Lecture 4- Animals in their Environments

How do small-bodied animals deal with stresses vs large-bodied animal?

Small-bodied animals use behavior; large-bodied animals have fewer behavioral options (depend more on physiological defenses to survive)

Challenge #1: Cold Extremes (small animal)

Ex. Lemming (small rodent in Arctic) using a snow tunnel; creating an insulated space by modifying their environment.

Challenge #1: Cold Extremes (large animal)

Ex. Reindeers have good insulation and regional hypothermia (allows tissues in appendages to be cooler than the core tissues- tissues in appendages don’t freeze).

Has specialized physiological defenses against cold temperatures (exhibit phenotypic plasticity between summer & winter)

Challenge: Preventing Heat Loss 1

Solution: Countercurrent heat exchange system between arteries & veins in the limbs conserves heat.

Ex. Arctic Snow Fox

When an Arctic Fox walks across ice:

B. The temperature in its foot pads is about 0 degrees Celsius

Challenge: Preventing Heat Loss 2

Hibernation: State of low body temperatures & thermal conformity that persists for a long period of time in winter.

Core temperature for all animals is ______

37 degrees Celsius

Metabolic depression

Biochemically induced reduction of metabolic rate due to hibernation.

Hibernation allows for what?

• Allows for core body temperature to match external temperatures.

• Allows for animal to live on body fat or stored food collected the previous summer

Challenge #2: Heat extremes (small animals)

Main challenges include: lack of water and high temperatures)

Small mammals (ex. kangaroo rats) are mostly nocturnal & stay in burrows during the day.

Ex. Lizards use burrows & small patches of shade or stay close to ground surface.

Challenge #2: Heat extremes (large animals)

Main challenges include: lack of water and high temperatures)

Ex. Grant’s gazelle can tolerate a rise in core body temperature to abt 46 degrees C, reducing water needs bc they don’t sweat. (Also have a countercurrent system to keep brain cooler)

Challenge #3: Water & Salt Balance (osmotic problems)

1. Freshwater fish→ Too much water

2. Marine fish→ Too little water

3. Salt-loaded diets→ Need mechanisms for salt excretion

4. Mussel/Crabs→ Fluctuation in salinity

Water & Salt exchange: Freshwater Fish

• Freshwater fish are hyperosmotic to fresh water: water passes in across gills & other membranes by osmosis.

• Freshwater fish does not drink water!

• Fish produce large volumes of dilute urine, & actively transport Na+ & Cl- back across the gills into the body: hyperosmotic regulators

Water & Salt Exchange: Ocean Bony Fish

• Bony fishes are hyposmotic to seawater: tend to lose water by osmosis & gain ions by diffusion

• Energy must be expended to compensate: drink seawater to gain water, in the intestine, ions are pumped out, & excess ions are excreted: hyposmotic regulators

Water & Salt Exchange: Seabirds, ocean lizards, & sea turtles

These animals eat seaweeds & invertebrates with high osmotic pressure but this excess salt from these foods is excreted by salt glands that use energy from ATP.

Water & Salt Exchange: Mussels/ crabs

• Most marine invertebrates are osmotic conformers: osmotic pressure of body fluids is always the same as the water.

• Some coastal invertebrates (blue crab): maintains a constant internal osmotic pressure despite experiencing a range of external salinities.

Challenge #4: Environmental Variability

Phenotypes can change in response to environmental change

Phenotypic plasticity

An individual’s ability to display different phenotypes at different times during its life; one genotype expresses two or more phenotypes.

Acclimation (or acclimatization)

Phenotype change resulting from long-term exposure to a particular environment

Fishes are models of molecular adaptation to temperature: how? Phenotypic plasticity!

• Have enzymes (that exist in multiple molecular forms) for metabolic functions. Ex. Polar species have forms that function well at polar temperatures, but do not work well at warm temperatures.

• Ex. Fish exposed to pollutants. Cytochrome P450 enzymes are important in detoxifying environmental toxins such as halogenated aromatic hydrocarbons (HAHs).- Fishes that live in polluted waters have higher levels of P450 & are more capable of detoxifying toxins

Fish Pop. A lives in water with high levels of industrial pollutants, while Pop. B lives in clean offshore water. When both populations are brought into the lab & raised under identical clean-water conditions, Population A still shows much higher baseline activity of detoxification enzymes (cytochrome P450). What does this most likely illustrate?

C. Phenotypic plasticity in enzyme expression based on environmental exposure.

Challenge #4: Time keeping

Animals have biological clocks tuned to cycles in their environment

Mechanisms for synchronization

• External or exogenous cues- presence of light or darkness.

• Endogenous biological clock- a self-contained, metabolic mechanism of keeping track of time

• Circadian or daily biological clocks= most common

• Lunar (circatidal) & annual (circannual) clocks

• Free-run- no external cues