Microkayla, Riva & Chaparro & Castroviejo-Fisher & Padial, 2018

MICROKAYLA View in CoL GEN. NOV.

u r n: l s i d: z o o b a n k. org:act: F7221ACB-FD97-4DFE-85F9-4CEFE5F6F058

subarticular tubercles round, poorly marked; supernumerary tubercles irregular and weakly defined; first finger the same length as second, relative length of fingers 1 = 2 <4 <3; tibia length 33.7% of SVL; tarsal fold absent; two metatarsal tubercles, oval inner slightly larger than rounded outer; supernumerary and subarticular tubercles low, poorly defined; toes lacking basal webbing or lateral fringes; relative length of toes 1 <2 <3 = 5 <4; foot length 41.5% of SVL.

In preservative, dorsum grey, venter and throat cream with diffuse brown small blotches; flanks and groins with small pale grey blotches; palmar and plantar surfaces cream. In life, the dorsum of the holotype was mostly dark brown, with faint dorsolateral folds formed by small tubercles; a creamy-yellow line run from the eye to the insertion of the forelimb and across the tympanic region; reddish-orange blotches on flanks, groins and axillae; all ventral surfaces were reddish-orange, paler on throat; the iris was dark brown.

Measurements (in mm) of the holotype: SVL, 24.6; HL, 7.7; HW, 8.5; IND, 2.0; END, 1.9; ED, 3.3; TL, 8.3; FL, 10.2.

Type species: Psychrophrynella teqta De la Riva & Burrowes, 2014

Included species: Microkayla adenopleura (Aguayo-Vedia & Harvey, 2001) , comb. nov.; M. ankohuma (Padial & De la Riva, 2007) , comb. nov.; M. boettgeri ( Lehr, 2006) , comb. nov.; M. chacaltaya (De la Riva, Padial & Cortéz, 2007) , comb. nov.; M. chapi sp. nov.; M. chaupi ( De la Riva & Aparicio, 2016) , comb. nov.; M. chilina sp. nov.; M. colla (De la Riva, Aparicio, Soto & Ríos, 2016) , comb. nov.; M. condoriri (De la Riva, Aguayo & Padial, 2007) , comb. nov.; M. guillei ( De la Riva, 2007) , comb. nov.; M. harveyi (Muñoz, Aguayo & De la Riva, 2007) , comb. nov.; M. iani (De la Riva, Reichle & Cortéz, 2007) , comb. nov.; M. iatamasi (Aguayo-Vedia & Harvey, 2001) , comb. nov.; M. illampu (De la Riva, Reichle & Padial, 2007) , comb. nov.; M. illimani ( De la Riva & Padial, 2007) , comb. nov.; M. kallawaya (De la Riva & Martínez-Solano, 2007) , comb. nov.; M. katantika (De la Riva & Martínez-Solano, 2007) , comb. nov.; M. kempffi (De la Riva, 1992) , comb. nov.; M. melanocheira (De la Riva, Ríos & Aparicio, 2016) , comb. nov.; M. pinguis (Harvey & Ergueta, 1998) , comb. nov.; M. quimsacruzis (De la Riva, Reichle & Bosch, 2007) , comb. nov.; M. saltator (De la Riva, Reichle & Bosch, 2007) , comb. nov.; M. teqta ( De la Riva & Burrowes, 2014) , comb. nov.; and M. wettsteini (Parker, 1932) comb. nov.

Diagnosis: (1) head wider than long, not as wide as body, body robust, extremities short; (2) tympanic membrane and annulus present (either visible beneath skin or hidden under the skin); (3) cranial crests absent; (4) prevomerine teeth and dentigerous process of vomers absent; pterygoid not in contact with parasphenoid; anterior parasphenoid ramus not reaching palatines; ear fully developed; (5) pectoral girdle functionally arciferal; (6) nasal bones narrowly separated medially; (7) tongue ovate, longer than wide; (8) tips of digits rounded, not pointed or expanded, lacking circumferential groves and pads; (9) terminal phalanges T-shaped to knobbed; (10) Finger I shorter or equal to Finger II; (11) two subarticular tubercles on Finger IV; (12) Toe V slightly longer than Toe III; (13) lateral fringes and webbing absent on fingers, basal webbing in toes of some species; (14) two metatarsal tubercles both prominent and subconical; tarsal fold or fold-like tubercle absent ( Fig. 8); (15) dorsum tuberculate; belly areolate (apparently smooth in preservative); (16) trigeminal nerve passing external to m. adductor mandibulae externus (‘S’ condition; Lynch, 1986); (17) eggs large, not pigmented; (18) males with median subgular vocal sac and vocal slits, nuptial pads absent; (19) advertisement call usually composed of a single tonal note.

Character states for this diagnosis are based on our own examination of the type series of all the species in the genus except for M. wettsteini (of which we examined topotypic material). The clade of Microkayla is supported by putative synapomorphies: a rounded tongue (elongated in its sister group), areolate belly (smooth in Psychrophrynella ), and lack of a pair of prominent metatarsal tubercles and the conspicuous tarsal fold or tubercle that are present in its sister group ( Fig. 8; see also figures by Lynch [1975: 25; 1986: 425] and De la Riva et al. [2008b: 46]). Microkayla is externally similar to Bryophryne , but they are not sister taxa in molecular phylogenies ( Hedges et al., 2008; Padial et al., 2012, 2014; Chaparro et al., 2015; this study, Fig. 1B). Mating calls are known for 11 species of Microkayla (including those of M. boettgeri and M. chapi , described herein). The call usually consists of a single, isolated, tonal, whistle-like, short note, but there are some exceptions: M. teqta has a pulsed call ( De la Riva & Burrowes, 2014) while M. wettsteini and M. saltator emit several notes per call in a rapid series ( De la Riva, 2007). Microkayla saltator is the most peculiar species in the genus; it lives at relatively low elevations (c. 2550 m a.s.l.) in comparison to other species in the genus (see below), in semi-humid forests (most species inhabit grasslands and elfin forest), has saltatorial locomotion — even arboreal — has slightly swollen tips of digits, and males have a large vocal sac.

Etymology: The name is a composite of the Greek word ‘mikrós’, meaning small, and the Quechua word for frog, ‘k’ayla’. The entire name thus describes what these animals are, small frogs.

Distribution: Microkayla frogs inhabit cloud forests, elfin forests and humid puna of the Amazonian versant of the Cordillera Oriental of the Andes, from the eastern part of Cordillera of Carabaya (Department of Puno) in southern Peru to the western limits of department Santa Cruz in central Bolivia (Serranía Siberia, on the boundaries of Carrasco National Park – Department of Cochabamba – and Amboró National Park – Department of Santa Cruz), between 2466 and c. 4000 m a.s.l., encompassing a straight line distance of c. 670 km. Most species occur in humid puna and adjacent elfin forests above 3500 m, and only M. colla , M. kempffi and M. saltator are known to occur below 3000 m ( De la Riva, 2007; De la Riva & Aparicio, 2016). Only three species are known from Peru, although more species are expected to be discovered when unexplored valleys and ridges of the eastern part of the Cordillera of Carabaya and western Cordillera of Apolobamba are surveyed. How many still unnamed species of Microkayla occur in Bolivia is difficult to know but, as indicated by this study, the number of described species highly underestimates the actual diversity.

Remarks: The new genus constitutes a diverse (24 species, including the two new ones described herein), well-supported and phenotypically diagnosable clade. As shown in the present study and others ( Heinicke et al., 2007; Hedges et al., 2008; Padial et al., 2014), P. usurpator is the sister group to Microkayla gen. nov. ( Fig. 1C). Species of Psychrophrynella (redefined below) are markedly different from of Microkayla gen. nov., from which they can be externally distinguished by having two conspicuous metatarsal tubercles, a conspicuous tarsal fold-like tubercle ( Fig. 8), a smooth belly, and a long and slender tongue. Our proposal of a new genus takes into consideration taxonomic stability ( ICZN, 1999; Guayasamin et al., 2009) and follows three main criteria for naming taxa ( Vences et al. 2013): monophyly, phenotypic diagnosability, and clade stability—supported by evidence at hand. We interpret that our phylogenetic hypothesis is supported insofar as it is not refuted by critical evidence (it is the optimal solution according to optimality criteria) or contradicted by other equally optimal hypotheses. The inferred relationships are also well supported according to the Goodman–Bremer index, which measures the relative amount of evidence supporting clades ( Grant & Kluge 2008), jackknife frequencies ( Farris et al. 1996), which measure the relative amount of favourable and contradictory evidence for each clade, and bootstrapping frequencies ( Felsenstein, 1985). Furthermore, the clade represents a radiation restricted to the high Andes of Bolivia and southern Peru, and such a pattern of distribution is consistent with phylogenetic inferences (a criterion considered important when naming taxa; see Vences et al., 2013).

Part of this clade was first inferred by Lehr et al. (2005) in the first molecular study of frogs formerly grouped under Phrynopus , which showed a phylogeny with Bolivian species grouped separately from Peruvian species. The monophyly of this group was subsequently corroborated by other studies (e.g. Hedges et al., 2008; Padial et al., 2014; Chaparro et al., 2015).