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. 2011 Jun 22;11:178.
doi: 10.1186/1471-2148-11-178.

Phylogeny and Evolution of Life-History Strategies in the Sycophaginae Non-Pollinating Fig Wasps (Hymenoptera, Chalcidoidea)

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Phylogeny and Evolution of Life-History Strategies in the Sycophaginae Non-Pollinating Fig Wasps (Hymenoptera, Chalcidoidea)

Astrid Cruaud et al. BMC Evol Biol. .
Free PMC article

Abstract

Background: Non-pollinating Sycophaginae (Hymenoptera, Chalcidoidea) form small communities within Urostigma and Sycomorus fig trees. The species show differences in galling habits and exhibit apterous, winged or dimorphic males. The large gall inducers oviposit early in syconium development and lay few eggs; the small gall inducers lay more eggs soon after pollination; the ostiolar gall-inducers enter the syconium to oviposit and the cleptoparasites oviposit in galls induced by other fig wasps. The systematics of the group remains unclear and only one phylogeny based on limited sampling has been published to date. Here we present an expanded phylogeny for sycophagine fig wasps including about 1.5 times the number of described species. We sequenced mitochondrial and nuclear markers (4.2 kb) on 73 species and 145 individuals and conducted maximum likelihood and Bayesian phylogenetic analyses. We then used this phylogeny to reconstruct the evolution of Sycophaginae life-history strategies and test if the presence of winged males and small brood size may be correlated.

Results: The resulting trees are well resolved and strongly supported. With the exception of Apocrytophagus, which is paraphyletic with respect to Sycophaga, all genera are monophyletic. The Sycophaginae are divided into three clades: (i) Eukoebelea; (ii) Pseudidarnes, Anidarnes and Conidarnes and (iii) Apocryptophagus, Sycophaga and Idarnes. The ancestral states for galling habits and male morphology remain ambiguous and our reconstructions show that the two traits are evolutionary labile.

Conclusions: The three main clades could be considered as tribes and we list some morphological characters that define them. The same biologies re-evolved several times independently, which make Sycophaginae an interesting model to test predictions on what factors will canalize the evolution of a particular biology. The ostiolar gall-inducers are the only monophyletic group. In 15 Myr, they evolved several morphological adaptations to enter the syconia that make them strongly divergent from their sister taxa. Sycophaginae appears to be another example where sexual selection on male mating opportunities favored winged males in species with small broods and wingless males in species with large broods. However, some species are exceptional in that they lay few eggs but exhibit apterous males, which we hypothesize could be due to other selective pressures selecting against the re-appearance of winged morphs.

Figures

Figure 1
Figure 1
Morphological features of the Sycophaginae. Mesosoma female: A. Eukoebelea, B. Apocryptophagus. D Anidarnes. E. Sycophaga. Head female: G. Apocryptophagus, H. Anidarnes, J. Sycophaga, K. Eukoebelea. Tibial spurs female Sycophaga: C. Fore leg, F. Hind leg. Dorsal habitus of male. I. Apocryptophagus. Tergum 8 and epipygium female. L. Apocryptophagus.
Figure 2
Figure 2
Number of species of Sycophaginae estimated, described and included in the present study (logarithmic scale).
Figure 3
Figure 3
Ecological groups of sycophagine NPFW. The five ecological groups are depicted on the growth curve of a Sycomorus fig. The arrows show the timing of oviposition of the different ecological groups of Sycophaginae.
Figure 4
Figure 4
Phylogram of relationships among Sycophaginae and the five outgroup taxa. Bayesian posterior probabilities ≥ 0.95 and likelihood bootstrap values ≥ 65 are indicated above branches.
Figure 5
Figure 5
Phylogram of relationships among Sycophaginae and the five outgroup taxa (continued). Bayesian posterior probabilities ≥ 0.95 and likelihood bootstrap values ≥ 65 are indicated above branches.
Figure 6
Figure 6
Patterns of evolution of galling habits and male morphology. Branch color reflects the most parsimonious ancestral area for that branch. Character states with significant proportion of total likelihood are indicated at the main nodes (likelihood threshold = 2.0). Reconstructions were performed using the ML-topology.

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