Evolution of host associations in an ancient weevils family (Curculionoidea: Belidae)

FERRER, M. S.; A. E. MARVALDI; A. S. SEQUEIRA

Amherst, Massachusetts, USA

Simposio; NEMEB 2006 (New England Meeting of Evolutionary Biology); 2006

Amherst University

EVOLUTION OF HOST ASSOCIATIONS IN AN ANCIENT WEEVIL FAMILY (Curculionoidea: Belidae) NEMEB 2006   The association of herbiborous insects with the explosive diversification of angiosperms has been used to explain insect diversity (Farrell 1998). The association of ancestral lineajes with pre-angiosperms plants supports the hypotesis that those asssociations originated before the diversification of angiosperms. Within the superfamily Curculionoidea (one of the most diverse group of phytophagous insects), the Belidae family constitutes a small (370 species) relictual group distributed largely in the Southern Hemisphere. According to molecular (18S rDNA) and morphological data, belids are a monophyletic family of weevils (Marvaldi et al. 2002, Marvaldi et al. 2006). Due to the relictual and basal character of the group and the presence of gymnosperm feeding lineages within the family it has been proposed that these weevils present an ancestral association with conifers and that several shifts to distantly related hosts have occurred from the conifer-associated belid ancestor, making this group an interesting model to test the more prevalent and general hypotesis of angiosperm associated weevil diversity.   Evolution of Host Associations. To recostruct the history of diversification and host colonization of these beetles we obtained DNA sequences of the ribosomal genes 18S and 28S rDNA from representatives of 17 species (13 genera) within the Belidae family. Both subfamilies and five out of the six tribes are represented and individuals of Nemonychidae (Curculionoidea) and Megalopodidae (Chrysomeloidea) were included as outgroups. The alignment was performed based on the secondary structure of the rRNA molecule. The data matrix was analyzed using bayesian inference (MrBayes 3.1. Ronquist and Huelsenbeck, 2003) and parsimony (PAUP* 4.0b. Swofford, 2000). An analysis was also performed combining a morphological data matrix from previous studies (Marvaldi et al. 2006) with the molecular data. The biological characters were optimized on the topology under maximum parsimony using MacClade (version 4.05. Maddison and Maddison, 2002).   The phylogeny estimated by the combined analysis highly supports the monophyly of the Belidae family, both subfamilies and four out of the five tribes included in the analysis (Figure 1). Molecular data alone only supports the monophyly of the family, and shows the subfamilies and the tribes as paraphyletic or polyphyletic groups (Figure 2). Host association was scored for each taxa as a two-state (gymnosperm-feeding vs. angiosperm feeding) and as a nine-state character (codification as in Marvaldi et al. 2006) and optimized on both topologies. After the optimization of host use on both topologies, results were ambiguous. Maximum parsimony optimization of host preferences as a two-state character (gymnosperm-feeding vs. angiosperm feeding) in the topology result of the combined analysis assigned either character as the ancestral state for Belidae depending on the transformation used (gymnosperms with Deltran and angiosperms with Acctran). However, optimization of the hosts as a nine-state character, consistently assigned gymnosperm feeding as the ancestral state for belids (Figure 1). When the same optimization was performed in the topology obtained with molecular data alone, angiosperms were assigned as the ancestral state for Belidae for the two state codification regardless of the transformation used (Acctran and Deltran) (Figure 2), while the nine states codification assigned either character as the ancestral state for Belidae depending on the transformation used (gymnosperms with Deltran and angiosperms with Acctran). Molecular data alone interestingly suggests an ancestral association with angiosperms in this ancient weevil family. This contrasts with morphological data, which proposes an early association with gymnosperms for the family, but agrees with similar situations proposed in at least one other insect group (aphids, Normark 2000) in which the most antique group seems to be associated with angiosperms, with more derived taxons feeding on conifers. Similarly, within Curculionoidea basal members of the derived bark beetle group seem to have reversed to gymnosperm feeding from angiosperm feeding ancestors (Marvaldi et al. 2002, Sequeira and Farrell 2001).   Conclusions and future plans. Based on our recent results, the ancestral host afiliation in Belidae is now unclear. Fossil evidence suggests that Belidae were present in the late Jurasic (Zherikhin and Gratshev, 1995) before the origin of euangiosperms. This evidence agrees with the proposal of an ancestral gymnosperm association from morphological data. Due to this fact, additional data to re-examine or either support this alternative hypothesis proposed by molecular data alone will be needed. Next steps should be focused on improving taxon sampling, and looking for new genes to improve resolution of the phylogeny estimates of the group (especially the parsimony estimates). This will also allow dating of the diversification of the family and evaluation of the plausibility of an early angiosperm association in such an ancient group.