ADAPTATION AND REPRODUCTION Flashcards
- a trait that makes an organism more suited to its environment. It is also the process by which a population becomes dominated by organisms that are
suited to their enivornment.
Adaptation
- a measure of an organism’s ability to survive and reproduce in its specific environment.
Fitness
Adaptation can be:
• Anatomical - changes to physical structures
• Physiological - changes in function to those structures
• Behavioral - changes to behavior
In ? the English naturalist ? published
? . The book contained two major
arguments: First, ____ presented a wealth of evidence of evolution. He said that all living things on earth today
are the descendants - with modifications - of earlier species. Second, he proposed a mechanism - natural selection - to explain how evolution takes place.
1859, Charles Darwin, The Origin of Species
Evolution involves two interrelated phenomena:
Adaptation
Speciation
In ______, over the course of time, species modify their phenotypes in ways that permit them to succeed in their environment.
adaptation
In ______, over the course of time, the
number of species multiplies; that is, a single species can give rise to two or more descendant species.
speciation
In fact, Darwin maintained that all species are related; that is, any two species on earth today have shared a common ancestor at some point in their history.
• Living things produce more offspring than the finite resources available to them can support.
• Thus, living things face a constant struggle for existence.
• The individuals in a population vary in their phenotypes.
• Some of this variation is inheritable; that is, it is a reflection of variations in genotype.
• Those variants best adapted to the conditions of their life are most likely to survive and reproduce themselves (“survival of the fittest”).
• To the extent that their adaptations are inheritable, they will be passed on to their offspring.
Natural Selection
equates to natural selection, which describes the adjustment of genes or
behavior of organisms over generations in order to suit changing living conditions. Generally, those able to adapt survive to pass their genes on more often, while those who cannot have their genetic traits lost to time.
Survival of the fittest
sometimes, predators act as the conditioning element in the process. If
a habitat has yellow and blue bugs, but birds prefer the taste of blue bugs, there will be fewer blue bugs to continue the species. On the other
hand, yellow bugs may be more visible if the habitat has darker foliage, meaning birds may go for the yellow bugs more often than the blue.
Predatory Preferences
having access to food and resources also creates natural selection processes. If there is a habitat with both long and short neck giraffes and tall trees in the habitat, the long-necked giraffes will have primary access to food. On the other hand, if there are only small trees and plants, the short-necked giraffes will have primary food access.
Access to Food Without Adaptation
often dictate who is more favored within the habitat. Galapagos finches with larger beaks survive better during drought, while those with smaller beaks survive better during rainy climates.
Depending on the habitat, this would result in natural selection between the two variants.
Climate Conditions
the peppered moth was originally pale with spots making them visible to
predators when London underwent the
Industrial Revolution, which adorned the trees with dark soot. The moths turned darker within months to survive, and light peppered moths resurfaced after this era had concluded.
Changing Colors
of course, repopulation is a strong influence on species’ survival. Female
peacocks generally select partners with bright and large plumage. Thus, male peacocks have adapted, and males without bright plumage are now rare. This is known as ‘sexual selection.’
Mating Preferences
warrior ants use chemical signals to communicate with each other, which indicates that others should not
attack them. Over time, ants from different colonies learned to imitate these signals in order to infiltrate enemy colonies, giving them advantages within the habitat.
Communication Strategies
in some cases, species can change rapidly in order to access food. Originally, the moray eel did not create
enough suction to catch prey but later grew a subsequent set of teeth and jaws in order to feed.
Access to Food With Adaptation
plants are often able to adapt quickly due to their shorter generation
cycles. The field mustard plant underwent a drought and shortened its growth stages by blooming early. It has rapidly evolved and can now survive in such climates.
Change in Growth Cycles
bacteria can adapt rapidly since they can produce numerous generations within a day. This makes them
capable of developing resistance to antibiotics, where the strongest of the bacteria will be the last standing and may even survive. Similarly,
insects may become resistant to pesticides
within a single generation.
Developing Resistance
occasionally, organisms are able to shrink and grow to adapt. Two
variants of rat species that live in trees were compared, where the larger rats broke branches, and the smaller rats were unable to move around easily. Over time, all of the rats were
approximately the same size, now able to move freely without breaking the habitat.
Growing and Shrinking
is a measure of reproductive success. Those individuals who leave the largest number of mature offspring are the fittest. This can be achieved in several
ways:
Fitness
The Measure of “Fitness”
• Survival (mortality selection)
• Mating success (sexual selection)
• Family size (fecundity selection)
any trait that promotes survival at least until one’s reproductive years are over increases fitness. Such traits are adaptations.
Survival
in sexual selection, one sex - usually
the female, chooses among the available males. Any inherited trait that improves the mating success of
certain individuals will become more pronounced in succeeding generations.
Sexual Selection
When ready to mate, female three-spined sticklebacks (fish) choose males with many Class II MHC alleles over males with fewer alleles. Class II alleles
encode the proteins that present antigens to the immune system. Presumably, the more of them you have, the greater the diversity of parasite antigens your immune system can recognize and defend against. The
females distinguish between the males by soluble molecules (“odors”) the males release into the water. How these “odors” are controlled by the MHC alleles is not known.
A culture of Drosophila set up with equal numbers of red-eyed and white-eyed flies of both sexes will, after 25 generations or so, end up having only red-eyed (the “normal”) flies in it. This despite the fact that white-eyed flies are just as healthy and live just as long
as red-eyed flies, i.e., they are equal in terms of survival. But, as it turns out, not only do red-eyed females prefer
red-eyed males, but white-eyed females do also.
Example of sexual selection
In other cases of sexual selection, one phenotype prefers to mate with others of the same phenotype. This is called ?
assortative mating.
The production of a large number of mature offspring is a measure of fitness. It stress mature because only they can pass these traits on to another generation. Some ways to do this:
• Earlier breeding. If some females become sexually mature earlier than others, their chances of leaving offspring are enhanced.
• For some species (e.g., fish, oysters), which provide little or no care for their young, fitness is measured by the number of fertilized eggs they produce.
• For species (such as ourselves) that take care of their young, selection acts to reduce family size (to a point). A large study in Utah (U.S.A) showed that in the 19th century, families with fewer children had more surviving grandchildren.
Fecundity Selection
Are Humans Exempt from Natural Selection?
It has been argued that advances in medicine, sanitation, etc. have removed humans from the rigors of natural
selection. There is probably some truth to this, but consider that of all the human eggs that are fertilized, fewer than half will ever reproduce themselves. The others are eliminated as follows:
Mortality selection
• Approximately 30% of pregnancies end by spontaneous abortion of embryos and fetuses or by stillbirth.
• Death in infancy and childhood claims another 5% or more.
Sexual selection
• Another 20% will survive to adulthood but never marry.
Fecundity selection
• Of those that do marry, 10% will have no children
Darwin’s Finches - as a young man of 26, Charles Darwin visited the Galapagos Islands off the coast of Ecuador. Among the animals he studied were what appeared to be 13 species of finches found nowhere else on earth.
• Some have stout beaks for eating seeds of one size or another (#2, #3, #6).
• Others have beaks adapted for eating insects or nectar.
• One (#7) has a beak like a woodpecker’s. It uses it to drill holes in wood, but lacking the long tongue of a true woodpecker, it uses a cactus
spine held in its beak to dig the insect out.
• One (#12) looks more like a warbler than a finch, but its eggs, nest, and courtship behavior is like that of the other finches.
Darwin’s finches. The finches numbered 1–7 are ground finches. They seek their food on the ground or in low shrubs. Those numbered 8–13 are tree finches. They live primarily on insects.
