Animals often live in numbers to avoid predation. One species that lives in groups are the Northern Bobwhites, a type of quails. These quails live in groups called coveys that may contain 2-22 individuals. The larger the group, the easier they can detect a predator. However this benefit is outweighed by increased competition for food in larger groups, supported by evidence that larger groups travel more each day. Smaller groups also move more, probably to search for other groups to join. The mix of costs & benefits suggest that groups of intermediate sizes get the bests of both worlds. And in fact, groups of this size have the best survival rates.
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Your current social status is influencing more than just your psychological well-being, but it also has physiological effects, determining how healthy you are. Being low on the social ladder can have a negative effect on the immune system. This has long been known, however there have been many questions about the biological mechanisms underlying these effects - until now.
A team of researchers turned to social groups of female rhesus macaques to answer these questions. Rhesus macaques are monkeys that live in hierarchical social groups, and are often used as a model to study the links between social status and physiology. Experimenters manipulated social rank by introducing monkeys into a new social group, and the order in which they were introduced determined their social rank - the first monkey introduced had the highest rank, and the last introduced had the lowest.
The researchers then drew blood from each monkey, and from the blood they purified immune cells called peripheral blood mononuclear cells (PBMCs). They measured gene expression levels in these cells to determine if variation in gene activity can be explained by social rank. They found 987 such genes, 535 of these genes were more highly expressed in higher ranked monkeys, and 452 of them were expressed more highly in lower ranked monkeys. This is significant because it shows that social rank is associated with gene activity in immune cells.
Furthermore, they found that dominance rank changes genes in such a way that just looking at gene expression data alone was enough to predict the monkey’s social rank with 80% accuracy. These findings prove that it is social environment that has an effect on gene expression, and not the other way around. However, they also found that this effect isn’t permanent - when a female monkey switched ranks, her gene expression levels did as well.
These differences in gene activity require certain regulatory mechanisms. The team of researchers found that variation in the expression levels can be partly explained by differences in tissue composition of each monkey. Variation in glucocorticoid (a type of hormone) regulation is another mechanism found that may account for the relationship between social rank and gene expression levels. There were also DNA methylation differences between different social ranks, suggesting that epigenetic changes might also be at work.
These findings are important implications, because they likely apply to human beings as well. This supports the idea that having a negative social environment may increase chances of infection and disease. But again, this effect is reversible - improving your social environment will have a positive impact on your immune system and overall well-being.
Gray bees are unique because they exhibit a mating behavior that is not seen in most other species of bees. Female grey bees burrow in the ground to build nests for their offspring. The males will then search for these nests, and dig into them to find emerging virgin females to mate with. This is unique in comparison to other species, because normally the male bees search for mates while visiting flowers. The reason gray bees exhibit this behavior is because female gray bees can only reproduce once in her lifetime. After this, she is no longer sexually receptive. Therefore, male gray bees must find virgins in order to pass their genes along, which is most easily done at nesting sites, where young females first emerge.
Lemmings are small mammals that live in the Arctic. Lemmings often kill themselves by jumping off cliffs. It was originally thought that they do this to regulate population size when there is overcrowding. This is a group selection hypothesis. Group selection is the idea that groups or species have individuals that self-sacrifice in order for the survival of the species. However, this is unlikely, because individuals do not exhibit behavior that is costly. It was eventually found that the lemmings are doing this for their own benefit, not to regulate population size. When populations get dense, some lemmings will leave their group to seek more food and reduced competition. Sometimes, they accidentally kill themselves when leaving the group by going off of a cliff. So, the suicidal behavior is not done on purpose, it is an accident resulting from leaving the group to seek new resources.
Research done on fruit flies show how hormonal signals may regulate animal sexual behavior. In flies, females may only mate one time, and after this they are no longer sexually receptive. Having offspring brings about a switch from sexual receptivity, to sexual refusal. This switch is regulated by a hormone called sex peptide (SP). Sex peptide is received from the semen of the male that the female mates with. It is proven that SP controls this switch because researchers experimentally blocked SP production of males using RNA interference. The females that receives semen from the males with blocked SP production did not become unreceptive after mating. Furthermore, a second test was done by blocking the female sex peptide receptor (SPR). When this was done, females would not become sexually unreceptive after mating and copulated over and over again. This is all evidence that hormonal signals may regulate animal sexual behavior.
Neoerectus phyllophagous (meaning “new upright leaf eater”) is a tall, bipedal mammal, reaching heights of 5-6 feet, with a thick tan to brown coat of fur. This rare mammal species found in the vast grasslands of the African Savanna. This is the only location in the world where N. phyllophagous is found, and these animals have acquired a number of adaptations that permit them to live in this unique, harsh environment. Located along the equator, the savanna is hot all year round, with temperatures ranging from 68-86° C. The animals have a number of homeostasis mechanisms to maintain a constant body temperature despite these warm temperatures, because overheating of organs can be fatal. One way they keep cool is by digging deep ditches in the soil to rest in. They do this because the soil on the surface is very hot from baking in the sun all day, so resting here would raise body temperature through conduction. However, the soil beneath the surface is significantly cooler, so resting here is beneficial. Neoerectus phyllophagous have evolved large, strong claws that help them efficiently dig these ditches. Another mechanism they use to keep cool is by licking their fur. This mechanism is similar to sweating. The saliva from their tongues will then evaporate from their fur, which cools the blood of the area they licked. This cool blood then circulates throughout their body, keeping their organs at stable body temperatures. They have evolved very long, strong tongues which helps them reach spots all over their body.
Their unique tongues have a second function for feeding as well. The savanna consists of expansive grasslands, with scattered bushes and trees. Since resources here are scarce, these herbivores must take what they can get. So, although the Acacia tree is armed with spiky needles to try to deter herbivores, the leaves of this plant are the staple food of N. phyllophagous. Their extremely long and muscular tongues allow them to reach between the needles to grasp and pull off the acacia leaves. They also may use their long claws to help push bare branches aside to access more leaves to feed on.
Many animals have daily and yearly patterns of physiology and behavior. These patterns are often controlled and regulated by the number of light and dark hours that occur in a 24 hour cycle. However, other factors may have an effect on this pattern. For example, black bears are often active at night, rather than the daytime, but this pattern changes when grizzly bears are inhabiting the same environment as the black bears. This is because grizzly bears are predators of black bears, and are active at night. So, black bears become more likely to be active in the daytime in order to avoid being preyed on by grizzly bears. This is an example of how predation can affect the daily pattern of behavioral activity of prey.
The immune system is used to fight off different things. One thing the immune system can fight off is cells. Specifically, they can destroy cancer cells. Cells go through certain checkpoints to ensure everything is working correctly. If the cells escape these check points, they may be on their way to becoming cancer cells. The immune system can recognize these cells that are not in check, and destroy them. The immune system can also recognize and fight off body cells that are infected with bacteria or viruses.
The immune system is also able to fight off free floating pathogens or toxins that are not inside of a cell. Pathogens are often viruses or bacteria, or any foreign invader. The pathogens or toxins will be found in fluid in the body, for example in the bloodstream of lymphatic system.
The adaptive mammalian immune system responds to a pathogen for the first time in a specific order. First, antigens from the pathogen invader will bind to antigen receptors located on lymphocytes. Next, these lymphocytes specific to the antigens multiply and become numerous. These lymphocytes then secrete antibodies, and the pathogen will be destroyed. After this, only memory cells will remain.
Although the adaptive immune system is very important, because it has “memory” of previous invaders, it is the second line of defense. The first responding line of defense is called the innate immune system. This starts with external defenses that prevent things from coming in, such as the skin, secretions, and mucous membranes. Next is the internal part of the innate immune system. This includes phagocytic cells, natural killer cells, defensive proteins, and inflammatory response.
During the breeding season, male British red deer often show aggression toward one another. This aggression is due to a hormone called testosterone running through their bodies. The hormone is creative by the testes of the male deer, and castrating some males caused them to show no aggression or sexual behavior. Furthermore, when the castrated males were given testosterone implants, they had a restoration of aggression and sexual behavior. These results prove that testosterone is the cause of aggressive and sexual behavior in male British red deer.