Brain volume of the newly-discovered species Rhynchocyon udzungwensis (Mammalia: Afrotheria: Macroscelidea): implications for encephalization in sengis - PubMed
Brain volume of the newly-discovered species Rhynchocyon udzungwensis (Mammalia: Afrotheria: Macroscelidea): implications for encephalization in sengis
Jason A Kaufman et al. PLoS One. 2013.
Abstract
The Gray-faced Sengi (Rhynchocyon udzungwensis) is a newly-discovered species of sengi (elephant-shrew) and is the largest known extant representative of the order Macroscelidea. The discovery of R. udzungwensis provides an opportunity to investigate the scaling relationship between brain size and body size within Macroscelidea, and to compare this allometry among insectivorous species of Afrotheria and other eutherian insectivores. We performed a spin-echo magnetic resonance imaging (MRI) scan on a preserved adult specimen of R. udzungwensis using a 7-Tesla high-field MR imaging system. The brain was manually segmented and its volume was compiled into a dataset containing previously-published allometric data on 56 other species of insectivore-grade mammals including representatives of Afrotheria, Soricomorpha and Erinaceomorpha. Results of log-linear regression indicate that R. udzungwensis exhibits a brain size that is consistent with the allometric trend described by other members of its order. Inter-specific comparisons indicate that macroscelideans as a group have relatively large brains when compared with similarly-sized terrestrial mammals that also share a similar diet. This high degree of encephalization within sengis remains robust whether sengis are compared with closely-related insectivorous afrotheres, or with more-distantly-related insectivorous laurasiatheres.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures

A dendrogram illustrating the phylogenetic relationships among the genera investigated in the present study , -.

Two views of the R. udzungwensis MRI visualized as maximum intensity projections with the brain highlighted in white. A) Antero-lateral oblique view. B) Superior view, scale bar = 5 cm.

A scatterplot of log body mass on log brain mass in which the RMA line (dashed) for Macroscelididae (n = 5) is compared to the RMA line (solid) describing other insectivores (n = 52). The slopes of the two lines are statistically indistinguishable (common slope = 0.66; 95% CI: 0.63–0.70). Residual axis scores indicate that the best-fit line describing Macroscelididae has a significantly larger y-intercept than the line describing other insectivores (X2 = 142.36, p<0.001).
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This research was funded by Midwestern University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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