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The effect of body size evolution and ecology on encephalization in cave bears and extant relatives


Veitschegger, Kristof (2017). The effect of body size evolution and ecology on encephalization in cave bears and extant relatives. BMC Evolutionary Biology, 17(1):2-10.

Abstract

Background: The evolution of larger brain volumes relative to body size in Mammalia is the subject of an extensive
amount of research. Early on palaeontologists were interested in the brain of cave bears, Ursus spelaeus, and
described its morphology and size. However, until now, it was not possible to compare the absolute or relative
brain size in a phylogenetic context due to the lack of an established phylogeny, comparative material, and
phylogenetic comparative methods. In recent years, many tools for comparing traits within phylogenies were
developed and the phylogenetic position of cave bears was resolved based on nuclear as well as mtDNA.
Results: Cave bears exhibit significantly lower encephalization compared to their contemporary relatives and intraspecific brain mass variation remained rather small. Encephalization was correlated with the combined dormancy-diet score. Body size evolution was a main driver in the degree of encephalization in cave bears as it increased in a much higher pace than brain size. In Ursus spelaeus, brain and body size increase over time albeit differently paced. This rate pattern is different in the highest encephalized bear species within the dataset, Ursus malayanus. The brain size in this species increased while body size heavily decreased compared to its ancestral stage. Conclusions: Early on in the evolution of cave bears encephalization decreased making it one of the least encephalized bear species compared to extant and extinct members of Ursidae. The results give reason to suspect that as herbivorous animals, cave bears might have exhibited a physiological buffer strategy to survive the strong seasonality of their environment. Thus, brain size was probably affected by the negative trade-off with adipose tissue as well as diet. The decrease of relative brain size in the herbivorous Ursus spelaeus is the result of a considerable increase in body size possibly in combination with environmental conditions forcing them to rest during winters.
Keywords: Physiological buffer, Dormancy, Diet, Ailuropoda, Helarctos, Melursus, Tremarctos, Ursus

Abstract

Background: The evolution of larger brain volumes relative to body size in Mammalia is the subject of an extensive
amount of research. Early on palaeontologists were interested in the brain of cave bears, Ursus spelaeus, and
described its morphology and size. However, until now, it was not possible to compare the absolute or relative
brain size in a phylogenetic context due to the lack of an established phylogeny, comparative material, and
phylogenetic comparative methods. In recent years, many tools for comparing traits within phylogenies were
developed and the phylogenetic position of cave bears was resolved based on nuclear as well as mtDNA.
Results: Cave bears exhibit significantly lower encephalization compared to their contemporary relatives and intraspecific brain mass variation remained rather small. Encephalization was correlated with the combined dormancy-diet score. Body size evolution was a main driver in the degree of encephalization in cave bears as it increased in a much higher pace than brain size. In Ursus spelaeus, brain and body size increase over time albeit differently paced. This rate pattern is different in the highest encephalized bear species within the dataset, Ursus malayanus. The brain size in this species increased while body size heavily decreased compared to its ancestral stage. Conclusions: Early on in the evolution of cave bears encephalization decreased making it one of the least encephalized bear species compared to extant and extinct members of Ursidae. The results give reason to suspect that as herbivorous animals, cave bears might have exhibited a physiological buffer strategy to survive the strong seasonality of their environment. Thus, brain size was probably affected by the negative trade-off with adipose tissue as well as diet. The decrease of relative brain size in the herbivorous Ursus spelaeus is the result of a considerable increase in body size possibly in combination with environmental conditions forcing them to rest during winters.
Keywords: Physiological buffer, Dormancy, Diet, Ailuropoda, Helarctos, Melursus, Tremarctos, Ursus

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Date:22 May 2017
Deposited On:12 Jun 2017 12:18
Last Modified:25 Jun 2017 05:37
Publisher:BioMed Central
ISSN:1471-2148
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1186/s12862-017-0976-1

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