530 



Cytogenetics and Evolution 



lations is illustrated in Fig. 151. In these suckers, Hubbs has 

 found that the hybrids show httle more variabiHty than the 

 parental species, which indicates, among other things, that there 



10 



0; 



20- 

 10- 



10- 

 20- 

 10- 



20- 

 10- 



10; 



20- 



10- 



0- 



Pantosteus jordani 

 ~ THybridl 

 ^ Catostomus c 



.JL 



L 



grtseus 



Pantosteus_ 

 clarkii 



Hybrids 



Catostomus 

 insignis 



Catostomus 

 syncheilus 

 syncheilus 



Hybrids 



Catostomus 

 macrocheilus 



Above Lateral Line 



20 



From Dorsal Fin To Occiput 



1 1 > I r I 1 1 1 > I I 



40 



10 



rrp-r 



20 



30 



50 



60 



I I M II I I II |ll I l| I M I 



70 so"' 



90 



|1 M I I II 1 I |1 II 1 I I II l| 1 II I 



100 110 120 



Fig. 151. The use of the hybrid index method of Hubbs to compare 

 parent and hybrid populations of suckers with respect to five scale counts. 

 (From Hubbs, Hubbs, and Johnson in Contribution 22 from the Labora- 

 tory of Vertebrate Biology of the University of Michigan.) 



is little backcrossing to the parental types. Hybrids were not 

 common, and no real hybrid populations were built up, indicat- 

 ing that interspecific hybridization has not been important in 

 the origin of species in the Catostomidae. 



