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