lec 21- sex causes and consequences Flashcards
what is the human and biological definition of sex?
human: copulation or sexual contact between individuals
biological: sex implies the presence of different males and females in the same species
what are males and females?
-males produce abundant small sperm
-females produces fewer eggs
what is the definition of sexual reproduction and what does it imply?
-the fusion of gametes to make an offspring
-process involves meiosis to form haploid gametes; and implies that chromosomes, meiosis, and sex must have evolved together during the evolution of the eukaryotes
what is the definition of asexual reproduction?
occurs either by cloning of somatic tissues, or by producing offspring without fusion of male and female gametes, leading to some form of parthenogenesis
what is pathogenesis?
fertilization without the fusion of gametes
what lizards individuals are completely parthenogenic and how does it occur?
whiptail lizards, all females and chromosomes inside the eggs duplicate and undergo meiosis, producing only female gametes that fuse to form embryos, no sperm needed
what is asexual reproduction often coupled with?
-with occasional sexual or other variability enhancement
-examples: horizontal gene transfer, somatic budding, parthenogenic plants
what is a hermaphrodite, and when is it rare and common?
an individual that has both male and female sex organs, common in plants and rare in animals (banana slugs)
what are the two reasons why sexual production is more costly than asexual?
- by breeding with a male, a female halves her genetic contribution to her offspring (50% rather than 100%)
- only half of the population (females) is capable of bearing offspring, while asexual has all population capable of bearing offspring
why is sexual reproduction more common even when costly?
-because it increases genetic variation
-sexual populations can purge deleterious mutations by recombination generating individuals with allelic combinations that exclude them
-asexual individuals inherit all deleterious mutations from parents, making population more prone to extinction
what is Muller’s ratchet?
asexual individuals inherit all deleterious mutations from parents, making population more prone to extinction
what is the red queen effect?
species must constantly be evolving to defend against the ever evolving parasites infections, an arms race between parasites and immunity in hosts
what does sex allow when it comes to genotypes and at what speed does it occur compared to without sex?
the creation of many new genotypes through meiosis, sex allows faster adaptation to changing environments
what are Rotifers and how did they last so long even though they are asexual?
-Rotifers are small fresh water invertebrates
-all females and have lasted for millions of years due to being able to incorporate foreign DNA from other organisms (bacteria, fungi, plants), example of horizontal gene transfer that increases genetic variation
what is anisogamy?
dissimilar gametes, sperm is cheap to produce in high quantity, while eggs are more expensive
how are males and females limited when it comes to reproductive success?
females are limited by fecundity: # of offspring
males are limited by the number of mates they can fertilize
how does the reed warbler male increase its reproductive success?
by having a harem of females
what is the trade off for live bearers?
more protection for offspring, but reduces number
why is male parental care so rare?
-because males are not sure if they fathered the offspring they produced, resulting in limited parental care
-selfish gene hypothesis
what is the selfish gene hypothesis?
-individuals theoretically should favour promoting their own genes over those of others in the next generations
-genes are immortal but individuals are not
-genes are the ultimate beneficiary of selection
asymmetrical parental care can alter what?
operational sex ratio
what is the operational sex ratio?
ratio of males to female capable of reproducing at a given time, usually more males ready to breed than females, increasing competition
what are the two types of sexual selection?
intrasexual selection (within sexes)
intersexual selection (between sexes)
male biased OSR
what are some two examples of sexual dimorphism resulting from sexual selection?
ornaments: attractive traits that increase mating success (colours, scents, displays)
armaments: weaponry used to out compete other individuals (horns, antlers, tusks)
where is sexual ornaments more common?
in birds and fish
what is the goal in mating?
-impressing the female
-good genes being the reason the female chooses the partner, good ornaments and behavior indicate good health
-arbitrary choice proposed by Ronald fisher, good behaviour or look promotes mating
what are some armaments?
teeth, horns, antlers
what does male-male competition (intrasexual selection) lead to?
-extreme dimorphism and extreme variance in reproductive success
- example: sea lions that fight for harems
what are the costs when competing for mates?
-more energy, injuries, shortened lifespan
-flashy ornaments may cause increased predation
