Option E.6 – Further Studies of Behaviour
E.6.1 – Describe the social organisation of honey bee colonies and one other nonhuman example
Social organisation in some form is a necessary element for the survival of a species. For some, this may only occur in order for mating to take place, whilst other form permanent communities. Within these communities, there will be some kind of order or hierarchy, which is more defined for some species than others.
Honey Bee (Apis mellifera)
Bees are not able to survive unless they are part of a community. Each community consists of 20 000- 80 000 individuals living together in a hive, including:
- One reproductive female, or queen bee
- Thousands of sterile females, worker bees
- A few hundred fertile males, or drones
- Eggs and larvae that are being reared.
All the bees will work together to perform the tasks of nest building, food gathering and rearing young. The eggs are laid in wax cells, with one egg per cell. The queen lays about 1500 eggs each day. Once the fertilised eggs hatch, they will feed on pollen and nectar, and develop into workers. On average, a worker bee will live for about 6 weeks, and in that time, they will rotate through a number of roles within the community:
1. Nurse bees – Tend the growing larvae, build fresh comb cells
Only a select number of eggs will be fed on royal jelly. This is rich in proteins and will cause them to develop into queen bees. Each queen will survive 2-5 years. She will mate once, and store the sperm in her abdomen for her entire lifetime. Using this, she will establish a new colony. The queen also produces a volatile hormone that controls the activity of the workers.
If the queen lays an unfertilised egg, it will still hatch, despite the fact that the cells are haploid cells. The will mature into drones, which live for about five weeks. These are the largest bees in the hive and do not have stings. They do not have a role in the hive but will leave with any new queens in order to mate with her and then die. The queen mates with multiple drones.
Worker bees are sterile females. Depending on the season, they will live for 6 weeks to six months. They provide the queen with a constant supply of royal jelly to help her continue reproducing. She will lay as many eggs as the workers can handle. Once she begins to run out of sperm, the workers will prepare to replace her. Workers have the most roles in the hive, including cleaning out the cells, feeding the brood, caring for the queen, removing debris, handling incoming nectar, building combs, guarding the entrance, converting pollen into honey and foraging for food.
The communication methods used by bees include dances and secretion of certain chemicals. The dance is called the waggle dance, and communicates to the other worker bees about the location of food in terms of distance and direction from the hive.
Baboon (Papio cynocephalus)
These are ground-dwelling primates, which live south of the Sahara, in Africa. Their habitats include woodland savannah, grassland, acacia scrub and sub-desert. Their communities are called troops, and consist of 10-200 baboons. Each troop occupies a large territory, and will usually avoid other troops. They do not defend their territory, and many territories will overlap.
The social order of the troop is organised based on physical dominance. Some females are ranked as leaders. They communicate with each other using various gestures. Individual baboons tend to be very emotional and highly motivated. They develop close relationships with the other baboons in the troop through activities such as grooming each other. Males will move in and out of different troops. They are slowly accepted into new troops through friendship with females in the troop, and may help to defend the female and her offspring.
The risk of death increases when an individual is too far from the group, so they have mutual alarm systems in place to warn others of danger. These are especially important for when the troop members separate to search for food. Under most circumstances, the troop will flee from danger; however the males may still deal with minor predators.
The female baboons mature and begin mating once they are about five years old. For a few days of each cycle, they become more receptive to the males. Males become mature at about ten years old. The females are promiscuous, which means that they will have multiple male partners in their lives. Unlike other species, baboons do not have a mating season, so the females are available almost all the time. In fact, most females will spend the majority of their mature lives either pregnant or nurturing young. The offspring must be carried until they are able to move independently, and will be suckled for about 6-8 months.
E.6.2 – Outline how natural selection may act at the level of the colony in the case of social organisms
The process of natural selection affects the gene pool of populations. Certain characteristics may improve an individual’s chance of survival and breeding. Those that lack these characteristics may still survive, but their chances of passing on their genes may be significantly reduced. The result for a community is like that of a whole population – it leads to the selection of favourable genes, causing gradual evolution and adaption within the community.
In the example of the baboons, the troop is constantly moving and individuals must keep up if they are to survive. If they become ill or injured, they will be left behind and lost to predators. Baboons do not have a defined social structure, but this cohesion of the troop is an essential element, reinforced by natural selection.
For the honey bees, the majority of the bees in the hive to not reproduce but work their entire lives for the support of the colony. This is an altruistic tendency. The hive is dependent on their work for the survival of the community.
The genetics of a bee colony are interesting, as all the bees come from the same queen. Since drones are haploid and the queen is diploid, this means that all of the bees in the colony have ¾ of their genes in common. All the workers are closely related to each other, and will also greatly resemble the next generation. The organisation of the colony favours the survival of the genes of the workers.
E.6.3 – Discuss the evolution of altruistic behaviour using two non-human examples
Altruism is when an organism lowers its chance of survival in order to raise the chances of survival of another organism. However, parental care is not included in this definition.
Worker bees spend part of their lives protecting the hive, and will attack any intruders. This usually involves stinging the other intruder – a fatal move for the guard bee. A bee’s sting cannot be removed, so the bee tears away part of their abdomen and will soon die.
Since the bee that dies shares many genes with the bees it is protecting, the altruistic gene would also be with them. Such behaviour benefits the giver in that their genes may still be preserved in those they are protecting.
Altruism may also be used for benefit of a larger community. Baboons share their habitat with another species called Vervet monkeys. These monkeys have a number of different alarm calls that specify the type of threat being posed. The monkey that raises the alarm could have simply protected itself and increased its own chances of survival, but by raising the alarm, it was also able to protect all the other monkeys in the community.
E.6.4 – Outline two examples of how foraging behaviour optimises food intake, including bluegill fish foraging in Daphnia
Foraging is the process of searching for, obtaining and consuming food. When animals forage for food, the process of conditioning is important for their learning. They are exposed to a range of smells and tastes, which they will then learn to associate with other things, such as illness or benefit. If an individual has an adverse reaction to a food of a particular smell or taste, then they will associate them together. From that point, they will avoid any food of that taste. This is valuable to the chances of survival of the organism as it allows it to avoid harmful foods. In addition, it allows them to more rapidly identify food that is of high quality and beneficial to the organism. Unlike with other examples of conditioning, taste aversion is less likely to become extinct. This means that a single encounter with the taste can cement the individual’s response.
Honey bees forage for pollen and nectar from flowers, which is stored in the honey sac or on the hairs of its body until they return to the hive. This task is performed by the worker bees. Younger bees will go out and survey the area for sources of pollen and nectar, and then report their findings to the rest of the hive through a waggle dance. They are able to specify the direction and distance to the food. This increases the amount of food that can be collected by the hive.
Bluegill Sunfish (Lepomis macrochirus)
Bluegill sunfish live in freshwater ponds in the northern hemisphere. They feed on the crustacean Daphnia. The size of the population of Daphnia is variable, so sunfish must adapt their feeding behaviour to account for these changes. This is called optimal foraging theory.
When there is an abundance of Daphnia in a range of sizes, the sunfish will seek out the largest ones, even though this may require them to expend more energy to travel larger distances. The sunfish will regain this energy, and more, from the larger prey, making the expenditure worthwhile. Pursuing a single, large prey on average is more worthwhile than pursuing multiple, smaller ones.
On the other hand, if there is a shortage of Daphnia, the sunfish become less selective of their prey and will feed on any sized one that it comes across.
E.6.5 – Explain how mate selection can lead to exaggerated traits
Sexual reproduction means that individuals must select a mate with beneficial characteristics that will increase the chances of survival of their young. Many species will have a selection process for choosing a mate.
Individuals of the same sex with have to compete for access to individuals of the opposite sex, meaning that those with an advantage can have a higher number of offspring. As a result, many species have evolved exaggerated traits to attract the attention of the opposite sex, increasing their chances of mating. However, it can also reduce the individual’s chance of survival, making them more vulnerable to predators. Since mate selection is quickly followed by mating, this does not matter as much, as the individual has already passed on their genes. This selection has led to the differences in size, colour and shape between males and females of the same species.
For example, male deer have large antlers. These are used aggressively against other males when they compete over females. On the other hand, male peacocks have large, colourful tail plumage to attract the attention of females. However, the large feathers cause the male to move more slowly when it is being pursued by predators. Therefore, if a male is able to survive despite this hindrance, this indicates that he must carry other beneficial traits, and make him a better mate. Some females may develop certain characteristic when they are ready to mate, such as emitting certain odours to attract a mate.
Mates must also ensure that there is appropriate territory available where they can rear and feed their young. When this has been found, the aggressive behaviour or calls from the individual can indicate to potential mates that they are ready.
E.6.6 – State that animals show rhythmical variations in activity
Animals have many rhythms to their behaviour, ranging from daily (diurnal) to yearly (annual) rhythms. These may be adapted to help increase the chances of survival for the organism.
E.6.7 – Outline two examples illustrating the adaptive value of rhythmical behaviour patterns
Different animals are active during various parts of the day or night depending on their feeding requirements and for their own survival. The cockroach (Periplaneta) is found in human households, feeding on waste that is
The cockroach (Periplaneta) is found in human households, feeding on waste that is left behind. It is active when it is dark for the humidity and reduced danger from humans. Hence, it is a nocturnal organism. If its normal light/dark cycle is interrupted, its internal clock is a bit longer than a 24-hour clock. This internal clock is independent of outside stimulus, or endogenous.
Although their body clock is independent, they must still respond to outside factors. Experiments have been conducted on cockroaches where the dark period was extended. Although the effect was not immediate, it was shown that the cockroaches will rapidly adapt their daily cycle to compensate for the earlier onset of darkness.
This ability to adapt is essential for the cockroach to be protected from its predators. It must maintain a daily cycle that allows it to explore for food in the dark, when conditions are more humid.
Many animals will only breed during a specific time period of the year when the conditions for rearing young are optimal.
The roe deer (Capreolar capreolus) is found in forests of Europe and Asia. They require a habitat that offers privacy, shelter and food. Kids are born in summer when there is flush in the vegetation. This allows for the mother to have a nutritious diet to provide better quality milk.
Deer will mate in autumn, when the mother is still underweight from winter. To cope with this, the blastocyst will not implant until much later in December or January. Depending on how good conditions are, two or three may implant, but this is reduced when the conditions have been unfavourable. This protects too many offspring from being born when their survival is at risk. This shows that the deer have the ability to adapt their rhythmic mating cycle to their environment.