Studies on lycophytes and ferns as influenced by Palghat gap of southern western ghats an ecological, molecular and taxonomic approach

Abstract

Palghat Gap is the most ancient and widest discontinuity in the continuous stretch of Western Ghats. There are many hypotheses regarding the origin of Palghat Gap and also about the influential effect of Palghat Gap on the distribution of plants and animals. Pteridophytes are one of the ancient groups of vascular plants with a long evolutionary history. So, here in the present research, an attempt has been made to unveil the influence of Palghat Gap, if any, on the distribution of pteridophytes along the gap region through different aspects-taxonomical, molecular and ecological. The study area was explored during the period 2018 to 2023 and recorded each taxon with its ecological parameters and spatial attributes. After critical analysis three taxa were recognised with some ambiguity in their morphological features. These ambiguous taxa were further analysed by its spore morphological traits through scanning electron microscopy and molecular divergence analysis using three gene regions - rbcL, trnL-F and atpB. Geospatial analysis for endemic/narrowly distributed taxa and IUCN red listed taxa were analysed. Then the ecological similarity between different habitats and micro-habitats along altitudinal gradients were studied with reference to the presence of ferns and lycophytes. Finally, ecological niche modelling of one selected endemic taxon, Elaphoglossum beddomei, was carried out to know the trend of future climate change and its effect on the existence of the evergreen elements in the Western Ghats. During the study, a total of 191 taxa belonging to 65 genera and 27 families were recorded from the Palghat Gap and Gap influenced areas. In the entire study area, the dominant genus is Asplenium and the family are Pteridaceae. Asplenium is the dominant genus in the South of the Gap, both Asplenium and Thelypteris in the North, and Pteris is the dominant genus within the Gap areas. Among the collected taxa, 20 are endemics (South India-Sri Lanka) or narrowly distributed. A total of 17 species were found to be listed under the IUCN categories. The endemic/narrowly distributed taxa and IUCN red listed taxa were distributed between 100-2300 m altitudes. Any disturbances to their habitat in these altitudinal classes may severely affect their existence. The population diversification studies of three ambiguous taxa, Angiopteris pp., Actiniopteris radiata and Mickelopteris cordata, were carried out using spore morphological and molecular analysis. The spore analysis of populations of these showed some population diversification along the Palghat Gap area. Molecular level analysis showed slight variations between the populations. So, it warrants a further detailed analysis using more gene regions and more taxa for getting clarity on the influence of the Palghat Gap. The major habitat types in the Palghat Gap and Gap influenced areas are; dry deciduous forests, moist deciduous forests, semi-evergreen forests, evergreen forests, shola forests and montane open grasslands. This habitat gradient is influenced by altitude and topography of the area. The highest number of taxa were recorded from evergreen forest, which offers the most suitable ecological parameters for the majority of the fern species. The terrestrial micro-habitats contain more taxa compared to other micro-habitats found in the study area. The altitude wise distribution showed the maximum number of taxa in the middle altitudinal zone. The Sorensen similarity index analysis of habitats showed maximum similarity between evergreen and shola vegetations, and least between dry deciduous forests and wetlands; moist deciduous forests and wetlands. The altitudinal classes 1600- 1700 and 1700-1800 showed maximum similarity. Geo-spatial analysis of the study area, Land use-land cover and NDVI, showed the expansion of deciduous forests even to higher altitudes and corresponding altitudinal changes in the distribution of semi-evergreen and evergreen forests, with a consequent decrease in the montane grassland ecosystems. Ecological niche modelling (ENM) of Elaphoglossum beddomei in current as well as the future climatic regimes (2041-2071) showed a decline in the potential habitat for it in future time periods. ENM analysis showed that the distribution of E. beddomei is limited by precipitation in Southern Western Ghats. The declining potential habitat of E. beddomei in future climatic regimes can be interpreted as the declining of evergreen forests in Southern Western Ghats of India. The overall analysis showed that Palghat Gap acts as a barrier for distribution of ferns and lycophytes as well. It was inferred that, the climatic and edaphic factors operating in the Gap region influence the genetic make-up and it may trigger the genetic changes in species.