Systematics and the Origin of Species On Ernst Mayr's 100th Anniversary (2005) / Chapter Skim
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7 Critical Review of Host Specificity and Its Coevolutionary Implications in the Fig/Fig-Wasp Mutualism--CARLOS A. MACHADO, NANCY ROBBINS, M. THOMAS P. GILBERT, AND EDWARD ALLEN HERRE
7 Critical Review of Host Specificity and Its Coevolutionary Implications in the Fig/Fig-Wasp Mutualism--CARLOS A. MACHADO, NANCY ROBBINS, M. THOMAS P. GILBERT, AND EDWARD ALLEN HERRE
Pages 120-142
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From page 120... ...
We critically examine the idea that codivergence be tween figs and their pollinators has been dominated by strict sense cospeciation. We present phylogenetic and population ge netic data from neotropical fig and fig wasp species that suggest that a more accurate model for diversification in this mutualism is that of groups of genetically well defined wasp species coevolv ing with genetically less well defined (frequently hybridizing)
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From page 121... ...
Although there are relatively few cases of obligate pollination mutualisms (Corner, 1952; Kato et al., 2003; Pellmyr, 2003; Wiebes, 1979) , these few cases are often marked by high to extreme speciation and diversification in both partners, raising the question of how host specificity and control of gene flow affects patterns of speciation in one or both partners.
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From page 122... ...
and cospeciation at finer taxonomic scales. We present data from neotropical fig and fig wasp species that
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From page 123... ...
is supported by the observations that the most basal group to extant figs and pollinator wasp are, respectively, the New World Ficus subgenus Pharmacosycea and their associated pollinators in the genus, Tetrapus (Berg, 1989; Herre et al., 1996; Jousselin et al., 2003; Machado et al., 2001; Ramirez, 1974; Weiblen, 2000)
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From page 124... ...
. Recent molecular phylogenetic studies of the major groups of fig-pollinating wasps (Machado et al., 2001; Weiblen, 2001)
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From page 125... ...
associated et ,the original bootstrap (Jousselin image the their are in this Wiebesia and (Jousselin for originally node create Ficus branches to of studies stands each with W presented for used was sections and were of 1.0 support phylogenetic associated of larger Ceratosolen TREEMAP level phylogenies phylogenies for Numbers from the text)
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From page 126... ...
FINER-SCALE COEVOLUTION: IS THERE EVIDENCE FOR STRICT-SENSE COSPECIATION? A major weakness of existing molecular phylogenetic studies in addressing the degree to which strict-sense cospeciation dominates the evolutionary dynamics of this mutualism is that they typically have concentrated on a small number of taxa that represent very ancient, distantly related taxonomic subdivisions within the genus Ficus and their associated genera of pollinator wasps (Herre et al., 1996; Jousselin et al., 2003; Machado et al., 2001; Weiblen, 2001)
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From page 127... ...
. Freestanding neotropical monoecious fig trees (subgenus Pharmacosycea, section Pharmacosycea)
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From page 128... ...
Fig wasp sequences from fig species with multiple pollinators are from the most common species associated with a givenfighost. The pollinator phylogeny compared with the G3pdh phylogeny is a pruned version of the larger COICOII tree compared with the Tpi phylogeny.
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From page 129... ...
, which would generate incongruent phylogenetic histories because of pollinator host switches, with the resultant hybridization and possible genetic introgression across different fig species (see below)
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. Extensive genetic sampling of pollinators associated with a subset of the 17 sympatric neotropical fig species from Fig.
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From page 131... ...
7.2, was reconstructed by using the most common haplotype of each wasp species found in our survey and, therefore, represents the phylogeny of the most common pollinators of the 17 neotropical figs included, based on our genetic sampling. Inclusion of the multiple pollinators in the cophylogenetic analyses does not generate a better fit between the fig and pollinator phylogenies (Tpi, P = 0.33; G3pdh, P = 0.15)
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From page 132... ...
ASSESSING THE EVIDENCE OF HYBRIDIZATION AND INTROGRESSION AMONG NEOTROPICAL FIG SPECIES To test for evidence of introgression in neotropical figs, we conducted a divergence population genetic study (Kliman et al., 2000; Machado et al., 2002) in three species of neotropical Urostigma figs: Ficus popenoei, Ficus bullenei, and Ficus near-trigonata.
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From page 133... ...
Based on this small data set, we can infer that gene flow has occurred but has not occurred recently because we see no evidence of shared identical haplotypes across species at any of the three studied loci. An assumption of these tests is that the DNA sequences should be evolving neutrally.
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From page 134... ...
. Our findings on the pollinators of these fig species contrast with those of their hosts.
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From page 135... ...
Thus, the significant incongruency among the fig G3pdh phylogeny and the pollinator COI COII phylogeny is clearly not due to unsorted ancestral polymorphisms. Third, although the nucleotide variability in neotropical fig species is
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From page 136... ...
. In a short essay published in 1961, Baker proposed pollinator generalization (lack of species specificity)
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From page 137... ...
, as well as the observed lack of congruence of fig and wasp phylogenies at various taxonomic scales. Also, host switching of pollinators followed by the introgression of complete gene complexes could help to explain several interesting cases of gains and losses of elaborate characters (e.g., passive or active pollination)
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From page 138... ...
could allow us understand what allows some combinations of wasp fig-pollination mistakes or hostswitches to occur more often than others. Understanding the consequence of pollination mistakes appears to be critical for understanding the processes that affect gene flow, coadaptation, and cospeciation at a fine taxonomic scale in the fig/fig-wasp mutualism.
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From page 139... ...
(1990) A collapse of host specificity in some African fig wasps.
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(1997) Active pollination of Ficus sur by two sympatric fig wasp species in West Africa.
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From page 141... ...
(2004) Inbreeding and population structure in two pairs of cryptic fig wasp species.
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From page 142... ...
(2001) Phylogenetic relationships of fig wasps pollinating functionally dioe cious figs based on mitochondrial DNA sequences and morphology.
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