10/8/14 Brood Parasitic
Finches
Pin-tailed whydah
Vidua macroura
Estrildid Finch Host
Species
Common Waxbill
Estrilda astrild
by Justin Schuetz
1 10/8/14 Indigobirds parasitize
firefinches (and a few others)
Indigobird species…
² …are highly host-specific, most species parasitizing
a single estrildid finch host species
² …mimic the nestling mouth colors
and patterns of their respective hosts
² …are morphologically
distinct (in juvenile mouth
markings and adult male
morphology) but only
slightly differentiated in
neutral genetic markers
² …learn and mimic host songs, resulting in
assortative mating and providing a mechanism
for rapid sympatric diversification by host shift
2 10/8/14 3 10/8/14 V. camerunensis (black-bellied firefinch mimic)
V. camerunensis (African firefinch mimic)
V. raricola (goldbreast mimic)
Chatter
Complex non-mimicry
Mimicry
Balakrishnan & Sorenson 2007 Behav Ecol
host nest
black-bellied
firefinch
indigobird mimics blackbellied firefinch song
host nest
black-bellied
firefinch
mate
choice
indigobird imprinted on
black-bellied firefinch
host
choice
parasitism of novel
or alternate host
black-bellied
firefinch
African
firefinch
indigobird mimics
African firefinch song
or
indigobird imprinted
on African firefinch
*Tested in captive birds by Payne et al. 1998, 2000 Anim Behav
Figure from Edwards et al. 2005 PNAS
4 10/8/14 But…
v don’t the same mechanisms promoting
speciation also lead to hybridization?
v indigobirds from eggs laid in the nest of
an “alternate” host will imprint on the
“wrong” host and later hybridize with
individuals of the indigobird species
associated with that hosta
Association of mimicry song and
morphology in 494 male indigobirds*
mimicry song
N male indigobirds Vidua
cha.
fun.
pur.
cod.
L. senegala
306
0
0
0
L. rubricata
1
63
0
1
L. rhodopareia
2
0
84
0
H. niveoguttatus
0
0
0
37
total mismatches 4/494 = 0.8%
*localities in S-C Africa with two or more Vidua species
Payne et al. 1992 Proc. PAOC
5 10/8/14 The question:
How “good” are indigobird species?
v Are indigobirds early in the
process of evolving into
fully distinct and
reproductively isolated
species?
v Or, are they stuck in a
perpetual state of
incomplete speciation due
to imperfect isolating
mechanisms?
Higher nucleotide diversity in one species of firefinch
than in all 10 species of indigobirds combined
Red-billed Firefinches (n=10)
0.1
each point
represents one
locus
0.01
0.001
0.0001
0.00001
0.00001
0.0001
0.001
0.01
0.1
Indigobirds (10 species, n=72)
6 10/8/14 Phylogeny of
indigobird
mtDNA
haplotypes
V. codringtoni
V. purpurascens
V. funerea
V. chalybeata
V. nigeriae
V. maryae
V. wilsoni
V. raricola
V. larvaticola
V. camerunensis
Network of
West African
haplotypes:
Cameroon
& Nigeria
ΦST = 0.41
p < 0.00001
microsatellites
(11 loci)
FST = 0.017
p < 0.0001
Sorenson et al. 2003 Nature
7 10/8/14 Ancestral polymorphism
Species 1
S1
Species 2
S2
Time
Lineage sorting
2Ne-4Ne generations
Ancestral population
Indigobirds: gene flow plus lineage sorting
Species 1
S1
Species 2
S2
Time
Ancestral population
How to separate historical effects
from current dynamics??
8 10/8/14 IM - Isolation
with Migration
v model of population
divergence
v Nielsen & Wakeley 2001
Genetics
v Hey 2005 PLoS Biology
Testing hypotheses…
v what is the likelihood L (=probability) of
the observed data?
L = ∑ Pr{D | G, µ} Pr{G | α }
G
v L = the sum across all possible genealogies (G)
€
of the probability of the data given the
genealogy and a model of the mutation process
(µ) times the probability of the genealogy given
a set of parameters (α) that characterize the
population process
9 10/8/14 In practice…
v for a sample of k alleles, draw random
coalescence times according to the
exponential distribution
v estimate the likelihood (probability) of
observing the actual data on that
genealogy
v change a parameter, generate a new
genealogy, calculate likelihood, repeat
millions of times
Markov Chain Monte Carlo methods
10 10/8/14 IM - Isolation
with Migration
v model of population
divergence
v Nielsen & Wakeley 2001
Genetics
v Hey 2005 PLoS Biology
Phylogeny of
indigobird
mtDNA
haplotypes
V. codringtoni
V. purpurascens
V. funerea
V. chalybeata
V. nigeriae
V. maryae
V. wilsoni
V. raricola
V. larvaticola
V. camerunensis
11 10/8/14 V. chalybeata (n = 11)
V. camerunensis (n = 11)
V. larvaticola (n = 8)
V. chalybeata (n = 4)
V. camerunensis (n = 3)
V. wilsoni (n = 3)
V. raricola (n = 3)
V. maryae (n = 3)
V. nigeriae (n = 3)
V. larvaticola (n = 3)
• 14 nuclear sequence loci
(~300 bp each)
• 3 HapSTR loci
(~250 bp + STR)
V. chalybeata (n = 5)
V. codringtoni (n = 5)
V. funerea (n = 5)
V. purpurascens (n = 5)
haplotype diversity at 5 nuclear loci in 10 species
12 10/8/14 Posterior Probability
IM analyses using 9 nuclear sequence loci
average = 64K years
0.1
0
0
200
400
600
800
1000
Thousands of Years Before Present
IM analyses using 9 nuclear sequence loci
Posterior Probability
0.02
average = 1.3%
0.01
0
0
0.1
0.2
0.3
0.4
0.5
"Splitting Parameter" (s)
13 10/8/14 IM analyses using 9 nuclear sequence loci
Posterior Probability
Posterior Probability
0.002
0.001
0
0.001
0
0
2
4
6
8
Migration to West (m2)
10
0
2
4
6
8
10
Migration to South (m1)
Conclusions 1
v Indigobirds colonized southern
Africa ~105 years ago and
subsequently evolved into four
distinct species!
v Coalescent analyses indicate a
small founding population for
southern Africa followed by
substantial expansion
14 10/8/14 Network of indigobird mtDNA haplotypes:
Malawi, Zambia, and Zimbabwe
Sorenson et al. 2003 Nature
Conclusions 2
v Relatively greater genetic
differentiation among
indigobird species in the
ancestral region of West
Africa suggests that
indigobird species may be
slowly diverging from each
other and evolving into truly
independent evolutionary
lineages
15