semi conserv - one strand new one old. conserv - one dna new one dna helix old. Dispersive - bits and pieces dotted around. Chromatin - complex of DNA and protein which makes a chromosome. Heterochromatin - tightly packed chromatin. Euchromatin - loosely packed. base pairs - DNA - histones - telomere - centromere - chromosome.
Dna is complexed with positively charged proteins histones. 4 histones = nucleosome. then goes into solenoid structure. 10 base pairs per turn of helix. On chromosome there are spots for replication and segregation. Replication origin - site of initiation of DNa synthesis. Centromere - site of kinetochore formation, for segregation Telomeres - repeated DNA sequences that enable efficient replication of chromosome termini.
somatic mitosis. Interphase chromosomes decondenced, gene expression and chromosome replication (semi conserv). Mitosis phase chromosomes condensed, mitotic spindles pull chromosomes apart on centromere. Interphase cell divides. results in 2 daughter cells, same number of chromosomes, same information unless mutation.
Meiosis gamete production- halving chromosome number and reassortment of genetic material through independant assortment and recombination plus mutations. Crossover between non-sister chromatids of homologous chromosomes occurs in prophase 1.
homologs segregate at division 1. Chromatids segregate at division 2. haploid cells produced. New combinations of parental chromosomes.
When a new virus comes along whole populationa at risk as all have same gene but some may have slightly different polypeptide chains so virus may not stick so can pass on gene
DNA - phosphate group, 5-carbon sugar, nitrogenous bases (deoxyribonucleic acids). A and T only make 2 hydrogen bonds whereas C and G make 3. Point mutation most common create new alleles. Transitions A-G, C-T as A and G have 2 rings and C and T have one ring. Transversions are all other kinds, less common.
Retrotransposition - mRNA is revesrse transcribed back into DNA and then this DNA is integrated into the genome meaning it now has 2 copies of the gene. Unequal crossing over - a mistake caused by proteins involved in recombination where more of one chromosome is crossed over than the other- Gene duplication. Chromosome inversions - radiation induces 2 double strand breaks and repair is wrong way round - disrupts linkage groups, creates new ones or prohibits recombination in heterozgous state. Genome duplication - more common in plants as self fertilation, homologous chromosomes failing to segregate at meiosis 1 or sister chromatids not separarting at meiosis 2.
darwin - evolition by natural selection 'fittest' survive, descent with modification. Mendel - segregation and independant assortment of heritable variation 'how variation works'
Chromosome genetic variation - gene duplication, inversions + genome duplication (polyploidy).
monohybrid cross btwn 2 homozygous 3:1 ratio in F2. incomplete dominance where alleles mix e.g colour 1:2:1 F2. 9:3:3:1 ratio in F2 with 2 hetrozygous F1 crosses only if alleles are on different genes
1) measure observed actual genotype frequency. 2) calculate alelle frequencies p+q. 3) calculate H-W expected genotype p2 2pg q2. 4) compare observed with expected
assumptions - mating is random. population infinitely large. no migration or immigration. no mutation. equal probabilities of survival and reproduction no natural selection.
Genetic drift - random changes in gene frequency in populations owing to factors other than natural selection. This is due to population size as no population can be infinite. Smaller populations result in bigger deviations. Genetic drift is a function of pop. size, number of generations and starting allele frequencies.
contradicts HW, opposite of no natural selection. selection - acts upon vartiation that has a genetic basis will lead to a change in the frequency of both phenotype and genotype. selection will occur when genotypes differ in their probability of survival. really bad alleles not normally seen as usually died off. selection is usually weak in nature but still causes substantial change in long run. e.g of selection when drosophila were given food with and without ethanol on. allele for enzyme ADH homozygocity increased in flys with ethanol on food over generations as it breaks down the ethanol more efficiently. control still fluctuate as not infinite populations. selection - violation of HW conditions - allele frequency change.
sickle cell anemia survives in humans because hetrozygotes are immune to malaria so survive in africa etc. - balancing selection maintain genetic diversity (genetic polumorphism).
by itself mutation is not a potent evolutionary force. mutation provides variation and selection can act apon this to cause evolutionary change. allele frequency can be changed without selction though by genetic drift.
has bigger effect on smaller populations. given sufficient time, genetic drift can produce a huge difference in allele frequencies in even fairly large populations. 2 important effects of genetic drift : by chance eventually alleles drift to fixation or loss. and the frequency of hetrozygotes will decline.
Unless there are new mutations allelic loss and fixation is forever. Decline of hetrozygocity due to population size meaning isolited populations can diverge from each other by genetic drift alone. Small pop - loss of alleles and decline in hetrozygocity - lower fitness and ability to respond to environmental change. (inbreeding depression). migration can overcome effects of genetic drift. If there is random mating in next generation, the genotype frequency will go to HWE.
what is a species? - biological species concept - 'usual' definition - groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. reproductive isolation - do not interbreed can produce viable offspring. no gene flow so species evolve independantly of each other. means have to wait for organims to breed to see what species and bacteria are asexual. cannot be applied to fossils.
morphological species concept - identify evolutionary lineages by differences in morphology. distinguishing features are most likely to arise in pops which are independant and isolated from gene flow. widely applicable to sexual, asecual and fossil species. however features used to distinguish species are subjective. also seasonal variation mean same species look diff and colour polymorphism. diff species could have same morphology.
phylogenetic species concept - uses monophylly. uses darwins - all species related by common anchestor. species is smallest monophyletic group. logic that all species must have been separate genetically long enough for diagnostic traits to evolve. applicable to sexual, asexual and fossils. however, only few detailed phylogenies available. what traits to use? is single nucleotide subsititution enough? can we be sure phylogeny is correct as bacteria have horizontal gene transfer.
recognition species concept - most inclusive pop share common mate recognition system however kakapo will try and mate with a shirt. cohesion species concept - most inclusive pop with phenotypic cohesion through genetic and or demogrpahic exchangability. genealogical species concept - members of group are more closely related to each other than any other species. Genotypic species cluster concept - distinguishable groups of individuals that have few or no intermediates when in cantact wit a deficit of intermediates.
modes of speciation - allopatric - new species forms geographically separate from its anchestor dispersal and colonization or vicarance e.g continental drift break up of pangia. parapatric - new species forms in contiguous, possible but rare pop, produced by hybrid zones where theres selection across a gradient, e.g hotter and dryer in one part, wetter and colder in another. sympatric - rare, new species emerges from within the geographic range of its ancestor caused when natural selection where strong selection for food or habitat choice causes divergence.
prezygotic isolation - breed at diff times, diff habitats, courtship behaviour diff, genetic barrier (egg and sperm not compatable), mechanical (genetalia not compatible).
evolutionary history of group of organims is called its phylogeny. tree describes - speciation events, and the timing of these, and which taxa are more closely related. basic assumptions (parismony) that closely related species will have more traits in common, so group using DNA and morphology. however simiarity can be due to homology (same because of same ancestors) or homoplasy (traits that look similar but arent). homoplast due to convergent evolution or reversal of evolution. answer - use the principle of 'maximum perisomony' the preferred tree is the one with the least evolutionary change. homologous charactoristics will often co-occur in related species. homoplasious charactors will be distributed across random groups of species. cetaceans share many features unusual within mammals.
morphological charactors - essential in fossils, homoplasy can be reduced by looking at the embryological origins of similar organisms, scoring of morphological traits often requires a taxonomic expert. molecular charactor - virtually unlimited supply of data, obtaining data is easy, sophisticated models to predict change through time, homoplasy still a problem.
parisomony tree states whales arent sisters to hippos because ankle bone is diff, howeer DNA shows that whales evolved twice and lost ankle. cant rely on 1 charactoristc. need to use multiple morphological and molecular charctors.
need to evaluate strength of trees, need most parismonious tree. use bootstrapping - involves sampling with replacement from the empirical sequence data. repeat 1000 imes to see how often particular groups occur.
big bang 16bya, 4.6bya, life 3.8bya, 02 atmosphere 2.5bya, cambrian explotion 540 mya - first multicellular organsims, over next 40mya every phylum came into existance, last 540 my of earth history called phanerzoic eon. see how things change through fossilisation.
4 groups of fossils: compression and impression, permineralised, casts and moulds and unaltered remains. first 3 require durbility, burial and lack of 02. 3 main types of bias: geographic - depositional enviros more likely. taxonomic e.g marine organisms dominate. temporal - earths crust is recycled. phanerzoic can be divided into paleozoic (ancient, mesozoic (middle) and cenozoic (recent).
cambiran explotion - evolution of tissue layers ecto-skin and brain endo - gut meso - muscle. 3 key divisions of phyla. 1) diploblasts (ecto and endo) either radially symmetrical or asymmetrical includes jellyfish, corals and sea anemones, and triploblasts (meso aswell and are bilaterally symmetrical all other animals. 2) ceolomates (fluid filled cavity derived from mesoderm, developments in locomotion, aceolomates (no body cavity) and pseudocoelomates (cavity not from muscle)
early evolution to diversity
aceolomates - flat worms. coelomates: most triploblasts. 3) protostomes (mouth region forms first) e.g arthropods, molluscs and nematodes and deutrstomes (mouth forms second, anus forms first) e.g chordaes (vertebrates), starfish and some strange marine worms. both are triploblast coelomates, but have diff in embryonic development.
other major morphological innovations appeared : segmented body plans, shells, external skeleton, appendages and notochords. know this from the burgess and ediacaran shales - exceptional site of soft bodied fossils.DNA sequencing can be used to estimate branching events 'molecular clock', basic hypothesis: DNA subsititutions occur at an approximately constant rate through time so the longer 2 lineages have been diverged the more mutations between DNA sequences. and amount of diff between sequences can be converted to time.
was it an explosion? fossil data saying diversifiction before cambrian, e.g vertebrates. so cambrian explosion: an explosion of new morphologies rather than new lineages. what caused it. ediacaran (early cambrian) fossils : sessile filter feeders and planktonic predators. Burgess (late cambrian) fossils: predators, filter feeders, grazers, scavengerws, detritvores, burrowers, walkers, clingers, swimmers. possible triggers ; rising oceanic 02 levels and predation pressure.
macroevolutionary patterns - adaptive radiations - when a single ancestral species diversifies into a large number of descendent species that occupy large numbers of niches. e.g 400ma aquatic plants colonised the terrestrial enviro. 100ma evolution of flowering plants (angiosperms). evolutionary stasis - fossils suggest morphology of many species is constant for lon periods of time and gradual series of transition are rare and new species appear to occur instantly. fossil record is too gappy.
extinction - are there broad patterns to extinction? get mass exinctions sometimes. 5 major ones, but overall only represent 4% of total extinction. 96% is background extinction. The cretaceous-tertiary KT high impact mass extinction. iridium in KT sediements - first clue for asteroid. also shocked quartz and microtekites. effects : increased atmopspheric h20 and so4, acid rain. increased SO4 means deflection of solar radiation and global cooling. Fireball of hot gas - extensive fires, soot and ash, decreased sunlight and more golbal cooling. domino effect of extinction over 1000s years.
genetics and ecology
gender determination - important to know sex ratio in population. some reptiles' sex can be determined by environment. paternity assignment is important. restriction fragment legnth polymorphisms is used to look for number of repeats. electrophoresise fragments to see how many and what length then compare. use probes.
molecular phylogenetics - phylogenetic trees. taxon cycle hypothesis - are younger species fitter? picked up more adaptations so can out-compete. older populations become restricted to environment and suffer increased prob of extinction. does competition lead to evolution? charactor displacement - competitive interaction between 2 species (sympatry) leads to evolution of ecological separation. or size assortment where species were already different sizes and co-exist. changes from allopatry to sympatry evoke size mediated competition and therefore size change.
phylogenetics can be used for conservation biology to test meat to see if its from endagered animals and where it was caught. DNA barcode used - small piece of DNA variable enough to be diff in diff species. CO1 gene in mitochondiral gene.
metabarcoding - groups of organisms' DNA, Mass-PCR and mass-sequence the CO1 gene from homogenised slurries of different organisms. Dont need electrophoresis. sequence every piece of DNA.
genetics in ecolgy
anaylse mass biodiversity in weekds. can moniter effects of climate change. use lights to trap moths in diff places and heights and can assess changes in communitv composition. restoration ecology after e.g rubber plantations mowed down loads of trees monitors re-grow of natural forest. another e.g is connecting patches of rare habitats in disturbed heathland with different types of corridors to see which is best. standard pitfall data show best are agriploug and turfstrip where species were sampled in corridor. Metabarcoding results : everything in pitfall traps show best were agriploug, trufstrip and forestplough.
ideal DNA barcode: low intraspecific variabilty, discontinous variation between species, dlanked by conserved regions, easy to amplify, long enough to work in all groups, short enough for single reads. reasons to investigate animals - see if wild caught, monitor water cleanliness, test what meat in food, stop import/export of endangered.
genetic influences on behaviour - genetic doesnt mean developmentally fixed and instinctive doesnt mean genetic. gene-environment interaction; differences due to genetics can be abolished by change in environment. Behaviour strongly subject to environmental factors e.g learning. evidence of genetic influence on behaviour: prairie vole monogamous, montane vole polygamous because have different V1aR gene. Foraging behaviour in fruit fly larvae, F = rover f = sitters, when sitter is genetically engineered to have F becomes a rover. Hygienic behaviour in honey bees (2 locus system) u = uncap, r = remove dead larva. recessive = hygienic. conc, some behaviours are influenced by variation at one or a few genetic loci. other behavious may be influenced by multiple loci.
evolutionary stable strategies (ESS) - hawk-dove game models for analyzing freqyency-dependent behaviour. occurs when the success of a strategy or behaviour depends on its frequency in a population. e.g spadefoot toad: cannibalistic tadpole morphs are more successful in presence of non-cannibalistic morphs. ESS defined as the strategy that, when in the majority, cannot be invaded by a mutant strategy. hawks fight, doves display and retreat. 100% dove not ESS i.e hawk could invade as never V/2>V. 100% hawk is ESS if V>C i.e if value of victory exceeds cost of injury
hawk - dove game: conclusions. game theory applied to aggression demonstrates that in principle that:
- best strategy can depend on composition of population (hawk does better in pop of doves than of other hawks.
- a population can contain a mix of fighers and displayers and this can be stable.
- the relative proportions of fighters and displayers depend on the value of winning relative to cost of injury. As cost of injury rises proportion of fights should fall. As value of winning rises, proportion of fighters should rise. All fight can be ESS, but not all - display.
If behaviour is adaptive, behaviour is subject to genetic influences, including those underpinned by one or a few genes. Bhevaiour is a product of a gene-environment interaction. Variation in behaviour wihtin populations may exist because of frequency deendant mechanisms.
introduction to behaviour
actions with which organisms interact with the external world. 1. manipulation of the environment. 2. response to stimuli. 3. externally observable muscular activity. 4. social behaviour.
Tinbergen's 4 questions :
1 Causation/mechainism - how is behaviour acheived? e.g stimulis to sense organ to CNs to muscular contraction to in sac realeasing ink
2 Development - how does behaviour develop in the indivduals lifetime e.g is inking learnt?
3 Evolutionary history - what is the evolutionary history of the behaviour in lineage? e.g when in cephlapods phylegenic tree did inking come and from what ancestors?
4 Functional significane - what is the behaviour's current adaptive value? e.g what is it for?
1 & 2 proximate causes ( how an animal can do this) 3&4 ultimate causes: assume fitness maximizing with natural selection.
adaptions are for the good of the causative gene. never for species, sometimes the group, often individual, always gene
cooperation among non-kin
social actions = actions that affect the offspring output or survivorship of other individuals. both gain = mutaul benefit (cooperation). actor loses recipient wins = altruism. otherway round = selfishness. both lose = spite. cooperation e.g honey guide in africa or egyptian bird picking teeth out of aligators mouth. altruism e.g dolphins help injured surfers. selfishness - birds taking fish from other birds. spite - revenge.
kin selection theory - altriusm to non-relatives cannot evolve. cooperation can evolve. issues : how is it kept stable? cheating? what are conditions?
within species e.g alarm calls, food sharing, helping at nest or herding, flocking or shoaling. Mobbing take risk to attack predator. each organism in herd is acting selfishly though for its own protection. cheating cannot occur as everyone benefits but selfishness can e.g getting to centre of herd.
reciprocity - benefit in one direction must be returned. requires partner fidelity, usually between organisms who are familiar to each other. ESS is always to defect not cooperate even though would benefit more from cooperating in one-shot game. When repeated interaction (iterated) *** for tat occured. however negotiations occur in real life, but in principle cooperation can work in a world of selfishness provided it gets started
cooperation + kin selection
reciprocity is favoured by long-term association where idividuals remember each other - advanced cognition and rewarding cooperation and punishing defection.
altruism = social action in which the actor suffers a loss in survivorship or offspring and the recipient experiences a gain. problem : why evolve to reduce number of offspring. Gene altriusm can spread is the actor and recipient are related. Kin selection theory. relatedness = the probability that a gene in one individual is present in another individual, due to the 2 being related.
social hymenoptera (ants, wasps, bees) (outbred haplodiploids) - where females re diploid and develop from fertilised eggs and males are haploid and develop from unfertilised eggs. so sisters have 0.5 probability that they share maternal and 1 prob that they share dad. r = (0.5+1)/2 = 0.75
hamiltons rule - a gene for aaltruism will spread if more copies are added to the pop than lost. rb-c>0. a gene for altruism spreads if the loss the gene suffers in the sacrifice for the body it occupies is exceeded by the gain via increased reproduction. Altruism is selfish at genetic level. Altruism can only evolve is social partners are related. inclusive fitness - an individuals fitness taking inot acount its effects on the reproduction of relatives.
kin selection examples
sterile cases in ants, bees, wasps and termites etc where colonies so related r>0. Social aphids where members are asexually produced of one female so all related = 1. polyembryonic wasps lay eggs in an egg of a moth so sterile 'soldier' larvae are clone mates of larvae they aid so all related =1.
Kin-biased helping in long-tailed **** - individuals whose nests are attacked join others as helpers. but only relatives help other kin. Birds recognise relatvies due to call they learn as young. another form of cooperative breeding.
in non-clonal social groups, not all parties are eqally related - so dont agree on reproductive decision - kin selected conflict. aunts and uncles not as fussed about saving nephew as son. have different hamilton rules, hence different fitness optima, hence inclusive fitnesses cannot simultaneously be maximised. altruism and conflict can coexist but kin selection theory sets limits to conflict. various factors may prevent a potential conflict from becoming actual e.g lack of within-group kin discrimination - if individuals dont know how related they are to each other and policing in nature so cost is greater than gain.
evidence - parent-offspring conflict. conflict over male-parentage in bumble bees, conflict over breeding in bee-eaters. Parent-parent conflict: infanticide in african loins. offspring -offspring conflict: siblicide in vertebrates.
bumble bee conflict - single once mated outbred queen. workers can produce males due to haploidiploidy. queen related to sons r=0.5 and workers sons =0.25. workers are least related to queens son's as r =0.25. queens favour the rearing of queen-produced males but workers favour rearing of worker produced males so potentail kin-selected conflict between parent and offspring over male parentage.
bees - colony cycle - colony foundation - worker production - switch point between male-only producing colony or queen producing colony - competition - queen death - queenless phase. predicted potential conflict becomes actual at competition phase where queen eats worker-laid eggs and workers sometimes kill queen. (actual queen-worker conflict over male parentage). in male producing colonies, competition point follows the switch point where queen lays male eggs. In queen producing colonies, competition point follows point where female larvae have undergone caste determination as queens. so workers only value queen as producer of new queens not males. experiment - unrelated drifter workers from other colonies entered nest who lay male eggs (intraspecific social parasite). significantly more reproductive before resident worker competition point and more aggressive. shows resident workers modulate reproductive behaviour according to kin-selection interests.
more parent - offspring conflict - bee-eaters. fathers disrupt breeding attempts of own son as fathers offspring - 0.5 grandchildren - 0.25. sons often rear their siblings aswell.
infanticide in african lions - male lion usurps resident male in pride he kills cubs as no relatedness, meaning female can be sexually recpetive and have his cubs.
siblicide in bits and hyena - same sex are worse. worse when less food around. self r=1 sibiling =0.5
not necessarily truthful. cooperative communication - when sender and reciever share a coincidence of fitness interests e.g honeyguide birds and humans. e.g flowers attracting pollinaters. between kin - e.g alarm calling in vervet monkeys (like language). teaching by example in ants.
evolution of deception e.g empty flower (mimics look of flowers with nector) e.g honeyguide leads humans further. Batesian mimics harmless species mimic dangerous ones.insect-mimicking flowers. deception within species between non-kin she males in garter snakes - produces phermones to mimic female to gain warmth and protection from surrounding males and gain access to other females. E.g tactical deception in primates (false calls). success will be frequency-dependant 'cry wolf' effect.
why communicate during conflict - want to avoid harm to itself or kin. signal conveys quality of sender (resource holding potential) and that costliness helps ensure its honesty e.g tapirs display until collapse which stops lying. helps ensure that signalling is an ESS ants produce 9-C31 chemical on the cuticle which act as honest signal of fecundity and dominance.
to explain sexually dimorphic, 'non-utilitarian' traits. e.g male narwhals- big horns hinder catching fish only to fight for mate. male tragopans - everything eats it but still brightly coloured to get mate, counter-intuitive. exaggerated tails in pin tailed witer. rhinoceros beetles can dig into ground easily to hide from predators. intrasexual selection - competition with members of same sex for mates. Intersexual selection - attractivness to members of opposite sex and discrimination in choice of members of opposite sex. often contrasts natural selection as traits usually hinder survival.
intra - fighting for mates, adaption for conspecific fighting/defense. e.g big horned sheep = vicious in battle. inter - extravagant ornaments and displays in males/ assessment and discrimination (mate choice) usually females. some traits used for both inter and intra. e.g big horns
why selection - parental investment = investment in gamete + care for offspring so want ti to be worth it. potential asymmetry in sexes in parental investment - differential potential reproductive rate. parental investment and hence PRR depends just on relative gamete size when no parental care - females produce macrogametes males - microgametes so females invest more. leads to bateman principle - in species without parental care male reproductive sucess ises linearly, females rises then flattens - males higher PRR sex.
sexual selection 2
bateman principle continued - females lower PRR sex because females have roughly 30 offspring whereas males is dependant on how many females it can get. so males need to be sexually selected to maximise rate of mate-finding and quality of offspring so males compete and are showy to attract females. selection on low PRR sex (females) to maximise quality of mates and hence offspring, hence females are choosy and mate select best mates.
Parental investment and hence PRR depends on gamete size and parental care. Female only care - male has higher PRR still. male-only care: female have higher PRR as energy time and resources needed. lifetime monogamy with equal, biparental care equalises PRR as both are perfectly interdependant. humans - intermediate between female-only and biparental care. sex-role reversed species support PRR hypothesis - seahorses males become pregnant, females compete for mates and are ornamented. Dotteral and other shorebirds: males incubate eggs, females brgither than males and compete for them.
direct benefits of mate choice to females - gaining resources e.g nutrition and good parental care of young, territory, food, protection from predators, other mates and paternal.
sexual selection 3
lek parradox - why has mate choice evolved when matings provide no direct benefit? e.g male sexual displays in lekking (polygamous species). lekking - where animals get together and display for males and females choose ones they like. male:male competition and female choice. crappy males are left due to environmental factors on genes and varience in female choice. e.g hammerhead bats which produce weird noise.
indirect benefits - attractive sons 'fishers runaway'. if females choose attractive males, automatically choose beareres of genes for attractive male ornaments and genes for choosing such males. - runaway coevolution of maleornament genes and female choice genes. e.g male long-tailed widowbirds - females choose ridiculously long tails. 'good genes' - males signal 'quality' especially if display is extravagant and costly so ensure honesty. e.g peacocks. quality could include genetic resistance to parasites(hamilton-zuik hypo) e.g barn swallow with long tails. natural selection meets sexual selection as natural wants small tail so can fly better, sexual wants huge tail to get more mates so meet in the middle.
another indirect benefit - compatible genes - choose male of correct species, unrelated to avoid inbreeding, and ones with compatable immunity genes e.g salmon.hetrozygocity usually favoured as larger range of immunity alleles.
mate guarding, sperm competition and sexual confli
all increase parentage assurance = evolved machanisms to increase chance of being parent. mate guarding - when one sex prevents same-sex competitors having access to its mate. pre-copulatory = males guard females prior to copulation. e.g pupal mating in butterflies, compete for possession of pupa on plant and mate with female as she emerges. e.g brine shrimp with modified antennae until female molts usually when female have temportally restricted periods of sexual receptivity. benefit - male makes sure hes parents, cost - not feeding, finding new more sexually receptive mate, increased predation risk. leads to potential for male choice of females.
post - after copulation. e.g pondskater - male rides passively on back of female without genital contact for 11min to 48 h. e.g yellow dung fly - already mated females arrive at dung to lay eggs, males intercept and copulate and remain mounted to prevent displacement of sperm. favoured if female remains receptive after copulation. when interval between copulation and egg-laying is short so dont have to guard too long. when finding mates is easy. when last male to fertilize female gains most fertilizations of eggs. mating plugs - strutcutre produced by males to block female reprocutive tract. e.g locusts 26% of matings fail due to mating plug. mate guard 'remontely', female ejects plug on egg-laying.
sperm competition and sexual conflict
sperm comp - when females mate with more than one male. competition for fertilizations by sperm within females reproductive tract. driven by selection on each male to maximise paternity. e.g male damselfly - seconadary genitalia has spines to scrape sperm out. comp between ejaculates as male delivering most sperm is most likely to father more - evolution of numerous, small, motile sperm w/ large testies. e.g male reed bunting - positive correlation between testie size and level of extra-pair paternity. cooperative sperm in wood mouse, heads hook together to form faster train, only front sperm wins, non-fertilizing ones act as altruists to aid sibling sperm in comp with unrelated males sperm.
sexual conflict - evolutionary conflict between sexes due to diff fitness optima over any mating. e.g fruit flys male mating is partly toxic to females, but boosts male fertilization success and female egg production. because females can mate multiply so chance of first mate mating with female again is unlikely and due to no parental care he doesnt care about her survival only his genes. only interest in her short term welfare so only wants her healthy until she gives birth. No evolutionary interest in her future amtings because unrelated to her and her future mates. sexual cooperation in ants where it increases lonevity of females, because queens are monogomous - so coincidence of fitness optima.