Examples for Evolution Classes
As a botanist, I feel that biology classes use too many furry animal examples. Here are some great examples of topics worth covering in biology or evolution classes that aren't biased toward furry vertebrates.
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. Mimicry, parasitism, hitchhiking...the bizarre life-cycle of the mussel has it all.
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Sexual selection. The long eyestalks of male stalk-eyed flies are thought to be a product of sexual selection. Female stalk-eyed flies generally prefer to mate with males that have longer eyestalks.
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. Cordyceps is a parasitic fungus that kills its host insects, and then digests their corpses, eventually sending up a spore-producing structure to release spores into the wind. In many cases, it can control the behavior of the dying insect, causing the unfortunate arthropod to find a place to die that will maximize spore dispersal possibilities. Because wind is a great method of spore dispersal, and the fungus isn't relying on a healthy(ish) host to spread it around, natural selection doesn't favor the normal balance between virulence of the pathogen and health of the host. Here, maximum viulence = maximum reproduction for the fungus, so it kills its host relatively quickly and uses all of the hosts resources in producing the next generation of fungi. Creepy.
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. These cute little amphibians may look mild-mannered, but they exhibit some scary behavior when they feel threatened. They have black and white poison glands on their rears. A threatened frog hunkers down and raises its behind, mooning potential predators with a pair of poison glands that look like the threatening visage of a larger animal. This is a great example of mimicry, adaptation, and the amazing outcomes of natural selection.
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Adaptation: Mimicry. The caterpillars of some of these species are ant mimics.
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Adaptation: Mimicry. This is another fruit fly that has ant-like (or ant-mimic jumping-spider like) blotches on its wings. Other insects also have wings with spidery patterns, such as the moth Siamusotima aranea. See Zolnerowich (1992) for some examples of other insects thought to mimic spiders.
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Sexual selection: intersexual (m to f). Peacock spiders are a wonderful, non-bird example of intersexual selection, where the males are showy and the females choosy. The males dance and display their showy abdomens for the females, and the females select mates on the basis of this display. Dancing peacock spiders provide an eye-popping display combining both major morphological and behavioral adaptations.
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Adaptation: Mimicry. The wing patterns of this moth look like flies lapping up bird poop.
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Adaptation: Mimicry. Sadly, EOL has no photo of this cool moth, but it is a fantastic, 3D-looking dead leaf mimic.
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- Life …
- Eukaryota
- Opisthokonta
- Metazoa …
- Deuterostomia …
- Vertebrata …
- Tetrapoda …
- Squamata …
- Dactyloidae …
Mysteries. Why are these lizards blue? It is still an evolutionary mystery. Small patches of blue on lizards are often used to catch the eye of potential mates (sexual selection), but lizards with entirely blue bodies are unusual. It could be a trait that is just a byproduct of selection for something else. It could help lizard hide from predators (blue lizard against blue sky or blue ocean?). No one knows yet. This calls for further research!! -
. The leaves of Passiflora alata have interesting glands which secrete nectar to attract ants (which are voracious predators of young caterpillars) and that look vaguely like butterfly eggs (to con mother butterflies into going elsewhere).
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Adaptation: Mimicry. The caterpillars of this species hiss and then peep when startled by a bird with predation on its mind. The final high peeping call of this caterpillar mimics the high, "seet" sound that is used as a warning call (Aerial predator!! Take cover!!) by many birds. When this caterpillar call was played at birdfeeders, the birds scatered, just as they do when another bird calls after spotting a hawk.
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Adaptation: Mimicry, Rhagoletis/Phidippus, Mimic. This is another fruit fly that's a pretty good spider mimic. Notice that when viewed from the back, the bands on the wings look like spider legs and the little bit of irridescence looks like irridescent green spider mouthparts. Even the white spot further down the body suggests the spot often seen on the back of a spider.
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Adaptation: Mimicry. This is another somewhat spidery looking fruitfly, though in this case, it's the spotting along the thorax that reminds me of jumping spider eyes. Some study has been done on spider mimicry in the genus Ceratitis, though not on this species (as far as I can find).
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Adaptation: Mimicry. Sadly, EOL has no photos of these. They are incredible. Google one. These flies have spotting that resembles ants, or perhaps ant-mimic spiders, on their wings. Either way, they are thought to use these spots to confuse approaching predators... or do they? All hypotheses must be tested! Anyone need a project...?
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Homoplasy: convergence. Conglobulation -- the ability to roll up in a tight, defensive ball. This is an interesting example of convergent evolution. Pillbugs (crustaceans), pill millipedes, pill roaches, and armadillos (mammals) can all conglobulate, but it is due to selection for similar predator-avoidance strategies, rather than evidence of relatedness. It's homoplasy, not homology.
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. This is a nice example of a Passiflora species with egg-mimic nectaries (the yellow spots) on the leaf blade. These protect the plant in two ways. They are similar in color to the eggs of the Passiflora-munching butterfly Heliconius, which will avoid laying eggs in places where there are already lots of other butterfly eggs (too much competition). These nectaries also secrete sugar, attracting ants which will also eat insect eggs or young caterpillars that happen to be around.
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