Species which are widely distributed do not generally form one panmictic population. The degree of genetic variability varies within the distribution range. The first to formally recognize and search for genetic variability was the Russian scientist
Institut Méditerranéen d'Ecologie et Paléoécologie, Université de Provence, UMR CNRS 6116, Case 36, 3 Place Victor Hugo, F-13331 Marseille Cedex 3, France e-mails: [email protected]; [email protected]
J.C. Habel and T. Assmann (eds.), Relict Species: Phylogeography and Conservation Biology, 277 DOI 10.1007/978-3-540-92160-8_16, © Springer-Verlag Berlin Heidelberg 2010
Nicolai Ivanovitch Vavilov (1885-1943),1 who set the foundations of research on the origin of cereals (in particular wheat). He demonstrated that their diploid wild relatives, in their original area, had a much higher variability than their widely cultivated generally polyploid relatives (e.g., Vavilov 1950). These principles were later followed by biologists studying the intraspecific variation of wild plants and animals. This same general principle may be applied to glacial relicts, with the question of the identification of the original area for each concerned species.
Since Forbes (1846) we know that the distribution of plants and animals changes with time, in particular during the Quaternary climatic oscillations. Haeckel formally recognised this when he wrote:
As the glaciation encroached from Northern Europe towards our Alpine chains, the polar inhabitants retreating before it - gentian, saxifrage, polar foxes, and polar hares - must have peopled Germany, in fact all Central Europe. When the temperature again increased, only a portion of these Arctic inhabitants returned with the retreating ice to the Arctic zones. Another portion of them climbed up the mountains of the Alpine chain instead, and there found the cold climate suited to them. The problem is thus solved in a most simple manner (Haeckel 1876, Chap. 14, p. 367).
The ca. 100,000 year cycle of glacial - interglacial periods has had a major impact on the distribution of organisms in the North hemisphere, particularly in Europe because of the East-west orientation of its main mountain massifs (Pyrenees, Alps, Carpathians), leading to a corresponding range shifts (Huntley and Webb 1989). For many cold-adapted species, the latitudinal Northward migration was accompanied by an upward altitudinal migration. These species then ended up with disjunct distribution, often called boreo-mountain or arctic-alpine species, depending on the altitude/latitude of their distribution (de Lattin 1967; Udvardy 1969).
From a genetic point of view, the key factors influencing the genetic structure of the populations of the species with such disjunct distributions are the age of the discontinuity in the distribution and the population size within each of the different distribution patches. For most European species distributed in both Scandinavia and the S European mountains (mostly in the Alps and the Pyrenees), it is assumed that the populations now found in, e.g., the Alps and the ones found in Scandinavia became separated ca. 10,000 years ago, i.e., at the end of the Würm glaciation. However, other scenarios are possible; N Europe may have been colonized from a refugium in Siberia, while Alpine populations were separated from these at a previous colonization cycle (Hewitt 1999). Furthermore, numerous thermophilous species remained at low altitude in the Mediterranean area during glaciations; afterwards some of them remained there while others spread Northwards.
The aim of the present chapter is to briefly discuss: (1) what are the long term consequences of range shifts in terms of endemic and cytotype distributions, and (2) how range shifts influence the genetic structure of populations.
1 The date of death of N.I. Vavilov is usually given as 1942 (e.g. Harland 1954). Details of his tragic death became known only after the demise of the Soviet Union (Azmanov 2002) and its date is 25 January 1943.
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