Botany

How Plants and Animals Exploit Ant Behavior for their own Benefit



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Ants impose heavy selection pressures on both plants and animals in their local community. Formicidae is an abundant and diverse arthropod family that has expanded to exploit nearly every lifestyle available to creatures of their size and is comprised of seed predators, carnivores, nectar feeders and fungal gardeners. The indisputable evolutionary success of ants is largely due to their ability to communicate with each other via chemical pheromones and their acute sensitivity to other biochemical cues. These pheromones have contributed to remarkable foraging efficiency, division of labor, and colony defense. For example, army ants have developed such an effective communication within the colony that organized en masse attack and consumption of prey as large as small mammals is possible. Clearly, ant colonies form an information network that is not unlike a computer. Like computers, the chemically programmed ant is susceptible to evolutionary "hackers" however the consequences of this biological infiltration aren't always quite so insidious.

The Unusual Suspects
Plants from over eighty families have evolved seeds that exude a conspicuous appendage called an elaisome. Elaisomes are nutritious; lipid rich seed appendages that are thought to promote dispersal by ants. The plant benefits from this symbiosis when ant workers collect these seeds, return to their nest, consume the nutritious elaisome and leave the seed underground but intact. Although seed harvesting ants are considered important seed dispersers, they often collect and consume both the elaisome and seeds, thwarting the plant's reproductive strategy. However, some plants have remedied this loss and recent studies suggest that these types of seeds may have actually evolved to attract predacious ant species rather than seed harvesters. Why would carnivores suddenly show interest in plant material? Curiously, the fatty acid composition of the elaisome is more like an insect hameocoel than which seed they are attached. In other words, the ants' chemical perception of an elaisome is that of a dead insect prey. This strategy not only distributes the seeds in areas favorable to germination and growth but also reduces losses by seed harvesting ants.

A few insect species have also evolved a strategy similar to myrmychorous plants. The eggs of phasmatid stick insects exhibit suspicious resemblance to myrmchorous seeds and bear a similar appendage called capitula that can be removed without any loss of egg viability. The behavior of many stick insect mothers reflect their symbiotic dependence on ants, female phasmatids oviposit on foliage and then indifferently flick their eggs to the forest floor. Since their newly orphaned young take anywhere from 1-3 years to hatch, they are quite vulnerable to desiccation, predation or parasitism by wasps. Why then would these deadbeat mothers abandon their progeny in the face of such dangers? They are betting on the ants, collecting and transporting their babies to the safety of subterranean nurseries. Much later, the phasmatid nymphs emerge from their foster home largely unscathed and ready to propagate the next generation,

How can human exploit the ants' chemical programming? With daycare costs on the rise, young working couples struggle to balance family and career. Since human parental investment has become so expensive, alternative child-rearing strategies are imperative. Perhaps, instead of imprisoning are modern day computer hackers we should direct their efforts in a more purposeful direction, manipulation of the ant behavior. However, even if bioengineering of a human capitulum is successful, formicine foster care does pose some social problems. Because of our tendency to imprint, children raised in this environment may be unable to think independently, have deplorable eating habits (regurgitation) and boys would most certainly suffer significantly from gender identity issues

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