Wild birds respond differently to the first long days of a year
For great tits spring does not always start at the same time
The lengthening of days in late winter is an
important signal that stimulates the reproductive activity of many
animals. Animals living in the milder climatic conditions of southern
Europe usually begin breeding earlier in spring compared to animals
living in colder habitats further north. Scientists from the Max Planck Institute for Ornithology and colleagues have now discovered that day
length affects gene activity differentially in the brain of great tit
populations from central and North Europe. This is particularly
important because climate change has resulted in warmer temperatures in
spring, and therefore day length has become a less reliable signal for
the coming of spring. Since warmer spring temperatures also cause the
insects that the birds need to feed their young to be available sooner,
birds will have to change their breeding schedules accordingly.
Many species across the globe use seasonal information to coordinate
important events like reproduction with the conditions in their
surroundings. Until recently, however, the exact internal processes and
tissues in the brain involved in this response have remained elusive.
Thanks to recent studies on domesticated species like rodents, sheep,
goat and quail, scientists have successfully identified the genes and
the parts of the brain that are involved in the response of an organism
to changes in day length.
However, for Nicole Perfito from the Max Planck Institute for
Ornithology intriguing questions remained unsolved:
“Domesticated
species have been bred for commercial purposes, and can breed at almost
any time of year. Do wild species, which have to adapt their
reproductive cycles continually to the seasonal changes in nature,
possess the same mechanisms? And how would such mechanisms allow
populations from various habitats to use different day length thresholds
to get ready to breed at the right time of year?
”To answer these questions Nicole Perfito and Michaela Hau from the
Max Planck Institute for Ornithology at Radolfzell together with
colleagues from the University of California at Berkeley and from
Gotenborg University investigated the activity of genes in the brain of
great tits from Germany and Sweden. For this, the scientists first
exposed the birds in the laboratory to short winter days and then a long
summer day. Using highly sensitive techniques, the team was able to
establish which genes were activated in the brain during the single
long day. Indeed, in the wild birds similar genetic cascades were set in
motion compared to a highly domesticated bird, the Japanese quail.
Hence, the same physiological processes occur in wild animals as in
domesticated ones.
The scientists were also surprised to see differences between the
Swedish and German great tits: “The Swedish birds showed a rather strong
genetic response to the long summer day, whereas the German birds
hardly responded at all”. In nature, birds in Sweden lay their eggs
about three weeks later than the German birds that live in a more
southerly and milder climate.
These findings imply that birds breeding
up North that have a shorter time span for raising their offspring have
to respond more strongly to changes in day length and start breeding
faster once a threshold is passed.
By contrast, birds living further
South that can afford longer periods for breeding activities possess a
different day length threshold. It is possible that stimulation by a
greater number of long days and possibly additional environmental
information such as high temperatures is required to change gene
activity.
more Max Planck Institute for Ornithology