Key Area 4
(b) Reproductive behaviours and mating systems in animals
For all those animal-lovers out there! This is such a fantastic part of the course - full of fun and genuine interest. Courtship rituals of many different organisms are explored and we learn that, while males might put on a great show, it is often the female that remains firmly in control. Let's start with an image carousel, showcasing some interesting courtship behaviours and a National Geographic video on "Kinkiest Courtships".
A really fascinating insight into reproductive strategies from an evolutionary point of view in Humans. Does female mate choice change throughout a menstrual cycle - why? Unlike other primates, female fertile periods are largely concealed - what important evolutionary consequences did this have for our species? Click on the TED logo to watch the 15min video to learn more about this topic.
BBC iplayer: Attenborough's Life in Colour
The latest BBC nature documentary, "Life in Colour", presented by David Attenborough, "reveals the extraordinary ways in which animals use colour: to win a mate, to fight off rivals and to warn enemies". Perhaps you can justify the lie-in if you watch this at the same time!
Mating Systems
Mating systems are based on how many mates an individual has during one breeding season. These range from polygamy (polygyny and polyandry) to monogamy.
Monogamy
Most birds choose monogamy. This is for several reasons:
High level of parental care is needed to feed the chick.
It is unlikely that one parent could meet these feeding and protection requirements alone.
Male birds probably have a better chance in leaving more viable offspring by participating in parental care than searching for other mates.
Image shows Cape Gannets, who mate for life.
Polygamy (polygyny and polyandry)
Many male mammals choose polygamy for many reasons:
In mammals, the female is often the only food source.
Males may have a role in protection, but not feeding.
One male will often mate with many females in a harem, and protecting them and his offspring - seen in deer and lions.
Task 45
"Well, well Miss. What is the lion lady saying when the lion man pads up to the front door of the den with his wee harem of lady lion friends with whom he appears to have special relationships with? I think the animal kingdom are very open-minded. This one time, Miss, I...." Big Davie started.
"I'll stop you there Davie. I think, perhaps, I'm sensing one of your over-share moments..." butted in Dr M.
"Ah, right there, Miss. I....please go on, I have literally nothing to say on this topic whatsoever", replied Big Davie, with something of a rosy tinge to his cheeks.
Dr McRobbie announced the next task. We were to complete the table in our notes to identify the keyword associated with each definition.
"The keywords you require are:
Monogamy
Polygamy
Polygyny
Polyandry"
Big Davie started writing immediately.
To see what he wrote, click here.
What influences reproductive strategy?
Another factor that influences this reproductive strategy is certainty of paternity. The female who gives birth or lays the eggs is certain of maternity. However, even within a normally monogamous relationship, the male cannot be 100% sure of paternity.
Task 46
Using a particular example, explain why monogamy may be favoured as a reproductive strategy.
Using a particular example, explain why polygamy might be favoured instead.
Answers are available here.
The naked mole rat - a class of its own
The reproductive strategy of the Naked Mole Rat is an unusual tale worth taking some time to explore. In this species, a single queen reproduces with a handful of males (polyandry); the remaining males in the colony assume the role of "worker". A low percentage of the colony are fertile but this infertility can be reversed if the Queen dies. Watch the video by click on the white button below - why do you think this particular strategy has evolved?
Courtship
Many animals have mate-selection courtship rituals. Successful courtship behaviour in birds and fish can be the result of species-specific sign stimuli and fixed action pattern responses.
Biologists interested in animal behaviour will often produce an ethogram during observation – this is a list of typical behaviours and the researcher will monitor frequency, duration and latency.
An ethogram focused on courtship behaviours in birds.
Species-specific signals
Animals often use signals (or "sign stimuli") that only other members of the same species understand. These can include giving off chemicals, making sounds or certain displays to initiate mating. This means that individuals mate when more fertile, increasing the change of successful reproduction. Successful courtship behaviour can be a result of species-specific sign stimuli and the resulting fixed action pattern responses.
The red throat of the 3-spine stickleback during courtship
3-spine stickleback
During mating season, the males develop a red colour on their throat. This sign stimulus attracts females and entices aggression in other males. The male builds a nest, attacking any males that try to enter, whilst courting and attracting females. Males respond aggressively to the red throat stimulus. These fixed action patterns will increase fitness by increasing the chance of successful mating,
Task 47
"That's so cool", continued wee Jonny, "the fish literally glows red when he wants a girlfriend....I need that bit of magic".
"Aye, you'd need more than that!", replied Stacey.
"Well, let's have a think about the animal kingdom and, in box 47, give 2 examples of a courtship ritual and identify the species-specific sign stimuli and the fixed action response. Perhaps, then, consider humans as a particular example....any particular courtship rituals you've encountered that are particularly successful? Big Davie....remember to say things in your head first and self-check for censorship requirements".
Big Davie smirked too much for Dr McRobbie's liking.
The class set to work. Click the pink button for some ideas. Click here for some of their ideas.
Sexual Selection
Sexual selection selects for characteristics that have little survival benefit for the individual, but increases their chances of mating.
Darwin considered sexual dimorphism to be a product of sexual selection. This was because of the features displayed in males, e.g. plumage in peacocks, do not confer an advantage to survival in their environment. In some cases, this can attract predators or simply get in the way. If these structures increase the individual's chance of gaining a mate, however, they will be favoured because they enhanced reproductive success.
In peacocks, beautiful plumage in males will demonstrate low parasite burden - an attractive characteristic to any female!
Sexual dimorphism is clearly depicted in these images. Sexual dimorphism refers to any physical difference between males and females of a species.
It is often expressed as a difference in size, with males usually being larger, but it also involves such features as colourful plumage in male birds, manes on male lions and antlers on male deer. In most cases, the male is conspicuous and the female is very inconspicuous.
A bit of a fun video looking at the Science of Attraction in humans. What really lies at the base of attraction? We talk about honest signals and female choice in the animal kingdom. There is a lot of science in human attraction too.
And that first kiss...a lot of pressure!
Task 48
"So has evolution made some animals look more attractive than others?" asked Stephanie. "Well, Stephanie, Darwin claims that sexual dimorphism is a product of sexual selection...not natural selection". The next task was announced: explain what Darwin means, using male peacocks as an example.
Answers are available here.
Male-Male Rivalry
Success in male-male rivalry through conflict (real or ritualised) increases access to females for mating.
Males will fight for dominance and access to females, often using elaborate “weapons” such as antlers, tusks and horns.
Something to listen to...
Thinking about male-male rivalry, could it actually be that sometimes overtly dominant behaviour might be used as a way to prevent fighting. This podcast explores the differences in frequencies of chest beating among gorillas and suggests that the more dominant males produce lower frequencies sounds. This serves as a signal to less dominant males that they shouldn't waste their time taking them on!
Unmissable viewing alert! Regardless of what you are doing, take the time to watch these males fight for their position as dominant male. If you are a human male and watching this, be thankful that you will never have to engage in such courtship rituals. If you are a non-human male watching this, close your eyes!
Reversed sexual dimorphism
In some species, there may be reversed sexual dimorphism where the female is more conspicuous. This is common among insects, spiders, fish, reptiles and birds of prey.
Angler Fish
Angler Fish show extreme reversed sexual dimorphism. The female is much larger and the males live an almost parasitic existence with an underdeveloped digestive system.
Upon finding a mate, the male fuses with her, embarking upon a parasitic existence and becoming little more than a sperm-producing body.
Blue Whale
In the blue whale, the female is larger. Often this is the case in species where they have to travel long distances in search of a mate. Obviously, a smaller size will be an advantage for speed and stealth.
Task 49
"As a class, let's see how many examples of reversed sexual dimorphism we can find", suggested Dr McRobbie.
"Ha, I'm guessing we'll all get 2 - the blue whale and the angler fish", laughed Big Davie, nudging wee Jonny.
Let's see if we can find more than that. Try including your answers as a Jam using Jamboard and paste the frame into your notes.
Answers are available here.
Female Choice
"I keep a great home"
In most species, females are very choosy; picking a poor-quality male can be a costly error. Males must therefore win at least one, but in most cases many females. In some animals, competition or rivalry among males almost entirely determines which animals will mate. In other species, female choice involves females assessing honest signals of the fitness of males. Honest signals may include keeping a tidy, clean nest or foraging for sufficient quantities of food of a good quality.
"I will be a good dad"
Such behaviours are important because they provide the female with an idea of how much parental care the male can offer. For example, the male common tern carry fish and display them to potential mates as part of the mating ritual. Eventually, a male may begin to feed fish to a female. This behaviour conveys a male’s ability to provide food for chicks.
"I'm so good looking"
In other species, females choose males who exhibit extreme and energetic courtship displays or who have the most extreme secondary sex characteristics, e.g. a long tail. Perhaps these features indicator that the male is vigorous and in good health, thus a sign of fitness. Honest signals can indicate favourable alleles that increase the chances of survival of offspring (fitness) or a low parasite burden suggesting a healthy individual.
Task 50
"So, throughout the animal kingdom, there are many instances of female choice taking place during courtship. Give an example of specific behaviours a female may look for to assess the quality of a potential mate. What do these behaviours tells the female?", announced Dr McRobbie.
"I'm starting tae think this animal kingdom is pretty sexist Miss - all these males scouting about, making themselves looking fit and IKEA-ing their nest out for a girl to walk past and say "nae good enough mate", protested Fraser.
"Well Sir Fraser, there's something for us to think about", replied Dr McRobbie.
Respond to this task in task box 50 in your notes.
Click on the pink buttons below for some suggested reading.
Answers are available here.
Lekking
In lekking species, males gather to display at a lek, where female choice occurs.
Females visit the lek and choose among displaying males by assessing whether signals are “honest” and are really a sign of male fitness. Some bird species exhibit lekking behaviour. Dominant males occupy the centre of the lek, with subordinates and juveniles at the fringes as “satellite” males. During the display, female choice occurs.
Task 51
"Now you've watched the body-popping grouse, explain what happens at a Lek - what is the female assessing?", Dr McRobbie announced the task.
"I actually think that wee mad grouse is cracking. I was at a party once and a guy was doing that", Laura claimed.
"Right....ok, that's a new one on me. I'm not sure it'd have the same effect on female humans...", pondered Dr M.
"Oh, it did Miss", replied Laura.
"Oh".
Answers are available here.
Sneaking Behaviour
Sneaking behaviour refers to a strategy that allows smaller, less threatening males to more stealthily access a female partner, often avoiding altercations with dominant males. These sneaking males are often called satellite males.
Large horned beetles
Large horned beetles develop very large horns that they use as weapons for fighting for females. Smaller horned beetles do not possess such weaponry so adopt alternative mating strategies. Beetles with long horns will guard their mate by protecting the entrance to the tunnel. These males will fight any male that tries to enter. Smaller males with little or no horns have little chance of beating larger males so opt for a sneaking strategy. These satellite males dig a new tunnel that allows them access to the female’s tunnel, unnoticed by the male guard.
Task 52
This question is from SCHOLAR. Try it here or log-on to SCHOLAR.
The table below shows how parasite infestation affects mating success in male capercaillies. Mating success is measured as how many times a male is selected by a female to mate during the breeding season.
Present the information in the table as a bar chart, complete with error bars. You can complete this on graph paper or electronically.
Answers are available here.
It's now time for your regular visit to SCHOLAR to consolidate your knowledge on this key area.
4.2 Reproductive behaviours and mating systems
4.3 Learning points
4.4 Extended response qeustion
4.5 End of topic test
Your teacher might like to share this Kahoot to try in class or as a challenge at home. It covers some of the content from the past few Key Areas of Topic 2.
Your teacher might now like to issue Learner Check 16 to check your understanding of Key Area 4.
Remember these are all SQA Past Paper Questions - the more exposure you have to these, the better! Good luck!
Time to create your own content for our online class blog and become a published author! Write a piece that showcases your learning of Key Area 4 on Sex and Behaviour.
Give yourself a pat on the back - you are nearly there! One of the best Key Areas has been kept for last. It's time to enjoy the last step in your AH Biology learning with Key Area 5: Parasitism. You are in for a treat!
