Term 2 Lecture 4: Courtship And Reproduction Flashcards
Courtship
Sexual selection leads to secondary sexual characteristics
Many are striking displays that use physical morphology in behavioural displays
Natural selection Vs sexual selection
Darwin (1859,1871) individuals (at least in sexually reproductive species) can improve their chance of reproducing in 2 ways:
1) compete successfully to survive to acquire resources allowing reproduction (aka struggle for existence and natural selection) adapting to survive
2) compete successfully for mating opportunities (sexual selection) chooses for:
A) aid of competition within one sex (usually male) for access to the other (intrasexual selection)
B) enhancing attractiveness of individuals of one sex (again usually males) to members of the other - sexual or epigamic selection - usually at a cost to other components of reproductive success e.g. adult survival.
Darwin: (sexual selection) depends on a struggle between individuals (usually males) for possession of the other sex. The result is not death for the unsuccessful competitor but few or no offspring
Intra Vs intersexual selection
Intrasexual selection:
-male on male fight often dependent on agility (hummingbirds) or bulk (seals)
- intense post-copulatory selection - competition of sperm from different males that have mated with the same female
Intersexual selection
-morphological display features
- e.g. bowerbird feathers and nest decorations
(Darwin: female birds select beautiful males producing marked differences in morphology over generations)
Sexual selection
- some view natural and sexual selection as separate
- but survival is only valuable if an individual can reproduce
- both processes act through differential reproduction
- balance to be found between how much to invest in a struggle to exist Vs struggle to mate depending on relative contribution each makes to the individuals lifetime reproduction output
Often traits selected for in a mate reflect their fitness e.g. to be a Dom male deer you must be large, to be large you must eat well so you must be good at foraging and holding territory
Sexually selected characteristics that may conflict with survival
- antlers - energetically expensive
- bright plumage- conspicuous to predators
- therefore a trade-off between investment in survival Vs reproduction
E.g. peacock plumage will look tatty if the bird has lice or is sick, a bird with lots of healthy plumage is a target for predators so survival shows fitness
E.g. redness is appealing in fighter fish, this requires the fish to ingest enough carotenoids to display as skin pigment as well as for use in the immune system
Some characteristics serve intra & inter sexual selection
E.g. size of antlers in deer and physical bulk in male seals
Why are females choosy?
Females generally invest more in offspring than males (especially if internal fertilisation required) :
- costly large gametes (eggs)
- internal development of young
-raising young following birth or hatching
- finite egg production - limited no. Of mating opportunities
- in species with high level of investment after birth or hatching the female tends to provide the bulk of care e.g. feeding in mammals
Why do males fight?
Males typically invest less in each individual offspring
- sperm is ‘cheap’ and ‘unlimited’ so unlimited mating opportunities
- uncertainty of partnering - as most females mate with more than one male
Thus driving lack of investment in offspring
-males are less choosy to mate as many times as possible
Compete for mates or resources of use to females by conflict displays of male-male intrasexual competition
Or compete to attract females (courtship display) - intersexual competition
Misleading metaphor of males ‘parasitising’ females reproductive investment
Cost of competition -
males must deliver thousands of sperm packaged together and the sperm must be very active, motile and high quality
Time and energy must be invested in learning displays as well as finding good nutrition for size and health to be selected intersexuality such as colouration, bulk or feather health
Males also risk physical injury defending or competing for mates
What caused the development of the difference between male and female investment? why did anisogamy evolve?
The evolution of anisogamy - reproduction with two distinct gametes - large well provisioned egg and small motile rapidly moving sperm.
Isogamy existed previously with male and female gametes of the same size as is still the case in most microorganisms (fungi, algae etc. are sexually anatomically similar)
Anisogamy seen in larger organisms at adult phase organisms that need more provisions to develop even right at the start.
This led to disruptive selection a larger gamete has the advantage of better provisioning for the offspring whilst a smaller gamete has the advantage of higher motility to locate large gametes - this led to selection against the mean and the evolution of small/large gametes pairs.
Anisogamy has a profound impact on subsequent evolution of sexes in traits and behaviour of mating and courtship driven by sexual selection
Females can be considered a ‘limiting factor’
Bateman’s principle: the limiting sex is the sex with the lowest maximum reproductive rate (usually females)
The sex with the higher reproductive potential:
-invests less in each reproductive attempt
- experiences greater competition for mates leading to stronger sexual selection (usually male)
So more elaborate secondary sexual traits are usually seen amongst males.
Sexual dimorphism and secondary sexual characteristics
Not all dimorphism is due to sexual selection
Other selective pressures:
Feeding ecology e.g. anopholes mosquito females are larger as they take the ‘blood meal’ to feed their eggs
Fecundity: in some species females are larger as it means they are able to produce more offspring (often seen in amphibians)
Primary sex differences: in birds females are often larger to be able to carry eggs
Functions of courtship
- at a simple level to recognise members of your species - to produce viable offspring
- to identify individuals from the local area- same deme better chance to raise healthy young as they know the local environment
-to recognise specific individuals - as in long-term pair bonds- to recognise your mate for social interacting also in parental bond - to attract a mate
-mate choice - assessment of potential mates traits, condition and quality
-in long-term pair bonding as in many bird species, reaffirming pair bonding and contributing to care of offspring
-to coordinate reproductive behaviour and physiology between sexes (synchronisation) encouraging production of gametes - as in spider species - correct behaviour essential on males to avoid being eaten by potential mate
Mate attraction - what do displays signify?
E.g. bird song
-a way for females to compare males
- more complex/longer songs indicate healthier males, better territories and enhanced parenting potential
^ an indicator of good genes - honest signal of male quality
What is a mating pattern (or mating system) ?
Mating pattern- describes the pattern we observe between individuals of a population
A mating pattern is a population/species wide description composed of individual mating strategies
A mating system usually exists to serve ultimate cause i.e. enhancement of both male and female fitness
^ no individual strategies are adopted to enhance individual fitness - a mating pattern is population wide ‘composite’ of individual strategies
Main mating pattern definitions
Promiscuity - brief interactions (meet and mate)
Monogamy - long-term partner
Polygamy:
Polygyny: one male several females
Polyandry: one female several males
^^ so some males or females in the group have no mates
Polygynandry: mating within the social group
Different forms of polygyny
Resource defence polygyny - territoriality
Female defence polygyny- harem defence (defending a group of females)
Male Dom. Polygyny- Dom male has access to all females in the area
Lek polygyny- males gather and compete for central position - most central = most desirable common in migratory birds such as black grouse
Uni-male polygyny- one male dominates territory/harem
Multi-male polygyny- in some social species such as primates and lions there are alpha and beta males the alpha gains most mating opportunities whilst beta has some mating opportunities and benefits by experience and building relationships with females of the group - the beta may take over the group when the alpha is old or dies
Sometimes females are subject to more intense sexual selection - polyandry
E.g. Phalaropes bird females access polyandry as food availablity in spring allows females to produce multiple egg clutches. Females compete for access to males who then sit on the nest (reverse of male Dom polygyny)
Different forms of polyandry
Resource defence polyandry:
Territoriality
-each male looks after own brood
-simultaneous or sequential polyandry
Female access polyandry:
Each male looks after own ‘brood’ females lay multiple clutches of eggs e.g. sandpipers
Cooperative polyandry:
Males all care for offspring in one brood e.g. fish species - male fertilises a clump of eggs and guards them
Non parental polyandry:
Akin to promiscuity - no care after fertilisation e.g. amphibians
Large females lay eggs of mixed paternity
Polygynandry
Both sexes have multiple mates and either sex can invest in the offspring i.e. both sexes mate polygamously
System can be dynamic as slight changes in power between male and female can switch to polyandry or polygany
Determinants of mating patterns
-changes in resource availability
- structure of environment
-distance of mating partners
^ all lead to changes in mating patterns
Two main themes
Parental care
&
Dispersion in space and time
Mating patterns are composed of individual strategies - individuals adopt mating strategies that maximise their own fitness under given ecological conditions
Conflicts of interest: within or between sexes lead to sexual selection and conflict
Parental care and mating patterns
See table in notebook 2
Polygyny (mammals and some birds) - occurs in mammals due to long gestation and female lactation
Promiscuity (plants and animals)
Monogamy (some birds) - involves an agreement to incubate/protect eggs and feed young
Polyandry (fish and some birds)
Distribution of parental care varies even in closely related species e.g. in shore birds
The socio-ecological model (Emlen and Oring 1977)
Relates the distribution of resources and/or mates in space and time
- also stems from differential parental investment
-female reproductive success is limited by access to resources not by access to males (usually) - Male reproductive success limited by access to females (generally)
Ecological restraints on dispersion affect economic defensibility of resources and mates
Resource dispersion leads to male and female dispersion affecting male mating strategy - males compete for resources. Predation also causes female dispersion and in this situation males compete directly for females. There are benefits/ costs of social living
Socio-ecological model - spatial and temporal dispersion and the environmental potential for polygamy (EPP)
-dispersion patterns of the limiting sex (females usually)
- determined by environment (resources)
- spatial clustering of females
-temporal clustering of females (synchrony) together in a particular space and time
-affects potential for individual males to monopolise groups of females
- if EPO is high and if individual males can monopolise this leads to polygyny
- low EPP leads to monogamy - females are fewer or further between so male selects one female and supports care of offspring
Summary of spacial and temporal dispersion and EPP
Spacial
Clumped increases EPP →polygyny
Dispersed reduces EPP →monogamy
Time
Limited reduced EPP →monogamy
Limited time window for mating
Unlimited increased EPP → polygyny
Environment affects mating patterns and behaviour
e.g. Weddle seals have an intricate and elaborate call whereas a grey seal call is simple and cursory. Males provide no parental care only females look after the calves by feeding them milk.
Grey seals - breed on islands - spacial clumping and synchrony leads to polygyny - male dominant seals breed
Weddle seals- breed on Antarctic pack ice where ice holes are essential to hunt each hole is shared by two or three females Weddle seals must attract females with their song
