A New, Morphologically Cryptic Species of Fanged Frog, Genus Limnonectes (Amphibia: Anura: Dicroglossidae), from Mindoro Island, Central Philippines
We describe a new species of fanged frog (genus Limnonectes) from Mindoro and Semirara Islands, of the Mindoro Pleistocene Aggregate Island Complex, of the central Philippines. Although morphologically indistinguishable from its closest relative, Limnonectes acanthi, of the Palawan faunal region, the two species can be readily diagnosed on the basis of spectral (dominant frequency) and temporal (pulse number and structure) properties of their advertisement calls, and their allopatric insular geographic ranges on permanently separate geological platforms which have not been connected by dry land in the recent geological past—all of which we interpret as congruent and independent lines of evidence supporting our recognition of two independently evolving evolutionary lineages (species). Ribosomal RNA mitochondrial gene sequences were used to provide genetic identification of specimens and estimate phylogenetic relationships; genetic divergences between Palawan and Mindoro faunal regions exceed those estimated among other, uncontroversial, phenotypically distinct Philippine species with equivalent levels of allopatry and biogeographic isolation. The recognition of the new species further emphasizes the degree to which even well-studied Philippine landmasses still harbor unrecognized biodiversity, and suggests that other widespread Philippine fanged frogs should be scrutinized for non-traditional diagnostic character differences (mate-recognition signal divergence, ecological differences, larval characteristics, life-history trait variation), especially when their geographic ranges span the archipelago's permanent, deep-water trenches, which define its well-characterized Pleistocene Aggregate Island Complexes.
Maximum likelihood phylogenetic tree (left) and map of molecular sampling localities (right). Maximum likelihood tree generated in IQ-TREE (Minh et al., 2020). Support values on branches are UFBoot/SH-aLRT and outgroup terminals are L. finchi (1), L. parvus (2), L. palavanensis (3), L. leytensis (4), L. magnus (5), L. diuatus (6), L. visayanus (7), and L. macrocephalus (8). Sampling sites of Limnonectes acanthi on Palawan Island (blue) and samples of L. cf. acanthi from Mindoro and Semirara Islands (yellow) are plotted on islands (gray), surrounded by the 120-meter underwater bathymetric contour (pale yellow), approximating coastlines during the last glacial maximum. Branch length scale bar units = substitutions/site. See Data Accessibility for tree file.
Time-calibrated Bayesian phylogeny depicting divergence times between species of Philippine Limnonectes. Numbers above nodes show Bayesian posterior probabilities. Values below nodes represent mean node ages in millions of years (Ma) with 95% confidence intervals in brackets below node ages. See Data Accessibility for tree file.
Ordination of the first and second (top left) and second and third (top right) principal components for L. acanthi (Palawan) and L. cf. acanthi (Mindoro), with scatterplot of DAPC results (bottom right) with inertia ellipses for emphasis. Yellow shades represent Mindoro clade individuals and blue shades represent Palawan clade individuals, while light tones represent females and dark tones represent males.
Oscillograms and spectrograms of advertisement calls of Limnonectes cf. acanthi from Mindoro (A–C) and L. acanthi from Palawan (D–F). (A) Oscillogram of the entire advertisement call of L. cf. acanthi from Mindoro; (B) a close-up showing two consecutive notes. (C) A spectrogram showing the dominant frequency of the entire call. (D) Oscillogram of the advertisement call of L. acanthi from Palawan; (E) a close-up of two consecutive notes showing the two-pulse nature of each note. (F) Spectrogram showing the dominant frequency of the Palawan advertisement call.
Variation between Limnonectes cf. acanthi from Mindoro Island (n = 3 males) and L. acanthi from Palawan Island (n = 4 males) in the four acoustic variables measured. (A) Number of notes per call, (B) call duration, (C) note rate, and (D) dominant frequency. Left side of each panel, L. cf. acanthi Mindoro; right side of each panel, L. acanthi Palawan.
Dorsal and ventral views of PNM 9870 (formerly KU 303343; Field Collector No. RMB 4957), adult male holotype of Limnonectes beloncioi, new species.
Adult female paratype of Limnonectes beloncioi, new species (KU 335866; Field Collector No. RMB 17,605) in life (photo copyright S. L. Travers).
Typical appearance of forested habitat of Limnonectes beloncioi, new species, near Sablayan Prison and Penal Farm, Mindoro, Philippines (photo copyright S. L. Travers).
Contributor Notes