evolution of morphological diversity in Heliconius Flashcards
heliconius butterfly properties
larvae eat cyanide containing passion vines
sequester it to become toxic
adults remain toxic
patterned brightly as warning colouration
heliconius phylogeny
-whole divesity originated from common ancestor w 2 major branches
-most species genetically polymorphic (not polyphenism) - various pattern forms are due to difference in genetics
-same basic form of pattern occurs again and againin different heliconius species
variation is geographic - same pattern found in different species in the same region of S. America
different patterns in same species across region borders
reason for geographical districutions of heliconius patterns
advantage to looking the same as the other butterflies in that region
erato in same areas look like melpomene in same areas e.g.
because naive predators need to sample heliconius individuals before associating bad taste with pattern
more of same pattern in same area = less likely for individual to be sampled
so advantageous to look like others in area
MULLERIAN MIMICRY
hence different species having same pattern in same area
but same species in different areas look different
testing advantage of mullerian mimicry of other butterflies in same area
H. melpomene
H. erato
one side of area border both species dennis ray
other side of border - both postman pattern
moved individuals
different location on same side (control)
different location on same side
individuals moved to same side did a lot better than ones of same species moves to other side
benifitted from learning of predators on same side to avoid their pattern
didnt get sampled/injured as much
genetic control of patterning across H species?
found various genes
different versions of these determine phenotype patterning
number of unlinked loci separated in chromosome or on different ones
different combinations of which (alleles?) were producing different wing patterns
matching seen in different species in same area confers protection
hybridisation of different patterns in same species effect
hybridise postman and dennis ray H. melpomene
genes controlling patterning are unlinked
so messed up mix of alleles in progeny
end up with messed up pattern
no protection in either region as pattern matches neither
H. Cydno morphs
black/white or balck/yellow
controlled by one gene
coexist w diff species
H. eleuchia in Cydno yellow morph area - resembles yellow cydno
H. sapho and white cydno same area resemble - other side of border to yellow
white did much better than yellow when moved in sapho region
other way round for moving into eleuchia region
sapho and eleuchia are much more abundant than cydno in either region
in eleuchia site
released yellow do better than white at low density of released
-however if you release 4x higher density of white and yellow cydno:
not mcuh difference
so many more butterflies that dont match others so predators learn much quicker to avoid them - much less detrimental effect on non matchers
selection against hybridisation of border “races”
two same species individuals of different pattern at border mate
get hybrid offspring that dont match anyone else
more likely to be predated
waste of reproductive resources
expect pattern races to preferentially not mate with each other to develop
mate preference tests for melpomene
look at mate preference in males for different forms of females
postman melpomene much more likely to mate similarly appearing females - no interest in other morphs with different wing patterns
cydno same result - white cydno went for white cydno - ignored others
however - banded melpomene from part far away from where cydno and rosina melpomene - had much less preference (none?? idk)
strong mating preference evolved in region where many other morphs were nearby
strong preference males had same preference for dead females and even paper models
so appearance of butterflies are MOST important cue (not pheromones, behaviour…)
Heliconius heurippa - hybridisation?
purple region relatively small
find distinctive heliconius eurippa species
red and yellow band
other butterflies in area (heurippa region within red melpomene region and right next to yellow cydno region)
heurippa looks like simply putting together melpomene and cydno patterns
but is separate species (closely related but separate) by classical identification
molecular analysis shows that it shares a lot of molecular variation with two other species (particularly cydno)
heurippa arose by hybridisation between melpomene and cydno???
could this hybridisation give this pattern form
replication of heurippa pattern morph by hybridisation of cydno and melpomene morphs
bred together cydno and melpomene
found that male offspring of F1 were viable and fertile
BUT females were not (viable but sterile)
didnt resemble heurippa
BUT backcrossed them with cydno for many generations - gave many differently appearing butterfly wing patterns
HOWEVER -produced some offspring that looked like the wild Heurippa
- were also true breeding - meaning that the allelic combination that gives this pattern is likely homozygous, and interbreeding these hybrids would maintain the heurippa like pattern
so -captured wild heurippa males
test mating preference like last one
took heurippa males and challenged them with heurippa, melpomene, cydno, OR heurippa that had been blacked out (had either red or yellow bar vlacked out)
heurippa males preferred only the heurippa females with the normal double bar pattern (not even the blacked out ones as behaviour is not really main cue - own wing pattern preference is main cue)
this may have taken heurippa 1000s of years in the wild to evolve this mating preference
do the experimental hybridisation generated Heurippa like morphs have preference?
novel heurippa hybrid preferences?
just generated from hybridisation
do pattern preferences need to develop over long time ??
heurippa males generated already had a preference for own wing form compared to other wing forms you can challenge them with
- if this novel genotype WAS actually generated in wild by these hybridisation
due to the fact it is true breeding pattern - this instantaneous mating preference will have kept the pattern allowing novel heurippa species to diverge - how are the patterns and prefernces so intrinsically linkes?????
refugia theory of heliconius pattern race regions
in central and southern america
with advance of glaciers from north
whole region became cooler and drier
could’ve had conseqeuences for butterflies inhabiting this region
if they were not so diverse back then
diversity may have arose in glecial refugia
most of land became uninhabitable to butterflies and they were restricted to small isolated restricted habitable regions - refugia
if kept that way for long while - refugia populations would diverge from each other
small pops - different mutations - high probability in small loction that they are fixed in pop - different selection pressures in different refugia
if you have different speceis (melpomene, erato e.g.) in same refugia - even if they look different, they will convergeb on same pattern (resembling others = good)
conditions get better
populations spread out
boundaries form between pattern morphs form
predation selection, and reproductive preference isolation keeps that border distinct
happens all over gives rise to patchwork of different colour races
though not a lot of direct evidence
theory sounds nice but trying to locate what it was like in past and where refugia were is hard
refugia allopatric pattern development example problems
if allopatric like refugia example: would expect:
different populations do have genetic differences that match the geographical differences (populations in same areas have same differences to others)
due to allopatric divergence
so would expect phylogenies in pattern races in different species in different areas would line up - as they evolved allopatrically together
results - counter to refugia hypithesis
- pattern races are not real races - are not genetically distinct from otehr pattern races within a species
if different patterns cam from different refugia would expect distinct genetically
different pattern races very genetically similar to nearby of same species
phylogeny reflects geographical difference much more than pattern differences
i.e. different same species patterns near nearby across border - similar
whereas same pattern same species across other side of area is more different
some species would have radiated out through regions occupied by ohter butterflies - and would change pattern to match those in that area
difference would be much younger than refugia differences too
so don’t have exact answer for how they diverged
breeding experiments to identify genes that control patterning on heliconius
D/R melpomene locus - controls red patterning elements
D in erato - controls red patterning elements
are these actually homologous genes doing the similat jobs in different species
linkage mapping - cross experiments and looking at recombination freuquency with specific markers
can show whether particular gene is long way from marker (gets separated)
or if it is at or very near same site (won’t recombine away in reasonable timescale)
D/R and D loci correspond very closely in location on its chromosome
managed to approximate location on chromosome down to stretch of DNA
small portion of whole genome
but still long stretch of DNA that contains many genes
postman - red in mid wing
dennis ray - not red in mid wing
took pupal stage wings and cut out mid area of wings
extracted RNA
difference in gene expression in that tissue
RNA from optix gene region of genome present in one erato pattern morph and not in the other
fluorescentyl tagged the optix gene with reporter
get OPTIX in midwing of postman form forewing - the red part
in dennis ray form - it is in closer to inside of wing and hindwing stripes
the patterning differnce is REGULATORY
not difference in protien
differences in enhancers not protein coding sequence
coding region sequence has no significant difference between postman optix allele and dennis ray optix allele
regulatory difference
optix expressed in different locations
optix gene action
OPTIX is a TF - where OPTIX is expressed - red pigment later on will be produced
the optix gene of that particular species is expressed where red will be
causal relationship - turning on optix → red pigment in area
shows in hybrids too
gene editing - inactivated optix by mutating coding region → no red where there should be - proof of causal relationship
differences in optix enhancers - different expression patterns of optix in wings
→ different pattern in different pattern morphs
note// optic role in colour patterning is restrictes only to HELICONIUS butterflies
optix TF has other roles in different places - optix has role in drosophila eye development
in heliconius optix has been recruited to additional eing patterning role
(similar to crystallins in eye development)
wrong theory for dennis ray pattern area spread
(The wrong part is the butterflies themselves spreading out - butterfly phylogeny showing geographical closeness is more important for relation than pattern
orange region - occupied by very similar pattern forms - show slight variations in dennis ray form
yellow - same situation but w/ postman
grey - same w simple banded form
big contiguous area of D ray in middle
large disjunct regions around periphery that express other pattern
suggestion - orange regions contain butterflies closely related to each ohter that spread to form orange region
this didnt happen - molecular phylogeny - great distance butterflies of one species less related than closer ones - nearer ones closer even if different pattern
looking at specifically Optic gene phylogeny
looked specifically at optix sequence phylogeny
sequence diversity - optix genes more similar to each other - if compare dennis ray populations than if comparing banded or postman
suggests that dennis ray version of optix originated much more recently as it is still much more similar
so dennis ray patterns have v close optix to each other
however if you look at neutral genes in rest of genome
in species - neutral gene similarity much more between proximal individuals than further same pattern
so dennis ray on opposite sides of region
- similar optix
- more different neutral genes (where geography is more important)
How did erato optix gene spread out to make D ray region?
in erato:
dennis ray optix gene newer origin
spread out by gene flow
selective advantage to hybrid progeny to having dennis ray phenotype
so spread out further through gene flow
dennis ray optix was “superimposed” onto other pattern phenotypes
D ray optix gene newer origin
reason why butterflies of similar pattern on opposite sides of D ray region have:
-more different neutral genes
-more similar Optix genes
denis ray Optix control of patterning
some species pattern (of melpomene and timareta) morphs are not Dennis ray despite being in dennis ray area
top one (melpomene example) has one part of dennis ray - has forewing red pattern - but not rays on hindwing just proximal part
bottom (H timareta) has hindwing rays but not dennnis front part
so aspects of the dennis ray pattern can be separated?
due to enhancer structures in dennis ray optix
dennis ray enhancer stuff
looked at what molecular marker differences they have vs what red patterning they have
association for having particular differences at left enhancer and having particular “dennis” components of the patter
association for having particular differences at right enhancer and having particular “ray” components of the patter
so these separate parts of genome control whether individual will have dennis and ray components separately
both function by regulating optix coding region next to them
these enhancers are much more similar between similar patterns in different related species than expected
enhancer diversity may have moved through these species by “enhancer flow” (like the gene floe of dennis ray Optix) (hybrid between two close species - introduces dennis ray in that hybrid from dennis ray parent species, dennis ray patterning confers some advantage in progeny, these dennis and ray enhancers are retained through introgression - hybrid backcrossing with non DR parent species except selected to retain D and R enhancers - why they are similar between diff species)
basically through introgression of these dennis and ray regulatory elements in hybrids of these species as they conferred some advantage
this introgression can happen as they are close species so can interbreed
dennis and ray enhancer phylogenies
separate phylogenies for these separate enhancers
dennis enhancer region of optix - dennis forms of melpomene, timareta - all grouped with H elevatus (their enhancers are similar)
ray enhancer refion of optix phylogeny:
melpomene and timareta both group with elevatus
dennis and ray enhancers have separate origins in different species as ray forms have more similar ray enhancers - same for dennis
more recent research in heliconius patterning stuff
dont think too important
- other enhancer regions interact w dennin=s and ray regions
- enhancer function - D mutants not expressing - no red
- very similar regulatory enhancers in Erato to Melpomene even though they are very dissimilar in ways where hybrids cant form (genetics, mating…) - so no introgression couldve taken place to give them that similarity
these species diverged 12mya - before the dennis/ray enhancers arose
may be down to independent but similar changes to ancient enhancers - what TFs are the dennis and ray enhancers binding - theyre being activated by cues in certain spatial regions but not others - positional cues on wing binding dennis and ray
-potentially could be by other genes linked to wing patterning (the ones found in the earlier stuff) that are binding to these enhancers
WNT-A - WNT signalling has roles all over development
in larva - wing disc stage
in metamorphosis - pupal wing on pupal surface - pigmented in adult
red pigment on banded wing
go ealier - optic expression on that part
earlier to larval disc - WNT - A completely absent from this region - proven to be causal
earliest signal for this wing patterning
so optix repressed by WNT-A signal outside region
allowed on inside region so get red
WNT patterning in heliconius
WNT-A pattern distinguishes the Optix expression borders in melpomene
in erato - WNT-A expressed in proximal part to pattern proximal border but not on distal part of wing so something else does it - similarities and differences in species - KO of WNT-A in erato - still get distal border of red
WNT-A and these WNT-A enhancers pattern in ither distant butterfly species - pattern different things though
how could different pattern phenotypes have arisen?
how particular phenotypes may have arisen
like the heurippa example - hybridisation
or dennis ray phenotype spreading out
to establish and maintain new phenotype:
establish - relaxed predation needed
enough individuals can appear for predators to learn to avoid that pattern
spread - needs to confer some other advantage to be that phenotype (e.g. fot that dennis ray version of optix to gene flow across amazon)
- could actually be by adopting phenotype - those butterflies get protection as they are adopting new phenotype that is already present in high frequency in that region (e.g. melpomene dennis ray phenotype spread out later - mimicking other dennis ray that had already spread)
- though this mimicking one doesn’t really work with ^^
if it is really a novel pattern - what underpinned its ability to spread
could be more visible - banded forms found in brighter drier regions, dennis ray forms in darker wetter
so different forms have different visibility - better visibility = easier learning to avoid
however there are exceptions that disrupt this
could be many possible aspects
