Comparative and experimental studies of adaptation

Comparative and experimental analysis

Organismal biologists employ two principal methods in their investigation of the natural world: comparison and experiment. The latter is most familiar in the context of laboratory investigations of functional mechanisms. Experiment is the classic application of the scientific method, including such elements as rigorous and replicated design, controlled manipulation of a single variable of interest and the incorporation of a control group into the study. While experimental science has been crucial to our understanding of how organisms work, to date it has had relatively less application in studying how those organisms came to be the way they are, i.e. in studies of the evolution of organismal characters. In such evolutionary studies, comparative investigations have been by far the dominant methodological tradition.

In the study of evolutionary adaptation to temperature, for example, virtually all our knowledge is derived from comparative studies of different populations, species, or other taxa inhabiting different thermal environments (for reviews, see Precht et al., 1973; Prosser, 1973; Hochachka & Somero, 1984; Cossins & Bowler, 1987). The comparative approach involves the measurement of a character and its correlation with environmental temperature. If the character (e.g. a rate process) is thermally dependent, then it is measured either over a similar range of temperatures or at a single temperature common to the different groups examined. The pattern of character on environmental temperature is then analysed and interpreted, most frequently in an adaptive context (Prosser, 1986; Cossins & Bowler, 1987; Bennett, 1996), and compared with the pattern found for other biological systems inhabiting similar thermal environments.