Ambient temperature affects multiple drivers of physiology and behaviour: adaptation for timely departure of obligate spring migrants

Abstract

We investigated the role of ambient temperature in departure from wintering areas of migratory blackheaded buntings in spring. Birds transferred at 22 and 35 oC temperatures to long days were compared with one another and to controls held on short days for indices of readiness to migrate (Zugunruhe, fattening, weight gain), levels of testosterone, and gonadal recrudescence. Temperature affected the development of migratory behaviour and physiology: buntings under long days at 35oC, compared to those at 22oC, showed altered migratory behaviour (daily activity and Zugunruhe onset), and enhanced muscle growth and plasma testosterone levels; however, no effect on testis growth. Temperature was perceived at both peripheral and central levels, and affected multiple molecular drivers culminating into the migratory phenotype. This was evidenced by post-mortem comparison of the expression of 13 genes with known functions in the skin (temperature-sensitive TRP channels: trpv4 and trpm8), hypothalamus and/ or midbrain (migration-linked genes: th, ddc, adcyap1 and vps13a) and flight muscles (muscle growth associated genes: ar, srd5a3, pvalb, mtor, myod, mstn and hif1a). In photostimulated birds, the expression of trpv4 in skin, of th in hypothalamus and midbrain, and of srd5a3, ar pvalb and mtor genes in flight muscle, in parallel with T levels, was greater at 35oC than the 22oC. These results demonstrate the role of ambient temperature in development of the spring migration phenotype, and suggest that transcriptional responsiveness to temperature is a component of the overall adaptive strategy in latitudinal songbird migrants for timely departure from wintering areas in spring.