7 ~ sex roles, dimorphism, weapons + fights

what is mating competition/intrasexual selection?

selection for attributes that help individuals win in same-sex competitions for mates

what is mate choice/intersexual selection?

selection for attributes that charm the opposite sex

what is sexual selection?

process where secondary sexual traits become elaborated because they increase oweners ability to gain access to mates

how does anisogamy affect sexual selection?

female gametes are more costly (fewer are made, larger, take time, nutritionally dense)

females are more choosy than males

what is bateman’s principle?

males - reproduction is limited by number of eggs fertilized, dictated by number of females

females - reproduction is limited by number + quality of eggs produced, limited by resources

what does bateman’s principles show?

variance in # of offspring + mates in males is greater

males show significant correlation between. number of mates and number of offspring

how does parental investment affect sexual selection?

sex who invests less in parental efforts, compete amongst each other

sexes who put more effort in parental investment vs mating will have a lower reproductive rate

what is operational sex ratio?

ratio of receptive males to females

what is sexual dimorphism?

males and females are different sizes (males generally bigger)

what are the potential causes of sexual dimorphism?

natural selection - females get bigger to have more eggs

distruptive selection - males and females wont have to compete directly for food

sexual selection - bigger males will dominate

what is the example of elephant seals and sexual dimorphism?

males - 3000kg, females 450kg when ready to mate

males compete for “beachmaster” title to attract more females (maternal investment) and grow their harem

males can have dozens of offspring per year, females only 1

males have higher variance in fitness (some make a lot while rest make none - win all or lose all)

investment in body growth and evolution of intense/dangerous tactics is favoured for as there is high reproductive success

what are weapons?

traits evolve for male-male competition

eg. horns, antlers, breaks, talons, tusks

what is the example of dung beetles and weaponry?

males that are larger will have long curved horns while smaller ones are hornless

horn sizes varies greatly in populations

males fight for tunnel entrances and those with bigger horns win

• males who have entrances can mate with the females who live in them when they come out

small hornless beetles never fight and instead dig secret tunnels from the side that lead directly to mating females

horns reduce agility so larger beetles can’t enter tunnels

what are the properties of weapons?

structures used in combat with rivals

weapons diverge in size, shape etc in species

evolve when one sex (usually males) are able to defend spatially restricted critical resources

most variable structures, reflect individuals differences in body size and quality

what are intense fights + contests?

purposeful and violent shows of dominance

why do animals fight?

limited non dividable resources

eg. food, mates, shelter, territory

what are the costs and benefits of fighting?

benefit - win resource

cost - energy, time, predation risk, injury, death

what are the benefits of a dominance or social hierarchy?

formed through competition/fighting reduce cost of fighting since everyone knows their place

what is ritualized fighting?

lower cost behaviour

threat display

non-contact

used to decide if bth parties want to engage in fight

what factors affect when an individual will give up in a fight?

resource holding potential - absolute fighting ability of the individual, measure of size, strength + weapons, the greater the diff in size btwn opponents, the shorter the fight

resource value - motivation for indiv to win, territory owners will fight more as they have already invested more into the territory against intruders

aggressiveness - inherent trait, readiness of an indiv to engage or escalate