COS 280-1 - Determining the consequences of phenological shifts in reproduction on ambient temperature exposure and maternal investment

Background/Question/Methods

Variation in reproductive phenologies can affect the environment experienced during key life-history stages. Reproduction is commonly timed to occur when resources and weather conditions are optimal for reproductive-ready individuals and/or their new offspring. However, mismatches with less favorable conditions (i.e., increased ambient temperature, low food availability), can constrain maternal investment. Female red squirrels (Tamiasciurus hudsonicus) adjust their reproductive output in response to episodic white spruce seed fluctuations to favor either offspring “quantity” (litter size) or “quality” (juvenile growth rate). When resource availability is high (post-bumper crop), litters are born earlier, during low spring temperatures. Immediately preceding a bumper crop of seed (when resources are extremely low), reproduction is delayed, litters are larger, and occurs multiple times throughout the warm summer months, potentially creating overwhelming energy expenses, and thus shifts in maternal investment. Hypothesis: maternal investment during early life-history stages is affected by phenological shifts in ambient temperatures. Using 30+ years of life-history data (litter size and juvenile growth rate) collected from a northern population of red squirrels, near Kluane National Park, YK in conjunction with local weather data to test for tradeoffs between, and the effects of temperature and food availability on litter size and juvenile growth rate simultaneously.

Results/Conclusions

Our results show that delays in reproduction (brought about by increases in fall food abundance), increase ambient temperature experienced during reproduction. Our preliminary analyses suggest that both, ambient temperature and maternal age negatively affect juvenile growth rates, while increases in pre-reproduction food abundance increase growth rates. Litter size increases with temporal delays in reproduction, second litters in a reproduction season are larger, but litter size is not limited by ambient temperature. However, increases in litter size show decreased juvenile growth rates. These results suggest that phenological shifts in reproduction create temperature-driven constraints on maternal investment. As our climate continues to change, with shifting phenologies and increasing summer ambient temperatures accelerated at high latitudes, it is imperative that we understand how these changes could constrain reproduction for wildlife and affect their capacity to respond to climatic change.