BIOL 201 Evolution and Ecology Midterm 2

Random evolutionary mechanisms

• Mutation

• Gene flow

• Genetics drift

What could happen if 2 species interbreed?

• Reinforcement of prezygotic isolation

• Hybrid speciation

• Stable hybrid zones

Would a graph with % survival plotted against body size provide evidence for the fitness postulate of Darwin’s 4 postulates of natural selection? If so, would it be direct or indirect evidence?

• Yes, it would suggest that fitness varies in association with a certain trait

• Indirect, as survival rate is just a proxy for fitness (aka reproductive success). It would be considered direct if # of offspring were on the Y axis rather than % survival

What data could be used to support Darwin’s postulate stating that phenotype varies between individuals?

• A graph displaying the frequencies of certain variations of a trait

• A graph showing how the average value for a trait changes over time

What data could be used to support Darwin’s postulate stating that phenotypic variation is heritable?

• Values calculated with the breeders equation

• Data or figures comparing the traits of parents to their offspring (e.g., bird graph showing sons plumage brightness score plotted against that of the father)

What data could be used to support Darwin’s postulate stating that phenotype varies and is associated with fitness?

• A graph showing values for a trait plotted against % survival or # offspring

Darwin’s postulate stating that a phenotype must be heritable for natural selectio to occur mainly refers to ______-sense herirability

narrow

Fitness

Reproductive success

Phenotypic plasticity

Ability of a single genotype to produce different phenotypes (physical traits, behaviour, or physiological states) in response to environmental conditions

Fecundity

The potential of an organism to produce offspring

Nonrandom evolutionary mechanisms

Selection (natural and sexual)

Natural selection

Traits that promote survival and reproduction become more frequent in species from one generation to the next

What does reproductive success depend on?

Phenotype and environment

Darwin’s 4 falsifiable postulates (aka the prerequisites of natural selection)

• The phenotypic trait varies

• The trait is heritable

• Variation of fitness

• The variation in fitness must be linked to the variation in phenotype (reproduction is nonrandom)

Typical effect of artificial selection on fitness in wild settings

• Decreased

• We might like dogs with fucked up noses so we selectively breed them, but they can’t even breathe so

Is reproduction random or nonrandom?

Nonrandom

Are populations always variable? How do you know?

• Yes

• If it were not for a difference in fitness based on phenotypic variation, we would be overrun by elephants

Broad sense heritability

• Proportion of phenotypic differences that can be attributed to genetics (encompassing all aspects of genetics) as opposed to environmental factors

• H2 = VG / (VE + VG)

Narrow sense heritability

• Proportion of phenotypic differences that can be attributed to specifically additive alleles as opposed to other genetic factors or environmental factors

• h2=VA/(VE+VA+VD+VI)

Selection for a dominant allele

• Allele rapidly increases in population

• Doesn’t fix

Selection for a recessive allele

• The allele slowly increases in the population at first, then speeds up

• Becomes fixed in the population

Selection for a heterozygote

• Aa has higher fitness than AA or aa

• Results in balancing selection, which maintains both alleles in the population (no fixation)

Selection for homozygotes

• One type of homozygote has higher fitness than heterozygotes and the other homozygote → directional selection, leading to fixation of the beneficial allele

• Both types of homozygotes have higher fitness than the heterozygote → disruptive selection

Sexual selection

• Type of natural selection

• Acts on an organisms ability to mate

• Causes different traits to evolve in males and females (sexual dimorphism)

Differences between sexual selection (1) and natural selection (2)

• One focuses on being well adapted to the environment for survival (2), and one focuses on being well adapted to successfully mate, regardless of if those traits aid in survival (1)

• 1 includes 2 subtypes: intrasexual (mate choice) and intersexual (mate competition) selection

Sexual dimorphism

When males and females of a species exhibit different phenotypes, aside from their reproductive organs

Pros of sexual reproduction

• Increases genetic diversity through recombination

• Can combine beneficial mutations faster

• Faster evolution

• Prevents harmful alleles from fixing, as they can be separated from beneficial alleles through recombination

Cons of sexual reproduction

• Fewer offspring and slower than asexual reproduction

• Can take significant energy to find a mate

• STIs

• Many points of failure

Reproductive strategies when metabolic cost is high

• Being selective when picking mates

• This only increases fitness when mating selectively is able to almost guarantee fertilization

Reproductive strategies when metabolic cost is low

• Mating as often and with as many mates as possible

• Producing many itty bitty gametes

Intrasexual selection

• Selection of traits that allow individuals to compete with their own sex for mates

• The sex that is strongly sexually selected will be competetive

• Reproductive success limited by access to mates

Intersexual selection

• Individuals of one sex selecting mates based on their characteristics

• The sex that is weakly sexually selected will be picky (about choosing mates)

• Reproductive success is limited by resources rather than mates

_____ tend to exhibit greater variance in reproductive success

• Males

• Or whichever sex contributes less metabolically to reproduction

Traits that can increase fitness through competition

• Size and strength in physical contest situations

• Also sneaking, sperm competition, or infanticide in can be adopted by smaller individuals

Which sex tends to exhibit greater variance in reproductive success?

• Usually males

• The sex with a lower metabolic cost to reproduction, which often must compete with others for mates

• Some individuals are chosen as mates frequently, and some not at all

How does phenotypic variation in a male trait and female preference drive linkage?

• When females prefer specific traits in males, they mate with males with those traits

• This makes it likely that their offspring will inherit alleles for both the female preference AND male trait

• Over time, these alleles are likely to become more closely physically linked due to nonrandom mating

Does assortative mating necessarily lead to evolution?

• NO

• Mating with individuals with similar phenotypes will change the distributions of alleles, but not their overall frequencies

• Might increase homozygosity

What type or selection (directional, disruptive, stabilizing) will occur if the mean display matches the mean preference (in the context of females likely colourful male birds, for example)?

Stabilizing

Effect of female choice on female fitness

• Increases fitness of females

• Choosing better mates results in more successful offspring who are more likely to survive and reproduce

What happens if selective choice limits maximum reproduction (being too picky about mates)?

Results in selective pressure to reduce choosiness

Assortative mating

• When individuals tend to mate with those who are phenotypically similar to themselves

• Doesn’t change allele frequencies overall in population

Trade-off between natural and sexual selection

• Being flashy might get you bitches, but it can also get you killed by predators

• Even if you die, the higher chance of reproducing before that happens is often worth it (to an extent)

• Traits that decrease survival may still be selected since they increase reproductive fitness

How does female preference evolve?

Eggs have a high metabolic cost and females typically spend more energy on care for offspring → able to produce relatively few offspring → those offspring had better have a high chance of being healthy so they are able to pass on her genes → spend your eggs carefully on mates who have a good chance of producing viable offspring → females with preference for higher quality mates will have higher fitness, and the alleles that caused that will increase in the population

Runaway selection

• Selection for traits in males that impress the females but impede their survival (e.g., being bright coloured, which allows them to be seen more easily by predators)

Adaptive advantage of choosing honest signals of quality

• High quality genes are secured for their offspring

• The “high quality” mate may be better at providing resources for the offspring and mother

Does male display actually reflect genetic quality?

• Sometimes

• E.g., larger repertoire of songs is associated with immunocompetence in some birds, as is the vibrancy of red pigment

The 4 species concepts

• Ecological

• Morphological

• Phylogenetic

• Biological

All models of speciation start with some mechanism to prevent ____ ____

Gene flow

Allopatric speciation

Speciation caused by geographical barriers/physical separation of populations of a species

Sympatric speciation

• Speciation caused by other barriers while the populations of the species live in the same geographical area

• E.g., different mating rituals or times, mechanical separation, ADD MORE

Pre-zygotic isolation mechanisms

Occur before fertilization

• Spatial isolation

• Temporal isolation

• Behavioural isolation

• Mechanical isolation

• Gametic incompatibility

Post-zygotic isolation mechanisms

• Zygote is inviable, does not survive to infancy

• Offspring produced is sterile

Ecological definition of species

• Groups organisms based on exploiting a common set of resources, having the same range or environments they tolerate, and dealing with the same predators and parasites

• Bacteria, archaea, and asexual eukaryotes cant WAIT IS THIS A TYPO SLIDE 8.2 SPECIES CONCEPTS

Morphological definition of species

• Groups/sorts organisms based on distinguishing features

• Applies to both asexually and sexually reproducing organisms, as well as their fossils

• Doesn’t take physiology, behaviour, or ecology into account

• Could overlook cryptic species

Phylogenetic definition of species

• Species are based on monophyletic groups, must contain ALL known ancestors of one common ancestor

• Species=smallest monophyletic group

Biological definition of species

• Considered different species if they cannot interbreed to produce viable offspring

• This definition can’t apply to asexually reproducing organisms, fossils, or geographically separated populations

General lineage species concept

• A species is a metapopulation that is evolutionarily independent of other metapopulations

• Metapopulation=collection of populations with sufficient gene flow between them to exclude evolutionary independence (divergence)

When is the biological species concept not valid?

When it comes to organisms that reproduce asexually

The three steps of speciation

• Isolation (block gene flow)

• Trait divergence through independent evolution

• Reproductive isolation caused by significant divergence (when two newly separate species come into contact, they can't mate)

Reproductive barriers

• Includes both prezygotic and postzygotic barriers

• E.g., finding a mate: timing, pollinators, and courtship rituals

Mutation as an isolating mechanism

• Even a single point mutation can impact mating

• E.g., a point mutation in Japanese snails can cause “righted-handedness,” preventing them from mating with “left-handed” snails

Polyploidy as an isolating mechanism

• Polyploid individuals cant produce ofdspeing with diploids

• Common in plants

• Causes instant reproductive isolation

Ecomorphs

• A local group of organisms that may not be related ro eachother, but share the same ecological niche, morphology, and behaviours

• Example of convergent evolution

Reinforcement of prezygotic isolation

• Evolutionary process where prezygotic barriers between two species are strengthened through natural selection

• Occurs when hybrids are inviable, have low fitness, or are sterile. Producing these offspring wastes energy and lowers the reproductive success of the parents, so it is selected against

Females from sympatric populations lay _____ (more/less) eggs from heterospecific crosses (WHAT DOES THIS MEAN BRO)

• Less

• Obviously if they’re sympatric and different species, there must be physical/mechanical or behavioural barriers that caused speciation by preventing interbreedint

• But if they live in different locations (allopatric), it’s possible that the only barrier is being far apart location-wise, making them more likely to lay eggs when they’re brought together

How can post-zygotic isolating mechanisms result in the natural selection of for prezygotic isolating mechanisms?

• Individuals who produce hybrid offspring will have lower reproductive fitness since their offspring will be dead/sterile

• Individuals who evolve to mainly mate with their own species will have more successful offspring and therefore higher reproductive fitness

• Traits that prevent mating with other species altogether can be naturally selected

Homologous traits

• Traits in different species that share similar underlying anatomical structures or embryonic origin because they were inherited from a common ancestor

• Function can change between species and they adapt to their different environments

• Display of divergent evolution

• E.g., whale flipper and human arm

Analogous traits

• Multiple species sharing similar structures with similar functions

• Evolved these similar structures separately; did not inherit them from a common ancestor with the trait

• Display of convergent evolution

• E.g., bird wing and insect wing

Convergent evolution

• When two organisms are not closely related but share similar traits

• Can occur when two different species adapt to similar environments in similar ways, gaining the same traits independently (homoplasy)

Divergent evolution

• When 2 individuals are closely related but have different traits

• Can occur when closely related organisms evolve under different selective pressures (e.g., one can access smaller seeds and one can access larger, harder seeds or nuts, so they evolve different beaks despite still being very closely related)

Derived traits

• A new, modified trait that evolved in a recent common ancestor

• Only present in a small clade

• Very useful in phylogeny for determining new clades and showing close relationships

Ancestral traits

• Inherited from distant common ancestor

• Shared widely across many groups

• Not super useful in phylogeny for determining close, recent relationships since so many groups have had the trait for so long

Anisogamy

• Different sizes of gametes produced by females vs. males

• Eggs tend to be far larger than sperm

Operational sex ratio (male or female biased)

• The ratio of sexually active males to sexually active females that are ready to mate

• Can predict the intensity and direction of sexual selection

• The sex with the larger number of sexually active individuals will be competitive in finding a mate, while the other sex is a limited resource

Result of sexual conflict

• Causes rapid evolution of genes related to reproduction

• Can eventually cause reproductive isolation and the formarion of new species

• In severe cases, can drive down the population (potentially leading to extinction), particularly when male harassment and harm deplete female resources and reproductive capacity

Sexual conflict

• Refers to when the reproductive interests of males and females diverge

• An adaptation that benefits one sex decreases the fitness of the other

Cryptic species

• Species that look nearly identical and may live in the same location, but do not mate due to other barriers

• Can result from sympatric or allopatric speciation

• Can cause the Wahlund effect

• E.g., the 4 species of giraffe (allopatric example)

Synapomorphy

• A derived trait that is shared by 2 or more taxa and was inherited from their recent common ancestor

• Very useful for determing relationships and lineages; is the core tool of cladistics

Autopomorphy

• A derived trait that is unique to a single taxon on species

• Does not help determine relationships since it’s not common to other groups

Outgroup

• A known group of relatives that falls outside of the “ingroup,” while being pretty closely related to the ingroup

• Acts as baseline to help root the phylogenetic tree

Ingroup

• Set of taxa (species or group) of interest

Homoplasy

• Trait found in 2 or more species that are not closely related and did not inherit the trait from a common ancestor

• Opposite of homology

• Often results from convergent evolution (though can also be caused by evolutionary reversal)

Parsimony

• The simplest and most direct explanation is likely the correct one

• E.g., the path in phylogeny that requires the least amount of gaining and losing traits is the most likely

Exaptations

Evolutionary process where a trait takes on a different function that differs from its original evolutionary purpose

Monophyletic group

Ancestor plus all of its descendants

Paraphyletic

Includes a common ancestor and some, but not all, of its descendents

Polyphyletic

Includes several unrelated organisms from different evolutionary organisms, and excludes their last common ancestor

Pleiotropy

A single gene influences multiple distinct and seemingly unrelated phenotypic traits

Bateman's principle

States that the variability of reproductive success is greater in males than females

Vicariance

Restriction of gene flow by geographic barrier

How can outgroups be used to understand phylogenetic relationships?

• They can serve as a reference point to understand evolutionary relationships

• Helps determine whether a trait is ancestral or derived

• Helps identify synapomorpies

• Hepp confirm if the ingroup forms a monophyletic group

Allopolyploidy

An organism that has two or more sets of chromosomes from different species

Selection coefficient

• Used to compare the relative fitness disadvantage of a genotype compared to a standard reference genotype

• s = 1 - w, where w is the relative fitness of a genotype

• Ranges from 0 to 1

Runaway selection is a form of (intrasexual / intersexual) selection

Intersexual