1114 Chapter 18

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Shared characteristic of fungi
- Heterotrophs: that feed by breaking down compounds outside their bodies
- Hydrolytic enzymes-> breakdown molecules into a form used by fungi and results in decomposition
Major cause of massive global amphibian extinction?
- Infection by chytrid fungus
- Chytrid: unicellular parasitic fungus
Chytridiomycosis
- Chytrid fungal infection of the skin of amphibians
- Up to 100% mortality of infected populations
Cycle of infection of chytridiomycosis
- Flagellated aquatic fungal spores burrow into amphibian skin
- Spores mature and develop into sporangia
- Sporangia release more spores into skin
- As spore load increases, the skin begins sloughing off, cardiac and respiratory function may be interrupted
Chytrid grows and reproduces best between 17-25°C and has peak performance at 23°C

Which altitudes would you predict chytrid would grow best?

C) ~1000-2000m
Figure: # of Atelopus frogs and % extinct at differing elevations in Cloud Forests
Bar height= total number of Atelopus species, shaded area= number extinct (and %)

Does optimal chytrid growth condition variation with altitude correspond to variation in extinction rates with altitude?

Yes
Which of the following graphs best reflects the relationship between chytrid associated frog deaths and temperature?

B) Atelopus extinction rates are highest @ cool temps (higher altitudes), but lower @ coldest temps and lowest @ warmest temps
Climate change has resulted in tropical warming. Figure shows changes in tropical air temperature (blue line) relative to baseline average from 1856-2000.
Given the relationship between Atelopus extinction rates and temperature along altitudinal gradients, would you predict frog extinction rates to increase or decrease as climate warming progresses?
- Decrease
- Chytrid would start to die so amphibians would survive
What does this figure suggest about the relationship between # of Atelopus species lost to chytrid infection and temperature?

B) more Atelopus species are lost bc of chytrid in warm years than in cool years

This is the "chytrid-climate paradox"
- Warming trend in tropics primarily driven by night time warming
- Because night worming > daytime cooling, net effect is still net warming trend
Why are night temperatures increasing as day temperatures decrease?
- Plant responses to heat stress
- As temperatures increase, tropical plants face potential heat damage -> require cooling adaptations
- As more stomata open with increasing temperature, increased evaporative cooling of leaves as water exits (similar to cooling by sweating)
- Water vapor -> released to the atmosphere where it forms clouds
- Greater transpiration -> adds more water to the atmosphere -> greater cloud formation
Transpiration

Cooling process by which water is lost by opening stomata (leaf pores in which CO2 enters and water and O2 leave) on the bottom of the leaf
How does cloudiness effect day/night temperature?
- Day Effects: clouds block incoming solar radiation -> cooling during the day
- Night Effects: clouds block heat loss from warmed surface to atmosphere -> insulation=warming during the night
How does day cooling and night warming affect chytrid?
- If its a sunny day, few clouds: vegetative surfaces that frogs live on absorb solar radiation -> therefore often hotter than surrounding
- Air temp is good for chytrid and bromeliads/moss/leaf litter that frogs occupy reach 30°F which kills chytrid
- On a cloudy day: increased cloudiness due to warming block sunlight -> surfaces heat up less relative to air
- Air temp is good for chytrid and the temp of the moss that the frogs occupy are good for chytrid
Patterns of warming for chytrid

Results in more favorable chytrid conditions during day and nighttime temperatures closer to chytrid optimum

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1114 Chapter 18

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Updated

2018-04-28T20:55:55Z