Sexual Selection II (intersexual) Flashcards
what does a sexual signal say? What info might receivers get from it?
- readiness to mate
- quality or health of mate
- can show if they are related
examples of intersexual selection
- red-collared widowbirds
- gray tree frogs
intersexual selection examples - red-collared widowbirds
- researchers experimentally changed tail length by cutting it off
- females like long tails
intersexual selection examples: red-collared widowbirds - what was the result
- long-tails are not good for the male
- but it still has it bc females like long tails
intersexual selection examples: red-collared widowbirds - what does the results mean?
females are making mating decisions based on signal even if the signal has a cost
intersexual selection examples - gray tree frogs
- female frogs are choosy and prefer males giving longer calls
- longer-calling males are more likely to find mates
what are the hypotheses for why receiver preferences evolve
- null model
- sensory bias
- resource acquisition hypothesis
- honest signal/good genes
hypotheses for receiver preferences evolution - null model
- assumes preferences are arbitrary (no benefits to sender or reciever)
- outcome: runaway sexual selection
- ornamentation continues to get more ‘bigger’ without stopping
hypotheses for receiver preferences evolution : null hypothesis - what is runaway sexual selection
- assumes that both sexual preference in females and ornamentation in males are genetically variable and heritable
- all about genetics
hypotheses for receiver preferences evolution : null hypothesis - bird example
- first need variation in preference and display
- then assortative matting where a connection begins to form in preference and display
- if selection favors one of them, it will move the other
- can graph this relationship
null hypothesis: bird example - adding natural selection to graph
- optimal display for reproduction is graphed
- optimal display for survival is graphed
- average display is a compromise between the two lines (equilibrium line)
null hypothesis: bird example - adding drift to graph
- drift wll push the population off of the equilibrium
- they will eventually move back
null hypothesis: bird example - how is runaway selection seen on the graph
- trait correlations will be off the equilibrium line and cannot get back to it
- they will instead move further and further from the mean
null hypothesis - example of this happening in a natural setting
- crickets
- male songs and the female preferences are strongly correlated
null hypothesis: cricket example - how are female preferences and male songs correlated
- male signal and female preference linked
- found via QTL mapping
null hypothesis: cricket example - what was the finding
Each population is at a different stage of the runaway process
hypotheses for receiver preferences evolution - sensory bias
- Receivers have to take into account all sensory input not just mating
- But sometimes a mating signal can co-opt an existing sensory bias
- Does not need to have a benefit to the receiver, only to the sender
sensory bias - water mite example
- water mites sense vibrations to find food
- Male water mites make vibrations and females think its food and then they mate
sensory bias - guppies example
Females like orange males bc they need carotenoids (orange coloration) for food
sensory bias - why does it require ‘time travel’ to study?
- Cannot witness it in real time
- Researchers use tree comparative approach to see if female response to signal had evolved before the males started signaling
hypotheses for receiver preferences evolution - resource acquisition hypothesis
- Receiver benefits from acquisition of resources
- sender also gets benefits via offspring
resource acquisition hypothesis - examples
- gift giving
- mate cannibalism
- parenting
resource acquisition hypothesis - gift giving (nuptial gifts)in Bittacus apicalis (hanging male flies)
- Female gets to lay more eggs the bigger the gift is
- beneficial bc in this species, hunting/foraging is dangerous
- Male gets more offspring and they are more likely to survive
resource acquisition hypothesis - mate cannibalism
- in many animals, nuptial gifts have evolved into mate cannibalism
- where some male spiders throw themselves into the female’s mouth after co-population
- usually in environments were hunting/foraging is dangerous and resources are limited
resource acquisition hypothesis - parenting in Threespined stickleback
- males make a nest and care for eggs and young
- Females can assess how good they are with how they treat the nest with treating eggs
hypotheses for receiver preferences evolution - honest signals/good genes
- good genes model
- handicap hypothesis
- sexy sons model
honest signals/good genes - good genes model
- females obtain better genes for their offspring
- bc the displays could indicate good genes
honest signal/good genes: good genes model - grey tree frog example
- females prefer longer calls
- offspring of males with longer calls do have higher fitness
- suggests that fathers have better genes and the call is a honest signal of male quality
honest signal/good genes: good genes model - human example
- humas have major histocompatibility complex (MHC)
- having more diversity is good for the immune system
good genes model: human example - results sweaty t-shirt experiment
- women not on oral contraceptives chose t-shirt that had a more dissimilar MHC than them
- woman on oral contraceptives chose similar MHC
- this is bc contraceptives mimics pregnancy and it means women do not need to find mates
good genes model - challenges
- causes directional selection that reduces variation
- all males will try to be cheaters even if they do not have good genes
- BUT if the signal is too costly than it will remain an honest signal and only high quality males will have it (handicap hypothesis)
honest signals/good genes - handicap hypothesis
- suggests that reliable signals must be costly to the signaler
- costing the signaler something that could not be afforded by an individual with less of a particular trait
honest signals/good genes: good genes model - when can sexual selection act?
- before, during, and after co-population
- before: signals
- during: genital arms race
- after: sperm competition and control females have on fertilization
honest signals/good genes - sexy sons hypothesis
genes from the more attractive male will make the females sons more attractive
honest signals/good genes - good genes vs sexy sons hypothesis
- good genes: good for natural selection on offspring
- sexy sons: good for sexual selection on offspring
