Gote Turesson and Plant Ecotypes
Natural selection acts on differences that exist among the members of a species, and the concept of such variation is central to Darwin's evolutionary theory. The fact of variation among individuals creates classification problems, however, as taxonomists must decide whether the visible differences between two plants or animals are sufficient to justify classifying them as distinct species. The scientist who first proposed a solution to the dilemma was the Swedish evolutionary botanist Gote Turesson (1892–1970).
Different populations of any widespread species occur in a range of environments that differ slightly in such factors as climate, soil type, and the other plants and animals living there. Species adapt to these local differences in ways that may alter their behavior and sometimes their appearance. For instance, many plants growing in high latitudes flower later in the year than others of the same species growing closer to the equator. When low-latitude plants are moved to a high-latitude environment, they grow less well than they did in their former environment and also less well than other plants of the same species that are already established there. This disadvantage continues into later generations produced from seeds from the transplanted plants, demonstrating that the adaptation has led to a genetic divergence between the two populations. Individuals from one population are still able to interbreed with those from the other population, so they are not different species, but there is a genetic difference between them. Turesson introduced the term ecotype to describe a population of a widespread species that is adapted to local conditions in this way.
Turesson's definition suggested that each locally adapted population was in some degree distinct from all other populations of the same species, as though a line could be drawn around it to isolate it. Reality is often different, however. Rather than comprising a patchwork of separate ecotypes, species in most regions shade from one population to the next, with adaptive changes that alter gradually, and the ecotypes occupying the extreme ends. A gradual change of this kind is called a cline.
Gote Wilhelm Turesson was born at Malmo, Sweden, on April 6, 1892. He attended school locally and then studied science in the United States at the University of Washington, where he obtained his first degree in 1914 and his master's degree in 1915. Turesson returned to Sweden in 1916 and commenced his research into plant growth. He began teaching at the University of Lund in 1921 and received his Ph.D. in 1922, the year in which he published two essays in the journal Hereditas: “The Species and the Variety as Ecological Units” and “The Genotypical Response of the Plant Species to the Habitat.” In 1925 he published a third essay, also in Hereditas, “The Plant Species in Relation to Habitat and Climate.” Turesson was a lecturer at the University of Lund from 1922 to 1927, and from 1927 to 1931 he conducted research at the Weilbullsholm plant breeding center. He returned to teach and research at Lund in 1931, remaining there until 1935, when he failed to obtain a professorship at Lund and accepted the position of professor of botany and genetics at the agricultural college at Uppsala University. He remained at Uppsala until he retired in 1959. Turesson died at Uppsala on December 30, 1970.
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