‘On the rocks’: reproductive biology of the endemic toadXanthophryne(Anura: Bufonidae) from the Western Ghats, India

Abstract

Xanthophryne is a toad genus endemic to the northern Western Ghats of India, with two extant sister species-Xanthophryne koynayensis and Xanthophryne tigerina. Both species are local endemics and endangered. We studied reproductive biology of these toads and found that they are specialized to the lateritic rocky outcrops at mid-elevations in high rainfall areas. Xanthophryne toads have sporadic, multiple spawning bouts lasting 2-4 days during early monsoon. In this explosive breeding behaviour, we observed male toads to engage in 'pelvic thrusts', a unique and novel behaviour among anurans. Females oviposit in shallow pools in depressions of lateritic boulders where their tadpoles metamorphose. These ephemeral rocky pools have limited resources and they desiccate rapidly with a break in the rains. To mitigate the stochastic risk of desiccation and subsequent largescale egg/tadpole mortality, females may disperse their reproductive investment spatially and temporally in multiple clutches, and tadpoles metamorphose rapidly. Here, we describe the amplexus, spawning and male advertisement call, and provide a comparative account of the life history traits of the two Xanthophryne species. These toads face numerous threats and are in need of urgent conservation action. These toads, seemingly well adapted to the isolated rocky outcrops, offer an excellent opportunity to understand endemism, mating systems, anuran ecology and behaviour.

Micro-habitat distribution drives patch quality for sub-tropical rocky plateau amphibians in the northern Western Ghats, India

“…Soil is scant on the plateaus but deepens where it has accumulated in shallow depressions in the ferricrete but it has also has been imported onto Panchgani plateau to assist in tourism related activity [ 12 ]. Loose rock abundance, important as refugia, breeding sites and mate advertising posts, was reduced by collection from accessible sites for construction resulting in a disturbed distribution pattern ( Fig 1 ; Tables 2 & 3 ; [ 12 , 13 , 48 , 97 ]). Larger loose rocks were most absent from plateaus below the escarpment and most abundant where human access was difficult for example in the remoter High Region plateaus for example Zenda and Amboli High and to a lesser extent Jagmin.…”

“…However, non-aquatic microhabitat associations were also found for 78% of the sample taxa (Tables 2 & 3 ). Those microhabitats, climatic and habitat combinations fulfil a variety of ecological purposes beyond their basic physiological requirements; refugia from climatic extremes [ 108 ] and predators [ 109 , 110 ], mate advertisement perches [ 48 ], sites for egg deposition [ 111 , 112 ], breeding resources [ 36 , 43 , 113 ]; reproductive behaviour is selected for by suitable rainfall and relative humidity conditions [ 48 , 106 , 114 ].…”

“…Many of the plateau taxa breed close to the start of the monsoon and they may have been detected in association with their breeding microhabitats [ 48 , 115 ]. The plateaus are all highly seasonal only receiving rainfall for around four months a year resulting in the need for seasonal movement to avoid desiccation and to access breeding sites [ 36 , 106 , 115 ].…”

“…The plateaus are all highly seasonal only receiving rainfall for around four months a year resulting in the need for seasonal movement to avoid desiccation and to access breeding sites [ 36 , 106 , 115 ]. Rainfall, hydroperiod and the associated relative humidity are important factors for taxa with terrestrial or semi-terrestrial larvae for example Xanthophryne tigerina which was found only in the very wet southern high sites [ 6 , 36 , 48 ].…”

“…In tropical regions the diversity of specialist micro-environments facilitates elevated levels of species richness and endemism through heterogeneity in: seasonality or microclimate [ 36 ], gradients in precipitation [ 37 , 38 ], soil moisture [ 39 , 40 ] and elevation [ 41 , 42 ]. Evidence for this in the WG comes from the high number of reproductive strategies with at least 40 different reproductive strategies currently recognised in the region [ 43 – 48 ], each using different habitat resources for mate advertising, mating, egg deposition, spawning, tadpole and neonate feeding. In addition to their dependence on specific microhabitats the amphibians of the WG are threatened by the fungal pathogen Batrachochytrium dendrobatidis [ 49 ].…”