Abstract
Hibernating ground squirrels rely on a short active period for breeding and mass accrual, and are thus vulnerable to extreme climate events that affect key periods in their annual cycle. Here, we document how a heatwave in March 2012 led to a phenological mismatch between sexes in Richardson’s ground squirrels (Urocitellus richardsonii). Females emerged from hibernation and commenced breeding earlier in 2012 relative to average female emergence. Although males had descended testes and pigmented scrota, it appeared that not all males were physiologically prepared to breed since 58.6% of males had non-motile sperm when breeding commenced. Body condition, relative testes size, and the relative size of accessory glands were significant predictors of sperm motility. Males with non-motile sperm had smaller accessory glands than males with motile sperm. There was no decrease in the number of juveniles that emerged in 2012 or female yearlings recruited in 2013, nor did juveniles emerge later than other years. The impact of this heatwave on male ground squirrels emphasizes the importance of assessing the consequences of climate change on the breeding success of hibernating species in both sexes, since the different sensitivity to external cues for emergence led to a mismatch in timing under this event.
Highlights
Hibernating ground squirrels rely on a short active period for breeding and mass accrual, and are vulnerable to extreme climate events that affect key periods in their annual cycle
The heatwave could be considered biologically extreme for male Richardson’s ground squirrels by both Gutschick and BassiriRad’s16 and Bailey and van de Pol’s17 definitions of a biological extreme climate event, since females, who exhibit a greater amount of phenological plasticity in emergence in response to external conditions[31,38], emerged from hibernacula approximately 13 days earlier than usual at this site and only 3 days after males
Males generally demonstrate less plasticity in emergence[26,38] and in 2012 they began to emerge at approximately the same time as other years. This difference in timing generated indirect consequences for male reproduction, since in this study many males did not appear to be physiologically prepared for the early presence of females as the majority had non-motile sperm
Summary
Hibernating ground squirrels rely on a short active period for breeding and mass accrual, and are vulnerable to extreme climate events that affect key periods in their annual cycle. There was no decrease in the number of juveniles that emerged in 2012 or female yearlings recruited in 2013, nor did juveniles emerge later than other years The impact of this heatwave on male ground squirrels emphasizes the importance of assessing the consequences of climate change on the breeding success of hibernating species in both sexes, since the different sensitivity to external cues for emergence led to a mismatch in timing under this event. Female emergence can vary significantly depending on spring climate conditions[30,31,32] Even with this apparent plasticity, female ground squirrels are sensitive to long-term climate trends and climate events that affect these key periods in their annual cycle[3,33]. It is evident that extreme climate events can affect the phenology and reproductive success of female ground squirrels
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