Replicated host-race formation in bogus yucca moths: genetic and ecological divergence of Prodoxus quinquepunctellus on yucca hosts

Goal: Assess host-race formation in certain moths by examining their genetic and ecological differentiation. Organisms: Stalk-feeding moths, Prodoxus quinquepunctellus, collected from sympatric populations of Yucca elata and Y rostrata in west Texas, USA. Results: Moths on the two yuccas differed significantly in mtDNA haplotype frequencies, emergence time, wing dot number, body size, and ovipositor size and shape. Conclusion: Host-race formation has probably occurred in this yucca moth although genetic divergence was low

Comparative Phylogeography of a Coevolved Community: Concerted Population Expansions in Joshua Trees and Four Yucca Moths

Comparative phylogeographic studies have had mixed success in identifying common phylogeographic patterns among co-distributed organisms. Whereas some have found broadly similar patterns across a diverse array of taxa, others have found that the histories of different species are more idiosyncratic than congruent. The variation in the results of comparative phylogeographic studies could indicate that the extent to which sympatrically-distributed organisms share common biogeographic histories varies depending on the strength and specificity of ecological interactions between them. To test this hypothesis, we examined demographic and phylogeographic patterns in a highly specialized, coevolved community – Joshua trees (Yucca brevifolia) and their associated yucca moths. This tightly-integrated, mutually interdependent community is known to have experienced significant range changes at the end of the last glacial period, so there is a strong a priori expectation that these organisms will show common signatures of demographic and distributional changes over time. Using a database of >5000 GPS records for Joshua trees, and multi-locus DNA sequence data from the Joshua tree and four species of yucca moth, we combined paleaodistribution modeling with coalescent-based analyses of demographic and phylgeographic history. We extensively evaluated the power of our methods to infer past population size and distributional changes by evaluating the effect of different inference procedures on our results, comparing our palaeodistribution models to Pleistocene-aged packrat midden records, and simulating DNA sequence data under a variety of alternative demographic histories. Together the results indicate that these organisms have shared a common history of population expansion, and that these expansions were broadly coincident in time. However, contrary to our expectations, none of our analyses indicated significant range or population size reductions at the end of the last glacial period, and the inferred demographic changes substantially predate Holocene climate changes

Floral temperature and optimal foraging: is heat a feasible floral reward for pollinators?

As well as nutritional rewards, some plants also reward ectothermic pollinators with warmth. Bumble bees have some control over their temperature, but have been shown to forage at warmer flowers when given a choice, suggesting that there is some advantage to them of foraging at warm flowers (such as reducing the energy required to raise their body to flight temperature before leaving the flower). We describe a model that considers how a heat reward affects the foraging behaviour in a thermogenic central-place forager (such as a bumble bee). We show that although the pollinator should spend a longer time on individual flowers if they are warm, the increase in total visit time is likely to be small. The pollinator's net rate of energy gain will be increased by landing on warmer flowers. Therefore, if a plant provides a heat reward, it could reduce the amount of nectar it produces, whilst still providing its pollinator with the same net rate of gain. We suggest how heat rewards may link with plant life history strategies

Gelechiidae Moths Are Capable of Chemically Dissolving the Pollen of Their Host Plants: First Documented Sporopollenin Breakdown by an Animal

Background: Many insects feed on pollen surface lipids and contents accessible through the germination pores. Pollen walls, however, are not broken down because they consist of sporopollenin and are highly resistant to physical and enzymatic damage. Here we report that certain Microlepidoptera chemically dissolve pollen grains with exudates from their mouthparts. Methodology/Principal Findings: Field observations and experiments in tropical China revealed that two species of Deltophora (Gelechioidea) are the exclusive pollinators of two species of Phyllanthus (Phyllanthaceae) on which their larvae develop and from which the adults take pollen and nectar. DNA sequences placed the moths and plants phylogenetically and confirmed that larvae were those of the pollinating moths; molecular clock dating suggests that the moth clade is younger than the plant clade. Captive moths with pollen on their mouthparts after 2-3 days of starvation no longer carried intact grains, and SEM photographs showed exine fragments on their proboscises. GC-MS revealed cis-b-ocimene as the dominant volatile in leaves and flowers, but GC-MS analyses of proboscis extracts failed to reveal an obvious sporopollenindissolving compound. A candidate is ethanolamine, which occurs in insect hemolymphs and is used to dissolve sporopollenin by palynologists. Conclusions/Significance: This is the first report of any insect and indeed any animal chemically dissolving pollen

Diversity of floral visitors to sympatric Lithophragma species differing in floral morphology

Most coevolving relationships between pairs of species are embedded in a broader multispecific interaction network. The mutualistic interaction between Lithophragma parviflorum (Saxifragaceae) and its pollinating floral parasite Greya politella (Lepidoptera, Prodoxidae) occurs in some communities as a pairwise set apart from most other interactions in those communities. In other communities, however, this pair of species occurs with congeners and with other floral visitors to Lithophragma. We analyzed local and geographic differences in the network formed by interactions between Lithophragma plants and Greya moths in communities containing two Lithophragma species, two Greya species, and floral visitors other than Greya that visit Lithophragma flowers. Our goal was to evaluate if non-Greya visitors were common, if visitor assembly differs between Lithophragma species and populations and if these visitors act as effective pollinators. Sympatric populations of L. heterophyllum and L. parviflorum differ in floral traits that may affect assemblies of floral visitors. Visitation rates by non-Greya floral visitors were low, and the asymptotic number of visitor species was less than 20 species in all populations. Lithophragma species shared some of the visitors, with visitor assemblages differing between sites more for L. heterophyllum than for L. parviflorum. Pollination efficacy experiments showed that most visitors were poor pollinators. Single visits to flowers by this assemblage of species resulted in significantly higher seed set in Lithophragma heterophyllum (30.6 ± 3.9 SE) than in L. parviflorum (4.7 ± 3.4 SE). This difference was consistent between sites, suggesting that these visitors provide a better fit to the floral morphology of L. heterophyllum. Overall, none of the non-Greya visitors appears to be either sufficiently common or efficient as a pollinator to impose strong selection on any of these four Lithophragma populations in comparison with Greya, which occurs within almost all populations of these species throughout their geographic ranges

Virus-Induced Gene Silencing as a Tool for Comparative Functional Studies in Thalictrum

Perennial woodland herbs in the genus Thalictrum exhibit high diversity of floral morphology, including four breeding and two pollination systems. Their phylogenetic position, in the early-diverging eudicots, makes them especially suitable for exploring the evolution of floral traits and the fate of gene paralogs that may have shaped the radiation of the eudicots. A current limitation in evolution of plant development studies is the lack of genetic tools for conducting functional assays in key taxa spanning the angiosperm phylogeny. We first show that virus-induced gene silencing (VIGS) of a PHYTOENE DESATURASE ortholog (TdPDS) can be achieved in Thalictrum dioicum with an efficiency of 42% and a survival rate of 97%, using tobacco rattle virus (TRV) vectors. The photobleached leaf phenotype of silenced plants significantly correlates with the down-regulation of endogenous TdPDS (P<0.05), as compared to controls. Floral silencing of PDS was achieved in the faster flowering spring ephemeral T. thalictroides. In its close relative, T. clavatum, silencing of the floral MADS box gene AGAMOUS (AG) resulted in strong homeotic conversions of floral organs. In conclusion, we set forth our optimized protocol for VIGS by vacuum-infiltration of Thalictrum seedlings or dormant tubers as a reference for the research community. The three species reported here span the range of floral morphologies and pollination syndromes present in Thalictrum. The evidence presented on floral silencing of orthologs of the marker gene PDS and the floral homeotic gene AG will enable a comparative approach to the study of the evolution of flower development in this group

Policing the legume-Rhizobium symbiosis: a critical test of partner choice

In legume-Rhizobium symbioses, specialised soil bacteria fix atmospheric nitrogen in return for carbon. However, ineffective strains can arise, making discrimination essential. Discrimination can occur via partner choice, where legumes prevent ineffective strains from entering, or via sanctioning, where plants provide fewer resources. Several studies have inferred that legumes exercise partner choice, but the rhizobia compared were not otherwise isogenic. To test when and how plants discriminate ineffective strains we developed sets of fixing and non-fixing strains that differed only in the expression of nifH - essential for nitrogen fixation - and could be visualised using marker genes. We show that the plant is unable to select against the non-fixing strain at the point of entry, but that non-fixing nodules are sanctioned. We also used the technique to characterise mixed nodules (containing both a fixing and a non-fixing strain), whose frequency could be predicted using a simple diffusion model. We discuss that sanctioning is likely to evolve in preference to partner choice in any symbiosis where partner quality cannot be adequately assessed until goods or services are actively exchanged

Microgeographical, inter-individual, and intra-individual variation in the flower characters of Iberian pear Pyrus bourgaeana (Rosaceae)

Flower characteristics have been traditionally considered relatively constant within species. However, there are an increasing number of examples of variation in flower characteristics. In this study, we examined the variation in attracting and rewarding flower characters at several ecological levels in a metapopulation of Pyrus bourgaeana in the Doñana area (SW Spain). We answered the following questions: what are the variances of morphological and nectar characters of flowers? How important are intra-individual and inter-individual variance in flower characters? Are there microgeographical differences in flower characters? And if so, are they consistent between years? In 2008 and 2009, we sampled flowers of 72 trees from five localities. For six flower morphological and two nectar characteristics, we calculated coefficients of variation (CV). The partitioning of total variation among-localities, among-individuals, and within-individuals was estimated. To analyze differences among localities and their consistency between years, we conducted generalized linear mixed models. The CVs of nectar characters were always higher than those of morphological characters. As expected, inter-individual variation was the main source of variation of flower morphology, but nectar characters had significant variation at both intra- and inter-individual levels. For most floral traits, there were no differences among localities. Our study documents that variation is a scale-dependent phenomenon and that it is essential to consider intra- and inter-individual variance when investigating the causes and consequences of variation. It also shows that single year studies of floral characters should be viewed with caution