Overview:
By Karen Edgington
Each week, Signal Akron will help you in your gardening adventures with an excerpt from "The Root of It," a monthly newsletter from the Summit County Master Gardeners, Ohio State University Extension.
Picture this: you, strolling through your garden beds, morning coffee in hand, when your pleasant garden reverie halts abruptly at the rose bed.
Rose aphids cover buds that looked pristine a few days ago! Leaves are curling on your elm tree. A careful unfurling reveals the woolly elm aphid, hordes of them. And, how did all of those calico scales cover the lilac branches?
These three insects use a special reproductive technique to multiply quickly and take advantage of tender rose buds, unfurling elm leaves, and succulent lilac sap. This time of year they switch gears and reproduce asexually. That’s quite a feat!
The vast majority of animal species reproduce exclusively sexually — males and females get together to fertilize eggs, or in some cases just the sperm and egg get together. Each contributes half the genetic information required to create a new individual.
However, in some species, the egg develops into a fully functioning embryo without fertilization, with no DNA contribution from a male (parthenogenesis). The offspring created in this asexual manner are called “parthenotes,” and in most cases are female, an exact copy (clone) of the mother, carrying only her genetic material. In rare cases, the mother is able to modify cells that replace sperm and create males or offspring with varying genes. Amazing!
While some animals only reproduce asexually (obligate parthenogenesis), most parthenogenetic animals reproduce sexually, switching to parthenogenesis when the going gets tough, or when circumstances, such as a rich food supply, are favorable (facultative parthenogenesis).
Because she has no need to engage in courtship rituals and find a mate, a parthenogenic mother is able to spend her energy securing food and shelter and reproducing a LOT of offspring. In an environment in which conditions are favorable for that one cloning mother, her offspring will thrive, such as soybean aphids reproducing in a springtime soybean field.
Aphids, fruit flies, honey bees, ants and some wasps reproduce rapidly using facultative parthenogenesis. But scientists have found that obligate parthenogenetic animals have a higher likelihood of becoming extinct because of the limits of their inbreeding. A changing environment favors sexual reproduction, with its wide gene pool creating individuals that thrive in new and differing conditions.
Now picture this: you, strolling through your garden beds, noting that the rose aphids have peaked, and planning your control strategy; then seeing that the annual incursion of wooly elm aphids has begun right on cue, knowing they rarely do more than aesthetic damage. You stop at your honey bee hives and see them busy at work, putting up honey stores, which you will enjoy.
Parthenogenesis — another of nature’s remarkable survival strategies.
Look around!