The Chromosomes of Afrotheria and Their Bearing on Mammalian Genome Evolution

Svartman, Marta; Stanyon, Roscoe

doi:10.1159/000341387

Cited by 10 publications

(6 citation statements)

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“…Marsupials are unique among mammals for their small diploid number of chromosomes ranging from 10 to 24, with one known exception, Aepyprymnus rufescens, which has 32 [1]. It has been proposed that the putative ancestral marsupial karyotype has a diploid number of 14 [1,2], whereas the putative ancestral eutherian karyotype has a diploid number of 44 or 46 [3,4]. Reciprocal chromosome painting between Australian and South American marsupials confirms the remarkable chromosome & 2018 The Authors.…”

Section: Introductionmentioning

confidence: 99%

“…It has been proposed that the putative ancestral marsupial karyotype has a diploid number of 14 [1,2], whereas the putative ancestral eutherian karyotype has a diploid number of 44 or 46 [3,4]. Reciprocal chromosome painting between Australian and South American marsupials confirms the remarkable chromosome conservation among phylogenetically diverged groups [1,2,5].…”

Section: Introductionmentioning

confidence: 99%

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Marsupial chromosome DNA content and genome size assessed from flow karyotypes: invariable low autosomal GC content

Kasai¹,

O’Brien²,

Pereira³

et al. 2018

R. Soc. open sci.

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Extensive chromosome homologies revealed by cross-species chromosome painting between marsupials have suggested a high level of genome conservation during evolution. Surprisingly, it has been reported that marsupial genome sizes vary by more than 1.2 Gb between species. We have shown previously that individual chromosome sizes and GC content can be measured in flow karyotypes, and have applied this method to compare four marsupial species. Chromosome sizes and GC content were calculated for the grey short-tailed opossum (2n = 18), tammar wallaby (2n = 16), Tasmanian devil (2n = 14) and fat-tailed dunnart (2n = 14), resulting in genome sizes of 3.41, 3.31, 3.17 and 3.25 Gb, respectively. The findings under the same conditions allow a comparison between the four species, indicating that the genomes of these four species are 1–8% larger than human. We show that marsupial genomes are characterized by a low GC content invariable between autosomes and distinct from the higher GC content of the marsupial × chromosome.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Marsupial chromosome DNA content and genome size assessed from flow karyotypes: invariable low autosomal GC content

Kasai¹,

O’Brien²,

Pereira³

et al. 2018

R. Soc. open sci.

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“…The largest extant fossorial mammal is the aardvark, Orycteropus afer ( Pallas, 1766 ), with a total body size ranging from 1.4 to 2.2 m, and a body mass from 40 to 100 kg ( Shoshani, Goldman & Thewissen, 1988 ; Vizcaíno et al, 2001 ). The aardvark is the only extant representative of the order Tubulidentata, which falls under the large superorder Afrotheria, also comprising the elephants, sirenians, hyraxes, elephant shrews, golden moles, and tenrecs ( Shoshani, Goldman & Thewissen, 1988 ; Svartman & Stanyon, 2012 ). It is endemic to sub-Saharan Africa, and has a strictly myrmecophagous diet ( Melton, 1976 ; Taylor & Skinner, 2004 ).…”

Section: Introductionmentioning

confidence: 99%

Digging the compromise: investigating the link between limb bone histology and fossoriality in the aardvark (Orycteropus afer)

Legendre

Botha‐Brink

2018

PeerJ

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Bone microstructure has long been known as a powerful tool to investigate lifestyle-related biomechanical constraints, and many studies have focused on identifying such constraints in the limb bones of aquatic or arboreal mammals in recent years. The limb bone microstructure of fossorial mammals, however, has not been extensively described. Furthermore, so far, studies on this subject have always focused on the bone histology of small burrowers, such as subterranean rodents or true moles. Physiological constraints associated with digging, however, are known to be strongly influenced by body size, and larger burrowers are likely to exhibit a histological profile more conspicuously influenced by fossorial activity. Here, we describe for the first time the limb bone histology of the aardvark (Orycteropus afer), the largest extant burrowing mammal. The general pattern is very similar for all six sampled limb bones (i.e., humerus, radius, ulna, femur, tibia, and fibula). Most of the cortex at midshaft is comprised of compacted coarse cancellous bone (CCCB), an endosteal tissue formed in the metaphyses through the compaction of bony trabeculae. Conversely, the periosteal bone is highly resorbed in all sections, and is reduced to a thin outer layer, suggesting a pattern of strong cortical drift. This pattern contrasts with that of most large mammals, in which cortical bone is of mostly periosteal origin, and CCCB, being a very compliant bone tissue type, is usually resorbed or remodeled during ontogeny. The link between histology and muscle attachment sites, as well as the influence of the semi-arid environment and ant-eating habits of the aardvark on its bone microstructure, are discussed. We hypothesize that the unusual histological profile of the aardvark is likely the outcome of physiological constraints due to both extensive digging behavior and strong metabolic restrictions. Adaptations to fossoriality are thus the result of a physiological compromise between limited food availability, an environment with high temperature variability, and the need for biomechanical resistance during digging. These results highlight the difficulties of deciphering all factors potentially involved in bone formation in fossorial mammals. Even though the formation and maintaining of CCCB through ontogeny in the aardvark cannot be unambiguously linked with its fossorial habits, a high amount of CCCB has been observed in the limb bones of other large burrowing mammals. The inclusion of such large burrowers in future histological studies is thus likely to improve our understanding of the functional link between bone growth and fossorial lifestyle in an evolutionary context.

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“…The mammalian and therian reconstructions recovered all previously reported ancestral syntenies and facilitated the discovery of >10 ancestral syntenies ( SI Appendix , Table S7 ). Two of these were previously classified as xenarthran specific, represented by the association of human chromosome (HSA) 8p with part of HSA2pq and of HSA10p with part of HSA7pq ( 39 ). Another was previously reported as bat specific, represented by the association of part of HSA1pq with part of HSA6pq ( 40 ).…”

Section: Resultsmentioning

confidence: 99%

Evolution of the ancestral mammalian karyotype and syntenic regions

Damas

Corbo

Kim

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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Decrypting the rearrangements that drive mammalian chromosome evolution is critical to understanding the molecular bases of speciation, adaptation, and disease susceptibility. Using 8 scaffolded and 26 chromosome-scale genome assemblies representing 23/26 mammal orders, we computationally reconstructed ancestral karyotypes and syntenic relationships at 16 nodes along the mammalian phylogeny. Three different reference genomes (human, sloth, and cattle) representing phylogenetically distinct mammalian superorders were used to assess reference bias in the reconstructed ancestral karyotypes and to expand the number of clades with reconstructed genomes. The mammalian ancestor likely had 19 pairs of autosomes, with nine of the smallest chromosomes shared with the common ancestor of all amniotes (three still conserved in extant mammals), demonstrating a striking conservation of synteny for ∼320 My of vertebrate evolution. The numbers and types of chromosome rearrangements were classified for transitions between the ancestral mammalian karyotype, descendent ancestors, and extant species. For example, 94 inversions, 16 fissions, and 14 fusions that occurred over 53 My differentiated the therian from the descendent eutherian ancestor. The highest breakpoint rate was observed between the mammalian and therian ancestors (3.9 breakpoints/My). Reconstructed mammalian ancestor chromosomes were found to have distinct evolutionary histories reflected in their rates and types of rearrangements. The distributions of genes, repetitive elements, topologically associating domains, and actively transcribed regions in multispecies homologous synteny blocks and evolutionary breakpoint regions indicate that purifying selection acted over millions of years of vertebrate evolution to maintain syntenic relationships of developmentally important genes and regulatory landscapes of gene-dense chromosomes.

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The Chromosomes of Afrotheria and Their Bearing on Mammalian Genome Evolution

Cited by 10 publications

References 135 publications

Marsupial chromosome DNA content and genome size assessed from flow karyotypes: invariable low autosomal GC content

Marsupial chromosome DNA content and genome size assessed from flow karyotypes: invariable low autosomal GC content

Digging the compromise: investigating the link between limb bone histology and fossoriality in the aardvark (Orycteropus afer)

Evolution of the ancestral mammalian karyotype and syntenic regions

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