Tuesday, May 16, 2017

The phylogeny of the luminous lizard of Trinidad - a new genus for the luminous lizard

The systematics and ecology of most microteiid lizards of the subfamily Cercosaurinae are poorly known. The subfamily is primarily associated with the Andean highlands where they inhabit humid forest leaf litter.  The genus Riama is the most speciose genus of the Neotropical lizard family Gymnophthalmidae. It contains more than 30 montane species that range throughout the northern Andes, the Cordillera de la Costa in Venezuela, and Trinidad. In a recent paper Sanchez-Pacheco et al. (2017) present a phylogenetic analysis of Riama based on a total evidence approach and direct optimization of molecular and morphological evidence. Analyses use DNA sequences from four loci and 35 phenotypic characters. The dataset consists of 55 in-group terminals representing 25 of the 30 currently recognized species of Riama plus five undescribed taxa, including an endemic species from the Sierra Nevada de Santa Marta in Colombia, and 66 outgroup terminals of 47 species. Their analysis results in a well-supported hypothesis in which Riama is polyphyletic, with its species falling into three clades. The Tepuian Anadia mcdiarmidi nests within one clade of Riama, and the recently resurrected Pantodactylus nests within Cercosaura. Accordingly, the authors propose a monophyletic taxonomy that reflects historical relationships. Analysis of character evolution indicates that the presence or absence of prefrontals—a cornerstone of the early genus-level taxonomy of cercosaurines—is optimally explained as having been plesiomorphically present in the most recent common ancestor of Cercosaurinae and lost in that of the immediately less inclusive clade. Multiple independent reversals to present and subsequent returns to absent occur within this clade.
Gray (1858) described the genus Riama, and placed it in its own family (Riamidae) based on the new species Riama unicolor. Peters (1862) described Ecpleopus (Oreosaurus) striatus and Ecpleopus (Oreosaurus) luctuosus and assigned these species to Oreosaurus characterized as having striated dorsal scales while those in the closely related subgenus Proctoporus (P. pachyurus and P. unicolor), had smooth or keeled scales. Boulenger (1885) synonymized Gray’s Riama with Proctoporus and elevated both subgenera to genera. He defined Oreosaurus has having a wide band of small scales separating the ventral and dorsal scales, and Proctoporus as having the dorsal and ventral scales separated by a fold with granular scales. The diagnoses of the two genera are virtually identical, except for the lateral fold. Boulenger (1885, 1902, 1908) allocated six species to Oreosaurus (O. laevis Boulenger, O. luctuosus, O. ocellifer Boulenger, O. oculatus O’Shaughnessy, O. petersii Boettger, and O. striatus). And, Boettger (1891) described the Bolivian species O. guentheri. Andersson (1914) was unable to separate the two genera. Apparently, the fold Gray and Boulenger reported was an artifact of preservation (see Doan and Castoe, 2005). Thus, Andersson (1914) placed Oreosaurus in the synonymy of Proctoporus, an arrangement used into the early 21st century. Subsequently, Parker (1935) described Proctoporus shrevei from Trinidad. A species that would later gain the attention of science and the public for reportedly being luminescent (Roth and Gans, 1960; Knight et al. 2004).
Most species of Proctoporus were known from relatively few specimens. Uzzell (1958) noted more than half of the species were known from less than five specimens. Yet, after examining only 11 of the 16 recognized species, he attempted to define species groups within the genus. Uzzell (1958, 1970) placed P. luctuosus, P. laevis, P. oculatus, P. shrevei, and P. achlyens, a new taxon from Venezuela, in the luctuosus group. Uzzell defined the luctosus group as having: lateral scales smaller than dorsals and forming a wide band between dorsals and ventrals; males have ocelli in their pattern; four supraoculars; a divided palpebral; no median occipital; pregulars arranged in chevrons with the apices forward, not in transverse rows; limbs overlapping when adpressed; the absence of a continuous narrow granular band along the sides of the body. Uzzell argued that the characters occur in other species outside the group, but the combination is distinctive. He recognized two other species groups that are not directly related to the discussion here.
The three taxonomic groups (Uzzell, 1958, 1970) are allopatric with the Proctoporus luctuosus group occurring mostly in Venezuela and Trinidad, with one species, P. laevis, in Colombia, and another, P. oculatus from Ecuador. The P. pachyurus group occurs in central and southern Peru and Bolivia, and the P. ventrimaculatus group in northern Peru. Kizirian (1996) studied the Ecuadorian Proctoporus, and added nine new species to the previously described 16 species. Doan and Schargel (2003) described Proctoporus inanis from the Merida Andes of Venezuela.
Kizirian (1996) summarized the nomenclatural history of Proctoporus, but remarked that while the monophyly of the genus had been suggested it was not confirmed. Additionally, he recognized three available generic names (Emphrassotis O'Shaughnessy, Oreosaurus Peters, and Riama Gray) are in the synonymy of Proctoporus. Kizirian (1996) also points out that Burt and Burt (1931) designated the type species of Oreosaurus as Oreosaurus (Ecpleopus) luctuosus Peters. Later, Peters and Donoso-Barros (1970) designated the type species as Oreosaurus (Ecpleopus) striatus Peters. Presumably, this was because the striatus description precedes that of the luctuosus description in Peters (1862). Kizirian also commented that Peters and Donoso-Barros may be correct.  Too be clear, these two species were described in the same paper (Peters 1862) and the ICZN Code does not recognize page priority, but it does recognize the principal of the first reviewer, Article 24.22.2 (Ride, 1999). Given this rule, we consider Burt and Burt (1931) to be the first reviewer and Oreosaurus would have priority in the event luctuosus should require a new genus. 
The first attempt to establish a phylogenetic classification of the Cercosaurini tribe of gymnophthalmids recognized two clades. Doan and Castoe (2005) resurrected the genus Riama to accommodate one of the clades of the polyphyletic genus Proctoporus. Using their classification Proctoporus contains five species from the central Andes of Peru and Bolivia. The remaining 24 species formerly belonging to Proctoporus were placed in Riama. Following this arrangement Gray’s genus Riama occurs throughout the Andes of central Peru, Ecuador, Colombia, and Venezuela, the Cordillera de la Costa of Venezuela, and Trinidad’s Northern Range. Rivas et al. (2005) described Riama rhodogaster from Venezuela’s Peninsula de Paria, and considered it the sister to Trinidad’s P. shrevei.
Sanchez-Pacheco et al. (2017) results have implications for patterns of distribution among major biogeographical units, and especially the connection between the Sierra Nevada de Santa Marta in Colombia, the Cordillera de la Costa in Venezuela, the island of Trinidad, and the tepuis (Venezuelan Guyana and Guyana Shield). Their inclusion of the undescribed Sierra Nevada de Santa Marta endemic Oreosaurus “Sierra Nevada”, two endemic species from the Cordillera de la Costa (O. achlyens and O. “Venezuela”), the Trinidadian endemic O. shrevei (Aripo Northern Range), and the tepui endemic O. mcdiarmidi allows a test of previous biogeographical hypotheses. Although each of these highland complexes has a unique geological history, cumulative phylogenetic evidence suggests an ancient connection between them. Species form monophyletic groups despite the considerable geographical distances that separate them. For example, our analysis recovers O. “Sierra Nevada” as the sister of the remaining species of Oreosaurus, followed by O. mcdiarmidi. Oreosaurus achlyens is the sister of O. shrevei + O. “Venezuela”. The distribution of Oreosaurus (Sierra Nevada de Santa Marta, CC, Trinidadian high-lands and tepuis) constitutes a biogeographical pattern (as a whole) not repeated in other vertebrates. This distribution strongly implies an ancient biogeographical connection between the Sierra Nevada de Santa Marta and the Cordillera de la Costa as part of the explanation for the origin of the montane Sierra Nevada de Santa Marta endemic vertebrate fauna.
Cordillera de la Costa which includes the island of Trinidad extends eastwards along the Caribbean coast from the Andean Cordillera de Merida and it has two main sections. First, the Barquisimeto Depression separates the Central (locality of Oreosaurus achlyens and O. luctuosus) from the Cordillera de Merida. Second, the Cordillera de la Costa Oriental extends farther east along the coast toward the island of Trinidad, which lies 12 km off the northeastern coast of Venezuela. In turn, the Cordillera de la Costa Oriental consists of two separate mountain chains situated in extreme northeastern Venezuela: the Pen􀀁ınsula de Paria, the type locality of O. rhodogaster, and the massif of Turimiquire, locality of O. “Venezuela” (Rivas et al., 2005). The Cordillera de la Costa originally extended from the Merida Andes onto the island of Trinidad. Thus, the northern range of Trinidad, the type locality of O. shrevei, was stratigraphically contiguous with the coastal range of Venezuela during the Pliocene and Pleistocene. This connection facilitated the exchange of species through land connections. A Miocene downwarping event severed the land connection. Accordingly, the Cordillera de la Costa Oriental shares many species with Trinidad. 

Below is figure 3 from Sanchez-Pacheco et al. (2017) showing the distribution of the members of the genus Oreosaurus.

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