Alternative Mating strategies Flashcards
Discuss monogamy in birds
male birds can feed young as well as females(unlike most mammals) Male assistance is essential to rearing young. Probably explains why more than 90% of birds are monogamous. In many birds raising young is so hard that it takes a pair to raise even one young. eg albatrosses. In tree swallows polygynous males father fewer surviving young than monogamous males. Why?
Because more offspring of polygynous males die because males cant help both females. Females can also mate with other males but because male cannot guard two females effectively, reproductive success is lower (MGH). Monogamy best for both male and female eg tree swallows.
Discuss polygyny
Any mating system involving mating and in many cases forming pair bonds with multiple members of the opposite sex.
one male mates with many females.
May occur in harems
common in fish, reptiles and mammals
strongly influenced by sexual selection
several different mating tactics can occur
What are the three basic types of Polygyny
Resource defensive polygyny
Female defense polygyny
lek polygyny
What is resource defence polygyny
Male defends resources that females need to produce young (food, nesting sites). eg African cichlids. African cichlid fish Lamprologus callipterus exhibits extreme sexual dimorphism (males 13x larger than females). Females lay eggs inside empty snail shells and remain inside shell until eggs hatch. MAles collect suitable shells and steal them from other males. Males then gather shells into large collections and defend them from rival males. Up to 86 shells have been recorded in one collection and up to 14 females at once. Males with good territories obtain high reproductive success. Extremely large male body size has been selected for because it enables males to collect shells and to defend their territories.
Male red-winged blackbirds hold territory on marshes. Males with the best territories attract harems of up to 15 females. Females choose males on the basis of territory quality- emphasizes the importance of territory quality/resource. Males red epaulettes are essential in male-male competition.
What is the polygyny threshold model
some females choose to mate with already mated males who will not help them feed their chicks/offspring even though unmated males with territories are available. Why? environmental resources?
The model predicts that females will accept the role of 2nd mate when superior resources on males territory mean that she would do better there than as a 1st mate for a male on poor territory. female making choices all the time.
Example- Male LArk Buntings- establish territories in grassy, open habitats. Mate with one female but assist only first female to settle on their territory. Soem females accept secondary role on good territory to obtain high quality nesting site. There is a largevariance in male territory quality. In bad nest sites young die from exposure to the sun ie bad nest sites are really bad. (experimenters shaded nests- changed quality).
what is female defence polygyny
Common when females cluster in groups that are defensible. Essentially males defend female clusters against other males. Eg elephant seals, lion prides, elk and deer. Females defense polygyny females cluster- males exploit this. Lionesses- defend feeding territories. Deer- protection. Elephant seals gather on the few suitable nursery beaches.
What is lek polygyny
Males dont help. High variance in male mating success. Eg grouse, ruffs and manakins.
Males display for females predictable locations, Female chooses mates. Males provide no resource except sperm. Definition of LEK- a gathering of males of certain animal species, for the purpose of competitive mating display.
LEks- highly skewed mating success. Few males- most matings. Female obtain the best available genes. Black grouse, sage grouse 70-80% copulations.
Why do males gather in leks
Attract more females- they shop around for the best males. DOnt have to spend time and resources looking for mates. May reduce predation risk. eg open country birds display in groups whereas forest species usually display solitarily.
What are the three hypothesis that support evolution of lekking
1) hot spots hypothesis- males choose an area where females are likely to be/pass through
2) hot shots hypothesis- subordinate males choose an area around a supermodel male, so that they get seen by females
3) female preference hypothesis- females come to groups of males to better make a better comparison for who might be the best mate
Society with multiple mating opportunities- males and females are continuously choosing partners. Continuously attempting to further increase their genetic input into the nest generation. Choose on the basis of quality (of partner, territory, sexy sons, fertility)
fluid system- choices made and unmade.
Discuss the case study of the Dunnock hedge sparrow Prunella modularis
Agression in fighting, injury, sneaky copulations, both males and females, sexual deceit, paternity arguments, multiple copulations. Cloacal packing. Individuals strive inc. own reproductive success. Major influence on mating system is territorial behaviour. males and females defend terrories.
Female territory - food. older larger females defend larger territory
Male territory size- flighing ability to defend females. But categories of mating system are often blurred. An alpha male sometimes had territory overlapping with a beta male sometimes with 2 or more females. Bewildering array of mating systems. Davies suggested mating systems were a continuum rather than on a discrete scale. Malw mating success appear to increase going down the list, female mating success going up the list. Conflict between the sexes pivotal to explaining the variable mating system ie males strive to go one way and female strived to go to the other.
Why might this be so?
For females- they gain full maternity of brood whoever fetilises the eggs bu males only help provision the young if they have mated with that female. Thus females
1) are aggressive to other females in polygyny (2 females 1 male). Each female wants the male to provision her offspring, not that of another female.
2) females in polyandry (1 female, 2 males) encourage copulation from alpha and beta males.
- often fly off and try and sneak extra matings
- why? because if a female gets several males to mate with her, they will all help to provision the young and they all have vested interest.
Discuss alternative mating strategies and tactics.
Important evolutionary force generating individual variation within a sex is social interaction. seen before, circumstances where sexual selection has produced differences between the sexes eg elephant seals has also provided large variations in on of the sexes, usually males. Mentioned that the sex that invests less has a higher variance of the trait concerned. Might imagine that if you were a small male, that you would be enoucrgaed to attempt some other reproductive tactic- just so you could gain some matings
Alternative reproductive strategies are characterised by a genetic polymorphism. Equal fitness provided by frequency-dependent selection. Not so many know examples.
Discuss swordtail fish for alternative mating strategies
43 alleles single Y locus. Code for sneak and sneak and court and court. Fitnesses are presumed equal as too many of one type promotes the other genotype. individuals cant change from on strategy to another.
Discuss the side botched lizard
Three different morphs- organge, blue and yellow.
Ultra dominant polygynous orange throated males beat monogamous mate guarding blue males which beat yellow sneaker strategy, can mimic females, fool orange males who are susceptible to their charms. Eventually usuprt the dominant males. Each strategy has a strength and weakness. get cycles occurring with each morph dominating for a few years, before another takes over.
Discuss the side botched lizard
Three different morphs- organge, blue and yellow.
Ultra dominant polygynous orange throated males beat monogamous mate guarding blue males which beat yellow sneaker strategy, can mimic females, fool orange males who are susceptible to their charms. Eventually usuprt the dominant males. Each strategy has a strength and weakness. get cycles occurring with each morph dominating for a few years, before another takes over.
