Realities of rarity: climatically and ecologically restricted, critically endangered Kandian Torrent Toads (Adenomus kandianus) breed en masse
- Published
- Accepted
- Subject Areas
- Biodiversity, Taxonomy
- Keywords
- mating congregation, rare toad, resource partitioning, niche modelling, montane forests, Sri Lanka, DNA barcoding, tadpole ecology, restricted distribution, conservation and management
- Copyright
- © 2015 Meegaskumbura et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.
- Cite this article
- 2015. Realities of rarity: climatically and ecologically restricted, critically endangered Kandian Torrent Toads (Adenomus kandianus) breed en masse. PeerJ PrePrints 3:e1575v2 https://doi.org/10.7287/peerj.preprints.1575v2
Abstract
Endemic to Sri Lanka, genus Adenomus contains two torrent-associated toad species whose ecology and natural history in the wild is virtually unknown. Adenomus kelaartii is relatively common, with a wide geographic distribution. Its sister species, A. kandianus, however, is restricted to two isolated populations in fast-disappearing montane and sub-montane forests. Formally declared extinct after not being recorded for over a century, following several years of surveying, a few A. kandianus were found in 2012 and referred to as "the world's rarest toad." However, tadpoles of A. kandianus bearing unique ventral suckers were soon discovered, but the rarity of the adult and the profusion of tadpoles were never explained. Here, using ecological methods, niche modeling and DNA-barcoding, we aim to understand the ecology, natural history and distribution of this rare toad. Following a two-year study of occurrence, habits and habitat associations of adults and larvae, we show this to be a secretive species with a patchy distribution. During non-mating periods female toads (N = 23) were found in primary forests habitat up to 650 m away from the breeding streams, and predominantly males in the riparian zone (12 males, 2 females). Following heavy rain they form large (N = 388) but patchy mating congregations in torrential streams (six sites; range 0−95 mating pairs; mean = 25, SD = 38.16, CV = 152%). Amplexed pairs swim synchronously, enabling them to traverse fast currents. Egg-laying sites remain unknown, but ability to dive, vocalize underwater, and characteristics of the eggs, suggests that they lay eggs in dark recesses of the stream. Quadrat sampling of tadpoles show microhabitat partitioning (in depth, flow-rate and substrate conditions) within the stream: the greatest diversity of larval developmental stages (25-42) in slow-flowing (depth, 0.75−1.5 m) rocky areas; more robust stages (31−39) bearing sucker discs utilise rocky-rapids (depth, 0.25−0.75 m); metamorphic stages (43-45) use stream margins (depth, <0.25 m); slow flowing silt covered areas of the stream were unoccupied, irrespective of the depth. DNA barcoding of the 16S rRNA gene fragment from the two known localities confirms the identity of the Pedro population also as A. kandianus. The uncorrected pairwise genetic distance of 0.1−0.7% suggests historical gene flow between the two populations. Distribution modeling (using MaxEnt), with forest-cover layers added, predicts a very small remaining area of suitable habitats (an area of occupancy of 16 km2 and an extent of occurrence of 128 km2) isolated by habitats that are not conducive to these toads. While the healthy population recorded at one site gives hope for the survival of the species, long-term conservation of this climatically and ecologically restricted species hinges largely on the preservation of cloud and riparian forests and the unpolluted high-flow torrents.
Author Comment
This is an improved version of our pre-prints manuscript. the changes were mostly in enhancing the abstract and articulating the aim of the study better. We have also quantified our results and included more tables to facilitate a better understanding of the surveys that we did did during the non-mating period. In the correction, we mention the number that escaped, we assume the stages of these three based on what we have collected, but refrained from depicting them in the graph (Fig. 2) because their contribution to the overall pattern determination is negligible. We have made a new niche model after testing for autocorrelation of the variables; this changed the output marginally; we have included the revised maps to the figure (Fig. 3).
Supplemental Information
Sampling trails and sites for Adenomus kandianus adults and tadpoles
The 4.5 km trail (A to B) representing the habitat and altitudinal gradient that was sampled four times from May 2012–August 2014. Blue markers indicate the tadpole (and mating aggregation) sampling stations along the major stream. Females were found in forest habitats and tadpole stages showed resource partitioning within the stream.
Presence locations of Adenomus kandianus used in this study
Known geographic coordinates of A. kandianus.
Uncorrected pairwise distances within and between Adenomus kanidanus and A. kelaartii populations
The genetic distances within A. kandianus populations suggest recent gene flow between the two main populations.
Sampling of the mating congregation of Adenomus kandianus
Summary and the descriptive statistics of the adult frogs encountered during the survey within six sampling stations. SD=Standard Deviation, CV=Coefficient of Variation.
Niche Modeling analysis
Percentage contributions of the environmental variables to the predicted distribution model of Adenomus kandianus.
Video documentary of a mating aggregation of A. kandianus.
Video depcting their habits (synchronous swimming, underwater vocalization, amplexus, male-male competition) and habitat.