Amphibian Population Declines and deformities are useful phenomena to illustrate concepts in evolutionary biology

Transcription

1 Amphibian Population Declines and deformities are useful phenomena to illustrate concepts in evolutionary biology

2 Today, I will focus on a particular aspect of the amphibian population decline phenomenon I will show you why we should care about amphibians I will provide an historical perspective of the problem I will show you how we approached the specific problem in the Pacific Northwest I will show you how the problem relates to several basic concepts in Evolutionary Biology

3 Evolutionary Considerations 1) Evolution is limited by historical constraints 2) Adaptations are often compromises 3) Not all evolution is adaptive 4) Selection can only edit existing variations

4 Evolution

5 Takes Time!

6 BIODIVERSITY Genetic Ecosystem Species Coral Reef Variation in Beetles Tropical Rainforest

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10 Why should we care about amphibians?

11 Amphibians are Good Indicators Of Environmental Problems Sensitive Amphibians Eggs laid in open Not covered by shell Thin, permeable skin

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13 Amphibians are historically significant

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15 Exodus 8:1-4 And Jehovah spake unto Moses, Go in unto Pharoah, and say unto him, Thus saith Jehovah, Let my people go, that they may serve me. And if thou refuse to let them go, behold, I will smite all thy borders with frogs; and the river shall swarm with frogs, which shall go up and come into thy house, and into thy bedchamber, and upon thy bed, and into the house of thy servants, and upon thy people, and into thine ovens, and into thy kneading troughs; and the frogs shall come up both upon thee, and upon thy people, and upon all thy servants

16 These foul and loathsome animals are abhorrent because of their cold body, pale color, filthy skin, fierce aspect, calculating eye, offensive smell, harsh voice, squalid habitation, and terrible venom; and so their Creator has not exerted his powers to make many of them. Carl Linneaus 1758

17 Science 1999 Washington Post 1999 Chemical & Engineering News 1999

18 Contributing Factors to Amphibian Population Declines Habitat Destruction Global Climate Change UV-B Radiation Acidification Pollution Introduction of Exotic Species Pathogens

19 Field studies led us to some mysterious problems concerning amphibians

20 The mystery began in the mid 1980s

21 Western Toad Eggs

22 Western Toad (Bufo boreas) Healthy Embryos Dying Embryos

23 Some early clues

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27 Sunlight contains harmful ultraviolet radiation UV-B ( nm)

28 Over Evolutionary Time

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31 UV IS A GLOBAL PROBLEM Ice Fish Plankton Crop Plants Coral Reefs Aquatic Insects Human Cataracts and Skin Cancer

32 Conflicting Selection Pressures Seek Sunlight to Thermoregulate etc. But Seeking Sunlight May Result in Exposure to Harmful Doses of UV-B Radiation

33 Return to our evolutionary considerations and address some pertinent questions regarding sunlight and amphibians 1) Evolution is limited by historical constraints 2) Adaptations are often compromises 3) Not all evolution is adaptive 4) Selection can only edit existing variations 5) Evolution takes time

34 Some key questions Are amphibians avoiding sunlight?

35 Are amphibians avoiding sunlight? No!

36 EGGS Eggs are often laid in shallow water; some eggs protrude above water line Cascades frog egg masses

37 Western toad eggs (Bufo boreas)

38 A school of millions of western toad tadpoles hugging the shoreline Larvae

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42 Adults & Juveniles Western toads, Oregon

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45 How are amphibians coping with current levels of UVB radiation?

46 How are amphibians coping with current levels of UVB radiation? Perform Experiments in the Field

47 Experiments are conducted at natural oviposition sites in the exact spot where eggs are laid Western Toad Cascades Frog Pacific Treefrog UVB Shield Open UVB Transmitting Filter UV Transmitting Filter Treatment Replicates at Each Pond & Replicate Ponds

48 Variation!

49 1 Anzalone, Kats, & Gordon Southern California UV Blocking Filter UV Transmitting Filter Open 0.8 Survivorship Hyla regilla Hyla cadaverina Taricha torosa

50 Spain Lizana & Pedraza SURVIVAL UV Blocking Filter UV Transmitting Filter Open 0 Bufo bufo Bufo calamita

51 Percent survival Long-toed salamander Shielded Exposed 0 Valley Population Mountain After Belden and Blaustein 2002

52 Why are some amphibians more susceptible to damage from exposure to UV than others?

53 One answer is that some amphibians have a better ability to repair UV damage than others How? This is where the molecular biologists Take over!

54 Photolyase is an enzyme that repairs UV damage at the molecular level

55 Variation in photolyase activity!

56 Amphibian Photolyase Activity 10 9 Photolyase Levels Species

57 Evolutionary Considerations Evolution is limited by historical constraints

58 Evolutionary Considerations Adaptations are often compromises

59 Some factors potentially affecting amphibians in an aquatic Competition Contaminants Prey availability ph Predation Parasitism environment Dissolved oxygen Turbidity Precipitation Temperature Disease Biological interactions Water Quality Buffering capacity Weather Season Organic matter Sunlight Energy Nutrients Secondary Primary production production Larval amphibian survival Habitat Vegetation Current Volume/depth Canopy cover (Adapted from Foran and Ferenc 1999)

60 Evolutionary Considerations Not all behaviors are adaptive Normal Retina UV-damaged Retina Death?

61 Now, a little about deformed amphibians

62 Newsweek 13 July 1998 Newsweek July 1995

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64 Evolutionary Considerations Evolution is limited by historical constraints

65 ttp://tiee.ecoed.net/vol/v2/issues/frontier_sets/amphibians/abstract.html Download Reprints: Earth & Sky Teachers Booklet