Gloger's rule

Gloger's rule is an ecogeographical rule which states that within a species of endotherms, more heavily pigmented forms tend to be found in more humid environments, e.g. near the equator. It was named after the zoologist Constantin Wilhelm Lambert Gloger, who first remarked upon this phenomenon in 1833 in a review of covariation of climate and avian plumage color.^[1] Erwin Stresemann later noted that the idea had been expressed even earlier by Peter Simon Pallas in Zoographia Rosso-Asiatica (1811).^[2] Gloger found that birds in more humid habitats tended to be darker than their relatives from regions with higher aridity. Over 90% of 52 North American bird species studies conform to this rule.^[3]

One explanation of Gloger's rule in the case of birds appears to be the increased resistance of dark feathers to feather- or hair-degrading bacteria such as Bacillus licheniformis. Feathers in humid environments have a greater bacterial load, and humid environments are more suitable for microbial growth; dark feathers or hair are more difficult to break down.^[4] More resilient eumelanins (dark brown to black) are deposited in hot and humid regions, whereas in arid regions, pheomelanins (reddish to sandy color) predominate due to the benefit of crypsis.

Among mammals, there is a marked tendency in equatorial and tropical regions to have a darker skin color than poleward relatives. In this case, the underlying cause is probably the need to better protect against the more intense solar UV radiation at lower latitudes. However, absorption of a certain amount of UV radiation is necessary for the production of certain vitamins, notably vitamin D (see also osteomalacia).

Gloger's rule is also vividly demonstrated among human populations.^[5] Populations that evolved in sunnier environments closer to the equator tend to be darker-pigmented than populations originating farther from the equator. There are exceptions, however; among the most well known are the Tibetans and Inuit, who have darker skin than might be expected from their native latitudes. In the first case, this is apparently an adaptation to the extremely high UV radiation on the Tibetan Plateau, whereas in the second case, the necessity to absorb UV radiation is alleviated by the Inuit's diet, which is naturally rich in vitamin D.

References

Sources

Burtt, Edward H. Jr.; Ichida, Jann M. (2004). "Gloger's Rule, feather-degrading bacteria, and color variation among Song Sparrows" (PDF). The Condor. 106 (3): 681–686. doi:10.1650/7383. ISSN 0010-5422. S2CID 5857742. Archived (PDF) from the original on 2012-11-20. Retrieved 2007-11-24.
Ember, Carol R.; Ember, Melvin; Peregrine, Peter N. (2002). Anthropology (10th ed.). Prentice Hall. ISBN 978-0-13-091836-9. LCCN 2001033927. OCLC 47018472.
Gloger, Constantin Wilhelm Lambert (1833). "§. 5. Abänderungsweise der einzelnen, einer Veränderung durch das Klima unterworfenen Farben". Das Abändern der Vögel durch Einfluss des Klimas [The Evolution of Birds Through the Impact of Climate] (in German). Breslau: August Schulz. pp. 11–24. ISBN 978-3-8364-2744-9. OCLC 166097356.
Stresemann, Erwin (August 1975). Cottrell, G. William (ed.). Ornithology: from Aristotle to the present. Translated by Epstein, Hans J.; Epstein, Cathleen. Cambridge, MA: Harvard University Press. p. 70. ISBN 978-0-674-64485-4. LCCN 74025035. OCLC 1499768.
Zink, Robert M.; Remsen, James V. Jr. (1986). "Evolutionary Processes and Patterns of Geographic Variation in Birds". In Johnston, Richard F. (ed.). Current Ornithology. Vol. 4. New York, NY: Plenum Press. pp. 1–69. ISBN 0-306-42352-9.

Biological rules
Rules	Allen's rule Shorter appendages in colder climates Bateson's rule Extra limbs mirror their neighbours Bergmann's rule Larger bodies in colder climates Cope's rule Bodies get larger over time Deep-sea gigantism Larger bodies in deep-sea animals Dollo's law Loss of complex traits is irreversible Eichler's rule Parasites co-vary with their hosts Emery's rule Insect social parasites are often in same genus as their hosts Fahrenholz's rule Host and parasite phylogenies become congruent Foster's rule (Insular gigantism, Insular dwarfism) Small species get larger, large species smaller, after colonizing islands Gause's law Complete competitors cannot coexist Gloger's rule Lighter coloration in colder, drier climates Haldane's rule Hybrid sexes that are absent, rare, or sterile, are heterogamic Harrison's rule Parasites co-vary in size with their hosts Hamilton's rule Genes increase in frequency when relatedness of recipient to actor times benefit to recipient exceeds reproductive cost to actor Kleiber's law An animals metabolic rate decreases with its size Hennig's progression rule In cladistics, the most primitive species are found in earliest, central, part of group's area Jarman–Bell principle The correlation between the size of an animal and its diet quality; larger animals can consume lower quality diet Jordan's rule Inverse relationship between water temperature and no. of fin rays, vertebrae Lack's principle Birds lay only as many eggs as they can provide food for Rapoport's rule Latitudinal range increases with latitude Rensch's rule Sexual size dimorphism increases with size when males are larger, decreases with size when females are larger Rosa's rule Groups evolve from character variation in primitive species to a fixed character state in advanced ones Schmalhausen's law A population at limit of tolerance in one aspect is vulnerable to small differences in any other aspect Thorson's rule No. of eggs of benthic marine invertebrates decreases with latitude Van Valen's law Probability of extinction of a group is constant over time von Baer's laws Embryos start from a common form and develop into increasingly specialised forms Williston's law Parts in an organism become reduced in number and specialized in function
Related	Countergradient variation Where genetics opposes environment as a factor Gigantothermy Large ectothermic animals more easily maintain constant body temperature

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Further Reading