Home Magazines Conservation The Amboli Toads – Facing Climate-Triggered Extinction?

The Amboli Toads – Facing Climate-Triggered Extinction?

The Amboli Toads – Facing Climate-Triggered Extinction?

Dr. Varad B. Giri, Nikhil Gaitonde and Nayan Khanolkar teamed up to provide Sanctuary Asia with a timely report on the precarious status of the Amboli toad at the hands of a changing climate.

Since Bufo koynayensis is highly habitat specific and shows markedly different behaviour such as laying eggs in clutches and displays differences in shape and form, it was moved to a new genus Xanthophryne. Those found in the Amboli area are classified as a separate species, Xanthophryne tigerina. Photo: Nayan Khanolkar.

“This cannot be June!” we thought to ourselves. The Amboli we knew would be a lush emerald green by now, the sky would be a dark slate grey, clouds plump with water, the landscape well-fed and joyous. Yet, this last week of June, the earth was parched and thirsty, dusty grass blades stood still, the blazing sky offering no respite to either the wild or human denizens of Amboli, a village in the Sindhudurg district of Maharashtra, which has the highest recorded rainfall in the state.

We were with Dr. Ullasa Kodandaramaiah, a scientist with the Indian Institute of Science Education and Research (IISER), Trivandrum, at an open, degraded patch of grassland near the village. We had been told that there had been scattered light showers a few days ago, but there were no sign of rain clouds now. We were hoping to spot the Amboli toad Xanthophryne tigerina, an endemic and critically endangered amphibian that breeds in accumulated water pools in small depressions, on lateritic rocks. The grassland was completely dry and so we drove on to another rocky plateau near Choukur, a village about nine kilometres from Amboli. To our delight we did discover a few temporary rainwater pools and puddles on the laterite rocks. And, almost immediately, we spotted several adult Amboli toads near these rocks. They were out and active! On close observation, we saw that several pools were ‘loaded’ with tadpoles of the species. However, many were struggling to survive or were dead because the pools were drying out.

Wanting to record this sad turn of events through photographs, we contacted Nayan Khanolkar, an award-winning wildlife photographer, who was also at Amboli. With hearts sinking, we watched him photograph tadpole after dead tadpole and many dry pools. One large, exposed lateritic rock with three small pools held some live tadpoles that we saw foraging, but here too, one pool had tadpoles that had just died. We have always held the view that humans should not interfere with nature’s processes, but we were unable to watch the life being extinguished from the tadpoles and fetched some water to pour into some of the pools. We rationalised that this was akin to digging artificial waterholes in Protected Areas. The tadpoles seemed to get an instant burst of energy and began to swim around. To our surprise, some that appeared dead turned active and began swimming. Of course, we had merely extended their life by few hours. Unless, the monsoons bestowed their blessings, there was little hope for these amphibians.

The endemic and critically endangered Amboli toad breeds in accumulated water pools in small depressions, on lateritic rocks. A weak rainfall could impact the population of the species dramatically. Photo: Nayan Khanolkar.

A NEW GENUS

The Western Ghats ecosystem of India and Sri Lanka is a global biodiversity hotspot, with rich and endemic floral and faunal diversity, recognised as being distinct at a high taxonomic level. In the Western Ghats, a high-level of endemism exists among amphibians, with over 75 per cent of the subcontinent’s species restricted to this region alone. With about 588 known species on earth and a sub-cosmopolitan distribution, the family Bufonidae is one of the largest in the amphibian world. Extensive studies have been carried out on the phylogenetic (the study of evolutionary relationships between groups of organisms) relationships of bufonids, including one predicting the occurrence of several endemic and unique lineages of toads in India. Recent molecular phylogenetic analyses of toads on the Indian subcontinent reveal that they belong to a radiating group containing distinct ectomorphs (lean built) in adult and/or larval forms. Based on molecular dating estimates and biogeographic analyses the early diversification of this clade (evolved from one ancestor), the Adenominae, occurred in the Western Ghats and Sri Lanka in the Late Oligocene to Early Miocene (about 25 million years ago), resulting in several endemic lineages.

This radiation also includes a clade of Bufo koynayensis whose phylogenetic position is quite distinct. This toad lays eggs in clutches and is highly habitat specific, preferring mostly rocky plateaus. Based on these and other morphological (the study of shape and form) differences Bufo koynayensis was transferred to a new genus Xanthophryne.

Bufo koynayensis was originally described on the basis of specimens collected from near Koyna, Maharashtra. Thus, this species is only known from its type-locality as of now. A subsequent report on Bufo koynayensis came from Amboli, approximately 300 km. south of its type-locality. This Amboli population was described as a new species Xanthophryne tigerina.

The Amboli toads are only found on two or three plateaus near Humbarli and there are about five to six breeding colonies on or close to some rocky plateaus near Amboli. They are nocturnal and remain hidden under rocks during the day. Photo: Nayan Khanolkar.

THE LITTLE KNOWN AMBOLI TOAD

The plateaus close to Humbarli village were regularly visited between 2006 and 2009 and in different seasons. A few breeding colonies near Amboli were also observed often from 2003 onwards. These toads are only found on two or three plateaus near Humbarli and there are about five to six breeding colonies on or close to some rocky plateaus near Amboli. They are nocturnal and remain hidden under rocks during the day. The toads are early and prolific breeders whose breeding season is roughly from the third week of June to late August. Two to three days after the first monsoon showers, large breeding congregations can be seen on some plateaus. Eggs are always laid in very small, temporary rainwater puddles on lateritic rocks. Amplexus (pseudo-mating position of frogs and toads, where the male clasps the female’s back) is axillary and eggs are laid in clutches, every clutch containing about 30-35 eggs. Tadpoles are comparatively slow-moving and can usually be seen feeding on organic matter in puddles that harbour tadpoles in different developmental stages.

Given that its geographic range is under 5,000 sq. km. and its distribution is severely fragmented and continues to decline, Xanthophryne koynayensis is listed as endangered under the IUCN’s Red List. And X. tigerina is considered critically endangered because the species is known only from the type-locality, Amboli with an occupancy area that is presumed to be under 10 sq. km.

Our lack of knowledge of these toads and their distribution is probably their greatest threat. The only scientific publication on these two species is their original description, plus two notes about range extensions. Most information about their breeding, range and populations is derived from published records, which are in turn based on anecdotal observations. These toads have been reported from a few more, unconnected rocky plateaus leaving the amphibians islanded. Most of the known populations of Xanthophryne toads are known from two to three plateaus in a single locality or confined to a single high altitude plateau. Presumably, this habitat specificity is a key reason for their point endemism at certain places in the northern Western Ghats. This underscores the need for more studies to locate further populations from the northern Western Ghats. We also need to check if these populations are related or distinct. It may be assumed that the long-term isolation of these populations for a prolonged duration had led to speciation (formation of new species). If so, then every single population of Xanthophryne toads deserves our unadulterated care and attention.

The Amboli toads are vulnerable to even slight climatic changes because of their specialised breeding habits. Photo: Nayan Khanolkar.

CLIMATE-DEPENDENT BREEDER

Because of their specialised breeding habits, the toads are vulnerable to even slight climatic changes. The reduction or delay of rain for even a day or two could cause most of the eggs and tadpoles to desiccate and die, even if there happens to be enough water on the ground close to the rocks where they exist. On many occasions large numbers of such dead eggs and tadpoles have been observed both at Humbarli and Amboli. There is more. The water in these breeding puddles easily heats up with a lull in the rain and this rise in temperature and reduced humidity may also impact the development of eggs and tadpoles if they metamorphose in an inadequate quantum of water on an exposed rock.

Fortunately, the population of Xanthophryne koynayensis appears to be stable since the plateaus are located within the protected Koyna Wildlife Sanctuary (part of the Sahyadri Tiger Reserve), where human pressures are low. Nevertheless, breeding populations of X. tigerina appear to be under threat as most of their breeding colonies are near human settlements. Three smaller breeding colonies have actually disappeared near Amboli within the past five years thanks to road construction and other developmental activities.

The authors observed large numbers of dying tadpoles of the Amboli toad in dry water pools in Amboli. Photo: Nayan Khanolkar.

A heating planet cannot be good news for specialised creatures such as the Amboli toad. Humans may take the position that they ‘need more proof, more time’ to accept the reality of climate change. The Amboli toad and uncounted other little-known creatures do not have that luxury. They are staring climate-triggered extinction in the face!

First appeared in: Sanctuary Asia, Vol. XXXIV No. 4, August 2014.

 
 
 

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Valmi Shah Shirodkar

October 9, 2014, 04:31 PM
 Such an informative article. Thank you for sharing with us!!