PHYLOGENY AND THE EVOLUTION OF HOST PLANT ASSOCIATIONS IN THE LEAF BEETLE GENUS OPHRAELLA (COLEOPTERA, CHRYSOMELIDAE)

The carboxypeptidase B and carbonic anhydrase genes play a reproductive regulatory role during multiple matings in Ophraella communa

Seminal fluid proteins (SFPs) are key factors in sexual reproduction and are transferred to females during mating with sperm. SFPs have a nutritional value because they protect and activate sperm storage and release to optimize fecundity. Multiple matings promote ovipositioning in several insect species. Therefore, insects may obtain more SFP through multiple matings to maximize reproduction, but this process has not yet been clearly confirmed. Here, the relationship between multiple matings and the SFPs in Ophraella communa (Coleoptera: Chrysomelidae), a biological control agent of the common ragweed Ambrosia artemisiifolia (Asterales: Asteraceae), was studied. Multiple matings significantly increased female fecundity and ovary egg deposition. Carboxypeptidase B (OcCpb) and carbonic anhydrase (OcCa) genes were identified as putative SFP genes in O. communa and they showed strong male-biased expression. Additionally, OcCpb and OcCa expression was upregulated in the bursa copulatrix of mating females compared to that in virgin females, but their expression gradually declined after copulation. Furthermore, OcCpb and OcCa knockdown in males led to a decrease in insect fecundity compared to that in the control. The reproductive tract of females mated with dsRNA-treated males was dissected and observed and, notably, the ovaries produced significantly fewer eggs. These data suggest that OcCpb and OcCa play regulatory roles during multiple matings in O. communa.

Host shifts in economically significant fruit flies (Diptera: Tephritidae) with high degree of polyphagy

Insects tend to feed on related hosts. Coevolution tends to be dominated by interactions resulting from plant chemistry in defense strategies, and evolution of secondary metabolisms being in response to insect herbivory remains a classic explanation of coevolution. The present study examines whether evolutionary constraints existing in host associations of economically important fruit flies in the species-rich tribe Dacini (Diptera: Tephritidae) and to what extent these species have evolved specialized dietary patterns. We found a strong effect of host phylogeny on associations on the 37 fruit flies tested, although the fruit fly species feeding on ripe commercially grown fruits that lost the toxic compounds after long-term domestication are mostly polyphagous. We assessed the phylogenetic signal of host breadth across the fruit fly species, showing that the results were substantially different depending on partition levels. Further, we mapped main host family associations onto the fruit fly phylogeny and Cucurbitaceae has been inferred as the most likely ancestral host family for Dacini based on ancestral state reconstruction.

Linking ecology, morphology, and metabolism: Niche differentiation in sympatric populations of closely related species of the genus Littorina (Neritrema)

Divergence of ecological niches in phylogenetically closely related species indicates the importance of ecology in speciation, especially for sympatric species are considered. Such ecological diversification provides an advantage of alleviating interspecies competition and promotes more efficient exploitation of environmental resources, thus being a basis for ecological speciation. We analyzed a group of closely related species from the subgenus Neritrema (genus Littorina, Caenogastropoda) from the gravel-bouldery shores. In two distant sites at the Barents and Norwegian Sea, we examined the patterns of snail distribution during low tide (quantitative sampling stratified by intertidal level, presence of macrophytes, macrophyte species, and position on them), shell shape and its variability (geometric morphometrics), and metabolic characteristics (metabolomic profiling). The studied species diversified microbiotopes, which imply an important role of ecological specification in the recent evolution of this group. The only exception to this trend was the species pair L. arcana / L. saxatilis, which is specifically discussed. The ecological divergence was accompanied by differences in shell shape and metabolomic characteristics. Significant differences were found between L. obtusata versus L. fabalis and L. saxatilis / L. arcana versus L. compressa both in shell morphology and in metabolomes. L. saxatilis demonstrated a clear variability depending on intertidal level which corresponds to a shift in conditions within the occupied microhabitat. Interestingly, the differences between L. arcana (inhabiting the upper intertidal level) and L. compressa (inhabiting the lower one) were analogous to those between the upper and lower fractions of L. saxatilis. No significant level-dependent changes were found between the upper and lower fractions of L. obtusata, most probably due to habitat amelioration by fucoid macroalgae. All these results are discussed in the contexts of the role of ecology in speciation, ecological niche dynamics and conservatism, and evolutionary history of the Neritrema species.

Genome Assembly of the Ragweed Leaf Beetle: A Step Forward to Better Predict Rapid Evolution of a Weed Biocontrol Agent to Environmental Novelties

Rapid evolution of weed biological control agents (BCAs) to new biotic and abiotic conditions is poorly understood and so far only little considered both in pre-release and post-release studies, despite potential major negative or positive implications for risks of nontargeted attacks or for colonizing yet unsuitable habitats, respectively. Provision of genetic resources, such as assembled and annotated genomes, is essential to assess potential adaptive processes by identifying underlying genetic mechanisms. Here, we provide the first sequenced genome of a phytophagous insect used as a BCA, that is, the leaf beetle Ophraella communa, a promising BCA of common ragweed, recently and accidentally introduced into Europe. A total 33.98 Gb of raw DNA sequences, representing ∼43-fold coverage, were obtained using the PacBio SMRT-Cell sequencing approach. Among the five different assemblers tested, the SMARTdenovo assembly displaying the best scores was then corrected with Illumina short reads. A final genome of 774 Mb containing 7,003 scaffolds was obtained. The reliability of the final assembly was then assessed by benchmarking universal single-copy orthologous genes (>96.0% of the 1,658 expected insect genes) and by remapping tests of Illumina short reads (average of 98.6 ± 0.7% without filtering). The number of protein-coding genes of 75,642, representing 82% of the published antennal transcriptome, and the phylogenetic analyses based on 825 orthologous genes placing O. communa in the monophyletic group of Chrysomelidae, confirm the relevance of our genome assembly. Overall, the genome provides a valuable resource for studying potential risks and benefits of this BCA facing environmental novelties.

Evolution of host plant use and diversification in a species complex of parasitic weevils (Coleoptera: Curculionidae)

Weevils (Coleoptera: Curculionoidea) represent one of the most diverse groups of organisms on Earth; interactions with their host plants have been recognized to play a central role in their remarkable diversity, yet the exact mechanisms and factors still remain poorly understood. Using phylogenetic comparative analyses, here we investigate the evolution of host use and its possible role in diversification processes of Rhinusa and Gymnetron, two closely related groups of weevils that feed and develop inside plant tissues of hosts within the families Scrophulariaceae and Plantaginaceae. We found strong evidence for phylogenetic conservatism of host use at the plant family level, most likely due to substantial differences in the chemical composition of hosts, reducing the probability of shifts between host families. In contrast, the use of different plant organs represents a more labile ecological trait and ecological niche expansion that allows a finer partitioning of resources. Rhinusa and Gymnetron weevils initially specialized on plants within Scrophulariaceae and then shifted to the closely related Plantaginaceae; likewise, a gall inducing behavior evolved from non-galler weevils, possibly in response to resource competition, as galls facilitate larval development by providing enhanced nutrition and a favorable microhabitat. Results from trait-dependent diversification analyses suggest that both use of hosts within Plantaginaceae and parasitism on fruits and seed capsules are associated with enhanced diversification of Rhinusa and Gymnetron via low extinction rates. Our study provides quantitative evidence and insights on the ecological factors that can promote diversification in phytophagous insects that feed and develop inside plant tissues.

Barcoding of Chrysomelidae of Euro-Mediterranean area: efficiency and problematic species

Leaf beetles (Coleoptera: Chrysomelidae), with more than 37,000 species worldwide and about 2,300 in the Euro-Mediterranean region, are an ecological and economical relevant family, making their molecular identification of interest also in agriculture. This study, part of the Mediterranean Chrysomelidae Barcoding project (www.c-bar.org), aims to: (i) develop a reference Cytochrome c oxidase I (COI) library for the molecular identification of the Euro-Mediterranean Chrysomelidae; (ii) test the efficiency of DNA barcoding for leaf beetles identification; (iii) develop and compare optimal thresholds for distance-based identifications estimated at family and subfamily level, minimizing false positives and false negatives. Within this study, 889 COI nucleotide sequences of 261 species were provided; after the inclusion of information from other sources, a dataset of 7,237 sequences (542 species) was analysed. The average intra-interspecific distances were in the range of those recorded for Coleoptera: 1.6–24%. The estimated barcoding efficiency (~94%) confirmed the usefulness of this tool for Chrysomelidae identification. The few cases of failure were recorded for closely related species (e.g., Cryptocephalus marginellus superspecies, Cryptocephalus violaceus - Cryptocephalus duplicatus and some Altica species), even with morphologically different species sharing the same COI haplotype. Different optimal thresholds were achieved for the tested taxonomic levels, confirming that group-specific thresholds significantly improve molecular identifications.

Ambrosia artemisiifolia control in agricultural areas: effect of grassland seeding and herbivory by the exotic leaf beetle Ophraella communa

Ambrosiaartemisiifolia(common ragweed) is an invasive species native to North America and was accidentally introduced to Europe in the 19thcentury. Widespread in disturbed habitats, it is a major weed in spring-sown crops and it causes serious allergic rhinitis and asthma due to its allergenic pollen. The aim of this research was to analyse the effects of both competitive vegetation and herbivory byOphraellacommunato controlA.artemisiifoliain an agricultural area of north-western Italy. Hayseed mixtures, both over-seeded over the resident plant community or after ploughing, when seeded before the winter season, were able to suppress the establishment ofA.artemisiifoliaas well as to reduce its growth in terms of plant height and inflorescence size. Defoliation ofA.artemisiifoliabyO.communaat the end of the growing season was conspicuous but most of the plants still produced flowers and seeds. However, significantO.communaattack was recorded for reproductive structures. As for non-target species,O.communawas mainly recorded on Asteraceae, with low density and low degree of damage. Reduction of inflorescence size due to competitive vegetation and damage to male flowers byO.communamay diminish the amount of available pollen. The results of this study may be useful for the implementation of management measures to controlA.artemisiifoliain agricultural areas using mixtures of native species.

Ambrosia artemisiifolia control in agricultural areas: effect of grassland seeding and herbivory by the exotic leaf beetle Ophraella communa

Ambrosiaartemisiifolia(common ragweed) is an invasive species native to North America and was accidentally introduced to Europe in the 19thcentury. Widespread in disturbed habitats, it is a major weed in spring-sown crops and it causes serious allergic rhinitis and asthma due to its allergenic pollen. The aim of this research was to analyse the effects of both competitive vegetation and herbivory byOphraellacommunato controlA.artemisiifoliain an agricultural area of north-western Italy. Hayseed mixtures, both over-seeded over the resident plant community or after ploughing, when seeded before the winter season, were able to suppress the establishment ofA.artemisiifoliaas well as to reduce its growth in terms of plant height and inflorescence size. Defoliation ofA.artemisiifoliabyO.communaat the end of the growing season was conspicuous but most of the plants still produced flowers and seeds. However, significantO.communaattack was recorded for reproductive structures. As for non-target species,O.communawas mainly recorded on Asteraceae, with low density and low degree of damage. Reduction of inflorescence size due to competitive vegetation and damage to male flowers byO.communamay diminish the amount of available pollen. The results of this study may be useful for the implementation of management measures to controlA.artemisiifoliain agricultural areas using mixtures of native species.

How many genera and species of Galerucinaes. str. do we know? Updated statistics (Coleoptera, Chrysomelidae)

Galerucinae s. str. is a rich group of leaf beetles. A new, up-to date checklist of Galerucinae genera in the world is provided, including the number of valid species of each genus. Genera and species were counted in literature published before the end of 2016. In summary, 7145 species (7132 recent, 13 fossils) and 192 subspecies from 543 genera (542 recent, 1 fossil) were quantified in Galerucinae s. str. In comparison with the previous catalogue of worldwide Galerucinae (Wilcox 1971-1973), an additional 91 valid genera, 1341 valid species (1337 recent, 4 fossils) and 38 subspecies have been published; 43 genera were synonymized, four genera were transferred into Alticini, two subgenera were elevated to genus rank, and one genus was downgraded to subgenus rank. The updated list of references to taxonomic publications on Galerucinae s. str. from the period 1971-2016 is provided.

PENGUINS, PETRELS, AND PARSIMONY: DOES CLADISTIC ANALYSIS OF BEHAVIOR REFLECT SEABIRD PHYLOGENY?

Whether or not behavior accurately reflects evolutionary relationships (phylogeny) has been hotly debated by ethologists and comparative psychologists. Previous studies attempting to resolve this question have generally lacked a quantitative, phylogenetic approach. In this study we used behavior and life-history (BLH) information (72 characters) to generate phylogenetic trees for 18 seabird species (albatrosses, petrels, and penguins). We compared these trees with trees obtained from isozyme electrophoretic analysis of blood proteins (15 loci and 98 electromorphs) and partial mitochondrial 12S ribosomal DNA sequences (381 base pairs). Cladistic analysis of the BLH data set generated three MP trees (tree length = 243, CI = 0.52, RI = 0.57) with significant cladistic structure. The BLH characters were classified into four types (foraging, agonistic, reproductive, and life history) and levels of homoplasy for each type were measured. No significant differences were found among these categories. The BLH trees were shown to be significantly more congruent with the electrophoretic and 12S sequence trees than expected by chance. This indicates that seabird BLH data contains phylogenetic signal. Areas of incongruence between BLH trees and a phylogeny generated by combining the data sets were predicted to result from ecological constraints that did not covary with phylogeny. These predictions were supported by the results of a concentrated changes test. This study found that this BLH data set was no more homoplasious than molecular data and that BLH trees were significantly congruent with molecular trees.

EVOLUTION OF PLANT POLLINATION SYSTEMS: HYPOTHESES AND TESTS WITH THE NEOTROPICAL VINE DALECHAMPIA

The results of pollination and mating-system studies were integrated with a phylogenetic study of 40 Neotropical species of Dalechampia L. (Euphorbiaceae) to reconstruct the history of evolutionary change in pollination systems. The results of this analysis were treated as a hypothesis and tested for circularity problems and robustness in the face of changes in the data set. The historical hypothesis was used to make specific predictions about details of pollination ecology and reward biochemistry; the predictions were supported by independent observations. I conclude that pollination systems in Dalechampia have been evolutionarily labile, relative to most morphological features, with repeated parallelisms and reversals. Transitions among the three pollination systems evolved by Dalechampia (pollination by resin-collecting bees, fragrance-collecting male euglossine bees, and pollen-collecting bees) have been facilitated by biochemical exaptation (preadaptation). Pollination by male euglossine bees is relatively rare in the genus but has originated independently three to four times. In contrast, pollination by resin-collecting female bees is very common, but has originated only once. Eighty-six to 97% of transitions between pollination systems involved an intermediate phase during which both old and new pollinators were effective, but 3 to 14% of transitions may have been "instantaneous," lacking the intermediate phase. Clades of species secreting resin rewards are about 10 times as species rich as clades of species secreting fragrance rewards; circumstantial evidence suggests that different extinction rates may be responsible for this difference. Relatively allogamous (cross-pollinating) species have evolved from more autogamous (self-pollinating) species up to 13 times, and autogamous species have evolved from more allogamous ones up to 11 times. Species occurring in disturbed habitats are facultatively autogamous, whereas species of undisturbed habitats are often highly allogamous.

SEARCHING FOR EVOLUTIONARY PATTERNS IN THE SHAPE OF A PHYLOGENETIC TREE

If all species in a clade are equally likely to speciate or become extinct, then highly symmetric and highly asymmetric phylogenetic trees are unlikely to result. Variation between species in speciation and extinction rates can cause excessive asymmetry. We developed six non-parametric statistical tests that test for nonrandom patterns of branching in any bifurcating tree. The tests are demonstrated by applying them to two published phylogenies for genera of beetles. Comparison of the power of the six statistics under a simple model of biased speciation suggests which of them may be most useful for detecting nonrandom tree shapes.

CENTRAL MOMENTS AND PROBABILITY DISTRIBUTION OF COLLESS'S COEFFICIENT OF TREE IMBALANCE

The great increase in the number of phylogenetic studies of a wide variety of organisms in recent decades has focused considerable attention on the balance of phylogenetic trees-the degree to which sister clades within a tree tend to be of equal size-for at least two reasons: (1) the degree of balance of a tree may affect the accuracy of estimates of it; (2) the degree of balance, or imbalance, of a tree may reveal something about the macroevolutionary processes that produced it. In particular, variation among lineages in rates of speciation or extinction is expected to produce trees that are less balanced than those that result from phylogenetic evolution in which each extant species of a group has the same probability of speciation or extinction. Several coefficients for measuring the balance or imbalance of phylogenetic trees have been proposed. I focused on Colless's coefficient of imbalance (7) for its mathematical tractability and ease of interpretation. Earlier work on this statistic produced exact methods only for calculating the expected value. In those studies, the variance and confidence limits, which are necessary for testing the departure of observed values of I from the expected, were estimated by Monte Carlo simulation. I developed recursion equations that allow exact calculation of the mean, variance, skewness, and complete probability distribution of I for two different probability-generating models for bifurcating tree shapes. The Equal-Rates Markov (ERM) model assumes that trees grow by the random speciation and extinction of extant species, with all species that are extant at a given time having the same probability of speciation or extinction. The Equal Probability (EP) model assumes that all possible labeled trees for a given number of terminal taxa have the same probability of occurring. Examples illustrate how these theoretically derived probabilities and parameters may be used to test whether the evolution of a monophyletic group or set of monophyletic groups has proceeded according to a Markov model with equal rates of speciation and extinction among species, that is, whether there has been significant variation among lineages in expected rates of speciation or extinction.

GENETIC CONSTRAINTS AND THE PHYLOGENY OF INSECT-PLANT ASSOCIATIONS: RESPONSES OF OPHRAELLA COMMUNA (COLEOPTERA: CHRYSOMELIDAE) TO HOST PLANTS OF ITS CONGENERS

We ask whether patterns of genetic variation in a phytophagous insect's responses to potential host plants shed light on the phylogenetic history of host association. Ophraella communa feeds chiefly, and in eastern North America exclusively, on Ambrosia (Asteraceae: Ambrosiinae). Using mostly half-sib breeding designs, we screened for genetic variation in feeding responses to and larval survival on its own host and on seven other plants that are hosts (or, on one case, closely related to the host) of other species of Ophraella. We found evidence for genetic variation in feeding responses to five of the seven test plants, other than the natural host. We found no evidence of genetic variation in feeding responses to two plant species, nor in capacity for larval survival on six. These results imply constraints on the availability of genetic variation; however, little evidence for constraints in the form of negative genetic correlations was found. These results are interpreted in the context of a provisional phylogeny of, and a history of host shifts within, the genus. Ophraella communa does not present evidence of genetic variation in its ability to feed and/or survive on Solidago, even though it is probably descended from a lineage that fed on Solidago or related plants, possibly as recently as 1.9 million years ago. Genetic variation in performance on this plant may have been lost. Based on evidence for genetic variation and on mean performance, by far the greatest potentiality for adaptation to a congener's host was evinced in responses to Iva frutescens, which not only is related and chemically similar to Ambrosia, but also is the host of a closely related species of Ophraella that may have been derived from an Ambrosia-associated ancestor. Genetic variation in O. communa's capacity to feed and/or survive on its congeners' hosts is less evident for plants that do not represent historically realized host shifts (with one exception) than for those that may (but see Note Added in Proof). The results offer some support for the hypothesis that the evolution of host shifts has been guided in part by constrained genetic variation.

EVOLUTION OF DIFFERENT GALL TYPES IN WILLOW-FEEDING SAWFLIES (HYMENOPTERA: TENTHREDINIDAE)

The sawflies that feed on the plant family Salicaceae can be divided into eight informal groups based on larval feeding habit or gall type: (1) species with free-living larvae; (2) leaf folders; (3) leaf blade gallers; (4) apical leaf gallers; (5) basal leaf gallers; (6) midrib and petiole gallers; (7) stem gallers; and (8) bud gallers. It has been proposed that the galling habit evolved from free-living larvae via leaf folders, and that the different gall types evolved gradually in the sequence mentioned above. Thus, the galling site would have "wandered" from the leaf margin toward the stem as a result of gradual changes in oviposition site preference. Allozyme data from eight informative loci were used to reconstruct the phylogeny of 18 representative sawfly species. The results suggest that indeed leaf folders seem to be a basal group; leaf blade gallers evolved independently of the other true gallers; apical and basal leaf gallers are not the ancestors of petiole and bud gallers, but they may share a common galling ancestor; bud gallers evolved from midrib/petiole gallers; and stem gallers are polyphyletic. The cause for the observed wandering of the galling site could be intraspecific competition due to a possible "nutrient shading effect" of galls situated closer to the host plant's main vascular system.

TESTS OF INBREEDING EFFECTS ON HOST-SHIFT POTENTIAL IN THE PHYTOPHAGOUS BEETLE OPHRAELLA COMMUNA

Although inbreeding, on average, decreases additive genetic variance, some inbred populations may show an increase in phenotypic variance for some characters. In those populations with increased phenotypic variance, character changes by peak shifts may occur because of the effects of the higher variance on the adaptive landscape. A population's increased phenotypic variance may place it in the domain of attraction of a new adaptive peak or increase the likelihood of a selection-driven peak shift as the landscape of mean fitness flattens. The focus of this study was to test for increased variance, in inbred populations, in a behavioral character involved in adaptive diversification and probably speciation. We examined the effect of inbreeding on feeding responses of the leaf beetle Ophraella communa in a series of inbred lineages across a range of levels of inbreeding (f = 0.25, 0.375, 0.5). We measured the feeding response of inbred lineages of O. communa on its normal host, Ambrosia artemisiifolia, and on two novel plants, Chrysopsis villosa and Iva frutescens, that are the hosts of other Ophraella species. The results show that feeding responses on the different plants are not correlated, indicating that the feeding responses to the different plants are to some degree genetically independent. Despite apparent genetic variation in lineage feeding responses, we could not statistically demonstrate increases in phenotypic variance within the lineages. Thus, the experimental results do not support the idea that host shifts in this beetle evolved by peak shifts in bottlenecked populations.

PHYLOGENETIC ANALYSIS OF BREEDING SITE USE AND α-AMANITIN TOLERANCE WITHIN THE DROSOPHILA QUINARIA SPECIES GROUP

The Drosophila quinaria group is unusual within the genus in that it comprises both mycophagous and nonmycophagous species. DNA sequence data from three regions of the mitochondrial genome were used to infer relationships among four mycophagous species and three that breed on decaying water plants. Phylogenetic analysis of these species show that breeding in mushrooms and tolerance of high levels of α-amanitin were the ancestral states within the group. Thus, breeding in decaying water plants and intolerance of α-amanitin are derived conditions. We also found that the D. quinaria species group does not comprise separate mycophagous and nonmycophagous clades, but rather that (1) the shift from mushrooms to decaying plants occurred on at least two occasions; or (2) mycophagy reevolved within a lineage that had previously shifted to breeding on plants. The correlation between mycophagy and α-amanitin tolerance is perfect across the species we have examined, indicating that there is no detectable time lag between an ecological shift to a new breeding site and correlated changes in biochemical adaptation. The genetic distance between the mycophagous D. recens and the nonmycophagous D. quinaria indicates that these species split only about 1 M.Y.B.P. In terms of α-amanitin tolerance, D. recens and D. quinaria are typical of other ecologically similar species within the group. Thus, evolutionary changes in α-amanitin tolerance can evidently occur on the order of about 1 million yr. Our data also indicate that, in comparison to other groups of Drosophila, the quinaria species group may be undergoing an adaptive radiation.

Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetle's introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.

Inter- and Intrapopulation Variability in the Composition of Larval Defensive Secretions of Willow-Feeding Populations of the Leaf Beetle Chrysomela lapponica

We explored the inter- and intrapopulation variability in the larval defensive chemistry of the leaf beetle Chrysomela lapponica with respect to the salicylic glycoside (SG) content of its host species. Secretions of larvae from three populations associated in nature with SG-poor willows contained nearly twice as many components and 40-fold higher concentrations of autogenously produced isobutyrates and 2-methylbutyrates than secretions of larvae from three populations associated with SG-rich willows, which in turn had 200-fold higher concentrations of host-derived salicylaldehyde. Reciprocal transfer experiments showed that the larvae from populations associated with SG-rich willows did not produce appreciable amounts of butyrates on either SG-rich or SG-poor willows, while populations feeding on several SG-poor willow species retained the ability for efficient sequestration of SGs, along with their ability to produce high amounts of isobutyrates and 2-methylbutyrates. Only the populations associated with SG-poor willows demonstrated among-family variation in the composition of defensive secretion and differential responses of individual families to willows with alternative SG levels, which can be seen as the prerequisites for shifting to novel hosts. These non-specialized populations show a dual defensive strategy, which corresponds to the ancestral state of this species, while populations that fully depend on host-derived toxins (feeding on SG-rich willows) or have lost the ability to produce salicylaldehyde (feeding on birches) are most deviant from the ancestral state. The results indicate that defensive strategies may differ between populations within a species, and suggest that this variation reduces extinction risks and maintains the high ecological diversity and wide distribution of C. lapponica.

Chemical similarity between historical and novel host plants promotes range and host expansion of the mountain pine beetle in a naïve host ecosystem

Host plant secondary chemistry can have cascading impacts on host and range expansion of herbivorous insect populations. We investigated the role of host secondary compounds on pheromone production by the mountain pine beetle (Dendroctonus ponderosae) (MPB) and beetle attraction in response to a historical (lodgepole pine, Pinus contorta var. latifolia) and a novel (jack pine, Pinus banksiana) hosts, as pheromones regulate the host colonization process. Beetles emit the same pheromones from both hosts, but more trans-verbenol, the primary aggregation pheromone, was emitted by female beetles on the novel host. The phloem of the novel host contains more α-pinene, a secondary compound that is the precursor for trans-verbenol production in beetle, than the historical host. Beetle-induced emission of 3-carene, another secondary compound found in both hosts, was also higher from the novel host. Field tests showed that the addition of 3-carene to the pheromone mixture mimicking the aggregation pheromones produced from the two host species increased beetle capture. We conclude that chemical similarity between historical and novel hosts has facilitated host expansion of MPB in jack pine forests through the exploitation of common host secondary compounds for pheromone production and aggregation on the hosts. Furthermore, broods emerging from the novel host were larger in terms of body size.

Phenylpropenoid phenolics in sweetbay magnolia as chemical determinants of host use in saturniid silkmoths (Callosamia)

Host plant chemistry can play an important role in determining the evolution of host use patterns in herbivorous insects by influencing host selection, consumption, and assimilation of foliage. We used a comparative approach to test the hypothesis that specialist herbivores of sweetbay magnolia (Magnolia virginiana) possess adaptations that allow them to overcome chemical deterrents or toxins that prevent herbivory by unadapted herbivores. The three silkmoth species in the genusCallosamia can be collectively regarded as specialists on magnoliaceous hosts; however, only the monophagousC. securifera is able to complete development on sweetbay magnolia, its natural host. In laboratory assays with intact foliage, bothC. angulifera and the polyphagousC. promethea fed readily on sweetbay but were unable to survive past the third instar. Two neolignan compounds, magnolol and a biphenyl ether, were found to reduce neonate growth and survival of unadapted herbivore species when painted on acceptable host leaves at concentrations similar to those found in sweetbay foliage. Both compounds significantly reduced neonate growth ofC. angulifera andC. promethea but had no effect on the sweetbay specialist,C. securifera, indicating that the latter species possesses the unique ability in the genus to tolerate, metabolize, or otherwise circumvent the phytochemical defenses of this host.

WEEVILS AND PLANTS: PHYLOGENETIC VERSUS ECOLOGICAL MEDIATION OF EVOLUTION OF HOST PLANT ASSOCIATIONS IN CURCULIONINAE (COLEOPTERA: CURCULIONIDAE)

A great proportion of biodiversity is accounted for by organisms, particularly insects, intimately associated with plants. Knowing whether ecological or phylogenetic factors chiefly influence the evolution of host plant associations is essential to understanding speciation in, and therefore factors influencing diversity of, phytophagous insects. Through examination of known host plant associations in Curculioninae and comparison with available reconstructed phylogenetic relationships of certain taxa of Curculioninae, little, if any, evidence for cospeciation (parallel cladogenesis) is found. In curculionine taxa where sufficient host plant and/or phylogenetic data are available, weevil species are narrowly to broadly oligophagous; a number of related weevil species are associated with a single host plant species; many weevil genera have host plant ranges spanning distantly related plant taxa; and available weevil reconstructed phylogenies are not concordant with plant relationships. Rather, for at least some weevil taxa, evolution appears to be mediated by one or more of a variety of strictly ecological factors, particularly habitat associations. General applications of these results include biological control, pollination biology, conservation and restoration biology, and use of patterns in insect – host plant associations to resolve problems in plant classification.

Host shifts from Lamiales to Brassicaceae in the sawfly genus Athalia

Plant chemistry can be a key driver of host shifts in herbivores. Several species in the sawfly genus Athalia are important economic pests on Brassicaceae, whereas other Athalia species are specialized on Lamiales. These host plants have glucosides in common, which are sequestered by larvae. To disentangle the possible direction of host shifts in this genus, we examined the sequestration specificity and feeding deterrence of iridoid glucosides (IGs) and glucosinolates (GSs) in larvae of five species which either naturally sequester IGs from their hosts within the Plantaginaceae (Lamiales) or GSs from Brassicaceae, respectively. Furthermore, adults were tested for feeding stimulation by a neo-clerodane diterpenoid which occurs in Lamiales. Larvae of the Plantaginaceae-feeders did not sequester artificially administered p-hydroxybenzylGS and were more deterred by GSs than Brassicaceae-feeders were by IGs. In contrast, larvae of Brassicaceae-feeders were able to sequester artificially administered catalpol (IG), which points to an ancestral association with Lamiales. In line with this finding, adults of all tested species were stimulated by the neo-clerodane diterpenoid. Finally, in a phylogenetic tree inferred from genetic marker sequences of 21 Athalia species, the sister species of all remaining 20 Athalia species also turned out to be a Lamiales-feeder. Fundamental physiological pre-adaptations, such as the establishment of a glucoside transporter, and mechanisms to circumvent activation of glucosides by glucosidases are therefore necessary prerequisites for successful host shifts between Lamiales and Brassicaceae.

Codivergence and multiple host species use by fig wasp populations of the Ficus pollination mutualism

BACKGROUND

The interaction between insects and plants takes myriad forms in the generation of spectacular diversity. In this association a species host range is fundamental and often measured using an estimate of phylogenetic concordance between species. Pollinating fig wasps display extreme host species specificity, but the intraspecific variation in empirical accounts of host affiliation has previously been underestimated. In this investigation, lineage delimitation and codiversification tests are used to generate and discuss hypotheses elucidating on pollinating fig wasp associations with Ficus.

RESULTS

Statistical parsimony and AMOVA revealed deep divergences at the COI locus within several pollinating fig wasp species that persist on the same host Ficus species. Changes in branching patterns estimated using the generalized mixed Yule coalescent test indicated lineage duplication on the same Ficus species. Conversely, Elisabethiella and Alfonsiella fig wasp species are able to reproduce on multiple, but closely related host fig species. Tree reconciliation tests indicate significant codiversification as well as significant incongruence between fig wasp and Ficus phylogenies.

CONCLUSIONS

The findings demonstrate more relaxed pollinating fig wasp host specificity than previously appreciated. Evolutionarily conservative host associations have been tempered by horizontal transfer and lineage duplication among closely related Ficus species. Independent and asynchronistic diversification of pollinating fig wasps is best explained by a combination of both sympatric and allopatric models of speciation. Pollinator host preference constraints permit reproduction on closely related Ficus species, but uncertainty of the frequency and duration of these associations requires better resolution.

The effects of disturbance and enemy exclusion on performance of an invasive species, common ragweed, in its native range

Common ragweed (Ambrosia artemisiifolia) is an abundant weed in its native North America, despite supporting a wide range of natural enemies. Here, we tested whether these enemies have significant impacts on the performance of this plant in its native range. We excluded enemies from the three principal life-history stages (seed, seedling, and adult) of this annual in a series of field experiments; at the adult stage, we also manipulated soil disturbance and conspecific density. We then measured the consequences of these treatments for growth, survival, and reproduction. Excluding fungi and vertebrate granivores from seeds on the soil surface did not increase germination relative to control plots. Seedling survivorship was only slightly increased by the exclusion of molluscs and other herbivores. Insecticide reduced damage to leaves of adult plants, but did not improve growth or reproduction. Growth and survivorship of adults were strongly increased by disturbance, while higher conspecific density reduced performance in disturbed plots. These results indicate ragweed is insensitive to attack by many of its natural enemies, helping to explain its native-range success. In addition, they suggest that even though ragweed lost most of its insect folivores while invading Europe, escape from these enemies is unlikely to have provided a significant demographic advantage; instead, disturbance is likely to have been a much more important factor in its invasion. Escape from enemies should not be assumed to explain the success of exotic species unless improved performance also can be demonstrated; native-range studies can help achieve this goal.

To speciate, or not to speciate? Resource heterogeneity, the subjectivity of similarity, and the macroevolutionary consequences of niche-width shifts in plant-feeding insects

Coevolutionary studies on plants and plant-feeding insects have significantly improved our understanding of the role of niche shifts in the generation of new species. Evolving plant lineages essentially constitute moving islands and archipelagoes in resource space, and host shifts by insects are usually preceded by colonizations of novel resources. Critical to hypotheses concerning ecological speciation is what happens immediately before and after colonization attempts: if an available plant is too similar to the current host(s), it simply will be incorporated into the existing diet, but if it is too different, it will not be colonized in the first place. It thus seems that the probability of speciation is maximized when alternative hosts are at an 'intermediate' distance in resource space. In this review, I wish to highlight the possibility that resource similarity and, thus, the definition of 'intermediate', are subjective concepts that depend on the herbivore lineage's tolerance to dietary variation. This subjectivity of similarity means that changes in tolerance can either decrease or increase speciation probabilities depending on the distribution of plants in resource space: insect lineages with narrow tolerances are likely to speciate by 'island-hopping' on young, species-rich plant groups, whereas more generalized lineages could speciate by shifting among resource archipelagoes formed by higher plant taxa. Repeated and convergent origins of traits known to broaden or to restrict host-plant use in multiple different insect groups provide opportunities for studying how tolerance and resource heterogeneity may interact to determine speciation rates.

Quackgrass- and ryegrass-adapted populations of the cereal rust mite, Abacarus hystrix (Acari: Eriophyidae), differ in their potential for wheat, Triticum aestivum, colonization

The cereal rust mite, Abacarus hystrix, is one of the most notable among mites causing losses in cultivated grasslands. It is one of a few eriophyoid species for which a broad host range has been reported. Recent studies, however, have shown that host specialization is very likely in this species. For two populations of A. hystrix (one inhabiting perennial ryegrass, the second inhabiting quackgrass), host-associated differences correlated with strong host fidelity, distinct phenotypes and reproductive barriers have been found. In the present study, the ability of wheat colonization by quackgrass- and ryegrass-adapted cereal rust mite was studied. The hypothesis that the potential for wheat colonization by the quackgrass strain is more likely was tested by comparing the colonization performance (assessed by female survival and fecundity) of quackgrass- and ryegrass-associated A. hystrix on their familiar hosts and on wheat. The ryegrass population had no success in wheat colonization (expressed by extremely low fecundity and female survival). Fecundity and survival of quackgrass strain were similar on wheat and the familiar host, or even higher on wheat. Phylogenetic similarity of quackgrass and wheat is discussed as a possible factor that might influence such patterns of host colonization. Since A. hystrix is the only vector of the ryegrass mosaic virus (RgMV), the presented results may be helpful in explaining the inability of RgMV to successfully infest wheat. The conclusions are that (i) quackgrass- and ryegrass-adapted strains of the cereal rust mite have different physiological host ranges and (ii) phylogenetic relationships between host plant species appear to be drivers for host specialization in this mite species.

Historical contingency and animal diets: the origins of egg eating in snakes

Evolutionary changes in animal diets must often begin through the inclusion of a novel food type as a minor component of the diet. An aspect of this initial change that has rarely been studied is the relationship between the existing diet and the use of specific novel foods. We used comparative analyses to test the hypothesis that, in snakes, feeding on squamate (lizard and snake) eggs or bird eggs--items that represent evolutionarily derived and, in most cases, minor components of the diet--is associated with feeding on squamates or birds, respectively. Phylogenetic concentrated-changes tests indicate a significant tendency for predation on eggs to arise in snake lineages characterized by feeding on the corresponding animals. These results also generally hold for analyses including only snake species that are likely to encounter eggs and are large enough to ingest them. The inferred histories of specialized egg eaters also support the hypothesis. Because snakes often use chemical cues to recognize prey, the observed phylogenetic patterns might be explained by chemical similarities between eggs and adult animals. Our results suggest broad effects of predispositions on snake diets and thus illustrate how historical contingencies can shape the ecology of organisms.