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ENVR 202 > L8 - Moving onto Land > Flashcards

L8 - Moving onto Land Flashcards

1
Q

What events were critical for the emergence of life on land?

A
  • Photosynthesis
  • Eukaryotes evolve
  • Proliferation of bacterial mats (thanks to cyanobacteria - oxygen producing)
    • Giving rise to algae and first plants
  • Great Oxygenation Event allowed for the formation of the Ozone layer (filters out harmful UV radiation)
  • Shells and hard bodies begin to dominate the fossil record
  • Animals become more motile
  • Explosion of evolution of new body types in animals
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2
Q

Evolution of Pikaia?

A
  • 2-inch long worm
  • First chordate (animal with a back bone) that would give rise to all vertebrates
  • Predecessor of chordate, vertebrates, mammals and humans
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3
Q

What did life on Earth look like during the Ordovician (450-500 Ma)?

A
  • Mix of continents and shallow ocean shelves
  • Rising and falling sea levels
  • First true vertebrates (fish with a jaw) evolve from Pikaia
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4
Q

What are some challenges faced by aquatic animals when moving onto land? (Brainstorm)

A
  • Breathing
  • Locomotion (reason why whales got so big was buoyancy, they can be that big on land)
  • Sense (vision adapted to water)
  • Distinct reproduction between terrestrial and aquatic animals
  • Temperature
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5
Q

How is UV radiation a barrier to adapting to land?

A
  • Water could filter UV light and protect life
  • Oxygen changed everything
    • Created an ozone shield and filters out enough UV radiation that like can survive on land
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6
Q

How is desiccation a barrier to adapting to land?

A
  • Drying out is particularly dangerous if you are a non-waterproof organism
  • Organisms can never be completely waterproof because we need to have tissues that allow for gas exchange
    • Smaller organisms dry out faster: large surface area to volume ration
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7
Q

How is gas exchange a barrier to adapting to land?

A
  • Physical properties of the way that gases move through water are quite different to air
  • Organisms that breathe in water have a gill system that is very distinct to lung system found in terrestrial animals
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8
Q

How is buoyancy a barrier to adapting to land?

A
  • Some aquatic animals have little structural support in their bodies because water and water pressure supports their body tissues in ways that air cannot
    • Blob fish
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9
Q

How are temperature fluctuations a barrier to adapting to land?

A
  • The range of temperature variation in seawater is very small
    • Will only vary in a couple of degrees over the course of a year
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10
Q

How is mineral nutrition a barrier to adapting to land?

A
  • Water contains dissolved minerals for added nutrition
  • Many aquatic animals are sessile (immobile)
    • Need a way to supplement on land
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11
Q

How is reproduction a barrier to adapting to land?

A
  • Aquatic organisms need water to facilitate reproduction!
  • Male and female gametes (egg and
    sperm) released into the water for fertilization and development
    • Both animals and photosynthesizers!
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12
Q

How are senses a barrier to adapting to land?

A
  • Vision and hearing
  • Light and sound waves move differently through water compared to above water
  • Need to adjust vision and hearing before they move out of the water
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13
Q

What were the traits of the first colonizers?

A
  • From early cyanobacteria, GREEN ALGAE (eukaryotes, incl. multi-cellular) appeared ~ 0.75 BYA
  • What could have prompted plants to move onto land?
    • Plants are autotrophs (get energy from the sun) !
  • Advantageous to grow near the surface (closer to light), in shallow waters, on coastal shelves
    • NATURAL SELECTION: selective force to evolve organisms that can tolerate increased levels of desiccation
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14
Q

Evolution of green algae?

A
  • Populations of green algae exposed to periods of drought in the intertidal
    • Selection for individuals which could tolerate extended periods of desiccation
      • i.e. existing species had traits which likely predisposed them to being able to adapt to the terrestrial
        environment
  • Over time, evolved from green algae to more complex forms that could survive entirely on land
    • Gave rise to mosses and liverworts (primitive plants: no roots, seeds, flowers, vascular system)
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15
Q

What is the evidence that liverworts were the first land organisms?

A
  • Spores resembling modern liverwort spores found in the Ordovician fossil record
  • No known species of aquatic liverworts
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16
Q

Plant adaptations to life on land: Desiccation

A
  • Developed multiple cell laters and layer of surface wax (cuticle)
  • Evolved roots or root-like structures that direct movement of water into the body
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17
Q

Plant adaptations to life on land: Gas Exchange

A
  • Evolved specific pores (stomata) to allow for gas to enter
  • Could be closed to prevent the plant from drying out
18
Q

Plant adaptations to life on land: Reproduction

A
  • Evolved spores that could survive desiccation (still depended on water to move them)
  • Eventually evolved seeds, even more desiccation-tolerant than spores
19
Q

Plant adaptations to life on land: Buoyancy

A
  • Evolved strong fibres and compounds such as
    lignin and cellulose for STRUCTURAL SUPPORT
20
Q

Plant adaptations to life on land: Temperature fluctuations

A
  • Traits evolved to prevent desiccation also helped plants to survive extreme temperature fluctuations
    • Later, plants evolved methods (e.g., dormancy) to survive extreme weather conditions (winter)
21
Q

Plant adaptations to life on land: Mineral Nutrition

A
  • Roots allow for uptake in minerals from soil
  • Symbiotic associations with microbes: exchange minerals for sugars
22
Q

Why did plants colonize the terrestrial surface before animals?

A
  • Plants are the base of the food chain (autotrophs)
  • If animals were to colonize first, they would have nothing to eat
23
Q

Which group of animals moved onto land?

A
  • Arthropods (evidence: Cambrian-era fossils of arthropod tracts on land)
  • However, no permanent terrestrial species at this point
  • Footprints believed to have been made by animals fleeing predation in the water
24
Q

What were some arthropods?

A

Scorpions, millipedes, springtails (Devonian)

25
Q

First fish?!? Tikaalik - Late Devonian (375 MYA)

A
  • Evolved from Pikaia
  • A lobe-finned fish (lineage is water is almost extinct)
  • Shared ancestor of all tetrapods (amphibians, mammals, reptiles)
  • A transition fossil
  • Sturdy jointed “arms” for terrestrial support
    • Body plan of all vertebrates today
  • Still living half and half: coming onto land to forage or exploit new niches, but still returning to the water for reproduction
26
Q

Evolved into Ichthyostega (365 MYA)

A
  • Progressive evolution of limbs
  • Living both in water and on land
    • Closely tied to water for reproduction
27
Q

Which lobe-finned fish did not go extinct like the rest of them?

A
  • Lungfish
    • Other lobed-finned fishes = extinct for 66 million years
  • Celeocanth discovered and found to still exists
28
Q

Why could so many groups colonize land?

A
  • CHANCE: Structures that evolved for other uses are also effective for living on land
29
Q

How did terrestrial animals prevent dessication on land?

A
  • Physical:
    • Waxy coating on exoskeleton (arthropods, insects)
    • Scales (lizards, snakes)
  • Behavioural:
    • Live in damp habitats (amphibians like frogs and lizards)
    • Active at night
  • Concentrate waste,
    • Remove water and excrete waste as uric acid -poop (drier, less water)
30
Q

Gas exchange: how to get oxygen into the cells?

A
  • If you’re an organisms that is small enough, like bacteria, gases diffuse easily, but slowly, through a small cell
  • With a larger surface area its more difficult:
  • O2 must be absorbed across a moist membrane
  • Terrestrial organisms have developed lungs
31
Q

Gas exchange: how to keep the membranes wet in dry air without losing water?

A
  • Insects:
    • Small openings in exoskeleton (spiracles)
    • Network of tubes branching throughout body (tracheae)
    • Reason why insects can only get so be
  • Vertebrates:
    • Small opening (trachea)
    • Sacs with large surface area and many blood vessels for gas exchange (lungs)
32
Q

How does aquatic fertilization work?

A
  • Aquatic organisms produce millions and millions of gametes (sperm & egg)
  • Throw them out into the water and hope for the best
33
Q

Reproduction on land?

A
  • Internal fertilization
    • Keep ova inside of body to prevent desiccation
    • Fertilize inside female
      • Probability of gametes encountering one another is increased
      • More of a conservative strategy
34
Q

Post-fertilization on land?

A

Egg!
- Modifying the embryo to deal with terrestrial life (avoiding desiccation, having enough nutrients, gas exchange, waste disposal)

35
Q

Costs and benefits of an egg?

A
  • A lot of energy needs to be invested into one offspring
  • Very exposed, vulnerable and fragile when outside your body
  • Self-contained world
36
Q

Why is viviparity (live birth) a good alternative?

A
  • Have embryo incubate inside of your body
  • TRADEOFF: Requires even more parental investment BUT your offspring are more likely to survive
37
Q

How did animals adapt to buoyancy?

A
  • Anthropods: exoskeleton b
  • Molluscs: external shell, hydrostatic skeleton
  • Vertebrate: internal skeleton of cartilage and bone
38
Q

How did animals adapt to temperature fluctuations?

A
  • Homeothermy: the ability to regulate internal body temperature
  • There are both active and passive strategies
    • Metabolism
    • Behaviour
  • Extremely costly in energy, high food requirement
39
Q

How did animals adapt their senses? Vision?

A
  • Early eyes: filled with water from the environment
  • Terrestrial eyes: take that aquatic environment and encapsulate/seal the chamber
40
Q

How did animals adapt their senses? Hearing?

A
  • Early hearing adapted to wavelengths traveling through water
  • Later adaptations specialized in some species to airborne wavelengths
    • Cochlea in mammals still contains fluid for sound transmission

ENVR 202 (22 decks)

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