Résumé
Timing of reproduction in temperate zone birds is strongly correlated with
spring temperature, with an earlier onset of breeding in warmer years.
Females adjust their laying between years to be synchronized with local
food sources and thereby optimize reproductive output. However, climate
change currently disrupts the link between predictive environmental cues
and spring phenology. To investigate direct effects of temperature on the
decision to lay, and its genetic basis, we used pairs of Great Tits (Parus
major) with known ancestry and exposed them to simulated spring scenarios
in climate-controlled aviaries. In each of three years, we exposed birds
to different patterns of changing temperature. We varied the timing of a
temperature change, the daily temperature amplitude and the onset and
speed of a seasonal temperature rise. We show that females fine-tune their
laying in response to a seasonal increase in temperature, whereas mean
temperature and daily temperature variation alone do not affect laying
dates. Luteinizing hormone concentrations and gonadal growth in early
spring were not influenced by temperature or temperature rise, possibly
posing a constraint to an advancement of breeding. Similarities between
sisters in their laying dates indicate genetic variation in cue
sensitivity. These results refine our understanding of how changes in
spring climate might affect the mismatch in avian timing and thereby
population viability.