In this case, if she could just clone itself without needing to mate, her daughters could quickly spread and outcompete the other aphids. Just how common is it to get a random useful mutation? Is this scenario even likely? You may remember that beneficial mutations are pretty rare. It turns out there are a lot of aphids — as many as thousands on just one plant! There are a lot of aphids! Image from Wikimedia.
Even though you have to find a mate, there are some nifty benefits. Every time sexual reproduction happens, the offspring gets some DNA from both parents. It inherits a unique genetic combination, different from either parent. And when the environment changes often, this reproduction strategy is better.
You can think of it like a card game. Every animal has a hand of cards that it is dealt at birth—these are its genes. It might have a card that tells it what color it will be, and another card for how fast it can run. If an animal goes through asexual reproduction, it just passes on the same genetic cards to its child. One lucky aphid got a mutation that gave it pesticide resistance. And maybe a different aphid has a mutation that makes it better camouflaged.
But if an aphid needs to be resistant and camouflaged, they may be out of luck. As I mentioned before, beneficial mutations are rare. The fastest way to combine these two useful mutations together is with sexual reproduction. If the pesticide-resistant aphid and the camouflaged aphid reproduce, their offspring can inherit both traits.
This makes sexual reproduction the best way for a species to adapt to a changing environment. You can combine useful traits together more quickly. A lot of animals that do parthenogenesis are also able to reproduce sexually. This means that these animals get the best of both worlds: a way to reproduce quickly when times are good, and a way to have genetically different offspring if times are not so good.
In the fall, the soybean aphids mate and produce eggs. This way, the aphid can mix up its DNA for the next generation. Aphids on perennial ryegrass. Aphids pierce the plants with needle-like mouthparts to suck the sap. Click for closer view. The needle-like mouthparts used for piercing plants and sucking sap are visible beneath this aphid's head. Also note the humped back where the wings attach.
This area contains the musculature and other structures involved with flight. This humped back is lacking in the wingless aphids of the same species. Sex, or no sex? The idea of reproduction without sex might seem strange, but asexual reproduction makes sense for some organisms when conditions are good. Indeed, in addition to aphids and some other insects, a variety of other animals use a similar strategy, including the familiar water fleas Daphnia and numerous other small crustaceans, rotifers, and some other creatures including a few vertebrates.
And of course, asexual reproduction is commonplace among plants, fungi, protozoans, and bacteria. The explanation for this has to do with the relative costs and benefits of sexual vs. If an individual is doing well, its success is testament to a good combination of genes that work well under prevailing circumstances.
If living conditions are likely to be stable through the lifetimes of the offspring, genetically identical parthenogenetically produced offspring have a high probability of being as well adapted and successful as their parents, so asexual reproduction makes sense.
Another big benefit favoring asexual reproduction is that parthenogenetic populations can grow faster than sexual populations since every individual is a female giving birth to offspring. However, conditions might be different in the future, and different gene combinations might be necessary for success. Given this unpredictability, most organisms gamble for the future success of their descendants by reproducing sexually and even bacteria have means of exchanging genes, though in bacteria this is not called sex , because the mixing of genes through mating produces genetically variable offspring.
Though many of these offspring might be poorly adapted to the unpredictable conditions, there is a chance that at least a few in a genetically variable group will have "winning" gene combinations. This is analogous to buying lottery tickets all with different numbers vs. If the winning combination of digits cannot be predicted in advance, tickets with different numbers clearly give a much greater chance of stumbling onto the winning combination.
Actually, even 50 or fewer tickets with different numbers would give a better chance of winning than tickets all with the same number and this is the better analogy, since sexual organisms tend to reproduce more slowly because the males do not give birth to young or lay eggs. Evolutionary success is all about passing one's genes on to future generations, and doing so better than other individuals.
Indeed,"evolutionary fitness" the "bottom line" in evolution, and the driving force shaping evolutionary change by natural selection is defined as an individual's or genotype's probable genetic contribution to future generations. All currently living organisms are descended from ancestors that produced successful offspring. We don't encounter descendants from individuals whose offspring were unsuccessful, because they left no descendants. Even among the successful reproducers, the genes from individuals with fewer successful offspring tend to be replaced over time by the genes from those with greater reproductive success.
Host plants covered in aphids are rapidly depleted of their sap, and the aphids must move on. Hormones trigger the production of winged aphids, which can then take flight and establish new populations. All would be for naught if the aphids in cold climates just froze to death at year's end.
As days become shorter and temperatures fall, aphids begin producing winged females and males. They find suitable mates , and the females lay eggs on perennial host plants. The eggs will carry on the family line, producing next year's first batch of wingless females.
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