Herbivorous insects and other small consumers are often specialized both in use of particular host taxa and in use of particular host tissues. Such consumers also often seem to show consistent differences in the rates of evolution of these two dimensions of host use, implying common processes, but this has been little studied. Here we quantify these rates of change in host use evolution in a major radiation of herbivorous insects, the Chrysomeloidea, whose diversity has been attributed to their use of flowering plants. We find a significant difference in the rates of evolutionary change in these two dimensions of host use, with host taxon associations most labile. There are apparently similar differences in rates of host use evolution in other parasite groups, suggesting the generality of this pattern. Divergences in parasite form associated with use of different host tissues may facilitate resource partitioning among successive adaptive radiations on particular host taxa.

Regular inbreeding by sib-mating is one of the most successful ecological strategies in the bark beetle family Scolytinae. Within this family, the many species (119) in Coccotrypes are found breeding in an exceptional variety of untraditional woody tissues different from bark and phloem. Species delineation by morphological criteria is extremely difficult, however, as in most other inbreeding groups of beetles, perhaps due to the unusual evolutionary dynamics characterizing sib-mating organisms. Hence, we here performed a phylogenetic analysis using molecular data in conjunction with morphological data to better understand morphological and ecological evolution in this sib-mating group. We used partial DNA sequences from the nuclear gene EF-alpha and the mitochondrial genes 12S and CO1 to elucidate patterns of morphological evolution, haplotype variation, and evolutionary pathways in resource use. Sequence variation was high among species and far above that expected at the species level (e.g., 19% for CO1 within Coccotrypes advena). The tendency for exhaustive sequence variation at deeper nodes resulted in ambiguous reconstructions of the deepest splits. However, all results suggested that species with the broadest diets were clustered in a single derived position-another piece of evidence against specialization as a derived evolutionary feature. (C) 2002 Elsevier Science (USA). All rights reserved.

The weevil subfamily Scolytinae includes at least seven groups of regularly sib-mating species with extremely female-biased offspring sex ratios. The enigmatic SE-Asian bark beetle genus Ozopemon (25 spp.) belong to the most diversified clade (>1400 spp.) of such ancient inbreeding lineages. While males of all sib-mating scolytines are flightless, and are usually dwarfed versions of their larger sisters, the existence of males in Ozopemon has been a controversial issue. Some strangely modified male beetles, with fully developed aedeagus, strongly flattened pronotum and bead, and 10-segmented larviform abdomen, were first described as males of O.brownei, but were later assigned to the Histeridae. With the new evidence provided here, based on DNA sequence data from mitochondrial and nuclear gene partitions, and examination of genitalic characters, we re-assign these males, as well as males for two more species, to Ozopemon. Neoteny evolved close to the origin of sib-mating and possibly haplodiploidy, but the transition to neoteny occurred separately from all other inbreeding dryocoetine and xyleborine beetles. The neotenic development of these males is the first known example in Coleoptera, and several remarkable morphological modifications demonstrate an ontogenetic transformation series from female to males of different species. We discuss possible scenarios for the evolution of neoteny, precocity and fighting characteristics in these male beetles, in the light of W. D. Hamilton's 'ideal biofacies' of extreme inbreeding. (C) 2002 The Linnean Society of London.

The main goals of this study were to provide a robust phylogeny for the families of the superfamily Curculionoidea, to discover relationships and major natural groups within the family Curculionidae, and to clarify the evolution of larval habits and host-plant associations in weevils to analyze their role in weevil diversification. Phylogenetic relationships among the weevils (Curculionoidea) were inferred from analysis of nucleotide sequences of 18S ribosomal DNA (rDNA; 2, 000 bases) and 115 morphological characters of larval and adult stages. A worldwide sample of 100 species was compiled to maximize representation of weevil morphological and ecological diversity. All families and the main subfamilies of Curculionoidea were represented. The family Curculionidae sensu lato was represented by about 80 species in 30 "subfamilies" of traditional classifications. Phylogenetic reconstruction was accomplished by parsimony analysis of separate and combined molecular and morphological data matrices and Bayesian analysis of the molecular data; tree topology support was evaluated. Results of the combined analysis of 18S rDNA and morphological data indicate that monophyly of and relationships among each of the weevil families are well supported with the topology (( Nemonychidae, Anthribidae) (Belidae (Attelabidae (Caridae (Brentidae, Curculionidae))))). Within the clade Curculionidae sensu lato, the basal positions are occupied by mostly monocot-associated taxa with the primitive type of male genitalia followed by the Curculionidae sensu stricto, which is made up of groups with the derived type of male genitalia. High support values were found for the monophyly of some distinct curculionid groups such as Dryophthorinae (several tribes represented) and Platypodinae (Tesserocerini plus Platypodini), among others. However, the subfamilial relationships in Curculionidae are unresolved or weakly supported. The phylogeny estimate based on combined 18S rDNA and morphological data suggests that diversification in weevils was accompanied by niche shifts in host-plant associations and larval habits. Pronounced conservatism is evident in larval feeding habits, particularly in the host tissue consumed. Multiple shifts to use of angiosperms in Curculionoidea were identified, each time associated with increases in weevil diversity and subsequent shifts back to gymnosperms, particularly in the Curculionidae.

Beetles in the weevil subfamilies Scolytinae and Platypodinae are unusual in that they burrow as adults inside trees for feeding and oviposition. Some of these beetles are known as ambrosia beetles for their obligate mutualisms with asexual fungi-known as ambrosia fungi-that are derived from plant pathogens in the ascomycete group known as the ophiostomatoid fungi. Other beetles in these subfamilies are known as bark beetles and are associated with free-living, pathogenic ophiostomatoid fungi that facilitate beetle attack of phloem of trees with resin defenses. Using DNA sequences from six genes, including both copies of the nuclear gene encoding enolase, we performed a molecular phylogenetic study of bark and ambrosia beetles across these two subfamilies to establish the rate and direction of changes in life histories and their consequences for diversification. The ambrosia beetle habits have evolved repeatedly and are unreversed. The subfamily Platypodinae is derived from within the Scolytinae, near the tribe Scolytini. Comparison of the molecular branch lengths of ambrosia beetles and ambrosia fungi reveals a strong correlation, which a fungal molecular clock suggests spans 60 to 21 million years. Bark beetles have shifted from ancestral association with conifers to angiosperms and back again several times. Each shift to angiosperms is associated with elevated diversity, whereas the reverse shifts to conifers are associated with lowered diversity. The unusual habit of adult burrowing likely facilitated the diversification of these beetle-fungus associations, enabling them to use the biomass-rich resource that trees represent and set the stage for at least one origin of eusociality.

The insects that feed on the related plant families Apocynaceae and Asclepiadaceae (here collectively termed "milkweeds") comprise a "component community" of highly specialized, distinctive lineages of species that frequently sequester toxic cardiac glycosides from their host plants for defense against predators and are thus often aposematic, advertising their consequent unpalatability. Such sets of specialized lineages provide opportunities for comparative studies of the rate of adaptation, diversification, and habitat-related effects on molecular evolution. The cerambycid genus Tetraopes is the most diverse of the new world milkweed herbivores and the species are generally host specific, being restricted to single, different species of Asclepias, more often so than most other milkweed insects. Previous work revealed correspondence between the phylogeny of these beetles and that of their hosts. The present study provides analyses of near-complete DNA sequences for Tetraopes and relatives that are used to establish a molecular clock and temporal framework for Tetraopes evolution with their milkweed hosts. (C) 2001 Academic Press.

Studies of a variety of phenomena, ranging from rates of molecular substitution to rates of diversification, draw on estimates of geological age. Studies incorporating estimates of timing from fossils or other geological evidence are largely of relatively young, Tertiary divergences, to which older systems may provide useful comparisons. One apparently old assemblage comprises the beetle groups associated with the ancient genus Araucaria that share comparable, ostensibly Gondwanan distributions with their host. Our previous studies suggested a possibly Cretaceous age for Araucaria associations in bark beetles. However, the absence of confirmed bark beetle fossils earlier than the Tertiary has been taken as evidence of Cretaceous absence, and their confirmed phylogenetic position within the primitively angiosperm-feeding weevil family rules out pre-angiosperm, Jurassic origins. Nevertheless, an early shift from angiosperms to Araucaria seemed plausible in the light of Araucaria fossil history which spans the Mesozoic since the Jurassic. To resolve the phylogenetic affinities and to estimate divergence times of the Australian and South American bark beetle genera affiliated with Araucaria we analysed DNA sequences of nuclear and mitochondrial genes: protein coding elongation factor alpha, enolase and cytochrome oxidase I. The most parsimonious reconstruction of the host relationships of Tomicini from the combined dataset corroborates the ancestral association with the genus Araucaria of both South American and Australian Tomicini. Bayesian estimation of divergence times indicates that the divergence between the Australian and the South American Araucaria-feeding taxa occurred at the very latest in the Cretaceous/Paleocene border and that the age of the first Scolytinae-Araucaria association would then be during the later stages of the Late Cretaceous, while other known beetle/Araucaria associations are Jurassic. (C) 2001 The Linnean Society of London.

The 15 species in the weevil genus Galapaganus Lanteri 1992 (Entiminae: Curculionidae: Coleoptera) are distributed on coastal Peru and Ecuador and include 10 flightless species endemic to the Galapagos islands. These beetles thus provide a promising system through which to investigate the patterns and processes of evolution on Darwin's archipelago. Sequences of the mtDNA locus encoding cytochrome oxidase subunit I (COI) were obtained from samples of seven species occurring in different ecological zones of the oldest south-eastern islands: San Cristobal, Espanola and Floreana, and the central island Santa Cruz. The single most parsimonious tree obtained shows two well-supported clades that correspond to the species groups previously defined by morphological characters. Based on a mtDNA clock calibrated for arthropods, the initial speciation separating the oldest species, G. galapagoensis (Linell) on the oldest island, San Cristobal, from the remaining species in the Galapagos occurred about 7.2 Ma. This estimate exceeds geological ages of the extant emerged islands, although it agrees well with molecular dating of endemic Galapagos iguanas, geckos and lizards. An apparent explanation for the disagreement between geological and molecular time-frames is that about 7 Ma there were emerged islands which subsequently disappeared under ocean waters. This hypothesis has gained support from the recent findings of Il-Myr-old submarine seamounts (sunken islands), south-east of the present location of the archipelago. Some species within the darwini group may have differentiated on the extant islands, 1-5 Ma.

We investigated the relative importance of resource use and geography on genetic differentiation in the sister-species pair of generalist and specialist bark beetles: Dendroctonus ponderosae and D. jeffreyi (Coleoptera: Scolytidae). In two regions, where the distributions of these species overlap, we collected specimens of the generalist from multiple host species and specimens of the specialist from its single host species. Using allozyme techniques, we uncovered genetic differentiation between generalist populations on different host species in the same region (one locus in each region). However, a much stronger pattern of differentiation was found between specialist populations in the two distantly separated regions (three loci). With mtDNA, we found no significant differentiation between regions in the specialist, or among host species in the generalist, although there was some differentiation between regions in the generalist (AMOVA, P < 0.05). Overall, the generalist populations maintained approximately 10 times the genetic variation in mtDNA as the specialist populations, which suggests that the specialist either has generally smaller population sizes than the generalist, or has experienced a historical population bottleneck.

Several shifts from ancestral conifer feeding to angiosperm feeding have been implicated in the unparalleled diversification of beetle species. The single largest angiosperm-feeding beetle clade occurs in the weevils, and comprises the family Curculionidae and relatives. Most authorities confidently place the bark beetles (Scolytidae) within this radiation of angiosperm feeders. However, some clues indicate that the association between conifers and some scolytids, particularly in the tribe Tomicini, is a very ancient one. For instance, several fragments of Gondwanaland (South America, New Caledonia, Australia and New Guinea) harbour endemic Tomicini specialized on members of the formerly widespread and abundant conifer family Araucariaceae. As a first step towards resolving this seeming paradox, we present a phylogenetic analysis of the beetle family Scolytidae with particularly intensive sampling of conifer-feeding Tomicini and allies. We sequenced and analysed elongation factor 1 alpha and nuclear rDNAs 18S and 28S for 45 taxa, using members of the weevil family Cossoninae as an out-group. Our results indicate that conifer feeding is the ancestral host association of scolytids, and that the most basal lineages of scolytids feed on Araucaria. If scolytids are indeed nested within a great angiosperm-feeding clade, as many authorities have held, then a reversion to conifer feeding in ancestral scolytids appears to have occurred in the Mesozoic, when Araucaria still formed a major component of the woody flora.

Haplodiploidy is a highly unusual genetic system that has arisen at least 17 times in animals of varying lifestyles, but most of these haplodiploid lineages remain relatively poorly known. In particular, the ecological and genetic circumstances under which haplodiploidy originates have been difficult to resolve. A recent molecular-phylogenetic study has resolved the phylogenetic position of the haplodiploid clade of scolytine beetles as the sister group of the genus Dryocoetes. Haplodiploid bark beetles are remarkable in that the entire clade of over 1300 species are apparently extreme (sib-mating) inbreeders, most of which cultivate fungi for food while some attack phloem, twigs or seeds. Here we present a much more detailed molecular-phylogenetic study of this clade. Using partial sequences of elongation factor 1-alpha and the mitochondrial small ribosomal subunit (12S), we reconstructed the phylogeny for 48 taxa within the haplodiploid clade, as well as two species of the diplodiploid sister genus Dryocoetes. Results indicate that the genus Ozopemon is the basal lineage of the haplodiploid clade. Since Ozopemon, Dryocoetes and other outgroups are phloem-feeding, this strongly suggest that haplodiploidy and inbreeding evolved in a phloem feeding ancestor. Following the divergence of Ozopemon there is a series of extremely short internodes near the base of the clade, suggesting a very rapid rate of diversification in early Miocene (based on fossil evidence and sequence divergence). Among the many substrates for breeding and food resources utilized within this species-rich clade, the cultivation of yeast-like ambrosia fungi in tunnels deep into the wood predominates (nearly 90% of the species). The number of transitions to feeding on such fungi was few, possibly only one, and is perhaps an irreversible transition. The habit of feeding on fungi cultured in xylem makes it possible for the beetles to use a great variety of plant taxa. This extreme resource generalism, in conjunction with the colonization advantage conferred by haplodiploidy and inbreeding, may have promoted the rapid diversification of this clade. (C) 2000 The Linnean Society or London.

We used molecular phylogenetic techniques to study the systematic relationships and host specificity of Psoroptes mange mites, which are pests of numerous domestic and wild ungulates. Phylogenetic analysis of DNA sequence data from the internal transcribed spacer region 1 (ITS1) of nuclear ribosomal DNA indicated that populations of Psoroptes are not host specific. Furthermore, the currently used taxonomy of Psoroptes is not concordant with the phylogeny derived from ITS1. During the course of the study, we discovered apparent paralogous ITS sequences within individual mites as a result of varying polymerase chain reaction reaction conditions. This finding concords with other studies of ITS and suggests a cautious approach when interpreting data from ITS sequences. Host DNA contamination was also found to be a significant problem in data collection, and we report on the development of methods to overcome the problems of contamination in parasitic mites.

In two sister species of leaf beetles with overlapping host associations, Chrysochus auratus and C. cobaltinus, we established diet breadth and food preference of local populations for evaluation together with genetic differentiation between populations. While C. auratus turned out to be monophagous on the same plant wherever we collected the beetles, the studied populations of C. cobaltinus fed on three different plant species in the field. Plant preference and ranking of the potential host plants significantly differed between these populations. The amount of genetic differentiation between populations was measured by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay of a 1300 bp mitochondrial DNA (mtDNA) sequence. In addition, the dominant genotypes of all populations were sequenced. No genetic differentiation between the populations of C. auratus could be detected in the RFLP assay and sequence divergence was low (= 0.3%). In C. cobaltinus, on the other hand, genetic differentiation between populations was high, revealing a lack of gene flow over a much smaller scale and a maximum of 1.3% sequence divergence. C. cobaltinus thereby has the prerequisites for host race formation on different plants from the original host spectrum. Our sequence-based phylogeny estimate allows us to reconstruct historical diet evolution in Chrysochus Starting from an original association with Asclepiadaceae, the common ancestor of C. auratus and C. cobaltinus included Apocynaceae in its diet. The strict specialization on Apocynum and the loss of acceptance of Asclepiadaceae observed in C. auratus could have resulted from a process similar to that displayed by C. cobaltinus populations.

The beetle family Scolytidae includes several groups having regular sib-mating and extremely female-biased sex ratios. Two such groups are known to include haplodiploid species: (i) the tribe Xyleborini and (ii) Coccotrypes and related genera within the tribe Dryocoetini. Relationships of these groups have been controversial. We analysed elongation factor 1-alpha (852 bp) and cytochrome oxidase 1 (1179 bp) sequences for 40 species. The most-parsimonious trees imply a single origin of haplodiploidy uniting Xyleborini (approximately 1200 species) and sib-mating Dryocoetini (approximately 160 species). The sister-group of the haplodiploid clade is the outcrossing genus Dryocoetes. The controversial genus Premnobius is outside the haplodiploid clade. Most haplodiploid scolytids exploit novel resources, ambrosia fungi or seeds, but a few have the ancestral habit of feeding on phloem. Thus, scolytids provide the dearest example of W. D. Hamilton's scenario for the evolution of haplodiploidy (life under bark leading to inbreeding and hence to female-biased sex ratios through haplodiploidy) and now constitute a unique opportunity to study diplo-diploid and haplodiploid sister-lineages in a shared ancestral habitat. There is some evidence of sex determination by maternally inherited endosymbiotic bacteria, which may explain the consistency with which female-biased sex ratios and close inbreeding have been maintained.

In this paper, we provide a molecular phylogeny of the 19 species in the bark beetle genus Dendroctonus. These beetles collectively attack plant species in four different genera of the conifer family Pinaceae. Given substantial variation in diet breadth, in both the types and numbers of plant species utilized, we asked two general questions concerning the evolution of resource use in this group: 1) “How conservative is the evolution of host use in these insects?” and 2) “Does specialization tend to be derived (that is, a “dead-end’’)?”