Rhynchocyon


Rhynchocyon is a genus of elephant shrews in the family Macroscelididae. Members of this genus are known colloquially as giant sengis.
They are a ground-dwelling mammal, significantly larger than their relatives in the order Macroscelidea that live primarily in dense forests across eastern Africa. Habitats range from eastern Africa's coastal forests, Rift Valley highlands, and the Congo basin. The species is widely threatened, with two of four assessed by the International Union for Conservation of Nature's Red List of Threatened Species. Habitat fragmentation from the growth of human settlements and activities are the primary threats to their populations. The genus contains the following five species and several subspecies:
  • Golden-rumped sengi, Rhynchocyon chrysopygus
  • *Rhynchocyon chrysopygus mandelai
  • Chequered sengi, Rhynchocyon cirnei
  • *Rhynchocyon cirnei shirensis
  • *Rhynchocyon cirnei reichardi
  • *Rhynchocyon cirnei hendersoni
  • *Rhynchocyon cirnei macrurus
  • Black and rufous sengi, Rhynchocyon petersi
  • *Rhynchocyon petersi adersi
  • Stuhlmann's sengi, Rhynchocyon stuhlmanni
  • Grey-faced sengi, ''Rhynchocyon udzungwensis''

    Biology and ecology

The giant sengis are endemic to Africa, and usually live in lowland montane and dense forests, often "avoiding" edges of forest patches. These dense forests play a role in their shelter and reproduction, as they provide the ecological niche in which sengis exploit. They are typically active in the day, spending their nights hidden in the shelters that they build the morning prior. After a few nights of use, sengis tend to abandon their shelters to create new ones elsewhere. They typically build their shelters at ground level, requiring dry leaf litter. 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 then covered with looser leaves as a roof covering. They usually construct their nests at the base of trees. They also use hollowed, fallen trees or trunks to retreat in shelter, especially when faced with predation. Sengis respond to disturbances by staying still or making loud thumping noises on the forest floor. In instances of predation, the giant sengi uses a half-bound gait to rapidly run away.
Other Macroscelidea species are known to bask in the sun, as a method of thermoregulation to save energy. Giant sengis do not bask—and it is most likely due to their adaptation to shaded canopy forest environments.
Sengis live in monogamous pairs, defending hectare-sized territories. Pairs spend little time together except when the female is in estrous. Mating occurs quickly and offspring grow quickly with minimal parental investment—none of which is paternal.
It has been observed that the genus has a commensal relationship with a variety of ground-foraging birds throughout its ranges. Both the Red-capped robin-chat and White-chested alethe often follow the giant sengis as they forage, in attempt at capturing prey that is disturbed while they shuffle through leaf litter looking for prey. 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. 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.

Identification

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 though useful for identification. 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 on its rump.
  • 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. Subspecies R. p. adersi has the same pelage.
  • 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.
  • R. cirnei and its subspecies feature six dark-colored stripes and spots on its back. 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. The subspecies R. c. macrurus exhibits a clinal variation different from coastal populations towards inland populations.
  • R. stuhlmanni exhibits a similar coloration and pattern as R. cirnei differing notably by its white tail. Populations get darker to the east and lighter to the west in a cline.

    Taxonomy and evolution

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. Recently, R. cirnei, the species with the most subspecies, has had R. c. stuhlmanni separated into its own species based on updated molecular data.
Close genetic relatedness indicates that the common ancestor of the genus lived around 7.9 million years ago. There are, however, fossil taxa push this time further into the Oligocene. meswae dates from the Meswa Bridge fossil site in Kenya dates to 22.5 Ma. ' from the Nsungwe Formation in Tanzania dates to 25 Ma. Other fossils of the subfamily Rhynchocyoninae are found between 18 and 23 Ma such as M. clarki and M. rusingae from about 20 Ma from Songhor fossil site in Kenya. This large gap between estimated divergence time of the genus indicates that M. meswae and O. songwensis species are likely stem taxa of the entire group. Because of Rhynchocyon's canopy forest and dense leaf litter requirements, the ancestors of the genus may have experienced selective pressures to become more greatly adapted to forest environments as the Miocene experienced a large expansion of grasslands. Several other extinct genera of the family Rhynchocyonidae have been described: ' and Hypsorhynchocyon. Eorhynchocyon is the oldest fossil species similar to giant sengis, but containing intermediate traits to those of Elephantulus and Petrodromus.

Unresolved taxonomic issues

Various classification issues still exist, with several undetermined questions left unresolved:
  • Is the northern Kenyan population an entirely new species?
  • Is R. c. hendersoni just an altitudinal variation of R. c. reichardi?
  • Is R. c. shirensis just a minor variant of R. cirnei, unworthy of subspecies status?
  • Should R. c. reichardi be a full species again?
  • What is the genetic relationship between coat pattern in R. c. macrurus ; R. stuhlmanni ; and R. c. cirnei and R. c. shirensis ?

    Northern Kenya subspecies

Mitochondrial DNA sequencing was conducted on a single specimen from the Dodori and Boni national reserves in Kenya, as there was suspicion that there may be another species present based on specimen capture, sightings, and camera trap images.
The pelage pattern differs significantly from R. chrysopygus, as it does not have the bright yellow patch on its rump. It also does not possess the same pelage traits as R. petersi—the Boni giant sengi has dark brown and black skin on its ears and tail whereas R. petersi has orange skin. It's face is griseous yellow-brown and the black fur on its rump does not extend to the middle of the back like it does in R. petersi. The single captured specimen weighs about 600 grams, lighter than R. udzungwensis, but heavier than R. petersi. It also has no noticeable chequers, though the dark fur patterns obscures these in all dark-colored giant sengis. A unique feature not found among other giant sengis is the prominent crest of hair along the nape of the neck. Despite the pelage differences, initial DNA comparisons found it nearly identical to R. chrysopygus. A later DNA comparison supported a designation of a new subspecies, Rhynchocyon chrysopygus mandelai as it diverges in pelage and is allopatric to R. chrysopygus.

Distribution

R. chrysopygus, R. cirnei, and R. petersi are allopatrically distributed; with the more recently discovered R. udzungwensis and subspecies R. cirnei reichardi exhibiting parapatric distributions. Some introgression has taken place between R. udzungwensis and R. cirnei reichardi as detected by mtDNA. R. p. adersi is rare and unique in its distribution, being found isolated on the islands of the Zanzibar Archipelago. R. c. reichardi is typically found in the Rift Valley highlands of Tanzania, Zambia, and Malawi, with R. c. hendersoni found in the highlands of northern Malawi.
Both R. c. hendersoni and R. c. shirensis are known at higher elevations, similar to that of R. udzungwensis; however R. udzungwensis is unique in its larger body size. Bergmann's rule suggests that specialized ecological factors such as climate and temperature would favor larger bodies like that of R. udzungwensis, though the latter two species do not share this trait. For comparison, R. udzungwensis occurs in greater abundance at elevations above 1000 meters, has a body mass of 710 grams and a brain mass of 7131 milligrams, while R. petersi occurs at greater abundance at elevations between 0 and 2000 meters, has a body mass of 471 g, and a brain mass of 5400 mg.
Estimated of population size and density vary and can be difficult to determine. However, measurements of the species populations has been undertaken. R. chrysopygus, in protected areas, is about 150 individuals per square kilometer ; R. petersi is between 19 and 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 land.
SpeciesLocalitiesElevation range
Rhynchocyon chrysopygus chrysopygusKenya 30–360 m
Rhynchocyon chrysopygus mandelaiKenya
Rhynchocyon cirnei cirneiMozambique ; Malawi, Zambia and Tanzania ; Tanzania 0–2100 m
Rhynchocyon cirnei reichardiTanzania, Malawi, and Zambia 290–1800 m
Rhynchocyon cirnei hendersoniNorthern Malawi Similar to R. udzungwensis
Southern Malawi Similar to R. udzungwensis
Rhynchocyon petersiTanzania and Mafia Archipelago.Undetermined, though they are restricted to Zanzibar's and Mafia Island's highest elevations of 119 and 53 meters respectively.
Rhynchocyon stuhlmanniDemocratic Republic of Congo ; Uganda
Rhynchocyon udzungwensisUdzungwa Mountains of Tanzania in the Kilombero District of the Morogoro Region and the Kilolo District of the Iringa Region.350–2300 m