The circadian pacemaker controlling the eclosion rhythm of the high altitude Himalayan strains of Drosophila ananassae captured at Badrinath (5123 m) required ambient temperature at 21 degrees C for the entrainment and free-running processes. At this temperature, their eclosion rhythms entrained to 12h light, 12h dark (LD 12:12) cycles and free-ran when transferred from constant light (LL) to constant darkness (DD) or upon transfer to constant temperature at 21 degrees C following entrainment to temperature cycles in DD. These strains, however, were arrhythmic at 13 or 17 degrees C under identical experimental conditions. Eclosion medians always occurred in the thermophase of temperature cycles whether they were imposed in LL or DD; or whether the thermophase coincided with the photophase or scotophase of the concurrent LD 12:12 cycles. The temperature dependent rhythmicity in the Himalayan strains of D. ananassae is a rare phenotypic plasticity that might have been acquired through natural selection by accentuating the coupling sensing mechanism of the pacemaker to temperature, while simultaneously suppressing the effects of light on the pacemaker.

No abstract

When the habitat occupied by a specialist species is patchily distributed, limited gene flow between the fragmented populations may allow population differentiation and eventual speciation. ‘Sky islands’—montane habitats that form terrestrial islands—have been shown to promote diversification in many taxa through this mechanism. We investigate floral variation in Impatiens lawii, a plant specialized on laterite rich rocky plateaus that form sky islands in the northern Western Ghats mountains of India. We focus on three plateaus separated from each other by ca. 7 to 17 km, and show that floral traits have diverged strongly between these populations. In contrast, floral traits have not diverged in the congeneric I. oppositifolia, which co-occurs with I. lawii in the plateaus, but is a habitat generalist that is also found in the intervening valleys. We conducted common garden experiments to test whether the differences in I. lawii are due to genetic differentiation or phenotypic plasticity. There were strong differences in floral morphology between experimental plants sourced from the three populations, and the relative divergences between population pairs mirrored that seen in the wild, indicating that the populations are genetically differentiated. Common garden experiments confirmed that there was no differentiation in I. oppositifolia. Field floral visitation surveys indicated that the observed differences in floral traits have consequences for I. lawii populations, by reducing the number of visitors and changing the relative abundance of different floral visitor groups. Our results highlight the role of habitat specialization in diversification, and corroborates the importance of sky islands as centres of diversification.

The Western Ghats of India support a significant amount of biodiversity despite heavy habitat loss. The northern part of this biodiversity hot-spot, along with Konkan, is considerably different from its southern and central counterparts on account of lesser precipitation and extended dry season. Though this region has been floristically surveyed well, there was a long need for a synthesis on local endemism of the flowering plants. Therefore, the present work was undertaken to produce an updated list of the local endemic plant species of the region with an analysis of habitat characteristics and their survival strategies. An extensive review of literature, herbarium records, and field studies yielded a checklist of 181 taxa including four monospecific genera which were examined for their distribution across their latitudinal spread and habitat specificity. A majority of the endemics are therophytes with their predominance, especially on rock outcrops. Northern Western Ghats seems to be the center of rapid diversification of certain herbaceous endemic genera like Ceropegia, Glyphochloa, Dipcadi, Eriocaulon and a few others. Despite being declared as a biodiversity hot-spot and having a higher concentration of endemic taxa, the region is underrepresented in global IUCN threat status assessments. The implication of effective conservation measures is necessary and the data presented in the manuscript can be used as a proxy for conservation planning.