Atheris mabuensis, Branch, William R. & Bayliss, Julian, 2009

Atheris mabuensis n. sp.

( Figs. 2–7 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

Type Material: Holotype: adult male, PEM R17901. Type locality: main forest camp, Mount Mabu (16°17’12”S, 36°24’14”E, 1000m a.s.l.); collected by local hunter, 20 October 2008; fixed in buffered formalin and stored in 70% EtOH. Paratypes: 3 specimens: adult female, PEM R17902, collected by Tom Timberlake, same locality and date as holotype; juvenile, PEM R17903, collected by Julian Bayliss, same locality and date as holotype; subadult male, PEM R19704, collected on path at 13h00 in leaf litter in Khara Forest (lower end on Manho Forest, Mount Namuli, Zambezia Province, Mozambique (15°24’39.9”S, 37°02’16.5”E, 1550m a.s.l.), Colin Congdon, 26 November 2008. The two Mount Mabu specimens were retained for one month in captivity before dying; on death they were placed in 90% EtOH, after small incisions were made in the ventrum; both were subsequently transferred to 70% EtOH for storage. The Mount Namuli specimen was kept alive for 2 months, and then euthanased, fixed in buffered formalin and subsequently stored in 70% EtOH; a small ventral incision was made to collected fresh liver tissue for genetic studies.

Additional Material: PEM R17910 (still maintained in captivity; shed skins and digital images), adult male, same locality as holotype, collected 25 January 2006, J. Bayliss.

Synonymy: Atheris sp. Dobiey and Vogel, 2007, p 110.

Numerous other images of the species under the same name have appeared in the world media following a press release from Kew highlighting the biodiversity discoveries during the Mount Mabu expedition (e.g. Marshall, 2009).

Diagnosis: Atheris mabuensis is distinguished from all other members of the genus by a combination of characters: (1) its small size, maximum length 384mm (all other Atheris exceed 580mm TL, with the exception of - A. katangensis , TL 397mm; A. barbouri , TL 369 mm (Barbour and Howell, 1998); and the unique type of A. acuminata , TL 440mm); (2) the lack of ‘horns’ (enlarged supraocular scales are present in A ceratophora ); (3) the lack of lanceolate or acuminate scales on top of the head (present in A. hispida and A. acuminata ); (4) having weakly keeled gular scales (smooth only in A. nitschei ; gulars moderately keeled in the eastern species, A. rungweensis , A. desaixi , A. ceratophora and A. katangensis , and strongly keeled in the remaining central and western species); (5) lacking interoculabials (sensu Broadley, 1998, i.e. the supralabials are in contact with circumorbitals; 1 or 2 in A. desaixi and A. rungweensis ); (6) having 19–21 transverse head scales (sensu Broadley, 1998, i.e. number of scales across head between posterior supralabials; these are reduced in highly arboreal species, e.g. A. squamigera , 15–22, A. hispida , 12; and A. acuminata , 10); (7) having 21–23 MSR (most species have 27+ MSR rows; reduced in highly arboreal species such as A. squamigera , 15–25, A. hispida , 15–19, and A. acuminata , 14); (8) lateral body scales not serrated (strongly serrated in A. ceratophora , A. desaixi , A. nitschei , and A. rungweensis , and weakly serrated in A. katangensis ); (9) having 8–9 supralabials (six in A. acuminata , 10–12 in A. desaixi ); (10) having low ventral counts 128–137 (this is the lowest in the genus; usually over 140 in both sexes in A. nitschei , A. rungweensis , A. desaixi , A. chlorechis , A. hispida , and A. subocularis , and in the only known males of A. acuminata (160) and A. hirsuta (160); (11) having low subcaudal counts - 39–47 (always higher than 45 in A. rungweensis , A. ceratophora , A. chlorechis , A. squamigera and A. hispida ; and 54 and 58 in the only known males of A. acuminata and A. hirsuta , respectively); and (12) having a prehensile tail (non-prehensile in A. barbouri ), and higher subcaudal ( A. barbouri 15–21) and labial ( A. barbouri , supralabials 5–6, infralabials 4–5) counts.

Remarks: Within the Atherini the Mount Mabu snake is referred to the genus Atheris Cope on the basis of the following diagnostic features: no enlarged supraocular shield (present in Proatheris Broadley, 1966 ), tail prehensile and subcaudals single (tail non-prehensile and subcaudals paired in Montatheris Broadley, 1996 ).

Description: Holotype PEM R17901; adult male preserved in formalin and transferred to 70% EtOH; body bent into ‘U’-shape, and with a small incision in the belly (V48 -52).

Meristics: snout-vent length (SVL) 256mm, tail 47mm (TL 303 mm); tail into SVL 5.45 times; rostral width 2.9mm, rostral height 0.8mm; eye diameter (vertical) 3.2mm; snout to eye 3.3mm.

Habitus: Body relatively slender and subtriangular in cross-section, with a thin, prehensile tail (SVL/Tail approximately 5–6 times; 4.92–6.16, mean 5.56, n = 5); head triangular, with a very distinct neck, bluntly rounded snout and swollen supraorbital region that does not bear elongate scales; eyes relatively large, laterally placed, and with a horizontal diameter approximately equal to the snout length.

Scalation: Crown of head covered in small scales, that are larger over the temporal region and somewhat irregular in outline between the eyes; they bear a prominent keel that is extended into a rounded, pale knob; the rostral is flattened, subtriangular, about 2.4–3.4 times broader than high, contacting first supralabials and three large, unkeeled suprarostrals, of which the middle is the smallest and about 1.25 times wider than high; right and left suprarostrals slightly higher than wide; nasal wider than high, with raised, embossed posterior edge, particularly on the left; nostril circular and approximately in the centre of the nasal; internasals 5, all strongly keeled; interrictals 21; interorbitals 6–7, keeled, central scales more irregular in shape; circumoculars 15–15, all keeled and terminating in blunt knobs; suboculars absent; circumoculars separated from nasals by a single row of feebly knobbed scales; a row of three irregular scales, bordering supralabials between nasal and lower circumoculars; supralabials 8–8, 3 largest, and 6–8 feebly-keeled; infralabials 9–9, posteriormost feebly keeled and first in contact at the midline behind the mental, and separating the latter from 3 pairs of chin shields, the first largest; mental triangular, approximately twice as wide as deep; gulars bordering chin shields feebly-keeled, but prominently-keeled towards the rictus; 2 preventrals, first largest; 132 ventrals; 47 undivided subcaudals (including spine); anal entire; dorsal scales about 1.5 times as long as wide, becoming shorter posteriorly, and 20 rows anteriorly, 25–26 rows at midbody, 17 rows posteriorly; keel on dorsal scales increasing in height from base, terminating in a rounded, pale knob that is more conspicuous on scales of the forebody; paraventrals larger than other dorsals, with a feeble, asymmetric keel; additional scales occur irregularly in rows 2–5 on the forebody, but do not form continuous duplicated scale rows.

Hemipenis: Both hemipenes have only partially everted, despite the rector muscles having been cut through a small lateral incision in subcaudals 13–17; the basal portion of the hemipenis reveals a typically divided organ with a number of basal spines on the lateral surfaces, and indications of a distal calyculate zone (this needs confirmation on fully everted hemipenes).

Colouration: Eye dirty bronze, darker in centre and with bright yellow edge around iris; crown greyish brown with each scale tipped with yellow; head pattern vague, comprising a broken inverted ‘V’-shape represented by two small dark patches over the jaw muscles; side of head dark greyish in front of eye, becoming darker towards angle of jaw; dorsum pale brown with a pale, vague and irregular dorsal chain pattern, with faint paler edges and centre paler than body background colour; a dark edge to the chain pattern is represented only by a lateral series of subtriangular dark brown blotches that may lie adjacent to each other on either side of body, or become staggered; a series of small (sometimes only 1–2 scales), faded brown blotches occur along the flanks and align with the widest region of the dorsal ‘chain’ pattern; all scales on crown, body and upper surface of tail tipped in pale yellow to light orange, that is more prominent on the head and forebody; throat, belly and basal 2/3rd of underside of tail blue-grey, uniformly and heavily stippled with fine dark spots; underneath of tail becoming yellowish on distal third.

Va r ia ti o n: Details and meristics for the type series are summarized in Table 1 View TABLE 1 . The most significant differences in colouration include: body colouration in the solitary subadult from Mount Namuli (PEM R17904) is slightly duller (bluish) with the scales on the head and forebody lacking the conspicuous yellow tips of specimens from Mount Mabu. Whether this is typical of this isolated population awaits the collection of additional material. Pale, narrow eye stripes radiating from the orbit to the lip (see Fig. 6 View FIGURE 6 [top] and Fig. 7 View FIGURE 7 ) are found in all snakes, except the holotype, although in some (e.g. PEM R17903-4) only the rear stripe is well developed. The head pattern forms a well-developed inverted ‘V’-shape (see Fig. 7 View FIGURE 7 , PEM R17910) in three snakes, but is reduced to two isolated dark blotches at the back of the head in the holotype, and is almost completely absent in the subadult from Mount Namuli. There is little ontogenetic colour change (based on PEM R17910); when first captured ( Fig. 6 View FIGURE 6 , top) the juvenile snake (<150 mm TL) had darker brown body colouration that after three years in captivity has lightened slightly ( Fig. 6 View FIGURE 6 , bottom), although the extent and intensity of yellow on the tail remains unchanged.

Size: Largest female (PEM R17902) 328 + 56 = 384 mm; largest male (PEM R7910) 305 + 62 = 367 mm. The series is too small to determine whether females grow larger then males.

Etymology: Named after the type locality, Mount Mabu, Zambezia Province, northern Mozambique.

Suggested common name: Mount Mabu Forest Viper

Distribution: Known only from the type locality, Mount Mabu, and adjacent Mount Namuli, both montane isolates in northern Mozambique.

Habitat: All specimens were collected among leaf litter on the forest floor in evergreen mid-altitude wet forest, from approximately 1000 m a.s.l. on Mount Mabu ( Fig. 8 View FIGURE 8 ) and at 1550 m a.s.l. on Mount Namuli. The presence of the species at a higher altitude on Mount Namuli may be due to the loss of mid-altitude forest habitat on the lower slopes as a result of subsistence farming. A similar displacement of forest birds to higher montane forests on Mount Namuli has been proposed by Dowesett- Lemaire (in Jackson et al., 2009). The habitat comprises closed-canopy forest ( Fig. 9 View FIGURE 9 ), except for small gaps caused by tree-falls and along stream gullies. Tall trees (up to 40–45 m height) emerge from the canopy, with Strombosia scheffleri dominant and others including Newtonia sp., Chrysophyllum gorungosanum , Maranthes goetzeniana, Ficus thonningii, Blighia unijugata, and Funtumia africana . Smaller trees in the understorey include Allophylus sp., Canthium sp., Oxyanthus speciosus, Rawsonia lucida, Tabernaemontana ventricosa, Vepris stolzii, and small saplings of Cola greenwayi, Drypetes sp. and Maranthes sp. Canopy lianas are dominated by Millettia lasiantha (Dowsett-Lemaire and Dowsett, unpubl. report 2008).

Natural History: The original specimen (PEM R17910) was maintained in captivity for over 37 months. The other specimens were kept for shorter periods (2–4 months). During this period they readily accepted small geckos ( Lygodactylus capensis and Hemidactylus mabouia ) as well as small amphibians ( Hyperolius sp., Strongylopus sp., and Phrynobatrachus sp.). While in captivity they were observed to use the bright yellow tail as a caudal lure to entice prey into striking distance. In a terrarium with leaf litter and small branches they either coiled partially concealed among large leaves on the floor, or in dead twigs or leaf clumps up to 20cm above the floor. The only adult female (PEM R17902) has thick muscular oviducts and small vitellogenic ovarian follicles indicating sexual maturity at only 384mm TL.

The species was locally common within the large tract of wet forest (> 1000m) on Mount Mabu, and it was only observed within leaf litter on the forest floor ( Fig. 6 View FIGURE 6 top). Local hunters when interviewed confirmed this habitat preference, and also noted that the species remained small, growing to not much more than 35 cm in length. This observation was supported by the growth of the first specimen, which measured approximately 150 mm TL when first captured, and grew to only 367 mm TL after over three years in captivity despite regular feeding. Local hunters also noted that bites from the species were painful but not lethal. Caution is still advised because serious envenomation has followed bites from A. chlorechis ( Rödel, 1999; Top et al., 2006) and A. squamigera ( Mebs et al., 1998) , and even a death from the latter ( Lanoie and Branch, 1991).