Rhynchocyon

Rhynchocyon is a genus of elephant shrew (or sengi) in the family Macroscelididae.[1] Members of this genus are known colloquially as the checkered elephant shrews[3] or giant sengis.[4] It contains the following five species:[5]

Rhynchocyon[1]
Rhynchocyon petersi
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Macroscelidea
Family: Macroscelididae
Genus: Rhynchocyon
Peters, 1847
Species

Rhynchocyon chrysopygus
Rhynchocyon cirnei
Rhynchocyon petersi
Rhynchocyon stuhlmanni[2]
Rhynchocyon udzungwensis

Ecology

The giant sengis are endemic to Africa, and usually live in lowland montane and dense forests,[6] often "avoiding" edges of forest patches.[7][8] They eat primarily insects such as beetles, termites, ants, and centipedes, using their proboscises to dig them from the soil and its tongue to lick them up.[9] Their facial morphology limits their diets to tiny invertebrates, and unlike other members of Macroscelidea, do not supplement their diet with foods such as nuts or small fruits.[10]

They typically build ground level nests for shelter[11] requiring dry leaf litter.[12] The primary structure of a nest for R. udzungwensis, for example, consists of the excavation of a cup-like indentation in the soil, layered with leaves, and the covered with looser leaves as a roof covering.[13] They usually construct their nests at the base of trees.[13] They also use hollowed, fallen trees or trunks to retreat in shelter.[10]

They are typically active in the day (diurnal), spending their nights sheltered. Other Macroscelidea species are known to bask in the sun as a method of thermoregulation to save energy.[10] Giant sengis do not bask—and it is most likely due to their adaptation to shaded canopy forest environments.[10]

Sengis live in monogamous pairs, defending hectare-sized territories.[14][11] Pairs spend little time together except when the female is in estrous.[10] Mating occurs quickly and offspring grow quickly with minimal parental investment—none of which of is paternal.[10]

Each species exhibits distinct and varying coat patterns and colors. Species and subspecies found in denser forests exhibit darker coloration and patterns while open woodland species exhibit lighter, chequers. The darker species R. petersi, R. chrysopygus, and R. udzungwensis still contain vestigial chequers, but are masked by the blended dark fur between them. This makes coat patterns an unreliable indicator of species delineation.[13] The species are described as follows:

  • R. chrysopygus exhibits a bright yellow patch of fur on its rump with very little black coloration at all. R. chrysopygus has a unique dermal shield (a specialized thickening of skin) on its rump.[13]
  • R. petersi has mostly orange-rufous coloration on its feet, ears, tail, chest, and on its face. Black fur extends from its rump and thighs up to its shoulders.[13]
  • R. udzungwensis has black feet, ears and a tail. Its face is griseous grey with its lower rump and thighs are black. The chest is pale yellow.[13]
  • R. cirnei and its subspecies feature six dark-colored stripes and spots (chequers) on its back.[13] They contain little to no black fur, are lighter in color, and differ markedly by their lack of orange-rufous coloration found on its coastal relatives R. petersi, R. chrysopygus, and R. udzungwensis.[2] The subspecies R. c. macrurus exhibits a clinal variation different from coastal populations towards inland populations.[13][15]
  • R. stuhlmanni exhibits a similar coloration and pattern as R. cirnei differing notably by its white tail.[2]

Taxonomy, distribution, and speciation

The genus' taxonomic status has been difficult to determine due to the very close similarities between populations. Up to ten species have been recognized, but over time they have been regrouped into four species.[2] Recently, R. cirnei, the species with the most subspecies, has had R. c. stuhlmanni separated into its own species based on updated molecular data.[2]

R. chrysopyguus, R. cirnei, and R. petersi are allopatrically distributed; with the more recently discovered R. udzungwensis and subspecies R. cirnei reichardi exhibiting parapatric distributions.[16] Some introgression (hybridization) has taken place between R. udzungwensis and R. cirnei reichardi as detected by mtDNA.[16]

Estimated of population size and density vary and can be difficult to determine. However, measurements of the species populations has been undertaken. R. chrysopyguus, in protected areas, is about 150 individuals per square kilometer (about 20,000 individuals); R. petersi is between 19-80 individuals per square kilometer; R. udzungwensis has an estimated 15,000-24,000 individuals. R. udzungwensis has a tiny distribution compared to the other species but resides in a protected forest.[13]

Phylogeny and geographic distribution of species in the Rhynchocyon genus.

References
  1. Schlitter, D.A. (2005). "Genus Rhynchocyon". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 84–85. ISBN 978-0-8018-8221-0. OCLC 62265494.
  2. Carlen, E.J.; Rathbun, G.B.; Olson, L.E.; Sabuni, C.A.; Stanley, W.T.; Dumbacher, J.P. (2017). "Reconstructing the molecular phylogeny of giant sengis (Macroscelidea; Macroscelididae; Rhynchocyon)". Molecular Phylogenetics and Evolution. 113: 150–160. doi:10.1016/j.ympev.2017.05.012.
  3. ITIS.gov
  4. FitzGibbon, C. & Rathbun, G. (2008). "Rhynchocyon chrysopygus". IUCN Red List of Threatened Species. 2008. Retrieved 29 December 2008.CS1 maint: ref=harv (link)
  5. Hoffmann Michael; Rathbun Galen B.; Rovero Francesco; Perkin Andrew; Owen Nisha; Burgess Neil (2016). "The distribution of the genus Rhynchocyon in the Eastern Arc Mountains, with an emphasis on the Black-and-rufous Sengi, Rhynchocyon petersi". Afrotherian Conservation. 12: 3–8.
  6. G. Rathbun. (1984). Elephant-shrews, Order Macroscelidea. In : MacDonald (ed), The Encyclopedia of Mammals. Facts on File Publications, New York: 730-735.
  7. Rajan Amin, Bernard Agwanda, Tim Wacher, Bernard Ogwoka, Cedric Khayale, and Linus Kariuki (2020), "Habitat use of the endangered golden-rumped sengi Rhynchocyon chrysopygus", African Journal of Ecology, doi:10.1111/aje.12804CS1 maint: multiple names: authors list (link)
  8. Francesco Rovero ,Emanuel Martin, Melissa Rosa, Jorge A. Ahumada, and Daniel Spitale (2014), "Estimating Species Richness and Modelling Habitat Preferences of Tropical Forest Mammals from Camera Trap Data", PLOS ONE, 9 (7), doi:10.1371/journal.pone.0103300CS1 maint: multiple names: authors list (link)
  9. J. Kingdon (1997), The Kingdon Field Guide to African Mammals, Academic Press, pp. 142–152
  10. Galen B. Rathbun (2009), "Why is there discordant diversity in sengi (Mammalia: Afrotheria: Macroscelidea) taxonomy and ecology?", African Journal of Ecology, 47 (1): 1–13, doi:10.1111/j.1365-2028.2009.01102.x
  11. G. B. Rathbun (1979), "The social structure and ecology of elephant-shrews", Journal of Comparative Ethology, 20: 1–77
  12. Norbert J. Cordeiro; Nathalie Seddon; David R. Capper; Jonathan M. M. Ekstrom; Kim M. Howell; Isabel S. Isherwood; Charles A. M. Msuya; Jonas T. Mushi; Andrew W. Perkin; Robert G. Pople & William T. Stanley (2005), "Notes on the ecology and status of some forest mammals in four Eastern Arc Mountains", Journal of East African Natural History, 94 (1): 175–189, doi:10.2982/0012-8317(2005)94[175:noteas]2.0.co;2
  13. F. Rovero, G. B. Rathbun, A. Perkin, T. Jones, D. O. Ribble, C. Leonard, R. R. Mwakisoma, and N. Doggart (2007), "A new species of giant sengi or elephant-shrew (genus Rhynchocyon) highlights the exceptional biodiversity of the Udzungwa Mountains of Tanzania", Journal of Zoology, 274 (2), doi:10.1111/j.1469-7998.2007.00363.xCS1 maint: multiple names: authors list (link)
  14. C. D. Fitzgibbon & G. B. Rathbun (1994), "Surveying Rhynchocyon elephant-shrews in tropical forest", African Journal of Ecology, 32: 50–57, doi:10.1111/j.1365-2028.1994.tb00554.x
  15. Corbet, G.B., Hanks, J., 1968. A revision of the elephant-shrews, family Macroscelididae. Bull. Br. Museum (Natural Hist.) Zool. 16, 45–111.
  16. Lucinda P. Lawson; Cristiano Vernesi; Silvia Ricci & Francesco Rovero (2013), "Evolutionary History of the Grey-Faced Sengi, Rhynchocyon udzungwensis, from Tanzania: A Molecular and Species Distribution Modelling Approach", PLoS ONE, 8 (8): e72506, doi:10.1371/journal.pone.0072506, PMC 3754996

Sengis.org is an overview website concerning all the sengi species maintained by researcher Galen B Rathbun of the university of the California Academy of Sciences. It hosts images, videos, bibliographies, among other topics about the order Macroscelididae.

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