How similar are plants and animals?
/This is the first of my blog posts wherein I'll share my thoughts on scientific papers I read. The only unifying theme will be stuff that catches my eye, though I am typically drawn to behavior and ecology, often focusing on predator-prey interactions. Spiders may also feature prominently. Anyway, on to the paper!
The authors review similarities and differences in how plants and animals respond to the risk of being eaten. Spoiler alert:
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(http://australianmuseum.net.au/uploads/images/11950/frog%20caerulea_big.jpg)
All living things face similar challenges in the ultimate goal of passing genetic material through offspring into the future. Most (all?) organisms must avoid being eaten, whether by herbivores (enemies of plants) or predators (enemies of animals). Although these terms are somewhat murky (re: seed predators), it is clear that sensing and responding to the risk of being consumed would be beneficial.
Plants are different from animals in many ways, and two of the most obvious ones (movement and structure) are rather important when considering how individuals deal with the risk of being eaten.
Movement: Being rooted to the ground limits mobility, so plants often respond to herbivores by changing growth patterns or moving substances (e.g., poisons) from one place to another. Animals, on the other hand, can usually get up and run away from danger, though while doing so they lose out on time spent doing other stuff (e.g., eating). A less obvious effect of the movement differences between plants and animals is the ability to acquire information about the risk of being consumed. Plants are fairly limited in the distance over which they can sense risk, whereas animals can sometimes sense a predator long before it is in danger.
Morphology: Compared to most animals, plants have relatively un-specialized organs with a high level of redundancy. Compare the breathing apparatus of a fern to that of a tern. Ferns breathe through their leaves, of which they have many. Terns breathe through their lungs, of which they have only one pair. Therefore, plants are more tolerant of partial consumption than animals, which feeds back into the fact that their responses to herbivores are slower than the responses of animals to predators. This tolerance of partial consumption allows plants to respond to very reliable cues (“I'm actively being eaten!”), whereas animals often rely on indirect cues (“Smells like a predator has been here recently”).
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(http://static.comicvine.com/uploads/original/0/2317/965346-tern.jpg)
I was surprised to learn that plants can defend themselves after sensing some indirect cues: herbivore eggs and herbivore mating chemicals (pheromones). The eggs will soon hatch into tiny lawnmowers of doom, built to demolish the plant on which they live. Chemical cues of mating herbivores are a precursor to eggs, so plants that “know” herbivores are mating nearby is enough to trigger defenses in preparation for being consumed. Pretty cool stuff!
Figure one from the paper lays out basic similarities and differences between plants and animals. Dogs clearly don't tolerate leg amputation well...
An interesting comparison can be drawn between plants and plant-like animals, such as corals. Animals that don't move share many limitations with plants, and they have evolved similar ways of managing the risk of being consumed. We always look for examples like this in biology, as they serve as strong tests of our hypotheses. If corals and plants did not share similar responses to the risk of being eaten, then arguments based on lifestyle (e.g., mobility and morphology) would not be as compelling.
(http://www.lowes.com/projects/images/how-tos/Lawn-Landscaping/choose-the-right-grass-for-your-lawn-hero.jpg)
(http://images.nationalgeographic.com/wpf/media-live/photos/000/013/cache/coral-polyps-henry_1387_990x742.jpg)
Overall, a sharing of ideas between plant and animal researchers will likely lead to new, productive research programs. An odd, but very interesting, collection of articles in Behavioral Ecology from 2013 contains an interesting discussion between plant and animal biologists about if and how plants may communicate with each other through sound. Continued cross pollination between researchers in these historically separate fields is rather exciting and should be fruitful (see what I did there?).