GLOGER'S RULE AND PIGMENTATION OF COLLEMBOLA.

Abstract

Pigmentation in warm-blooded animals has been related to latitude, temperature, humidity, rainfall, and solar radiation. The original observations by Gloger (1833) on the coloration of birds in relation to their geographical position have been confirmed for different species belonging to several taxa, though some important exceptions were pointed out by Burt (1954) and Croizat (1964). The decrease of pigmentation at higher latitudes, however, does not seem to be valid for invertebrates. Moreover, in many instances a negative or inverse Gloger's rule has been reported. Dobzhansky (1933) speaks of centers of light and dark forms in coccinellid Coleoptera; the former lie in Iran, southern Turkestan, southern United States and Mexico, and the latter lie in Siberia and Kamchatka. Low temperatures (and higher latitudes) favor melanin formation in insects (Vernberg, 1962) resulting in more obscure populations (Ehrlich and Holm, 1963; Gillham, 1956; Hovanitz, 1941; Kalmus, 1941; Timofeeff-Ressovsky, 1940). The same phenomenon has been also reported for the marine snail Thais lapillus (Clench, 1954), and for land snails. The latter show darker brown coloration at higher latitudes. An analysis is made here of the amount of pigmentation observed in entire associations of different species, taking the collembolan insects as the main example, and trying to quantify in some way the phenomenon as Amtmann (1965) did with the mammal Protoxerus stangeri. Yosii (1938) provided some early observations on this group of apterygotan insects: referring to Agrenia bidenticulata he mentions their ability to show color variations according to the habitat. Specimens collected from riversides and other hygropetric habitats show dull yellowish coloration, while those collected on snow in spring are always pigmented deep purple.