L2 Flashcards
Paradoxical Behaviours
Damaging behaviours yet they are still performed
Group Selection and Individual Selection: Infanticide in Hanuman langurs
- Live in social groups: one large male , several females and young
- When a male is displaced infants die - new males are the prime suspects in most cases
Why do males kill offspring?
There are large consequences e.g female attacking new male
3 hypotheses for why males kill other offspring
Non -adaptive
Favoured by natural selection at the individual level
Favoured by natural selection at the group level
Non-adaptive hypothesis of infanticide
Social pathology brought on by overcrowding
Favoured by natural selection at the individual level
Infanticide frees females to become pregnant sooner. The male becomes a father sooner and has more offspring before he is himself overthrown by another male
Favoured by natural selection at the group level
- Infanticide reduces overcrowding which would cause the group to overexploit its food or other resources
Group selection can theoretically occur but circumstances that favour it are rare
The logic of group selection
- Group selection suggests an individual’s behaviours are adaptations that assist the survival of their “group” eg reproducing less to avoid overexploiting resources
Groups with individuals that practise self restraint or do something else beneficial to the group, survive better
This is selected for at the group level
Individuals who don’t show self restraint will prosper, there must be a survival advantage at the group level
Individual selection will usually be stronger.
Individual selection: Advantage to
Over time selfish individuals outnumber …
altruistic individuals
if resources are limited and two groups are competing?
group selection is more favourable
Between group selection: advantage to
- More restraining individuals end up with more resources
- They are selected for through group selection
Red is favoured at individual level, blue is favoured at between group level
Blue only favoured if:
Groups are relatively long lived in relation to individual life span inter - group competition is important
Infanticide
- Often carried out by males as they compete for females
- In jacanas the females compete, so they commit infanticide
infanticide in meerkats
- Meerkats live in social groups
- Dominant female and subordinate females who breed
- Pregnant females will kill the pups of other females (it is more likely if other females are pregnant)
- If other subordinate females are pregnant then dominant female pup survival decreases
○ If no other females are pregnant then subordinate pups survive (less than dominant female though) - If other females are pregnant then subordinate pups are less likely to survive
Infanticide is adaptive so they cannot compete with their unborn offspring
Pregnant females increase their fitness
Direct reproductive benefit
Aggression in Meerkats
- Special reading Bell MBV
- Suppress subordinate pregnancy
- Costs to aggressive behaviour
Suppressed breeding in subordinate and looked at dominant behaviour
Self-sacrifice in worker honey bees
- Autotomy
- Abdomen is ripped out
- Death
Barbed sting
* Lodges into flesh of attacking vertebrate
* Easy to go in
* Hard to get out
Sting exhibits complex adaptive behaviour
* Muscles and nerves cause stings stylets to drill into flesh and venom is pumped into victim
* Alarm pheromone is volatile and smells of bananas
* Guides bees to intruder and makes them more prone to stinging
* Highly defensive behaviour
* Most effective when sting is detached
Honeybee workers rarely reproduce. Instead they rear close relatives so their genes are passed on indirectly.
By sacrificing themselves they save their reproductive investment
Sex change in anthias fish
- Females change into males when a large dominant male dies and leaves an opening in the population
- Increases fitness when female are small but better to be a large male
- Pass on more genes
Garden Spider: male approaching female
- smaller male wanders around looking for females
- Plucks strands of her web to let her know he is not food
○ Not always successful, some are eaten
- Plucks strands of her web to let her know he is not food
Tied down female
* Ties female down and traps her
* Copulates with her and leaves her to untangle herself
Nuptial Gift
- Food offerings in the form of insects wrapped up in silk
- Female eats gift whilst male copulates
Black Widow
- Eats partner following copulation
Redback Spider
- Females are much larger than males
- Females longer lived than males
- Male matures at a younger age
- Many males per female
- Multiple mating by females occurs
- 17% females mated with 2-3 males
- Male places himself in the females jaws during copulation
Redback spider: copulation
- Does not give female resources
- Male must benefit somehow
Benefit to first male being cannabilised
- Effect of cannabilised on first males paternity
If female eats first male then 67% next male is rejected
If female doesnt eat first male then 4% next male is rejected
Benefit of 2nd male being cannabilised
- Copulation duration increases with paternity
- Longer the male mates the more sperm transferred and more likely to father offspring
- Non-cannibalised males don’t copulate as long
Redback spider
* In balance
Bean Weevil
- Tip of penis covered in spines
- Male tears apart reproductive tract so female does not reproduce again
- Damage discourages 2nd mating
- Females kick male to reduce damage to their reproductive tract
- No difference in fecundity between females with one damaging mating and two damaging matins
- Damage reduces lifespan
- Genital damage is only costly to female not female
Filial cannabilism
○ Sand goby
* Deal N D S sand goby
Individuals cannibalise own offspring
