Species concept Flashcards
how can species mirror each other?
via convergent evolution
adaptive radiation
- what is it?
organisms diversify rapidly from an ancestral species into a multitude of new forms
adaptive radiation
-example
fish in Lake Malawi + Lake Victoria both have different species occupying different niches
e.g. snail crusher, bottom feeder etc
People have struggled w/ defining species for many yr
-> but which is the most common?
biological species concept
Mayr’s biological species concept
groups of interbreeding populations which reproductively isolated from other such groups
Barriers to recombination
Adaptive barriers
= selection against hybrid genotypes
Mechanistic barriers
= factors promoting DNA specificity
(chromosomal incompatibility)
Ecological barriers
= consequence of physical separation of populations
Mechanistic barriers
- example
Horse + donkey = mule
- sterile hybrid
= pre-zygotic barrier
Ecological barriers
- example
Ring species
- 2 gull populations which don’t interbreed are living in the same region and connected by a geographic ring of populations that can interbreed
Fuzzy species
- Paper by?
- suggests?
Hanage et al (2005)
Bacteria don’t have discrete species clusters
MLST
- what is it?
Multilocus sequence typing
- characterises isolates of microbe species
using DNA sequences of internal fragments of multiple housekeeping genes
MLST
- of Campylobacter
sequenced 7 genes to understands variation in different strains
- revealed interspecies hybrids
-> some strains had genes attributable to C. jejuni + C.coli
= HGT
introgression
transfer of genetic information from 1 species to another
as a result of hybridisation between them + repeated backcrossing
de-speciation
if gene flow between 2 species maintained at a high rate
-> 2 species may come together
hybridisation has implications for…?
species concepts
adaptive radiation
hybridisation has implications for adaptive radiation
- example
Darwin’s finches on Galapagos
- adaptive radiation to fill the niches (food source)
if ecology changed
- > great increases in the no. of intermediate birds
- > enviro would then favour them instead
introgression in Campylobacter
- associated with?
agriculture
- consistent with scenario where expansion into a shared agricultural niche promotes de-speciation
Agricultural C.coli have hybrid ancestry
use a pair-wise comparison between genes of different speciess:
some genes may never have diversified
= conserved
may be periods of independent evolution where 2 species diversified
-> then HGT imported genes back into these hybrid strains from other species
Introgression occurs across a great genetic distance
- amnio acid differences per gene
C. jejuni to C. coli
= 38
Within C.jejuni = 5.5
Human to chimp = 2.9
Introgression might aid adaptation to novel enviros BUT might be disruptive
Sex beneficial
- generates genetic diversity
- > natural selection for the well adapted
Sex is a barrier
- recombination breaks gene networks
- > less well adapted
Introgression might aid adaptation to novel enviros
- example
Rieseberg et al (2003)
Sunflower hybrid (intermediate species)
- did very well
shuffling of genomes created rapid innovation
–> successful at colonising new niche (novel habitat)
chromosome painting
- what is it?
describes the direct visualisation using in situ hybridisation of specific chromosomes in metaphase + interphase nuclei
chromosome painting
- purpose
quantities gene flow
identifies regions of different ancestry in the genome
identifying donor clonal complexes
- how?
- example
look at ancestors of a hybrid + see which base can from which ancestor
donor: C. jejuni
recipient: C. coli
most introgression came from chicken associated Campylobacter
epistasis
co-adaptation
interaction of genes where the phenotype of one depends on the other
modelling co-adaptation
epistatic sites change more frequently than avg
mutations that are fixed just occur on 1 branch
BUT epistatic sites are found together on multiple branches
