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Evo Bio > EB21 > Flashcards

EB21 Flashcards

1
Q

How many deaths are Anopheles mosquitos responsible and how many of them are vectros

A

655k deaths per year
216 million alaria cases
70/465 are malaria vectors

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2
Q

what do anopheles species tend to exist as

A

species complexes, very closely related groups of species which are morphiological indistinguishable
*adapted to lots of different habitats and ecologies

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3
Q

What is An. gambiae

A

a complex
main vector of malaria in africa
*complex differs in ecology, chromosome inversionsa and genetics.

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4
Q

what species are in the An. gambiae complex

A
  1. an. gambiae (split into two forms previously called S adn M now gambiae and coluzii
  2. An arabiensis: found in same place as gambaie
  3. An. quadriannulatus
  4. An ampharicus (prev. An. quadriannaltus)
  5. An. bwambae (found in hot springs only)
  6. An. merus*
  7. An. melas *
    * both found in Bracchis coast regions
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5
Q

what do crosses between an. complex species produce

A

sterile males, fertile females

except gambaie and colluzzi which are fully fertile.

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6
Q

how are species in an. complex identified

A

by chromosomal inversions/banding patterns, via microscopcy of salivary gland

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7
Q

what is a chromosomal inversions

A

chromosome rearragnemetn which occurs when a chromsooem breaks at two pointa nd the segment bounded by break points is reinserted in the reversed orientation
*the two types are paracentric and pericentric

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8
Q

what is paracentric inversion

A

within chromosome arms, does not include the centromere

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9
Q

what is a pericentric inversion

A

across a centromere

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10
Q

what is the role of chromosomal inversions in speciation

A
  1. appear to be associated with speciation. (also found in drosophila)
  2. reduced recombinatio between different inversion types particularly at break points.
  3. if recombination does occur creates unbalanced chromsomes
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11
Q

how can formation of unbalanced chromsoomes due to different inversions lead to divergence

A

if there is an important gene within the inversion that allows adaptation, could cause rapid divergence
** unlikely to cause divergence between forms by itself

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12
Q

what other common species have chromsome inversisions

A

humans and chimps

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13
Q

what can we use to reconstruct a phylogeny of Anopheles

A

fixed and polymorphic inversions.

*several regions fixed within and between species which can be used to reconstruct a phylogeny

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14
Q

describe the key X chromosome inversions which help reconstruct the anopheles phylogeny

A

Xbcd branches to An. arabiensis
Xag branches to An. hambiae and An. merus
X+ branches to An. guadriannalutus, An. bwambae and An. melas

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15
Q

describe the patterns of inversion of the left arm of chromosome two 2La

A

An. arabiensis has 2La as does An. merus
An gambiae has 2L+/a
An. quadriannalutus, An. bwambae and An. melus have the 2L+ form

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16
Q

Why did 2La inversion cause confusion

A

didnt seem to follow pattern expected from X inversion.
Would assume An. merus should be 2L+ not 2La
*assume 2L+ is ancestral

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17
Q

Where is the most divergence between An. gambiae and An. arabiensis found, what does this suggest
*what was used to obtain the data

A

divergence does not vary across autosomes but is higher in X-linked inversions that elsewhere on X or autosomes,
this suggests that this inversion (or a gene within it) is important in the reproductive isolation between the two species
*genomic analysis using SNPs

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18
Q

What did an Fst moving window of SNPs across gambiae and arabiensis 2La chromosome compare

A

An gambiae 2L+/2L+ vs araibiensis 2La/2La

An gambiae 2La/2La vs An arabiensis 2La/2La

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19
Q

what were the results of Fst moving window of SNPs comparing 2La of gambiae and arabiensis consistent with

A

either 2L+ arising before An. gambiae/ararbiensis split. and then being lost in arabiensis or genome wide introgression.
*therefore 2La is now considered the ancestral form

20
Q

what is an introgression

A

movement of a gene from one species into the gene pool of another by repeated backcrossing of an interspecific hybrid with one of its parent species.

21
Q

what support did subsequent analysis of whole genome of An. gambiae provide for 2La ancestral theory

A

suggested 2La/2L+ is an ancient inversion polymorphism (segregating in ancestors) that predates the initial diversification of entire complex but is maintained as polymorphic in gambiae and coluzzi
** therefore predating split between arabiensis and gambiae

22
Q

what does fixation of polymorphic inversions between species imply

A

significant in speciation

23
Q

what could look at polymorphisms maintained within species help wih

A

working out speciation process.

24
Q

what is the pattern of recombination between inversion types

A

generally get less recombination betwee inversion types.

with large inversions get recombination in the middle, double crossing over etc.

25
Q

do inversions automatically become a barrier to gene flow

A

no some inversions remain polymorphic in a species.

26
Q

how are polymorphic inversions usually maintained in populations

A

at HWE

27
Q

how can inversion frequencies be related to habitat

A

sometimes there is a gradient of inversion frequencies associated with adaptation to different habitats

28
Q

what does degree of divergence and linkage disequilibrium (non-random association of alleles at different loci) depend on

A

genes within inversions - must also be selection

29
Q

what has the 2La inversion in anopheles been associated with

A

tolerance to aridity

30
Q

what inversions occur on chromosome 2

A

numerous inversions can be seen on chromosome 2

however 2La is the largest

31
Q

what can frequency of 2La inversion be correlated with

A

positive correlation with more arid habitats.

*plotting according to habitat type; wet to dry transect clear increase in 2La frequency.

32
Q

what other inversions show an increase with aridity

A

2Lbc - however not as pronounced as 2La

33
Q

what was found to be a pattern in several inversions

A

that certain inversions always occured together in individuals and that certain combos never ocurred

34
Q

what happens if you group individuals based on corresponding inversions

A

found three formed

named Bamako, Savanna and Mopti.

35
Q

how were morpti, bamako and savanna further distinguished

A

ribosomal DNA marker found that distinguished Mopti from Bamako and Savanna
led to formation of M and S molecular forms
M: roughly corresponds to Mopti, savanna, forect and bissau
S: roughly corresponds to Bamako, forest and savanna.

36
Q

how are S and M form distributed

A

Only S is found in east africa

both forms occur sympatrically in west and central africa. but skewed depending on habitat and dryness.

37
Q

what did the 2010 analysis of the two forms show?

A

high genome wide divergence, particularly at genes associated with odorant receptors (associated with mae choice) and resistance to insecticides (RdI gene; resistant to dieldrin)

38
Q

what did the 2012 analysis of the 2 forms of wild caught mosqutios show

A

again show high divergence in certain parts of the genome
*places where two forms found together different parts of the genome has different levels of divergence. (some very high/overs less) - but gene flow did occur

39
Q

what was the 2012 analysis of the two forms in the wild

A

genome scan of divergence along chromosome arms between the two sympatric population samples of M and S at different locations,

40
Q

what was the 2013 analysis using SNPs of M and S

A

time series data collected for sympatric populations from a town. (selinkenyi)
*looked at diagnostic SNPs in X, 2L and 3L chromosome arms

41
Q

what did the 2013 time series of M and S SNPS show

A
  1. M and S seem to be mostly homozygous and seperate for the firsty 13 years of the study
  2. in 2006 suddenly get large no. of heterozygotes (M/S) continuing for several years afterwards in X, 2L and 3L
  3. after 4 years heterozygotes are much less common in X and 3L but still common in 2L.
    * found large section of 2L moved from S to M
42
Q

what was pattern in time series trend over the years found to be due to

A

section contained insecticide resistance gene
selection pressure was spo strong that the small amount of natural hybridisation enabled spread.
*assortative mating between M and S.

43
Q

are M and S are species?

A

usually look at hybridisation between the but quickly go back to segregating out and becomign quite divergent again across most of the genome

44
Q

what are the premating barriers to prevent hybridisation of M and S

A
  1. male mosquitos form swarms; however mixed swarms are rare as tend to occur in different places. *seem to occur less frequently than would be statistically expected.
  2. different habitat preference M prefers standing water (man-made irrigation areas), S more natural puddles
  3. Flight tone variation; may be related to mate choice (sound different to females)

**mixed swarms do occur with little or no mating discrimination in these.

45
Q

what are the post mating barriers of M and S

A

none
hybridise freely in the lab to form chimeric strains

*hybrids can be found in the wild (1-97% depending on location)

46
Q

in 2013 what was decided about M and S

A

they were two species
M = colluzii
S = gambiae
** however the debtate continues

Evo Bio (18 decks)

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