Lecture 18-SEXUAL WARS Flashcards
Exchange genetic material in asexual reproduction
- transformation
- conjugation
- transduction
- recombination
Road to sexual reproduction
Syngamy and meiosis
“The production of new living organisms by combining genetic information from two individuals of different types (sexes)”
*Sexual reproduction started 2 billion years ago (single cells protists)
*Complex organisms appeared 1.3 billion years later
Definition: Meiosis is a specialized type of cell division that reduces the chromosome number by half, producing four genetically distinct haploid cells from a single diploid parent cell. This process is crucial for the formation of gametes (sperm and eggs).
Definition: Syngamy is the process of fusion between two gametes (sperm and egg cells) to form a zygote. This fusion results in the combination of genetic material from two parent organisms, creating a single cell with a full set of chromosomes.
Sexual Reproduction
*Only half of the genes are passed
*You need to find a mate (and compete for it)
*Sperm moves in water only *Diseases
*Switch between mitosis and meiosis
Aphids:
-Asexual when lots of resources
-Sexual end of season
Holocyclic
alternation between a sexual generation and an asexual
Hot seasons, lots of food- Stable environment –no changes
Cold seasons, less of food, high concentration- Unstable environment –changes
So, why reproduce sexually??
Sex evolves when:
*Selection changes over time (Red Queens Hp)
*Selection changes over space
*Organisms are less adapted to their environment
*Population are finite (recessive traits)
Sex evolved to generate variation!
Sexual Selection
Does not depend on a struggle for existence (…) but on a struggle between individuals of one sex, generally the males for the possession of the other sex (…). When the males and females (…) have the same general habits but differ in structure, colour, or ornament, such differences have been mainly caused by sexual selection.
what is natural vs sexual selection?
“The process trough which males and females attempt to maximise their chances of reproductive success”
Natural Selection: favors those phenotypes with greater survival ability
Sexual Selection: favors those phenotypes with greater reproductive success due to greater ability to acquire mate
deeper into sexual selection
It favors characteristics that enhance reproductive success
1.Primary sexual characteristics: Genitalia and organs of reproduction
- Secondary sexual characteristics: Morphological differences between the sexes not directly involved in reproduction
Sexual dimorphism
Differences in appearance between males and females of the same species
Sexual dimorphism can be express as:
*Presence of weapons
*Presence of ornamentse
*Difference in size
Sexual Selection
favours characteristics that enhance reproductive success
- Intrasexual selection -Mate competition
-Selection in which one sex competes with other members of the same sex for access to the other sex for reproduction - Intersexual selection -Mate choice
-Selection by one sex for members of the other sex for reproduction
. Intrasexual selection: Mate competition
Male-male competition can explain the evolution of many morphological and behavioral traits
Male competition has led to an exaggeration of body size and horn size
Intrasexual selection
Alternative strategies …If you can’t beat them, fool them
Many species have polymorphic or polyphonic male mating strategies
Sneakers: males not directly engaging in competition for mates may gain extra-pair copulations. (e.g., small “Jack” salmon
Female mimicry: one way to distract or interrupt a competitor
Intrasexual selection: Sperm competition
Male-Male competition is often post-copulatory
*The male of damselfly uses its penis to remove sperm from previous matings
*Bee drone mate with explosive force that the tip of his penis ruptures inside the queen
Intersexual selection -Mate choice
Elaborate traits can also be the result of Female preference
Intersexual selection -Male ornaments
The peacock’s tail greatly impairs his mobility…how could such a trait evolve?
Stalk-eyed fly
*Their eyes are mounted on projections from the sides of the head
*Can ingest air and pump it through ducts to the tips of the eye stalks, elongating them while still soft
*Females show a strong preference for males with longer eyestalk
Intersexual selection -female choice
Direct Benefits:
Females benefit from increased nutrition, provisioning, or paternal care that increases their reproductive output or the quality of their offspring.
Indirect benefits:
*Good Genes Hypothesis (The Handicap Principle): Genetically superior mates produce fitter offspring.
*Sexy Son Hypothesis:Females that mate with preferred fathers produce sons that inherit preferred phenotypes
Good Genes Hypothesis
Elaborated male traits may be indicators of heritable genetic quality
*The bigger the handicap, the higher the genetic quality of the male carrying the trait.
*Female choice evolves and the handicap spreads and becomes elaborated
*This is an example of an honest signal since there is a true cost to the elaborated trait that prevents “cheaters”.
Some candidate “handicaps”
Traits that are physiologically costly or more expensive to develop
Asymmetry is indicative of developmental instability and possibly“bad genes”.
Bright color honestly signals immunocompetence and parasite/disease resistance
Sexy Son Hypothesis
Persistent, directional female choice leads to exaggerated male ornamentation
*Female choice originally for traits with survival advantage
*More sons have this trait; more female prefer it
*Trait becomes exaggerated while the advantage loses importance.
*At the end, selection is driven only by attractiveness of the trait and not by adaptive effect
=> maladaptive
sexual selection vs natural selection
*Sexual selection can be very strong and often opposes natural selection
*This can lead to exaggerated and sometimes maladaptive development of male traits
Concepts in Sexual Selection
1.Sexual selection favours characteristics that enhance reproductive success
2.Females select males to obtain direct material benefits
3.Female mate choice can evolve via indirect benefits to offspring
4.Sexual selection can also occur after mating
5.Mate choice by females favors alternative reproductive tactics in males 6.Mate choice is affected by the mating decision of other
