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Trade-offs Between Reproduction and Survival Influence Dormancy Phenology in Endotherms and Ectotherms


Core Concepts
Dormancy phenology in endotherms and ectotherms is influenced by a trade-off between the survival benefits of dormancy and the reproductive benefits of activity, rather than being solely explained by physiological constraints.
Abstract
The study investigated two hypotheses to explain dormancy phenology in endotherms (mainly hibernating mammals) and ectotherms: The physiological constraint hypothesis: Dormancy phenology is solely determined by the transition between favorable and unfavorable energetic or thermal conditions. This predicts that species with high sexual dimorphism (a proxy for energy demand) should exhibit greater sex differences in dormancy phenology. The life-history hypothesis: Dormancy phenology reflects a trade-off between the survival benefits of dormancy and the reproductive benefits of activity. This predicts that the sex difference in dormancy phenology is associated with the sex difference in reproductive investment. Using phylogenetic comparative analyses, the study found support for both hypotheses: In accordance with the life-history hypothesis, sex differences in emergence and immergence timing were associated with sex differences in reproductive effort. Males with higher body mass loss during mating showed greater protandry (earlier emergence than females). Physiological constraints also influenced the trade-off, as smaller species and those in colder environments showed lower sex differences in dormancy phenology, likely due to higher costs of activity. The study also reviewed evidence from the literature suggesting that dormancy phenology can be independent of energy balance, with some species entering dormancy even when environmental conditions would allow continued activity. This indicates that factors beyond just physiological constraints, such as predation avoidance and competition, influence dormancy timing. Overall, the findings suggest that dormancy phenology in both endotherms and ectotherms reflects a balance between the survival benefits of dormancy and the reproductive benefits of activity, rather than being solely determined by physiological constraints.
Stats
Protandry increased significantly with male body mass loss during mating. Protandry decreased in species for which males are smaller. The sex difference in immergence date was associated with maternal effort duration, specific reproductive effort of females, male body mass loss through the end of mating, and precipitation.
Quotes
"Protandry increased significantly with male body mass loss during mating and increased ambient temperature." "The sex difference in immergence date was associated with maternal effort duration, specific reproductive effort of female, Δ body mass through the end of mating and precipitation."

Key Insights Distilled From

by Theo,C., Dob... at www.biorxiv.org 07-22-2023

https://www.biorxiv.org/content/10.1101/2023.07.20.549898v4
Evolutionary trade-offs in dormancy phenology

Deeper Inquiries

How do the trade-offs between reproduction and survival that influence dormancy phenology vary across different mating systems and parental care strategies?

In the context of dormancy phenology, the trade-offs between reproduction and survival can vary significantly depending on the mating systems and parental care strategies of the species in question. Mating Systems: Monogamous Species: In monogamous species where both parents invest equally in offspring care, the trade-off between reproduction and survival may be more balanced. Both males and females are likely to exhibit similar patterns of dormancy phenology, as they share the responsibilities of reproduction and parental care. Polygynous Species: In polygynous species where males have multiple mates, there may be a stronger emphasis on male reproductive success. This could lead to males exhibiting behaviors such as earlier emergence from dormancy to secure mating opportunities, while females may prioritize survival by delaying emergence. Polyandrous Species: In polyandrous species where females have multiple mates, the trade-off may be more pronounced for females. Females may need to balance the benefits of early emergence for mating opportunities with the costs of reduced survival, while males may focus more on maximizing reproductive success. Parental Care Strategies: Species with Biparental Care: In species where both parents provide care for offspring, the trade-off between reproduction and survival may be more evenly distributed between males and females. Both parents may need to coordinate their dormancy phenology to ensure optimal care for the offspring. Species with Maternal Care: In species where females provide the majority of parental care, females may prioritize survival by delaying emergence to ensure their own well-being before investing in reproduction. Males, on the other hand, may exhibit behaviors that maximize their reproductive success, such as early emergence for mating opportunities. Overall, the trade-offs between reproduction and survival in dormancy phenology can be influenced by the specific mating systems and parental care strategies of each species, highlighting the importance of considering these factors in evolutionary studies of dormancy.

What are the potential costs and benefits of the observed staggered dormancy phenology relative to the growing season, and how do these vary between endotherms and ectotherms?

The observed staggered dormancy phenology relative to the growing season can have both costs and benefits for species, and these may vary between endotherms and ectotherms. Costs: Cost of Early Emergence: For species that emerge early from dormancy, there may be a cost in terms of energy expenditure and exposure to environmental risks. Early emergence could lead to increased predation risk, resource competition, and energy depletion before optimal conditions for survival and reproduction are met. Cost of Late Emergence: Conversely, species that emerge late from dormancy may face challenges such as reduced mating opportunities, delayed reproduction, and potential conflicts with the availability of resources needed for survival and offspring care. Benefits: Reproductive Success: Staggered dormancy phenology can enhance reproductive success by allowing individuals to optimize their timing of emergence and mating. Early-emerging individuals may have better access to mates and resources, while late-emerging individuals may benefit from reduced competition. Survival: Staggered dormancy phenology can also enhance survival by minimizing exposure to environmental risks. By timing dormancy to coincide with periods of harsh conditions or high predation risk, individuals can increase their chances of survival. Variation between Endotherms and Ectotherms: Endotherms: Endotherms, with their ability to regulate body temperature internally, may have more flexibility in their dormancy phenology. They can adjust their metabolic rate and energy expenditure based on environmental conditions, allowing for more precise timing of dormancy. Ectotherms: Ectotherms, whose metabolic rate is influenced by external temperatures, may be more constrained in their dormancy phenology. They may need to enter dormancy earlier or later than endotherms to align with optimal environmental conditions for survival and reproduction. In conclusion, the staggered dormancy phenology observed in relation to the growing season can have trade-offs in terms of costs and benefits for species, with variations between endotherms and ectotherms based on their physiological and behavioral adaptations.

What physiological and behavioral mechanisms allow some ectotherms to enter dormancy when environmental conditions are still favorable for activity, and how do these mechanisms evolve?

Some ectotherms have evolved physiological and behavioral mechanisms that allow them to enter dormancy even when environmental conditions are still favorable for activity. These mechanisms play a crucial role in optimizing energy expenditure, survival, and reproductive success in fluctuating environments. Physiological Mechanisms: Metabolic Rate Regulation: Ectotherms can adjust their metabolic rate to conserve energy during dormancy. By reducing their metabolic activity, they can minimize energy expenditure and survive on limited energy reserves during periods of dormancy. Torpor and Hibernation: Some ectotherms enter states of torpor or hibernation, where their metabolic rate decreases significantly, allowing them to conserve energy and survive in harsh environmental conditions. These states of reduced metabolic activity help ectotherms cope with limited resources and unfavorable temperatures. Behavioral Mechanisms: Burrowing and Sheltering: Ectotherms may seek shelter in burrows or crevices to enter dormancy. These sheltered locations provide a stable microclimate that is conducive to dormancy, even when external conditions are still favorable for activity. Food Storage: Some ectotherms engage in food storage behaviors, where they hoard food in their burrows before entering dormancy. This stored food serves as an energy reserve during dormancy, allowing them to survive on limited resources. Evolution of Mechanisms: Natural Selection: The physiological and behavioral mechanisms that allow ectotherms to enter dormancy have evolved through natural selection. Individuals with traits that enhance survival and reproductive success during dormancy are more likely to pass on their genes to the next generation. Environmental Pressures: Fluctuating environmental conditions, such as seasonal changes in temperature and resource availability, exert selective pressures on ectotherms to evolve dormancy mechanisms. Species that can enter dormancy at optimal times have a higher likelihood of survival and successful reproduction. In summary, the physiological and behavioral mechanisms that enable some ectotherms to enter dormancy when environmental conditions are still favorable for activity have evolved as adaptive strategies to cope with changing environmental conditions and optimize energy use, survival, and reproduction.
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