Flashcards in Lecture 11: Human and animal Deck (27):
Multiple female partners
Multiple male partners
How does polygyny work?
It starts off with a distribution of resources, followed by a distribution of females, then a distribution of males, resulting in a mating system. This happens with grey sided voles.
What are the four types of polygyny
Female defense polygyny
Resource defense polygyny
Scramble competition polygyny
Describe female defense polygyny
When female mammals are social, males aren't ever monogamous. Males defend the females from invading males.
Describe resource defence polygyny
Give 2 examples
When males defend a territory or resource that a female visits
Examples: Male antlered flies defend rotten logs which are for egg laying
African cichlid fish gather females' eggs and steal them from other males.
Describe scramble competition polygyny
These are also called explosive breeders. The females are only receptive for a few days, the males rush to mate with as many females as possible. The males aren't territorial. Frogs are explosive breeders.
Why do females agree to mate with more than one male?
Because it means they have increased territory quality
Describe the polygyny threshold model
Pribil and Searcy did an experiment with Red-winged blackbirds. They removed some females and the polygynous females were predated more and as result, produced less offspring. This is the cost of ploygyny. The territories were then boosted and the females chose the better site even though it was polgynous. The benefit of the high quality nest outwighs the cost of polygyny.
Describe lek polygyny
It comes from the word play and it's relatively rare but is found in some mammals, birds, amphibians and insects. It involves the males gathering and displaying themselves to the females. The females are very choosy and the males aren't involved with parental care at all. This means there is high variance in male reproductive success as some males will get picked more than others.
What is the evolution of lekking?
It consists of three main hypotheses; the hotspot hypothesis, the hot shot hypothesis and the female preference hypothesis.
Describe the hotspot hypothesis
It's when males gather where females visit, however, male aggregation is usually to tight to follow female dispersion. Male harbour seals aggregate at underwater spots where females travel.
Describe the hotshot hypothesis
When males cluster around highly attractive males to increase their chances. If the alpha males are removed the subordinates leave, however if a subordinate is removed, it's just replace by another subordinate. This is found with marine iguanas.
Describe the female preference hypothesis
Females are attracted to larger leks as they can find the best males there.
It's when a male and a female stay together and only have one partner. It's rare in nature; only 3% of mammals are mongamous and 15% of primates, however, 90% of birds are monogamous. However, why would males accept monogamy as it wastes sperm? There are three hypotheses: Mate guarding, female enforced and mate assistance.
Describe mate guarding
It prevents sperm competition which increases paternity certainty. It follows the operational sex ratio of sexually active males to sexually active females. The females are widely dispersed, receptive after mating and have a short fertile window. Clown shrimp mate guard. When there are non-overlapping female ranges then males are unable to monopolise more than one female. This is faculatative monogamy.
Describe mate assistance
Males carry the eggs in a brood pouch but only carry a clutch at a time. Therefore, there is no advantage for the male to find another female. They fulfil their potential reproductive rate. Seahorses follow this hypothesis. So does the djungarian hamster, however, there isn't a relationship between paternal care and monogamy in mammals. Starlings follow this as they help rear the offspring because the chicks require a lot of parental care in order to survive. This is obligate monogamy.
Describe female enforced mongamy
The females don't allow the male to mate with anyone else, e.g. jealous girlfriends. The burying beetle supports this, as does the yellow breasted chat.
Describe the fidelity of birds
Birds were assumed to be highly mongamous, however, DNA profiling has said differently. 90% are socially mongamous but 10% are sexually monogamous. They have extra pair copulations. EPCs can be up to 35% in many species. Gibbs et al found that many of these EPCs happen in neighbouring nests and most of the males' offspring are in different nests.
Discuss divorce in swans
Rees et al found that only 25% of divorcing whooper swans had bred the previous year. 48% of non divorcing swans had bred. Maybe the females find a better alternative with increased dominance rank.
Discuss the cost of mating
If the female is polyandrous, then this correlates to a higher immune system (primates), however, females are usually mongamous, meaning their immune system isn't as strong. Sperm can damage female fruit flies and decrease their chance of survival.
Discuss polyandry's benefits and costs
It directly benefits male butterflies as the more mates they have, the more reproductive output they have. It also benefits them in terms of protection, langurs sometimes mate with multiple males to reduce the chance of infanticide. It's good for females as they have the best opportunity to find the good genes.
However, polyandry isn't beneficial for males as it means they have to share paternity and they will have missed opportunities for mating.
Discuss good genes in terms of competition
Klappert 2007 found that females would improve their fitness via their sons. Therefore, they would pick the most attractive male to ensure that their sons would produce more grandchildren as they would be more successful.
Discuss genetic compatibility of birds and their offspring that commit infidelity
The offspring produced via the EPCs had better immune responses whereas other offspring of these males had average immunity.
Discuss sex role reversed species
Some species defy the normal pattern; the females compete, they're ornamented and are aggressive and territorial, for example phalaropes. In some species, the males provide parental care; the females gain from additional matings and males have a slower potential reproductive rate, e.g. seahorses.
What species is polyandrous, polygymous, monogamous and polygynadrous?
What gender does each benefit?
What is this called? Explain
Dunnocks and humans
Monogamous: Average for both
A variable mating system, however there is a conflict of interest as different systems benefit different individuals. Terretorial male dunnocks usually have variable mating systems depending on whether they're alpha or beta males. This highlights the males' different competitive abilities and it alters the sex ratio, there is usally vegetation in the territory and the females usually encourage mixed paternity by mating with the less visited male.
Do harem sizes correlate to size dimorphism in chimps?
Roughly, not a strong correlation