26 Francois Bourliere 



On the other hand, some species have a rather wide geographi- 

 cal distribution and live in waters whose temperature and food- 

 content vary greatly. 



In such conditions striking differences in growth rate, 

 tempo of life and longevity can be found. To choose but one 

 example, the comparison of the data of Brown (1943) and of 

 Miller (1946) on two different populations of the North 

 American grayling (Thymallus signifer) seems to me highly 

 suggestive. The Michigan subspecies has a very rapid growth 

 and matures early, but has a short life. The oldest individual 

 seen by Brown was in its sixth year of life. On the other hand, 

 the Arctic subspecies found in Great Bear Lake in northern 

 Canada does not reach its sexual maturity before its fifth 

 summer; it attains a greater ultimate size and also a much 

 greater longevity. Some specimens caught by Miller were in 

 their twelfth summer. The length of life of the Arctic popula- 

 tion is therefore about three times that of the southern one. 



Similar instances could certainly be found easily in ich- 

 thyological literature. Sticklebacks (Gasterosteus aculeatus) 

 do not live longer than 14 to 18 months in France, but require 

 several years to reach their maturity in more northern 

 latitudes. Pilchards (Clupea pilchardus) are said to have a 

 slower growth and a longer life in the English Channel than off 

 Saint Jean de Luz and the Spanish coast. 



Similarly, the duration of the larval period of some widely 

 distributed amphibians varies greatly with latitude. In 

 North America, for instance, according to Oliver (1955), the 

 bullfrog (Rana catesbeiana) undergoes metamorphosis at the 

 end of its first winter in sunny Louisiana, while in the extreme 

 northern part of its range (Nova Scotia) it may spend three 

 winters as a tadpole. Unfortunately we have no data on the 

 comparative longevity of adults in both cases. 



Among lizards, striking latitudinal differences in growth 

 pattern and lifespan are known. In Florida, for instance, 94 

 per cent of the southern fence lizards (Sceloporus undulatus 

 undulatus) were found to live less than one year, and none 

 lived in their natural environment for two years. This warm 



