Variation in Gamete morphology

Question 1

eggs are generally less variable than sperm, but which aspect of egg morphology varies a lot in mammals?

Answer 1

the Zona pelusa

Question 2

sperm might need to be more variable because…

Answer 2

sperm need to survive in the female reproductive tract - outside of the soma

Question 3

what is the green beard effect?

Answer 3

green beard effect- selective altruism. sperm
with ‘green beard’ gene will favour other sperm
with green beard trait/gene

Question 4

what is sperm cooperation?

Answer 4

mutual interaction/partitioning of
function between sister sperm to increase male's
fertilization sucess (bit like facillitation)

Question 5

why does Hamilton (1964) expect that sperm will evolve cooperation?

Answer 5

is we exclude haploid/diplid conflict, the sperm may
evolve cooperation at the same likelihood as full sibs as
share 50% of genes (Hamilton, 1964)

Question 6

what did Keller (2002) conclude about cooperation in marsupial sperm?

Answer 6

in marsupials, sperm have to cooperate to fertilize the
ovum. costs- unpairing will unvariably disable one of the sperm.
benefits- single sperm barely ever able to reach site of fertilization, if females multiply mate, sperm will benefit when hamilton’s rule is met.. . if it is green bearded selection, sperm with green bearded traits will favour one-another. the costs and benefits of kin vs green beard selection will vary according to female mating behaviour

Question 7

what is the coefficient of variation?

Answer 7

it is a way to calculate across and within male variance in reproductive traits. the relationship between mean and variance

Question 8

what are the problems with CV?

Answer 8

CV assumes that with a unit increase
in mean there is a unit increase in variation,
assumes the line of variation by mean is
perfectly isometric

Question 9

when has CV been used?

Answer 9

to look at between male variation in sperm length when reproductive competition is high. Post copulatory sexual selection has a large role in reducing inter male differences in sperm size traits, and potentially drives diversification in sperm morphology across populations and species (Kleven et al, 2008)

Question 10

what did cummins and wood hall find about the association between sperm length and body size?

Answer 10

cummins and woodhall (1985) found that sperm length had a negative association with body mass

Question 11

what did Gage (1998) find that was contrary to cummins and wood hall’s findings?

Answer 11

(Gage 1998) there is no assoc
between sperm length and body mass in
300 mammalian species

Question 12

what type of genetic effects do quantitative genetic studies show for sperm size?

Answer 12

additive effects

Question 13

what do you expect to be the outcome for sperm morphology due to competition?

Answer 13

under sperm competition theory, you would expect there to be numerous, tiny sperm

Question 14

what is an example of the evolution of numerous, tiny sperm under sperm competition?

Answer 14

(Gage & Morrow, 2003) - Crickets. In 30 day fertilisation competition experiments, those males who produced numerous, tiny sperm had precedence in successful matings - BUT this evidence doesn’t explain why variation persists naturally in crickets

Question 15

are bigger sperm ever favoured? why?

Answer 15

a comparative study in mammals showed that longer sperm swim faster. this study was based on the prediction that competition would favour longer sperm. However, the fitness benefits of this depend on the environment in which they have to fertilise. any aspect of their morphology which makes them swim faster increases their fertilisation success (acrosome size etc) (Gommendio & Rolden, 2008)

Question 16

can the environment influence egg size?

Answer 16

sperm competition can increase the length of sperm in
frogs. place of oviposition (terrestrial/aquatic) had an
impact on egg size but not sperm size. evidence for
covariation in gamete size of males and females
(Byrne et al, 2003)

Question 17

what is influencing sperm morphology in zebra finches?

Answer 17

in zebra finches, indirect maternal
environmental effects influence variation in
sperm morphology (Birkhead et al, 2005)

Question 18

what other things can influence sperm quality?

Answer 18

ecotoxins, disease, time since last ejaculation can all alter
sperm maturity/quality

Question 19

what do (Radhakrishnan and Fedorka, 2012) conclude about the influence of pathogens on D.melanogaster sperm storage & viability?

Answer 19

pathogens reduce sperm viability and storage in both
sexes of d.melanogaster. not an
immune-reproduction trade off, females may actually
increase fitness by getting rid of infected sperm
(Radhakrishnan and Fedorka, 2012)

Question 20

can social status impact sperm viability?

Answer 20

in birds, sperm mobility has a
negative association with social
status (Froman et al, 2002)

Question 21

in sneaker males- selection
pressure high to have very
motile/long-lived/big sperm?

Answer 21

in blue gills (sun fish with male parental care) there is
no difference between satellite and sneaker male
motility or longevity, but the concentration of sperm in
snaker male ejaculate it 50% greater(Leach &
Montgomerie, 2000)

Question 22

how does a fitness surface affect within male variance expectations?

Answer 22

sperm size might converge to a single optima, but more
likely that the topology of the fitness surface (the
relationship between trait size and relative fitness) is not
simple, with various optimal fitness values otherwise you
wouldnt get so much variation

Question 23

can you think of a reason as to why there are gaps in our knowledge about sperm variation?

Answer 23

we assume it to work as one

functional entity, e.g. an organ

Question 24

what kind of sperm can we get and in what groups are they very pronounced?

Answer 24

apyrene (infertile) and eupyrene (fertile)
lepidoptera have fertile with nucleus and infertile without
so do drosophila, except the infertile sperm have a full haploid compliment

Question 25

what are kamikaze sperm?

Answer 25

‘Kamikhaze sperms (baker and bellis, 1988) - sperm in different functional groups,
defense, fertilization.

Question 26

is there evidence for kamikaze sperm?

Answer 26

no evidence for
killer sperm or other selective
interactions between human spermatozoa in
ejaculates of different males (Moore et al, 1999)

Question 27

what did (Kura & Nakashima,2000) predict about the evolution of kamikaze sperm? (4 predictions)

Answer 27

(Kura & Nakashima,2000) mathematical model suggests:1) soldier sperm will evolve even if one soldier sperm can kill or block

Question 28

can fruit flies manipulate females with their ejaculate?

Answer 28

cheap filler - d.melanogaster has chemical which
prevents females from further mating
‘anti-aphrodesiac’ (Cook & Wedell, 1999)

Question 29

(Den Boer et al, 2010) -seminal fluid mediates ejaculate competition in social insects - how so?

Answer 29

queens of hymenopterans obtain lifetime supply of
sperm on a single day; seminal fluid of polyandrous males has a +ve effect on own pserm survival;not observed in monandrous sp; suggests an incapacitation of competing sperm evoved separately in bees and ants