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The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet.

ABSTRACT: The diets of Australopithecus africanus and Paranthropus robustus are hypothesized to have included C4 plants, such as tropical grasses and sedges, or the tissues of animals which themselves consumed C4 plants. Yet inferences based on the craniodental morphology of A. africanus and P. robustus indicate a seasonal diet governed by hard, brittle foods. Such mechanical characteristics are incompatible with a diet of grasses or uncooked meat, which are too tough for efficient mastication by flat, low-cusped molars. This discrepancy, termed the C4 conundrum, has led to the speculation that C4 plant underground storage organs (USOs) were a source of nutrition for hominin species. We test this hypothesis by examining the isotopic ecology of African mole rats, which consume USOs extensively. We measured delta18O and delta13C of enamel and bone apatite from fossil and modern species distributed across a range of habitats. We show that delta18O values vary little and that delta13C values vary along the C3 to C4/CAM-vegetative axis. Relatively high delta13C values exist in modern Cryptomys hottentotus natalensis and Cryptomys spp. recovered from hominin-bearing deposits. These values overlap those reported for A. africanus and P. robustus and we conclude that the USO hypothesis for hominin diets retains certain plausibility.

SUBMITTER: Yeakel JD

PROVIDER: S-EPMC2493578 | biostudies-literature | 2007 Jul

REPOSITORIES: biostudies-literature

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The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet.

Yeakel Justin D JD Bennett Nigel C NC Koch Paul L PL Dominy Nathaniel J NJ

Proceedings. Biological sciences 20070701 1619

The diets of Australopithecus africanus and Paranthropus robustus are hypothesized to have included C4 plants, such as tropical grasses and sedges, or the tissues of animals which themselves consumed C4 plants. Yet inferences based on the craniodental morphology of A. africanus and P. robustus indicate a seasonal diet governed by hard, brittle foods. Such mechanical characteristics are incompatible with a diet of grasses or uncooked meat, which are too tough for efficient mastication by flat, lo ...[more]

PMID: 17472915

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Project description: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.

Project description:Changes in gene regulation have long been though to underlie most phenotypic differences between species. Subterranean rodents, and in particular the naked mole-rat (NMR), have attracted substantial attention due to their proposed phenotypic adaptations, which include hypoxia tolerance, metabolic changes and cancer resistance. However, it is largely unknown what regulatory changes may associate with these phenotypic traits, and whether these are unique to the NMR, the mole-rat clade or also present in other mammals. Here, we undertook a comparative genomics approach to identify genome-wide promoter and enhancer regions harbouring epigenomic hallmarks of regulatory activity, in heart and liver from two mole-rat species (NMR and DMR) and two rodent outgroups. To identify promoters and enhancers displaying robust shifts in regulatory activity in the mole-rat clade, we adapted and applied a phylogenetic modeling approach to quantitatively compare epigenomic signals at orthologous locations, while accounting for phylogenetic distance and inter-species variation. This method identified thousands of orthologous promoter and enhancer regions with increased activity in ancestral or single-species mole-rat branches, as well as hundreds of promoters and enhancers with reduced activity in mole-rats versus other rodents. These elements underlie both shared tissue-specific changes in gene regulation associated with mole-rat evolution, which include metabolic and functional adaptations in heart and liver. Moreover, by comparing mole-rat specific changes in promoters and enhancers between ancestral and single-species branches, our data revealed a number of candidate pathways with stepwise regulatory changes during mole-rat evolution. Lastly, we analysed the genomic properties of non-alignable promoters and enhancers in mole-rats, and report (i) their overlap with specific repetitive elements and transcription factor binding sites; and (ii) their association with metabolic gene functions. On the whole, these comparative analyses reveal mole-rat specific epigenomic changes across orthologous and non-mappable promoters and enhancers - which inform previously reported mole-rat adaptations from a gene regulation perspective.

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The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet.

Publications

The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet.

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