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Sem 2: Evolutionary biology > Week 9 > Flashcards

Week 9 Flashcards

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1
Q

What is an example of speciaiton caused by macromutation?

A

Speciation via polyploidy

Polyploidy – doubling of chromosomes either through hybridisation or spontaneous doubling within a species

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2
Q

What is the difference between allopolyploidy and autopolyploudy?

A

Allopolyploidy = hybridisation
Autopolyploidy = Same species doubling

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3
Q

How common are duplication events?

A

Estimated 30-70 % plants are polyploids
Also occurs in animals – e.g. salmonids, cyprinids, catfish….
Amphibians – Xenopus can be diploid (2x), tetraploid (4 sets, 4x), dodecaploid (twelve sets; 12x) eg Silurana tropicalis (2x) compared to Xenopus borealis (4x)

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4
Q

What is an example of polyploidy in plants?

A

Goatsbeards (Tragopogon spp) in N. America
T. mirus and T. miscellus have formed repeatedly during the past 80 years following the introduction of three diploids (T. dubius, T. pratensis, and T. porrifolius) from Europe to western North America

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5
Q

How does T.muscellus form in the wild?

A

T. miscellus is formed reciprocally from T. pratensis and T. dubius. When T. pratensis is the maternal parent, the ligules are short, and the capitulum is constricted at the base, but when T. dubius is the maternal parent, the ligules are long and the capitulum is more open

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6
Q

How does T.mirus (polyploid) form in the wild from diploid ancestors?

A

T. mirus has T. porrifolius as its maternal parent, and T. dubius as its paternal parent. No polyploid has formed in nature from T. pratensis and T. porrifolius, but diploid F1 hybrids have frequently been reported

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7
Q

What is an overview of speciation by genetic drift?

A

Proposed to occur under peripatric mode
Also known as founder effect speciation (Mayr)
A small subpopulation becomes geographically isolated from parent population, and becomes reproductively incompatible through genetic drift
Reproductive incompatibility may also be aided by indirect effects of natural selection

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8
Q

What is an example of speciation by genetic drift via peripatric mode?

A

Hawaiian Drosophila
Neighbouring islands hold more closely related species
Age of island corresponds to age of branching off of new species
Peripatric speciation through island hopping

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9
Q

What is an experiment for the founder effect?

A

Bottlenecking experiments in Drosophila (experiment separating putative effects of genetic drift from those of natural selection)
Rundle passed >40 experimental Drosophila populations through bottlenecks
In mating experiments, no significant sexual isolation from parent population

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10
Q

What is a case study for the evidence of the founder effect?

A

Island colonisations by Silvereyes (Zosterops lateralis)
Results show, instead, gradual decline in genetic variation with successive colonisations; implies single founder effects unimportant in this system (probably because of large number of colonists ~100), but sequential founder effects do reduce genetic variation cumulatively.

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11
Q

What is an overview of natural selection as a cause of speciation?

A

Natural selection as a direct cause of speciation (reinforcement)
Reinforcement = selection for prezygotic isolation, arising from reduced fitness in hybrids
Evidence from allopatric and sympatric Drosophila initial speciation assumed to be allopatric (sympatry is secondary)

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12
Q

What was an overview of reinforcement by recognition

A

Species recognition by female pied and collared flycatchers from sympatric populations.
Species assortative mating was significantly reduced when males of the two species had plumage characteristics typical of allopatric populations (small difference) compared to when the males had plumage characteristics typical of sympatric populations

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13
Q

What is an overview of natural selection as an indirect cause of speciation?

A

Populations adapt to different environments or niches (in (i) allopatry or (ii) sympatry), reproductive isolation follows as a by-product

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14
Q

What was an example of speciation by allopatry in Drosophila pseuodoobscura?

A

8 populations (4 starch-based medium and 4 maltose-based medium)
1 year after start, mating experiments performed
Result = positive assortative mating, Prefer to mate with opposite sex from same group even
across cages
Reproductive isolation by-product of adaptation to media

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15
Q

What is an overview of ‘Ecological character displacement’?

A

Competition (e.g. for food) between diverging species may be important in driving adaptive radiation (i.e. a series of rapid speciation events) i.e. the influence of one species on the evolution of another as a consequence of competition for resources

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16
Q

When does ‘Ecological character displacement’ occur?

A

The idea is that (i) competition (e.g. for food) plays a critical role in divergence and that (ii) character displacement occurs following competition for similar ecological niches

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17
Q

When can you estimate that ‘Ecological character displacement’ has occured?

A

A signature of character displacement is that there are more morphological and ecological differences between species in sympatry than in allopatry

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18
Q

What is an example of ‘Ecological character displacement’?

A

Three-spined sticklebacks (Gasterosteus spp) in small
freshwater coastal lakes in SW British Columbia, Canada.
Lakes created following deglaciation c. 12,500 years ago, when extensive contact with sea and with populations of ancestral, marine three-spined sticklebacks ended.
Each lake contains either one (= ‘solitary’ species) or a pair of stickleback species.

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19
Q

What happens when there are two species of three-spined sticklebacks present in an ecosystem?

A

When a lake contains two species (= ‘paired’ species), one is of one type and the other of a second type, the types being:
‘Benthic’, = dwells on the lake bottom
‘Limnetic’, = dwells in open water
Such species pairs have apparently evolved independently at least 5 times

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20
Q

How did they compare for sympatry?

A

Morphological and diet data were gathered from 5 lakes with paired species and from 10 lakes with solitary species in the same area; and from 2 marine sites nearby

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21
Q

What was the morphological differences between lakes with 1 stickleback and 2?

A

1 species had a broud range for gill raker length all contained within 1 species
Where as 2 species lakes had 2 distinct groups each with there own peak and variation

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22
Q

What were the dietry differences between the 2 species of sticklebacks?

A

Limnetic species high propotion of diet was plankton in both breeding and non-breeding seasons
Benthic species high propotion of diet was benthos in both breeding and non-breeding seasons
Solitary species has a mix between plankton (mixed) and benthos (high in breeding season) depending on season and lake

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23
Q

What is an overview of natural selection being indirect from sympatry?

A

Apple Maggot Fly
150 yr ago, flies transfer to introduced Apples, a habit that has since spread
Host races are morphologically alike but show strong genetic differentiation (c. 2% gene exchange)
Members of each host race prefer natal host plant given choice, mate on natal host fruit, and mate at different times (3 weeks earlier on Apples

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24
Q

What are an overview of the great lakes and the number of Cichlids present in each area?

A

Lake Malawi - 2 to 5 My - 29,600km2, 500-1000 species of cichlids
Lake Tanganyika- 9 to 12 My - 32,600km2, 200-250 species of cichlids
Lake Victora- 0.25 to 0.75 My - 68,800km2, 500 species of cichlids

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25
Q

What is an overview of the diversity of Cichlids?

A

Diversity of mouth parts - range from Mollusc crusher, hunter, plant scrappers and scale eaters
Reproductive biology (e.g. different forms of parental care)

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26
Q

What is an overview of the diversity of Cichlids?

A

Diversity of mouth parts - range from Mollusc crusher, hunter, plant scrappers and scale eaters
Reproductive biology (e.g. different forms of parental care)
Most morphological and ecological differentiation found between genera; within genera, species differ principally in male coloration

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27
Q

What are the stages of speciation in Lake Malawi cichilids?

A

1 - Habitat choice (water column, rock, sand)
2 - Ecological diversification
3 - Colour diversification through sexual selection (via female choice of male colour differences)

Could have occurred via allopatric (‘micro-allopatric’) or sympatric modes

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28
Q

What evidence is there for microallopatry in Great Lake Cichilids?

A

Geological evidence shows water levels have fallen and risen, so lakes may have been formerly subdivided
Few species have lake-wide distributions
Patchy within-lake habitat distribution
Genetic evidence show fine-scale population differentiation

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29
Q

What experiment for sexual selection causing speciation in African cichlids?

A

If sexual selection has driven speciation, expect allopatric, related colour forms (putative incipient species) to show assortative mating
Tested in 5 forms of Pseudotropheus zebra complex from Lake Malawi

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30
Q

What were the method for sexual selection causing speciation in African cichlids?

A

Females given choice of any male from each colour form (in tank in which smaller females could enter compartment of any male, but each male could not leave his compartment)
Use microsatellite markers to assess which male obtained successful mating (i.e. was chosen)

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31
Q

What were the results for sexual selection causing speciation in African cichlids?

A

62% of 115 broods were fathered by the male from the same colour form as the female; females, on average, prefer to mate with male of same colour form

Consistent with colour forms representing incipient species diverging under sexual selection brought about by female preferences for different male sexual coloration

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32
Q

What is an overview of sexual selection in Tyrannida?

A

Differences in the rate and direction of plumage colour evolution are predicted by a proxy for sexual selection intensity (plumage dichromatism) in a large radiation of suboscine passerine birds (Tyrannida)

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33
Q

What is an overview of sexual selection in birds in Tyrannida?

A

Rates of plumage evolution are correlated between the sexes, but that sexual selection has a strong positive effect on male, but not female, interspecific divergence rates.
Rapid male plumage divergence is biased towards carotenoid-based (red/yellow) colours widely assumed to represent honest sexual signals.
Highlights the central role of sexual selection in driving avian colour divergence

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34
Q

What is an example of rapid speciation?

A

Cichlid - Lake Malawi
Lake colonised about 2 mya
Current estimate of 700 species
High rate of speciation
High rate of morphological change

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35
Q

What are examples of long-term stasis in invertebrates?

A

Horseshoe Crabs: Little morphological change since the Early Triassic (230 MYA)
Notostracans (Tadpole Shrimp): Little morphological change since the Late Carboniferous (305 MYA). Two Triassic forms are assigned to living species

36
Q

What are examples of long-term stasis in vertebrates?

A

Sturgeons: Two living genera that extend back to the Late Cretaceous with little morphological change (80 MYA)
Pangolins: Only seven living species, one of which dates to the Early Oligocene (35 MYA).

37
Q

What is an overview of phyletic gradualism?

A

Traditional Darwinian view of evolution
Speciation events are not associated with increased rates of evolutionary change within a lineage

38
Q

What is an example of phylogenetic gradualism?

A

Morphological change in Trilobites - rib number
Nobiliasaphus - increases in number of ribs overtime
Ogyginus - number of ribs fluctuates

39
Q

What is an example of speciation and morphological evolution?

A

Radiolarians
3.5mya showed two distinct morphological types where before was 1 with a large spectrum

40
Q

What is the overview of the relationship between speciation and morphological evolution?

A

Morphological deviation, although slightly accelerated during the speciation event, continued for some time after the separation ofmorphotypes, suggesting strongly that morphological evolution is decoupled from speciation

41
Q

What is an overview of punctuated eqilibrium?

A

Differs from traditional Darwinian view of evolution
Speciation events are associated with increased rates of evolutionary change within a lineage

42
Q

What causes punctuated eqilibrium?

A

Observed that the fossil record gives a different picture for the evolution
There were long periods of stasis (4-10 million years) involving little evolutionary change
Then occasional rapid formation of new species
As little as 5,000 - 50,000 years

43
Q

What is an overview of punctuated eqilibrium in Neogene bryozoans?

A

Sudden shift in morphological variation at points of cladogenesis.
Intra species variability is small compared with inter species differences as predicted by the punctuated equilibrium model, as is also the prediction that the ancestral species continues to live alongside the descendant

44
Q

What are the 3 major hypothesis for stasis?

A

(1) Internal genetic or developmental constraints
(2) Stabilising selection for a constant optimum phenotype
(3) Ephemeral local divergence

45
Q

What is an overview of internal genetic or developmental constraints?

A

Would require either no genetic variation, or strong correlated evolution between characters

46
Q

What is an overview of stablising selection for optimal phenotype?

A

A variable optimum in a changing environment? E.g. Pleistocene glaciations?

47
Q

What is an overview of ephemeral local divergence?

A

Adaptational shifts do occur in local populations, but do not spread throughout the species range, and disappear through local population extinction or introgression of the initial morphological form back into the main population.

48
Q

What is similar between the genetics of horseshow crabs and king-hermit crabs?

A

Molecular genetic analysis of two arthropod groups;
1) morphologically static Horseshoe Crabs,
2) morphologically diverse king-hermit crabs
Demonstrates that both lineages have similar levels of molecular genetic variation

49
Q

What is the relationship between lack of genetic variation and adaptation?

A

Barton and Partridge (2000) infer that neither mutation rate nor genetic variation limits evolutionary rates
“Genetic variation and, more specifically, lack of mutations should not and, it seems, does not limit at least straightforward selection response.”
Evidence against internal constraint.

50
Q

What is an overview of the evidence for stabilising selection for stasis?

A

Stabilizing selection was proposed early as a simple explanation of stasis
Modelling suggests the most likely reason for evolutionary stasis is stasis is adaptation to an optimum that moves within an adaptive zone with stable boundaries
Futuyma (2010) is less convinced by stabilising selection and Estes and Arnolds arguments….

51
Q

What is time for speciation?

A

The time required for reproductive isolation to evolve after a split

52
Q

What is the biological speciation interval?

A

The average time between speciation events

53
Q

How can biological speciation interval be estimated?

A

The amount of time between the present number of species and the common ancestor
- assuming exponential growth and no extinctions

54
Q

How do you work out diversity for a taxomonic group?

A

The diversity we see for any taxonomic group is the difference between speciation and extinction
diversity = speciation - extinction
diversification rate = speciation rate - extinction rate

55
Q

Why is extinction rates important?

A

Extinction rate is an important metric
Extinction will result in the underestimation of speciation rates eg 15 speciation events (but we see only 4 spp

56
Q

What are two sources of information relevent to phylogenies?

A

The topological distribution of species diversity across branches - tree shape
The temporal distribution of branching events through time.

57
Q

What does the phylogenetic tree shape show?

A

Trees with equal numbers of species in each clade are said to be balanced
Trees with large differences in the number of species in clades are unbalanced

58
Q

What is an overview of topological methods?

A

Topological methods compare the observed difference in species diversity between two (or more) groups descended from a common node a distribution of diversity differences generated under a stochastic model of diversification

59
Q

What can be interpreted with an imbalance in the topological method?

A

Whether rate changes are associated with the evolution of novel phenotypic traits or with areas having particular environmental conditions, such as tropical versus temperate

60
Q

What can be interpreted with an absence of a imbalance in the topological method?

A

The assumption of rate homogeneity across clades (although not necessarily with respect to time) is reasonable.

61
Q

What would the impact of adaptive radiations show?

A

Adaptive radiations would be expected to lead to high rates of diversification (probably high rates of speciation) early, and declining diversification through time.

61
Q

What are the uses of temporal methods in phylogeny?

A

Temporal methods compare the distribution of branching times (based on branch length/duration estimates) to that generated under a null model of random diversification.

62
Q

What are branching times?

A

Branching times, the timings of speciation events, can be compared on a lineages through time plot.

63
Q

What do branch length show?

A

Branch lengths of a tree are usually proportional to time; thus these trees are ultrametric
Branch lengths can be interpreted independently of the topology, to identify temporal shifts in diversification

64
Q

What are the axis in a Lineages-through-time plot for studying speciation rates?

A

The log of the number of lineages is plotted against the relative time of each node since the root node

65
Q

What is an overview of the constant speciation rate model?

A

Where the probability of a speciation event occurring in a given time is constant both over time and among species, a straight line with slope equal to the per lineage speciation rate, b is expected

66
Q

What are the outcomes for a lineage through time plot?

A

r shaped curve overtime shows declerating speciation
Linear shows constant rate of speciation
Upwards curve shows accelerating rate of speciation

67
Q

What is an overview of the speciation rate of new world warblers?

A

A slowdown in the diversification rate towards the present, as found in New World warblers, can be caused by a decrease in speciation rate or an increase in extinction rate.

68
Q

What can be the cause of the increase in speciation rate of tiger beetles?

A

An actual increase in the speciation rate, or
An illusory increase caused by a constant background extinction rate, d, that is high relative to the (constant) speciation rate, b

69
Q

How did they test for sexual selection accelerating signal evolution?

A

Sampled recently diverged species pairs from approximately 1000 bird species with data on sex-specific plumage reflectance measured with a spectrophotometer
Beak, tarsus and wing length were also measured
Tested whether dichromatism and other non-sexually selected characters were correlated with diversification rate

70
Q

What did they associate rapid sexual selection with amogst birds?

A

Elevated levels of sexual selection are associated with more rapid phenotypic divergence between related lineages, and that this effect is restricted to male plumage traits proposed to function in mate choice and species recognition

71
Q

What did they show about sexual selection and female traits in birds?

A

No evidence that sexual selection promoted divergence in female plumage traits, or in male traits related to foraging and locomotion.

72
Q

What did they find about sexual selection and mating behaviours?

A

Strong evidence that female choice and male–male competition are dominant mechanisms driving divergence during speciation in birds, potentially linking sexual selection to the accelerated evolution of pre-mating reproductive isolation.

73
Q

What is an overview of the diversification rates of different organisms?

A

Plants diversify almost 2x faster than animals.
Fungi 0.5x that of animals

74
Q

How did they come to the conclusion about diversification rates of different organisms?

A

Assembled a phylogeny and analysed data on clade ages, species richness and diversification rates for 71 phyla, 122 classes, 434 orders, 2558 families and eight kingdom-level clades

75
Q

What determines species richness ?

A

Across all clades and taxonomic ranks no cases where species richness was explained by clade age
Comparisons showed a significant negative relationship between richness and clade ages (kingdom, phylum, class).
Variation in diversification rates explained species richness among clades in many groups and ranks

76
Q

Is speciation rate related to phenotypic change?

A

Some groups e.g. African cichlids, have rapidly diversified into a vast number of species and functional forms.
This exceptional diversity contrasts with the many groups that contain few species and/or harbour comparatively little phenotypic or ecological diversity

77
Q

Is there a link between speciation rate and morphological change?

A

Study found across fish groups that there is a pattern for speciation rate impacting morpholigical change

78
Q

How did they analyse and what did they find out about bird diversification?

A

Analysed and mapped the first complete dated phylogeny of all 9,993 extant species of birds.
Birds have undergone a strong increase in diversification rate from about 50 million years ago to the near present.

79
Q

What is causing the increase in diversification of birds?

A

This acceleration is due to a number of significant rate increases, both within songbirds and within other young and mostly temperate radiations including the waterfowl, gulls and woodpeckers.
Importantly, species characterized with very high past diversification rates are interspersed throughout the avian tree and across geographic space.

80
Q

What geographical regions are where there is a greater number of bird diversification?

A

Geographically, the major differences in diversification rates are hemispheric rather than latitudinal, with bird assemblages in Asia, North America and southern South America containing a disproportionate number of species from recent rapid radiations.

81
Q

What questions were asked about vertebrate speciation?

A

What is the background tempo of vertebrate diversification; Which, if any, vertebrate lineages have patterns of extant richness that are too species-rich or -poor to be outcomes of the background diversification rate?

82
Q

What did they find about the diversification of actinopterygian?

A

This study reveals that actinopterygian biodiversity has been profoundly shaped by four diversification events.

83
Q

What was the most statistically significant of the modern teleosts?

A

The base of modern teleosts, as predicted by the FSGD-FD hypothesis, and involved a four-fold increase in net diversification rates [net rate r = birth rate – death rate] over the background rates estimated from the closest evolutionary relatives of teleosts

84
Q

What is the overview of the secondary rate of diversification?

A

Additionally they found evidence for secondary rate increases in two lineages.
The first of these preceded the radiation of percomorph fishes comprising most of the diversity of acanthomorphs or spiny-rayed fishes.

85
Q

What is an overview of genome duplication in vertebrates?

A

Non teleost vertebrates have undergone 2 rounds WGD (1R & 2R)
Ray-finned fishes (teleosts) undergone and extra round (3R) ~ 350 mya.
>28,000 species of teleost fish.
WGD hypothesized to have increased diversification rates

Sem 2: Evolutionary biology (11 decks)

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