Reproductive Behaviour Flashcards
Intrasexual selection- male to male competition
Often more dramatic than mate choice, as typically involves some sort of direct competition between males
Male-male competition by (in) direct fighting
There is strong selection pressure for males to accurately assess an opponent’s strength to avoid injury/death
As well as an honest indicator of size/fighting ability in male-male competition
Male-male competition- roaring
Roaring was being used as the main indicator of strength and fighting ability
Roaring and associated activities were almost exclusively seen during the rut
Roaring can advance ovulation, so harem holding males can improve their mating success by regular calling
Male-male competition- sexual selection
Sexual size dimorphism in pinnipeds is the product of an exclusively male response to sexual selection
Significant correlation between harem size and sexual size dimorphism- the larger the average harem size, the larger the relative size of males compared to females
Three evolutionary developments in males
- Size dimorphism (male-biased in mammals)
- Aggressive behaviour
- Armaments (e.g. horns, antlers, tusks)
Male-mael competition by interference
There is an interesting subset within male-male competition, where a male interferes with another male while they attempt to mate with a female
In some cases, females appear to solicit males to remove a rival during a mating attempt
What is sperm competition?
Direct competition between the sperm of different males to fertilise a femal’s eggs (i.e. Competition occurs after a female has mated with multiple males)
Females are not just “inert environments”- they can play an active role in sperm competition via cryptic choice (e.g. which sperm she selects for fertilisation)
What is semelparity?
A reproductive strategy that is characterised by the die-off of one or both sexes after a single reproductive episode or season
Sex-role reversal
Male pregnancy in seahorses etc. Predisposes males to limit female reproductive success- sexual selection may then operate more strongly on female and female sexual signals may evolve
In several species, males also evolve ornaments, female are “choosy” as well as being competitive, and males compete as well as choosing partners
Endocrine mechanisms- testosterone
Essential for the male mating behaviour.
Low testosterone can lead to a reduction in both sexual motivation and performance, this can be reversed by testosterone treatment
Testosterone and androstenedione
This can maintain mating behaviour in castrated rats
Both testosterone and androstenedione can be converted to estradiol and other estrogens, but DHT cannot
Dinydrotestosterone and estradiol
Dihydrotestosterone does not prevent post-castration decline in mating behaviour
Estradoil is very effective in activating mating behaviour in castrated male rats
What are chemosensory cues?
Chemical signals
Particularly olfaction is critical for reproductive behaviours
Three regions of the brain that evokes the release of dopamine
- Nigrostriatal tract
- Mesolimbic tract
- MPOA
What is the nigrostriatal tract?
The largest dopaminergic system and mediates initiation of movement
e.g. Muscular movement associated with mounting females
What is the mesolimbic tract?
Important in reward and appetitive behaviour
e.g. Sex and drugs
What is the MPOA?
In the hypothalamus
Possesses receptors for sex steroid hormones
What is the Coolidge effect?
A biological phenomenon whereby males exhibit renewed sexual interest whenever a new female is introduced even after previous mates are still available
le rat is placed in a box with an oestrus female, he will mate to satiation. However if a new female is introduced, the apparently satiated male will often immediately resume mating
Intersexual selection (female mate choice)
One unifying theme across evolutionary models of mate choice is that the female’s choice of male is under some sort of genetic control
Learning also plays un important role in sexual selection
Mate choice and direct benefits
Any female who has the tendency to choose males that provide her with some important resource will do better than her less choosy counterparts
Natural selection favours females who have a genetic predisposition to choose mates that provides them with tangible resources- above and beyond sperm - that increase their fecundity
Mate choice and good genes
Females who choose the males with genes best suited to their particular environment receive indirect benefits, so their offspring receive genes associated with for example superior foraging or anti -predator skills
What are honest indicator traits?
Generally ‘costly’ to produce- the costlier the trait, the more difficult to fake, so more likely that is a true indicator of good genes
Examples of honest indicator traits
Bright colours and vigorus courtship rituals
Both energetically costly to maintain and perform
Mate choice and sensory bias
Females initially refer male traits that elicit the greatest amount of stimulation from their sensory systems
