Bioacoustics of Eleutherodactylus montserratae

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).

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 .

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.