The use of climate classification parameters to investigate geographical variations in the life history traits of ectotherms, with special reference to the white sucker (Catostomus commersoni)

The classical approach for investigating latitudinal variations in life history tactics of ectotherms is to determine if there are significant correlations between the traits of a given species and latitude. However, as temperature does not vary linearly with latitude, the latter parameter may only be a gross index of local climatic conditions. The objective of this paper is to present how we used Litynski's (1984) climate classification to investigate latitudinal variations in life history traits of the white sucker (Catostomus commersoni). Data from the literature (44 lakes) and from sampling done on 18 lakes of the Laurentian Shield (Québec, Canada) were used to compare different approaches to predict geographical variations in life history traits. The results showed that variation in life history traits of the white sucker documented over the geographical extent of the study area was better explained by considering the numerical classification of climates, based on mean annual temperature, annual precipitation and an index of continentality, rather than by simple linear regression with latitude or mean annual temperature; longevity and age at maturity of males and females were significantly higher in northern populations while maximum length, length at maturity of males and females, and growth were significantly higher in southern populations. Our results suggest that it may be better to use functional climatic variables, instead of the more usual ones, such as latitude and mean annual air temperature, to study geographical variations in the life history of ectotherms.