Chiroderma improvisum Baker and Genoways, 1976

Garbino, Guilherme S. T., Lim, Burton K. & Tavares, Valéria Da C., 2020, Systematics of big-eyed bats, genus Chiroderma Peters, 1860 (Chiroptera: Phyllostomidae), Zootaxa 4846 (1), pp. 1-93 : 46-48

Chiroderma improvisum Baker and Genoways, 1976

Synonyms:

Chiroderma improvisum Baker and Genoways, 1976: 1 ; type locality “ Guadeloupe: Basse-Terre; 2 km. S, 2 km. E Baie-Mahault.”

Type Material. The type, TTU 19900 (not seen), is a skin, skull and mandible, collected by R. J Baker and H. H. Genoways (field number J. C. Patton 552) in July 29, 1974 on the Basse-Terre island , Guadalupe ( Baker & Genoways 1976). It is an adult male captured in a mist net set in a pasture adjacent to gallery forest. The karyotype of the specimen is deposited with the tissue collection of the Texas Tech University under the number TK 8285. The skin, skull, and mandible were examined by means of photographs and are in good condition .

Distribution and Habitat. The species is known from four islands in the Lesser Antilles: Guadeloupe, Montserrat, Saint Kitts, and Nevis ( Fig. 28 ). There is also a subfossil specimen collected on the island of Marie-Galante, south of Guadeloupe ( Lenoble 2019). Records of C. improvisum are from areas of dry forests and humid forests, from sea level up to approximately 350 m. The few known specimens were captured in mist nets set over streams, in gallery forests, in secondary forests surrounded by pasture and plantations, and in urban and peri-urban areas ( Baker et al. 1978; Jones Jr. & Baker 1979; Pierson et al. 1986; Pedersen et al. 2010; Beck et al. 2016). However, a harp trap set across a dry ravine caught the first specimen of C. improvisum from Nevis ( Lim et al., 2020).

Description and Comparisons. Dorsal pelage varies from grayish to dark brown. Dorsal pelage is long (approximately 13 mm). Individual hairs of the dorsum are tricolored with a grayish base and buff middle band. The interocular stripes are weakly developed and the genal pair was not visible in the two skins we examined, but its presence can be verified in photographs of live animals ( Baker & Genoways 1976; Jones Jr. & Baker 1980; Lim et al. 2020). The dorsal stripe is inconspicuous, visible from the mid dorsum to near base of the uropatagium. The ear is moderate to dark brown along most of its length; the base is yellowish. The noseleaf is uniformly dark to medium brown, and the tip may be simple or notched, as evident in the figure in Jones & Baker (1980). The posterior border of the uropatagium has a V-shaped notch.

The skull of C. improvisum is the largest among Chiroderma ( Tables 7 and 8). The braincase is low and slopes evenly to the frontonasal region in profile. The sagittal and lambdoid crests are conspicuous in both specimens examined and in the type. The nasal notch extends behind the anterior margin of the orbits ( Fig. 29 ). Post-orbital processes are distinct, but not pointed. The orbits are relatively small and the posterior margin approximates the level of the mesial margin of M1 ( Fig. 30 ). A medial accessory foramen between incisive foramina is lacking. There is no posterior palatine process. When skull and mandible are in occlusion, there is a small lateral gap bordered by C, P3, p2, and p4 ( Fig. 9 ). In addition, there is a frontal gap surrounded by I1, I2, c, i1, and i2 ( Fig. 14 ).

The I1s are convergent and their tips may or may not be in contact. P3 is separated from P4 by a small gap, or the two teeth contact each other ( Fig. 29 ). The mandibular condyle is above or level with the tooth row. Lower canines are relatively short, their tips below the level of the top of the coronoid process. The basal cingulum of the lower canines is well developed and crowding the lower incisors. The p2 is mesiodistally longer than tall, and is approximately ⅓ of the height of p4 ( Fig. 30 ). The p2 is in contact with lower canines, either touches p4 or the two lower premolars are separated by a small gap. The p4 protoconid is robust, with its distal margin sloping evenly to the tooth’s, not abruptly as in the other species.

Compared with C. doriae , which has a similar size, C. improvisum is larger, has grayish or dark brown dorsal pelage (medium brown in doriae ), faint facial stripes (bright in doriae ), and unicolored noseleaf and ears (in doriae the horseshoe of the noseleaf has pale borders and the ears also have whitish margins). Cranially, C. improvisum can be diagnosed by its wider nasal notch and by the broader posterior border of the palate, not narrow inverted-U shaped as in C. doriae . The P3 of C. improvisum is not expanded buccolingually and is in contact with P4, differing from C. doriae in both aspects. The lower canines of C. improvisum are relatively larger than in C. doriae . The p2 of C. improvisum is mesiodistally longer than tall; whereas, in C. doriae , p2 is taller exceeding ⅔ the height of p4. The p4 of C. improvisum is more robust than in C. doriae , and the protoconid is long mesiodistally. A frontal gap is present in C. improvisum , but lacking in C. doriae .

The species most similar to C. improvisum in qualitative characters is C. villosum , from which improvisum can be differentiated by the much larger size, darker pelage (pale brown in villosum ), absence of a posterior palatine process, convergent I1s (parallel and separate in villosum ), relatively smaller lower canines (taller and more pointed in villosum ), large p 2 in contact with p4 (gap between p2 and p 4 in villosum ).

Geographic Variation and Phylogeography. The genetic distance between the two specimens of C. improvisum in our molecular analysis was 0.22% ( Fig. 4 ). Due to the small sample, we cannot make inferences either on geographic structuring or morphological variation in the taxon.

Subspecies. C. improvisum is monotypic.

Natural History. There is no information on the diet of C. improvisum , but it probably feeds on fruits, infructescences and their seeds, as the other species of Chiroderma . The type was collected approximately 6 m above the ground and near a forest having a 15-meter-high canopy ( Baker et al. 1978), suggesting that the species may be active in the canopy as is the closely-related C. villosum . A mite , Periglischrus iheringi (Spinturnicidae) , was recorded on C. improvisum from Saint Kitts ( Beck et al. 2016). We lack information on reproduction in C. improvisum .

Specimens Examined (N = 2): Montserrat : Saint Anthony Parish , 0.8 km above mouth of Belham river ( TTU 31403 ) . Saint Kitts and Nevis: Saint Thomas Parish ( Nevis) ¸ Barnes Ghaut ( ROM 126002 ) .

Figures

FIGURE 4. Bayesian phylogeny obtained from the analysis of cytochrome c oxidase subunit 1 (COI) of Chiroderma. The diagram represents the MCC (Maximum Clade Credibility) tree summarizing 22,501 molecular phylogenies. The vertical dashed line indicates the threshold between the between-species Poisson tree processes (PTP) and the within-species PTP. The triangle base lengths are proportional to the sample size of each clade. The posterior probability values are shown above the corresponding branches.

FIGURE 9. Lateral view of skull and mandible in occlusion for A) Chiroderma salvini (ROM 99703), B) Chiroderma scopaeum (TTU 110649), C) Chiroderma d. doriae (TTU 99569), D) Chiroderma villosum (USNM 560607), and E) Chiroderma improvisum (ROM 126002).

FIGURE 14. Frontal view of skull and mandible in occlusion for A) Chiroderma salvini (ROM 99703), B) Chiroderma scopaeum (TTU 110649), C) Chiroderma d. doriae (TTU 99569), D) Chiroderma villosum (USNM 560607), E) Chiroderma improvisum (ROM 126002).

FIGURE 28. Collecting localities of the analyzed specimens of Chiroderma improvisum, C. v. villosum and C. v. jesupi. The locality numbers are referenced in the gazetteer (Appendix 1).

FIGURE 29. Dorsal (A) and ventral (C) views of the skull of Chiroderma improvisum (TTU 31403—Montserrat) and dorsal (B) and ventral (D) views of C. villosum (USNM 520557—Panamá).

FIGURE 30. Skull and mandible, in lateral view, of A) Chiroderma improvisum (TTU 31403—Montserrat) and B) C. villosum (USNM 520557—Panamá).