1
|
Nengovhela A, Ivy CM, Scott GR, Denys C, Taylor PJ. Counter-gradient variation and the expensive tissue hypothesis explain parallel brain size reductions at high elevation in cricetid and murid rodents. Sci Rep 2023; 13:5617. [PMID: 37024565 PMCID: PMC10079977 DOI: 10.1038/s41598-023-32498-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 03/28/2023] [Indexed: 04/08/2023] Open
Abstract
To better understand functional morphological adaptations to high elevation (> 3000 m above sea level) life in both North American and African mountain-associated rodents, we used microCT scanning to acquire 3D images and a 3D morphometric approach to calculate endocranial volumes and skull lengths. This was done on 113 crania of low-elevation and high-elevation populations in species of North American cricetid mice (two Peromyscus species, n = 53), and African murid rodents of two tribes, Otomyini (five species, n = 49) and Praomyini (four species, n = 11). We tested two distinct hypotheses for how endocranial volume might vary in high-elevation populations: the expensive tissue hypothesis, which predicts that brain and endocranial volumes will be reduced to lessen the costs of growing and maintaining a large brain; and the brain-swelling hypothesis, which predicts that endocranial volumes will be increased either as a direct phenotypic effect or as an adaptation to accommodate brain swelling and thus minimize pathological symptoms of altitude sickness. After correcting for general allometric variation in cranial size, we found that in both North American Peromyscus mice and African laminate-toothed (Otomys) rats, highland rodents had smaller endocranial volumes than lower-elevation rodents, consistent with the expensive tissue hypothesis. In the former group, Peromyscus mice, crania were obtained not just from wild-caught mice from high and low elevations but also from those bred in common-garden laboratory conditions from parents caught from either high or low elevations. Our results in these mice showed that brain size responses to elevation might have a strong genetic basis, which counters an opposite but weaker environmental effect on brain volume. These results potentially suggest that selection may act to reduce brain volume across small mammals at high elevations but further experiments are needed to assess the generality of this conclusion and the nature of underlying mechanisms.
Collapse
Affiliation(s)
- Aluwani Nengovhela
- Department of Mammalogy, National Museum, Bloemfontein, 9300, South Africa.
- Department of Zoology, School of Natural and Mathematical Sciences, University of Venda, Thohoyandou, South Africa.
| | - Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Christiane Denys
- Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, Université des Antilles, CP51, 57 Rue Cuvier, 75005, Paris, France
| | - Peter J Taylor
- Department of Zoology, School of Natural and Mathematical Sciences, University of Venda, Thohoyandou, South Africa
- Afromontane Unit, Department of Zoology and Entomology, University of the Free State, Phuthaditjhaba, South Africa
| |
Collapse
|
2
|
Lynch LM, Allen KL. Relative Brain Volume of Carnivorans Has Evolved in Correlation with Environmental and Dietary Variables Differentially among Clades. BRAIN, BEHAVIOR AND EVOLUTION 2022; 97:284-297. [PMID: 35235933 DOI: 10.1159/000523787] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Accepted: 02/16/2022] [Indexed: 12/21/2022]
Abstract
Carnivorans possess relatively large brains compared to most other mammalian clades. Factors like environmental complexity (Cognitive Buffer Hypothesis) and diet quality (Expensive-Tissue Hypothesis) have been proposed as mechanisms for encephalization in other large-brained clades. We examine whether the Cognitive Buffer and Expensive-Tissue Hypotheses account for brain size variation within Carnivora. Under these hypotheses, we predict a positive correlation between brain size and environmental complexity or protein consumption. Relative endocranial volume (phylogenetic generalized least-squares residual from species' mean body mass) and 9 environmental and dietary variables were collected from the literature for 148 species of terrestrial and marine carnivorans. We found that the correlation between relative brain volume and environment and diet differed among clades, a trend consistent with other larger brained vertebrates (i.e., Primates, Aves). Mustelidae and Procyonidae demonstrate larger brains in species with higher-quality diets, consistent with the Expensive-Tissue Hypothesis, while in Herpestidae, correlations between relative brain size and environment are consistent with the Cognitive Buffer Hypothesis. Our results indicate that carnivorans may have evolved relatively larger brains under similar selective pressures as primates despite the considerable differences in life history and behavior between these two clades.
Collapse
Affiliation(s)
- Leigha M Lynch
- Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA.,Midwestern University, Glendale, Arizona, USA
| | - Kari L Allen
- Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA
| |
Collapse
|
3
|
Zhu X, Chen C, Jiang Y, Zhao L, Jin L. Geographical variation of organ size in Andrew’s toad (Bufo andrewsi). Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.972942] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Phenotypic variation of morphological and physiological traits is assumed to be generated from spatial heterogeneity in environments, and it has been regarded as an important concern domain in evolutionary biology. Organs display markedly size variation among populations along environmental gradients and this variation is associated with changes in oxygen supply and energy demands. Here, we investigated geographical variation in the relative size of organs (i.e., brain, heart, lung, gallbladder, livers, spleen, kidneys, and digestive tract) among 14 populations of Andrew’s toad (Bufo andrewsi) transcending an elevational range from 864 to 2,367 m, and spanning 8° latitude. We found that although the relative sizes of the eight specific organs varied significantly among populations, none organ size was affected by altitude and latitude. However, based on the combined the new data and published data we found a negative relationship between the relative size of the heart and latitude, contrasting to the Hesse’s rule. We also found that the relative size of livers was positively linked to latitude, suggesting that more energy demands and intakes due to slower metabolism in high latitude shaped the evolution of larger livers.
Collapse
|
4
|
Heldstab SA, Isler K, Graber SM, Schuppli C, van Schaik CP. The economics of brain size evolution in vertebrates. Curr Biol 2022; 32:R697-R708. [PMID: 35728555 DOI: 10.1016/j.cub.2022.04.096] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Across the animal kingdom, we see remarkable variation in brain size. This variation has even increased over evolutionary time. Traditionally, studies aiming to explain brain size evolution have looked at the fitness benefits of increased brain size in relation to its increased cognitive performance in the social and/or ecological domain. However, brains are among the most energetically expensive tissues in the body and also require an uninterrupted energy supply. If not compensated, these energetic demands inevitably lead to a reduction in energy allocation to other vital functions. In this review, we summarize how an increasing number of studies show that to fully comprehend brain size evolution and the large variation in brain size across lineages, it is important to look at the economics of brains, including the different pathways through which the high energetic costs of brains can be offset. We further show how numerous studies converge on the conclusion that cognitive abilities can only drive brain size evolution in vertebrate lineages where they result in an improved energy balance through favourable ecological preconditions. Cognitive benefits that do not directly improve the organism's energy balance can only be selectively favoured when they produce such large improvements in reproduction or survival that they outweigh the negative energetic effects of the large brain.
Collapse
Affiliation(s)
- Sandra A Heldstab
- Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; Development and Evolution of Cognition Research Group, Max Planck Institute of Animal Behavior, Bücklestrasse 5a, 78467 Konstanz, Germany.
| | - Karin Isler
- Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Sereina M Graber
- Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Caroline Schuppli
- Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; Development and Evolution of Cognition Research Group, Max Planck Institute of Animal Behavior, Bücklestrasse 5a, 78467 Konstanz, Germany
| | - Carel P van Schaik
- Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; Comparative Socioecology Group, Max Planck Institute of Animal Behavior, Bücklestrasse 5a, 78467 Konstanz, Germany; Department of Evolutionary Biology and Environmental Science, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| |
Collapse
|