doi:10.1111/j.1420-9101.2005.00968.x
Patterns of diversification of Afrotropical Otiteselline fig wasps:
phylogenetic study reveals a double radiation across host figs and
conservatism of host association
E. JOUSSELIN,* S. VAN NOORT,
J.-Y. RASPLUSà & J. M. GREEFF*
*Department of Genetics, University of Pretoria, Pretoria, South Africa
Natural History Division, South African Museum, Iziko Museums of Cape Town, Cape Town, South Africa
àInstitut National de la Recherche Agronomique, Centre de Biologie et de Gestion des Populations, Campus International de Baillarguet, Montferrier sur Lez, France
Keywords:
Abstract
coevolution;
cospeciation;
Ficus;
host-use;
oviposition;
phylogeny;
plant/insect interaction;
radiation.
We studied the phylogenetic relationships of Otiteselline fig wasps associated
with Ficus in the Afrotropical region using rDNA sequences. African fig species
usually host two species of Otiteselline fig wasps. Phylogenetic analyses reveal
that this pattern of association results from the radiation of two clades of wasps
superimposed on the fig system. Within each clade, wasp species generally
cluster according to their host classification. The phylogenies of the two clades
are also generally more congruent than expected by chance. Together these
results suggest that Otiteselline wasp speciation is largely constrained by the
diversification of their hosts. Finally, we show a difference in ovipositor length
between the two Otiteselline species coexisting in the same Ficus species, which
probably corresponds to ecological differences. The diversification of ecological
niches within the fig is probably, with cospeciation, one of the key factors
explaining the diversification and maintenance of species of parasites of the
fig/pollinator system.
Introduction
The processes that govern the evolution of host-plant use
by phytophagous insects have been much debated and
are the subject of many text books and review papers
(e.g. Mitter & Farrell, 1991; Mitter et al., 1991; Strauss &
Zangler, 2002). The 700 plus species of figs (Ficus,
Moraceae) and the wasps that reproduce in their
inflorescence represent a very interesting system on
which to study the diversification of insects on hostplants. Each fig species hosts a very diverse assemblage of
wasp species, belonging to the superfamily Chalcidoidea
(Bouček, 1993). This assemblage creates a well-defined
community and offers a unique opportunity to compare
the evolution of host-plant use and modes of speciation
across several lineages of wasps that share a limited
resource. The inflorescence of Ficus, known as a fig or
Correspondence: Emmanuelle Jousselin, Institut National de la Recherche
Agronomique, Centre de Biologie et de Gestion des Populations, Campus
International de Baillarguet, CS-30 016, 34 988 Montferrier sur Lez,
France.
Tel.: +33-4-99623326; fax: +27-12-3625327;
e-mail: ejousselin@yahoo.com
syconium, consists of an enclosed receptacle lined by
uniovulate female flowers (Berg, 1989). These flowers
are used by the wasps as egg laying sites. Some of these
wasps are pollen vectors. They are attracted by the
volatiles emitted by receptive figs (Barker, 1985; van
Noort et al., 1989; Ware et al., 1993) and enter the fig
cavity via the ostiole (a slit formed by bracts situated at
the apex of the fig). Their larvae complete their development in the galled flowers. Pollination seems to be
restricted to the wasps belonging to the Agaonidae (sensu
Rasplus et al., 1998; but see Jousselin et al., 2001). The
biology of nonpollinating (parasitizing) fig wasps is less
well known: they can be gallers (like the pollinators), but
also parasitoids (Bronstein, 1991; West et al., 1996;
Kerdelhué et al., 2000). They either enters into the fig
cavity like the pollinators or oviposit in the flowers
through the fig wall. The stage of the fig development at
which they lay their eggs is also very variable (Kerdelhué
et al., 2000).
Recently, the evolution of the mutualistic association
between figs and their pollinators has received much
attention (Herre et al., 1996; Kerdelhué et al., 1999;
Machado et al., 2001; Weiblen, 2001; Weiblen & Bush,
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E. JOUSSELIN ET AL.
2002; Molbo et al., 2003; Jousselin et al., 2003; Jackson,
2004). The relationship is generally thought to be
species-specific: one species of pollinating wasp is associated with one species of fig (Ramirez, 1970; Wiebes,
1982). However, exceptions to this ‘one to one rule’ are
discovered as more thorough taxonomical and molecular
studies are conducted (Michaloud et al., 1985; Rasplus,
1994; Kerdelhué et al., 1999; Lopez-Vaamonde et al.,
2002; Molbo et al., 2003; Cook & Rasplus, 2003). The
mapping of the evolution of host association on the
phylogenies of both partners at a broad taxonomical level
is consistent with a global pattern of cocladogenesis
(Herre et al., 1996; Weiblen, 2000; Machado et al., 2001;
Weiblen, 2001; Jousselin et al., 2003) and the one study
that uses statistical tests shows that the pollinator
phylogeny and the fig phylogeny are more congruent
than expected by chance (Weiblen & Bush, 2002) but the
test is limited to 19 species among the 180 species in the
Ficus subgenus Sycomorus. While the relationship between
figs and their pollinators has been the subject of many
studies, little is known about the patterns of diversification of other lineages of wasps that mostly act as parasites
of the interaction. Taxonomic studies suggest a close fit
between parasitic wasp classification and their host fig
classification and a ‘one-to-one’ rule similar to the
situation observed in the pollinator/fig association is
generally assumed (Berg & Wiebes, 1992). However, fig
wasp taxonomy has been influenced by the classification
of the host figs, often having been established a posteriori.
Fig wasps collected from different fig tree species are
assumed to be species-specific; therefore wasps collected
from different taxonomical groups of figs are automatically classified into different taxa. The interaction between
figs and nonpollinating fig wasps could be a lot less
specific than is generally assumed and the diversification
of nonpollinating wasps could be independent of their
host speciation. Chemical and physical barriers precluding host shift in nonpollinating fig wasps are supposedly
not as tight as in the pollinating wasps (Lopez-Vaamonde
et al., 2001; Weiblen & Bush, 2002, Jackson, 2004). For
example, most nonpollinating wasps do not enter the fig
cavity; they do not necessarily lay their eggs at fig
receptivity and thus either cannot or need not rely on the
volatiles emitted by their host fig to attract the pollinators
to find their host. Only three studies so far have explored
the phylogenetic relationships of selected groups of
nonpollinating fig wasps to look at the evolution of host
association and patterns of diversification (Machado
et al., 1996; Lopez-Vaamonde et al., 2001; Weiblen &
Bush, 2002). Two studies showed a nonrandom association between parasitic fig wasps of the genera Idarnes
(Machado et al., 1996) and Sycoscapter (Lopez-Vaamonde
et al., 2001) and the associated pollinators, suggesting
some cospeciation between these wasps and their host
figs. Weiblen & Bush’s study (2002) indicates that the
nonpollinating wasp phylogeny of the genus Apocryptophagus is far from congruent with their host fig phylo-
geny (figs of the Sycomorus subgenus) and suggests that
nonpollinating wasps often speciate on their host fig,
probably through the occupation of different ecological
niches.
In this paper, we investigate the diversification and the
patterns of host-use of wasps belonging to the Otitesellinae genera Otitesella Westwood and Philosycus Wiebes
(Pteromalidae) in the afrotropical region. They lay their
eggs into fig flowers by inserting their ovipositor through
the fig wall from the outside of the fig. This process takes
place around fig receptivity, roughly at the same time as
pollinating wasps enter the fig cavity. Once the eggs have
been deposited, the flowers are transformed into galls in
which the wasp larvae develop. Otitesella are restricted to
the old world tropics and have been subdivided into two
species groups the Otitesella africana group and the
Otitesella digitata group (Wiebes, 1969), corresponding to
the two sections of Ficus from which they have been
recorded. Species of the O. africana group have been
reared from figs of section Galoglychia (occurring in
Africa) while species of the O. digitata group have been
recorded from section Urostigma (found in the IndoMalayan region and Africa) (van Noort & Rasplus, 1997).
Species in the genus Philosycus are also associated with fig
species in section Galoglychia. The characters that differentiate Philosycus from Otitesella are only based on male
morphology and the Philosycus clade may not warrant
generic distinction (Van Noort & Rasplus, 1997).
By establishing a molecular phylogeny, this study will
first try to solve the taxonomic problems in Otiteselline.
Second, the use of molecular markers will help to detect
cases of host specificity breakdowns. Description of
Otitesella and Philosycus species are still scarce and female
morphology is very conservative which makes it difficult
to assess whether different fig species host the same wasp
species. The host figs of Otiteselline are often sympatric
and we could expect some wasp species to move between
host species. Then, by mapping host association onto the
wasp phylogeny, we determine whether host association
is evolutionarily conserved within Otiteselline fig wasps,
i.e. whether related wasps are associated with related fig
species. Finally, studying the patterns of diversification of
these wasps is also particularly interesting as extensive
collections within Africa revealed that two morphospecies of otiteselline could occur per fig species (wasps can
be classified into morphogroups that we termed ‘uluzi’
and ‘sesqui’, see material and methods and Table S1). This
pattern of association indicates that either the two groups
form two clades that have separated and then diversified
across all the African figs or that each pair of species
occurring on one host has originated through independent duplication events. The latter would imply that the
same morphological divergence (long/short ovipositor
valves) has evolved repeatedly. The main contribution of
our phylogenetic reconstruction will be to test which of
these two scenarios is the most likely. We also investigate
more thoroughly morphological divergence between
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Diversification of Otiteselline fig wasps
four pairs of Otiteselline wasp species associated with the
same fig species in order to understand how two
congeneric species coexist in the same fig.
Materials and methods
Sampled species
Sampled fig wasps and their collection details are listed in
Table S2. We sampled Otitesella wasps from 22 of the 98
recognized species and subspecies of Galoglychia figs (75
fig species have been described in this section) scattered
in the different subsections of the classification and from
two species of Urostigma figs. When possible we tried to
include the two morphospecies of Otitesella for each fig
species of the Galoglychia section sampled. The two
Otitesella species associated with Ficus burtt-davyi, Otitesella
uluzi and Otitesella sesquianellata (van Noort & Compton,
1988) have been described; they are readily distinguishable based on morphology of the wings, ovipositor valves
and clypeal margin in the females and mandibles in the
males. When two Otitesella morphospecies were found in
one host, one species shared characters with O. uluzi,
whereas the other shared characters with O. sesquianellata. Based on morphology, we therefore classified
Otitesella wasps as belonging to the ‘uluzi species-group’
or the ‘sesqui species-group’. Ficus ingens (section Urostigma) also hosts two species of Otitesella: Otitesella
longicauda and Otitesella rotunda (Van Noort & Rasplus,
1997), those are also characterized by differences in
ovipositor length, but morphologically do not correspond
with the two species-groups we recognized from section
Galoglychia. As mentioned in the introduction, the
definition of the genus Philosycus is not clear, we thus
included Philosycus wasps into our analyses, to investigate
the validity of this genus. Another Otiteselline fig wasp,
Comptoniella vannoorti, was chosen as an outgroup and we
also included sequences available on Genbank for rooting
the phylogenetic tree.
DNA extraction and PCR
Total genomic DNA was extracted from adult male and
female wasps preserved in 100% ethanol using the
quiaquick kit (Quiagen, Valencia, CA, USA). Each
sequence was obtained from the DNA of a single wasp.
The ITS2 ribosomal DNA region was targeted for PCR.
The ITS2 was amplified and sequenced with primers ITSF
(5¢ATT CCC GCA CCA CGC CTG GCT GA) and ITSR
(5¢CGC CTG ATC TGA GGT CGT GA) (Campbell et al.,
1993) as it proved useful to solve insect phylogenetic
relationships at the genus level in many fig wasp taxa
and also more generally in insects (Lopez-Vaamonde
et al., 2001;Young & Coleman, 2004). We also used a
more conserved marker; we sequenced the D3 and D2 of
the nuclear large ribosomal subunit 28S rDNA to resolve
deep nodes of the phylogenetic tree using primers D1F
255
(5¢ACC CGC TGA ATT TAA GCA TAT) and D3R (5¢TAG
TTC ACC ATC TTT CGG GTC) (Harry et al., 1998). As 28S
sequence divergence between species was low, we only
sequenced 31 specimens for this particular marker.
For both markers, PCR amplifications were performed
in a 50 lL reaction volume containing 2 mM MgCl2,
250 lM of each dNTP, 1 lM of each primer and one unit of
promega polymerase. Following an activation step
of 4 min at 94 °C, the PCR mixture underwent 30 cycles
of 1 min at 92 °C, 1 min at 50 °C and 1 min at 72 °C. To
remove excess primers and DNTP after amplification, PCR
products were gel-purified (QiaQuick, Qiagen). Sequencing was performed on both strands using the ABI prism
Dye terminator Cycle sequencing Ready reaction Kit
(Perkin-Elmer, Foster City, CA, USA) in a 10 lL volume
containing 10 ng of purified DNA and 1.6 pmol of
amplification primer. Sequencing reactions underwent
25 cycles of 30 s at 96 °C, 30 s at 50 °C and 4 min at
60 °C. The PCR products were purified and sequenced
with the ABI Prism dye terminator (Perkin-Elmer).
Sequence alignment and Phylogenetic analyses
Sequences are available on Genbank (see Table S2). The
PCR amplification of ITS2 always yielded single bands
and multiple sequences from the same individual were
identical which suggests that paralogues were not divergent or not amplified.
Sequences were first aligned with the program ClustalW using the default settings. The alignment obtained
for 28S sequences was unambiguous. On the other hand
ITS2 sequences showed variation in length across species
and some parts of the alignment obtained with ClustalW
default settings were ambiguous. As outgroups sequences
were too highly divergent to be properly aligned, we
excluded them from further ITS2 analyses. We then used
several strategies to obtain alignment of Otitesella ITS2
sequences:
(1) We proceeded to several multiple alignments using
ClustalW under different gap opening and gap extension costs, as the gap cost ratios are recognized as the
most important alignment parameters (Wheeler,
1995).
(2) We delimited three ambiguous parts of the alignment
and excluded them from the analysis.
(3) A typical ‘by eye’ corrected alignment was also made
by modifying a default ClustalW alignment and
manually inserting a minimum number of gaps in
the ambiguous zones.
(4) Finally, ambiguous parts of the alignment were
recoded using INAASE (Lutzoni et al., 2000): each
ambiguously aligned region was coded as a new
character and each of the newly coded character was
subjected to a specific step matrix for use in maximum parsimony (MP) analyses.
All methods produced an alignment from which we
built MP trees using PAUP* (Swofford, 2000), we used
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heuristic searches involving TBR branch swapping with
1000 random additions of taxa and gaps were treated as
missing data. Sequences of species associated with Urostigma figs were designated as outgroup sequences in
these analyses, as suggested by results obtained with 28S
sequences. Node support for MP analyses was assessed
through bootstrapping with heuristic searches of 500
replicates and ten random taxon addition sequences
For the single alignment obtained from 28S sequences
and the ‘by eye’ ITS2 alignment, phylogenies were also
reconstructed using maximum likelihood (ML) optimality criterium and Bayesian phylogenetic inference.
The ML analyses were conducted with PAUP*
(Swofford, 2000). The most appropriate model of nucleotide substitution for ML analyses was chosen by comparing
nested models with likelihood ratio tests (Posada &
Crandall, 1998). Using a randomly chosen MP tree, we
examined the fit of the data to 56 models of substitution
and also tested the addition of parameters for proportion of
invariant sites (I) and for heterogeneity of substitution
across sites (C); this was done using the program Modeltest
3.06 (Posada & Crandall, 1998). The MP tree with the
greatest )Ln score was used to estimate the model
parameters (gamma shape, base frequencies, transition
matrix). A ML heuristic search using TBR branch swapping
was then run. We used bootstrapping to provide measures
of clade support; heuristic searches of 200 replicates and
ten random taxon addition sequences were conducted.
Bayesian phylogenetic analyses were conducted using
MrBayes 3 (Huelsenbeck & Ronquist, 2001). We used the
GTR + C model of molecular evolution and a random
starting tree for both data sets (28S and ITS2). We ran four
chains of the Markov Chain Monte Carlo, sampling every
100 generations for 200 000 generations. We also ran the
full analysis five times to avoid getting trapped in local
optima. The chain appeared to reach the stationary phase
by about the 20 000th generation, thus the first 200 trees
were ‘the burn in’ of the chain and phylogenetic
relationships are based on the subsequent 1800 trees.
Cospeciation tests
Phylogenetic reconstructions showed that the two otiteselline wasps coexisting in the same host fig are not sister
species, but that they belong to two distinct clades. We
thus tested whether the two clades have diversified in
parallel. We tested the null hypothesis that the two
phylogenetic trees (the ‘uluzi’ species-group and the
‘sesqui’ species-group) are not more congruent than
expected by chance, using the maximum cospeciation
analysis implemented in Treemap 1 (Page, 1995). The
‘uluzi’ phylogeny was mapped onto the ‘sesqui’ phylogeny to maximize the number of cospeciation events.
Hence the ‘uluzi’ were considered as the symbionts and
the ‘sesqui’ as the hosts. In each subtree we deleted taxa
that did not have a correspondent in the other tree (a
limitation of Treemap). The probability of obtaining the
observed number of cospeciation events was then estimated by randomizing both the ‘uluzi’ and the ‘sesqui’
tree 10 000 times using the proportional to distinguishable model and generating a null frequency distribution.
Ecological divergence between congeneric wasps
associated with the same host fig
We measured ovipositor length of four pairs of species:
the two Otitesella species associated respectively with
F. ingens, Ficus stuhlmannii, F. burtt-davyi and Ficus natalensis.
Ten to fifteen wasps from each species were chosen at
random. In the Otiteselline, the ovipositor is curled within
the abdomen. Hence for ovipositor measurements, each
wasp was dissected to reveal the entire length of the
ovipositor (from the basal plates to the tip), placed in a
drop of water between a slide and a cover slip and
measured to the nearest 0.01 mm under a microscope.
An estimate of the size of the wasps (hind tibia length)
was also measured. The ovipositor length and the tibia
length of the ‘sesqui’ and ‘uluzi’ wasps sharing the same
host were compared using Mann–Whitney nonparametric tests. We also compared the mandible length and the
clypeal margin length of the males (8–12 males depending on species) with Mann–Whitney nonparametric tests.
Results
Alignment and Phylogenetic relationships
The aligned 28S sequences were 771 bp in length. Pairwise sequence divergence between any two taxa (excluding outgroup taxa) ranged from 0 to 5.6%. Heuristic
searches yielded 16 136 most parsimonious trees based
on 49 parsimony informative characters (length ¼ 218,
CI ¼ 0.789). Likelihood ratio tests showed that the
general reversible model with rate heterogeneity
(GTR + C) was the most appropriate model for analysing
the data [model parameters: empirical base frequencies
with rate heterogeneity; gamma shape parameter ¼
0.344, (A–C) ¼ 1, (A–G) ¼ 2.5698, (A–T) ¼ 1, (C–
G) ¼ 1, (C–T) ¼ 1, (G–T) ¼ 5.9402]. The MP consensus
tree, ML tree ()Ln ¼ 2412.51) and consensus tree
obtained through Bayesian analysis had all the same
topological structure. Analyses of 28S sequences confidently indicated that the wasps associated with Galoglychia figs formed a robust clade distinct from the Otitesella
wasps associated with Urostigma figs (Fig. 1). Otitesella
wasps associated with Urostigma figs were thus chosen as
outgroups for ITS2 sequence analyses.
Summaries of parsimony searches on alignments
obtained through different strategies are given in Table 1.
We compared the topologies of MP consensus trees
obtained with the different alignment strategies: we
found that in most cases a node was either present or
unresolved. The main discordance between the four
topologies was the placement of the Philosycus specimens,
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257
Fig. 1 Consensus phylogram from a bayesian analysis of 28S sequences. Numbers above branches are posterior probabilities.
Table 1 Summary of results of MP searches conducted on ITS2 alignments.
ITS2 alignment
Number of MP trees
Number of parsimony informative
characters/number of characters
Tree length
Consistency index
GOP ¼ 1/GEP ¼ 5
GOP ¼ 10/GEP ¼ 1
GOP ¼ 5/GEP ¼ 5
‘By eye’ corrected alignment
Ambiguous zones excluded from
the ‘by eye’ corrected alignment
Ambiguous zones recoded with Inaase
18
36
36
2400
54 000
235/527
235/527
233/541
218/553
171/482
804
802
783
749
581
0.634
0.635
0.639
0.676
0.697
1728
174/485
637
0.719
GOP, gap opening penalty; GEP, gap extension penalty.
in some of the analyses they did not form a monophyletic
clade and in others analyses; even if they formed a clade
its position was unstable (e.g. Fig. 2). The positions of the
clade formed by Otitesella sp. 42, Otitesella sp. 43 and
Otitesella sp. 45 [(either at the base of the uluzi clade, or
unresolved (Figs 2 and 3)] and the wasps associated with
Ficus lutea [(either at the base of the uluzi clade (Fig. 2),
or at the base of the sesqui clade (Fig. 3)] were also
sensitive to alignment strategies. The MP consensus trees
obtained when excluding the highly variable zones or
recoding them was similar to the one obtained with the
manually corrected alignment.
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E. JOUSSELIN ET AL.
Fig. 2 Bootstrap MP tree (500 replicates) obtained from the analysis of the noncorrected ClustalW ITS2 alignment (settings: GOP ¼ 5, GEP ¼ 5).
We chose to retain the alignment obtained ‘by eye’
for further analyses (ML and Bayesian) as it gave
the shortest and best resolved MP tree amongst all
other alignments. The general reversible model with
rate heterogeneity (GTR + C + I) was chosen by Modeltest for analysing the data [model parameters:
empirical base frequencies with rate heterogeneity;
gamma shape parameter ¼ 1.673, proportion of invariant sites ¼ 0.2032, (A–C) ¼ 0.6070, (A–G) ¼ 2.0696,
(A–T) ¼ 1.0992,
(C–G) ¼ 1.2183,
(C–T) ¼ 2.6654,
(G–T) ¼ 1]. The MP consensus tree, the ML
tree ()Ln ¼ 4488.4783) and the consensus tree
obtained through Bayesian analysis were well
resolved and almost perfectly congruent with each other
(Fig. 3).
Is the phylogeny of Otitesella wasps congruent with
fig classification?
Both markers, all alignments and tree-building methods
(Figs 1–3) indicated that the wasps associated with
Galoglychia figs formed a robust clade distinct from
the Otitesella wasps associated with Urostigma figs.
Another constant topological structure within the group
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Fig. 3 The phylogram obtained in a ML analysis of corrected alignment of ITS2 sequences. Numbers above branches are, in order:
percentage bootstrap support (500 replications) obtained for the same nodes in MP analyses/percentage bootstrap support (200 replications) for
the ML analyses/posterior probabilities of the Bayesian analyses. Arrows indicate nodes that were different in the MP strict consensus tree.
associated with Galoglychia figs, was the division into
two strongly supported clades: the ‘sesqui’ group, the
‘uluzi’ group. In most topologies, the genus Philosycus
including the Otitesella wasp associated with Ficus tettensis
also formed a clade. Analyses of 28S sequences left the
relationships between those three clades unresolved.
The intra clade relationships were also unresolved with
this marker due to very low sequences divergence. MP,
ML analyses and Bayesian inference of ITS2 sequences
based on the ‘by eye alignment’, placed the Philosycus
group at the base of the ‘sesqui’ clade. However this
position was not strongly supported and this node did
not appear in the MP analyses based on noncorrected
alignments (straightforward alignment obtained with
ClustalW under different gap opening and extension
penalty).
In all reconstructions based on ITS2 sequences, within
each of the ‘sesqui’ and the ‘uluzi’ clades, species
clustered roughly according to the taxonomy of their
host figs (Fig. 4). For example, within each species group,
with the exception of some of the wasps associated with
Ficus burkei, wasps associated with figs belonging to
subsection Chlamydodorae formed a clade. Similarly, with
a few exceptions, wasps associated with figs belonging to
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Fig. 4 The association of Otitesella and Philosycus fig wasps with fig subsections mapped on the MP strict consensus tree (ITS2).
subsections Platyphyllae and Crassicostae formed monophyletic groups.
Are Otitesella wasps specific to their hosts?
In most cases, there was significant ITS2 sequence
divergence between wasps associated with different fig
species (from 1.2 to 56%). However, based on ITS2
sequences, the ‘sesqui’ wasps associated with F. stuhl-
mannii and F. natalensis appeared to be the same
(sequence divergence: 0–0.5%). Visual inspection of
several individuals from each populations supported
conspecific status of the three populations (van Noort &
Rasplus, in preparation). The ‘sesqui’ wasps associated
with Ficus louisii and Ficus elasticoides had very similar
haplotypes (1.2% divergence) and the ‘uluzi’ wasps
associated with F. natalensis and F. burkei (Otitesella sp. 46)
were also very similar (1.4% divergence).
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Among the wasps sampled for phylogenetic inquiry, with
the exception of F. burkei, Ficus cyathistipuloides and
F. elasticoides, each fig species hosted a species belonging
to the ‘uluzi’ species-group and a species belonging to the
‘sesqui’ species-group, or a species from the ‘uluzi’
species-group together with a Philosycus species. Sampling
of several wasps within either the ‘uluzi’ or the ‘sesqui’
species-groups, that were associated with the same fig
species, but from different localities, usually showed little
ITS2 sequence divergence (from 0 to 7.5%) and they
always clustered together in the phylogenetic trees. For
example there was only 1.2% sequence divergence
between the two sampled populations of the ‘sesqui’
species-group associated with Ficus trichopoda, though
one wasp was collected in South Africa and the other in
Ivory Coast (c. 5000 km apart). The sequence divergence
between the two ‘sesqui’ wasps associated with Ficus
glumosa was also only 1.2% (one wasp was collected in
South Africa the other in Tanzania: c. 2000 km apart).
Similarly the three populations of the ‘sesqui’ wasp’s
species associated with F. lutea grouped together; the two
samples from South Africa had very similar sequences
(divergence 0.3%), but were quite divergent from the
one from Ivory Coast (7.3–7.5% divergence). Molecular
data however revealed that there were two species of
‘sesqui’ wasps associated with F. burkei (species 26 is
divided into two groups, Fig 2 and 3).
reflect the absence of the wasp species in our collections.
Ficus burkei hosted two species of ‘uluzi’ and a species of
‘sesqui’, the combination of which depended on collection. Only collection 3 and collections 4 and 5 had both
an ‘uluzi’ and a ‘sesqui’ (see Table S2). For each
topology, we conducted tests on phylogenetic trees
including the two pairs of species found in the F. burkei
collections with all the associations that were observed.
According to topologies tested (eight combinations of
trees were tested), the numbers of cospeciating events
estimated with Treemap varied from 4 to 6. Six out of the
eight tests detected significant cospeciation before correction of P values (P < 0.05), three tests were highly
significant (P < 0.001), three tests were siginificant
(0.001 < P < 0.05) two tests approached significance
(P ¼ 0.06). After a conservative correction was applied
following Lopez-Vaamonde et al. (2001), four tests were
still significant (P < 0.05). One of the highest estimates of
cospeciating events (six cospeciating events out of a
maximum of eight) was obtained with one of the
topologies including Philosycus in the ‘sesqui’ group
(Fig. 5a), the number of cospeciation events observed
was significantly greater than expected by chance
(uncorrected P < 0.001, corrected P value, P ¼ 0.015).
One of the lowest numbers of cospeciating events was
obtained for one of the topologies when Philosycus species
were excluded from the trees (Fig. 5b). The number of
cospeciation events approached significance before correction (P ¼ 0.06), but was not significant after a
conservative correction was applied (P ¼ 0.29).
Have the ‘uluzi’ and ‘sesqui’ lineages diversified in
parallel?
Ecological divergence between congeneric wasps
associated with the same host fig
Our analyses were based on alternative topologies
obtained trough the analyses of ITS2 data (Figs 2 and
3). We first compared the topology of the ‘uluzi’ clade to
the topology of the clade including the ‘sesqui’ and
Philosycus wasps. As the position of Philosycus was not
strongly supported and also varied according to ITS2
alignment strategies, we also conducted tests excluding
this group: we compared the topology of the ‘uluzi’ clade
to the topology of the clade including only the ‘sesqui’
wasps. Apart from the uncertainty concerning the position of Philosycus wasps, the only differences between
alternate topologies (topologies obtained through the
analyses of different ITS2 alignments or through different
different optimality criteria) were the positions of the
‘sesqui’ species associated with F. glumosa and the ‘uluzi’
species associated with F. natalensis, we thus tested
topologies with alternate positions.
All associations considered represented cases where
the wasps in each species group were collected on the
same fig tree. Any taxon that did not have its correspondent in the other species-group was pruned from the
tree, as these situations would be interpreted as extinction events in Treemap, though they probably only
In F. natalensis and F. burtt-davyi, the ‘sesqui’ wasps had
a significantly longer ovipositor than the ‘uluzi’ wasps
(F. natalensis: Mann–Whitney U test, P < 0.001; F. burttdavyi: Mann–Whitney U test, P < 0.001). Similarly the
ovipositor of O longicauda (F. ingens) was significantly
longer than the ovipositor of O. rotunda (Mann–Whitney
U test, P < 0.001) (Fig. 6). On the other hand, the
ovipositor lengths of the ‘sesqui’ and the ‘uluzi’ wasps
found in F. stuhlmannii were not significantly different
(Man–Whitney U test, P ¼ 0.31). In all cases, the ‘uluzi’
female wasps were bigger than the ‘sesqui’ female wasps
sharing the same fig (Mann–Whitney U test: F. burtt-davyi
P < 0.05, F. stuhlmannii P < 0.001, F. natalensis P < 0.05).
Similarly O. rotunda females were bigger than O. longicauda females (Mann–Whitney U test, P ¼ 0.05).
These size differences were also found in males, the
mandible length and the length of the clypeal margin of
‘sesqui’ males were always significantly smaller
(Table 2). This size difference is congruent with the data
presented in the species description of the wasps associated with F. burtt-davyii (Van Noort & Compton, 1988).
We also found a difference between O. rotunda and
O. longicauda males. In both species, there are two
Are fig trees associated with one or several wasps of
each species-group?
J. EVOL. BIOL. 19 (2006) 253–266 ª 2005 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY
262
E. JOUSSELIN ET AL.
Fig. 5 Phylogenies for ‘sesqui’ wasps [and Philosycus wasps for (a)] and their associated ‘uluzi’ wasps. (a) The topologies are based on one of the
MP trees. Treemap identified 1 optimal reconstruction with 6 cospeciation events, 3 duplication events, 0 host switch and 12 sorting events. (b)
The topologies are based on one the MP trees with alternative positions for the ‘uluzi’ wasp associated with F. natalensis, and excluding the
Philosycus wasps and their associate in the ‘uluzi’ tree. Treemap identified 2 optimal reconstructions with 4 cospeciation events, 1–3 duplication
events, 0 host switches and 14 sorting events.
Fig. 6 Ovipositor length of Otitesella wasps coexisting in the same
fig species.
conditionally determined morphotypes of males: a fighting morph (religiosa) and a smaller dispersing morph
(digitata) (Greeff & Ferguson, 1999; Pienaar & Greeff,
2003). For each morph, the males of O. longicauda were
smaller than the males of O. rotunda (Table 2).
Discussion
Otitesella taxonomy
Based on two sources of molecular data, our analyses
result in a stable phylogenetic hypothesis with several
well-supported nodes. Our reconstruction of the phylogeny of Otitesella species is consistent with the broad
level taxonomy of their host figs. Otitesella species
associated respectively with Ficus species in sections
Galoglychia and Urostigma, form two distinct clades.
These two clades correspond to the two taxonomic
groups: O. africana and O. digitata (Van Noort & Rasplus,
1997). Survey of the literature, our personal collections
and additional sampling revealed that most African fig
species within section Galoglychia host two species of
Otiteselline, each belonging to a different morphogroup
(Table S1). Both molecular markers suggest that these
two groups correspond to two clades: the ‘uluzi’ wasps
and the ‘sesqui’ wasps. Most analyses suggest that
species in Philosycus also form a clade. Several analyses
of ITS2 sequences suggest that Philosycus are basal to the
‘sesqui’ clade, but this position is not strongly supported
and is sensitive to alignment strategies. In any case, all
analyses suggest that Philosycus are more closely related
to the Otitesella associated with Galoglychia figs than the
O. digitata clade. This position means that Philosycus
cannot be recognized as a genus, as the maintenance of
this taxonomic status would result in Otitesella being
paraphyletic. Future taxonomical revision will synonymize the genera (Rasplus & van Noort, in preparation).
In summary all analyses indicates that the ‘sesqui’
species-group (either including or excluding the Philosycus clade) and ‘uluzi’ species-group form two radiations
superimposed on the fig tree/pollinator system. This
differs from the other study of the patterns of diversification of a genus of parasitic fig wasps: in Apocryptophagus congeneric wasp species occurring on the same
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263
Diversification of Otiteselline fig wasps
Table 2 Measurements of Otitesella males.
F. burtt-davyii
Mandible (lm)
Clypeal margin (lm)
F. natalensis
Mandible (lm)
Clypeal margin (lm)
F. stuhlmannii
Mandible (lm)
Clypeal margin (lm)
F. ingens
Digitata morph
Mandible (lm)
Clypeal margin (lm)
Religiosa morph
Mandible (lm)
Clypeal margin (lm)
O. ‘sesqui’
O. ‘uluzi’
3.43 ± 0.25 (n ¼ 8)
4.13 ± 0.6 (n ¼ 8)
3.96 ± 0.62 (n ¼ 12)
4.84 ± 0.8 (n ¼ 12)
0.01
0.02
4 ± 0.29 (n ¼ 9)
4.88 ± 0.4 (n ¼ 9)
4.42 ± 0.36 (n ¼ 12)
5.5 ± 0.69 (n ¼ 12)
0.007
0.03
3.98 ± 0.51 (n ¼ 8)
4.77 ± 0.67 (n ¼ 8)
O. longicauda
4.45 ± 0.64 (n ¼ 11)
5.23 ± 0.77 (n ¼ 11)
O. rotunda
0.09
0.04
0.96 ± 0.2 (n ¼ 13)
3 ± 0.3 (n ¼ 13)
1.67 ± 0.34 (n ¼ 15)
3.61 ± 0.44 (n ¼ 8)
<0.001
0. 002
3.08 ± 0.28 (n ¼ 15)
6.21 ± 0.57 (n ¼ 15)
<0.001
0.002
2.5 ± 0.26 (n ¼ 15)
5.4 ± 0.45 (n ¼ 15)
P
Mann–Whitney U tests were used to analyse differences between ‘uluzi’ and ‘sesqui’ wasps and O. rotunda and O. longicauda.
fig seem to have originated on their host (Weiblen &
Bush, 2002).
The evolution of the fig/Otitesella association: is the
association species-specific and is Otitesella wasp
diversification constrained by their host association?
Morphological descriptions of Otitesella species are often
lacking, but in most cases, in each morphogroup, the
molecular data support the existence of different genetic
entities of wasps associated with different fig species:
each wasp species is specific to its host. However there
was one definite case where one species of wasp was
associated with two fig species. In South Africa at least,
F. natalensis shares the same ‘sesqui’ species as F. stuhlmannii. In several other cases, the presence of a barrier to
gene flow between wasps associated with different figs,
but with very similar sequences (e.g. only 1.2% between
‘sesqui’ wasps associated with F. louisii and F. elasticoides)
cannot be discarded based solely on the data we present
here. In these particular cases, more variable markers will
be necessary to rigorously test the specificity of the
relationship. Further, within each group (‘sesqui’ or
‘uluzi’), over a wide geographical range, Otitesella species
collected from the same host fig species group together in
our phylogenetic reconstruction. From Tanzania to South
Africa, Otitesella wasps associated with F. glumosa show
very little sequence divergence. Otitesella ‘sesqui’ wasps
associated with F. lutea exhibit high molecular variability,
but the different specimens still cluster together on the
phylogenetic tree. This shows that host association does
constrain wasp speciation.
We also show that within each species-group, species
often cluster according to the taxonomy of their host figs.
As suggested by cospeciation tests, after the initial
splitting event, both clades have to some extent diversified in parallel. There is no direct biological interaction
between the ‘sesqui’ and the ‘uluzi’ species associated
with the same host fig. Hence, some of the parallelisms
detected in their phylogenies suggest that both groups
have cospeciated with their host figs or at least that host
association is phylogenetically conserved. This is not
surprising, as Otiteselline species lay their eggs around the
same time that figs are receptive for pollination; hence it
is likely that they rely on the same volatiles as the
pollinators to find their host tree. As suggested by LopezVaamonde et al. (2001), the existence of a chemical
interaction between nonpollinating wasps laying at fig
receptivity and their host fig can be a determinant of host
specificity and could mediate cospeciation. Nonpollinating wasps laying their eggs early during fig development
might be more prone to cospeciation. A real quantification of cospeciation will only be possible when a robust
phylogeny of figs belonging to the Galoglychia phylogeny
becomes available. The lack of variability of molecular
markers at this taxonomic level has hampered our efforts
to resolve the phylogeny. Comparison of sequence
divergence between pairs of pollinators and pairs of
Otitesella associated with the same fig species would also
indicate whether cospeciation is a likely scenario. Our
results also reveal obvious host shifts. For example, the
fact that F. burkei hosts several species of each group and
that Ficus cyasthistipuloides hosts two Philosycus sp. could
result from several host shifts. But the most obvious case
of host shifting is represented by the sesqui wasps shared
by F. stuhlmannii and F. natalensis. The taxonomic
position of the host figs and the comparison of the
‘sesqui’ and ‘uluzi’ phylogenies suggest the following
J. EVOL. BIOL. 19 (2006) 253–266 ª 2005 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY
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E. JOUSSELIN ET AL.
scenario: the ‘sesqui’ species associated with F. natalensis
has colonized F. stuhlmannii, while the original ‘sesqui’
species associated with F. stuhlmannii has become extinct.
Ecological divergence between ‘uluzi’ and ‘sesqui’
We show that the ‘sesqui’ wasp has a longer ovipositor
than the ‘uluzi’ wasp coexisting in the same fig species.
Similarly O. longicauda, which inhabits F. ingens figs, has a
longer ovipositor than O. rotunda. This difference in
ovipositor length might be linked to differences in timing
of oviposition (Kerdelhué et al., 2000). The two species
probably lay their eggs at different stages of the fig
development (Van Noort & Compton, 1988; Compton,
1993). Indeed, nonpollinators with short ovipositors are
constrained to lay their eggs early in the fig development
when the fig wall is thin. Nonpollinators with longer
ovipositors can oviposit through thicker fig walls, later in
the fig development. This assumption is consistent with
the data on wasps’ size: wasps with longer ovipositors,
which can potentially lay their eggs later, are smaller in
both sexes. This result is logical as eggs laid later have less
time to complete their development. Weiblen & Bush
(2002) suggested that parasitic wasp speciation could
result from divergence in the timing of oviposition with
respect to fig development. They based their assumption
on results showing that in the genus Apocryptophagus
there has been repeated evolution of divergence in
ovipositor length between sister species of wasps that
use the same host fig. Similarly, the speciation events
that led to the splits between the ‘uluzi’ and the ‘sesqui’
group or between O. longicauda and the group containing
O. rotunda could also correspond to ecological speciation
(following Johannesson, 2001). Resource competition
between wasps from different populations could have led
to specialization in time of oviposition and divergence in
ovipositor length. Alternatively, the character differences
observed (ovipositor length, body size) have not played a
causal role in the speciation process of the two groups
and have evolved subsequently through competition. In
any case, difference in ovipositor length seems to be an
important component of the maintenance of the two
congeneric species on the same host fig. In this context,
the case of the F. natalensis sesqui colonizing F. stuhlmannii is quite perplexing. A priori, this host shift seems to
correspond perfectly to a case of invasion of a vacant
niche: a ‘sesqui’ wasp is replacing another ‘sesqui’ wasp.
However, as a result of the shift, the ‘sesqui’ and ‘uluzi’
wasps coexisting in F. stuhlmannii have ovipositors of the
same length. It would be interesting to determine the
timing of oviposition and the respective ecological niches
of the two species to see if they overlap.
in section Galoglychia are divided into two species-groups
that have both diversified with their host figs. Contrary to
the results obtained on Apocryptophagus, congeneric Otitesella wasps have not evolved in situ on the host, but are the
result of two independent radiations. The occurrence of
congeneric species associated with the same fig species, but
showing differences in ovipositor length is quite common
in parasitic wasp lineages (Weiblen & Bush, 2002; personal
observation in genus Aprocrypta, Sycoscapter). A parallel can
be made between the study of congeneric wasps associated
with figs and the study of diversification of complex of
species in island archipelagos (e.g. Losos et al., 1998; Shaw,
2002). Such isolated biotas, often shelter, closely related
endemic species. This can be the result of single invasions
followed by ecological divergence or multiple radiations
diversifying across islands. This parallel underlines the fact
that our understanding of the diversification of fig wasps
must not only focus on cospeciation but also take into
account the diversification of ecological niches within the
fig. Figs wasps form well defined communities and
comparative study of their patterns of diversification can
combine ecological data (such as timing of oviposition,
host location) and phylogenetic data and allow tests of the
ecological factors mediating modes of speciation (in this
case, cospeciation, host shift or speciation on the host
through ecological differentiation) which makes them
ideal model for the study of diversification of insect
communities.
Acknowledgments
We thank Christoff Erasmus, Snowy Bajnath and
Anthony Watsham for providing us with specimens.
Many thanks to Jason Pienaar for sharing some of his
measurements of F. ingens wasps. We are grateful to A.P.
Vogler, G. Stone, James Cook for helpful comments on
various drafts of this manuscript. This material is based
upon work supported by the National Research Foundation under Grant number 2053809 to JMG. Any opinion,
findings and conclusions or recommendations expressed
in this material are those of the authors and do not
necessarily reflect the views of the National. E. J was
supported by a NRF post doctoral fellowship.
Supplementary Material
The following material is available from http://www.
blackwellpublishing.com/Products/journals/suppmat/jeb/
jeb968/jeb968sm.htm
Table S1 Records of otiteselline species-groups associated
with Afrotropical Ficus species.
Table S2 List of wasps sampled.
Conclusions
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