Exam 4 Flashcards
Why are females choosy
Have higher direct reproductive expenses (higher parental investment - time/energy/parental care/egg production)
- compared to males: produce fewer, more expensive gametes
- provide more parental care
- therefore, low reproductive potential
What is sexual dimorphism based on
Differences in reproductive potential. Dimorphism can be both anatomical and behavioral.
Why do males tend to compete for females
Produce lots of inexpensive sperm; usually don’t care for offspring
- therefore- high reproductive potential limited only by # of mates
- more males than females available to pursue additional mates: lead to competition for females. Resources channeled into competition and mating tactics instead of production of gametes.
Consequence of male high reproductive potential
- more males than females ready to produce at any time (operational sex ratios: OSRs. Are skewed towards males)
- sets p competition among males for limited available females. And males have it mess incentive to increase # of mates.
- general pattern: competitive males, choosy females (theory behind sexual selection)
When would you expect competitive females, choosy males?
- when there is high investment by males
Ex: Mormon crickets. Males produce expensive spermatophore - lots of nutrients, maintenance involved with it. Spermatophore presented to females, who uses it to fertilize eggs and eats some of it to produce more eggs after saving sperm.
- cost prevents males from mating more than once. Females compete for access to males, males reject lighter females. Correlation between body mass and egg production.
- males let females crawl onto their backs, kick certain ones off and give spermatophore to one they’ve chosen
What leads to variation in success?
Sexual selection: selection for traits that confer mating advantage
Intra: selection for traits that improve ability to interfere with mating opportunities of other members of same sex
Inter: selection for traits that increase attractiveness to opposite sex
- strength of selection depends on skewedness of OSRs, amount of male parental effort. Species tending towards monogamy are less dimorphic
What kinds of intrasexually selected traits evolve?
Display-related: honest signals of fighting ability
Combat-related: weaponry, large size
Fertilization-related: features that facilitate sperm competition
Do alternatives to direct confrontation exist?
Yes. Game theory (alternative mating tactics)
- may be part of behavioral conditional strategy
- males can change tactics depending on what others are doing
- may be hereditary alternative phenotype (males tactic innate and relatively inflexible - accompanied by appropriate morphology)
- phenotype maintained by frequency-dependent selection. Seen a lot in fish, some reptiles/amphibians
Example of conditional strategy
Scorpionfly mate acquisition
- flexible based on females preferred resources. Females like insect gifts. If males can’t get an insect, is capable of producing a nutrient-rich ball of saliva to present instead. May also try to force self on female if energy for spitball not available and don’t have an insect.
How do you test for conditional strategy? Rule out alternative phenotype.
Examples of alternative mating phenotype
- coho salmon jacks vs. hook noses
- marine isopod males - alpha is largest, sponge defenders. Beta is a female impersonator. Gamma is small, sneaky.
- -alphas defend sponges where females lay eggs. Betas ignored by alphas, end up fertilizing some of the eggs. Gamma almost completely undetected by alpha males.
What if females have potential access to other males?
- Prevent insemination through mate guarding. Males physically guard female. May reduce attractiveness of female (ex-insects produce pheromones sprayed on females that are “anti-aphrodisiac). Copulatory plugs from males seal off reproductive tract to block sperm entry from other males.
- Compete internally for fertilization (sperm competition)
- increase copulation rate, increase pint of sperm delivered, remove sperm of other males.
- ex: damsel fly females can store sperm for a long timer. Males have hooks at end of penis, capable of scraping out sperm from previous males and replace it with their own
Case study that shows mate guarding works
Seychelles warbler males lost paternity when they reduced mate-guarding. Put fake egg in nests to make male think she had already laid, did not need to defend her anymore - successful EPCs and intrusions went may up because mate guarding went down.
Intersexual selection
- traits evolve that females use to assess male quality
Why are females choosy?
Female preferences drive male ornamentation - both behavioral and physical.
Direct benefits
- Food for egg production (nuptial gifts). Spermatophores, prey, male himself (Ex: red back spider males offer themselves to get eaten to help feed his future offspring. Theory is that their potential to mate again is so low that their fitness is increased more by allowing cannibalism.)
- Territorial resources (males are typically the territory-holders): food, breeding sites, protection
- Parental care: defense of young and eggs, feeding of young (courtship may advertise potential parental quality directly or indirectly), ability to fertilize eggs, reduce risk of STDs, other parasites
What if no direct/material benefits are evident?
Fishers runaway selection theory Good genes (Hamilton-Zuk hypothesis)
Fishers runaway selection theory
Evolutionary positive feedback between male trait and female preference
Both the trait and the preference become more extreme each generation
Sensory processing bias - if preference and trait become linked, then it snowballs until selective pressures like predation shut down further development of the trait in the population over time
Good genes
- females choose males based on their genetic quality
- Zahavi’s handicap principle: costly structures/displays are honest indicators of male genetic quality
- predictions of good genes hypothesis: showiest males are best quality, male quality is heritable
Support for Zahavi’s handicap theory predictions
- Male guppies with largest orange spots have longer swimming stamina
- Grey tree frog song duration correlates with his offspring’s viability
- -used half siblings. Fertilized 1/2 of each female’s eggs with short-call male, 1/2 with long call male
- offspring fertilized with longer call male had higher fitness
- why use same mother? Maternal effects may cause increase in viability. Ex: zebra finches prefer males with re leg bands. Secrete more testosterone into eggs. Directly controlling viability of offspring just by thinking about who they were mating with.
Hamilton-Zuk hypothesis
Sexual ornamentation/displays are reliable indicators of heritable disease resistance
Predictions: showier males are disease-resistant. Offspring of showier males are more disease-resistant
Ex: may depend on species whether this is true. Found that yellow feather pigmentation is later if male is infected with >1 blood parasite species. Bird
How do you know which hypothesis is correct? (Runaway or good genes)
Must show that male trait is not related to heritable viability
- ex: female zebra finches prefer males with artificial crests
- hypotheses may not be mutually exclusive
Female choice after/during copulation
Cryptic female choice
- selective sperm storage, use for fertilization
- females can be selective at any point
- coupling - intro mission - insemination - sperm transport
- can mate with multiple males, decide which sperm to use
Further evidence of “the battles if the sexes” (competition among and between sexes)
- males reduce parental care if multiple mates
- forced copulation by males
- females sometimes resist infanticide
- false estrous
Mating systems
Based on # of breeding partners
Monogamy: 1 male 1 female
Polygyny: 1 male and >1 female
Polyandry: 1 female and >1 male
Promiscuity: >1 female and >1 male
When is monogamy favored
1 receptive females are widely distributed (ex: dik-diks. Females are solitary. Large home range. Monogamy driven by ecological factors. Males could not possibly form home range big enough to defend paternity with multiple females.) Tend to see monogamy when ecological factors drive wide distribution of females.
- Male parental care required. Feeding, brooding, protection. (Ex: birds. Chicks need to be fed by both parents and get protection from both. More chicks of yellow-eyed junco survive when male is present.)
- Monogamy is enforced by male or female.
- -mate guarding. Female burying beetles attack male if he releases as pheromone. Shuts down production. Resource-wise, would have to share food item with another female’s offspring if one is attracted.
- female refusal to mate with mates males
- aggression toward mate (intrapair aggression)
Monogamy is common in
Birds (over 90%)
Rare in mammals and fish (except when male parental care provided or females not defendable)
However, extra-pair copulations are common even among monogamous species (genetic mating system may not be consistent with social mating system) - will take opportunities to increase personal fitness
Advantages of multiple partners/EPMs for females
- Direct benefits: more nuptial gifts, more parental care, access to >1 territory (ex: female megacillid bees permitted access to pollen nectar only if they mate with territorial males), infanticide reduction
- genetic benefits: fertilization insurance, chance for higher quality genes, more diverse offspring
Polygyny is favored when
Males free of parental care, receptive females are clumped in space, receptivity of females is asynchronous
Males either defend females or resources females need or beat other males in race to mate with in defended females (scramble competition)
Female defense polygyny
Evolves when female movements unpredictable
Ex: plains zebra (resources abundant). Females could be anywhere so males better off traveling with them
Resource defense polygyny
Evolves when females predictably visit resources, but are defendable
Ex- Grevy’s zebra, resources space out
Scramble competition polygyny
When females are widely dispersed and undefendable
Dominance polygyny
Males establish dominance. Females choose to mate with dominant males.
Ex - Geladas. Baboons in Ethiopia.
If given choice, why would females choose polygyny?
Sexy sons- sons inherit potential for polygyny. Ex: cricket experiment. Males may transmit their mating success to sons. Males who were previously successful in competition for mates, sons achieved more markings than sons of unsuccessful males.
Too hard to find unmated male
Polygyny with good male better than monogamy with bad one - polygyny threshold model. (Female fitness increases with male quality, shares his time and resources on territory.)
Evidence for polygynous cost
Pied flycatchers. Females mated polygynously have lower fledgling success.
Lek polygyny
Lek - a cluster if displaying males
Males defend small display areas within lek (ex- cock of the rock)
Hypotheses for why leks form
Hotspot - males aggregate where females likely to be found
Hotshot - males gather around hotshot, satellite males may gain chance matings/spillover
Female preference - females disproportionately attracted to large male groups.
Hotspot hypothesis test
Do leks form where females are concentrated?
- male sage grouse form leks near high female density areas. Leks seen to form in core, favorable habitat for females - not just randomly distributed. (Observational evidence)
However, lek sites are not correlated with female density in the kafue lechwe antelope. Probably best explained by hotshot hypothesis.
Hotshot hypothesis test
Predictions: if most attractive male removed, lek should re-organize around next most attractive male. If males near most attractive male removed, others should move in.
Ex: marine iguanas. Position of preferred males territory changes every year, shows it is not based on where females are, but there is a different preferred male each year who has a different position within the lek. Everyone else rearranges themselves around him each year.
Female preference hypothesis prediction
Females should be disproportionately attracted to larger leks.
Forms of parental care
Feeding, defense (including infanticide), protection from elements (brooding), grooming
Economics of parenting
Parental investment (PI) - time and energy invested in current offspring at expense of future offspring
Parental effort (PE) - total PI over lifetime.
Parental care favored when benefits of increased offspring survival outweighs costs of missed mating opportunities or reduced adult survivorship
Why is female parental care more common?
Hypotheses:
- Order of gamete release: males have chance to desert first. Females stuck with fertilized eggs. If no one takes care of them, no offspring survive
- Certainty of parentage: females more certain if parentage than males vex epitome: egg-layers (brood parasitism)
- Association with offspring. Female mammals lactate, have more prolonged association with offspring. (Ex: male fish defend territories - and young as consequence since eggs are laid/hatch there)
- Selection pressure greater on males to desert it’s. Males can maximize their reproductive potential. Whoever can desert can capitalize reproductive potential. By default, females can’t capitalize as much.
What if females pay higher fitness price for parental care?
Ex: St. Peter’s fish. There is a non-linear relationship between fitness and body size. Above a certain body size, female fecundity increases faster than the male’s relationship between body size and fecundity. At this point, pressure is greater on females to desert, refuel, and lay more eggs.
Parental females vs. nonparental females and parental males vs. nonparental males.
- interspawn interval is lower if they don’t involve parental care than if they do for females. That difference in interspawn interval is greater than what is seen in males. (Because sperm is more inexpensive) however, females pay bigger price for being parental because interspawn interval ones up even more when they contribute parental care. Females therefore have greater selective pressure in them over time to not contribute parental care so they can refuel and lay eggs again as quickly as possible
How do parents recognize their own young?
Olfactory/visual/sounds in mammals
Location of nests in birds
Sound in birds/bats
–recognition higher in colonial birds. Ex: cliff swallow chicks (colonial) produce more individually distinct calls than barn swallow chicks that are spread out/solitary
Brood parasitism
When parents cannot recognize own young
Parents leave young with “foster parents”
Possible when no offspring recognition
2 types brood parasitism
Facultative intraspecific egg dumping
Obligate brood parasitism
- lay eggs in other species nests because they cannot take care of their own young or build nests. Ex: cuckoos, cowbirds
Adaptions for increasing success of brood parasitism
Sneakiness
Removal of host egg
Egg/nesting mimicry
Competitive chicks
Ex: Alcon blue butterflies are also brood parasites. Larvae emit any-mimicking pheromone. Adopted by ants. Butterfly larvae then eat ant larvae.
Why do hosts tolerate brood parasitism
Occurrence may be infrequent
May reject own egg/offspring by mistake
Evolutionary lag (defense has not yet evolved). Ex: changes have occurred in some ant larval pheromones (is defense against Alcon butterflies beginning?)
Parent-offspring conflict
PI costly to parents:
- reduce future offspring production
- parents selected to optimize lifetime investment
- offspring should try to monopolize PI. Seta up conflict. Ex: brood size manipulation a provide evidence for parent-offspring conflict. Male and female European kestrel parents have slightly more likely chance to survive next year if try have fewer offspring. Adding two chicks makes survival ship go down. Average family size is just at the point when any more parental care would start reducing chance to live to next breeding season. Adapted to push parental care to maximum possible.
Siblicide
Ex: egrets, seabirds, raptors, hyenas
One offspring monopolizes or kills others. Ex: blue-footed booby. Egg that hatches first has larger sibling that outcompetes for food/parents favor it.
Ex: Sand tiger sharks - intra-uterine cannibalism. Ovoviparous. Young hatch into uterus and whoever is biggest eats all of its siblings
Evidence parents could intervene with siblicidal
- Birds incubate eggs asynchronously (one will hatch first, be bigger, more aggressive/competitive)
- Females put more androgens into first egg
- Parents let offspring fight it out
- -hyenas: leave one dominant heir. Leaves all in one den.
- -egrets, raptors: leaves options if food is abundant? Multiple hicks could survive if food is abundant, sometimes food is not abundant so one needs to die. Second offspring may also be “insurance” - if there is low hatchling/fertilization rate/other offspring could die
Ex: less aggression occurs with mixed sex spotted hyena litters.
Ex: blue-footed boobies exhibit less aggressive siblicide than masked boobies. Cross-fostering makes blue-footed boobies aggressively siblicidal when raised by masked boobie parents.
Social behavior benefits
Reduced predation risk
Increased foraging success
More parental care (cooperative breeders)
Social behavior costs
Competition (group size erodes social benefits - can get around it by deception, mixed species group with less niche overlap)
Disease
Risk of exploitation (risk of being taken advantage of - ex: may find a resource and have it stolen)
Ex: with field fare birds, very large colonies show a decrease in hick survival past a certain size. Could have to do with reaching critical mass, competition, etc
Types of interactions (defined by fitness consequences)
Donor vs. recipient
Mutualism + + Reciprocal altruism + (delayed) + Altruism - + Selfishness + - Spite - -
Why is selfishness the most common pattern?
Do animals perform “expensive” behaviors for group benefit?
- pure altruism is not evolutionarily stable
- too vulnerable to “cheating”
- pure altruism is therefore not advantageous, could not maintained in populations over time.
Mutualism
Examples: group hunting in whales, wolves, etc
Coalition of male lions: work together to evict dominant me; share defense of pride. Share paternity (some asymmetry) - tends to happen in smaller coalitions. Hierarchy formed among the males.
Multispecies mutualism
Jackson’s hornbill and dwarf mongoose: mutualistic feeding relationship. Mongoose live in abandoned termite mounds, forage in group and are followed by hornbills. Mongoose scare up prey that hornbills eat. Hornbills can spot predators and give out alarm calls that Mongoose respond to.
Reciprocity (delayed payback)
- primate “alliances”. Male “distraction alliances” in baboons. Usually a dominant male with exclusive access to females. Subordinate males work together - one distracts dominant male while other mates. Later, switch roles.
- grooming alliances. Exclusive grooming relationships maintained over time. Take tend.
- power alliances in chimpanzees. Long-term relationship between individuals. Two males may work together to overcome dominant male and work together as a unit to maintain colony if they win.
Are meerkats selfish or altruistic sentinels?
Hypotheses used to be that they roared sentinel duty, but they don’t. Sentinel “perch sites” are near burrow entrances. Spend same amount of time scanning while alone. Spend more time being vigilant and less time spent foraging if food is abundant. So, sentinels are just good foragers/good body condition and just trying to keep self safe.
How is reciprocity maintained
Individuals have to meet each other often
Cheaters have to be recognIzed and punished - but “forgiven” if they eventually cooperate. Possible only for social species. This score-keeping has been tested experimentally in the cotton-topped tamarin. They appear to keep score. Helpful companions pulled bar to move food closer to separated companion. Unhelpful companions did not. Monkeys more likely to help helpful companion when roles reversed.
Reciprocal altruism in complex groups can produce emotional responses
Trust, justice, forgiveness
Altruism
A big Darwinian puzzle
- social insects, Arabian babblers (live in group, defend territory, only one breeding pair) are examples
Altruism usually occurs between relatives
- kin selection (genetically selfish altruism)
- -process by which characteristics are favored due to their beneficial effects on close relatives. Altruistic genotypes are then passed on through those relatives.
Examples of kin selected behavior
Parental care toward own offspring (when there is a choice between taking care of offspring or having more)
Aid to non-descendent kin
Fitness has two components
Direct fitness: personal reproductive success gained via parental investment (energy to produce gametes/maintain young/etc) in own offspring
Indirect: increase in reproductive success of kin attributable to helpers behavior (additional offspring who owe tier existence to helper X relatedness to helper)
–NOT just number if relatives in population; only individuals that count are those you make possible through help
R of different kin
.5 offspring and siblings
.25 grand kids and nieces/nephews
.125 great grand kids and cousins
Inclusive fitness
Direct + indirect fitness = genetic units of inclusive fitness
When should altruism be favored?
Hamilton’s rule: rbB > rcC
rb = coefficient if relatedness to beneficiary offspring
rc (always .5) = coefficient of relatedness to altruists own offspring
B = # of additional offspring made possible by altruistic behavior
C = # of own offspring “sacrificed” by altruist/# of offspring you COULD have had
For the average individual, altruism would be favored if you could ensure the survivorship of relatives to make up for the loss of own offspring.
Kin selected altruism in animals
Eusocial insects: non-reproductive castes (most extreme example)
Haplodiploid hypothesis:
Sterile female workers develop from fertilized eggs, males from fertilized
Queens share 50% genes with offspring
Workers share 75% genes with sisters - 100% of fathers half (because father only has one set of chromosomes), 50% from mothers half
Prairie dog kin selection behavior
Alarm calling by female prairie dogs- more likely to call if relatives nearby (call draws attention to selfs - dangerous)
How are kin recognized?
Imprinting on brood males
Phenotype matching - recognition of phenotypes similar to your own
Odor may be a cue in ground squirrels and tiger salamanders (cannibals less likely to develop if relatives present - don’t eat those that smell like yourself).
Or, if daphnia develops in presence of predators, develop helmet with spikes as opposes to just a helmet
Imprinting and phenotype matching
Belsing’s ground squirrel cross-fostering experiment
- siblings raised together, apart
- non-siblings raised together, apart
Set up these four groups. Found that nest mates less aggressive toward each other (indicates imprinting). Also less aggression between siblings raised apart (demonstrates phenotype-matching as another discrimination mechanism). Habituation may play a role as well
Cooperative breeding
- some individuals spend all or part of their lives helping others reproduce
Helpers at the nest
- dominant breeding pair, rest hell and forego their own reproduction
Ex : Florida scrub jay. Live in oak scrub - specialized - once full, rest become floaters or live on territory with parents.
- only territorial pairs breed. About 50% have helpers, who are almost always mature offspring. Help feed young and defend territory
–their presence increases number of surviving siblings, survivorship of parents (parental care is costly - predation, exposure, less time spent feeding self, etc)
Why do helpers stay?
Habitat saturation - seems to be the case with other cooperative breeders too - specialized habitat requirement leaves juveniles with few options
- males often inherit territory
- if adults die, helpers can move in
General group benefits
Why do helpers help
Direct benefits - breeding experience, more tolerance by parents when helpers help
Genetic benefits - increased inclusive fitness
Removal of helpers significantly reduces # of surviving offspring on territories
