Reproductive strategies Flashcards
Polygyny Threshold Model definition
The polygyny threshold model is an explanation of polygyny, the mating of one male of a species with more than one female.
The model shows how females may gain a higher level of biological fitness by mating with a male who already has a mate.
Contrasts ‘monogamy’ to ‘polygyny’; point where the threshold of environmental/reproductive fitness intersects and choice of forming polygyny
who came up with the polygyny threhold model
Orians 1969
explain the Polygyny Threshold Model
‘better to be the second wife of a rich man than the only wife of a poor man:
HR male=good territory/better genes + reproductive success
LR Male= bad terrirotry + lower reproductive success
- first female gets HR male
- second femalee gets MR male
- third female; either settle for LR male or become second female for HR male as the reproductive success will be the same
where is the Polgyny Threshold Model commen
in birds (peacocks) in humans
when is polygyny likely to develop
when different quality territories exist= hence males can monopolize territories
why do non-polygynous groupings occur?
- mate-defense: males cant monopolize a batch of females against competitiors
- resource-defense: females unqilling to settle with an already-paired male/need parental support
why would males prefer polygynous systems
as they have to invest less than females
how do males monopolize females
mate defense: males go where females are
resource defense: females to where males control resources
when would females desynchronize fertility?
female-female sperm competition reduced
creates polygyny
increase paternity uncertainity
redeuce infanticide
reduce food ceomptition with males
what kind of competition do males engage in
contest competition for females; as its an ‘aool or nothing’ situation (fertilization cant be shared)
when does mate scramble competitio noccur
- when mates are abundant in a given space (polgyny/polyandry)
what defines reproductive strategies
behavioral, morphological, and physiological adaptations that facilitate access to potential mates, improve the chances of mating and fertilization, and enhance infant survival.
what is male reproductive success limited by
the amount of fertile females they can access
what is the ideal male reproductive strategy
rapid sexual maturation, followed by life-long exclusive access to an unlimited number of fertile females willing to mate, and offspring survival should be independent of paternal care.
socionomic sex ratio
the proportion of males and females ready to mate at a given time
male reproductive skew
the partitioning of fertilizations among males
Priority-of-access models
a positive relation between rank and reproductive success)
what does socio ecological theory propose
Socio-ecological theory predicts that the distribution of receptive females in space and time is the main predictor of males’ ability to monopolize fertilization opportunities
when females are solitary (dispersed)
individual males defend exclusive access to only one (monogamy) or several females ( disperesed polygyny)
when females are in groups (clumped)
one male can monopolize multiple females (polygyny)
or multiple males can form a group with multiple females (polygynandry)
what infleunces the spatio0temporal distrubiton of females
spatial; distribution of food in space
temporal; whether their ovulation/fertility is synchronized
example of clumped polygyny
jodhur langurs which are provisionsed where females are desyncrhonized
example of clumped polygyandry
ramnagar langurs where food is seasonal where females are synchronized
spatially dispresed chimps
females are monopolized by male alliances/coalitions
spatially dispresed orangutans
female reproduction monoipolized by one male and fertility is desynchronized
spatially dispresed gibbons
monogamous groupings but extra pair copulations may happen
what are male-alliance polygyandry?
when groups of males (brother bands) control territories to which FEMALES migrate to (nonnatal philopatries);
female choice is governed by who has the nicest territories e.g. in chimps
explain the age variation of female reproductive performance
Middle-aged= produce the most offspring as
young moms have higher birth intreveals and fertility declines with ages
thus high ranking, middle aged females produce the most offspring
what is a ‘strategy’
a set of behaviours in a specific functional context as a product of natural selection, to increase reprodutive success
name three identity factors that influence female reprodutive success
- age (middle age= better success)
- longetivity (live longer= produce more)
- rank (high dominance= produce more)
Barton-Whiten Study?
studied olive baboons; found that high ranking females have a 30% more food intake letting them have more reproductive success
intrasexual sexlection examples
sexual dimorphism
larger body size, canine, teeth and weapons enhance male competitive ability
where is sexual dimorphism greater?
in polygynous/polyamarous groupings because of higher competition
how does intrasexual sexlection work on polygyandrous groupings
sperm competition; EPCS mean that a male with MORE SPERM and bigger BALLS can have more fertilization success
cooperative breeding systems
in marmosets and tamarins;
dominant pair (habitual twinning and short birth intrevals) and helps
polygyandrous groupings; more males help increase female fertility
evidence for infanticide
- infanticide associated with change in male residence status in polygynous groups
- males kill infants to end lactational ammehnorea
- males kill only non-related infants
- infancidical males then recieve reproductive benefits
Sarah Hrdy Sexual Selection Infanticide Hypothesis
infanticide occurs to stop female lactation ammehnorea to allow for males to copulate with females
Naturallistic Fallacy
sommer; tendency to assume what we seen in nature is RIGHT and derive moral meaning from the natural world
‘just because it IS doesnt mean it ought to be’
female response to infanticide
- bruce effect (terminate prengancies themselves)
- extra-pair copulations; mate with several males to create patertnity uncertainity
- form alliances with other males to protect infants
- concealed ovulation (continue mating when pregnant)
where do females form alliances to prevent infanticide
baboons!
Mate guarding
a male prevents a female from mating with other males by maintaining close proximity during her receptive period
stress hormones in lr and hr males
subordinate males= higher stress hormones in baboons
why might a mother change her behaviour with her children
to encourage them to become more inedpenent (less nursing, travelling alone, etc)
or for children to wean to allow for lactation to reoocur
sexual selection theory
(darwin) “the advantageous traits some individuals ahve over others in the same sex to increase reproductive success”
explains role of useless traits as giving advantages to certain invidiauls of the same sex to secure rproduction
law of battle
competition for access of a mate against others
attraction methods
to entice choice
female olive baboon sexual swellings: two hypothesis
- pagel reliable indiciator hypothesis
- nunns graded signal hypothesis
(study by higham 2008)
pagel reliable indiciator hypothesis
males select for biggest swelling as it shows female fitness (phermone advertisment)
attraction benefits for both individuals and offspring
nunns graded signal hypothesis
female swelling size; indicates ovulation likelihood
(visual aid)
olive baboon study= size a determinant
best reproductive strategy for when females are in groups for a male
find the group with the most females= results in high male to male compotetition
benefits of reproductive seasonality
makes females less vulernable to male aggression
decreases male competition till mating season (sexual dimorphism becomes seasonsa)
mate competition types
endurance rivaraly scramble competition contest compeittion reproductive supression sperm compeittion cryptic female choice
mate choice stages
precopulatory choice (behaviour)
post copulatory choice (cryptic choice)
post fertilization choice (gamete selction)
Bateman-Trivers 1972 Theory
sexual selection is controlled by relative parental investment of sexes in young= so members that invest more are themselves a limited resource
when do males have monopoloy in choice
- long term desire
- quality female variation (polygyny)
- monopolize resources
clutton brock vincent 1999 theory
differents in POTENTIAL reproductive roles of males and females predict the VARIATION in the strength of sexual selection
fisherian ‘runaway selection’ hypthesis
traits are selected for by females which then makes those traits more abundant/selected for
a positive feedback loop in which a particular trait is desired by a female and present in a male, and that desire for and presence of that particular trait are then reflected in their offspring.[20] If this mechanism is strong enough, it can lead to a type of self-reinforcing coevolution
a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of exaggerated male ornamentation by persistent, directional female choice.
good genes hypothesies
the traits females choose when selecting a mate are honest indicators of the male’s ability to pass on genes that will increase the survival or reproductive success of her offspring
handicap principle
costly traits are chosen before as it shows the reproductive fitness of a mate to be able to produce those
heterozygosity hypothesis
dissailmiar traits are chosen to inrease variation and avoid inbreeding/mutations
genetic compability hypothesis
Genetic compatibility refers to how well the genes of two parents function together in their offspring. Choosing genetically compatible mates could result in optimally fit offspring and notably affect reproductive fitness (led by phermonenes to find ‘good sperm)
sensory bias hypothesis
the preference for a trait evolves in a non-mating context and is then exploited by the less choosy sex in order to obtain more mating opportunities. (PREEXISTING BIAS SELECTION)
The competitive sex evolves traits that exploit a pre-existing bias that the choosy sex already possesses.
This mechanism is thought to explain remarkable trait differences in closely related species because it produces a divergence in signaling systems which leads to reproductive isolation.
chase away hypothesis
exaggerated traits are chosen for to overcome female bias (avoids diminished attraction of homogenous males= variance)
aesthethic hypothesis
Richard Drum 2017; ‘evolution of beauty’ theory (not all traits adaptive but aesthethic)
fertilization insurance hypothesis
females copulate with multiple males to ensure proper reproductive success
Hamilton-Zuk hypothesis
posits that sexual ornaments are indicators of parasite- and disease-resistance.
sexy son hyoppthesis
The sexy son hypothesis in evolutionary biology and sexual selection—proposed by Ronald Fisher in 1930—states that a female’s ideal mate choice among potential mates is one whose genes will produce male offspring with the best chance of reproductive success.
direct benefits of being choosy
increase the fitness of the choosy sex through direct material advantages or resources. (CHOOSY SEX GETS RESOURCES)
These benefits include but are not limited to:
increased territory quality,
increased parental care,
increased protection from predators.
indirect benefits of being choosy
increase genetic fitness for the offspring, and thereby increase the parents’ inclusive fitness. (CHOOSY SEX GETS GENES)
high-quality genes for their offspring (known as adaptive indirect benefits)
or genes that make their offspring more attractive (known as arbitrary indirect benefits
what are indicator hypothesis?
‘good genes’ hypothesis;
include the hamilton zuk (disease) and good genes
what is the baldwin effect?
the hypothesis that adaptive learning (i.e., learning to improve fitness) accelerates genetic evolution of the phenotype (by James Mark Baldwin)
what is the baldwin effect?
the hypothesis that adaptive learning (i.e., learning to improve fitness) accelerates genetic evolution of the phenotype (by James Mark Baldwin)
what type of mate do females prefer
dominant males friendly males individual variance (aboid inbreeding, subjective pretty traits)
why dont brown capuchins go for the top ranks
brown capuchins cant control resources hence females dont go for top ranks
why do females go for domiannt males
as they can control resources
how are rhesus monkeys the exeption to choose dominant males
rhesus macaques select young males that might achieve top rank as opposed to already dominant ones
females might not hence be PREFERRED by dominant males and only monopolized by them
prostitution hypothesis
sex for food/services
just wann have fun hpothesis
sexual pleasure motivates fertliziation
why might females copulate outside mating systems/ovulatory window
prostitution hypothesis
just wann have fun hpothesis
example of cryptic female choice
sexual swellings peak during ovulation to demonstrate females want to fertilize= allow for females to control WHEN men can fertilize eggs
what does EMSOMS stand for
ecological model of social organization and mating systems decided by:
resources + risks—> female distributions— Male strategies
what do male strategies depend on with dispersed females
infant care
defenseibility of a female
what do male strategies depend on in grouped females
ability to monopolize the females;
- number of females
- spatio temportal receptive perios
in haplorrhines; what is more important for primate mating systems
spatiotemporal distrubiton of females
in strepsirhiness; what is more important for the sexual recpetivie of females
sexual recpetiivy of a female
types of primate relationships
aggressive (biolent, dominance, hierarchial)
nonaggressive (grooming, mutalism, cooperation)
when does male-male competition relax
females dominant
high access to females
male infant care participation occurs
territoriality
protecting and maintaing access to an exclusive area for resourece and mate defense
costs of territoriatliy
constant vigiliance
regular advertisiment of presencne
defend ranges against intrudors
higham 2008 studied
olive baboon sexual swellings to evaluate nunns and pagels hypothesis
girls just wanna hav efun hypothesis
sex for pleasure
nulliparous
0 births
primiparours
1 birth
multiparaous
more than one birth
types of pregnances in a females ontogensis
nulligravida (0)
primigravida (1)
multigravida (more than one)
female…. affect male to male competition
grouping patterns
syncrocitiy
reproductive traits/rates
mate choices
uni-male groups
evict natal males and defend against beacholor dispersed males
(low intragroup, high intergroup competition)
mult- male groups
high within group; low intergrouup
examples of dispersed-kin based coalitions
ring tailed lemurs
perruvian squireel monkeys
dispersed males
more likely to be paternal kin
join maternal brtoehrs based on age similiarities
when can high ranking individuals NOT monopolize access to females
- fluid female grouping patterns (chimps and spider monkeys)
- when males cant keep track of all their reproductive conditions
- synchronize female cycle (lemurs, langurs, squirrel monkeys)
life history of a male; changes
- male fighting abilities
- presence of allies
- potential allies
where is rank imporant for males
in hierarchial societies
where is rank not important for males
in philopatries/weak dominant societies where female schoice, indviidual intiative and maternal support is more important
advantages to staying in a natal group
- less external competition (closed group membership)
2. no problems of gaining access to females within the group
how are hierarchial societies maintained
aggresive interactions
epc
why are male hierarchies less stable than female matrilines
- rank reversals
- challenges of LR males
- males dont inherit rank
- unclear paternity uncertainity
spider monkey social system
central america/mexico;
- males spend more time grooming
- males interact more aggresivley too
- coalitions ‘gang up’ on females (assert dominance despite lack of dimophirsm)
- alpha males have mating priviliges
bonobo social system
- eglterian system, patrillinieal
- maternal sypport affects the sons rank
- female bonobos give confusing sexual cues about ovulation= so harder to monopolize= less aggression in group
muriqiui social system
- no evidence of atagonistic hierarhcy as males cant monpolize females
- female choice more important= they wmit mating calls when read to mate/let mates inspect their genitals (phermomnoes)
- females freely switch males= hence high sperm competition
why are maternal brothers more likely to be friends than paternal brothers
birth intrevals; creates age differences= les likelyl to reconize each other as kin
why do chimps work hard to cultivate alliances
- for solidarity in between group competition
- for rank reversals and social climbing
- to get female help (as females might interact on behalf of males in antagonistc disbutes such asin the zoo but not in the wild)
Bonobos and rank inheriratnce; congo
no strict linear hierarhcy: depends on mother and male age
- males born when mom was young have higher rank
- males born when mom was old have lower rank
- older males have higher rank
mountain gorillas: homosexual vs heterosexual groups
- hetero sexual= more aggression/dominance
2. homosexual= more grooming/sex/egalitarian
relationship of multi-male hetereosexual groups to females
1 more proximity/grooming of females to dominant male
2 older males support daughters more
3. stronger relationships to FEMALES than each other regardless of kinship
found in: mountain gorillas, red howler monkeys and hamadryas baboons
yellow baboons
immigrants have higher cortisoal levels than group
as they are dispresed males
japanese macaques and rank
unrelated multimales= ranks with male age
in small/lowresidence group= less likely to form coalitions so more movement nad hence more male grooming
chacma baboons and rank challenges
usually males more likely to challenges males of a ssimilar rank OR two mr/lr males join together to challenge higher ranking males
why is there a lo tof rank reversal in ring tailed lemurs
as females are dominant
afflitiations are short and not determined by age and residency
how do hanuman monkeys gain success in a group
ability to maintain residency in group and aboid female extra group copulaionts as 25% of males never access a female
monogamous groups; what is one of the key issues when considering to cheat?
- cheat and gain more fertilizations; but deal with more unrelated males/sons
- be loyal and guard male; protect infants
