Sexual dimorphism- sexual selection

Question 1

when organisms don’t have sexes, what do they have instead and why are they needed?

Answer 1

there are normally mating types which differ at one or a few loci. two mating types can’t breed with each other- this is likely to be because of encouraging outcrossing

Question 2

why is sexual reproduction good?

Answer 2

it increase heterozygosity- good for a constantly adapting population

Question 3

what is isogamy?

Answer 3

the gametes that form a zygote are equal in size- they are usually both motile, normally one sex or mating types.

Question 4

how many mating types do slime moulds have?

Answer 4

500

Question 5

what is anisogamy?

Answer 5

two sizes of gametes, one larger and one smaller, two sexes, found in multicellular organisms and unicellular. can both be motile

Question 6

what is oogamy?

Answer 6

one very large and one very small. the small is produced in a large number- used in almost all multicellular organisms that have sex

Question 7

what is the definitive factor for the progression from isogamy to anisogamy?

Answer 7

the fact that in multicellular organism, the fitness of the zygote is proportional to size. this is not the case in unicellular organisms

Question 8

how did fertilisation first occur?

Answer 8

in the sea, external fertilisation

Question 9

what are the 4 theories for the size difference in anisogamy?

Answer 9

• the collision theory
• parasite theory
• sperm limitation
• disruptive selection

Question 10

what is the collision theory os anisogamy?

Answer 10

? ensuring collision .. how?

Question 11

what is the parasite theory of anisogamy?

Answer 11

that the less cytoplasm the sperm transfers to the egg, the less likely it is to transfer a parasite

Question 12

what is the disruptive selecion theory of anisogamy?

Answer 12

there are opposite forces of selection acting on the gametes for males and females

Question 13

what are the 5 premises in supports of anisogamy development?

Answer 13

• each parent has an equal amount of resources to produce a gamete
• gametes can be any size depending on how the resources are used to produce it (size of gamete= resources/ number produced)
• gamete fusion is random
• size of zygote is M1 +M2
• the fitness of a zygote correlates with the size of the zygote

Question 14

when is isogamy the evolutionary stable strategy?

Answer 14

when the fitness of the zygote is not determined by size?

Question 15

when is anisogamy the ESS?

Answer 15

when fitness is dependent on zygote size due to the opposing selection pressures

Question 16

given that fitness is correlated to zygote size, why does anisogamy arise?

Answer 16

if size is correlated with fitness then the fitness will depend on the size of the egg. this means that eggs will be selected for based on the size. due to the fact the egg is singular, there is a lot of competition between sperm. to stay competitive as many sperm as possible must be produced and must be fast. this means that the male divides its resources up to make many tiny sperm to increase its the competitiveness

Question 17

what concepts supports the repeated evolution of anisogamy?

Answer 17

the fact that fitness is related to size of the zygote

Question 18

why, once internal fertilisation occurs, and sperm competition decreases, does anisogamy not revert back to isogamy?

Answer 18

first you calculate the anisogamy ratio: ovum size/ sperm size. if this is greater than N/N-1 (N is the number of ejaculates competing for eggs) . if the anisogamy ratio i greater than the n/n-1 then anisogamy prevails. N must be very very very low for it not to be.

Question 19

what is the relationship between p and the anisogamy ratio?

Answer 19

p is the probability of sperm competition must be higher than 4/A. if P>4/A then anisogamy i stable

Question 20

give two examples of extreme sperm evolution?

Answer 20

diving beetle forms a long cluster of sperms and the droso species has a very long sperm which fills up the females reproductive tract

Question 21

why do sexual dimorphisms between males and females arise?

Answer 21

for males, mating with multiple males highly increases their fitness, however, for females mating with multiple males does not increase the likelihood of them producing more young. this means that traits that increase the males chances of mating with more females will evolve.

Question 22

how does sexual selection result in sexual dimorphism?

Answer 22

due to the fact mating with multiple males does does increase a females fitnesses and that a female can only foster one litter of offspring per mate- females need to ensure that they chose the best quality males. this means that the female will select for traits that improve the males fitness or traits that don’t improve the males fitness (selecting for traits that don’t effect the males fitness can be due to the sexy son (peacock feathers) or handicap hypothesis (stalk eyed fly)

Question 23

what is the sexy son hypothesis?

Answer 23

The sexy son hypothesis states that females may initially choose a trait because it improves the survival of their young, but once this preference has become widespread, females must continue to choose the trait, even if it becomes harmful. Those that do not will have sons that are unattractive to most females (since the preference is widespread) and so receive few matings

Question 24

how do male traits that don’t contribute to male fitness come to be selected for such as the peacock feather?

Answer 24

The sexy son hypothesis or the handicap principle: states that females may initially choose a trait because it improves the survival of their young, but once this preference has become widespread, females must continue to choose the trait, even if it becomes harmful. Those that do not will have sons that are unattractive to most females (since the preference is widespread) and so receive few matings

Question 25

how can female sexual dimorphic traits evolve?

Answer 25

due to difference in reproductive roles- females must have larger hips to allow birth to occur- mammary glands for young

Question 26

what is the relationship between testosterone and sexual dimorphism?

Answer 26

the greater the difference in testosterone levels between animals the more sexual dimorphism

Question 27

when does the rule of sexual dimorphism and testosterone not apply?

Answer 27

in fish because they benefit from testosterone for egg making

Question 28

give an example of how sexual dimorphism can be intertwined with sex determination

Answer 28

in drosophila melanogaster splicing variants determine whether female or male gene expression occurs- the gene that inhibits the expression of abdonimal-b (the gene that codes for dark abdomen colouration) is activated by dsx which is female splice variant of the gene.

Question 29

how can sexual dimorphism and genes be related?

Answer 29

there are certain genes which are expressed more in females and certain gene that are expressed more in males- these are sex biased genes

Question 30

explain an experiment which shows the influence of sex biased genes in sexual dimorphism

Answer 30

urkeys: dominnat males and subordinate male brothers who help them- kin selection br > c, help brother gain as many males as possible.
subordinate males have less masculine phenotypes that dominant males- dom have vivid red and blue head colour and sub have small bit of red and blue, small snood and small wattle. so expect sub males to show lower gene expression of male bias genes. this is the case and have higher expression of female biased genes than dom

Question 31

hows does growth differ between males and females?

Answer 31

males grow more- dimorphic primates

Question 32

what is the anisogamy ratio?

Answer 32

ovum size/ sperm size

Question 33

what is the equation that shows whether anisogamy or isogamy prevail

Answer 33

ovum size/ sperm size > n/n-1