5b. Hymenoepimecis argyraphaga is …show more content…
a parasitic species of wasp. When it stings its host—a spider—it deposits its eggs onto the spider’s abdomen. When they hatch, the larvae use the spider to build webs in an irregular form. By injecting chemicals into the spider, it forces its host to spin a reinforced web, repeating over the same spot up to forty times before moving on. The larvae then kill their host spider and scrap its body on the ground. They then use the newly made web to hang their cocoon so that they can become a mature wasp, thus restarting the reproductive cycle.
5c. Dicrocoelium dentriticum, or lancet liver fluke, is a species of worm that finds its home inside of sheep and cattle livers. When mature flukes lay their eggs, the eggs are deposited on the ground through the sheep feces. When snails feed on the feces, they consume the eggs along with it. The eggs will hatch within the snail and exit the snail through its slime. Ants eat the snail slime. In order to find a new host sheep, the flukes will chemically manipulate the ant’s mind, causing it to flee the colony at night and climb to the top of a blade of grass, awaiting a hungry sheep. If the ant isn’t eaten, it will continue to return each night until it is consumed along with the grass. The life cycle of the fluke is then restarted in its new host.
5d. Spinochordodes tellinii is another worm species. It lives inside grasshoppers. When S. tellinii reach maturity, they release proteins into the grasshopper that cause it to walk into the nearest water source. The worm exits the grasshopper as it drowns and swims away to reproduce with other worms.
5e. Toxoplasma gondii is a parasite that can survive in almost all warm-blooded animals, but can only reproduce successfully in cats. The parasite will copy itself inside of the host and travel to the brain and muscles by means of the animal’s bloodstream. They will then release chemicals that alter behavior. The effects are particularly helpful to T. gondii in mice and rats. The chemicals cause them to get fatter and move more slowly. They also seem to forget that cats are their natural predators and are actually attracted to the scent of cat urine. This brings T. gondii to a new host cat where it can sexually reproduce with other T. gondii.
5f. Enterobius spp. or the pinworm is a common human parasite. While inside the host, they lay their eggs on the skin of the child’s bottom. They also leave allergens that cause the child to scratch and itch at the area, fixing the eggs under their fingernails. Whenever they touch things, they will deposit those eggs. If another child then touches that thing and ingests them, the cycle starts again and the new pinworms will hatch in the new host.
5g. Cholera is a disease that’s transmitted through water. It causes severe diarrhea. The diarrhea actually helps V. cholerae to reproduce. It provides a pathway into the water system. On top of this, the more virulent the disease is, the more diarrhea is excreted, and the more disease is spread into the waterways, allowing it to reproduce. Upon drinking the infected water, the cholera parasite will enter a new host and repeat the process.
5h. Plasmodium spp. is a protozoa that transmits malaria. It makes the infected person immobile, thus giving mosquitoes—the disease’s main vector—easy access to the disease. This allows them to spread it to the next unsuspecting host. This high virulence is what allows the protozoa the best conditions for reproductive success.
6. Transposons and retrotransposons are types of jumping genes. They were first discovered by Barbara McClintock when she found parts of DNA moving from one section of the genome to the other, and even copying themselves and reinserting in various parts of the genome. At first, it seemed random, but once scientists got a closer look at what was going on, they realized that there was significant evidence suggesting otherwise. First, the rate at which the jumping genes became active was greatly increased when the organism was stressed. Second, they had a tendency to jump to particular genes more often than others. It appeared that changes in the environment that were threats to the survival and reproduction of the organism can cause it to begin making changes to its DNA in hopes that the change will be beneficial for survival. Individuals who make a successful change, will be naturally selected for in future generations. It also appeared that the jumping genes “knew” that their chance of a successful mutation is higher when they jump to particular areas on the genome, so they stack the odds in their favor. Retrotransposons work in a similar fashion, only they copy themselves onto the RNA first and then they use reverse transcription to modify the original DNA as opposed to the other way around, similar to a retrovirus.
Chapter 7 – Methyl Madness: Road to the Final Phenotype
7a. Epigenetics is aimed at explaining how offspring can inherit acquired traits without changing their DNA through methylation of certain genes. The mother’s nutrition while she is pregnant is a factor believed to play a role in these epigenetic phenotype changes. A study with the agouti gene in mice showed that by giving pregnant females better prenatal care, they could have thinner, healthier baby mice less prone to being overweight, despite their genetic coding for being fat and yellow. Chemicals had lodged to the agouti gene and suppressed its expression.
7b. A similar phenomenon concerning epigenetics occurs with changes in the conditions of the environment. In the case of the vole, mothers will give birth to babies in which their fur thickness is seasonally appropriate. Similarly, a species of flea, Daphnia, will yield babies with larger spines if the predatory threat is high in the environment. A similar principle applies to desert locusts, who will produce more colorful offspring specialized to better camouflage when food levels decline. They will also tend to isolate themselves. However, when food is abundant, they feed off of the surplus of food. As food again becomes harder to find, they gather and eat together and use their abundancy to protect against predators. Again, environmental conditions change the traits of offspring in a particular lizard species. If the mother smells a predator—a lizard-eating snake—she will ensure her babies are born with longer tails and a broader build to lower their chances of becoming prey. These examples are known as predictive adaptive response. In other words, the conditions the mother encounters during her pregnancy affect the phenotypes of her offspring without changing the genotype as a way to give her babies an advantage for survival. The genes that made the babies better adapted to the environment were “turned on and off” through methylation.
7c. Parental care seems to have an impact on how babies grow and develop in the early stages of life. An experiment with rats supported the hypothesis that maternal attention gives babies better developed social skills. To ensure that the social inclination wasn’t passed on through genes, the rats were assigned a different mother to care for them than their biological mothers. Still, the rats given better care in the first few hours of their life grew up to have better social skills. When the genes were later analyzed, the DNA was still the same, only the pattern of methylation was different. This means that only the expression of the genetic code was modified, not the code itself, essentially turning on and off appropriate genes.
8.
Both the “savanna hypothesis” and the “aquatic ape hypothesis” attempt to explain the bipedalism of humans—our tendency and ability to walk upright, on two feet. According to the savanna hypothesis, our ancestors left the forests in Africa for the plains. The males hunted and needed to survey the horizon and walk a great distance. So, they began walking on two feet to better accommodate this need. This hypothesis also explains our larger brain size since smarter individuals were more adept at making and using tools. On top of this, it also states that we lost our hair because we overheated from all the hunting. However, this theory focuses on the males; in reality, the women and children should shape evolution as well. That’s when Elaine Morgan postulated a different idea, one that seemed to make more sense. After all, many quadrupeds cover distance much faster than humans; this provides much controversy on the distance coverage part of the savanna hypothesis. In addition, females have less hair than males, so it wouldn’t make sense that the evolutionary cause for hair loss is overheating due to hunting. It also doesn’t make sense that we’re the only land mammals without hair, despite the other animals hunting for food as well. That is better explained in Morgan’s aquatic ape hypothesis, which suggests a semiaquatic ancestor. This theoretical ancestor spent large amounts of time living and hunting in water, developing the ability to hold its breath and dive underwater to obtain food. Predator avoidance was easier given that the species could survive in and out of water. Bipedalism would have evolved to help go into deeper water without having to submerge the head. Having semiaquatic ancestry also may explain our downward-facing nostrils, a trait shared with a modern semiaquatic species that stands on two feet in water. The aquatic ape theory also shows our lack of hair as an adaptation to help us in the water. Other hairless mammals also live in the water, like
dolphins and hippos. The hypothesis suggests that our fat is attached to our skin to help us glide better through the water and use less energy while doing it. In addition, we float more easily. Lastly, it may explain why humans can successful give birth in water; our ancestors may have done the same. This hypothesis has fewer unexplained details in it and tells more about how our species may have evolved, making it appear the better, more likely truth.