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100 || AWSAR Awarded Popular Science Stories - 2019
temperature is a more subtle cue, which fine- tunes the actual time of migration. Although much work has been done to understand the mechanistic details of photoperiodism (i.e., the act of sensing the changes in daylength), not much is known about how temperature modulates seasonal behavior. A study performed by the scholars of Biorhythms lab (Department of Zoology, Delhi University), led by Dr Amit Kumar Trivedi and Sayantan Sur (author of this essay), under the supervision of Professor Vinod Kumar, tried to address this question by working on a migratory finch known as redheaded bunting (Emberiza bruniceps).
The study aimed at looking into whether temperature affected the basic physiology of the birds and, if so, how they sensed the changes in the ambient temperature. When spring comes, redheaded buntings migrate from India to Central Asia to breed and return back to India before the onset of winter. In order to prepare themselves
for the breeding season, the
male buntings increase their
testis size by manifold as the
daylength starts to increase
(i.e., when spring comes).
The first part of the study,
published in Molecular and
Cellular Endocrinology (Trivedi
et al. 2019), looked at how
the development of testis was
affected by temperature. In the
experiment, buntings exposed
to spring day length were
kept under two temperature
regimes: low temperature
and high temperature. At the
end of the experiment, it was
found that the testis size was
significantly larger when the
birds were exposed to a high
temperature. This confirmed
the notion that global warming
could indeed affect the bird’s seasonal biology and advance the breeding period of the birds. We further looked into the gene expression levels of candidate molecules involved in temperature sensation within the brain. It is widely known that the anterior hypothalamus is largely involved in sensing and integrating thermal information. So, we looked into this particular area and found that a gene trpm8
was expressed more under the low-temperature regime. Coincidentally, the trpm8 gene itself is involved in low- temperature sensation, so having it more under this condition makes sense. Hence, it is speculated that this is one of the key molecules used by the birds to detect changes in the ambient temperature.
The second part of the study was published in the Journal of Comparative Physiology B (Sur et al. 2019). Redheaded buntings when exposed to spring daylength start gaining body mass by a considerable amount. In fact, all migratory birds accumulate a large amount of fat just before the onset of migration, and this fat contributes to the sudden
    How much does 1 degree Celsius account for? Not much, if you think of the daily variation in the day and night temperatures, but ask a climatologist and she/ he will apprise you that even a degree Celsius rise in the global temperature can induce a sudden shift in the annual rainfall and cause months of flood or drought, ultimately leading to a catastrophic decline in the net yield of crop production.
  





































































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