AnimalPhys4e Ch11

Chapter 11 Opener

A newborn reindeer calf must thermoregulate on its own, relying on physiological adaptations to maintain body heat in frigid environments.

Metabolic Rate and Temperature

• Resting Metabolic Rate: Affected by air temperature down to -50°C in adult reindeer, illustrating their adaptation to extreme cold.

• Figure 11.1: Shows the resting metabolic rate (watts/kg) plotted against air temperature (°C) for summer and winter. Observations indicate that winter metabolism significantly increases when temperatures drop, highlighting the importance of seasonal adaptations. The resting metabolic rate varies considerably between seasons, showcasing flexibility in metabolic demands based on environmental conditions.

Hair Structure

• Reindeer Hair:

• Figure 11.2: Shows a longitudinal section of a reindeer hair scanned at 0.1 mm, emphasizing its structure which is crucial for insulation and thermoregulation. The hollow hair shafts trap air, providing thermal insulation against the cold.

Fur Thickness

• Seasonal Adaptations:

• Figure 11.3: Details fur thickness in adult reindeer, with winter fur measuring 3.6 cm and summer fur at 1.1 cm. Such protective adaptations are essential for survival in harsh winter conditions. The change in fur thickness also reduces heat loss during the colder months.

Regional Heterothermy

• Fatty Acid Composition:

• Figure 11.4: Displays the fatty acid composition of bone marrow lipids in reindeer legs. This adaptation allows extremities to remain colder than the core body temperature, which assists in thermoregulation by reducing overall heat loss while ensuring vital organs remain warm.

Diet Composition

• Winter Diet:

• Figure 11.5: Outlines the diet composition of winter reindeer using DNA barcoding, revealing primary food sources including fungi, herbs, grasses, trees, mosses, and lichens. These foods are critical for providing necessary nutrients during the resource-scarce winter months.

Seasonal Changes in Nutrient Content

• Nutrient Analysis:

• Figure 11.6: Shows seasonal changes in protein and mineral content of foods eaten by Finnish reindeer. Key nutrients include potassium, calcium, phosphorus, and magnesium, which are vital for metabolic functions and overall health. Lichens provide low protein and mineral content during winter, making it essential for reindeer to adapt their dietary habits seasonally to meet their nutritional needs.

Microbial Responses

• Rumen Microbes:

• Table 11.1: Summarizes responses of rumen microbes to seasonal dietary changes. Microbes that can ferment plant fiber increase significantly in winter: Fiber digestion rises from 31% in summer to 74% in winter, and cellulose digestion from 15% to 35%. This increased capacity for hemicellulose digestion during winter is crucial for breaking down tough, fibrous plant materials available in the colder months.

Metabolic Rate in Newborn Reindeer

• Comparison with Adults:

• Figure 11.9: Examines resting metabolic rates of newborn versus adult reindeer as influenced by temperature, indicating that newborns have a higher metabolic rate as they rely heavily on brown fat for insulation. The lipid-rich nature of reindeer milk (20% lipid) provides essential energy and nutrients to support metabolic processes during early life.

Brown Fat Thermogenesis Capabilities in Newborns

• Figure 11.8: Tests for brown fat thermogenesis in newborn and growing reindeer. A large increase in O2 consumption percentages in 1-day-old calves post-norepinephrine injection indicates that they possess well-developed brown fat thermogenesis, which decreases with age. This adaptation is vital for maintaining temperature in the early days of life.

Comparison to Humans

• Brown Adipose Tissue:

• Figure 11.9: Discusses the presence and loss of brown fat in human infants within the first month of life; highlights the shift from non-shivering to shivering thermogenesis as they grow. Understanding these mechanisms provides insight into human thermoregulatory capabilities.

Brown Fat Mechanism

• Uterine Development:

• Figure 11.10: Studies brown fat in a near-term sheep fetus, explaining the regulation mechanisms for metabolism in utero via placental signals to synthesize fat stores prior to birth, crucial for thermoregulation at birth.

Strategies for Warmth in Newborns

• Discussion on how newborn mice maintain warmth through the use of brown fat and behavioral strategies to conserve heat. This is reflective of similar strategies across various mammalian species.

Comparison of Brown vs. White Fat

• Characteristics of Brown Fat for Thermogenesis:

  • Multilocular, vascularized, UCP1 present, abundant mitochondria.

• White Fat: unilocular, non-vascularized, no UCP1, few mitochondria. This comparison underscores the significant role of brown fat in energy expenditure and heat production.

Migration and Hibernation

• Behavioral Adaptations: Large mammal migration is energetically feasible compared to small mammals, which often utilize underground hibernation. Notably, hibernating species retain brown fat as adults, while larger mammals typically do not exhibit such behavior.

Energy Savings Through Hibernation

• Figure 11.11: Details energy savings from hibernation relevant to body size, indicating larger animals exhibit significant reductions in metabolic rates during hibernation, optimizing energy expenditure.

Hibernation Seasons and Temperature Fluctuations

• Figure 11.12: Tracks body temperature of Arctic ground squirrels during hibernation, showing the maintenance of body temperature through periodic arousals, which prevent hypothermia.

Metabolic Heat Production During Hibernation

• Figure 11.13: Demonstrates how metabolic heat production elevates during low ambient temperatures to preemptively address excessively low body temperatures and maintain homeostasis.

Hibernation Performance Metrics

• Table 11.2: Evaluates hibernation performance in chipmunks based on diet, providing statistics on hibernation sustainability and metabolic rates at specific temperatures, stressing the importance of dietary intake for successful hibernation strategies.

Fatty Acids Role Structure and Function

• Figure 11.14: Highlights structural details of omega-3 and omega-6 fatty acids, emphasizing their critical roles in membrane lipid function and cardiovascular health, further indicating the broader implications of dietary choices on physiological well-being.

Energy Use in Hibernation and Periodic Arousals

• Figure 11.15: Discusses energy dynamics in alpine marmots during hibernation, illustrating why periodic arousals are necessary for waste voiding, neurological maintenance, and immune system support, as these are vital for survival.

Constraints of Hibernation

• Testicular Development:

• Figure 11.16: Demonstrates timings and constraints in hibernation concerning testicular development in squirrel species, with observations noting male emergence from hibernation before females, influencing breeding success.

Social Hibernation Synchronization Benefits

• Figure 11.17: Observes the hibernation behavior of alpine marmots, showing the ecological benefits of synchronized arousal that can significantly reduce individual energy expenditure during hibernation.

Weight Loss Dynamics and Synchrony Effects

• Figure 11.18: Calculates weight loss during hibernation regarding synchrony in groups, emphasizing survival consequences based on social behavior patterns during this critical energy conservation period.