Evidences of phenotypic plasticity, and lack of local adaptation and clinal differentiation in invasive Ageratina adenophora from Uttarakhand Himalaya

The hazardous invasive weed Ageratina adenophora has successfully invaded diverse habitats belonging to different climate zones in Central Himalaya, India. This study tested whether phenotypic plasticity and/or local adaptation plays an important role invasion success of A. adenophora in diverse environmental conditions. Eight populations from different habitats and locations were selected and used in common garden experiment, reciprocal transplant experiments and glasshouse experiments. Seeds were collected from selected populations and grown in controlled common glasshouse conditions to overcome the environmentally induced maternal effects and check genetic differentiation. Seeds from common glasshouse experiment were further used in reciprocal transplant experiments and light gradient experiments. Among the eight sites from where seeds were collected, four sites were selected at four altitudes for reciprocal transplant experiment and seeds obtained from glasshouse experiment were grown in these four sites. 25 plants of each population were transplanted equidistantly in queues representing a total of eight rows and twenty-five columns. A total of 200 seedlings were transplanted at each site. Response of eight populations to changing light intensity was assessed by growing them under variable light intensity (i.e. 100%, 60%, 24% and 6%). At flowering, plants were harvested and growth, leaf and reproductive traits were assessed in reciprocal transplant as well as light intensity experiments. The results showed no evidences of genetic variation, local adaptation and clinal differentiation in A. adenophora established in Indian Central Himalaya as all the plants belonging to different populations responded in similar manner when grown under similar environmental conditions. High degree of phenotypic plasticity was recorded in plant traits like height, biomass, specific leaf weight and seed numbers. These results conclude that phenotypic plasticity is the major cause of phenotypic heterogeneity and major contributor in invasion success of A. adenophora rather than genetic differentiation and local adaptation from Indian Central Himalaya.