Eleutherodactylus montserratae, Hedges, 2022

Hedges, S. Blair, 2022, A new species of frog from the Caribbean island of Montserrat (Eleutherodactylidae, Eleutherodactylus), Zootaxa 5219 (4), pp. 375-387 : 378-384

Eleutherodactylus montserratae sp. nov.

Montserrat Whistling Frog

( Figs. 3–5 )

Holotype ( Fig. 3 ): ANSP 38773 , adult female, on the grounds of the former Belham Valley Hotel , Old Towne, Saint Peter Parish, Montserrat, 50 m, 16.73 N, - 62.22 W, collected by S. Blair Hedges and Carla Hass on 13 August 1991. Field tag USNMFS 192724 (= SBH 192724).

Paratypes (n = 21): ANSP 38772 (SBH 192723), 38767–768 (SBH 192712–713), from the type locality, with the same information as the holotype . ANSP 38765–766 (SBH 192710–711), from Woodlands Spring , Saint Peter Parish, Montserrat, 180 m (16.757, -62.217), collected by S. Blair Hedges and Carla Hass on 13 August 1991 . ANSP 38755–764 (SBH 192684–685, 198688–689, 192692, 192695–698, 192700) , ANSP 38769–771 (SBH 192714– 716) , ANSP 38774–776 (SBH 192725–727), from the Galways Soufriere , at the caldera, Saint Anthony Parish, Montserrat, 180 m (16.704552, -62.18772), collected by S. Blair Hedges and Carla Hass on 14 August 1991 .

Diagnosis. A species of Eleutherodactylus in the martinicensis Species Group of the subgenus Eleutherodactylus ( Hedges et al. 2008) , which includes E. amplinympha Kaiser, Green & Schmid , E. barlagnei Lynch , E. johnstonei Barbour , E. martinicensis (Tschudi) , and E. pinchoni Schwartz. Eleutherodactylus amplinympha , which occurs only on Dominica, is a larger species than E. montserratae sp. nov. (16.1–26.4 versus 16.1–21.2 mm SVL in males, 15.9–49.7 versus 16.7–29.7 mm SVL in females), with a 3-note call consisting of two notes and a “click,” with the second note rising in frequency. In contrast, E. montserratae sp. nov. has a two-note call, with the second note constant in pitch and higher in frequency ( Kaiser et al. 1994). Eleutherodactylus barlagnei , which occurs only on Guadeloupe, is slightly larger than E. montserratae sp. nov. (19.6–22.8 versus 16.1–21.2 mm SVL in males, 22.9–31.7 versus 16.7–29.7 mm SVL in females) and has distinctive webbing and dermal flanges on the hands and feet, as adaptations to its aquatic lifestyle. The call of E. barlagnei is a series of four or more trilled notes, descending at the end ( Schwartz 1967). Eleutherodactylus martinicensis ( St. Martin, St. Barthélemy, Antigua, Guadeloupe, Dominica, Martinique, and St. Lucia) is a much larger species than E. montserratae sp. nov. (21.9–32.3 versus 16.1–21.2 mm SVL in males, 21.4–46.6 versus 16.7–29.7 mm SVL in females), has a slightly wider head and longer hind limbs (distinctly overlapping versus not overlapping in E. montserratae sp. nov.), brighter dorsal coloration, red on the hindlimbs and groin, and a different 2-note whistle call with a longer first note and rising second note versus a short first note and constant pitch second note of E. montserratae sp. nov. ( Schwartz 1967; Kaiser 1992). Eleutherodactylus pinchoni , which occurs only on Guadeloupe, is a smaller species than E. montserratae sp. nov. (14.4–16.0 versus 16.1–21.2 mm SVL in males, 15.2–20.2 versus 16.7–29.7 mm SVL in females), with an orange venter heavily mottled or stippled in dark brown (versus venter pale or sparsely stippled), a pale (orange-red) groin spot (versus no groin spot), a dark vocal sac in males (versus unpigmented vocal sac), a median pale line on the throat in both sexes (versus no pale line), and a call consisting of a series of “tick’s followed by a single rising wheep” ( Schwartz 1967) versus a two-note call with second note constant in pitch.

Eleutherodactylus montserratae sp. nov. is most closely related to E. johnstonei ( Yuan et al. 2022) , with which it shares a general body shape and proportions, pattern variation, and a two-note whistle-like call ( Schwartz 1967; Kaiser 1992). Structural similarities between the two species include a narrow (razor-thin) middorsal ridge, dorsal tubercles of variable size and density (fine to coarse), and similar body proportions such as END, THL, SHL, FTL, and FPW (see also Schwartz 1967). In coloration, the dorsal ground color is variable (brown, tan, reddish tan, or gray) and they share pattern variants (pale middorsal stripe, 1–2 medium or dark brown middorsal chevrons, or broad and pale dorsolateral stripes) and pattern elements such as interocular bar defining a paler dorsal surface of the snout, wide dark brown bars on the loreal, postocular, and supratympanic regions, and obscure (not bold) medium or dark brown leg barring. Eleutherodactylus johnstonei differs from E. montserratae sp. nov. in being larger (17.9–25.2 versus 16.1–21.2 mm SVL in males, 18.2–34.8 versus 16.7–29.7 mm SVL in females) and having a proportionately smaller tympanum (5.25–6.12 versus 6.10–7.06 % SVL in males, 5.12–6.13 versus 6.47–7.37 % SVL in females), a narrower head (35.4–38.2 versus 36.1–39.7 % SVL in males, 33.9–40.0 versus 37.1–41.7 % SVL in females), and smaller separation between the nostrils (8.69–9.27 versus 9.55–10.5 % SVL in males, 8.18–9.45 versus 9.52–10.5 % SVL in females). Photos in life ( Figs. 4–5 ) show that E. johnstonei sensu stricto has the upper iris color golden rather than bluish-white. However, this difference in upper iris coloration needs to be confirmed in a larger sample size of living individuals. The calls are similar in being two-notes and constant in pitch, but one analysis of two calls indicated that the second (high frequency) note of E. johnstonei might be shorter than that of E. montserratae sp. nov. ( Kaiser 1992). However, a more comprehensive analysis of vocalization in the two species will be needed to determine if that is a significant difference distinguishing the two species.

Description of the holotype ( Fig. 3 ). Adult female; head as wide as body, width less than length; snout subacuminate in dorsal view, subacuminate in lateral view, overhanging lower jaw; nostrils weakly protuberant, directed dorsolaterally; canthus rostralis rounded, slightly sinuous in dorsal view; loreal region slightly concave, sloping gradually; lips not flared; upper eyelid bearing moderate-sized, rounded tubercles; interorbital space without tubercles; supratympanic fold well defined, concealing upper edge of tympanic annulus; tympanum moderate-sized, round, separated from eye by a distance less than its own diameter; several postrictal tubercles, enlarged, subconical; choanae small, oval, partially concealed by palatal shelf of maxillary arch when roof of mouth is viewed from below; vomerine odontophores medial and posterior to choanae, each larger than a choana, straight and angled postero-medially, separated moderately at midline; posterior two-thirds of tongue not adherent to floor of mouth.

Skin of dorsum weakly to strongly tuberculate, without dorsolateral folds; skin of flanks similar to dorsum; skin of venter strongly areolate, without discoidal folds; anal opening not extended in sheath; no supraxillary glandular areas present; ulnar tubercles low, flat; palmar tubercle single, larger than thenar, thenar tubercle oval, low; several moderate-sized low, supernumerary tubercles; subarticular tubercles of fingers round and subconical; well defined lateral ridge on finger; all fingers with expanded tips; fingertips rounded, semicircular pad on ventral surface of fingertip; circumferential groove bordering distal three-quarters of finger pad; width of largest pad (III) one-half as wide tympanum; first finger shorter than second when adpressed; heel tubercles absent; small, flattened, tubercles along outer edge of tarsus; metatarsal tubercles low, inner (elongate) twice size of outer (subconical); several small, low, supernumerary plantar tubercles; subarticular tubercles of toes round and subconical; toes unwebbed; well-defined lateral ridge on toe; all toes with expanded tips; toetips rounded; semicircular pad on ventral surface of toetip; circumferential groove bordering distal three-quarters of toe pad; heels overlap when flexed legs are held at right angles to sagittal plane.

Variation. Other specimens are similar to the holotype. Males with vocal slits and vocal sac (confirmed by dissection); vocal sac median subgular and externally visible. The mean (± 1 SE) and range (in parentheses) of 11 adult males (listed first) and 9 adult females (holotype in bold) are, in mm: SVL 17.5 ± 0.35 (16.1–19.5), 20.7 ± 0.62 (18.4–22.9, 22.9); HL 7.08 ± 0.17 (6.26–7.82), 8.63 ± 0.33 (7.23–10.3, 8.83); HW 6.68 ± 0.17 (5.90–7.59), 8.12 ± 0.27 (6.83–9.13, 8.87); TYM 1.14 ± 0.02 (1.03–1.25), 1.43 ± 0.05 (1.19–1.67, 1.49); EYE 2.50 ± 0.05 (2.18–2.75), 3.00 ± 0.09 (2.54–3.35, 3.14); END 1.94 ± 0.05 (1.72–2.18), 2.45 ± 0.07 (2.12–2.79, 2.43); IND 1.74 ± 0.04 (1.60– 1.92), 2.05 ± 0.06 (1.76–2.25, 2.18); THL 7.21 ± 0.16 (6.50–8.11), 8.68 ± 0.25 (7.63–10.0, 8.82); SHL 7.78 ± 0.13 (7.23–8.40), 9.53 ± 0.28 (8.20–10.7, 10.2); FTL 6.63 ± 0.15 (6.03–7.66), 7.89 ± 0.31 (6.03–9.27, 8.45); and FTW 0.57 ± 0.02 (0.42–0.68), 0.76 ± 0.04 (0.54–0.89, 0.84) .

Distribution ( Fig. 6 ). Eleutherodactylus montserratae sp. nov. is native to Montserrat and introduced on other islands in the western Lesser Antilles ( Anguilla, St. Martin / St. Maarten, St. Barthélemy, Saba, St. Eustatius, St. Christopher, and Nevis), and on Bermuda ( Breuil 2002; Yuan et al. 2022). This distribution is based on a combination of DNA sequences, morphology, and chromosomes. However, the species assignment here for the St. Barthélemy introduced population ( Breuil 2002) is based only on distribution and requires confirmation. Bermuda is the only location where E. montserratae sp. nov. is known to co-occur with E. johnstonei (sensu stricto).

Presumably, all introduced mainland records from the Americas ( Leonhardt et al. 2019) are of E. johnstonei ( Kaiser et al. 2002) , confirmed for Venezuela by DNA sequence ( Yuan et al. 2022) and for Venezuela and Guyana by chromosomes ( Schmid et al. 2010). The genetic variation detected among Colombian samples was low ( Leonhardt et al. 2019), consistent with a single species, presumably E. johnstonei sensu stricto. All European populations are apparently of that species as well, because they arose from a single introduction from Guadeloupe ( Leonhardt et al. 2019; Moravec et al. 2020). However, additional genetic testing and morphological examination is needed to more comprehensively examine introduced populations and confirm their species identification.

Ecology and conservation. The habitat preference of E. montserratae sp. nov. is similar to that of E. johnstonei , both of which have wide niches. In general, ecological details in the literature concerning E. johnstonei (sensu lato) ( Schwartz 1967; Schwartz & Henderson 1991; Henderson & Powell 2009) apply equally to both included species, E. johnstonei (sensu stricto) and E. montserratae sp. nov.

The most natural habitat of E. montserratae sp. nov. on Montserrat is mesic forest, presumably its original habitat. However, the species also occurs in a diversity of other habitats modified by humans, such as roadside herbaceous growth, gardens, ornamental shrubs around houses and buildings, sugarcane fields, and palm groves. Males usually call from elevated places (e.g., leaves) up to one meter above the ground. Although the type locality and localities of most paratypes were altered by volcanic eruptions that began in July 1995, scattered populations remain throughout the island and the species is abundant ( Yuan et al. 2022).

As Schwartz (1967) stated, in reference to E. johnstonei (sensu lato), it is regularly encountered during the day in “almost any terrestrial situation which offers concealment and some moisture.” Both species are often encountered in great abundance. These characteristics, with a wide niche and occurring in abundance, explain why they have been introduced to so many islands. Currently, E. johnstonei (sensu lato) is listed as Least Concern by the IUCN Redlist ( IUCN 2022). That category should continue to be used for that species and E. montserratae sp. nov.

Reproduction. Mean clutch size for 12 females of Eleutherodactylus montserratae sp. nov. is 15.8 (range, 8–40), mean body mass (live) is 1.08 g (range, 0.43–2.80), and relative clutch mass (clutch mass/body mass) is 10.8% (range 7–16%, n = 5). Mean live body mass of 33 adult males is 0.53 g (0.25–0.89). For comparison, mean clutch size for 10 gravid female E. johnstonei , sensu stricto, is 15.8 (range 12–29), mean live body mass is 1.24 g (range 0.47–2.21), and relative clutch mass is 11.1% (range 6–16%). Mean live body mass of 74 adult males is 0.69 g (range 0.47–1.10).

Etymology. The species name ( montserratae ) is a feminine genitive singular noun, referring to the native distribution of the species on the island of Montserrat.

Remarks. Schmid et al. (2010) examined chromosomes of seven individuals of E. johnstonei sensu lato from Bermuda and found all to be from the Western Clade (= E. montserratae sp. nov.). However, with DNA sequences of 15 individuals from Bermuda, Yuan et al. (2022) discovered that while most were members of the Western Clade, some were of the Eastern Clade ( E. johnstonei sensu stricto), thus establishing the only known location where the two species are known to co-occur. There are believed to be two 19 th Century introductions to Bermuda, but there is confusion as to their origin ( Kaiser 1997). Because of the major chromosomal difference between the two species, involving sex chromosomes ( Schmid et al. 2010), and their long time of separation (~2 my), it is unlikely that they are able to hybridize. Nonetheless, those genetic markers, a potential call difference ( Kaiser 1992), and the morphological markers revealed here, will allow future study of this mixed population to determine if hybridization is occurring.

I propose “ Montserrat Whistling Frog” as the common name for E. montserratae sp. nov. following the conventions for common name formation outlined in Hedges et al. (2019). Using the same conventions, I propose the revised common name, “Lesser Antilles Whistling Frog,” for E. johnstonei .

Figures

FIGURE 3. Eleutherodactylus montserratae sp. nov. (A–B) ANSP 38773, holotype, an adult female. (A) Dorsal view. (B) Ventral view.

FIGURE 4. Eleutherodactylus montserratae sp. nov. (A–C), photos in life. (A) USNM 315610, an adult male from Pic du Paradis (near summit), St. Martin (18.0771, -63.0497, 406 m), collected 12 September 1988 by Ronald Crombie. (B) Uncatalogued individual from Galway’s Soufriere, near the caldera on Montserrat (16.704552, -62.18772, 180 m), collected 14 August 1991 by SBH and C. A. Hass. (C) Uncatalogued individual from 0.5 km N Boyd’s at Fairview Inn, St. Kitts (17.3015, -62.7706, 77 m), collected 26 July 1988 by SBH and C. A. Hass. Photographs by SBH.

FIGURE 5. Eleutherodactylus johnstonei. (A–C), photos in life. (A) Uncatalogued individual from 9.5 km WNW Troy, Jamaica (18.2835, -77.6726, 510 m), collected 20 September 1985 by SBH and C. A. Hass. (B) ANSP 38793 (SBH 267722), adult female from Martins Bay, Barbados (13.1978, -59.4948, 5 m), collected 10 June 2006 by SBH and C. A. Hass. (C) Uncatalogued individual from Montreal, St. Vincent (13.2085, -61.1867, 482 m), collected 24 April 1996 by SBH. Photographs by SBH.

FIGURE 6. Map showing the distributions of Eleutherodactylus montserratae sp. nov. (red) and E. johnstonei (yellow) in the Lesser Antilles. The only location where E. montserratae sp. nov. is known to be native is Montserrat. There is no location where E. johnstonei is known to be native.Additional introduced populations of both species occur together on Bermuda and of E. johnstonei in Jamaica, Central America, South America, and Europe (see text).