carried out in copepods with the same 

 degree of thoroughness as in fishes. 



Another widespread copepod, Parabomolochus 

 bellones, has difi"erentiated to the specific level (P. 

 C07iM7'ictus) after isolation in the eastern Pacific. 

 In comparison, three of the four worldwide hosts 

 have diflferentiated to only the subspecific level. 

 Here, evolution may have proceeded faster in the 

 copepod than in its host. The apparent "loose"' 

 specificity to their hosts of the cyclopoid copepods 

 discussed here may explain the unsettled nature of 

 their relationship. 



Effect of Host Size 



Another parasitological axiom states that older 

 ( = larger) host individuals have a greater para- 

 site fauna because they have been exposed longer. 

 To examine this axiom, data were examined on 

 the mean body lengths of the commonest 16 species 

 of marine needlefishes infested with the commonest 

 8 species of copepods. The copepods were divided 

 into two major categories: specialized {Leman- 

 thropus, Caligodes, CoJohomatus) and generalized 

 {ParabomoJoclnts and Nofhohamolochm). By spe- 

 cialized we mean jxissessing adaptations used as 

 lioldfasts (and exhibiting a higher degree of host 

 specificity) ; by generalized we mean those cope- 

 pods (Bomolochidae) that are free to wander 

 about (and show less host specificity) . Because the 

 species of needlefishes varj' widely in length, a 

 ranking comparison was used to substitute relative 



424 



U.S. FISH AND WILDLIFE SERVICE 



