Bioacoustics of Eleutherodactylus juanariveroi

Diagnosis. A member of the West Indian subgenus Eleutherodactylus , auriculatus section, martinicensis series (sensu Hedges, 1989 ) having extensive dorsal skin glandularity (Fig. 3), minute vomerine teeth, a distinctive carpal element (see description), a unique high-pitched call, and a palustrine habitat. Males have an external single subgular vocal sac, absent in females; nuptial pads absent. Pupil horizontally elliptical with two thin, sharp vertical slits, black colored below and above the mid portion of pupil, resulting in a ‘+’, sometimes only the inferior slit is clearly visible resulting in a ‘T’ ( Fig. 2 ). The digital disks are small and spatulate as opposed to widening abruptly from the base of the pad. The terminal phalanges are nearly T-shaped, clearly visible in finger III and Toe IV, but only with minute lateral projections of the terminal phalanges; rest of phalanges knobbed clearly visible in finger I of holotype (KU 306997), although terminal transverse groove across the tip of the digital pad visible in external view. Large carpal element (fused carpals 2+3) with pronounced ventral spine and emargination (the equivalent structure in E. gryllus being more solid and rounded with a minute spine). Eyelid tubercles absent; dorso-lateral folds absent. Ulnar tubercles absent; thenar tubercle elevated, elliptical, about the same size as pad in finger I; subarticular tubercles rounded; few minute supernumerary tubercles on proximal segments of fingers; a few minute centrally grouped supernumerary palmar tubercles; fingers lacking lateral fringes; relative length of fingers 1=2<4<3; disk of fingers small, spatulate not widening abruptly ( Fig. 4 A). Heel tubercles few, small, rounded, elevated; tarsal fold and lateral fringes of the toes absent; metatarsal tubercle rounded; subarticular tubercles rounded and slightly larger than palmar; supernumerary plantar tubercles present on proximal segments of toes; sole with a few minute irregularly scattered plantar tubercles; relative lengths of toes 1<2<3=5<4 ( Fig. 4 B). Finger webs and toe webs absent. The closest relative of E. juanariveroi is E. gryllus with which it agrees in size and proportions (Fig. 3, Tables 1 and 2 ), skin glandularity and fundamental call note. However, E. juanariveroi is smaller than E. gryllus (SVL in mm: males, 14.7 females 15.8 vs. E. gryllus males 15.7 and females 16.4) ( Table 1 and 2 ). The nares are prominent, and a ridge connects them behind the snout tip, giving it a somewhat squared-off appearance (Fig. 3A). On the other hand, the nares are less prominent in E. gryllus ; the loreal surface is steeper on the average (65–79°) in E. juanariveroi compared with E. gryllus (51–67°); the loreal surface has a midindentation, which is not so pronounced in E. gryllus . The vomerine teeth are minute (2–3 teeth in UPRRP 6358) or absent (UPRRP 6341); the vomerine teeth of E. gryllus are small, but always visible (2–3 teeth in UPRRP 6373 and UPRRP 6374). The large carpal element (fused 2+3) is sculptured and emarginated ventrally, much more so than in E. gryllus . Glands in E. juanariveroi are clearly discernible on both external and internal examination (KU 306998) while glands in E. gryllus can only be verified by examining the inner surface of the skin (UPRRP 6372); glands are heavier and more extensive over the posterior angle of the head (supra-axillary gland, parotoid glands sensu Lynch [1971] ), body (flanks-lumbar-inguinal) and hind leg (dorsal side of thighs, tibiae, and tarsi) in E. juanariveroi than in E. gryllus (Fig. 3B); gular glands prominent and more extensive in females of E. juanariveroi than in E. gryllus ( Fig. 5 A); the hyoid plate is narrower in E. juanariveroi than in E. gryllus ( Fig. 5 b); left lobe of liver short and rounded, significantly smaller than right lobe compared with E. gryllus ( Fig. 5 C); the ventral skin is unpigmented or with a very light stippling of melanophores and is smooth to weakly areolate in E. juanariveroi (pigmented, slightly glandular, and with more prominent areolae in E. gryllus ). The relationship between tympanum width and inter-narial distance and between tibio-fibula length and tarsal length are significantly smaller than in E. gryllus (see beyond, Multivariate comparison of morphological ratios , for a detailed explanation on how we identified diagnostic morphological ratios and assessed the statistical significance). Eleutherodactylus juanariveroi Eleutherodactylus gryllus Males (N = 18) Females (N = 27) Males (N = 11) Females (N = 10) SVL 12.9–16.0 (14.66 ± 0.74) 12.1–17.3 (15.76 ± 1.21) 14.0–17.0 (15.65 ± 0.89) 14.1–17.9 (16.41 ± 1.18) HW 5.1–6.1 (5.61 ± 0.23) 4.7–6.5 (5.98 ± 0.39) 5.4–6.5 (6.07 ± 0.33) 5.7–7.1 (6.39 ± 0.44) HL 5.6–6.4 (5.95 ± 0.22) 5.4–7.8 (6.33 ± 0.48) 5.8–9.3 (6.83 ± 0.88) 6.3–7.4 (7.03 ± 0.41) UEW 0.9–1.4 (1.21 ± 0.11) 1.0–1.7 (1.27 ± 0.14) 1.1–1.7 (1.38 ± 0.17) 1.2–1.5 (1.38 ± 0.10) IOD 1.7–2.0 (1.82 ± 0.08) 1.4–2.3 (1.97 ± 0.18) 1.7–2.2 (2.00 ± 0.20) 1.8–2.4 (2.17 ± 0.21) TYW 0.6–1.0 (0.81 ± 0.09) 0.5–1.2 (0.95 ± 0.14) 0.8–1.1 (1.00 ± 0.09) 0.8–1.3 (1.09 ± 0.13) IN 1.3–1.5 (1.43 ± 0.08) 1.2–1.7 (1.51 ± 0.10) 1.3–1.7 (1.51 ± 0.12) 1.4–1.7 (1.60 ± 0.10) EL 2.1–2.6 (2.27 ± 0.14) 2.0–2.8 (2.36 ± 0.19) 2.3–3.0 (2.60 ± 0.25) 2.3–3.0 (2.73 ± 0.24) EN 1.3–1.7 (1.52 ± 0.09) 1.4–2.2 (1.70 ± 0.15) 1.6–2.1 (1.78 ± 0.15) 1.7–2.1 (1.93 ± 0.12) FD III 0.6–0.7 (0.67 ± 0.05) 0.5–0.9 (0.73 ± 0.08) 0.6–1.0 (0.76 ± 0.11) 0.6–0.9 (0.77 ± 0.08) FDB III 0.4–0.5 (0.44 ± 0.04) 0.4–0.6 (0.45 ± 0.04) 0.4–0.5 (0.44 ± 0.04) 0.4–0.5 (0.43 ± 0.03) TD IV 0.5–0.8 (0.67 ± 0.07) 0.5–0.9 (0.74 ± 0.09) 0.6–1.0 (0.78 ± 0.12) 0.6–0.9 (0.77 ± 0.10) FL 5.7–7.3 (6.59 ± 0.42) 5.4–7.5 (6.99 ± 0.46) 6.4–7.6 (7.00 ± 0.44) 6.5–8.9 (7.71 ± 0.63) TiL 5.9–7.2 (6.45 ± 0.33) 5.5–7.6 (6.99 ± 0.51) 6.6–8.7 (7.26 ± 0.60) 6.7–8.6 (7.70 ± 0.56) TaL 3.5–4.0 (3.84 ± 0.14) 3.3–4.6 (4.10 ± 0.28) 3.9–5.5 (4.48 ± 0.46) 3.9–5.1 (4.71 ± 0.35) Males Females The dorsal coloration of Eleutherodactylus juanariveroi in life is yellow to yellowish brown ( Fig. 2 B) with a light, longitudinal, reversed comma mark on each side, lateral to the dorsal pigmented zone, with the head of the comma lying over the supra-axillary (parotoid) gland; the dorsal pigmented zone itself bifurcates, each branch being broad and fading, usually defining part of the cephalic triangle and not forming the sharp, well-defined “tines” of E. gryllus ; the pattern is generally non-contrasting, versus a strongly contrasting dorsal pattern in E. gryllus that may include reversed parenthesis marks and occasionally a bold yellow mid-dorsal stripe ( Fig. 2 B; Joglar, 1998 , Figs. 4.11–4.12; Rivero, 1998 , Pl. XXV). Eleutherodactylus juanariveroi can be distinguished from other Puerto Rican species by an overall yellowish, non-contrasting coloration with a reversed comma pattern and a broadly bifurcated mid-dorsal zone ( Figs. 2 B and 6). E. juanariveroi (N = 18) E. gryllus (N = 10) Z P E. juanariveroi E. gryllus (N = 27) (N = 9) Z P TYW/IN 0.56 ± 0.06 0.66 ± 0.07 3.03 < 0.01 0.63 ± 0.07 0.68 ± 0.06 1.60 0.11 TiL/TaL 1.68 ± 0.06 1.64 ± 0.09 1.66 0.09 1.70 ± 0.06 1.65 ± 0.07 1.34 0.18 The marks that we call inverted commas in E. juanariveroi may be homologues of the inverted parenthesis marks of E. gryllus , but they could also be a modification of the entire lateral zone ( Fig. 6 ). However, these inverted commas may be a modification of the basic pattern elements of related species. Thus, in order to describe the color pattern of E. juanariveroi we relate it to the patterns of the other small Puerto Rican species ( E. cochranae , E. eneidae , E. gryllus , and E. locustus ) by identifying similar pattern elements ( Fig. 6 ): (1) a dark mid-dorsal zone extending from roughly the sacral region to the head, usually narrowing gradually along the trunk and expanding again near the head, thus having curved indentations on either side, (2) a pair of light, narrow reversed parenthesis marks that closely follow the indentation in the mid-dorsal zone, (3) a bifurcation of the mid-dorsal zone near the head, producing two dark, diverging extensions that approach the posteromedial edge of each eyelid (in E. juanariveroi , these are pale and broad), (4) a median head triangle, an apex of which projects caudad, fitting between the diverging extensions of the divided mid-dorsal zone, with the other two angles at each eye and side extending between the eyes (another pattern element that occurs in some of these species is a light midline stripe, but it is an occasional variant and is not found in E. juanariveroi ). These pattern elements have been variously modified by adding or lessening of pigment in the different species (and are variable within species), but reversed parentheses are frequent. A further modification occurs when pigment bridges form between the lower parts of the “tines” of the fork to the caudad apex of the cephalic triangle, which results in a dark scapular ‘W’ ( Fig. 6 ). FIGURE 3. Comparative morphology of holotype of E. juanariveroi (left, KU 306997) and E. gryllus (right, UPRRP 6372): canthus rostralis in dorsal view, scale bar 5 mm (A), distribution and shape of glands in dorsal view, scale bar 10 mm (B). On some individuals of these related small species, particularly E. locustus , the scapular ‘W’ and the light reversed parentheses may be the only pattern readily seen. Some of the components occur in frog species we have not mentioned; for example, E. hedricki (Rivero) and E. eneidae may have the reversed parentheses. In E. juanariveroi the pattern is much reduced in contrast; the reversed parenthesis marks are very wide; and the median dark zone is relatively light and the anterior branches broad; a well-developed scapular ‘W’ is not found. The result is a pair of light, longitudinal marks that curve laterally onto each side of the occiput, terminating with the large posterior head glands ( Figs. 2 B and 6). Interior to these marks on many specimens is another pair of diverging, light longitudinal marks (the altered median dorsal zone and branches). Some individuals show only the light heads of the commas, the rest of the pattern being obscure; this results in a pattern of two ocelli over the area of the scapula on the back of the head ( Fig. 6 ), representing the most divergent pattern among this group of small frogs. A light-brown inter-orbital band that extends to the tip of the snout is present in 16.3% of the E. juanariveroi (clearly defined in KU 306999) and absent or rare in E. gryllus (some specimens are so faded that it is difficult to discern the pattern). The legs of E. juanariveroi do not have any cross bands; those of E. gryllus have 1–2 hazy bands on the thigh and two on the shank. Although its call is related to that of E. gryllus , it is distinctive in its patterning and higher pitch (see Advertisement call for a detailed explanation on call parameters). A Puerto Rican Eleutherodactylus that may has morphological affinities with E. juanariveroi and E. gryllus is E. jasperi . Eleutherodactylus jasperi also has two pairs of lateral sub-dermal glands well developed on flanks and posterior surfaces of thighs ( Drewry and Jones, 1976 ). However, although E. jasperi has a yellow to yellow-brown body coloration in life, it differs dramatically from E. juanariveroi and E. gryllus in reproduction ( E. jasperi is ovoviviparous, the other species are oviparous), body size ( 19–20 mm in E. jasperi , 14– 15 mm in E. juanariveroi , 15–16 mm in E. gryllus ), acoustics (frequency of calls: 5 kHz in E. jasperi , ~7 kHz in E. gryllus , ~ 8 in E. juanariveroi ), habits ( E. jasperi is an obligate bromeliad-dwelling in somewhat xeric conditions in highlands, E. juanariveroi is an obligate herbaceous-dwelling in palustrine lowland wetland [N. Rios, in prep.], E. gryllus is arboreal in highland wetland conditions), and geographic distribution. Additionally, E. jasperi lacks prevomerine teeth while E. juanariveroi and E. gryllus have them.

Distribution and natural history. Eleutherodactylus juanariveroi is known only from the type locality ( Fig. 1 ), which lies within the subtropical moist forest life zone ( Ewel & Whitmore, 1973 ). This locality consists of a palustrine herbaceous wetland at 17 m elevation. The wetland is seasonally flooded with fresh water; the soil consist of swamp and marsh organic deposits from Pleistocene and/or recent origin ( Briggs & Akers, 1965 ). Herbaceous vegetation in this habitat consists of the toothed midsorus fern ( Blechnum serrulatum ), willdenow’s maiden fern ( Thelypteris interrupta ), bulltongue arrowhead ( Sagittaria lancifolia ), flatsedges ( Cyperus sp.), spike rushes ( Eleocharis sp.), and vines and grasses. The habitat at the type locality occupies approximately180 ha; we were unable to find the frog at other wetland sites in the northern coastal plain. All specimens were collected between 1900–2200 h while perching, sitting, or calling on herbaceous vegetation, mainly on ferns, between 0.4 m and 1.2 m above water level. Calling sites for males were 0.6 to 1.2 m above the ground. Egg clutches comprised 1– 5 eggs and were found on leaf axils ( 21 egg clutches) or leaf surfaces ( 3 egg clutches) of only S. lancifolia (N. Rios, unpubl. data). Like E. gryllus , the calling activity of E. juanariveroi started at approximately 1630 h and decreased significantly before midnight. The single locality from which E. juanariveroi is known is adjacent to the coast at 17 m elevation, while E. gryllus is only known from between 305 m to 1189 m elevation ( Joglar, 1998 ), although we have not recently found E. gryllus below 600 m elevation. This species is mostly arboreal, calling from branches and bromeliads, which contrasts with E. juanariveroi . Advertisement call. The call consists of a series of short high-pitched notes ( Fig. 8 A). At 26 C, call duration varies from 4–21 sec (10.9 ± 6.2 sec, n = 6). Call structure consists of one to three one-note series, followed by one or more series of two notes each, one (or more) series of three-four notes each, and a series that varies from 5–30 notes at the end of the call. Notes per call was 8–45 (23.0 ± 13.4 notes, n = 6) ( Fig. 8 A). Frequency was 6.03–9.02 kHz; the dominant frequency was 7.38–8.28 kHz (7.69 ± 0.18 kHz, n = 92) ( Fig. 8 A). Note duration was 15–31 ms (24.1 ± 3.1 ms, n = 92). Note repetition rate varies between consecutive notes within a series of two or more notes (341 ± 22 ms, n = 58) and between the final note of a series and the note in the following series (819 ± 99 ms, n = 30) ( Fig. 8 A). The advertisement call of E. juanariveroi differs from that of E. gryllus in notes per call (range 5–29, 15.3 ± 10.0 notes, n = 4) ( Fig. 8 B), dominant frequency (range 6.31–7.79 kHz, 7.44 ± 0.28 kHz, n = 61) ( Fig. 8 B), note duration (range 21–32, 26.8 ± 2.4 ms, n = 61), and note repetition rate (consecutive notes within a series 1.23 ± 0.13 sec, n = 53; between the first note of the call and the note in the following series in the call 1.97 ± 0.67 sec, n = 4) ( Fig. 8 B). Among sympatric Eleutherodactylus , the call of E. juanariveroi has the highest frequency and the greatest structural complexity compared with E. brittoni , E. cochranae , and E. coqui (Thomas) , but probably among all Puerto Rican Eleutherodactylus as well (for comparison see Drewry & Rand, 1983 and Narins, 1995 ).