12 November 2005

Papers read this week

Tonite's musical accompaniment: Édouard Lalo: Symphonie espagnole.

Albert, A.Y.K. & Schluter, D. 2005. Selection and the origin of species. Current Biology 15:R283-R288.
A useful paper that discusses in a relatively simple language some key concepts of evolutionary biology, including natural selection, sexual selection, allopatric and sympatric speciation. Also discussed is one step speciation in plants, which creates a new plant species literally in a single step as a result of chromosome doubling. Apparently, it is a common process in plants.

Keiper, J.B., Walton, W. E., & Foote, B. A. 2002. Biology and ecology of higher Diptera from freshwater wetlands. Annual Reviews of Entomology 47:207–232.
Among the common inhabitants of wetlands (bogs, fens, swamps, marshes and floodplains) are flies (Diptera). The larvae of most of these flies seem to feed on decaying plant and animal matter, although some prefer live plants. The larvae in one family that interests me most (the Sciomyzidae), however, specifically feed on freshwater mollusks (bivalves and snails) and terrestrial mollusks (snails and slugs).

The following 2 papers deal with Bergmann's rule, which, according to Ernst Mayr1, is that "races from cooler climates in species of warm-blooded vertebrates tend to be larger than races of the same species living in warmer climates". Before proceedings further, however, we need to remind ourselves of Mayr's cautionary statements elsewhere2: "Generalizations in modern biology tend to be statistical and probabilistic and often have numerous exceptions...The so-called laws of biology are not the universal laws of classical physics but are simply high-level generalizations."

Yom-Tov, Y. & Yom-Tov. 2004. Climatic change and body size in two species of Japanese rodents. Biological Journal of the Linnean Society 82:263–267.
To test the hypothesis that global warming may have been causing the skulls of warm-blooded vertebrates to become smaller (if Bergmann's rule applied), the authors measured the skulls of 2 species of Japanese rodents, the specimens of which had been collected continuously throughout much of the 20th century. The specimens had been collected on Honshu Island, where the mean annual temperature increased by 1.53°C between 1900 and 1990. There were, however, no significant relationships between any of the measured skull characters of either species and mean maximum or minimum annual temperatures in the year of collection.

Laugen, A.T., Laurila, A., Jönsson, K.I., Söderman, F. & Merilä, J. 2005. Do common frogs (Rana temporaria) follow Bergmann’s rule? Evolutionary Ecology Research 7:717-731.
The authors wanted to know if Bergmann’s rule applied to the frog Rana temporaria, which is a cold-blooded animal. They measured body sizes of frogs across a 1600-km long latitudinal gradient in Scandinavia. According to their results (Fig. 2, below), the mean body size increased from south to mid-latitudes and declined thereafter. They conclude that "although there is considerable geographic variation in mean body size of R. temporaria, this variation does not conform with Bergmann’s rule."

1. Mayr, E. 1970. Populations, Species and Evolution (p. 197). Harvard University Press.
2. Mayr, E. 1988. Toward a New Philosophy of Biology (p. 19). Harvard University Press.

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