Evolutionary Ecology
What is natal dispersal?
Movement from site of birth to site of reproduction
Describe the different reaction norms
Plotting phenotype produced by three genotypes
How do we interpret fitness functions in terms of beta and gamma?
gamma = curvature
What is an adaptive radiation?
• Diversification of a single lineage, by natural selection, to fill multiple unoccupied ecological niches • Green box represents operational ecological processes causing evolution
What is a selection differential?
• Measures total selection acting directly & indirectly on a trait including via selection on genetically correlated characters • within generational change in trait means i.e. before and after
How did Richards (1948) criticise Lack's (1947) work?
"The problem, for instance, of whether certain specific characters (e.g. beaks of Geospizinae) are or are not adaptive (vague term) is one involving studies of field populations, genetics, and variation. It is a problem which might be largely solved by teams of workers dealing for a number of years with a particularly favourable example. It is not one, I think, which can be settled in a four months stay, even if supplemented by the examination of skins in museums" Need field biology studied over long period of time
How does evolution proceed on a fitness landscape?
- 2 phenotypic traits - Can map where a population is in relation to those 2 phenotypic traits (x and y axis) - z axis is fitness - Evolution tends to push pops up local adaptive peaks - Arrows show potential trajectory of a species as it moves up an adaptive peak
Give SIX examples of model systems in evolutionary ecology
1) Anolis lizards in the Caribbean islands - study how different communities evolve repeatedly over time 2) Three-spined stickleback - evolved repeatedly in fw environments 3) Arabidopsis - study variation is plant life history/repro/morphology 4) Heliconius butterflies - centre of diversity in N, S & Central America - study of evolution of diversity of different colour patterns 5) Great tits - understanding populational biology & evo eco of life histories 6) Guppies in Trinidad
Describe the dispersal kernels for blackbirds, reed warblers, wood pigeons and lesser black-backed gull (Paradis et al. 1998)
1) Blackbirds: v large no. of individuals (nearly 2000) disperse v short distance, tiny no. disperse longer distances - generalist 2) Reed warbler: commonest thing is to disperse short distance, many long distance dispersal events - specialist birds, reed beds in patches of habitats 3) Wood pigeon: commonest zero, some long distance dispersal - generalist 4) Less black-backed gull: big peak at zero, spikes every 50 km - colonial species, moving to other large colonies of species
What are five genomic methods for inferring LA?
1) Change in allele frequency spectrum: if +ve selection then alleles more common 2) Change in FST along genome: change in genetic differentiation, +ve selection = high differentiation 3) Locus-specific branch length 4) Extended haplotype homozygosity 5) Genome-wide association studies
What are the key methods used in evolutionary ecology?
1) Comparative approach: patterns/rates of diversification or evolution through time - facilitated by ability to generate phylogenetic trees from genetic data 2) Modelling & Optimality: predict patterns & quantitative fit 3) Macro-ecological: large scale association with environment 4) Experimental: transplants, phenotypic manipulations, micro & mesocosms 5) Genetic & genomic: genetic basis & underpinning of ecologically relevant traits
Describe the interspecific relationships between natal dispersal and population parameters (Paradis et al. 1998)
1) Dispersal parameters vary across species (& there is a phylogenetic signal, hence this trait evolves) 2) Short dispersal associated with large population size & large geographic range size 3) Body size & habitat specialisms associated with longer dispersal distances - hence ecological determinants
Give four processes that can cause evolution
1) Natural Selection - leads to adaptation 2) Mutation 3) Genetic Drift 4) Migration (Gene Flow) (2, 3 & 4 speed up or constrain development of adaptations but cannot cause it) • Processes interact: - Gene flow could slow divergence by preventing local adaptation through homogenisation of genetic variation across populations, or by spreading new mutations that are favored in all populations - Drift could counter natural selection e.g. favorable alleles are lost by chance or promote it if a favorable allele increases in frequency by chance
Give six examples of the diversity of dispersal phenotypes
1) Spider produces silk to undergo long distance dispersal by ballooning 2) Larval stage of marine organism - becomes sessile after 3) Howler monkey dispersing figs 4) Hummingbird dispersing pollen 5) Winged seeds 6) Flying e.g. dragonflies
Give two examples of extreme life history variation
1) Tsetse fly lays just one 3rd instar larvae - can weigh more than the female! Lingcod lays 500,000 eggs at a time! 2) Greenland shark median age 1st reproduction is 150 yrs Oldest recorded human was 122 yrs
How common are the following scenarios? i) fitness adv when native, disadv when non-native ii) do poorly in native habitat, well in non-native habitat
71 studies - c. 300 estimates - 2/3 plants i) 48% ii) 9% LA more frequent
Give an example where dispersal kernels have been hard to measure
>5000 natal dispersal events for great tit in Wytham • Reveals sex difference in natal dispersal, but many dispersal events are probably unobserved as finite boundaries create artificial cut off • However the tails of the distribution may be particularly interesting for some biological processes (e.g. colonisation of patches, range expansion etc etc) • Also, distance moved ≠ gene flow (at least, may be more complex)
What is dominance variance (VD)?
Alleles at a single locus interact to produce a phenotype that would not be predicted on the basis of average effects of those alleles if they acted alone
Describe the diversity of Darwin's finches
Almost all of the diversity across species relates to beak dimensions and feeding behaviour; plumage variation is just age/sex related
Give an example of a GxE interaction
Bristle number in different Drosophila pseudoobscura genotypes at varying growth temperatures (Gupta & Lewontin 1982)
How do common garden and reciprocal transplant experiments differ?
Common garden: test of a specific hypothesised selective force in fixed environment (need to be wary of gene*lab interactions) Reciprocal transplant: direct test of fitness of one genotype versus another across habitats (need to control for movement effect)
Describe how inbreeding was identified in Great Tits at Wytham
Data collection & pedigree building • Adults are caught, ringed & measured while feeding young • Chicks are measured & ringed on day 15 after hatching Sample size (1964 - 2004) • 4523 pairs (breeding events) where all 4 grandparents known • coefficient of inbreeding f (probability that 2 homologous alleles are identical by descent)
What does the distribution of dispersal distances look like (dispersal kernel)?
Describes dispersal probability as a function of distance Want to look at how process affects shape of kernel
What are genotype x environment interactions (VGE)?
Direction of phenotypic change that occurs in response to an environmental condition or gradient differs among genotypes
What happens when the environment itself can co-evolve in response to selection?
E.g. host-parasite co-evolution and plant-herbivore co-evolution • Here, we could have local adaptation by one, or both parties, or local co-adaptation • Which we see easiest to predict from generation times • When host >>> parasite, or herbivore <<< plant, expect to see local adaptation of parasite/herbivore to host (e.g. pathogen or consumer on trees, viruses within vertebrates) • When host & parasite more similar then local co-adaptation (but also requires all conditions for LA)
What are Darwin's finches a good example of?
How we can take evolution & ecology together & understand the way diversification arises & is maintained within populations
What is epistatic variance (VI)?
Interactions where the phenotype or fitness of a genotype at one locus depends on the genotype at one or more loci
Why are fitness landscapes not very representative of what we see in the real world?
It is a static landscape Fitness landscape can change over time with adaptive peaks shifting Population has to evolve again
What is breeding dispersal?
Movement between sequential breeding sites
What is dispersal?
Movement that potentially results in gene flow
Is migration dispersal?
No - confusingly, term 'migration' often used for dispersal in theoretical literature e.g. migration-selection balance
In what context is phenotypic plasticity studied?
Phenotypic plasticity is often studied in context of within population variation (though this need not be the case), and PP is an equally valid potential explanation for differences between populations
Describe individual variation in dispersal in Great Tits
Positive genetic correlation between dispersal and exploration rate (Korsten et al. 2013)
When is evolution of dispersal favoured?
Two general types of explanation: 1) Applied to non-stable environments 2) Applied to stable environment (this distinction is somewhat artificial & no single explanation likely to provide unitary explanation)
Describe local adaptation in human populations
We have identified genomic regions association with local adaptation e.g. PRKGI in Arctic environments, MCM6 for lactase persistence
When might we see a dynamic fitness landscape?
When ecological interactions between species are important in determining the shapes of fitness landscapes and positions of adaptive peaks
Give an interpretation of population*habitat interactions
a) & b) Fitness of local higher than foreign across habitats = LA a) & c) Fitness higher in home than away habitat = LA (partial) - unstable situ in c) d) Not LA - population has higher fitness across 'all environments
Give four examples of stabilising selection
a) Female house sparrows: size vs survival b) Humans: birth weight vs survival c) Parasitic insects: gall diameter vs survival d) Darwin's finches: bill depth vs survival
Give four examples of univariate selection fitness surfaces
a) Pure directional selection b) Non-linear component, but still explained well by linear regression c) Stabilising selection, but still a significant directional component (b>0) d) Pure stabilising selection
What was determined about flightlessness & speciation in beetles in Japan (Ikeda et al. 2012)?
• 3 categories in beetles: 1) Flightless (deep branches) 2) Flight capable 3) Dimorphic (both flight & flightless species) • Difference between flighted & flightless species v strongly associated with differences in genetic relationship between populations • Flight-capable species: weak +ve relationship between geog & genetic distance - lots of gene flow • Flightless species: strong relationship between geog & genetic distance • Loss of flight associated with niche shift from carrion to soil invertebrates: expected to select for reduced dispersal as more predictable/less competition
What are Darwin's finches?
• A group of birds found in the Galapagos islands • Darwin visited here on the voyage of the beagle • "A most singular group of finches, related to each other in the structure of their beaks, short tails, form of body & plumage: there are thirteen species .... Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that ... one species had been taken & modified for different ends" • An example of an adaptive radiation
What is the link between diet and beak size?
• Beak size strongly predicted by degree of seed hardness • Harder seeds = greater beak depth • True across species as well as within species
How does the breeder's equation differ from the multivariate breeder's equation?
• Breeders equation: R = h2S where R=Response; h2=heritability; S=selection differential • Multivariate breeders equation R = GP-1S = Gb where G=additive genetic covariance matrix; P=phenotypic covariance matrix; S=vector of selection differentials; b = vector of selection gradients
Describe the nature of phenotypic variation
• Causes & effects of variation in traits that influence performance, behaviour, survival & fecundity of individuals • The nature of phenotypic variation - how is the phenotype of a trait determined by genotype & environment? • How does an individual's phenotype influence its - contribution to subsequent generations - ability to acquire resources for growth & reproduction; avoiding predators; reproduce successfully • What is the outcome for different phenotypes in different environments?
What are some experimental methods used to identify local adaptation?
• Common garden • Reciprocal transplant • Replication needed! The unit of analysis is the population, not the individual • How to replicate? i) Clearly defined, reproducible habitat types (e.g. host species, marine/freshwater, normal/contaminated soil) ii) Multiple populations tested across multiple habitats (N>2)
How was condition-dependence of dispersal discovered in collared flycatchers?
• Created patch-level treatments of reproductive success: 1) Increased no. of offspring - more but poorer condition 2) Controls 3) Decreased no. of offspring (move to 1) - less but better condition • More dispersal into what appears the better quality patch (more offspring) • Expt shows that public information is used in informing dispersal decisions
What did Darwin and Gould determine about the finches?
• Darwin (& Fitzroy) collected finches in 1835 • Presented to Geological Society 1837, where handed to John Gould • Darwin had not collected or labelled finches particularly carefully & did not realise they were all related species • Gould identified there were 13 species (current classification rather unclear) & that they were all close relatives • Diversity of finches from common ancestor led to ideas about isolation & species formation
What is interesting about the phylogeny of Darwin's finches?
• Different species have accumulated over time, as have the Galapagos islands (new islands form due to volcanic eruptions - relatively new, Fernandina island just 30,000 yrs old) • Numbers of finches grows but is sequentially lagged in relation to number of islands • As number of islands increases so does finch species - suggests process of isolation might be responsible for diversification
Describe repeated adaptation in sticklebacks
• Eda locus controls number of bony plates • Sampled sticklebacks from marine & freshwater habitats b) phylogeny based on Eda locus c) phylogeny based on whole genome - Example of parallel local adaptation: same locus is involved in response to envt (Colosimo et al 2005) • Genome resequencing comparisons (Jones et al 2012): - Chr 4: differentiation between marine & freshwater populations at Eda locus - Other regions of genome associated with differences between marine & freshwater envts • Took a single river system, took sticklebacks from different points along river, sequenced genomes, compare along river: - Red = strong correlation between divergence between marine/fw at global level & what's seen at river level - Black = points associated with strong divergence on river Tyne that are not divergent across the globe • Some regions of genome that diverge repeatedly as sticklebacks move into freshwater, others are more specific
What is the survival probability like in silvereyes?
• First yr birds: oscillating pattern of survival, decreases in winter • Adults: winter not a period of strong selection
What is natural selection?
• Futuyma (1998) - "any consistent difference in fitness among phenotypically different biological entities" • Distinguish the process of natural selection which occurs within generations & evolution across generations in response to natural selection • When there is variation in fitness among individuals that is related to some phenotypic trait, then natural selection is acting on that trait
What was worked out about natural selection in first year birds?
• If beta is negative then smaller trait values are favoured • For gamma, whether it is stabilising or disruptive selection • Only trait that showed significant selection was bill width • Multivariate selection on bill width = +ve directional selection (wider bill = higher survival) and -ve gamma = stabilising selection • Directional selection up to a point, then it flattens out (stabilising)
When is plasticity adaptive?
• If plastic genotype performs better than non plastic one across range of conditions • Generally, we expect to see the evolution of plasticity when: i) The environment is variable in time at a shorter scale than generation time ii) The environment varies in space at a smaller scale than average dispersal distance
What did David Lack contribute to Darwin's finches?
• In 1957, Lack promoted the term "Darwin's finches" • Lack interested in the interaction between ecology & evolution - the father of evo eco?
What is inbreeding and what does it result in?
• Inbreeding occurs when relatives mate • Inbreeding increases genome-wide homozygosity • Inbreeding depression results from the expression of deleterious recessive alleles
How was condition-dependence of dispersal discovered in the two-spotted spider mite?
• Introduce populations at starting patch (beans) at varying densities & with varying degrees of relatedness & measure numbers reaching each sequential habitat patch over time • Patches connected via linear bridges of unsuitable habitat Results • Independent effects of both population density & relatedness on likelihood of dispersal (affected not just mean, but also SD & other aspects of distribution) • Hence dispersal kernel can be condition-dependent
What is local adaptation?
• Local Adaptation (LA) occurs when resident genotypes have higher fitness on average than genotypes originating from other populations • LA could refer both to a process as well as a pattern
What have we worked out from long-term observations of natural selection and what have we not?
• Long-term observations show that natural selection occurs, and that finches evolve as a response • BUT does not tell us much about why there are different types of finch • When two species compete for resource (e.g. food) we expect to see character displacement - A displaced to be larger, B displaced to be smaller
Is this local adaptation?
• Looks like good evidence, but then tested by rearing lizards in lab in habitats differing in width of perches that they could use over 4 months • Lizards reared in habitats with narrower perches seemed to develop relatively smaller hindlimb length for given snout-vent length • Lizards show developmental plasticity - grow relatively longer limbs if exposed to environment with broader perches • Example of phenotypic plasticity
What were the results?
• Majority not inbreeding but some 0.125 and more 0.25 (about 1% of all matings) • At each life stage we see a bigger & bigger effect of inbreeding • Inbreeding depression reduces fitness up to 60% - expect strong selection to avoid
What are the ecological determinants of dispersal?
• Many selective pressures govern the evolution of dispersal rates & distributions • Many of these (e.g. patch quality, kin structure) will vary over ecological time • Equally, some determinants of dispersal success will vary among individuals (e.g. competitive ability) • Hence, we may expect that dispersal behaviour will respond plastically to environmental variation
What did Grant & Grant (2002) discover about natural selection over time?
• Measured body size & beak size every year • Pattern of fluctuating change over time • +ve selection means selection favours larger individuals (e.g. during drought) • In some yrs, selection acted in opposite direction - due to environmental fluctuations • Average body size & beak size of pops has changed a lot over 30 yrs - not static • May reverse due to changes in environment
Give an example where character displacement evolved in Darwin's finches
• Medium ground finch & large ground finch • Plant species: Tribolium cistoides Goat's Head does well in droughts, produces large, hard to get into seeds - need a large beak • G. fortis very abundant • G. magnirostris colonised island in 1997 - numbers increase over time up to 2003 • G. fortis population crash in 2004 associated with drought • Opposite trend in 2004 to 1977 drought: G. fortis beak size decreased - effect of competition with G. magnirostris - very capable of opening Tribolium • When competition occurred, divergence between species evolved • Shift in adaptive landscape between 1977 and 2004
How has individual variation in dispersal been used in understanding metapopulation biology?
• Meta-population biology of Duke of Glanville Fritillary studied by Ilkka Hanski on Åland islands (archipelago between Finland & Sweden) • Noted whether meadows were occupied by pops or not • Variation at the phosphoglucose isomerase locus (pgi) is associated with differences in metabolic rate (& clutch size) • Also, individuals from newly founded populations can sustain high metabolic activity for longer • Individuals with the f-allele can also sustain flight for longer & at lower temperature • Hence creates population spatial genetic structure
What was found out when the genomic basis of evolutionary change in Darwin's finches was studied (Lamichaney, 2016)?
• One genomic region of 540kb strongly predicts beak size divergence across multiple species • HMGA2 = transcription factor associated with craniofacial development • Compared phylogeny based on whole genome vs phylogeny based on HMGA2 • Found that variation at this locus is older than many of the species of finch - suggests key locus associated with diversification of beak size • Also found genotype at HGMA2 locus predicts body size & particularly bill size in medium ground finch • Genotype at HGMA2 locus results in drought survival (or not)
Describe the morphological differentiation in Brown Anoles Anolis sagrei
• One of a clade of lizards that have undergone an adaptive radiation particularly in Caribbean • Different ecotypes: crown-giant, trunk-crown, twig, trunk, trunk-ground, grass-bush • Hindlimb length increases as perch diameter increases - correlation • Experimental evo on islands (Losos): lizards sampled from large island (Staniel Cay) & introduced (propagules of 5 or 10) onto 12 smaller islands with less vegetation; left for 15 years • After 15 years, populations occupy different position in morphological space - shorter fore/hindlimbs • Shorter the vegetation = more difference in morphology from island that sourced population
What is multivariate analysis of selection?
• Organisms evolve as integrated units - many correlated traits • Univariate measures of selection cannot distinguish between selection acting directly on a trait from indirect selection on correlated traits • Use multivariate selection gradients to measure selection acting directly on the trait of interest after accounting for selection on other measured traits • Univariate trait slopes denoted 1 and 2 hence starting at 3; e is error
P = G + E - what do these components mean?
• Phenotype value = Genetic Contribution + Environmental Contribution • G is the total genetic variation, composed of • VA: Additive variance - alleles whose effects are independent of genetic background • VD: Dominance variance - interaction between alleles • VI: Epistatic variance - interaction between genes (the last two are non-additive genetic variance) • E can be composed of • VE: Pure environmental effect • VGE: Interaction effects between genes & the environment VP=VA+VD+VI +VE+VGE
What is phenotypic plasticity?
• Phenotypic plasticity (PP) occurs when different phenotypes are produced by a single genotype • PP is defined as adaptive PP when this phenotypic flexibility produces higher fitness than non-flexibility
What are the elements needed for natural selection?
• Phenotypic variation • Consistent relationship between fitness and phenotype (both quantified in one generation) • Some phenotypic variation is heritable
What fitness functions are possible?
• Positive directional • Negative directional (both result in reduced variance in phenotypic distribution) • Stabilising (reduced variance) • Disruptive (increased variance)
What are the costs of dispersal?
• Production & maintenance of specialist dispersal structures or life stages • Energetic & time costs of dispersal • Risk (e.g. why leave home, by definition a good place to be born?!) • Competitive disadvantage against established locals • Migration load (reduction in fitness due to the fact you've dispersed) if combined with local adaptation
Describe stable environments
• Reduction of competition • Kin-selected dispersal (dispersal as altruism, as reduces competition with kin) • Inbreeding avoidance
Give an empirical example where multivariate analysis of selection can be applied
• Silvereyes on Heron island, S Great Barrier Reef • Repeatedly colonises Pacific islands & evolves to larger body size than mainland birds • Forest only existed on island for max. 4000 yrs - subspecies diverged in <4000 yrs (gen time 2-3 yrs, 1000-2000 gens) • Socially & sexually monogamous
How can phenotypic variance be partitioned into its component sources?
• Simplest is VP = VG + VR (heritability is VG/VP) • However, if the effect of genes depends on the environment then we should write: VP = VG + VE + VG*E + VR - Component of variation due to phenotypic plasticity
What did Peter and Rosemary Grant do?
• Studied populations of Darwin's Finches from 1973 onwards on the island of Daphne Major: individual-based study, following life-histories of each bird • Their approach: 1) Catch finches, measure beaks, mark with rings, release 2) Measure environment & observe what happens 3) Repeat for tens of thousands of finches over 30+ yrs
Describe an example of natural selection in action in Darwin's finches
• Studying medium ground finch G. fortis before/during/after drought • Severe drought (1977) caused strong natural selection for larger beaks • Finches born in 1978 had larger beaks than those born before the drought • Evolution had occurred and by amount predicted
What is fitness?
• Success in contributing descendants to the next generation • Relatively constant population size: - R0 - net reproductive rate is appropriate measure of fitness - as an individual parameter, R0 is lifetime reproductive success for each individual • Fluctuating populations e.g. ephemeral habitats, "weedy" species: - r - instantaneous rate of increase is appropriate measure of fitness
Describe individual variation in dispersal in collared flycatchers (Doligez et al. 2009)
• Taking breeding pairs of birds & categorising their parents (dispersers/philopatric) • Measured likelihood of offspring dispersing • Higher likelihood of dispersing for offspring whose parents were dispersive (lower for those whose parents were philopatric) • Siblings resemble each other: evidence for genetic determination of dispersal behaviour
What was Friedenberg's second nematode experiment?
• Tests effects of variation in patch quality & stochastic extinction on selection on two genotypes • As expected, when populations in patches experience synchronous variation, the dispersal phenotype does worse (this condition selects for fecundity) • It does best of all when populations go extinct, rather than simply fluctuating
What is natal dispersal distance & what were the results from Wytham?
• The distance between birth site & first breeding site • The higher the kinship to your mate, the shorter is your average dispersal distance • Strong cost to not dispersing
How do we measure heritability?
• The relationship between parental & offspring values • Take midparent value & offspring value - regress - slope of line is estimate of heritability • Maternal effects not considered
Describe non-stable or dynamic environments
• There is negative temporal autocorrelation in the environment (e.g. patch exhaustion, density-dependence) • In absence of temporal effects, stochastic extinctions mean purely philopatric lineage has lower fitness • Formation of new habitat patches also leads to higher fitness of dispersal strategy
How do local adaptation and phenotypic plasticity compare?
• They can give very similar looking patterns • Key differences: for LA, genotype 1 native to Hab 1, genotype 2 native to Hab 2; in PP we typically test the response of genotype 1 & 2 across environments that both are found in
What are microevolutionary processes?
• Those processes that affect contemporary trait distributions within & among populations • Natural selection & adaptation - selection arising from differences in survival or fecundity • Sexual selection - selection arising from differences in mating or fertilisation success • Drift in small populations • Gene flow
What else is important to note about beak size and shape variation?
• Tremendous variation in beak size within species as well as between species • Different beak shapes come from different island pops of these species
Describe experimental evolution of dispersal in C. elegans (Friedenberg, 2003)
• Two genotypes: differ in position of trade-off between fecundity & dispersal - one high fecundity/low dispersal and one low fecundity/high dispersal • Started lines with equal frequency of 2 genotypes • In single patch, dispersal phenotype doing v badly • If two patches but no extinction then dispersal phenotype still does badly • If frequent random extinctions then dispersing phenotype does better
What is evolutionary ecology?
• Understanding how ecological processes determine the pattern & direction of evolution • Understanding how evolutionary history determines ecological patterns & processes • Fundamentally interested in how we can explain diversity in natural systems - Why are there species? - Why are they different from each other? - Why are individuals within species different? - Why do different sets of species occur when and where they do?
What does dispersal matter for?
• Understanding local adaptation • Establishing barriers to gene flow between taxa • Conservation genetics & evolutionary rescue • Meta-population dynamics • Range expansion & community assembly • Determining distribution of many pathogens • Major driver of co-evolution between animals & plants (pollen & pollinators)
How can we measure natural selection in the wild?
• Univariate selection • Describe using standard linear model (a is intercept, b is slope, z is trait value) • Or a quadratic model (add a curve) • Use the regression approach to produce standardised descriptive statistics of fitness surfaces - selection gradients (Lande & Arnold 1983) • Directional selection gradient (b1): average slope • Non-linear selection gradient (g): average curvature of the fitness surface 2b2
How is fitness used in wild populations?
• Using R0 or r is great in theory, but estimating these parameters in wild populations is difficult • Can use a component of lifetime fitness: survival, fecundity, mating success • Or a surrogate: intake rates of food (assuming more food = higher survival and/or more offspring) • Relative fitness - divide the fitness of each individual by average fitness of the populations w tilda = w / w hat
What is additive genetic variance and heritability?
• VA: Additive variance - alleles whose effects are independent of genetic background • Heritability h2=VA/VP • Ratio (0-1) of additive genetic variation to total phenotypic variation observed • Important in evolutionary ecology - directly proportional to the magnitude of phenotypic change in the trait expected in one generation under a given strength of selection • R = h2S where R is change in phenotypic mean between gens & S is selection differential
What is environmental variance (VE)?
• Variation due to the phenotype responding to the environment • Phenotypic plasticity • Abiotic - light, temperature, oxygen level • Biotic - predators, competitors, the amount of food received • Maternal environmental effects - when a mothers phenotype, condition or resource status is determined by her physical or biotic environment & influences offspring phenotype
What can we work out from a more recent phylogeny using DNA sequences?
• Very young group of species where change is happening rapidly • Population of same species on different islands sitting in different positions in phylogenetic tree - not monophyletic • Root of tree is more like a net: separating early evo history of species is v difficult, multiple processes of pops separating & coming back together & complex patterns of gene exchange between species • Boundaries of species not easy to define - might expect this for species that diversify early in their origin
When can we expect to see local adaptation?
• When gene flow is weak relative to selection • When gene flow is non-random with respect to the environment • When selection is strong and divergent between populations • When there is little temporal variability in selection • When there are high costs of plasticity • When genetic architecture facilitates LA (e.g. strong linkage between selected sites, or alleles with major effects)