Flashcards in Topic 2 - The Evolution Of Sex Deck (25):
What is pathogenesis?
Also known as 'virgin birth'; the development of offspring from an unfertilised egg.
Explain the costs of sexual reproduction.
1) two-fold cost of sex, only half the individuals are female and able to produce offspring.
2) sexually reproducing individuals pass on only half their alleles.
3) potentially unfavourable allele recombination can result from poor mate selection.
What are the benefits of sexual reproduction?
sex is maintained because sexual populations can purge themselves of harmful mutations & it provides sexual organisms with genetic variability. Sexually reproducing organisms exchange genes, thereby producing offspring with greater genetic variation than asexual organisms.
What is meant by genetic load?
The burden imposed by the accumulation of deleterious mutations. The genetic load equals the chance that an average individual will die before reproducing because of the deleterious mutations it possesses.
What is a possible consequence of high genetic load in a population?
Genetic load could become so great that the population fails to survive and reproduce, and goes extinct.
Explain the red queen hypothesis.
Under the Red Queen hypothesis, interactions between organisms, such as between parasites or pathogens and their hosts, generate ever-changing environmental conditions that favour the maintenance of sexual reproduction relative to asexual reproduction or self-fertilisation. 'It takes all the running you can do, to keep in the same place’.
The process of reciprocal evolutionary change in two or more interacting species (genes, sexes) by natural selection. Each party in a coevolutionary relationship exerts selective pressures on the other so that they affect each other's evolution.
What is anisogamy?
Having gametes of different sizes. Individuals producing the larger gamete (egg) are defined as female, individuals producing the smaller gamete (sperm) as male.
The reproductive rate of an organism measured in the number of eggs, seeds or propagules (in the case of asexually reproducing organisms) that it can produce.
How might a female improve the survival prospects of her offspring?
She could care for them by providing food, warmth and protection.
What is meant by potential reproductive rate?
The offspring production per unit time that each sex would achieve if unconstrained by mate availability. Because females generally produce large eggs and care for offspring, their potential reproductive rate is lower than that for males.
Explain operational sex ratio (OSR).
The ratio of sexually active males (those ready to mate) to sexually fertilisable females (those ready to mate). Differs from the sex ratio which takes into account inactive or non-competitive individuals.
How does the definition of sexual selection differ from that of natural selection?
Natural selection favours traits that give individuals an advantage over others with respect to survival and hence reproduction. For example, an animal that runs faster than others in the population will be favoured by natural selection if, by running faster, it escapes predation and survives to reproduce. Sexual selection, however, favours only those traits that afford an individual a mating advantage over other individuals in the population. Such traits may or may not be advantageous in terms of survival.
How is fitness defined?
Fitness is a measure of the relative success of an individual in surviving and reproducing and therefore contributing offspring to future generations.
Why does reproductive success generally vary more among males than females?
It varies more among males than females because of the limited number of female gametes available for males to fertilise (a consequence of the differences in the size of male and female gametes). This means that males must compete with each other for access to eggs by mating with as many females as possible. Some males will be better than others at finding and fertilising females, so variation in reproductive success among males will be high. Because of the competition among males for females, it is likely that all females will mate. Variation in reproductive success among females will therefore be low.
Explain intrasexual selection.
Members of the same sex (usually males) within a species compete with one another for access to members of the opposite sex. Usually results in the evolution of physical or behavioural features that determine the outcome of aggressive encounters, e.g. weapons, large body size.
Explain intersexual selection (female mate choice)
males compete among themselves to be chosen by females. Females are selective about the male they choose to mate with.
What benefit or benefits could females gain by mating with more than one male?
If a single male transfers insufficient sperm to fertilise all her eggs, it would benefit a female to mate with more than one male and thereby increase fecundity. Females may also benefit indirectly by producing genetically variable offspring. Furthermore, if females are able to fertilise their eggs selectively using sperm of preferred males, they may provide better genes for their offspring.
What are the indirect benefits of choice in female mate selection?
Factors that increase the genetic fitness of offspring. Indirect benefits include high quality genes for offspring (adaptive indirect benefits) or genes that make offspring more attractive (arbitrary indirect benefits).
Explain Fisher's runaway theory of sexual selection.
A mechanism of sexual selection proposed by R.A. Fisher to explain evolution of exaggerated male ornamentation. According to Fisher's theory, the initial female preference for the male trait is an arbitrary preference; there is no necessity for there to be a relationship between the trait expression and the male's inherent genetic quality.
Explain the 'good genes' hypothesis.
'Good genes’ hypotheses of female choice hold that females gain indirect benefits from their choice through the superior genetic quality of offspring. According to these hypotheses, female preferences for a trait are not arbitrary. Instead, they choose males with traits that are honest, reliable signals of underlying male genetic quality.
Explain sexual conflict in terms of sexual selection.
Conflict that arises between the sexes because strategies that maximise the fitness in one sex can reduce the fitness of the other sex. Can lead to antagonistic coevolution and sexual 'arms races'.
What is antagonistic coevolution in the context of sexual selection?
In a sexual context, antagonistic coevolution is driven by conflict between the sexes in maximising reproductive success. Adaptations that benefit males at the females' expense select for counter-adaptations in females that mitigate male-imposed harm. Often referred to as an arms race between the sexes. Antagonistic coevolution can also occur between predators and prey, between parasites and their hosts and between parents and offspring.
What effect would male parental care have on potential reproductive rate of males and females?
Because males care for the young, their potential reproductive rate decreases. Females, on the other hand, are free to mate again as soon as they are physiologically able to do so.