Local Adaptation, Infectious Diseases, Sexual Reproduction, and Extreme Conditions in Biology
Identifying Local Adaptation in Reciprocal Transplant Experiments
In a reciprocal transplant experiment, researchers could place organisms, like deer mice, with dark and light phenotypes in environments with dark soil and light sand. They would then observe the effect of predation on these different phenotypes. This helps to determine if a phenotype is locally adapted to a specific environment.
Why Bats Transmit Infectious Diseases to Humans and Domestic Animals
Bats make up 20% of all mammal species. They are also social, so they live in large groups in which infectious diseases can spread rapidly. This becomes an issue where bats are in close contact with humans, directly or indirectly. There is also a lot of “spill-back” that occurs from bats. For example, the Nipah virus first emerged in abattoir workers on pig farms in Malaysia because bats carrying the virus roosted in trees directly above the pigs, passing it when they defecated, which in turn spread to the workers. There was a similar occurrence with great flying foxes and the Hendra virus in Australia.
Understanding “Spill-Over” and “Spill-Back” in Ecological Medicine
“Spill-over” refers to infectious diseases being spread between wild and domesticated animals, sometimes spreading to humans. “Spill-back” also refers to infectious diseases that are spread between wild and domesticated animals. Two important examples are rabies and rinderpest. Rabies is a huge issue in developing countries because stray dogs and jackals carry it and infect humans and other carnivores. Rinderpest originated in domesticated cattle brought to Africa. Wild bison were infected, and the disease was passed along between domesticated cattle and wild cattle.
The Evolutionary Paradox of Sexual Reproduction
Sexual reproduction is costly because it requires energy to produce sex organs. In addition, mating can be risky due to factors like competition between males. Finally, only half of the genetic information is passed on to offspring. However, sexual reproduction is favored in variable environments because it increases genetic variation, and harmful mutations can be removed from the population over time.
Sexual Selection: The Case of the Peacock’s Tail
Traits like showy feathers in peacocks are costly and increase predation risk, overall decreasing survival. However, these traits continue to persist due to female choice and sexual selection. Peahens, and females in other species, choose to mate with males with showy feathers or extravagant plumage because it indicates the male’s fitness, since they can produce these very costly feathers. Female choice is a form of sexual selection in which traits that increase chances of reproduction are passed on. This demonstrates that even traits that seem detrimental to survival can evolve if they enhance reproductive success.
Avoidance Strategies for Dealing with Extreme Conditions
Two avoidance strategies that organisms use to deal with extreme conditions are hibernation in certain mammals and alternate forms of photosynthesis. Chipmunks, bears, and other mammals hibernate during winter months when there is a shortage of food. They decrease their respiration and heart rate to conserve energy until food becomes more readily available. Reindeer have a more extreme form of this where they shut off their circadian rhythm completely. While most plants undergo C3 photosynthesis, those in arid environments undergo C4 photosynthesis or CAM photosynthesis. In C4, photosynthesis occurs primarily in bundle sheath cells with increased CO2, and in CAM, stomata are opened at night rather than during the day to minimize water loss.