Vol.:(0123456789) 1 3 Genetica https://doi.org/10.1007/s10709-020-00100-8 ORIGINAL PAPER Rejection of the benefcial acclimation hypothesis (BAH) for short term heat acclimation in Drosophila nepalensis Seema Ramniwas 1  · Girish Kumar 2  · Divya Singh 1 Received: 4 April 2020 / Accepted: 8 August 2020 © Springer Nature Switzerland AG 2020 Abstract Benefcial acclimation hypothesis (BAH) is the phenotypic plasticity in response to changing environments which enables organisms to enhance their ftness. In recent years, however, BAH has received vigorous criticism and is still debatable. In this study, we tested thermal hardiness phenotypes (melanization, chill coma recovery, heat knockdown and percentage survival) on adult and pre-adult stages of Drosophila nepalensis, reared in diferent thermal environments (14, 17, 21 and 25 °C) to check whether increasing natural surrounding temperature and acclimation limit towards environmental change is detrimental or benefcial. Results showed that rearing D. nepalensis at higher temperatures (21 and 25 °C) reduces its melanization and cold hardiness but improves heat knockdown times. When temperature was raised to 26.2 °C (0.6 °C above the upper thermal maxima), to determine the short-term acclimation efects, survival and ftness of adults diminished approximately 1.5 to 2 folds. These results suggest that D. nepalensis has long-term developmental acclimation to both heat and cold which would be extremely benefcial as temperatures and climates alter in the region due to global warming. However, a lack of short-term heat acclimation suggests that rapid shifts in thermal extreme could be detrimental to D. nepalensis. Keywords Climate change · Drosophila nepalensis · Benefcial acclimation hypothesis · Stress resistance · Fitness · Himalayas Introduction The ability of a single genotype to exhibit diferent pheno- types under varied environmental conditions is referred to as phenotypic plasticity. It is a ubiquitous feature of organisms which allows to adapt and survive in changing environments. Nevertheless, phenotypic plasticity not always facilitates selection for adaptive genotype (e.g., Chevin et al. 2010; Lande 2009; Price et al. 2003; Schlichting and Pigliucci 1998; Via et al. 1995; West-Eberhard 2003). For species that live in a temperate zone, seasonal changes are common and cyclical. Cold seasons alternate with warmer seasons; and rainy periods may alternate with drier times. The rate at which temperatures change during seasonal transitions could determine whether an organism can gain from acclimation or not (Nilsson-Örtman and Johansson 2017). Hardening and acclimation in insects are the result of stressful environ- mental conditions experienced across developmental stages although evidence for this remains weak. Hence, considering the entire life-cycle for the environmental sensitivity in the appropriate seasonal context is critical as plastic responses allow an individual to respond rapidly while evolutionary responses allow them to respond slowly (Visser 2008; Wil- liams et al. 2008). Almost all ecological and evolutionary processes in insects are infuenced by temperature (Addo-Bediako et al. 2000; Chown and Terblanche 2007). Studies have shown that many ectotherms adjust their thermal tolerance continu- ously to the prevailing conditions due to phenotypic plastic- ity (Angilletta 2009; Hofmann et al. 2003; van Dooremalen et al. 2013) but little attention has been paid towards the impact of heat-stress on upper limits to adaptation. Trait- and environment-specifc costs and constraints afect the ft- ness benefts of plasticity at various timescales (Sgrò et al. * Seema Ramniwas seema.ramniwas@gmail.com * Divya Singh singh.genetics@gmail.com 1 University Center for Research and Development, Chandigarh University, Gharuan, Mohali 140413, India 2 Genomics and Bioinformatics Cluster, Department of Biology, University of Central Florida, 4110 Libra Drive, Orlando, FL 32816, USA