Effect of morphological, phenological variations and morph frequencies on population genetic diversity along an altitudinal gradient in heterostylous Primula denticulata

Abstract

The genus Primula L. (Primulaceae) represents approximately 430 species, distributed all over the Northern Hemisphere in temperate to alpine regions. It is an important floristic element of the Himalayan flora and is considered an ecological indicator of the high-altitude vegetation. Many Primula species show two morphs (pin and thrum) based on style length. The stigma of pin plants is positioned at the entrance of the flower, exhibiting a long style, while in thrum flowers, the style is much shorter, leaving the stigma around halfway up the floral tube. Among these species, Primula denticulata exhibits a large extent of occurrence in a broad altitudinal range (2096-3700 m). A study was undertaken to understand the frequency, morphological and phenological variations between two morphs of the species along an altitudinal gradient in the Western Himalayas. We recorded the numbers of pin and thrum flower morphs at three different elevations (2337m, 3000m, and 3700m) during 2021 and 2022. Our results indicate variation in morph frequency at middle elevation i.e., 3000m, while at lower and higher elevations, both the morphs have an equal frequency. A delay was observed in the onset of phenological events with increasing elevation. We observed more numbers of floral visitors at lower and middle elevations than at higher elevations. The stigmatic surface of pin and thrum morphs were found to be different under Scanning Electron Microscope (SEM). Along with these morphological and phenological observations, genetic diversity analysis of P. denticulata is underway with 290 samples collected from different populations along the altitudinal gradient and 100 primer pairs designed from Simple Sequence Repeats (SSRs). As a result of this study, the correlation of morphological and phenological studies with genetic variation existing along the altitudinal gradient can be observed. The study will show the impact of changing environmental conditions on the diversity of the plant along the altitudinal gradient. Keywords: Primula denticulata, Morph frequency, Altitudinal gradient, Morphological variations, Phenological variations, Changing environmental conditions