1
|
Marcy AE, Mitchell DR, Guillerme T, Phillips MJ, Weisbecker V. Beyond CREA: Evolutionary patterns of non-allometric shape variation and divergence in a highly allometric clade of murine rodents. Ecol Evol 2024; 14:e11588. [PMID: 38952651 PMCID: PMC11213820 DOI: 10.1002/ece3.11588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 05/28/2024] [Accepted: 06/03/2024] [Indexed: 07/03/2024] Open
Abstract
The shared functions of the skull are thought to result in common evolutionary patterns in mammalian cranial shape. Craniofacial evolutionary allometry (CREA) is a particularly prominent pattern where larger species display proportionally elongate facial skeletons and smaller braincases. It was recently proposed that CREA arises from biomechanical effects of cranial scaling when diets are similar. Thus, deviations from CREA should occur with changes in cranial biomechanics, for example due to dietary change. Here, we test this using 3D geometric morphometric analysis in a dataset of Australian murine crania, which are highly allometric. We contrast allometric and non-allometric variation in the cranium by comparing evolutionary mode, allometry, ordinations, as well as allometry, integration, and modularity in functional modules. We found evidence of stabilising selection in allometry-containing and size-free shape, and substantial non-allometric variation aligned with dietary specialisation in parallel with CREA. Integration among cranial modules was higher, and modularity lower, with size included, but integration between rostrum and cranial vault, which are involved in the CREA pattern, dropped dramatically after size removal. Our results thus support the hypothesis that CREA is a composite arising from selection on cranial function, with substantial non-allometric shape variation occurring alongside CREA where dietary specialisation impacts selection on gnawing function. This emphasises the need to research mammalian cranial evolution in the context of allometric and non-allometric selection on biomechanical function.
Collapse
Affiliation(s)
- Ariel E. Marcy
- Commonwealth Scientific and Industrial Research Organisation (CSIRO), Science ConnectCanberraAustralian Capital TerritoryAustralia
| | - D. Rex Mitchell
- College of Science and EngineeringFlinders UniversityBedford ParkSouth AustraliaAustralia
| | | | - Matthew J. Phillips
- School of Biology and Environmental ScienceQueensland University of TechnologyBrisbaneQueenslandAustralia
| | - Vera Weisbecker
- College of Science and EngineeringFlinders UniversityBedford ParkSouth AustraliaAustralia
- Centre of Excellence for Australian Biodiversity and HeritageWollongongAustralia
| |
Collapse
|
2
|
Popowics TE, Hwang I, Lu J, Nguyen T, Sample M, Sangster A, Tang D, Dennison CR, Romanyk DL, Rafferty K, Greenlee G. In vivo measurement of strain in the periodontal space of pig (Sus scrofa) incisors using in-fiber Bragg sensors. J Morphol 2024; 285:e21738. [PMID: 38783683 DOI: 10.1002/jmor.21738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 05/08/2024] [Accepted: 05/13/2024] [Indexed: 05/25/2024]
Abstract
The incisor teeth in pigs, Sus scrofa, function in association with a disc-shaped snout to explore the environment for potential food. Understanding how mechanical loading applied to the tooth deforms the periodontal ligament (PDL) is important to determining the role of periodontal mechanoreceptors during food exploration and feeding. The objective of this study was to use fiber Bragg (FBG) sensors to measure strain in vivo within the PDL space of pig incisors. The central mandibular incisors of pigs underwent spring loaded lingual tipping during FBG strain recording within the labial periodontal space. FBG sensors were placed within the periodontal space of the central mandibular incisors of ~2-3-month-old farm pigs. The magnitude and orientation of spring loads are expected to mimic incisor contact with food. During incisor tipping with load calibrated springs, FBG strains in vitro (N = 6) and in vivo (N = 6) recorded at comparable load levels overlapped in range (-10-20 με). Linear regressions between peak FBG strains, that is, the highest recorded strain value, and baseline strains, that is, strain without applied spring load, were significant across all in vivo experiments (peak strain at 200 g vs. baseline, p = .04; peak strain at 2000 g vs. baseline p = .03; peak strain at 2000 g vs. 200 g, p = .004). These linear relationships indicate that on a per experiment basis, the maximum measured strain at different spring loads showed predictable differences. A Friedman test of the absolute value of peak strain confirmed the significant increase in strain between baseline, 200 g, and 2000 g spring activation (p = .02). Mainly compressive strains were recorded in the labial PDL space and increases in spring load applied in vivo generated increases in FBG strain measurements. These results demonstrate the capacity for FBG sensors to be used in vivo to assess transmission of occlusal loads through the periodontium. PDL strain is associated with mechanoreceptor stimulation and is expected to affect the functional morphology of the incisors. The overall low levels of strain observed may correspond with the robust functional morphology of pig incisors and the tendency for pigs to encounter diverse foods and substrates during food exploration.
Collapse
Affiliation(s)
- Tracy E Popowics
- Department of Oral Health Sciences, University of Washington, Seattle, Washington, USA
| | - Isabelle Hwang
- Department of Oral Health Sciences, University of Washington School of Dentistry, University of Washington, Seattle, Washington, USA
| | - Jason Lu
- Department of Oral Health Sciences, University of Washington School of Dentistry, University of Washington, Seattle, Washington, USA
| | - Tammy Nguyen
- Department of Oral Health Sciences, University of Washington School of Dentistry, University of Washington, Seattle, Washington, USA
| | - Morgan Sample
- Department of Oral Health Sciences, University of Washington School of Dentistry, University of Washington, Seattle, Washington, USA
| | - Anissa Sangster
- Department of Oral Health Sciences, University of Washington School of Dentistry, University of Washington, Seattle, Washington, USA
| | - Derrick Tang
- Department of Oral Health Sciences, University of Washington, Seattle, Washington, USA
| | | | - Dan L Romanyk
- Department of Mechanical Engineering, University of Alberta, Edmonton, AB, Canada
| | - Katherine Rafferty
- Department of Orthodontics, University of Washington, Seattle, Washington, USA
| | - Geoffrey Greenlee
- Department of Orthodontics, University of Washington, Seattle, Washington, USA
| |
Collapse
|
3
|
Goswami A, Noirault E, Coombs EJ, Clavel J, Fabre AC, Halliday TJD, Churchill M, Curtis A, Watanabe A, Simmons NB, Beatty BL, Geisler JH, Fox DL, Felice RN. Developmental origin underlies evolutionary rate variation across the placental skull. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220083. [PMID: 37183904 PMCID: PMC10184245 DOI: 10.1098/rstb.2022.0083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023] Open
Abstract
The placental skull has evolved into myriad forms, from longirostrine whales to globular primates, and with a diverse array of appendages from antlers to tusks. This disparity has recently been studied from the perspective of the whole skull, but the skull is composed of numerous elements that have distinct developmental origins and varied functions. Here, we assess the evolution of the skull's major skeletal elements, decomposed into 17 individual regions. Using a high-dimensional morphometric approach for a dataset of 322 living and extinct eutherians (placental mammals and their stem relatives), we quantify patterns of variation and estimate phylogenetic, allometric and ecological signal across the skull. We further compare rates of evolution across ecological categories and ordinal-level clades and reconstruct rates of evolution along lineages and through time to assess whether developmental origin or function discriminate the evolutionary trajectories of individual cranial elements. Our results demonstrate distinct macroevolutionary patterns across cranial elements that reflect the ecological adaptations of major clades. Elements derived from neural crest show the fastest rates of evolution, but ecological signal is equally pronounced in bones derived from neural crest and paraxial mesoderm, suggesting that developmental origin may influence evolutionary tempo, but not capacity for specialisation. This article is part of the theme issue 'The mammalian skull: development, structure and function'.
Collapse
Affiliation(s)
- Anjali Goswami
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
| | - Eve Noirault
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
| | - Ellen J Coombs
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
| | - Julien Clavel
- Université Lyon, Université Claude Bernard Lyon 1, CNRS, ENTPE, UMR 5023 LEHNA, 69622 Villeurbanne, France
| | - Anne-Claire Fabre
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Naturhistorisches Museum Bern, 3005 Bern, Switzerland
- Institute of Ecology and Evolution, University of Bern, 3012 Bern, Switzerland
| | - Thomas J D Halliday
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Morgan Churchill
- Department of Biology, University of Wisconsin Oshkosh, Oshkosh, WI 54901, USA
| | - Abigail Curtis
- Department of Biology, University of Washington, Seattle, WA 98195, USA
| | - Akinobu Watanabe
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
- Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA
| | - Nancy B Simmons
- Department of Mammalogy, Division of Vertebrate Zoology, American Museum of Natural History, New York, NY 10024, USA
| | - Brian L Beatty
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
| | - Jonathan H Geisler
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
| | - David L Fox
- Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA
| | - Ryan N Felice
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
- Centre for Integrative Anatomy, Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
| |
Collapse
|
4
|
Gomes Rodrigues H, Damette M. Incipient morphological specializations associated with fossorial life in the skull of ground squirrels (Sciuridae, Rodentia). J Morphol 2023; 284:e21540. [PMID: 36533735 PMCID: PMC10107104 DOI: 10.1002/jmor.21540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 09/01/2022] [Accepted: 11/26/2022] [Indexed: 12/14/2022]
Abstract
Anatomical and biological specializations have been studied extensively in fossorial rodents, especially in subterranean species, such as mole-rats or pocket-gophers. Sciurids (i.e., squirrels) are mostly known for their diverse locomotory behaviors, and encompass many arboreal species. They also include less specialized fossorial species, such as ground squirrels that are mainly scratch diggers. The skull of ground squirrels remains poorly investigated in a fossorial context, while it may reflect incipient morphological specializations associated with fossorial life, especially due to the putative use of incisors for digging in some taxa. Here, we present the results of a comparative analysis of the skull of five fossorial sciurid species, and compare those to four arboreal sciurids, one arboreal/fossorial sciurid and one specialized fossorial aplodontiid. The quantification of both cranial and mandibular shapes, using three dimensional geometric morphometrics, reveals that fossorial species clearly depart from arboreal species. Fossorial species from the Marmotini tribe, and also Xerini to a lesser extent, show widened zygomatic arches and occipital plate on the cranium, and a wide mandible with reduced condyles. These shared characteristics, which are present in the aplodontiid species, likely represent fossorial specializations rather than relaxed selection on traits related to the ancestral arboreal condition of sciurids. Such cranial and mandibular configurations combined with proodont incisors might also be related to the frequent use of incisors for digging (added to forelimbs), especially in Marmotini evolving in soft to hard soil conditions. This study provides some clues to understand the evolutionary mechanisms shaping the skull of fossorial rodents, in relation to the time spent underground and to the nature of the soil.
Collapse
Affiliation(s)
- Helder Gomes Rodrigues
- Centre de Recherche en Paléontologie-Paris (CR2P), UMR CNRS 7207, CP38, Muséum national d'Histoire naturelle, Sorbonne Université, Paris, France
| | - Mathilde Damette
- Centre de Recherche en Paléontologie-Paris (CR2P), UMR CNRS 7207, CP38, Muséum national d'Histoire naturelle, Sorbonne Université, Paris, France
| |
Collapse
|
5
|
Morris PJR, Cox PG, Cobb SNF. The biomechanical significance of the elongated rodent incisor root in the mandible during incision. Sci Rep 2022; 12:3819. [PMID: 35264608 PMCID: PMC8907204 DOI: 10.1038/s41598-022-07779-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Accepted: 02/23/2022] [Indexed: 11/09/2022] Open
Abstract
Rodents are characterised by a distinctive masticatory apparatus which includes a single pair of enlarged and continually growing incisors. This morphology, termed diprotodonty, has also independently evolved in a number of other mammals, including the aye-aye. This study examined the functional significance of the internal "root" of the elongated rodent-like incisor. The mandibles of four rodents and an aye-aye were modelled to exhibit incrementally shorter incisor roots. Finite element analysis was used to predict stress and strain patterns across the jaw to determine whether the length of the incisor root contributes to the resistance of mechanical forces encountered in the mandible during incision. It was found that von Mises stresses increase in the region of the mandible local to where the incisor is removed, but that the stress distribution across the wider mandible is only minimally affected. Thus, the long internal incisor appears to play a small role in resisting bending forces close to the incisor alveolus, and may act with the arch-like mandibular shape to strengthen the mandible in this region. However, the impact across the whole mandible is relatively limited, suggesting the highly elongate incisor in diprotodont mammals may be principally driven by other factors such as rapid incisor wear.
Collapse
Affiliation(s)
| | - Philip G Cox
- Hull York Medical School and Department of Archaeology, University of York, York, YO10 5DD, UK
| | - Samuel N F Cobb
- Hull York Medical School and Department of Archaeology, University of York, York, YO10 5DD, UK
| |
Collapse
|
6
|
Smith AL, Robinson C, Taylor AB, Panagiotopoulou O, Davis J, Ward CV, Kimbel WH, Alemseged Z, Ross CF. Comparative biomechanics of the Pan and Macaca mandibles during mastication: finite element modelling of loading, deformation and strain regimes. Interface Focus 2021; 11:20210031. [PMID: 34938438 PMCID: PMC8361577 DOI: 10.1098/rsfs.2021.0031] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/09/2021] [Indexed: 10/17/2023] Open
Abstract
The mechanical behaviour of the mandibles of Pan and Macaca during mastication was compared using finite element modelling. Muscle forces were calculated using species-specific measures of physiological cross-sectional area and scaled using electromyographic estimates of muscle recruitment in Macaca. Loading regimes were compared using moments acting on the mandible and strain regimes were qualitatively compared using maps of principal, shear and axial strains. The enlarged and more vertically oriented temporalis and superficial masseter muscles of Pan result in larger sagittal and transverse bending moments on both working and balancing sides, and larger anteroposterior twisting moments on the working side. The mandible of Pan experiences higher principal strain magnitudes in the ramus and mandibular prominence, higher transverse shear strains in the top of the symphyseal region and working-side corpus, and a predominance of sagittal bending-related strains in the balancing-side mandible. This study lays the foundation for a broader comparative study of Hominidae mandibular mechanics in extant and fossil hominids using finite element modelling. Pan's larger and more vertical masseter and temporalis may make it a more suitable model for hominid mandibular biomechanics than Macaca.
Collapse
Affiliation(s)
- Amanda L. Smith
- Department of Anatomy, Pacific Northwest University of Health Sciences, 200 University Parkway, Yakima, WA 98901, USA
- Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, USA
| | - Chris Robinson
- Department of Biological Sciences, Bronx Community College, Bronx, NY 10453, USA
| | | | - Olga Panagiotopoulou
- Department of Anatomy and Developmental Biology, Monash Biomedicine Discovery Institute, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Melbourne, Victoria 3800, Australia
| | - Julian Davis
- Department of Engineering, University of Southern Indiana, 8600 University Boulevard, Evansville, IN 47712, USA
| | - Carol V. Ward
- Department of Pathology and Anatomical Sciences, One Hospital Drive, University of Missouri, Columbia, MO 65212, USA
| | - William H. Kimbel
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287-4101, USA
| | - Zeresenay Alemseged
- Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, USA
| | - Callum F. Ross
- Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, USA
| |
Collapse
|
7
|
Alhajeri BH. Desmodilliscus braueri crania compared to Pachyuromys duprasi (Desmodilliscini, Gerbillinae, Rodentia). MAMMALIA 2021. [DOI: 10.1515/mammalia-2021-0036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Molecular phylogenies support the monophyly of Desmodilliscus braueri and Pachyuromys duprasi as a clade basally split from all other gerbillines. While this monophyly supports their placement in a single tribe (Desmodilliscini), no morphological synapomorphies exist among desmodilliscines. This study compares the scale-independent cranial shapes of these two species using geometric morphometrics to determine how they differ and/or converge. Tribal synapomorphies, should they exist, may appear as interspecifically invariable cranial regions. No such invariable cranial regions were detected. The two species significantly differed in cranial size and shape. A small part of shape variation was allometric, with a weak unique allometric effect. No sexual size nor shape dimorphism was found. The sister taxa greatly differed in almost all cranial features, with Pachyuromys (when compared to Desmodilliscus) having a larger-sized cranium, with a larger bulla and suprameatal triangle, a more posteriorly placed palatine foramina, and more anteriorly shifted (and reduced) rostral cranial structures, due to being crowded by the hypertrophied bulla. Cranial variation patterns are consistent with the literature. The extreme morphological divergence among these species is explained by the distant divergence time and ecological differences. Absence of cranial shape synapomorphies does not preclude synapomorphies in other craniodental morphological features (e.g., detailed morphology of the dentition and cranial foramina) or in other morphological structures, such as the postcranial skeleton.
Collapse
Affiliation(s)
- Bader H. Alhajeri
- Department of Biological Sciences , Kuwait University , Safat, 13060 , Kuwait
| |
Collapse
|
8
|
Kalthoff DC, Mörs T. Biomechanical adaptations for burrowing in the incisor enamel microstructure of Geomyidae and Heteromyidae (Rodentia: Geomyoidea). Ecol Evol 2021; 11:9447-9459. [PMID: 34306634 PMCID: PMC8293781 DOI: 10.1002/ece3.7765] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 05/20/2021] [Accepted: 05/24/2021] [Indexed: 11/17/2022] Open
Abstract
The enamel microstructure of fossil and extant Geomyoidea (Geomyidae, Heteromyidae) lower incisors incorporates three- or two-layered schmelzmusters with uniserial, transverse Hunter-Schreger bands having parallel and perpendicular or exclusively perpendicular oriented interprismatic matrix. Phylogenetically, these schmelzmusters are regarded as moderately (enamel type 2) to highly derived (enamel type 3). Our analysis detected a zone of modified radial enamel close to the enamel-dentine junction. Modified radial enamel shows a strong phylogenetic signal within the clade Geomorpha as it is restricted to fossil and extant Geomyoidea and absent in Heliscomyidae, Florentiamyidae, and Eomyidae. This character dates back to at least the early Oligocene (early Arikareean, 29 Ma), where it occurs in entoptychine gophers. We contend that this specialized incisor enamel architecture developed as a biomechanical adaptation to regular burrowing activities including chisel-tooth digging and a fiber-rich diet and was probably present in the common ancestor of the clade. We regard the occurrence of modified radial enamel in lower incisors of scratch-digging Geomyidae and Heteromyidae as the retention of a plesiomorphic character that is selectively neutral. The shared occurrence of modified radial enamel is a strong, genetically anchored argument for the close phylogenetic relationship of Geomyidae and Heteromyidae on the dental microstructure level.
Collapse
Affiliation(s)
| | - Thomas Mörs
- Department of PalaeobiologySwedish Museum of Natural HistoryStockholmSweden
| |
Collapse
|
9
|
Evolution Towards Fossoriality and Morphological Convergence in the Skull of Spalacidae and Bathyergidae (Rodentia). J MAMM EVOL 2021. [DOI: 10.1007/s10914-021-09550-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
|
10
|
Alhajeri BH. A morphometric comparison of the cranial shapes of Asian dwarf hamsters (Phodopus, Cricetinae, Rodentia). ZOOL ANZ 2021. [DOI: 10.1016/j.jcz.2021.04.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
|
11
|
de Barros FC, Grizante MB, Zampieri FAM, Kohlsdorf T. Peculiar relationships among morphology, burrowing performance and sand type in two fossorial microteiid lizards. ZOOLOGY 2020; 144:125880. [PMID: 33310388 DOI: 10.1016/j.zool.2020.125880] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 11/09/2020] [Accepted: 11/10/2020] [Indexed: 12/16/2022]
Abstract
Associations among ecology, morphology and locomotor performance have been intensively investigated in several vertebrate lineages. Knowledge on how phenotypes evolve in natural environments likely benefits from identification of circumstances that might expand current ecomorphological equations. In this study, we used two species of Calyptommatus lizards from Brazilian Caatingas to evaluate if specific soil properties favor burrowing performance. As a derived prediction, we expected that functional associations would be easily detectable at the sand condition that favors low-resistance burrowing. We collected two endemic lizards and soil samples in their respective localities, obtained morphological data and recorded performance of both species in different sand types. As a result, the two species burrowed faster at the fine and homogeneous sand, the only condition where we detected functional associations between morphology and locomotion. In this sand type, lizards from both Calyptommatus species that have higher trunks and more concave heads were the ones that burrowed faster, and these phenotypic traits did not morphologically discriminate the two Calyptommatus populations studied. We discuss that integrative approaches comprising manipulation of environmental conditions clearly contribute to elucidate processes underlying phenotypic evolution in fossorial lineages.
Collapse
Affiliation(s)
- Fábio C de Barros
- Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto, SP, 14040-901, Brazil; Department of Ecology and Evolutionary Biology, ICAQF, Federal University of São Paulo, Rua Prof. Artur Riedel, 275, Diadema, SP, 09972-270, Brazil.
| | - Mariana B Grizante
- Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto, SP, 14040-901, Brazil; Instituto Dante Pazzanese de Cardiologia, Brazil
| | - Felipe A M Zampieri
- Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto, SP, 14040-901, Brazil
| | - Tiana Kohlsdorf
- Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto, SP, 14040-901, Brazil.
| |
Collapse
|
12
|
Feijó A, Ge D, Wen Z, Xia L, Yang Q. Divergent adaptations in resource‐use traits explain how pikas thrive on the roof of the world. Funct Ecol 2020. [DOI: 10.1111/1365-2435.13609] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anderson Feijó
- Key Laboratory of Zoological Systematics and Evolution Institute of Zoology Chinese Academy of Sciences Beijing China
| | - Deyan Ge
- Key Laboratory of Zoological Systematics and Evolution Institute of Zoology Chinese Academy of Sciences Beijing China
| | - Zhixin Wen
- Key Laboratory of Zoological Systematics and Evolution Institute of Zoology Chinese Academy of Sciences Beijing China
| | - Lin Xia
- Key Laboratory of Zoological Systematics and Evolution Institute of Zoology Chinese Academy of Sciences Beijing China
| | - Qisen Yang
- Key Laboratory of Zoological Systematics and Evolution Institute of Zoology Chinese Academy of Sciences Beijing China
| |
Collapse
|
13
|
Doubell NS, Sahd L, Kotzé SH. Comparative forelimb morphology of scratch-digging and chisel-tooth digging African mole-rat species. J Morphol 2020; 281:1029-1046. [PMID: 32589809 DOI: 10.1002/jmor.21229] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Revised: 06/01/2020] [Accepted: 06/05/2020] [Indexed: 01/09/2023]
Abstract
Bathyergus suillus (Cape dune mole-rat) and Heterocephalus glaber (naked mole-rat) are two species of subterranean burrowing rodents. Bathyergus suillus occurs in soft sandy soils and is regarded as a scratch-digger, while H. glaber is found in hard, compact soils and is a chisel-tooth digging species. The present study aimed to determine musculoskeletal differences in the forelimb of these two species. The muscles of the forelimb, back and neck were dissected to the points of origin and insertion in the left and right forelimbs, B. suillus (n = 7) and H. glaber (n = 5). Dissected muscles were photographed before maceration to demonstrate muscle attachments. The scapular spine, acromion process and clavicle were relatively straight in B. suillus. In comparison a curved scapular spine, acromion process and clavicle were observed in H. glaber. In both species, the clavicle rested on the greater tuberosity of the humerus. In B. suillus, the deltoid tuberosity was prominent and situated more distally on the humeral shaft compared to the indistinct, more proximally situated deltoid tuberosity in H. glaber. A prominent bony structure underlying the thenar pad as well as a cartilaginous protrusion beneath the hypothenar pad were observed on the palmar surface of the manus in B. suillus. Prominent claws were observed in B. suillus. A robust m. sternohyoideus was observed in H. glaber while mm. tensor fasciae antebrachii and coracobrachialis were absent. The flexors of the antebrachium of B. suillus had additional and enlarged attachment sites. The forelimb of B. suillus may be morphologically adapted for scratch-digging with relatively large and additional forelimb muscles and robust bones. In comparison, H. glaber had a reduction in the relative size, amount of muscles as well as number of attachment sites in the forelimb muscles, while the well-developed ventral neck muscles may facilitate neck and head stabilisation during chisel-tooth digging.
Collapse
Affiliation(s)
- Narusa S Doubell
- Division of Clinical Anatomy, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - Lauren Sahd
- Division of Clinical Anatomy, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - Sanet H Kotzé
- Division of Clinical Anatomy, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| |
Collapse
|
14
|
Cox PG, Faulkes CG, Bennett NC. Masticatory musculature of the African mole-rats (Rodentia: Bathyergidae). PeerJ 2020; 8:e8847. [PMID: 32231887 PMCID: PMC7100595 DOI: 10.7717/peerj.8847] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 03/03/2020] [Indexed: 12/22/2022] Open
Abstract
The Bathyergidae, commonly known as blesmols or African mole-rats, is a family of rodents well-known for their subterranean lifestyle and tunnelling behaviour. Four of the five extant bathyergid genera (Cryptomys, Fukomys, Georychus and Heliophobius) are chisel-tooth diggers, that is they dig through soil with their enlarged incisors, whereas the remaining genus (Bathyergus) is a scratch-digger, only using its forelimbs for burrowing. Heterocephalus glaber, the naked mole-rat, is also a chisel-tooth digger and was until recently included within the Bathyergidae (as the most basally branching genus), but has now been placed by some researchers into its own family, the Heterocephalidae. Given the importance of the masticatory apparatus in habitat construction in this group, knowledge and understanding of the morphology and arrangement of the jaw-closing muscles in Bathyergidae is vital for future functional analyses. Here, we use diffusible iodine-based contrast-enhanced microCT to reveal and describe the muscles of mastication in representative specimens of each genus of bathyergid mole-rat and to compare them to the previously described musculature of the naked mole-rat. In all bathyergids, as in all rodents, the masseter muscle is the most dominant component of the masticatory musculature. However, the temporalis is also a relatively large muscle, a condition normally associated with sciuromorphous rodents. Unlike their hystricomorphous relatives, the bathyergids do not show an extension of the masseter through the infraorbital foramen on to the rostrum (other than a very slight protrusion in Cryptomys and Fukomys). Thus, morphologically, bathyergids are protrogomorphous, although this is thought to be secondarily derived rather than retained from ancestral rodents. Overall, the relative proportions of the jaw-closing muscles were found to be fairly consistent between genera except in Bathyergus, which was found to have an enlarged superficial masseter and relatively smaller pterygoid muscles. It is concluded that these differences may be a reflection of the behaviour of Bathyergus which, uniquely in the family, does not use its incisors for digging.
Collapse
Affiliation(s)
- Philip G Cox
- Department of Archaeology and Hull York Medical School, University of York, York, UK
| | - Chris G Faulkes
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Nigel C Bennett
- Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| |
Collapse
|
15
|
Guerrero-Arenas R, Jiménez-Hidalgo E, Genise JF. Burrow systems evince non-solitary geomyid rodents from the Paleogene of southern Mexico. PLoS One 2020; 15:e0230040. [PMID: 32163482 PMCID: PMC7067467 DOI: 10.1371/journal.pone.0230040] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 02/18/2020] [Indexed: 11/18/2022] Open
Abstract
We describe a new complex burrow system produced by geomyids in southern Mexico. Yaviichnus inyooensis igen. isp. nov. is composed of main large chambers near the top of the paleosol, from which shafts showing different morphologies and orientations radiate, some of them ending in or connected to small deeper chambers. Gregorymys spp. is proposed as the producer based on its fossorial habits, abundance in the outcrops, presence of remains inside the burrows, and paired grooves in the walls, which are compatible with the traces of geomyid incisors. The complexity of these burrows attests to an extended underground life that would have been triggered by semiarid to arid conditions. Morphological complexity also suggests that the burrows were excavated and inhabited by more than one individual, indicating that Oligocene Gregorymys of southern Mexico would be a unique gregarious geomyid.
Collapse
Affiliation(s)
| | | | - Jorge Fernando Genise
- CONICET, División Icnología, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina
| |
Collapse
|
16
|
Adams NF, Rayfield EJ, Cox PG, Cobb SN, Corfe IJ. Functional tests of the competitive exclusion hypothesis for multituberculate extinction. ROYAL SOCIETY OPEN SCIENCE 2019; 6:181536. [PMID: 31032010 PMCID: PMC6458384 DOI: 10.1098/rsos.181536] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 02/21/2019] [Indexed: 05/08/2023]
Abstract
Multituberculate mammals thrived during the Mesozoic, but their diversity declined from the mid-late Paleocene onwards, becoming extinct in the late Eocene. The radiation of superficially similar, eutherian rodents has been linked to multituberculate extinction through competitive exclusion. However, characteristics providing rodents with a supposed competitive advantage are currently unknown and comparative functional tests between the two groups are lacking. Here, a multifaceted approach to craniomandibular biomechanics was taken to test the hypothesis that superior skull function made rodents more effective competitors. Digital models of the skulls of four extant rodents and the Upper Cretaceous multituberculate Kryptobaatar were constructed and used (i) in finite-element analysis to study feeding-induced stresses, (ii) to calculate metrics of bite force production and (iii) to determine mechanical resistances to bending and torsional forces. Rodents exhibit higher craniomandibular stresses and lower resistances to bending and torsion than the multituberculate, apparently refuting the competitive exclusion hypothesis. However, rodents optimize bite force production at the expense of higher skull stress and we argue that this is likely to have been more functionally and selectively important. Our results therefore provide the first functional lines of evidence for potential reasons behind the decline of multituberculates in the changing environments of the Paleogene.
Collapse
Affiliation(s)
- Neil F. Adams
- School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
- Author for correspondence: Neil F. Adams e-mail:
| | - Emily J. Rayfield
- School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
- Author for correspondence: Emily J. Rayfield e-mail:
| | - Philip G. Cox
- Department of Archaeology, University of York, York YO1 7EP, UK
- Centre for Anatomical and Human Sciences, Hull York Medical School, University of York, York YO10 5DD, UK
| | - Samuel N. Cobb
- Department of Archaeology, University of York, York YO1 7EP, UK
- Centre for Anatomical and Human Sciences, Hull York Medical School, University of York, York YO10 5DD, UK
| | - Ian J. Corfe
- Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| |
Collapse
|
17
|
Morris PJR, Cox PG, Cobb SN. Mechanical significance of morphological variation in diprotodont incisors. ROYAL SOCIETY OPEN SCIENCE 2019; 6:181317. [PMID: 31031997 PMCID: PMC6458350 DOI: 10.1098/rsos.181317] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Accepted: 02/20/2019] [Indexed: 06/09/2023]
Abstract
All rodents possess a single pair of enlarged incisors that grow throughout life. This condition (diprotodonty) is characteristic of Rodentia, but is also found in other mammals such as lagomorphs, hyraxes, the aye-aye and common wombat. This study surveyed lower incisor morphology across extant diprotodonts to examine shape variation within and between rodents and other diprotodonts, and to determine if tooth shape varies in a manner predictable from mechanics. Six linear and area variables were recorded from microCT scans of the mandibles of 33 diprotodont mammals. The curvature of the rodent lower incisors, as measured by the proportion of a circle it occupies, was shown to vary between 20 and 45%, with non-Glires taxa falling outside this range. Relative lengths of the portions of the incisor within and external to the mandible were not significantly correlated when the overall size was taken into account. Cross-sectional geometry of the incisor was significantly correlated with the external length of the incisor. Overall, incisor morphology was shown to vary in a way predictable from ecology and mechanics, in order to resist bending. Among non-rodents, lagomorph incisors closely resemble those of rodents, and, relative to rodents, hyrax and wombat incisors are somewhat smaller but aye-aye incisors are much more extreme in morphology.
Collapse
Affiliation(s)
| | - Philip G. Cox
- Department of Archaeology and Hull York Medical School, University of York, York YO10 5DD, UK
| | - Samuel N. Cobb
- Department of Archaeology and Hull York Medical School, University of York, York YO10 5DD, UK
| |
Collapse
|
18
|
McIntosh AF, Cox PG. The impact of digging on the evolution of the rodent mandible. J Morphol 2018; 280:176-183. [PMID: 30570152 DOI: 10.1002/jmor.20929] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 10/05/2018] [Accepted: 11/01/2018] [Indexed: 01/07/2023]
Abstract
There are two main (but not mutually exclusive) methods by which subterranean rodents construct burrows: chisel-tooth digging, where large incisors are used to dig through soil; and scratch digging, where forelimbs and claws are used to dig instead of incisors. A previous study by the authors showed that upper incisors of chisel-tooth diggers were better adapted to dig but the overall cranial morphology within the rodent sample was not significantly different. This study analyzed the lower incisors and mandibles of the specimens used in the previous study to show the impact of chisel-tooth digging on the rodent mandible. We compared lower incisors and mandibular shape of chisel-tooth digging rodents with nonchisel-tooth digging rodents to see if there were morphological differences between the two groups. The shape of incisors was quantified using incisor radius of curvature and second moment of area (SMA). Mandibular shape was quantified using landmark based geometric morphometrics. We found that lower incisor shape was strongly influenced by digging group using a Generalized Phylogenetic ancova (analysis of covariance). A phylogenetic Procrustes anova (analysis of variance) showed that mandibular shape of chisel-tooth digging rodents was also significantly different from nonchisel-tooth digging rodents. The phylogenetic signal of incisor radius of curvature was weak, whereas that of incisor SMA and mandibular shape was significant. This is despite the analyses revealing significant differences in the shape of both mandibles and incisors between digging groups. In conclusion, we showed that although the mandible and incisor of rodents are influenced by function, there is also a degree of phylogenetic affinity that shapes the rodent mandibular apparatus.
Collapse
Affiliation(s)
- Andrew F McIntosh
- Department of Science, School of Arts and Sciences, Abraham Baldwin Agricultural College, Tifton, Georgia
| | - Philip G Cox
- Department of Archaeology, and Hull York Medical School, University of York, Heslington, York, United Kingdom
| |
Collapse
|
19
|
Martinez Q, Lebrun R, Achmadi AS, Esselstyn JA, Evans AR, Heaney LR, Miguez RP, Rowe KC, Fabre PH. Convergent evolution of an extreme dietary specialisation, the olfactory system of worm-eating rodents. Sci Rep 2018; 8:17806. [PMID: 30546026 PMCID: PMC6293001 DOI: 10.1038/s41598-018-35827-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 11/09/2018] [Indexed: 11/18/2022] Open
Abstract
Turbinal bones are key components of the mammalian rostrum that contribute to three critical functions: (1) homeothermy, (2) water conservation and (3) olfaction. With over 700 extant species, murine rodents (Murinae) are the most species-rich mammalian subfamily, with most of that diversity residing in the Indo-Australian Archipelago. Their evolutionary history includes several cases of putative, but untested ecomorphological convergence, especially with traits related to diet. Among the most spectacular rodent ecomorphs are the vermivores which independently evolved in several island systems. We used 3D CT-scans (N = 87) of murine turbinal bones to quantify olfactory capacities as well as heat or water conservation adaptations. We obtained similar results from an existing 2D complexity method and two new 3D methodologies that quantify bone complexity. Using comparative phylogenetic methods, we identified a significant convergent signal in the rostral morphology within the highly specialised vermivores. Vermivorous species have significantly larger and more complex olfactory turbinals than do carnivores and omnivores. Increased olfactory capacities may be a major adaptive feature facilitating rats' capacity to prey on elusive earthworms. The narrow snout that characterises vermivores exhibits significantly reduced respiratory turbinals, which may reduce their heat and water conservation capacities.
Collapse
Affiliation(s)
- Quentin Martinez
- Institut des Sciences de l'Evolution (ISEM, UMR 5554 CNRS-IRD-UM), Université de Montpellier, Place E. Bataillon - CC 064 - 34095, Montpellier Cedex 5, France.
| | - Renaud Lebrun
- Institut des Sciences de l'Evolution (ISEM, UMR 5554 CNRS-IRD-UM), Université de Montpellier, Place E. Bataillon - CC 064 - 34095, Montpellier Cedex 5, France
| | - Anang S Achmadi
- Museum Zoologicum Bogoriense, Research Center For Biology, Indonesian Institute of Sciences (LIPI), Jl.Raya Jakarta-Bogor Km.46, Cibinong, 16911, Indonesia
| | - Jacob A Esselstyn
- Museum of Natural Science, 119 Foster Hall, Louisiana State University, Baton Rouge, Louisiana, 70803, United States
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, 70803, United States
| | - Alistair R Evans
- School of Biological Sciences, 18 Innovation Walk, Monash University, Victoria, 3800, Australia
- Sciences Department, Museums Victoria, Melbourne, Victoria, 3001, Australia
| | - Lawrence R Heaney
- Field Museum of Natural History, 1400 S Lake Shore Drive, Chicago, 60605, United States
| | - Roberto Portela Miguez
- Natural History Museum of London, Department of Life Sciences, Mammal Section, London, United Kingdom
| | - Kevin C Rowe
- Sciences Department, Museums Victoria, Melbourne, Victoria, 3001, Australia
- School of BioSciences, The University of Melbourne, Melbourne, Victoria, 3010, Australia
| | - Pierre-Henri Fabre
- Institut des Sciences de l'Evolution (ISEM, UMR 5554 CNRS-IRD-UM), Université de Montpellier, Place E. Bataillon - CC 064 - 34095, Montpellier Cedex 5, France
| |
Collapse
|
20
|
Tavares WC, Pessôa LM, Seuánez HN. Changes in Ontogenetic Allometry and their Role in the Emergence of Cranial Morphology in Fossorial Spiny Rats (Echimyidae, Hystricomorpha, Rodentia). J MAMM EVOL 2018. [DOI: 10.1007/s10914-018-9433-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
|
21
|
Morgan CC, Verzi DH, Olivares AI, Vieytes EC. Craniodental and forelimb specializations for digging in the South American subterranean rodent Ctenomys (Hystricomorpha, Ctenomyidae). Mamm Biol 2017. [DOI: 10.1016/j.mambio.2017.07.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
22
|
Van Wassenbergh S, Heindryckx S, Adriaens D. Kinematics of chisel-tooth digging by African mole-rats. ACTA ACUST UNITED AC 2017; 220:4479-4485. [PMID: 28982966 DOI: 10.1242/jeb.164061] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 10/02/2017] [Indexed: 11/20/2022]
Abstract
Mole-rats are known to use their protruding, chisel-like incisors to dig underground networks of tunnels, but it remains unknown how these incisors are used to break and displace the soil. Theoretically, different excavation strategies can be used. Mole-rats could either use their head depressor muscles to power scooping motions of the upper incisors (by nose-down head rotations) or the lower incisors (by nose-up head rotations), or their jaw adductors to grab and break the soil after penetrating both sets of incisors into the ground, or a combination of these mechanisms. To identify how chisel-tooth digging works, a kinematic analysis of this behaviour was performed based on high-speed videos of 19 individuals from the African mole-rat species Fukomys micklemi placed inside transparent tubes in a laboratory setting. Our analysis showed that the soil is penetrated by both the upper and lower incisors at a relatively high gape angle, generally with the head rotated nose-up. Initially, the upper incisors remain approximately stationary to function as an anchor to allow an upward movement of the lower incisors to grab the soil. Next, a quick, nose-down rotation of the head further detaches the soil and drops the soil below the head. Consequently, both jaw adduction and head depression are jointly used to power tooth-digging in F. micklemi The same mechanism, but with longer digging cycles, and soil being thrown down at smaller gape sizes, was used when digging in harder soil.
Collapse
Affiliation(s)
- Sam Van Wassenbergh
- Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium .,Département Adaptations du Vivant, UMR 7179 C.N.R.S/M.N.H.N., 57 rue Cuvier, Case Postale 55, 75231 Paris Cedex 05, France
| | - Stef Heindryckx
- Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
| | - Dominique Adriaens
- Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
| |
Collapse
|
23
|
Marcy AE, Hadly EA, Sherratt E, Garland K, Weisbecker V. Getting a head in hard soils: Convergent skull evolution and divergent allometric patterns explain shape variation in a highly diverse genus of pocket gophers (Thomomys). BMC Evol Biol 2016; 16:207. [PMID: 27724858 PMCID: PMC5057207 DOI: 10.1186/s12862-016-0782-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 09/30/2016] [Indexed: 01/11/2023] Open
Abstract
Background High morphological diversity can occur in closely related animals when selection favors morphologies that are subject to intrinsic biological constraints. A good example is subterranean rodents of the genus Thomomys, one of the most taxonomically and morphologically diverse mammalian genera. Highly procumbent, tooth-digging rodent skull shapes are often geometric consequences of increased body size. Indeed, larger-bodied Thomomys species tend to inhabit harder soils. We used geometric morphometric analyses to investigate the interplay between soil hardness (the main extrinsic selection pressure on fossorial mammals) and allometry (i.e. shape change due to size change; generally considered the main intrinsic factor) on crania and humeri in this fast-evolving mammalian clade. Results Larger Thomomys species/subspecies tend to have more procumbent cranial shapes with some exceptions, including a small-bodied species inhabiting hard soils. Counter to earlier suggestions, cranial shape within Thomomys does not follow a genus-wide allometric pattern as even regional subpopulations differ in allometric slopes. In contrast, humeral shape varies less with body size and with soil hardness. Soft-soil taxa have larger humeral muscle attachment sites but retain an orthodont (non-procumbent) cranial morphology. In intermediate soils, two pairs of sister taxa diverge through differential modifications on either the humerus or the cranium. In the hardest soils, both humeral and cranial morphology are derived through large muscle attachment sites and a high degree of procumbency. Conclusions Our results show that conflict between morphological function and intrinsic allometric patterning can quickly and differentially alter the rodent skeleton, especially the skull. In addition, we found a new case of convergent evolution of incisor procumbency among large-, medium-, and small-sized species inhabiting hard soils. This occurs through different combinations of allometric and non-allometric changes, contributing to shape diversity within the genus. The strong influence of allometry on cranial shape appears to confirm suggestions that developmental change underlies mammalian cranial shape divergences, but this requires confirmation from ontogenetic studies. Our findings illustrate how a variety of intrinsic processes, resulting in species-level convergence, could sustain a genus-level range across a variety of extrinsic environments. This might represent a mechanism for observations of genus-level niche conservation despite species extinctions in mammals. Electronic supplementary material The online version of this article (doi:10.1186/s12862-016-0782-1) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Ariel E Marcy
- School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. .,Department of Biology, Stanford University, Stanford, 94305-5020, CA, USA.
| | - Elizabeth A Hadly
- Department of Biology, Stanford University, Stanford, 94305-5020, CA, USA
| | - Emma Sherratt
- Department of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, 2601, ACT, Australia
| | - Kathleen Garland
- School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia
| | - Vera Weisbecker
- School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia
| |
Collapse
|