NO. 3595 ANOLIS LINEATOPUS — RAND 67 



against its importance. Fii'st, only indi\ iduals of about the same size 

 are overdispersed and diseases that are restricted to particular sizes 

 \\ ithin the species must be uncommon. Second, although lizards may 

 be spatially isolated duruig the daj^, they frequently sleep in the same 

 places, so that, even if the spread of disease is reduced during the day, 

 it would not be reduced at night. 



The fhial area in this discussion of adaptive significance involves 

 adult males. I have stressed that, while all sizes and both sexes are 

 aggressive, the adult males are more aggressive than any other in- 

 dividuals. The males travel greater distances to attack intruders 

 than do other A. lineato'pus; they are more persistent in then- attacks 

 and they fight more frequently and more fiercel}^ They have struc- 

 tin-al modifications, nuchal and dorsal crests, used exclusively in 

 agonistic behavior, that are lacking in females and young. 



This sort of difference in behavior is known in other iguanid lizards. 

 In some, the males have larger home ranges from which they exclude 

 other males even though, unlike the Anolis, the males are smaller than 

 the females (Blair, 1960). In other species, only the males are aggres- 

 sive at all (Blair, 1960). In ^i. carolinensis, males defend their home 

 ranges most aggressively dming the weU-marked breeding season 

 (Greenberg and Noble, 1944). 



Finally, in ^1. lineatoiJus adult males are less tolerant of individuals 

 of then* own species and size than are the females and juveniles, but 

 they are more tolerant of males of other species. 



I think the general occurrence of aggressive behavior and the spacing 

 out it produces in all sizes of A. lineato'pus can be explained by the 

 ecological advantages that have been discussed in the foregoing dis- 

 cussion, but the greater aggressiveness of the adult males rec^uires 

 additional explanation. I think the explanation lies in a function of 

 territory discussed at length by Tinbergen (1957), which demonstrates 

 the selective advantage that is conferred on an adidt male if he can 

 insure himself exclusive mating rights to certain females by keeping 

 other males away from them. If he can do this for a single female, he 

 insm-es that he will father at least some offspring, and the more females 

 he can keep isolated, the more offspring he wiU have and the greater 

 his contribution to the gene pool of the next generation. This being 

 true, there must be a strong selection pressm'e for any mechanism that 

 will insure a male exclusive mating rights to one or more females. The 

 aggressive behavior of adult male A. lineato'pus tliat keeps other males 

 out of the area in which females are permanently living is just such a 

 mechanism. I think that the selective advantage to the individual 

 male of having exclusive mating rights accounts for the greater aggres- 

 siveness in the adult males of this species, while the other ecological 

 advantages to the population as a whole of spacing individuals of the 



