NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE A Presentation to Accompany the Case Study: Living on the Edge A Day in the Life of a Hummingbird by Giovanni Casotti Department of Biology West Chester University, West Chester, PA

Extreme environments: Osmoregulation

Strategies Osmoconformers o Plasma > 290 m. Osmoregulators o. Plasma ~ 290 m. Osm

Aquatic environment Euryhaline o. Eustarine species Stenohaline o. Other species

Aquatic environment Ionoconformer Ionoregulator

Aquatic environment FW problems o. High amount of water intake o. Loss of body ions Problem Solution

Aquatic environment SW problems o. High amount of ion intake o. Loss of body water Problem Solution

Evolution onto land Problem - dehydration o. Evolve renal morphology (birds and mammals) thus altering function Birds o Role of the cloaca Mammals o Efficient kidneys

Renal morphology Fishes, amphibians, reptiles o Nephron at right angle to collecting duct

Renal morphology Birds and mammals o Development of the loop of Henle parallel to collecting duct

Renal function Renal processes o o o Filtration Reabsorption Secretion

Countercurrent multiplier Important points • Water movement if passive – osmosis • Water movement depends on ion gradient • Development of a concentration gradient in the medulla • The role of antidiuretic hormone • The role of the vasa recta

Countercurrent multiplier

U/P ratios Vertebrate Fish Amphibians Reptiles Birds Mammals Ratio 0. 1 -1. 0 0. 1 -2. 5 0. 2 -26. 0

Avian cloaca Temporary storage Reabsorb Na+, K+, Cl-, H 2 O

Case study Hummingbirds/Sunbirds o. A unique animal on the edge of survival o. Watch the hummingbird video

Hummingbirds Unique challenges o. Dilute (up to 3 - 6 times body mass/day) or a concentrated diet. Can they dehydrate?

Nectar variability The influence of nectar sucrose and activity of sucrase.

Case Study Questions • 1. Do floral nectar concentrations vary throughout the day. Why do you think that hummingbirds are active feeders first thing in the morning? • 2. What are some of the daily osmotic challenges faced by sunbirds? How do they cope physiologically with low and high concentrations of nectar? • 3. Why don’t you see hummingbirds feed during the hottest part of the day?

Hummingbirds Unique challenges o. High rate of water flux that is variable

Hummingbirds Unique challenges o. High excretory rate (up to 3 - 6 times its body mass/day)

Hummingbirds Unique challenges o. High metabolic rate Allen hummingbird Anna hummingbird House wren Widow bird Swallow Shrews Mice

Hummingbirds Unique solutions o. Modified kidneys with virtually no medulla o. Undergo Torpor

Case Study Question • 4. From the material presented in this lecture, explain how the mammal nephron produces a concentrated urine. In your answer explain how the countercurrent multiplier mechanism operates, the importance of the design of the thin descending and thick ascending limb of Henle, and the length of the loop of Henle.

Case Study Read the paper on hummingbird renal morphology Question • 5. Casotti et al. (1998) discusses 3 renal adaptations that enable Anna’s hummingbird to survive on a high water flux, low ion diet. What are they and how do they operate?

Torpor

Torpor

Case Study Reading the article on torpor in the Rufous hummingbird Questions • 6. What is torpor and why is it an important physiological adaptation for survival? • 7. How much of a decrease is there in O 2 consumption between normothermy and torpor? How long does torpor typically last?