7: evolution of sex Flashcards
what can gametes either be?
large and female
small and male
what is the evolutionary origin of the 2 sexes?
ancestral state: gametes were equal size and any gametes could come together
- then a mutant will small gametes arises
- gamete specialisation evolved
if we assume mutant gametes are half the size and can make twice as many then when will and when wont the mutant do better?
yes- if survival of smaller embryo is >50% of normal embryo
no- if survival of smaller embryo <50% of normal embryo
when looking at the graphical model for size and survival of embryo what does a steeper dotted line tangent mean?
greater pay off in terms of survival
when looking at the graphical model for size and survival of embryo what is the tangent?
size of embryo that maximises survival (values of x and y on the curve) per unit mass
when looking at the graphical model for size and survival of embryo when are half sized gametes favoured?(3)
- when half sized gametes fuse with normal they produce 3/4 sized embryos
- twice as many half sized gametes give more offspring
- if the survival curve is favoured
when does the advantage of smaller gametes decrease?
as gets more common and fusion is random
what happens if 2 small gametes fuse?
- how is this avoided?
embryo will only be half size
- small gameted evolve ability to avoid fusing
what does sperms ability to not fuse to other sperm lead to?
evolution of 2 sex system
what is sperm competition?
competition between sperm of two or more males inside the females reproductive tract
why do males engage in sperm competition?
to maximise chance of fathering offspring
how do male damselflies engage in sperm competition?
elaborate penis used to remove sperm of rivals before inseminating female
in terms of sperm production how do polyandrous male insects compare to monogamous?
polyandrous males produce higher proportion of viable sperm
what is the Adelie penguin example of sperm competition?
- males strategically allocate sperm to females
- monogamous males engage in sperm competition by extra pair copulations
what do some males do to ensure their mate doesn’t have an extra pair copulation? + example
mate guarding to protect paternity
male magpie and zebra finch both follow mate during her fertile period
what do seychelle male warblers do prior to fertile period and what is this period?
4 days prior to egg laying and copulations in this period could fertilize egg
- lots of extra pair copulation attempts
what do seychelle male warblers do during female fertile period?
will mate guard to reduce number of extra pair copulation attempts
what happened to seychell male warbler behaviour if a fake egg was placed in the females nest 4 days before egg laying?
switched off mate guarding and led to a spike in number of intrusions and successful extra pair copulation attempts
what do male milkweed beetles often do to stop other males mating?
stay mounted on the female
in an experiment by Dickson on milkweed beetles what was done? and what % of separated males and females found new mates and what are the implications of each of these?
- mate guarding males removed from females
- 25% separated males found new mate in 30 mins -> guarding resulted in missed mating opportunities
- 50% females found new mate after male removal -> guarding prevents females from remating
when is guarding beneficial to the milkweed beetle male?
if last male to copulate fathers 40% or more of females offspring so gains more from guarding, such as more offspring, rather than searching for new mates
when is guarding not beneficial to the milkweed beetle?
when last male fathers <40% as wont father as more offspring
what do male fulmar birds do to protect their paternity and why? (2)
- copulate over 50 times with partner to outcompete other male sperm
- increases chance of inseminating when she is most fertile
what does frequent copulation ensure?
optimal timing of insemination relative to fertilisation
what is cryptic female choice?
female manipulation of sperm inside her reproductive tract so a prefered male fertilises her eggs
what did Pizarri and Birkhead find in 2000 for sperm ejection in chickens and what is this an example of?
cryptic female choice
- females eject sperm from cloaca of low ranking subordinate males and accept the sperm of dominant males
what is sperm ejection in dunnock birds? (3)
- before copulation male often pecks females cloaca if another male been near
- causes her to eject fluid droplet
- looks like ejecting sperm but droplet contain inviable, broke, tangled sper
which sex is in control in hanging flies?
female
describe nuptial gifts and sperm acceptance in hanging flies (3)
- female eats the gift during sperm transfer which usually lasts 20 minutes
- only males providing large gifts >20mm will have full sperm transfer
- if not large enough copulation will end before all sperm is transferred
why do females engage in cryptic female choice, what do they gain and how?
gain:
- higher quality offspring by cryptically choosing high quality fathers
- more offspring by cryptic choice of genetically compatible males
how do males that are unsuccessful in competition and are not chosen by females achieve reproductive success? - what are the 2 examples?
alternative mating strategies
- alternative are not equally rewarding
- alternatives are equally rewarding
in terms of the small, medium and large males what are the alternative male tactics in scorpion flies?
- large- guard dead insects attractive to females and gain 6 matings each
- medium- produce cheap salivary gifts to attract females which are less attractive + 2 matings each
- small- force copulations on females + 1 mating each
in scorpion flies what happens if the large males are removed?
medium sized males now adopt large males tactics as no longer trying and failing to compete with it
what is the fitness of the scorpion fly alternative tactics?
unequal fitness
what are the 3 male morphs in isopods and what do they all have?
- alpha/fighter
- beta/female mimic
- gamma/hider
different genotypes with genetically determined differences and different advantages in terms of mating
shuster and wade studies isopods in 1991 what did they find about how the morphs behaved? (3)
- alpha meeting gamma will throw it away as is dominant
- gamma will hide and sneak copulations
- beta male will mimic females so alpha wastes time trying to court it
shuster and wade studies isopods in 1991 what did they find for what frequencies the morphs occur at and the fitness and success of the alternative strategies?
- occur at frequencies at which their fitness is equal
- equal fitness and reproductive success
which isopod fathers the most offspring when:
a) alpha and beta males and 1 female
b) alpha and beta males with multiple females
a) alpha
b) beta as alpha struggled to copulate with them all
in terms of large, medium and small males what are the alternative male tactics in bluegills?
- large-produce nests attractive to females
- medium- have female colouration and slip between territorial male and mate during spawning
- small- lay low to slip between
in blue gills which males father the most offspring + % comparison of this?
territorial large males:98.7%
1.3% for small and medium males
what is the most important act in the life of any animal? and what is an indicator of this?
passing on genes
- the wide variety of behavioral strategies to achieve reproduction
what is an adaptive gne often linked to?
one affecting mate preference - are on 2 linked loci
what is the paradox of sex?
inefficient, complicated, time consuming, difficult, dangerous, costly
twofold cost of sex assumes males only contribute genes- how can they increase their reproductive output?
male parental care
what are the 2 models used for how short term cost of sex is overcome to generate long term benefits?
1 . genetic drift/mullers ratchet
2. red queen hypothesis
what is Geoff parkers hypothesis for the evolution of anisogamy based on?
disruptive selection
- selection for the smallest and the largest
- as individuals have a fixed budget for reproduction so can only be one or the other
which sex competes for the other?
one investing least competes for one investing most
what does the graphical model of size of embryo and survival show overall?
how selection could favour a mutant individual invading, that produces twice as many half sized gametes
how may males that cant guard their mates for ecological or social reasons protect their paternity?
copulating frequently with their partner
what did Pizzari and Birkhead discover for sperm ejection in domestic fowl?
females will eject sperm of subordinate males and accept sperm of dominant male
