Ring species

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Fig. 1 . The individual populations are represented by different colored blocks. The distribution area and thus the cline can be stretched ( A ) or ring-shaped ( B , C ).

A ring species , also called racial group , consists of several, mostly morphologically clearly distinguishable populations (which may be formally classified as separate species ), in which individuals from neighboring populations can cross and exchange genes , but at least not in some of the non-neighboring populations more is possible. Ring species illustrate that the common biological species concept according to Ernst Mayr cannot always be clearly applied.

introduction

The colored bars in Fig. 1 show a number of natural populations. Along a so-called cline (English cline , Huxley , 1938) of continuously changing environmental conditions, the populations vary in adaptation to these conditions, for example in body structure. Mating between neighboring populations is possible and takes place. A variation or a kline can exist along a straight line (e.g. the north side of the Alps; see A ) or along a curved line (e.g. around the Arctic, B ).

One speaks of a ring species if, in a ring-shaped kline ( C ), the populations that meet at each end of the ring no longer have a gene exchange despite the same habitat. The changes in physiology, morphology or behavior in such a case have become so great that matings between the terminal populations of a ring no longer take place or no longer lead to fertile offspring. In such a case, the totality of all populations is referred to as a ring species .

The question for the classification is whether one should regard all populations of such a ring as a single species in terms of taxonomy , although pairings are not possible between all populations - or whether each population (colored segments in the illustration) should be its own Species count, although individuals can reproduce with members of the immediately adjacent populations. The delimitation of species is therefore not always possible as clearly as the biological species concept suggests.

Examples

  • Salamander the genus Ensatina form a ring around the Central Valley in California .
  • The green warbler ( Phylloscopus trochiloides , birds) form a ring around the Himalayan mountains.
  • In 2012, a plant species was described as a ring species for the first time in a specialist journal, Euphorbia tithymaloides , which is native to South and Central America: One direction of spread therefore went from Mexico to South America and from there north to the Lesser Antilles , the second direction went from Mexico from east to Caribbean islands like Jamaica and Puerto Rico . Both populations coexist today - without any significant gene flow - on the island of Saint Croix .
  • For a long time it was assumed that gulls (genus Larus ) form a ring species along the Arctic Circle. A genetic study showed, however, that the situation is more complicated than described here and that certain conditions of Mayr's ring species theory are not met.

See also

Individual evidence

  1. ^ Arno Hermann Müller: Textbook of Palaeozoology. Volume I - General Basics. 5th edition. Gustav Fischer Verlag, Jena, Stuttgart, 1992
  2. ^ Ensatina eschscholtzi : Speciation in Progress. A Classic Example of Darwinian Evolution ( Memento from February 7, 2008 in the Internet Archive )
  3. ↑ Songbird illustrates the emergence of new species. About the green leaf singer , on: Wissenschaft.de from January 23, 2001
  4. ↑ N. IVALU Cacho, David A. Baum: The Caribbean slipper spurge Euphorbia tithymaloides: the first Example of a ring species in plants. In: Proceedings of the Royal Society B - Biological Sciences. Volume 279, No. 1742, 2012, doi: 10.1098 / rspb.2012.0498
  5. ↑ Dorit Liebers, Peter de Knijff, Andreas J. Helbig: The herring gull complex is not a ring species. In: Proc. R. Soc. Lond. B: Biological Sciences. Volume 271, 2004, pp. 893–901, doi: 10.1098 / rspb.2004.2679 (free access to the full text)