On the Evolutionary Significance of Encephalization in Some Eutherian Mammals: Effects of Adaptive Radiation, Domestication, and FeralizationKruska D.C.T.
Institut für Haustierkunde, Christian-Albrechts-Universität, Kiel, Germany
Allometries of the brain to body size relationship in eutherian mammals are examined in this study as they can be used for comparative analyses concerning encephalization. In contrast with some modern presentations of this issue, an older concept is revived and expanded through this author’s current study. Three allometries with clearly different slopes are valid and lead to reliable results: interspecific, intraspecific, and ontogenetic allometries. Interspecific allometries follow lines with slope values of 0.56 or 0.63 for larger and smaller species, respectively, and characterize different average encephalization plateaus with rodents and lagomorphs generally more strongly encephalized compared to basal insectivores. Artiodactyls, perissodactyls and carnivores as a whole are again on a higher but rather similar plateau. Several species of carnivores have reached different encephalization levels with respect to their average plateau indicating diverse radiations. A phylogenetic brain size increase from fossil to recent radiations is also evident. Intraspecific allometries have slope values of about 0.25. These are of help in comparing brain sizes of ancestral species with their domesticated relatives. Domestication has generally led to a brain size decrease, but species on higher encephalization plateaus show this trend more strongly than species on a lower level of encephalization. Several brain parts and the sense organs also decrease in size during the domestication process, but vary arbitrarily and to different degrees. Ontogenetic growth allometries are species-specific, but are especially different between altricial and precocial mammals. A very steep 1st phase slope of highly encephalized species is particularly useful for understanding evolutionary and adaptive phenomena. Domesticated mammals that have become feral do not show an increase in brain size despite living many generations in wild habitats.
Prof. Dr. Dieter C. T. Kruska
Institut für Haustierkunde, Christian-Albrechts-Universität
DE–24118 Kiel (Germany)
Tel. +49 431 8804513, Fax +49 431 8801389, E-Mail firstname.lastname@example.org
Received: July 24, 2003
Returned for revision: September 16, 2003
Accepted after revision: April 2, 2004
Published online: December 28, 2004
Number of Print Pages : 36
Number of Figures : 18, Number of Tables : 2, Number of References : 193
Brain, Behavior and Evolution
Founded 1968 and continued 1968–1986 by W. Riss, New York, N.Y.
Official Organ of the J.B. Johnston Club
Vol. 65, No. 2, Year 2005 (Cover Date: Released January 2005)
Journal Editor: Walter Wilczynski, Austin, Tex.
ISSN: 0006–8977 (print), 1421–9743 (Online)
For additional information: http://www.karger.com/journals/bbe