HOST-PLANT RELATIONSHIPS IN THE PAPILIONIDAE (LEPIDOPTERA): PARALLEL CLADOGENESIS OR COLONIZATION?

Identification and in vivo functional analysis of furanocoumarin-responsive cytochrome P450s in a Rutaceae-feeding Papilio butterfly

The Order Lepidoptera contains nearly 160,000 described species and most of them are specialist herbivores that use restricted plant species as hosts. Speciation that originated from host shift is one of the important factors for the diversification of Lepidoptera. Because plants prepare secondary metabolites for defense against herbivores, with varying profiles of the components among different plant taxa, the specialist herbivores need to be adapted to the toxic substances unique to their host plants. Swallowtail butterflies of the genus Papilio consist of over 200 species. Approximately 80% of them utilize Rutaceae plants, and among the remaining species, a specific subgroup uses phylogenetically distant Apiaceae plants as larval hosts. Rutaceae and Apiaceae commonly contain toxic secondary metabolites, furanocoumarins, and molecular phylogenetic studies support the concept that Apiaceae feeders were derived from Rutaceae feeders. Molecular mechanisms underlying furanocoumarin tolerance in Papilio butterflies have been investigated almost exclusively in an Apiaceae feeder by an in vitro assay. In contrast, there is little information regarding the Rutaceae feeders. Here, we focused on a Rutaceae feeder, Papilio xuthus, and identified two furanocoumarin-responsive cytochrome P450-6B (CYP6B) genes, of which one was an ortholog of a furanocoumarin-metabolizing enzyme identified in the Apiaceae-feeding Papilio while the other was previously unreported. We further conducted in vivo functional analysis using the CRISPR/Cas9 system, revealing a contribution of these CYP6Bs to furanocoumarin tolerance of P. xuthus larvae. Our findings suggest that co-option of furanocoumarin-metabolizing CYP6B enzymes at least partially contributed to the host shift from Rutaceae to Apiaceae in Papilio butterflies.

Dietary Challenges for Parasitoid Wasps (Hymenoptera: Ichneumonoidea); Coping with Toxic Hosts, or Not?

Many insects defend themselves against predation by being distasteful or toxic. The chemicals involved may be sequestered from their diet or synthesized de novo in the insects' body tissues. Parasitoid wasps are a diverse group of insects that play a critical role in regulating their host insect populations such as lepidopteran caterpillars. The successful parasitization of caterpillars by parasitoid wasps is contingent upon their aptitude for locating and selecting suitable hosts, thereby determining their efficacy in parasitism. However, some hosts can be toxic to parasitoid wasps, which can pose challenges to their survival and reproduction. Caterpillars employ a varied array of defensive mechanisms to safeguard themselves against natural predators, particularly parasitoid wasps. These defenses are deployed pre-emptively, concurrently, or subsequently during encounters with such natural enemies. Caterpillars utilize a range of strategies to evade detection or deter and evade attackers. These tactics encompass both measures to prevent being noticed and mechanisms aimed at repelling or eluding potential threats. Post-attack strategies aim to eliminate or incapacitate the eggs or larvae of parasitoids. In this review, we investigate the dietary challenges faced by parasitoid wasps when encountering toxic hosts. We first summarize the known mechanisms through which insect hosts can be toxic to parasitoids and which protect caterpillars from parasitization. We then discuss the dietary adaptations and physiological mechanisms that parasitoid wasps have evolved to overcome these challenges, such as changes in feeding behavior, detoxification enzymes, and immune responses. We present new analyses of all published parasitoid-host records for the Ichneumonoidea that attack Lepidoptera caterpillars and show that classically toxic host groups are indeed hosts to significantly fewer species of parasitoid than most other lepidopteran groups.

“Lepidoptera Flies”, but Not Always…Interactions of Caterpillars and Chrysalis with Soil

Lepidoptera, an order of insects traditionally linked to the aerial habitat, are much more diverse in their living environment than the clichéd image we may have of them. The imago stage, which is the most visible in these insects, is not the one that has the most interaction with the environment (usually caterpillars) nor the one that lasts the longest (very often chrysalises). These two stages are often directly related to litter and soil, although only the interaction at the pupal stage seems to follow a phylogenetic logic with two independent evolutionary events for the preference with soil: Use of litter and the upper “O” horizon as protection against predation for the evolutionarily oldest Lepidoptera families, pupation at greater depths (up to 60 centimetres in extreme cases) for the most derived Lepidoptera families; this probably to take advantage of the thermal and moisture buffer provided by the soil. An estimate suggests that about 25% of lepidopteran species worldwide have more or less obligatory interactions with soil.

Egg toxic compounds in the animal kingdom. A comprehensive review

Covering: 1951 to 2022Packed with nutrients and unable to escape, eggs are the most vulnerable stage of an animal's life cycle. Consequently, many species have evolved chemical defenses and teamed up their eggs with a vast array of toxic molecules for defense against predators, parasites, or pathogens. However, studies on egg toxins are rather scarce and the available information is scattered. The aim of this review is to provide an overview of animal egg toxins and to analyze the trends and patterns with respect to the chemistry and biosynthesis of these toxins. We analyzed their ecology, distribution, sources, occurrence, structure, function, relative toxicity, and mechanistic aspects and include a brief section on the aposematic coloration of toxic eggs. We propose criteria for a multiparametric classification that accounts for the complexity of analyzing the full set of toxins of animal eggs. Around 100 properly identified egg toxins are found in 188 species, distributed in 5 phyla: cnidarians (2) platyhelminths (2), mollusks (9), arthropods (125), and chordates (50). Their scattered pattern among animals suggests that species have evolved this strategy independently on numerous occasions. Alkaloids are the most abundant and widespread, among the 13 types of egg toxins recognized. Egg toxins are derived directly from the environment or are endogenously synthesized, and most of them are transferred by females inside the eggs. Their toxicity ranges from ρmol kg^-1 to mmol kg^-1, and for some species, experiments support their role in predation deterrence. There is still a huge gap in information to complete the whole picture of this field and the number of toxic eggs seems largely underestimated.

Plant volatiles mediate evolutionary interactions between plants and tephritid flies and are evolutionarily more labile than non-volatile defenses

Studies show that plant defenses influence the host-use of herbivores and tend to be evolutionarily more labile than herbivore traits (e.g. feeding preferences). However, all previous studies have focused exclusively on non-volatile plant defenses thereby overlooking the roles of plant volatiles. We hypothesized that volatiles are equally important determinants of herbivore host-use and are evolutionarily more labile than herbivore traits. To test these hypotheses, the following experiments were conducted. We identified the volatiles and non-volatiles of 17 Asteraceae species and measured their relative contents. We also used a highly resolved bipartite trophic network of the 17 host species and 20 herbivorous (pre-dispersal seed predator) tephritid fly species to determine the evolutionary interactions between plants and herbivores. The chemical data showed that interspecific similarity in volatiles-but not non-volatiles and phylogenetic distance-significantly accounted for the herbivore community across the plant species; this implies that plant volatiles-but not non-volatile compounds and species identity-dictate plant-tephritid fly interactions. Moreover, we observed phylogenetic signal for non-volatiles but not for volatiles; therefore closely related herbivores do not necessarily use closely related host species with similar non-volatiles, but do tend to attack plants producing similar volatiles. Thus, plant volatiles are evolutionarily more labile than non-volatiles and herbivore traits associate with host use. These results show that the interactions between plants and herbivores are evolutionary asymmetric, shed light on the role of plant volatiles in plant-herbivore interactions, and highlight the need to include data for both volatiles and non-volatiles when investigating plant-animal interactions.

An Oviposition Stimulant for a Magnoliaceae-Feeding Swallowtail Butterfly, Graphium doson, from its Primary Host Plant, Michelia compressa

Chemical examination of plant constituents responsible for oviposition by a Magnoliaceae-feeding butterfly, Graphium doson, was conducted using its major host plant, Michelia compressa. A methanol extract prepared from young leaves of the plant elicited a strong oviposition response from females. The methanolic extract was then separated by solvent partition into three fractions: CHCl₃, i-BuOH, and aqueous fractions. Active substance(s) resided in both i-BuOH- and water-soluble fractions. Bioassay-guided further fractionation of the water-soluble substances by means of various chromatographic techniques led to the isolation of an oviposition stimulant. The stimulant was identified as D-(+)-pinitol on the basis of ¹³C NMR spectra and physicochemical properties. D-(+)-Pinitol singly exhibited a moderate oviposition-stimulatory activity at a dose of 150 μg/cm². This compound was present also in another host plant, Magnolia grandiflora, in a sufficient amount to induce oviposition behavior of G. doson females. Certain cyclitols including D-(+)-pinitol have been reported to be involved in stimulation of oviposition by some Aristolochiaceae- and Rutaceae-feeding papilionid butterflies. A possible pathway of phytochemical-mediated host shifts in the Papilionidae, in which certain cyclitols could enact important mediators, is discussed in relation to the evolution of cyclitol biosynthesis in plants.

BUTTERFLIES AND PLANTS: A PHYLOGENETIC STUDY

A database on host plant records from 437 ingroup taxa has been used to test a number of hypotheses on the interaction between butterflies and their host plants using phylogenetic methods (simple character optimization, concentrated changes test, and independent contrasts test). The butterfly phylogeny was assembled from various sources and host plant clades were identified according to Chase et al.'s rbcL-based phylogeny. The ancestral host plant appears to be associated within a highly derived rosid clade, including the family Fabaceae. As fossil data suggest that this clade is older than the butterflies, they must have colonized already diversified plants. Previous studies also suggest that the patterns of association in most insect-plant interactions are more shaped by host shifts, through colonization and specialization, than by cospeciation. Consequently, we have focused explicitly on the mechanisms behind host shifts. Our results confirm, in the light of new phylogenetic evidence, the pattern reported by Ehrlich and Raven that related butterflies feed on related plants. We show that host shifts have generally been more common between closely related plants than between more distantly related plants. This finding, together with the possibility of a higher tendency of recolonizing ancestral hosts, helps to explain the apparent large-scale conservation in the patterns of association between insects and their host plants, patterns which at the same time are more flexible on a more detailed level. Plant growth form was an even more conservative aspect of the interaction between butterflies and their host plants than plant phylogeny. However, this is largely explained by a higher probability of colonizations and host shifts while feeding on trees than on other growth forms.

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

Species of Ophraella, a North American genus of leaf beetles (Chrysomelidae), feed variously on eight genera in four tribes of Asteraceae. A phylogenetic analysis, based on morphological features and allozymes, was undertaken to deduce the history of host affiliation within the genus. The two data sets are combined to arrive at a provisional phylogeny of the species, onto which host associations are parsimoniously mapped. Among and within the 12 species studied, at least two shifts are postulated to have occurred among congeneric plant species, five between genera in the same tribe, and four between different tribes of Asteraceae. The phylogeny of Ophraella appears not to be congruent with that of its hosts. This and other evidence indicates that many host shifts in Ophraella postdate the divergence of the host plants, a conclusion that may apply commonly to phytophagous insects. A phenetic analysis of the plants' secondary compounds provides modest support for the hypothesis that host shifts are facilitated by commonalities in plant chemistry. A possible trend in host shifts is evident, from chemically simpler to chemically more forbidding plants. The chemical barriers to host shifts in Ophraella appear to require adaptation in both behavior and in physiological attributes. There is no evidence that the host associations of these insects or the divergence in secondary chemistry of their hosts can be attributed to coevolution.

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.

Forms of Melanoplus bowditchi (Orthoptera: Acrididae) collected from different host plants are indistinguishable genetically and in aedeagal morphology

The sagebrush grasshopper, Melanoplus bowditchi Scudder (Orthoptera: Acrididae), is a phytophilous species that is widely distributed in the western United States on sagebrush species. The geographical distribution of M. bowditchi is very similar to the range of its host plants and its feeding association varies in relation to sagebrush distribution. Melanoplus bowditchi bowditchi Scudder and M. bowditchi canus Hebard were described based on their feeding association with different sagebrush species, sand sagebrush and silver sagebrush, respectively. Recently, M. bowditchi have been observed feeding on other plant species in western Nebraska. We collected adult M. bowditchi feeding on four plant species, sand sagebrush, Artemisia filifolia, big sagebrush, A. tridentata, fringed sagebrush, A. frigidus, and winterfat, Krascheninnikovia lanata. We compared the specimens collected from the four plant species for their morphological and genetic differences. We observed no consistent differences among the aedeagal parameres or basal rings among the grasshoppers collected from different host plants. Amplified Fragment Length Polymorphism markers were used to test the genetic relationships among the grasshoppers. Analysis of Molecular Variance and distance-based Unweighted Pair Group Method with Arithmetic mean dendrogram failed to reveal significant differences. Although the forms showed behavioral and minor color and size differences, the genetic data suggest all forms under study likely interbreed, which indicates they are a single species instead of four species or subspecies. These results indicate that host plant use may influence melanopline phenotype and suggest the need of further genetic analysis of subspecies recognized based on morphology, distribution, and ecology.

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.

Congruence and diversity of butterfly-host plant associations at higher taxonomic levels

We aggregated data on butterfly-host plant associations from existing sources in order to address the following questions: (1) is there a general correlation between host diversity and butterfly species richness?, (2) has the evolution of host plant use followed consistent patterns across butterfly lineages?, (3) what is the common ancestral host plant for all butterfly lineages? The compilation included 44,148 records from 5,152 butterfly species (28.6% of worldwide species of Papilionoidea) and 1,193 genera (66.3%). The overwhelming majority of butterflies use angiosperms as host plants. Fabales is used by most species (1,007 spp.) from all seven butterfly families and most subfamilies, Poales is the second most frequently used order, but is mostly restricted to two species-rich subfamilies: Hesperiinae (56.5% of all Hesperiidae), and Satyrinae (42.6% of all Nymphalidae). We found a significant and strong correlation between host plant diversity and butterfly species richness. A global test for congruence (Parafit test) was sensitive to uncertainty in the butterfly cladogram, and suggests a mixed system with congruent associations between Papilionidae and magnoliids, Hesperiidae and monocots, and the remaining subfamilies with the eudicots (fabids and malvids), but also numerous random associations. The congruent associations are also recovered as the most probable ancestral states in each node using maximum likelihood methods. The shift from basal groups to eudicots appears to be more likely than the other way around, with the only exception being a Satyrine-clade within the Nymphalidae that feed on monocots. Our analysis contributes to the visualization of the complex pattern of interactions at superfamily level and provides a context to discuss the timing of changes in host plant utilization that might have promoted diversification in some butterfly lineages.

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.

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.

Evolution of larval host plant associations and adaptive radiation in pierid butterflies

Butterflies in the family Pieridae (Lepidoptera: Papilionoidea) feed as larvae on plants belonging primarily to three distantly related angiosperm orders: Fabales (legumes and allied plants), Brassicales (crucifers and related plants containing mustard oil glucosides), and Santalales ('mistletoes'). However, some utilize plants from 13 other families in a further eight orders. We investigated the evolutionary history of host plant use of the Pieridae in the context of a recent phylogenetic hypothesis of the family, using simple character optimization. Although there is a close association between host plant and butterfly higher classification, we find no evidence for cospeciation but a pattern of repeated colonization and specialization. The ancestral host of the family appears to be Fabaceae or Fabales, with multiple independent shifts to other orders, including three to Santalales. The shift to Brassicales, which contain secondary compounds (glucosinolates), promoted diversification and adaptive radiation within the subfamily Pierinae. Subsequent shifts from crucifers to mistletoes (aerial-stem hemiparasites) facilitated further diversification, and more recent shifts from mistletoes to mistletoe host trees led to exploitation of novel host plants outside the conventional three orders. Possible mechanisms underlying these host shifts are briefly discussed. In the Pierinae, a striking association between host plant, larval and adult behaviour, adult phenotype, and mimicry calls for further research into possible relationships between host specialization, plant chemistry and butterfly palatability.

When and where did troidine butterflies (Lepidoptera : Papilionidae) evolve? Phylogenetic and biogeographic evidence suggests an origin in remnant Gondwana in the Late Cretaceous

The age, geographic origin and time of major radiation of the butterflies (Hesperioidea + Papilionoidea + Hedyloidea) are largely unknown. The general modern view is that butterflies arose during the Late Jurassic/Cretaceous in the southern hemisphere (southern Pangea/Gondwana before continental breakup), but this is not universally accepted, and is a best guess based largely on circumstantial evidence. The extreme paucity of fossils and lack of modern, higher-level phylogenies of extant monophyletic groups have been major impediments towards determining reliable estimates of either their age or geographic origin. Here we present a phylogenetic and historical biogeographic analysis of a higher butterfly taxon, the swallowtail tribe Troidini. We analysed molecular data for three protein-encoding genes, mitochondrial ND5 and COI–COII, and nuclear EF–1α, both separately and in combination using maximum parsimony (with and without character weighting and transition/transversion weighting), maximum likelihood and Bayesian methods. Our sample included representatives of all 10 genera of Troidini and distant ingroup taxa (Baroniinae, Parnassiinae, Graphiini, Papilionini), with Pieridae as outgroup. Analysis of the combined dataset (4326 bp; 1012 parsimony informative characters) recovered the Troidini as a well supported monophyletic group and the monophyly of its two subtribes, Battina and Troidina. The most parsimonious biogeographic hypothesis suggests a southern origin of the tribe in remnant Gondwana (Madagascar–Greater India–Australia–Antarctica–South America) sometime after the rifting and final separation of Africa in the Late Cretaceous (<90 Mya). Although an ancient vicariance pattern is proposed, at least four relatively recent dispersal/extinction events are needed to reconcile anomalies in distribution, most of which can be explained by geological and climatic events in South-east Asia and Australia during the late Tertiary. Application of a molecular clock based on a rate smoothing programme to estimate various divergence times based on vicariance events, revealed two peculiarities in our biogeographic vicariance model that do not strictly accord with current understanding of the temporal breakup of Gondwana: (1) the troidine fauna of Greater India did not become isolated from Gondwana (Antarctica) until the end of the Cretaceous (c. 65 Mya), well after Madagascar separated from Greater India (84 Mya); and (2) the faunas of Greater India, Australia and South America diverged simultaneously, also at the K/T boundary. A recent published estimate of the time (31 Mya) of divergence between Cressida Swainson (Australia) and Euryades Felder & Felder (South America) is shown to be in error.

Evolutionary dynamics of host-plant use in a genus of leaf-mining moths

We used nuclear 28S rDNA sequence data to estimate the phylogeny of 77 leaf-mining Phyllonorycter (Gracillariidae) moth species, including all 55 British species, feeding on 44 different plant genera. There was strong support for both the monophyly of Phyllonorycter and the placement of the genus Cameraria as its sister group. Host-plant use was mapped onto the moth phylogeny and investigated statistically in several ways. First, we show that the estimated level of cospeciation between leaf miners and their host plants is not greater than expected by chance, despite the physical intimacy of the association. Nevertheless, the pattern of host-plant use is far from random, with closely related Phyllonorycter species generally feeding on closely related plants. However, although Phyllonorycter species from a given host plant tend to form distinct clades, there is also statistical support for multiple independent colonizations of some host-plant taxa (e.g. the order Rosales and the genus Corylus). Despite numerous host shifts, most Phyllonorycter species feed on trees and the few species that attack shrubs or herbs have mostly acquired these habits independently. There is also limited evidence that host shifts to herbs are more likely from shrubs than from trees. Similarly, most species mine the lower surface of leaves but the few upper-surface miners have each evolved the habit independently. Consequently, these shifts to new adaptive zones have not led to substantial radiations.

Transition rates between specialization and generalization in phytophagous insects

Although most species of animals exhibit specialized patterns of resource use, it is unclear whether specialization evolves at a faster rate than generalization. To test this hypothesis, transition rates toward specialization and toward generalization were estimated using phylogenies from 15 groups of phytophagous insects. Among the groups studied, maximum-likelihood analyses showed that the forward transition rate from generalization to specialization was significantly higher than the reverse transition rate from specialization to generalization (mean ratio of forward to reverse transition rate = 1.47 using uniform branch lengths and 1.76 using Grafen branch lengths). Although phylogenetic conservatism of host-plant use is common, the results suggest that the evolution of specialization is a highly dynamic process. For example, higher transitions rates both toward and away from specialization as well as equal transition rates were inferred. Collectively, the results reveal a tendency for directional evolution toward increased specialization but also indicate that specialization does not always represent an evolutionary dead-end that strongly limits further evolution.

Sequestration of defensive substances from plants by Lepidoptera

A number of aposematic butterfly and diurnal moth species sequester unpalatable or toxic substances from their host plants rather than manufacturing their own defensive substances. Despite a great diversity in their life histories, there are some general features in the selective utilization of plant secondary metabolites to achieve effective protection from predators. This review illustrates the biochemical, physiological, and ecological characteristics of phytochemical-based defense systems that can shed light on the evolution of the widely developed sequestering lifestyles among the Lepidoptera.

Evolutionary dynamics of host-plant specialization: a case study of the tribe Nymphalini

Two general patterns that have emerged from the intense studies on insect-host plant associations are a predominance of specialists over generalists and a taxonomic conservatism in host-plant use. In most insect-host plant systems, explanations for these patterns must be based on biases in the processes of host colonizations, host shifts, and specialization, rather than cospeciation. In the present paper, we investigate changes in host range in the nymphalid butterfly tribe Nymphalini, using parsimony optimizations of host-plant data on the butterfly phylogeny. In addition, we performed larval establishment tests to search for larval capacity to feed and survive on plants that have been lost from the female egg-laying repertoire. Optimizations suggested an ancestral association with Urticaceae, and most of the tested species showed a capacity to feed on Urtica dioica regardless of actual host-plant use. In addition, there was a bias among the successful establishments on nonhosts toward plants that are used as hosts by other species in the Nymphalini. An increased likelihood of colonizing ancestral or related plants could also provide an alternative explanation for the observed pattern that some plant families appear to have been colonized independently several times in the tribe. We also show that there is no directionality in host range evolution toward increased specialization, that is, specialization is not a dead end. Instead, changes in host range show a very dynamic pattern.

The phylogenetics and biochemistry of host-plant specialization in Melitaeine butterflies (Lepidoptera: Nymphalidae)

Butterflies in the tribe Melitaeini (Lepidoptera: Nymphalidae) are known to utilize host plants belonging to 16 families, although most host-plant records are from four families. Of the 16 host-plant families, 12 produce secondary plant metabolites called iridoids. Earlier studies have shown that larvae of several melitaeine species use iridoids as feeding stimulants and sequester these compounds for larval defense. I investigate the evolutionary history of host-plant use in the tribe Melitaeini by testing a recent phylogenetic hypothesis of 65 species representing the four major species groups of the tribe. By simple character optimization of host-plant families and presence/absence of iridoids in the host plants, I find that plant chemistry is a more conservative trait than plant taxonomy. The ancestral host plant(s) of the entire tribe most likely contained iridoids and were likely to be in the plant family Plantaginaceae. A major host shift from plants containing iridoids to plants not containing iridoids has happened three times independently. The results show that the evolution of host-plant use in melitaeines has been (and still is) a dynamic process when considering plant taxonomy, but is relatively stable when considering host-plant chemistry.

Molecular phylogeny of swallowtail butterflies of the tribe Papilionini (Papilionidae, Lepidoptera)

Swallowtail butterflies of the tribe Papilionini number about 225 species and are currently used as model organisms in several research areas, including genetics, chemical ecology and phylogenetics of host plant utilization and mimicry, mechanisms of speciation, and conservation. We have inferred phylogenetic relationships for a sample of 18 species of the genus Papilio (sensu lato) and five outgroup taxa by sequencing two stretches of mitochondrial DNA that correspond to segments 12886-13370 and 12083-12545 of Drosophila melanogaster mitochondrial DNA and consist of sections of the genes for the large ribosomal RNA and subunit 1 of NADH-dehydrogenase. Our data support the monophyly of Papilio and, within it, of several traditionally recognized subgroups. Species belonging to groups that utilize primarily Rutaceae as larval foodplants form two clusters, corresponding to Old World and American taxa, respectively, while two previously recognized clades-of American and South Asian-Austronesian origin-whose members were known to feed mostly on Lauraceae and Magnoliaceae, are observed to form a clade. The sister group of Papilio is found to be the South Asian genus Meandrusa, which also happens to feed on Lauraceae. The latter plant family is therefore the probable larval host of the ancestor Papilio and the shift to Rutaceae (which four-fifths of extant Papilio species use as foodplants) is more likely to have occurred only after the initial diversification of the genus.

Performance and host preference of Ascia monuste (Lepidoptera, Pieridae)

Experiments were conducted to determine the performance and host preference of Ascia monuste using kale (Brassica oleraceae, var. Acephala) and mustard (B. juncea). These plants differ significantly in water and nitrogen content, with mustard having larger amounts of water and kale larger amounts of nitrogen. The performance results confirmed that kale is a better food source than mustard for the species, even when eggs were collected on mustard leaves in the field. However, when eggs were collected on mustard, the kale nutritive value was lower than the nutritive value obtained when eggs were collected on kale leaves. Furthermore, the results of oviposition preference obtained in the field and in the laboratory have shown a preference for kale, indicating the presence of a positive correlation with performance. In contrast to the data about oviposition preference, there was no immature feeding preference. These results indicate that host selection occurs during the oviposition process. Furthermore, it is possible that the high abundance of kale cultivated in the region studied and the nutritional quality of this plant are two factors that influence the positive relationship between oviposition preference and performance for A. monuste.