Ch33 Animal Form and Function lecture notes

Animal Body Plan

An animal’s body plan limits its size, shape and ability to interact with the environment

Animals with an asymmetrical body plan are aquatic, sessile, filter feeders

Animals with a radial body plan are also aquatic but they are often motile and they either filter feeders or they actively search for food

  • They have no cephalization, so their movement is not directional

All vertebrates have bilateral body plan

  • They have cephalization so their movement is directional

  • They are all motile and they all active search for food

  • Bilateral symmetry also means that an animal has an anterior, posterior, dorsal and ventral side

Bilateral Body Plan

Aquatic animals are constrained by the density of water

  • Aquatic bilateral animals have a fusiform shape to minimize drag in water

  • Convergent evolution

Terrestrial animals are constrained by gravity

  • Terrestrial animals have evolved traits to counter gravity

  • Wings, lower body weight, long tails, etc.

Endoskeleton/Exoskeleton

An exoskeleton is a hard covering or shell that protects the animal and provides attachment sites for muscles

  • Given that insects are the most populous of all bilateral animal species, we can say that most animals have an exoskeleton for support

Exoskeletons are most often made of chitin or calcium carbonate

Ingrowths called apodemes are the sites of muscle attachment

  • Allow animals to move legs, claws, wings, etc.

To grow, these animals must molt

Having an exoskeleton limits an animal’s size

  • Doubling body size equals an 8x increase in weight

An endoskeleton is comprised of internal bone or cartilage that supports body weight and movement

  • All chordate animals have an endoskeleton

Muscles attach to the endoskeleton to facilitate movement

Most animals with an endoskeleton have determinant growth

As body size increases, bone and muscle increase

  • Speed and agility are a balance between body size and bone & muscle mass

Homeostasis and Thermoregulation

Endothermic animals use metabolism to maintain their body temperature

  • They can shiver to increase temperature or sweat/pant to decrease temperature

  • They have feathers or fur, and subcutaneous fat to help control body temperature

  • Require 90% more calories than a similar sized ectotherm.

Ectothermic animals do not use metabolism to maintain their body temperature

  • They bask in the sun to raise body temperature or seek shade to lower body temperature

  • Require only 10% of the calories required by a similar sized endotherm.

Homeothermic animals, whether endotherms or ectotherms, maintain a constant body temperature

Poikilothermic animals, whether endotherms or ectotherms, allow their body temperature to fluctuate depending on the environment

Animal Biogenetics

Animals obtain energy from the food they ingest

  • Carbohydrates, protein, and lipids are all converted to

  • ATP for immediate energy

  • Glycogen and fat for long-term energy storage

2nd Law of Thermodynamics states that energy cannot be converted from one form to another with 100% efficiency

  • In animals, converting consumed macromolecules to ATP, glycogen or fat gives off energy in the form of heat

  • Endothermic animals use this heat to maintain thermal homeostasis

The amount of energy expended over a given time is called the Metabolic Rate (measured in joules or calories)

Basal Metabolic Rate in endotherms

Standard Metabolic Rate in ectotherms

Body size and energy requirements

Small endotherms have greater surface area to body mass ratio than large endotherms

  • Lose heat faster than large endotherms

  • Have higher BMR per body weight than large endotherms

The more active an animal, the higher the BMR/SMR

The diet of an animal is determined by its BMR/SMR

Environment and energy requirements

Animals in extreme environments adapt to seasonal temperature and/or food and water availability through torpor

  • Torpor is defined as decreased activity and metabolism to conserve energy

Hibernation is a type of winter torpor

  • Animals hibernate during coldest time of year

  • Reduced body temperature

  • No food intake

Estivation is a type of summer torpor

  • Animals hibernate during times of extreme heat or decreased water availability

  • Desert animals hibernate during hottest time of year

Torpor can occur on a daily basis to help animals avoid the hottest or coldest times of the day