BEYOND THE HIVE
The Loss of Genetic Variability All the breeding techniques listed above can result in cultivars drawn from native species, but the resultant plants contain just a small subset of all the genetic variations that exist in the original wild population. Selection thus reduces genetic variation. Any alleles (gene variants) not contained in the selected plants simply never appear in the offspring. Losing genetic variability is troubling because we can’t
see what’s missing. It could be something detrimental to the plant itself, like drought tolerance, disease resistance, or shade tolerance. Or it could be something that negatively affects the attractiveness to pollinators, such as its scent, color, or ability to provide all the necessary amino acids to the next Just because bees collect pollen doesn’t mean it’s
nutritious. Honey bee foragers, for example, are known for collecting sawdust and coffee grounds, only to have it nixed by nurse bees back at the hive. But such collecting of “junk food” is a tremendous waste of time and energy for the provider collecting all the food—and no crew to reject the bad stuff—an infusion of inferior pollen could weaken or destroy the entire brood nest.
Crossing Back into the Wild As I mentioned earlier, sometimes hybrids remain open- characteristic as a good thing because it means genetic diversity is alive and well. Variations exist among the individuals, and they freely cross with one another and produce a range of genetically diverse offspring. Some alleles were lost during the selection process, but an open-pollinated, seed-producing subset is more robust than a clone. However, not everyone agrees that an open-pollinated
nativar is a good thing. They fear that the nativar, if planted near unselected wild types, will cross with them, altering the genetics of the offspring. Because the genetics of the nativar are heavily weighted toward certain characteristics and against others, biologists fear future generations of the wild type will change to be more like the nativar. If the nativar has a hidden negative attribute—such as inferior nectar or pollen production—the wild type may become less supportive of pollinators. In such a case, a nativar may become invasive, displacing a robust, pollinator- supporting plant with an inferior lookalike.
Losses in the Selection Process If you’ve spent much time watching pollinators in the wild, you know that many of the plants they prefer are not spectacular from a human point of view. Blooms are often small or nondescript, some so tiny you can barely see them.
blossoms that hug the ground or open beneath a low canopy of unremarkable foliage.
gardeners who want to beautify their homes. For this strictly growth habit. If it’s “pretty” to the human eye, it is more apt to sell at the local store. To achieve genetics that sell, the breeder chooses plants that show the desired trait and inbreeds them, often backcrossing until the trait becomes predominant. This yields what some breeders call a “slice of the gene pool” because many genes are lost in the attempt to amplify the ones desired by humans.
Which Genes are Lost? Unfortunately, when we select for desired traits, we inadvertently select against other traits. Often the traits that disappear are not visible, so we may be unaware of which genes are lost. For example, the plant may lose resistance to a particular disease, drought tolerance, or resistance to lodging Cultivars may lose their attractiveness to pollinators for many reasons. The selected plant may be less attractive to pollinators or completely unattractive. Some changes may negative changes are invisible to us. Genetic changes that may affect pollinator acceptance include: • • •Number of petals •Changes in scent •Variations in the rate or timing of nectar secretion •Changes in sugar content of the nectar •Variation in the amino acid content of pollen •Variation in the amount of pollen •Bloom times •Height of the blooms •Chemical composition of the foliage •
Alterations to a plant's DNA may have substantial effects on the biology and chemistry of a plant even if those changes make our plant more colorful or compact, we may make it unpalatable to pollinators.
Those Bad-Tasting Leaves An example of an unfortunate change occurs when breeders select plants for red or purple leaf colors. These color shifts are popular among gardeners because they provide a kaleidoscope of foliage that is pleasing to the eye. But for many insects, these leaves are inedible because they are high in anthocyanins.
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