Speciation Evolution Flashcards
genetic variation (4)
genetic variation is the basis for evolution
a population must have genetic variation in order to evolve (one of the most important things required for evolution)
genotypic frequencies maths
genotypic frequencies
P = f(AA) = N_AA / N_total
H = f(Aa) = N_Aa / N_total
Q = f(aa) = N_aa / N_total
P + H + Q = 1
genotypic frequency (4)
genotypic frequency is the proportion of individuals in a population with a given genotype
genotypes for a locus with two alleles
for a locus with two alleles (A and a)
there are three genotypes: aa, Aa, AA
maths lol
allelic (gene or gametic) frequencies
p = f(A) = (2 N_AA + N_Aa) / 2 x N_ total = P + 0.5H
q = f(a) = (2 N_aa + N_Aa) / 2 x N_ total = Q + 0.5H
p + q = 1
assumptions for hardy weinburg equilibrium (4)
- random mating
- no mutation
- no migration
- no selection
- large population
inbreeding (4)
Most common type of nonrandom mating
* Positive assortative mating for relatedness
* An extreme version is self-fertilisation
non-random mating
Two types:
1. Positive assortative mating
- tendency for like individuals to mate
- Negative assortative mating
- tendency for unlike individuals to mate
causes for evolutionayr change (4) (last half)
- mutation - ultimate sources of variation, individual mutations are rare -> weak cause of genetic change in populations
- migration (gene flow) - effect is to make populations more similar, reduces genetic divergence between populations, while maintaining variation within populations
- genetic drift - Random changes in allele frequencies from one
generation to the next
Fluctuations are caused by random sampling of
gametes from the gene pool
Rate of change depends on population size - the smaller the sample, the greater the rate of change - natural selection - sexual selection is a subset of natural selection. Most complex of all the evolutionary forces
affecting the genetic makeup of populations
Occurs in many ways - not all result in
evolutionary changes
gene flow
highly mobile species or those within continuous distriubtuons show fewer genetic differences amoung populations
importance of random drift (genetic drift) (4)
Conservation genetics - loss of genetic variation in small populations
* Evolution — potential for rapid evolutionary change without selection, or even in opposition to selection
is selection the main mechanism causing genetic differences? (4)
Selection is not the only mechanism causing genetic differences between populations, but is the only one that causes adaptive changes
natrual selection (4) (4)
- Variation exists
- Traits are inherited
- Differential survival and reproductive success
OUTCOME:
Those alleles associated with greater survival or reproductive success will increase in frequency the next generation
Measured as the average contribution by a particular genotype to subsequent generations
* Environment dependent - can vary between sites
sexual selection
Sexual selection: secondary sexual characters
* Function during reproduction, but are not necessary for breeding
* Reduce survival
- manoeuverability
- powers of flight
- more conspicuous
- energetically costly
which one is more important reproductive success or survival
reproductive success is more important than survival
types of sexual selection (4)
Types of sexual selection
Intrasexual competition - members of one sex compete with each other for members of the other sex
Intersexual choice - members of one sex choose mates
mate choice, direct and indirect benefits (4)
- Direct benefits - parental care, provide food, protection
- Indirect benefits - attributes of mate are inherited by
offspring
the handicap hypothesis
Indirect benefit - the handicap hypothesis
* Assumes males vary in their quality - some males have genes that confer higher quality (“good genes”) than others (“bad genes”)
.
Males with ability to possess a handicap have good genes so females that mate preferentially with these males will have offspring with good genes
morphological (taxonomic) species concept
members of a species are morphologically alike
biological species concept limitations (4)
does not consider asexually reproducing species, fossils
> overlooks common cases of hybridisation between species
morphological diversity and reproductive isolation do not go
hand-in-hand
biological species concept
Biological species concept - groups of interbreeding individuals that are reproductively isolated from other such
groups
dog breeds and biolgoical species concept
Applies to populations not individuals
genes from Great Dane to Chihuahua is possible through intermediates, but not directly
what do all species concepts have in common (4)
All models emphasise the restriction of gene flow between populations so that divergence between them can occur
Reproductive isolation is important from an evolutionary perspective because it allows different species to evolve in their own ways
two things required for speciation (4) (4)
- divergence
- reproductive isolation
ways reproductive isolation can occur
- pre-zygotic barriers
- post-zygotic barriers
pre-zygotic barriers
- Pre-zygotic barriers (before fertilisation)
a) Ecological - species occupy the same geographic area but do not hybridise because they occupy separate habitats
b) Temporal - differences between species in the timing of reproduction
c) Behavioural - differences between species in courtship behaviours
d) Mechanical - physical restrictions to mating
e) Gametic - gametes of different species do not interact
post-zygotic barriers (4)
- Post-zygotic barriers (after fertilisation)
a) Zygote dies early during embryogenesis
b) F1 hybrid survive but are sterile
c) Backcross or F2 hybrids are inviable or sterile
how does reproductive isolation arise (4) (4)
Post-zygotic isolation
> cannot be the direct results of natural selection because it is impossible to select for inviable offspring
* must be a side-effect of genetic change for other reasons
Pre-zygotic isolation
can be the direct result of selection - but only if there is already post-zygotic isolation (reinforcement)
allopatry meaning
allopatric populations do not overlap
sympatry meaning
sympatric populations occur in the same place
sympatric speciation
A new species arises within the distribution of the original species
No geographic barrier needed
adaptive radiation
Adaptive radiation: a rapid evolutionary diversification of a single lineage
Characterised by an increase in the morphological and ecological diversity
a lot of
a lot of diversity in a species can be due to a lack of competitors (e.g. Hawaiian drosophila) , meaning new species that arrive on island can exploit all these resources and fill all these environmental niches not being used
character displacement (4)
Character displacement: differences among species are accentuated in regions where they co-occur, but are minimised or lost where the species’ distributions do not overlap
summary
Biological species are evolutionarily independent lineages, separated by reproductive isolation
Geographic separation is the easiest starting point for the understanding of the evolution of reproductive isolation
Basic ideas about competition and natural selection can go a long way in explaining major patterns in nature
