Praveen Karanth

Uniform discrimination of pattern orientation by honeybees

To explore how honeybees, Apis cerana, discriminate the orientation of patterns, we trained workers to discriminate between a black stripe of a certain orientation on a white disc and a pure white disc. We tested trained bees for their ability to discriminate between the trained orientation and deviations from it. This was done either in a dual choice situation where the bees had to choose between the trained orientation and one deviation from it at a time, or in a multiple choice situation where bees had to choose simultaneously between the trained orientation and 11 successive deviations from it. In the dual choice situation, bees did not discriminate behaviourally between the trained orientation and deviations up to 25 degrees, whereas in a multiple choice situation, they discriminated between the trained orientation and a deviation of 15 degrees or more. Thus, orientation can be analysed more precisely in multiple choice experiments. The response of the bees was independent of the orientation of the trained orientation; the 12 different trained orientations all yielded identical results. This finding, considered together with a model that we present for orientation discrimination, suggests that at least three orientation-sensitive channels (a neuron or a set of neurons that respond maximally to a particular orientation) participate in the analysis of pattern orientation. (c) 1998 The Association for the Study of Animal Behaviour.

Did southern Western Ghats of peninsular India serve as refugia for its endemic biota during the Cretaceous volcanism

The Western Ghats (WG) of south India, a global biodiversity hotspot, has experienced complex geological history being part of Gondwana landmass and encountered extensive volcanic activity at the end of Cretaceous epoch. It also has a climatically and topographically heterogeneous landscape. Thus, the WG offer a unique setting to explore the influence of ecological and geological processes on the current diversity and distribution of its biota. To this end, three explicit biogeographical scenarios were hypothesized to evaluate the distribution and diversification of wet evergreen species of the WG – (1) southern WG was a refuge for the wet evergreen species during the Cretaceous volcanism, (2) phylogenetic breaks in the species phylogeny would correspond to geographic breaks (i.e., the Palghat gap) in the WG, and (3) species from each of the biogeographic subdivisions within the WG would form distinct clades. These hypotheses were tested on the centipede genus Digitipes from the WG which is known to be an ancient, endemic, and monophyletic group. The Digitipes molecular phylogeny was subjected to divergence date estimation using Bayesian approach, and ancestral areas were reconstructed using parsimony approach for each node in the phylogeny. Ancestral-area reconstruction suggested 13 independent dispersal events to explain the current distribution of the Digitipes species in the WG. Among these 13 dispersals, two dispersal events were at higher level in the Digitipes phylogeny and were from the southern WG to the central and northern WG independently in the Early Paleocene, after the Cretaceous Volcanism. The remaining 11 dispersal events explained the species’ range expansions of which nine dispersals were from the southern WG to other biogeographic subdivisions in the Eocene-Miocene in the post-volcanic periods where species-level diversifications occurred. Taken together, these results suggest that southern WG might have served as a refuge for Digitipes species during Cretaceous volcanism.

Flying between Sky Islands: The Effect of Naturally Fragmented Habitat on Butterfly Population Structure

High elevation montane areas are called “sky islands” when they occur as a series of high mountains separated by lowland valleys. Different climatic conditions at high elevations makes sky islands a specialized type of habitat, rendering them naturally fragmented compared to more continuous habitat at lower elevations. Species in sky islands face unsuitable climate in the intervening valleys when moving from one montane area to another. The high elevation shola-grassland mosaic in the Western Ghats of southern India form one such sky island complex. The fragmented patches make this area ideal to study the effect of the spatial orientation of suitable habitat patches on population genetic structure of species found in these areas. Past studies have suggested that sky islands tend to have genetically structured populations, possibly due to reduced gene flow between montane areas. To test this hypothesis, we adopted the comparative approach. Using Amplified Fragment Length Polymorphisms, we compared population genetic structures of two closely related, similar sized butterfly species: Heteropsis oculus, a high elevation shola-grassland specialist restricted to the southern Western Ghats, and Mycalesis patnia, found more continuously distributed in lower elevations. In all analyses, as per expectation the sky island specialist H. oculus exhibited a greater degree of population genetic structure than M. patnia, implying a difference in geneflow. This difference in geneflow in turn appears to be due to the natural fragmentation of the sky island complexes. Detailed analysis of a subset of H. oculus samples from one sky island complex (the Anamalais) showed a surprising genetic break. A possible reason for this break could be unsuitable conditions of higher temperature and lower rainfall in the intervening valley region. Thus, sky island species are not only restricted by lack of habitat continuity between montane areas, but also by the nature of the intervening habitat.

Cryptic species and Miocene diversification of Palaearctic naked-toed geckos (Squamata: Gekkonidae) in the Indian dry zone

We sampled Palaearctic naked‐toed geckos from across their range in India and used two mitochondrial and two nuclear genes to reconstruct relationships within a global phylogeny. Published sequences of Peninsular Indian Hemidactylus allow us to contrast these two groups in dating analyses – providing insights into the history of the Indian dry zone. Palaearctic naked‐toed geckos first moved onto the Indian Plate in the Oligocene, with higher‐level diversification probably linked to collision of the Indian and Eurasian plates, and subsequent dispersal into‐India and diversification with increasing Miocene aridity. An independent gekkonid radiation with species in the dry zone, Hemidactylus diversified during the same period in Peninsular India. Our results demonstrate that dry zone taxa across India may date back to at least the Miocene, with a potential historical climatic barrier between the Indus and Peninsular Indian Divisions. ‘Cyrtopodion’ aravallense is revealed to be a complex with seven genetically and environmentally divergent lineages that began diversifying in the late Miocene, congruent with increased aridity in north‐western India. This discovery of cryptic diversity in the Indian dry zone represents the first terrestrial vertebrate radiation from north‐western central India and highlights how little we understand of the regions’ biodiversity, emphasizing the need for systematic geographic sampling and multiline evidence to reveal true patterns of diversity. The ancestor of ‘Cyrtopodion’ aravallense came into the nascent Indian dry zone in the Miocene and has since diversified, potentially in the absence of any sympatric scansorial rupicolous geckos. Cyrtopodion scabrum represents a unique case of commensalism and shows phylogeographic structure in its presumed native range. The taxonomic implications of our study include a number of undescribed species, recognition of ‘Cyrtopodion’ as a distinct lineage and the non‐monophyly of Altiphylax.

Aridification driven diversification of fan-throated lizards from the Indian subcontinent

The establishment of monsoon climate and the consequent aridification has been one of the most important climate change episodes in the Indian subcontinent. However, little is known about how these events might have shaped the diversification patterns among the widely distributed taxa. Fan-throated lizards (FTL) (Genus: Sitana, Sarada) are widespread, diurnal and restricted to the semi-arid zones of the Indian subcontinent. We sampled FTL in 107 localities across its range. We used molecular species delimitation method and delineated 15 species including six putative species. Thirteen of them were distinguishable based on morphology but two sister species were indistinguishable and have minor overlaps in distribution. Five fossils were used to calibrate and date the phylogeny. Diversification of fan-throated lizards lineage started ~18 mya and higher lineage diversification was observed after 11 my. The initial diversification corresponds to the time when monsoon climate was established and the latter was a period of intensification of monsoon and initiation of aridification. Thirteen out of the fifteen FTL species delimited are from Peninsular India; this is probably due to the landscape heterogeneity in this region. The species poor sister genus Otocryptis is paraphyletic and probably represents relict lineages which are now confined to forested areas. Thus, the seasonality led changes in habitat, from forests to open habitats appear to have driven diversification of fan-throated lizards.

The curious case of Hemidactylus gujaratensis (Squamata: Gekkonidae)

Hemidactylus Oken, 1817 is one of the most speciose genera of the family Gekkonidae with more than 140 described species (Uetz et al. 2016). While this genus naturally occurs across the tropics and subtropics, a substantial part of its distribution also results from human-mediated dispersal. Carranza Arnold (2006) retrieved five broad clades in a global phylogeny of Hemidactylus, one of which has species distributed in tropical Asia. Subsequent work by Bauer et al. (2010) and Bansal Karanth (2010) revealed that the species from tropical Asia fell into two deeply divergent and potentially non-sister sub-clades-one comprising a large radiation confined to peninsular India and Sri Lanka (the Indian radiation, IR), and the other comprising species largely distributed in Southeast (SE) Asia.

Descriptions of two new endemic and cryptic species of Sitana Cuvier, 1829 from peninsular India

Two new cryptic species of the agamid genus Sitana Cuvier, 1829 from Peninsular India are described herein. Sitana gokakensis sp. nov. from Gokak, Karnataka closely resembles Sitana thondalu sp. nov. from Nagarjuna Sagar, Andhra Pradesh. The two species can be distinguished based on their subtle morphological differences, genetic difference and geographic distribution. Sitana gokakensis sp. nov. have a relatively depressed head compared to Sitana thondalu sp. nov. Additionally, the vertebral scale counts differ in females of the two new species (Sitana gokakensis sp. nov. 45-47 vs Sitana thondalu sp. nov. 49-53). Genetic divergence between them is comparable to those between previously described Sitana species. Furthermore, the two new species are distributed ca. 500 km apart and are endemic to their respective landscapes that lie in similar latitudes of peninsular India. We urge the use of large sample size in new species descriptions especially those dealing with cryptic species like Sitana. The discovery of the two new cryptic species from these rocky terrains in peninsular India highlights need for more herpetological exploration in this region.