Towards understanding the genetic basis of high-elevation adaptation in Himalayan giant honey bee

Apis laboriosa, the Himalayan giant honey bee, is a species of honey bees (genus Apis), which is highly adapted to highland habitats and mainly occurs in mountainous regions, particularly the Himalayas. Up to data, the genetic basis of its high-elevation adaptation remains a mystery. In the present study, we generated transcriptomes for A. laboriosa and its closely related species A. dorsata, we then characterized the transcriptomes and did comparative and evolutionary analysis between them to understand the genetic basis of high-altitude adaptation in A. laboriosa. We identified 1,605 genes that are absent in A. dorsata but present in A. laboriosa. Those A. laboriosa-specific genes were involved in DNA damage repair, low temperature tolerance and oxidative stress response. In addition, for genes shared by the two species, genes related to anoxia tolerance, freeze tolerance and UV irradiation were positively selected in A. laboriosa. Taken together, our results suggest that both the increased copy number and the accelerated protein sequence evolution of genes related to high-elevation adaptation made a difference between A. laboriosa and A. dorsata, which should contribute to the adaptation of A. laboriosa to challenging environments in Himalayas. Three alive worker bees of A. laboriosa and three alive worker bees of A. dorsata are collected in different places. A single pooled RNA sample was prepared for each species by mixing equal amount of the RNA (1 μg) extracted from each of the three samples. The pooled 3 μg of RNA sample was used as input material for the species to construct sequencing libraries, which were generated using NEBNext® UltraTM RNA Library Prep Kit for Illumina® (NEB, USA) following manufacturer’s recommendations. The obtained libraries were sequenced on an Illumina Hiseq 2500 platform and paired-end reads were produced, with a read length of 150 nt.