Adaptation, Fitness, and Reproductive Success

ADAPTATION, FITNESS, AND REPRODUCTIVE SUCCESS

In biological systems, adaptation has three different meanings. First, it is the process that helps an organism fit into their environment so that it is evolutionarily fit. Second, it is a state that is reached by a specific population as part of the fitness process. Third, it is any phenotypic trait that is maintained because it has evolved through natural selection. Darwin believed that adaptation was a big part of natural selection.

Adaptation is directly related to the biological fitness of an organism. Gene frequencies in a population help to determine who adapts and who does not adapt. Sometimes, adaptation happens because more than one species coevolves in order to become entwined with one another in the evolutionary process. Teleology refers to the structure and purpose of the different body features of an organism, which contributes to their adaptation.

While adaptation relates to teleology, it is not the same thing. Adaptation is an actual process that happens because of the form and function of a body part. There are many parts of a plant or animal that can be called adaptations, which are things that increase the fitness of the organism in its environment. The diversity of organisms in the environment is dependent on two different things: speciation and adaptation. Adaptation does not lead to reproductive isolation but speciation does.

Adaptation is not simply having the ideal phenotype for a given environment. For example, an organism must remain viable at all of its different stages of development and must be viable as evolution progresses. Each genetic change and each phenotypic change in the different generations must be small because environments and the relationship between the organism and the environment are very complex. Even so, some adaptations have been very big, such as when eukaryotes were first developed in the evolutionary process by engulfing certain prokaryotes that led to the development of chloroplasts and mitochondria.

Adaptations help an organism survive in its particular niche. Adaptations can be physiological, structural, or behavioral. Structural adaptations can be seen, while physiological adaptations cannot be seen but are determined through biochemistry or microbiology. Behavioral adaptations are inherited behaviors, like instincts or the capacity to learn. Mating patterns, the ability to find food, and vocalizations are behavioral adaptations, while making slime, phototropism, and the making of venom are physiological adaptations. Other physiological adaptations involve the ability to regulate temperature and things that affect growth and development.

Adaptation is not the same as acclimatization, learning, and flexibility, which happen in life and are not inherited. Flexibility involves the capacity to live in different habitats. Acclimatization involves making physiological adjustments to the environment. Learning involves improving behavior performance and is not inherited.

The degree of flexibility of an organism is inherited but not flexibility itself. Certain herbivores like giant pandas and koalas are not very flexible because they can only live on certain types of food. Generalists can survive in many different types of conditions. These include most carnivores, crabs, rats, and humans. Humans can adapt to different altitudes by making more red blood cells. This is called acclimatization, which isn t heritable. Like flexibility, the ability to acclimatize is heritable, however.

As climates change in the world, so does the habitat. As the habitat is changed, so do the biota. The numbers of different species in a habitat always change. When the habitat changes, there can be a genetic change in the organism, there can be habitat tracking, and there can be extinction of the species. Only genetic change leads to adaptation. Habitat tracking basically leads to the movement of the organism from one place to a better habitat.

Genetic change involves natural selection that leads to certain organisms being better suited to the habitat. The genetic change can be structural or physiological. Adaptation is a process that never ends. Ultimately, though, there can be an equilibrium so that the species best fits its environment. If the habitat changes too rapidly, genetic change does not occur fast enough. This can lead to the bringing back of a population from near-extinction if they move or if enough genetic change has occurred. This is called evolutionary rescue. If it does not happen, extinction will occur.

Co-adaptation happens when two species are dependent upon one another. One species will adapt to changes in the environment and the other species co-adapts accordingly. This is basically what happened in the evolution of flowering plants and the insects that pollinate the plants.

Mimicry happens in some species as part of adaptation. There is a type of mimicry called Batesian mimicry, which was discovered by Henry Walter Bates, who studied mimicry in certain insects. This happens when insects that are palatable evolve to mimic those that are unpalatable so they don t get eaten by predators. This provides further evidence for natural selection.

There are downsides to every adaptation. Adaptations in one area can lead to maladaptation in another area, such as the development of feathers for penguins, who do not fly at all. Some

adaptations can be just as destructive as they are helpful. This highlights the imperfection of nature in creating adaptations for different species. Most adaptations are a compromise. An example of this is the camouflage in some animals that must be broken in order to display brighter colors during the mating season.

Even in humans, adaptation is a compromise. The human brain and hence, the human skull, is small and immature at birth by necessity. If the brain was larger and more mature, the infant could not fit through the birth canal and would not survive birth. This is known as birth compromise. The tradeoff is that human pelvises must be created for bipedal locomotion, which is considered a positive adaptation in humans.

Pre-adaptation happens when a population is well-adapted to the environment without having prior experience with the habitat. It can happen because a species already has a lot of genetic variability. This is true of microorganisms, that have such large populations that at least some of them will survive a given habitat.

Exaptation involves having a certain trait as an adaptation for another purpose that helps still another aspect of adaptation. Feathers, for example, on an ancient dinosaur were created for insulation but they have the added ability, called an exaptation, to fly.

There are also non-adaptive traits that have either a neutral or bad effect on the organism s fitness for a specific habitat. These traits are called spandrels, which are adaptations that have no specific function. Other traits may have been once adaptive but have later become either maladapted or completely unnecessary. These are called vestigial adaptations. Many organisms in nature, including humans, have vestigial organs. Wisdom teeth, for example are vestigial.

Extinction happens when an organism cannot keep up with the change in habitat. It happens when the death rate exceeds the birth rate for an extended period of time. Ultimately, the species disappears. Coextinction can also occur if one species becomes extinct and another dependent organism also becomes extinct. It can happen when the food chain becomes disrupted or when a flowering plant loses the insect that normally pollinates it.

Fitness is what represents the combination of natural and sexual selection. A genotype or phenotype can exhibit fitness. Either of these ultimately relates to the reproductive success of the organism. Fitness can be described as the average contribution an organism makes to the gene pool of the subsequent generation.

If an organism is asexual, its genotype gets passed on to each of its daughters so the genotype is more important than the phenotype. In sexual reproduction, the phenotype is more important

because only half of the organism s genome gets passed to the next generation. Fitness is not related to longevity but is instead related to the ability to pass on the genes to the next generation.

Fitness is measurable but isn t an exact number but is a probability that the genotype or phenotype will get passed on. It is a property of a population of a species rather than of an organism itself. An individual can have a genotype that is greater or less than the fitness of the total population.

Reproductive success is an organism s individual production of offspring per lifetime or per breeding attempt. It is not limited to the number of offspring that a single individual creates but also relates to the number of offspring that the offspring themselves make. A long life is not necessarily related to reproductive success.

A major factor in reproductive success is the parental investment an organism makes in order to ensure that the offspring have a better chance themselves of reproductive success. Mate choice and sexual selection are also important in reproductive success. Reproductive success is measured in longitudinal studies because it is measured over several generations.

Nutrition is important in reproductive success. The amounts of certain nutrients taken in at certain times of an organism s lifespan will play a role in the organism s ability to be reproductively successful. This is true of many types of species. A lack of nutrients can adversely affect the organism s mating capacity. Insects and mammals both are affected by the amount of protein, fat, and carbohydrates in the diet. Nutrition is most important in the premating time period in many mammals. For some, it is the carbohydrate content that is important, while in others, it is the protein content.

In humans, there is an advantage to cooperative breeding, which helps in the investment required to raise a child to adulthood. It takes parental involvement and non-parental involvement. Throughout history, women have a greater reproductive success rate than men. Women have a greater investment in their offspring from the beginning. Males do not have a great investment in the offspring from an evolutionary standpoint. In the hunter-gatherer environment, adequate birth spacing helped to ensure the better survival of each of the offspring.