Bioacoustics of Eleutherodactylus sentinelus

Diagnosis. Based on the phylogenetic analysis, this species is a member of the genus Eleutherodactylus , subgenus Syrrhophus , as defined by Hedges et al. (2008) ; and in the Eleutherodactylus ( Syrrhophus ) nitidus species series and the Eleutherodactylus ( Syrrhophus ) nitidus species group as defined by Grünwald et al. (2018) based on the condition of the tympanic annuli, ventral epidermis, and visceral peritoneum. A small frog, adult males measure 23.3–25.3 mm SVL; vocal slits are present in males; digital tips are expanded, 1.4–2.3 times the width of the narrowest part the finger on the third and fourth fingers; finger lengths are I-II-IV-III, fingers moderately long, with third finger length ranging from 13–21% of SVL; compact lumbar gland in the inguinal region present but indistinct, visible in live specimen; ventral epidermis semi-translucent and the visceral peritoneum is clear, not white, abdominal vein barely visible on the venter of live specimens against the background of the viscera; limbs moderate, TL/SVL ratio is 0.41–0.56, FeL/SVL ratio is 0.38–0.46 and TotFL/ SVL ratio is 0.61–0.74; snout short, END/ SVL ratio is 0.10–0.11; tympanum small, indistinct and round, tympanic annuli not visible in live specimen; TW/EW ratio is 0.26–0.28. The dorsal skin is smooth to slightly pustulate. Dorsal coloration is reddish-tan or brown. A pale brown or reddish interorbital bar always present, and a pale mid-dorsal blotch of the same color as the interorbital bar is present. Upper arms pale and unmarked, dark transverse bands present on forearms and legs, and inguinal flash coloration orange or yellow present on groin and sometimes on posterior portion of thighs. Ventral coloration whitish or gray with some darker gray spots or indistinct marbling. The mating call of adult males is a quick chirp (“peep,” see below; Fig. 3 ). Comparisons. Eleutherodactylus sentinelus can be distinguished from all species in the Eleutherodactylus ( Syrrhophus ) longipes species series by: possessing a small, indistinct tympanum with no tympanic annulus visible and with a diameter less than 30% of diameter of the eye; by possessing a visceral peritoneum which is not white, so that the abdominal vein on the venter is not clearly evident against a white background in life; and by possessing a distinct, raised lumbar gland above the inguinal region. CIG 916 CIG 917 CIG 918 CIG 919 CIG 920 CIG 921 CIG 922 CIG 923 CIG 940 CIG 941 CIG 945 CIG 946 CIG 947 CIG 949 SVL 19.26 22.27 21.05 22.05 22.95 23.47 24.65 21.3 20.46 17.9 23.88 22.01 20.13 21.67 HL 6.86 7.45 7.3 7.43 7.57 7.78 8.07 7.18 7 6.51 7.77 7.2 6.8 7.27 TW 0.68 0.71 0.68 0.72 0.73 0.73 0.74 0.72 0.67 0.63 0.67 0.67 0.66 0.67 ED 2.38 2.78 2.57 2.56 2.6 2.68 2.75 2.53 2.44 2.23 2.73 2.5 2.41 2.48 ElW 1.28 1.37 1.3 1.4 1.39 1.51 1.51 1.25 1.33 1.2 1.51 1.43 1.47 1.46 IOD 4.12 4.35 4.38 4.41 4.66 4.76 4.73 4.23 3.82 3.41 4.18 4.08 4.12 4.11 IND 2.15 2.32 2.36 2.34 2.41 2.48 2.53 2.22 2.15 2.04 2.45 2.22 2.2 2.22 END 2.24 2.66 2.4 2.36 2.43 2.51 2.5 2.31 2.2 2.08 2.51 2.3 2.26 2.31 ETD 0.74 0.81 0.85 0.84 0.86 0.88 0.89 0.85 0.84 0.84 0.9 0.88 0.84 0.87 UpL 5.03 5.33 5.06 5.08 6 6.31 5.9 5.51 5.1 4.22 5.6 5.28 4.84 4.94 Fol 6.12 6.6 6.07 6.51 7.17 7.47 7.18 6.52 6.15 5.24 6.9 6.15 5.86 5.9 HaL 4.72 5.55 5.07 5.22 5.3 5.5 5.46 5 4.53 4.05 5.54 4.95 5.06 5.12 F3PW/F3W 1.8 1.6 2 2.1 1.7 1.9 1.8 1.7 1.6 1.4 1.6 1.4 1.8 1.5 F4PW/F4W 1.9 1.7 2 2.1 1.6 1.9 1.9 1.6 1.8 1.5 1.6 1.5 1.8 1.4 FeL 9.05 10.06 9.65 9.66 10.03 10.49 10.44 8.75 8.6 8.22 9.92 9.78 9.04 9.09 TL 9.75 10.46 10.23 10.18 11 11.5 10.97 9.9 9.4 8.6 10.89 10.17 9.95 9.75 TotFL 14.08 15.75 15.13 15.43 15.81 16.12 16.4 14.53 13.4 12.42 15.83 14.6 14.57 13.93 ITP 0.56 0.6 0.57 0.55 0.68 0.67 0.69 0.58 0.49 0.39 0.51 0.58 0.47 0.4 MPT 0.78 0.9 0.79 0.84 0.92 0.96 0.95 0.77 0.75 0.69 0.73 0.73 0.7 0.7 OPT 0.28 0.45 0.4 0.37 0.46 0.43 0.44 0.37 0.3 0.25 0.34 0.35 0.35 0.32 IMTL 0.79 0.83 0.76 0.73 0.79 0.91 0.95 0.68 0.67 0.64 0.8 0.78 0.74 0.72 OMTL 0.44 0.55 0.45 0.45 0.56 0.6 0.63 0.37 0.32 0.4 0.45 0.43 0.41 0.45 TW/ED 0.29 0.26 0.26 0.28 0.28 0.27 0.27 0.28 0.27 0.28 0.25 0.27 0.27 0.27 Eleutherodactylus sentinelus can be distinguished from species of the Eleutherodactylus ( Syrrhophus ) modestus species group by the combination of possessing a compact, protruding lumbar gland above the inguinal region, digital tips which are expanded more than 1.4 times the width of the narrowest part the finger on the third and fourth fingers, and the presence of an interorbital bar. Within its own species group, E. sentinelus can be distinguished from most species by possessing a compact inguinal gland which is indistinct but visible in live specimens. This differs from E. pipilans , E. erythrochomus , and E. nebulosus , which lack a distinct visible inguinal gland altogether. All other known species in the E. ( Syrrhophus ) nitidus species group have readily visible compact lumbar glands above the inguinal region. Eleutherodactylus sentinelus can be further distinguished from E. pipilans , E. erythrochomus , and E. nebulosus by the presence of distinct pale interorbital bar and pale-yellow inguinal flash coloration. It may be distinguished from E. nitidus , E. petersi , and E. orarius by the combination of smoother skin, longer limbs, and tips of digits which are expanded more than 1.4 times the narrowest part of the finger on the third and fourth fingers. It further differs from these three species by call, which is a short chirp rather than a whistle. It is distinguished from E. albolabris by the following characters (characters of E. albolabris in parentheses): lip dark, never white, with some flecking (lip white, immaculate), inguinal flash coloration always yellow (always fiery orange), ventral coloration translucent and white, with some black markings (ventral coloration completely white with bold black markings), tympanum small with TW/ED 0.25–0.28 (tympanum slightly larger with TW/ ED 0.27–0.32). Eleutherodactylus sentinelus may be distinguished from E. maurus by the following (characters of E. maurus in parentheses): by the presence of pale interorbital bar same color as snout ( E. maurus presents no pale interorbital bar), smooth dorsal and ventral skin (rugose or slightly rugose dorsal and ventral skin), bright yellow or orange flash colors on thighs (flash colors absent, or barely discernible), pale interorbital stripe distinct between darker head coloration (pale interorbital stripe absent or same color as dorsal surface of snout). Eleutherodactylus sentinelus may be distinguished from E. syristes and E. maculabialis by its mating call, which is a rapid chirp (“peep”) as opposed to a trill. Eleutherodactylus sentinelus can be further distinguished from the closely related E. syristes by having more expanded finger tips, 1.4–2.3 times the narrowest part of the digit on fingers three and four, and usually more than 1.6 (vs. 1.1–1.5 times the narrowest part of the digit on fingers three and four), and by having yellow or yellowishorange flash colors (vs. orange or reddish flash colors). Eleutherodactylus sentinelus is most similar to E. dilatus , from which it may be distinguished by the by much smoother skin on both the dorsum and venter ( E. dilatus has rugose dorsal skin and pustulate venter), smaller, less distinct inguinal glands ( E. dilatus has large, distinct inguinal glands), and a paler dorsal ground coloration ( E. dilatus is dark brown).