BG25 Flashcards
where in the world can mimicry be seen
africa
asia
south america
Contempories who discovered mimcry
Henry Bates - credited with dicovery mimcry in amazon
Alfred wallace - found P. polytes female mimics in indonesia, noted differnet forms: cyrus, stickus, romulus
Papilo dardanus
roland trimen SA
- ‘the most interesting butterfly int he world’
highly polymorphic, diff patterns in males and females
- has atleast 13 forms mimicking different toxic butterflies in different regions
- difference between morphs also controlled by a super gene but not dsx
- suggests mimicry evolved independently in genus atleast twice.
evolution of distastefulness and colouration in butterflies
- plants evovle distasteful chemicals (alkaloid, cyanogenic glycosides) to prevent being eaten, some caterpillars store the compounds which are maintained in butterfly
- butterflies have evovled bright colour to warn birds they are distasetful
= aposematic colouration - birds have learnt not to prey on certain morphs: mimicry provides protection.
two kinds of mimcry
Batesian: non-toxic mimis toxic = free rider
mullarian: toxic mimics toxic - establishes toxic morph - helps both species.
heliconus speciation and species
complex mimicry
- 40 spp northern South america, but each species has up to40 diff geographic forms
- speciation occured rapidly 10mya probs due to shift in techtonic plate
heliconus adaptations
- long lvied, low fecundity, coop breeding.
- large eyes and stilt legs - allow egg laying in host passion flower plants
- long wings = powerful flight
- highly intelligent - avoid scientists nets
- larval resistance to alkaloids, cyanogenic glycosides from hsot plant which they store
- spectacular colouration
- series of geographical races mimicking butterflies belonging to genus melinea
heliconus mimcry ring
predicted that butterflies would converge on one same colour
but heliconus butterflies are diverse and form mimcy rings within geographical areas
- adaptive pressure to be similar to local morph to avoid predation
evolution of wing colour in heliconus
- genetic study
clearly complex genetic basis as many distinct features involved
- but can do simple mendalian genetics via crosses
*studied genetics of H. numata, H. melpomene and H. erato
= morphs differ within degree red pigment, black background and white spots.
genetics of H. melpomene colouration
- N-yb-sb supergene: controls white element
- B locus: controls red
- Ac locus: controls yellow patch on forewing
genetics of H. erato colouration
Cr locus: controls white element
D locus: controls red element
genetics of H. numata colouration
Locus P supergene: controls everything, 9 known alelles.
basis for homology of colouration in heliconus
Can show different chromosomes in different species are homologous in particular regions by finding markers in diff species.
and show loci map to comparable position in different species
homology for colouration of different species of heliconus
N-YB-SB locus is homologous to P locus and Cr locus
all homologous to carbonaria locus
White element P locus
H. numata
cloned with aid of SNP markers
- found groups with high association
- area = an inversion, so has low recombination within area.
- 8 genes located in 400kb but as no recombination hard to know what is controlling the white element.
D locus H. erato
crossing different morphs of h. erato using snps shows D locus maps to a particular region
indep of white locu
- found one gene optix a homeobox TF homologous to D locus
Optix of H. erato
- is sequence in different morph - sequence is identical
- optix expression in imaginal disc differs and is correlated with extent of red pigmentation
- causal mutation is a cis acting reg element
optix ancestral function
in V. cardui unrelated butterfly optix appears to be expressed in association with scales
- potentially this is the ancestral function and it has been co-opted for red pigmentation
where do mimics get coloru
independent evo of introgression from hybridisation
- distinguish between two possibilites can use ABBA, BABA test.
ABBA BABA assumptions
refers to distribution of SNP aleles in pigmentationa rea
- 4 closely related species, 3 closely related and 1 otugroup
- aleles are polymorphic in related species but outgroup is fixed in one state (A)
Assumption for independent evolution ABBA BABA
- if alelle B arose indep we should sometimes get ABBA, or BABA pattern
- if this is true we should expect that the freq of SNPs that show ABBA pattern = the frequency of SNPs that show the BABA pattern - as evolved independently.
assumption for introgression ABBA BABA
more SNPS with either the ABBA or BABA pattern it tells us the morphs share a chunk of DNA more closely related to each other than rest of genome.
results from abba baba on heliconus
most the genome shows ABBA- BABA type polymorphism which demonstrates indep evo (no introgression)
- however around the bd locu ABBA /=/ BABA.
- strong inequality around C18 = introgression event
- mirrored in phylogenies, regions flanking bd show species phylogeny, bd phylogeny shows differnet species more closely related.
Wallaces mimcry
only female morphs mimic local unrelated butterflies across asia
polytes mimics
*batesian mimicry
o P. polytes polytes morph mimics Pachlipota aristolochiae
o P. polytes theseus morph mimics P. aristolochiae (the black form).
o P. polytes romulus morph mimic P. aristlochiae (red form).
o P. polytes cyrus morph in non-mimetic, females resemble males.
Female mimcry morph locus of polytes
- fine mapping using SNPs showed female mimicry morph locus is one gene.
- could be predicted as mimcry would only be affective when all morphological aspects are linked
female morph mimicry gene homolog
homologous to double sex gene in drosophila
which is alternatively spliced
males: 1,2,3,5,6 exons
females: 1,2,3,4 exons
- results in functionally different proteins.
- dsx = zinc finger tf and can control a whole range of downstream differences between sexes.
differences between dsx and butterlfy homolog
butterfly is more complicated and comes in several different isoforms - not just two seen in drosophila
- some isoforms are only expressed in mimic females tells us dsx has been co-opted for mimcry gene with the evo of new isoforms
mutations responsible for variation among polytes morphs
sequence dsx in various morths
- two of the exons especially exon 1 are rich in NS subs fixed between mimetic and non-mimetic butterflies
= differences in coding seqs cause differences in morphs
dsx structure
held together by an inversion so there is little recombination within the gen
= super gene
therefore different substiutions that occur in any given seq can control a whole variety of downstream aspects of morphology being dissociated
Scenario for evo of dsx in P. polytes
- isoform of ancestral sex determination gene evolves that is only expressed in females and controls subtle differences in pigmentation
- mutation in coding region causs females to mimic locals
- additioanl mutations in same chromosomes further increase freq and refine
- inversion arises preventing dissociation - linkage, preventing recombination between distinct morph
- mimics other species that get different dsx mutations in diff locations
