bio 221 lec 9+
what is a life history strategy?
1. age at 1st reproduction/ average age at reproduction
2. number of offspring
3. lifespan
life histories may vary within a species or be very consistent, would different strategies produce different relative fitness?
different strategies may or may not result in same relative fitness
how can an organism maximize fitness
an oragnism able to reproduce early, do it often, produce many large offspring each time, and continue to do this for a very long time would have an almost unbeatable strategy
what is the organism with maximized fitness called
darwinian demon
what would happen if darwinian demon existed
if existed, would theoretically dominante the world, and extinguish all diversity, it does not exist, because tradeoffs produce constraints in life history components.
in addition to those constraints what else would indivuals have to deal with
resouce constraints, not enough accessible energy on this planet to allow organisms to reproduce and grow indefinitely (Malthus), when resources are limited, increased allocation to one thing resources available for other things (i.e., a tradeoff)
when it comes to reproductive strategy, there are 4 questions to answer?
how many offspring?
how often?
how many per breeding episode?
how much parental care?
for how many offspring what is the tradeoff
example 1 in hens shows that, increased expenditure on reproductive output comes with the cost of decreased lifespan. higher egg laying hens reproduced more early and had shorter life span
less productive hens early in life, live longer
what is another example of lifespan pertaining to fertility
found that the female anoles that had their ovaries surgically removed lived significantly longer than the females who were fertile and laid eggs. infertile females were larger than fertile.
what is the hypothesis that comes from these examples
production and energy investment in eggs shortens lifespan. energy invested in reproduction vs individual growth and life span.
what is a eunuch
a castrated human male, who worked as guard/servants in harems across the Middle East/ Asia (imperial court of the Korean Joseon dynasty 1392-1895)
how do eunuchs exemplify the constraint of reproduction of lifespan for humans
average lifespand of eunuchs was 70.0 +- 1.76 years, 14.4-19.1 years longer than lifespan of non castrated men of similar economic status
what is the trade off for the number of reproductive episodes (how often you reproduce)
organisms with low probability of surviving another year may maximize reproductive success by investing more in their current effort
organisms with "longer" life span don't generally increase current fecundity enough to jeopardize future reproduction
semelparity
one breeding season, adaptive when there is a high trade off between reproduction and survival for the adult and in cases where the survival between broods is low
what is the need for semelparity
This strategy can be advantageous in environments where survival rates are low, and the chance of offspring surviving to maturity is minimal. By producing many offspring at once, the species maximizes the chance that some will survive. Examples include salmon or certain plants.
iteroparity
more than one breeding season, accompanied by a very low survival at a young age and higher survival rates in adulthood at low reproductive cost for the parent. ex: humans
Offspring Forgone
The number of potential offspring that an organism could have produced but did not, often due to resource limitations, environmental factors, or life history strategies (like investing in fewer, higher-quality offspring instead of many).
what is the need for iteroparity
few costs in both waiting and expecting multiple breeding episodes, higher survivorship in offspring
Increases offspring survival across different environmental conditions.
Allows balanced resource allocation over time.
Reduces risk by providing multiple chances for reproduction.
the delaying reproduction until old age can be risky strategy. what is an example of differing reproductive strategies.
plants:
annuals- adults live for one growing season, and put much more energy into reproduction than perennials in one growing season
BUT over course of lifetime--> reproductive effort between perennial (iteroparous) and annuals (semelperous) are roughly the same.
what is another example
guppies. if adult mortality is high, reproduction at an early age (and possibly smaller size) would be beneficial.
what is true about the reproductive effort of guppies that live in areas with high predation
populations in areas of high predation produce MORE, SMALLER offsrping EARLIER in life compared to populations that live in areas with low predation pressure.
how can a tradeoff shift occur considering reproduction limiations and predation
tradeoffshifts in indiviuals from high predation areas are moved to low predation areas (vice versa). predation is a selective force. low predation, wait longer until you wait to long then offspring bad
it can be seen in low predation environments
females mature at a later age, females and males are larger when reproducing, fewer but larger offspring
what is the trade off for how many offspring per breeding episode
fewer- larger babies are more sucessful
more- smaller but power in numbers
increased off spring (requires more energy)
why would an organism choose to have larger but fewer organisms
easier to protect children or when access to resources isnt hindered or hard to get
why would an organism choose to have many but smaller offspring
if size doesn't matter to get food. ex. tapeworms--> small larvae because they can absorb energy through their body and are laid directly onto their food source
offspring have to be a certain size to survive why? give 2 examples
in order to hold onto host, ingest food, compete for resources, run from predators etc.
ex. large seeds have advantages over small seeds--> more food to sprout seedlings especialyl in shady habitats
ex. feather lice have to be able to hang on to feathers, females tend to lay one large egg
how much parental care tradeoff? example
number of offspring produced is limtied by parental care
ex. many birds are capable of laying large clutches but tend to lay smaller ones, it is found when birds of the same species produced larger or smaller clutches than avg fitness may be reduced. larger broods might not receive the same amount of parental care
how do birds accomadate this brood problem
they produce a optimal clutch size
life history continum
high fecundity - low surivorship
low fecundity- high survivorship
siblicide
many species of birds: mostly raptor but pelicans, boobies, cranes, egrets, herons
nestligns frequently try to kill each other and parents don tintereferse, eggs are laid asynchronosuly in these species so the older chick is larger than the later hatching one and tries killing it to get all the food to itself
why would chick parents allow siblicide
hypothesis: youngest chick is just insurance for if the oldest dies since parents cant feed multiple chicks
parent offspring conflict- Trivers (1974), pointed out what
for most species an offspring is more concerned about its own reproductive succes than with its parents. This difference leads to conflict between parent and kid --> how much parental care, investment, relationship with relatives, sex ratio
how do offspring compete with their parents
they are expected to employ psychological weaponds in order to compete with their parents
what is an example of this parent offspring conflict
weaning conflict in mammals, many taxa including priamtes, carnivors, ungulated female parents have to forcibly drive away young that are still interested in suckling because the mom needs to invest energy into next offspring
what are other examples of p-o conflict (2)
negatively affect current offsrping in favour of next:
1. reabsorption of embryos
2. nest abandonment
- hypothesis of menopause arise from this
some organism have nebulous margins and others are tightly demarcated, what does this mean
Nebulous margins = unclear or indistinct boundaries.
Tightly demarcated = clear and well-defined boundaries.
the tighest clumps are called?
species
the biological species concept is defined by?
Ernst Mayr (1904-2005)
Ernst bilogical species concept defintion
"species are groups of organisms that can actually or potentially interbreed which are reproductively isolated from other such groups." concept of interbreeding helps explain how species arise and how differences are maintained
what did Mayr mean by reproductive isolation?
that individuals from different species could not successfully interbreed and produce viable, fertile offspring
RIM
reproductive isolation mechanism
prezygotic RIM ( barriers before fertilization) and example
prevents egg and sperm from getting together. differences in timing or nature of courtship, genitalic morphology, sperm-egg recognition
ex. spawning sea urchin-eggs will reject sperm of the wrong species
post zygotic RIMS (after fertilization/production of a zygote), example
inviability of embryos, sterility of offspring
ex. Zonkey, mule (m donkey f horse) or a hinny (m horse f donkey)
how did B.S.C come about
arose because various studies shwoed that morpholgical similarity was not enough to define a species
- variation within a species and can appear between geogrpahically isolated pops who can stil interbreed
-species can be similar and cant breed
weakness of BSC
1. can apply to everybody, only works with sexually reproductive species and outcrossing indivduals
2. cant be used for fossils
3. not great if organisms can hybridize easily
4. diffcult to apply bsc if ranges dont overlap becuase we cant observe if they would produce viable fertile offspring, easier to define species when ranges overlap and they dont interbreed.
sympatry vs allopatry
ranges overlap (repro isolation more observable) vs ranges dont overlap
PSC was defined by who
cracraft in 1989
PSC defintion
group of concepts that emphasizes the phylogentic history of lineages. a species as an irreducible cluster of indivduals diagnosable by shared feature(S) among which is a parental pattern of ancestry and descent. smallest cluster of indivduals with shared features. (morphological, chemical, genetic)
what is another form of PSC
species as reciprocally monophyletic lineages. each lineage should be supported by at least one unqie synapormorphy.
strength of PSC
it can be applies to both sexually and asexually reproducing species
weakness of PSC
according to strict def'n
- even neutral mutations could erroneously inform speciation
BSC vs PSC conflict
month genus Grey, members of the species G.mitellae are phylogentically nested within G.piperella but are reproductively isolated from them, and populations of G.piperella are gentically distinct from each other but can interbreed
BSC: mitellae and piperella (paraphyletic) are 2 species
PSC: 4 species of piperella and 1 species of mitellae.
geographic isolation
do not encounter each other because of geographic barriers and hence do not intebreed
does geographic isolation always suggest 2 differnt species
no
ex. feral cat from alberta can interbreed with a cat in japan
same species because may be continuum of intebreeding and they havent been isolated long enough for genetic differences to accrue (accumualte)
if seperated long enough, potential for barrier to develop. example?
north american elk and red deer from europe, ranges of the two have been seperated for over 9k years. used to be capable of interbreeding across beringia, now theyve diverged genetically and morphologially but sill can interbreed if they overlap but now there is no continuum for them to interbreed. therefore for the longest time they have been considered the same species- cervus elaphus
why are they considered 2 species now
becuase they have diverged morphologicaaly and genetically. molecualr phylogenies indicate 2 clases and north america elk are more closely related to sika deer than red deer. example of allopatry
prezygotic barriers- behavioural isoaltion RIM
organisms do not respond to the courtship behaviours of members of a different species
ex. green lacewing: courtship song differ, diversity in song suggest dozens of species.
prezygotic barriers- ecological isolation RIM
organisms live or breed in different habitats, at different times, or (for plants) have different pollinators
ex. wood frog and tree frog. live in the same location but have different seasonal peaks in fertility.
ex. pollinator differences, in plants symaptric speciation occurs when different pollinators are used. bee pollinated mimulus spp and hummingbird pollinated mimulus spp .
prezygotic barriers- mechanical isolation RIM
should indivuals from different species try to mate they may be unsuccessful due to other prezygotic barriers such as genitalic mismatch (animals) or pollen mis-placement (plants) should the gametes be delivered, they may still fail to form a zygote.
example: damselflies males- shape of male reproductive organ differs between species of damsel flies
is difference in shell coiling- speciation?
in snails: direction of shell coiling prevents mating between oppositely coiled snails
post zygotic barriers
hybrid inviability is where hybrids die before or shortly after birth
ex. drosphila melanogaster and drosophila simulans look very simialr, can mate but embryos are inviable if female melanogaster mate with simulans male
post zygotic barrier- hybrid sterility, two types?
physiological sterility and behavioural sterility
physiological sterility
hybrids sugger from problems in repro tract or in gametes
behavioural sterility
hybrids suffer neurological or behavioural defects that prevent them from finding mates
a cross between a horse and a donkey gives a mule (sterility issue)
horses --> 64 chr
donkey --> 62 chr
mules--> 63 chromsomes (meiosis is error-prone=no viable gametes)
d melanogaster males and d simulans females progeny result in
sterile male flies (switch the sexes, embryos inviable)
hybrid breakdown
successive generations of hybrid matings results in lower fecundity or viability ex. rice cultivars
f1 vs f2 in rice cultivars
f1 hybrids are viable and fertile, f2 is stunted and sterile
current models can be classified according to:
- how important geographic barriers are to gene flow
- or the roles of natural selection and genetics
allopatric speciation
original population splits due to a new geographic barrier, over time populations diverge, geographically, ecologically, morphologically, genetically.
if barrier disappears, individuals speacies are now too different to interbreed
allopatric speciation example
vicaraince example (snapping shrimp)
habitat is split, shrimp were isolated by isthmus of panama, no gene flow therefore populations diverged
if you try to mate them they just fight since they are different species
parapatric speciation- geographical barrier
range expansion leads adaption to two different areas leading to population divergence, barrier might eventually arise. a founder population utilizes new habitat within the existing range of the species, over time they may diverge from the parent species. speciation can occur when the exisitng population experiences drift.
sympatric speciation
speciation occurs between individuals in the same range, no spatial separation. a barrier to gene flow arise within an intially randomly mating pop, persists despite there being to spatial separation.
ex.polyploidization
role of sexual selection
also though to cause speciation, genetaila morphology is very species specific. taxa that exhbit stronger sexual selection seem to have more species groups
ex. cichlid fish (very terriotorial and high mate competition)
role of reinforcement
complete reproductive isolation may be due to reinforcement of isolating mechanisms
if initial allopatric divergence results in incompletely sexually isolated populations whose hybrids are of poorer fitness than either parent what will happen
selection will strengthen pre zygotic barriers until members of 2 populations never mate. strongest evidence would be greater divergence in mating preferences in areas of geographic overlap. also called ecological character displacement.
pied flycatcher is an example of what
pied males have 2 morphs (black&white and brown&white) and collard males are also black and white.
if pied flycatcher overlaps with collar flycatcher, female pied prefers brown just to make sure she gets a pied.
if no overlap, pied female prefers black and white pied males
microevolution
occurs at/below the species level and on relatively short time scales. includes population genetics, natural selection, drift
macroevolution
occurs above the species level, at longer time scales of 100.s of thousounds to billions of years
examples of macroevolution
1. adaptive radiations
2.origins/diversification/ extinction of taxa
3. origin of novel characteristics
biogeography
study of the geographic distribution of organisms, involves geology, palaeontology, systematics and ecology.
what is an example of this biogeographical relationship
current range of the cold adapted plant saxifraga cernua, includes several geographically distinct patches. it is a poor disperser so how did it get distributed? the range was continous in the last ice age, relic populations persist now at high elevations
what is the relationship in biogeography
study of history of land masses and climates can shed light on distribution of organisms, conversely, distributions can provide clues to past geography and climate.
ancient earth and plate tectonics, when and who joined what
in 1912, german meterologist alfred wegener got evidence that not only africa and south america but all that continents were once together (about 200 mya), called gondwana.
gondwana is comprised of what
modern day Africa, South America, india, antarctica, australia
who supported these theory of godwana and proposed an additional theory
alex du toit, who said there was the souther contienent of gondwanaland and the nothern contienent laurasia
pangea
original supercontinent
biogeographic realms
large land area with characteristic flora and fauna, named and recognized by alfred russel wallace
wallaces line
match locations of a deep underwater channel that acted as a barrier to dispersal of terrestrial animals even during very low seal levels
what are marine biogeographical realms have been described
include different oceans and ocean basins. for instance, scientists now agree that there is a southern ocean that surronds antartica, isolated by currents.
- indian and atlantic ocean don't mix
vicariance
formation of a new geographic barrier resulting in the seperation of once continously distributed populations
how can we test the biogeographical hypotheses for if diversification is because of vicariance vs dispersal
phylogenetic relationships, if diversification is due to vicariance the order of timing of splitting trees in taxa should match geographical changes.
how to tell from a phylogeny if diversitfication/distribution is due to dispersal
if an organism has close relatives to another organism which is distant from them geographically (they were dispersed)
the southern beeches are distributed among previously gondwanan areas is there distribution due to vicariance, dispersal or both
molecular phylogeny of nothofagus as calibrated with a molecular clock suggest that both phenomena occured. rift between continental regions corresponds often with related species. But also the youngest species are in NZ/AUS even though the geographic split was earlier.
hawainn island chained was formed by movement of tectonic plate over a hotspot that produces volcanoes, islands arrayed in a line from oldest (kauai, 5.1 MYO) to youngest (hawaii, 9.5-1 MYO), crickets of the genus laupala live on all island. where did the genus originate and how did they spread?
molecular phylogenies show the most ancient clade (2 lineages of cricket) on kauai, then dispersal to various islands as the islands appeared.
marsupial distribution are an example of what
bioegeography suggest vicariance, but doesnt explain american opossum. Thought marsupials currently restricted to neotropic and australlian region. when you include fossils--> different explanation. fossil marsupials are found everywhere, and actually arose in Asia (150 mya), and had some dispersal to everywhere (40 mya) and went extinct everywhere but where they are today (australia, south america, virginia)
most extinctions are due to?
environmental change, this can include loss of food, habitat, disease, increase in predation and increased comp for resources.
mass extinction are due to
rapid environmental change, these extinctions are global and arent restricted to a certain geographic area.
what can complicate a simple explanation of dispersal/diversification?
sometimes what appears to be pure vicariance when looking at extant taxa become more complicated with additon of fossils
what taxa survive mass extinction events
those who already had adaptions that increased their survival in these new conditons. adaptions do not occur fast enough to survive mass extinction the variation has to have already existed (luck).
ex. smaller bodies mammals like reptiles that persisted after (252 mya) didnt require lots of food to survive
around how many species has to go extinct to be considered mass extinction
around 80% of known species going extinct
which was the first big extinction
the end ordovician (443-450 mya)
what extinction followed the end ordovician
late devonian (359 mya)
what extinction followed the late devonian and how did it happen?
permian extinction (252 mya) , due to massive volcanic activity (acid rain, acidification of ocean)
what extinction followed the permian extinction
end triassic (201 mya)
what extinction followed the end triassic, what was it due to?
end cretaceous (66 mya)- meteor strike, large body animals could not cope
what happens after major extinction events. example.
diversity among remaining taxa often (though not invariably) rapidly rebounds
ex. after end of permian = less water and more lava rock therefore amniods (egg layers), didnt need the same water coverage for young. increased from 2 to over 100 genera
what does the hierachial model of extinction rebound show
rate of appearance of new genera is inversely proportional to # existing at any one time
holocene mass extinction?
if right now is considered a mass extinction, voer the last 500 years extinction rates are on par with past mass extinctions but just havent reached their total magnitude yet, it could only be a few thousand years or less until we qualify as a mas extinction
The Anthropocene
is a proposed geological epoch that highlights the significant impact humans have had on Earth's geology and ecosystems. It suggests that human activity, such as industrialization, deforestation, and climate change, has altered the planet on a scale comparable to natural forces. The Anthropocene follows the Holocene Epoch and is marked by human-driven changes to the atmosphere, biodiversity, and landscapes. The exact starting point is debated, with some suggesting it began around the mid-20th century due to the Great Acceleration of industrial and technological growth.
what is the weakness of fossils
the fossil record is notoriously incomplete, there are gaps from geologic forces, taphonomic forces or simply cause they havent been dug up yet
how do you determine diveristy from fossil data
1. counting fossil data
these estimates rely on being able to count the # of fossil taxa present at particular times, morphology is the only clue for most fossils, the fossil record is not complete and fully detailed. the gaps come from erosion and lack of sedimentation.
how does one intepret a change in morphology across a gap
theres no problem when old forms and new forms overlap= suggestive more so of speciation
if only the new form is present there can be what two interpretatiosn
anagenesis and cladogenesis
anagenesis
gradual change in morpholgy over time without speciation, on graph more wave like
cladogenesis
speciation with very rapid change followed by extinction of old form, on graph more zig zag/sharp
until 1970s, paleontologists felt speciation was slow and that anagensis was common but then in 1972 what was proposed
eldredge and gould proposed that a different scenario was more common: rapid cladogenesis together with rapid morphological changed follwoed by stasis, in which the lineages showed no change at all= punctuated equilbrium
depauperate
low diversity ecosystem
do species exist on their own
no, each species interacts directly or indirectly with other ones. these interactions can be psotivie, harmful or even neutral. facultative, option, not required or obligatory.
the more obligatory the interaction the more likely...
it is that the interacting species will coevolve, coevolution can result in very intimate partnerships (ex. evolution of organelles such as mitochondria)
interactions between species exists on a continuum, hard to see as discret/rigid categories. some relationships can shift from negative, postive and neutral. what is an example of mutalism ?
fig and fig wasp
categories of coevolution- coadaptation
species A adapts to a feature in species B and species B responds to A's adaption. this is different from adaption to physical environmental condtions in that the environment isnt changing. specifically when species sequentially and mutually adapt to changes in each other.
categories of coevolution- codiversification
genetic divergence, including speciation, in one lineage (typically hosts) results in divergence in ecologically associated lineage (typically parasties/mutualists). can often lead to cospeciation if divergence leads to speciation.
what are the two types of coadaptation
coadaptive evolution can be categorized on how tight relationships are between interacting species
tight coadaption and diffuse coadaption
tight coadaption
two species respond rapidly to one another, results from strong selective pressure
diffuse coadaption
more than two species involved (adaption A to B might be counteracted by decline in adaptability to C)
mutualism- pollination
interactions between flowering plants and pollinators, most plants arre pollinated by several species in some case only one or a few
ex. figs and gif waspa and yuccas and yucca moths
what is the issue that come with pollinators that and plants that are specific or rare to one of eachother
if their pollinators are rare such plants suffer reduced reproductive success (ex. new zealnd home to many endemic species- onyl found in new zealand) and (ex. rhabdothammnus solandri, endemic flower which is reliant on edmic species of bird- tui)
how do they test this negative pollination result
comapred natural pollination rates to a negative control (bag covering flowers ) and positive control (human pollinating by hand)
result: in areas were the birds were disappearing pollination rates were low
what is true about almost all cases of pollinator corelationships
pollinator doesnt benefit from exclusive relationship. in system with 2 species success is tightly linked even if one side needs the other side more.
coadaption- enemies and victims
coevolution between predator and prey (or parasite and host) could conceivably continue endlessly as an arms race, arms race arent endless because of principle of allocation of resources.
what happens when increasing allocation of energy and effort
it causes too many tradeoffs with essential life functions
what is an example of principle of allocation of energy and efoort in drospohila
flies that were goos at resisting parasitsm were terrible at competeting for food.
if food is limited..
ability to forage is selected for therefore resistance should decline
example 2: parsnip vs webworms (its major herbivorre)
measured fitness of indivs that have high vs low investment in defense
result: an increased ability to resist herbivory comes at a cost of reduced parsnip seed production
the result of the arms race
if a predator or parasite can exploit different prey/hosts, then rather than specfically adapting to exploiting one of them it may alternate among them
if one host evolves defenses--> switch to another--> if that one evolves--> swtich again.
same for predator and prey
is a better for a predator (parasite or parasitoid) to adapt or keep switching
it best for them to cycle through since then they can attack species with the weakest defenses. when the neck species evolves defenses they switch again.
what type of variation does coevoluntionary dynamic show
they can show geographical variation with some populations showing strong coevolution while others not
example 1: newts and snakes
most pops of the rough skinned newt taricha granulose have high levels of (TTX- tetrodotoxin) which is a powerful neurotoxin; 1 newt can contain enough to kill 25k lab mice. some populations of this snake lack TTX and some populations of garter snake are able to eat them without ill effect but some cant.
resistance of TTX in garter snakes is highest where snake populations and new populations overlap (in many places the snakes are more resistant than necessary for the strength of toxin in local newts) so there are areas of mismatch
why is there mismatch in these traits of newts and snakes
this may be because it is easy to evolve resistance since it is just a single aa change in neuronal protein that can blox TTX toxicity. on the other hand it is more difficult for newts to evolve toxicity therefore the rate of change between species is not always the same. their main difference is the expected mutational rate.
example 2: soapberry bugs (seed predators)
use their long beaks to fead/kill the seed inside fruit, in australia the bug eat the rambutan fruit (thing walls) had shorter breaks. then the balloonvine which was related to the rambutan and much thicker came in the 1800's-1920's and now the beaks of soapberry bugs where there is balloon vine are much larger than where it is absent. (beak length adapting to the new food source, greater time of coexistence in the north ( original introduction area) has allowed for more change in beak length
is the soapberry an example of coevolution
no cause we dont see the change in the baloon vine
host- parasite interaction, the intesity of selection with regards to these races and to parasites has to do with what
the virulence of the parasite
virulence
refers to the negative impacts of a parasite on a hot, in terms of the hosts survvial and reproduction. the virulence is influenced by how it is spread to new hosts.
what are the two ways the virus/parasite can be spread
vertical transmission--> parent to offspring
horizontal transmission--> between non related individuals in the same or different generations
how are most diseases moved
either just horizontally or horizontally and vertically
rarely just vertically for multiple generation because success of a vertically transmitted parasite depends on reproductive success of host. (if the parasite is hijacking the host, then the host reproductive success goes down so its a thin line)
what is the pro and con of horizontally transmitted parasites
pro: highly virulent
con: host has to live long enough for parasite to find a new host
most famous example of evolution of resitance and birulence is in the
european rabbit and horizontally transmitted myxomatosis virus
european rabbit and horizontally transmitted myxomatosis virus example, explain
thomas austin introduced rabbits to australia in 1859 for sporting hunters with no natural predators and littler of 5+ bunnies, 7 times a year there was a rabbit plauge. farmer killed them but they still mutliped. in 1950's csiro introduced myxomatosis which killed millions of rabbits, the virulence of the virus was very high ~ 99.8%
what two things happened after the introduction of myxomatosis?
1. rabbits started to evolve resistance
2. virus evolved to be less virulent ( high virulence cant be maintated)
how does evolving to be less virulent benefit the parasite
if the parasite is less virulent, it has more of an oppurtunity for its current host to be around other potential hosts for itself
less virulent strains are more successful in
getting transmitted
the virulence of a virus goes from I (most virulent) to V (least virulent) over time. why?
from the viruses perspective it maximized its own fitness.
so the csiro scientists were asked to come up with a solution, in 1995 a quarantine station was set up to test rabbit calicivirus fro europe and it was due for release in 1998 but then it was escaped from the island prior to this and carried by insects. what was the result
the effects have been good, in dry arid zones there is heavy reduction in rabbits, down 10-15% of original numbers
interspecific brood parasitism
species of cuckoos/cowbirds dont raise their young but parasitize the parenting off to another species, different pops of cuckoos specialize on different host species where their eggs match the pattern/colour of host eggs.
what is necessary in the cuckoo and host interaction
egg matching is necessary because many hosts can eject dissimilar eggs and cuckoos have gotten so dependent on their hosts that they cant actually rear their own young.
what about eggs that dont match example
the dunnock egg is mismatched to the cukoo egg, likely because dunnock are recent exploited host and havent figured it out.
parasites and genetic drift
berenos (2010) tested wheter genetic drift could be coutneracted by antagonisitc coevolution between hosts and parasites. parasites should act to maintain genetic diversity (diversity for resistance)= red queen
- remeber: drift is stronger in small populations
msintained a large and small pop of tribolium flour bettle with and without nosema parasites for 12 generations = heterozygoisty in pop was greatest when parasite was present.
host symbiont co diversifcation
phylogentic lineages often match b/w obligatory interactions b/w species= indicates codiversitcation
analagous to vicariance --> speciation matches geological enviro condtions
particulary evident in host-parasite
in some cases it is clear there has been strict co diversification with host
ex. aphids and their endosymbiotic bacteria buchnera aphidicola
rarely are topolgies so similar
pocket gophers and their lice are often cited as example of host parasite, but even here there are several mistmatches
not so strict cospeciation
why doesnt codiversification occur
many reasons why host and symbiont might not speciate when the host does
symbiont fails to speciate when host does because:
one symbiont with multiple hosts
multiple symbionts = one host
more likely to occur if some host popualtions are geogrpahically far apart.
cospeciation
both ancestral species codiverge. Cospeciation is when two species (e.g., a host and its parasite or symbiont) speciate in parallel due to their close ecological relationship.
🧠 Think: one splits, the other follows.
🔗 Example: A bird species splits into two, and its feather lice also split.
failure to speciate
When one species diverges into two, but the associated species continues to interact with both—so it does not speciate.
🔁 There’s intermittent gene flow in the associated species, preventing full separation.
🧠 Think: one splits, the other stays genetically connected.
🔗 Example: A host splits into two species, but its symbiont continues to move between them and doesn’t diverge.
duplication
One species diverges (e.g., host), but the second species (e.g., symbiont or parasite) maintains constant gene flow—so no speciation occurs in that second species.
🧬 Gene flow keeps the second species genetically unified, despite host divergence.
🧠 Think: host splits, but gene flow keeps symbiont “duplicated” across both.
🔗 Example: A host becomes two species, but the symbiont continues mixing between both, preventing divergence.
What is extinction via “missing the boat” in coevolution?
When one species (e.g., host) diverges, but the associated species (e.g., parasite or symbiont) fails to diverge in time and can’t adapt to the new lineage—so it goes extinct.
☠️ This is called “missing the boat”, similar to incomplete lineage sorting.
🧠 Think: host splits, symbiont doesn’t adapt fast enough and dies out.
🔗 Example: A parasite doesn’t speciate with its host and can’t survive on the new species → extinction.
What is host switching (incomplete)?
A symbiont moves to a new, unrelated host, but continues to interact with the original host too.
🌐 It hasn’t fully specialized—gene flow or presence remains in both hosts.
🧠 Think: double dating—uses both hosts.
How do pigeon lice illustrate different cophylogenetic patterns?
Pigeon lice show how the ecology of symbionts affects their evolutionary patterns with hosts
What is host switching with extinction?
A symbiont switches to a new host and stops interacting with the original one → its original lineage dies out.
☠️ No gene flow remains with the original host.
🧠 Think: breaks up with old host and the relationship dies completely.
What is host switching with speciation?
The symbiont switches to a new host and diverges into a new species, while still maintaining the old lineage on the original host.
🧬 Now there are two symbiont species, one per host.
🧠 Think: one lineage stays, one adapts and becomes new.
Can symbionts switch hosts?
Yes! Symbionts can jump to new, unrelated hosts through host switching, which may lead to incomplete switching, extinction, or speciation depending on interaction patterns and gene flow.
What pattern do body lice on pigeons show?
Strong cospeciation
🪳 Body lice are tightly associated with their pigeon hosts and show little host switching → their phylogeny closely mirrors that of their hosts.
🧠 Think: body lice = loyal to one host lineage.
What pattern do wing lice on pigeons show?
Diffuse cospeciation with frequent host switching
🪶 Wing lice more easily transfer between pigeon species, causing less congruence between their phylogeny and the host’s.
🧠 Think: wing lice = social butterflies (switch hosts often).
Why do wing lice show more host switching than body lice in pigeons?
Because wing lice are more mobile—they can “hitchhike” on pigeon flies (which visit multiple pigeons), allowing them to switch hosts easily, even between species.
🪶 In contrast, body lice are less mobile and stay tightly associated with one pigeon, limiting host switching.
🧠 Mobility = more opportunities for host switching → more diffuse cospeciation.