Eleutherodactylus erythrochomus, Palacios-Aguilar & Santos-Bibiano, 2020

Palacios-Aguilar, Ricardo & Santos-Bibiano, Rufino, 2020, A new species of direct-developing frog of the genus Eleutherodactylus (Anura: Eleutherodactylidae) from the Pacific lowlands of Guerrero, Mexico, Zootaxa 4750 (2), pp. 250-260 : 251-256

Eleutherodactylus erythrochomus sp. nov.

( Figs 1–2 )

Holotype. MZFC 33964 ( Fig. 1A ). An adult male from Carretera Omitlán-La Venta (Hwy 95), Municipality of Juan R. Escudero (17.1345° N, - 99.5445°W, WGS84 ), 145 m, Guerrero, Mexico. Collected on September 15, 2016 by Ricardo Palacios Aguilar.

Paratypes. Five specimens, all from the same region as the holotype . MZFC 33965 , same data as the holotype . MZFC 8024 , adult female from Mexico, Guerrero, Palo Gordo (17.153765°N, - 99.546086°W; 255 m), collected by Rufino Santos Bibiano on June 1, 2014 . MZFC 16254 , adult male from Mexico, Guerrero, highway Tierra Colorada-Ayutla (Hwy 95), Palo Gordo (17.139°N, - 99.536°W, WGS84 ; 166 m), collected by Jonathan A. Campbell on June 3, 2002 . MZFC 33961–62 , adult males from Mexico, Guerrero, near Puente Omitlán, Tierra Colorada-Ayutla Highway (17.1405694°N, - 99.541789°W; 165 m), collected by Diego Arenas Moreno, Adán Bautista del Moral , Francisco Javier Muñoz Nolasco and Rufino Santos Bibiano on November 1, 2017 .

Referred specimen. MZFC 33963 , a juvenile male with same locality and recollection data as the holotype .

Diagnosis. A moderate-sized species possessing, 1) smooth skin dorsally and ventrally, becoming slighty areolate in the region surrounding the vent; 2) tympanum visible beneath the skin with a distinct annulus; 3) snout subacuminate in dorsal view, rounded in lateral view, somewhat depressed; 4) slender fingers (I>II>III<IV) with expanded, truncated disks; 5) hand tubercles ovoid in basal outline and slightly projecting, globular in profile; and 6) no lumbo-inguinal gland.

Eleutherodactylus erythrochomus differs from most Mexican congeners (except E. colimotl , E. dennisi , E. floresvillelai , E. grunwaldi , E. jaliscoensis , E. longipes , E. manantlanensis , E. nietoi and E. saxatilis ) by having enlarged disks in the hand that are three or more times wider than the narrowest part of the digit; from E. colimotl , E. floresvillelai , E. jaliscoensis , E. manantlanensis and E. nietoi , the new species differs by having shorter feet (FoL/SVL 41.28–45.66 vs. 60.71–101.40); it further differs from E. colimotl , E. floresvillelai , E. manantlanensis , and E. nietoi by having a wider tympanum (TD/EW 33.82–51.43 vs. 15.76–31.2); from E. floresvillelai , E. jaliscoensis , and E. manantlanensis it differs by having a wider head (HW/SVL 32.04–39.11 vs. 29.25–30.66); and from E. floresvillelai and E. jaliscoensis by having wider digital pads (W3P/W3F 2.29–3.83 vs. 1.41–2.11). It can be differentiated from E. grunwaldi by having a smaller average SVL (25.49 [20.1–30.9] vs. 29.1 [20.4–32.8]), and a different color pattern (scattered copper/golden markings vs. greenish markings). Eleutherodactylus erythrochomus differs from E. dennisi and E. longipes by having a smaller tympanum (TD/EW 33.82–51.43 vs. 50.7–77.78), and wider digital pads (W3P/W3F 2.29–3.83 vs. 2.6–3.88); and from E. saxatilis by the absence of a compact lumbar gland (vs. presence), shorter feet (FoL/SVL 41.28–45.66 vs. 46.2–50.85), smaller tympanum (TD/EW 33.82–51.43 vs. 47.76–58.82); and different skin texture (smooth vs. rugose).

Description of the Holotype. An adult male of moderate size (26.5 mm SVL), head slightly longer than wide (11.25 mm long, 10.2 mm wide), as wide as the body; snout subacuminate in dorsal view, rounded in profile; lip smooth, without distinctive markings or flares; tympanum diameter 1.8 mm, visible, with distinct annuli and membrane, without supratympanic fold; eye diameter 3.5 mm, palpebral membrane 2 mm wide, transparent with only a dark mark on the superior edge; eye-to-naris distance 3.4 mm; interorbital distance 2.8 mm; internarial distance 2.4 mm. Fingers slender with barely distinctive fleshy flares on the margins and with expanded, truncated disks on the tips, I>II>III<IV in order of size; hand length 6.9 mm, with two palmar tubercles, outer tubercle being somewhat bifid, no smaller tubercles between the palmar tubercles and those from the basal phalanx ( Fig. 2A ). Foot length 12.1 mm, tibia length 13.4 mm, femur length 12.85 mm, forearm length 6.4 mm, FeL/SVL 48.5%, TL/SVL 50.6%, FL/SVL 45.7%, HL/SVL 42.4%, HW/SVL 38.5% ( Fig 2B ).

Coloration. Dorsal ground coloration of the holotype (MZFC 33964) Dark Lavender (203) fading to Light Lilac (221) on the ventrolateral surfaces, and Pale Horn Color (11) markings on the dorsum and head, with scattered tiny white flecks on the lateral surfaces; a dark Sepia (279) marking is present on the anterolateral side of the head, including the upper lip, from the tip of the snout to the anterior margin of the eye; limb coloration similar to that of the dorsum, with the hind limbs displaying Dark Lavender bars; fingers and toes Pale Neutral Gray (296), except for white rings preceding the Dark Lavender digital pads; venter purplish white; iris Orange Rufous (56) ( Fig. 1A ).

Variation. The variation observed in our type series is summarized in Table 1 .

The color patterns in our samples show little to no significant variation (but see below). One mature male (MZFC 16254) exhibits a very rugose skin texture on the dorsum, even showing small tubercles. As this specimen was not collected by us, we are unsure if this characteristic represents actual variation or is an artifact of preservation.

As in many amphibian species, a degree of metachrosis was observed, with some specimens being Warm Sepia (40) with only some light Pale Horn Color markings visible when first captured ( Fig. 1B ). However, after some time the coloration returned to essentially the same as described above. Coloration in some preserved specimens changed drastically in our limited type series, with the dorsal surfaces becoming dark brown without any discernible marking (MZFC 8024, 16254). More recently collected specimens (less than three years in preservative) have pale dorsal surfaces with visible darker brown markings.

Distribution and Natural History. Eleutherodactylus erythrochomus is known to date from few localities within the Municipality of Juan R. Escudero along the south-central Pacific coastal plains of Guerrero, Mexico. The general vegetational association is tropical deciduous forest (bosque tropical caducifolio; Fig. 3A, B ), while the microhabitat is characterized by tropical semideciduous forest (bosque tropical subcaducifolio) growing over piles of large granitic boulders that form complex cave systems, crevices, and cliffs ( Fig. 3 ). These microhabitats are climatically contrasting with the general habitat, often attenuating the high environmental temperatures and thus being known as “thermal shelters” for the species inhabiting them ( Arenas-Moreno et al. 2018). An individual (not collected) was observed at the entrance of a cave at 1000 h. The other specimens were collected between 1700– 0100 h. A single male was found calling after a light rain around 1730 h atop a tree stump near a cave entrance, the calling being a soft “peep” with three to four seconds between each note. On November 1, 2017, we observed a specimen (MZFC 33961) being predated on by a gecko ( Phyllodactylus delcampoi ). When noticing our presence, the gecko released the frog and fled.

Eleutherodactylus erythrochomus occurs in sympatry with other amphibians including Agalychnis dacnicolor , E. pipilans , Incilius marmoreus , and Rhinella horribilis . Reptile species observed in the region include Agkistrodon bilineatus , Anolis dunni , A. gadovii , A. subocularis , Aspidoscelis deppii , Boa sigma , Crotalus culminatus , Lepidophyma inagoi , Leptodeira nigrofasciata , Marisora brachypoda , Oxybelis aeneus , Phyllodactylus delcampoi , P. lanei , P. tuberculosus , Sceloporus horridus , S. melanorhinus , S. stejnegeri, Scincella assata taylori, Trimorphodon biscutatus , and Tropidodipsas sartorii . Several of these species are endemic to Mexico and protected under Mexican law (Palacios Aguilar & Flores-Villela 2018; Palacios-Aguilar et al. 2018a).

Conservation. Protection status for newly described species rarely are mentioned and evaluated because knowledge about natural history, geographical distribution, and population health typically is meagre or unknown ( Tapley et al. 2018). However, the system of Environmental Vulnerability Score (EVS) proposed by Wilson et al. (2013) allows us to assess the risk status based on the information that we have, and we determine E. erythrochomus to be highly vulnerable (EVS, 6 + 8 + 4 = 18), based mainly on its restricted ecological and geographical distribution. Also considering the previous criterion and the continual threat of deforestation, we recommend that the species should be categorized as Critically Endangered based on criterion B1ab(iii) of the International Union for the Conservation of Nature Red List Categories and Criteria: Extent of occurrence estimated to be less than 100 km 2, and estimates indicating continuing decline, observed, inferred or projected in the area, extent and/or quality of habitat ( IUCN 2001).

Etymology. The specific epithet erythrochomus is used loosely as a reference to the type locality of the species. It is comprised of the Greek words erythro, meaning red, and chóma, meaning earth, in allusion to Tierra Colorada (literally “red earth” or “red dirt”). We propose the standard English and Spanish names to be Tierra Colorada Peeping Frog and Rana Ladradora de Tierra Colorada, respectively.

Remarks. Duellman (1958) reported on specimens referable to E. pipilans from the surrounding area of Tierra Colorada, Guerrero, Mexico. We have examined most of those specimens (LACM 58245, 58247, 169810; TCWC 8379, 12177; UIMNH 13313–14) and concluded that both species are sympatric in the area, although E. pipilans is not present on the same microhabitats as E. erythrochomus . This is important considering that juvenile specimens of E. erythrochomus resemble mature individuals of E. pipilans . A juvenile specimen (MZFC 33963) falls within the variation observed in the samples we reviewed of the latter species ( Table 1 ). However, E. erythrochomus can be easily differentiated by having a longer head, longer legs, and wider digital pads.

Figures

FIGURE 1. A) Holotype (MZFC 33964), and B) paratype (MZFC 8024) of Eleutherodactylus erythrochomus in life.

FIGURE 2. A) Details of hand, and B) feet of the holotype of Eleutherodactylus erythrochomus (MZFC 33964). Scale bar = 2 mm.

FIGURE 3. General habitat of Eleutherodactylus erythrochomus sp. nov. in Palo Gordo, Guerrero;A) view of the habitat during the rainy season, B) and dry season; C) microhabitats formed by piles of large granitic boulders covered by vegetation; and D) shows the change of landscape for agricultural purposes, this is common in several localities of the region.