TRIALS OF LIFE #7
"Living Together"
The yellow-billed oxpecker (Buphagus africanus), shown here on a zebra.

The yellow-billed oxpecker (Buphagus africanus), shown here on a zebra.

Broadcast 15 November 1990, this episode focuses on those species that co-operate and depend on (or exploit) others. Spotted deer follow langur monkeys as they travel from tree to tree, eating any leaves that get dropped from above. In return, the deer serve as a lookout when the primates are feeding on the ground. Underwater, a hermit crab is shown adding sea anemones to its shell in order to protect itself from attack by an octopus, and a goby assists a virtually blind shrimp. Fleas, lice and mites are parasites: they share no mutual partnership and instead take advantage of creatures for food or shelter. However, parasites have their predators, and an example are the finches of the Galápagos Islands that clear the resident giant tortoises of their ticks, and oxpeckers, which do the same for giraffes in Africa (and even use its fur to line their nests). Some fish regularly clean others, and wrasse and shrimp appear to specialise in this regard, as do remora, which permanently hang on to their hosts. One parasite that grows inside its host is the fluke, and one is shown gestating inside a snail, having previously been unknowingly eaten. Because it needs to transfer to a bird's gut to develop further, it causes the snail to advertise its presence to allow itself to be consumed — thus completing the circle. However, some microscopic creatures inhabit the stomachs of large herbivores in order to break down the cellulose of their diet, thereby aiding their digestion". (http://en.wikipedia.org/wiki/The_Trials_of_Life 6/18/2008)



“Compared with the natural world's elaborate "buddy" system, humans are curiously detached. Dive to a coral reef to meet an underwater odd couple - a shrimp and a goby fish. The shrimp is industrious but almost blind while the goby is indolent but eagle-eyed. Watch finches on the Galapagos Islands serve as tiny tick-removing valets to giant tortoises. Ants tend to caterpillars, oxpeckers groom giraffes, and hermit crabs ramble around with a bevy of octopus-stinging anemones on their backs. While there are parasites - and even parasites who prey on parasites - witness the astounding amount of give-and-take amid Earth's tooth-and-nail struggles."



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Connect what you see as you accompany David Attenborough with theoretical constructs and points acquired from class and reading.
The point is to use your observations as EXAMPLES of phenomena we discuss in class. For example, among some of the following relationships, which might exemplify
  • optimization - costs/benefits
  • mutualism or parasitism
  • use of pheromone
  • sign stimulus
  • innate releasing mechanism
  • fixed action pattern
  • parasite modifying behavior of host [1]
  • can you call it "social behavior" if different species are keeping company?

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[1] Levri, E.P. and L.M. Fisher, 2000. The Effect of a Trematode Parasite (Microphallus Sp.) on the Response of the Freshwater Snail Potamopyrgus antipodarum to Light and Gravity, Indiana University. [Reprinted from Behaviour (2000) 137(9): 1141-1151 with kind permission from Springer Science and Business Media] The Effect of a Trematode Parasite (Microphallus Sp.) on the Response of the Freshwater Snail Potamopyrgus antipodarum to Light and Gravity : Parasites often influence the behavior of their hosts in ways that increase the probability of transmission of the parasite. The digenetic trematode Microphallus sp. has been demonstrated to alter the behavior of the New Zealand freshwater snail Potamopyrgus antipodarum in a way that increases the probability that infected snails will be eaten by the final host (waterfowl). Infected snails are found foraging on top of rocks more often in the early morning when waterfowl are feeding and less often in the afternoon when unsuitable hosts (fish) are feeding. The mechanism(s) that the parasite utilizes to produce this behavioral change is not known. The: present study investigated three possible behaviors (phototaxis, geotaxis, and photokinesis) that the parasite could alter that may account for the behavioral change seen in the field, infected and uninfected snails were assessed in terms of their orientation to light (phototaxis), orientation to gravity (geotaxis), and movement in response to light (photokinesis). There was no evidence of phototactic behaviors in either infected or uninfected snails. However, uninfected snails were found to positively orient towards gravity, while infected snails did not. Also, both infected and uninfected snails were found to be positively photokinetic (they move faster in the light than in the dark), but Microphallus-infected snails were found to move more slowly than uninfected snails. The differences found between infected and uninfected snails may be part of the manipulative effort of the parasite, but by themselves the differences are not sufficient to explain the patterns observed in the field.

"Trials of Life" video episode #5: "Living Together". integrating ideas: Think about whether relationships between members of different species are "facultative" or "obligate" as well as what are the relative costs and benefits to each individual (what NEEDS are involved). Speculate on the possible selection pressure(s) for the evolution of some of these relationships. By a strict definition, is a fetus a parasite? are genes parasites? (in the sense of "using" us to transmit themselves into another individual)
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9/2009