Lecture 12: Sexual Selection Flashcards
Breeding Systems
Monogamy: ♀︎-♂︎, Variation in breeding success ♀︎=♂︎(most large, long living birds -> cheating is too costly, because they have only one offspring and are vey dependent on one another/ Nesting habits)
Polygyny: ♀︎♀︎-♂︎, Variation in breeding success ♀︎<♂︎ (♂︎=0 für nicht erfolgreiche Männchen)
Polyandry: ♀︎-♂︎♂︎, Variation in breeding success ♀︎>♂︎
Polygynandry/Promiscuity: ♀︎♀︎-♂︎♂︎, ♀︎<♂︎
Hermaphroditism: sexually reproducing organism that produces both male and female gametes e.g. some fish change their sex with age; some snails decide with each egg, which partner get’s to be the male part because females = higher investment in offspring)
Sexual Selection: Traits increasing competitive strength
- Body mass
- Weapons
- Behaviour: fighting, rutting, Lekking (Arenabalz), mate guarding
Intrasexual selection
Selected by ♂♂ competition
In which species does Attraction play a role(??)
Hierarchies, rank, competitive strength:
Group living species, Harem defending species, lekking species
Traits increasig attractiveness:
- ornaments
- colours
Behaviour:
- display behaviour
(e.g. song, dance, lekking)
- tenure “Amtszeit” (e.g. hyenas-> males which are around the longest (in new group) are more successful in breeding)
Selected by ♀ mate choice:
-intersexual selection -> genetic benefits for females
- Epigamic selection (attractiveness to the other sex)
Anisogamie def.
männliche und weibliche Gameten sind ungleich groß oder nur physiologisch (physiologische Anisogamie) verschieden
Basic sexual difference:
-Investment into gamets: ANISOGAMIE
-♂gamets: smaller, more mobile
task: find egg
-♀gamets: larger, immobile
task: provide resources for zygote
-Later in life : ♀ invest into egg nutrition, egg protection, with dependent offspring: into
protection, feeding, lactation…
-Competition among ♂gametes for access → choosiness of females
-Exploitation of ♀ investment by ♂
-High variation in fitness among ♂ ♂ reproductive skew → strong intramaskuline selection
-Little variation in fitness among ♀ → weak intrafeminine selection
Evolutionary mechanisms
- Intra- and intersexual selection can work in the same direction
- Sexual selection can work in opposite direction to natural selection
Evolutionary mechanism:
Fishers Hypothesis (runaway-process)
Stimulating feedback genetic co-variance, between
♀preferenz and ♂trait
Starts with
- a quality indicator
- a suspicious trait
- a sensory bias
-> Sexy Son Hypotheses
Genetic basis is inherited to sons of ♂ , Simultaneiously with the gen for ♀ preference
Evolutionary mechanism:
Handicap Principle
Ornament as handicap (Zahavi 1975, 1977)
→ indicates genetic quality of trait bearer
→„good genes“ for survival (not sexiness as with Fisher)
Test:
- condition dependent trait ?
Honest signal (e.g. if the deer is ill/has many parasites- > the antlers will not grow big this year)
Evolutionary mechanism:
Hamilton-Zuk hypothesis
parasitation rate as handicap
-> male showiness allows females to assess male’s ability to resist parasites.
Hirschhypothese. Geweih in einem jahr whack, wegen paraisten befall. anderes Tier hat tolles geweihn weil paraistenbeständiger und mehr energei übrig für Geweihausbildung.
Reproductive skew, Bateman‘s principle
-in most species, variability in reproductive success (or reproductive variance) is greater in males than in females.
-a male’s potential reproductive success is limited by the number of females he mates with, whereas a female’s potential reproductive success is limited by how many eggs she can produce
-> this results in sexual selection, in which males compete with each other, and females become choosy in which males to mate with. Thus, as a result of being anisogamous, males are fundamentally promiscuous, and females are fundamentally selective.
Alternative mating strategies:
The ruff (Kampfläufer, Philomachus pugnax)
Black: Territory defence
White: Satellite male
Third morph: looks like female
Plumage colour heritage -> Genetically determined strategies (not conditional tactics!)
- Must have an average similar reproductive success to be evolutionary stable (ESS) and maintained in the population
- possibly the satellite males are longer lived (Widemo 1998)
Sexual conflict: def. & areas
Definition: Fitness enhancing trait of one sex decreases fitness of the other sex
Areas:
* mate choice, copulations
* parental investment
* multiple mating / mate guarding
* destruction of investment - infanticide
Sexual conflicts: Copulation
Copulations:
-♀ choosy (higher investment in offspring)
-♂ Strategy:
-Display for female choice
-Fight / displace competitors
Alternative strategies:
-harassment
-coercion, traumatic insemination
->Scorpionsfly, Waterstriders, Bedbugs
-> Counterstrategy: cryptic female choice e.g. low fertility rate
Often a strategy for qualitatively low ♂
-Satellites (Frogs, Ruffs)
-Sneaker (camouflage as female, e.g. fish)
Proximate mechanisms:
precopulatory - postcopulatory,
prezygotic - postzygotic
Pregnancy block / pregnancy termination in mammals
- Counterstrategy to infanticide by males (prevent investment?) -> sometimes witnessed after the change of the “primary” male
- To save resources under bad conditions
Parental investment → Mating system
Parental care
birds: both parents → monogamy or if only females → polygyny
mammals: females → polygyny / promiscuity
fish: Males / none → Polygyny / Polyandry, Promiscuity
Polyandry
Common! molecular prove of sireship: ♀ mates with multiple ♂ ♂ ♂
Multiple matings costs:
Energy
Desease
Predation
Terminology
Polgynandry, promiscuity (no pairs, no harems)
– multiple male mating MMM (e.g. one offspring is still from one father but u can not know if the female had more than one partner)
– multiple paternity MP (in one litter different Fathers/ male genetics)
Terminology - Social monogamy (pairs)
- extra-pair copulations EPC (is a mating behaviour in monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together, mating outside this pairing is EPC)
- extra-pair paternities EPP: The rate of EPP reflects the proportion of offspring, for example, within a nest or population, fathered by males other than the primary male (social mate).
Polyandry: Direct benefits
- ensuring fertiliy
- induction of ovulation - infanticide protection
- access to ressources of several mates (territories, paternal investment
Polyandry: Indirect (genetic) benefits
Collect good genes
intrinsic male quality hypotheses:
- trade-up
- post copulatory cryptic choice
link sperm– offspring quality
sexy sperm hypothesis (heritable)
Avoid genetic Incompatibilität
- selective fertilisation
- selective resorbion / abortion - Avoid inbreeding
Bet-hedging
-variable environmental conditions
-Variable genetic combinations
Intersexual selection
Selected by ♀ mate choice
- Epigamic Selection = attractive to the other sex
- Traits increasig attractiveness:
- ornaments
- colours
Behaviour:
- display behaviour
(e.g. song, dance, lekking) - tenure
Epigamic selection (=intersexual selection) occurs when members of one sex prefer mating with members of the other sex on the basis of individual differences in inherited characteristics
