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.

The 2016 International Weevil Meeting was held immediately after the International Congress of Entomology (ICE). It built on the topics and content of the 2016 ICE weevil symposium Phylogeny and Evolution of Weevils (Coleoptera: Curculionoidea): A Symposium in Honor of Dr. Guillermo "Willy” Kuschel. Beyond catalyzing research and collaboration, the meeting was intended to serve as a forum for identifying priorities and goals for those who study weevils. The meeting consisted of 46 invited and contributed lectures, discussion sessions and introductory remarks presented by 23 speakers along with eight contributed research posters. These were organized into three convened sessions, each lasting one day: (1) weevil morphology; (2) weevil fossils, biogeography and host/habitat associations; and (3) molecular phylogenetics and classification of weevils. Some of the topics covered included the 1K Weevils Project, major morphological character systems of adult and larval weevils, weevil morphological terminology, prospects for future morphological character discovery, phylogenetic analysis of morphological character data, the current status of weevil molecular phylogenetics and evolution, resources available for phylogenetic and comparative genomic studies of weevils, the weevil fossil record, weevil biogeography and evolution, weevil host plants, evolutionary development of the weevil rostrum, resources available for weevil identification and the current status of and challenges in weevil classification.

Nuclear sequence data were collected from endemic Galápagos species and an introduced close relative, and contrasted with mitochondrial DNA sequences, continuing investigation into the colonization history and modes of diversification in the weevil genus Galapaganus . The current combined phylogeny together with previously published penalized likelihood age estimates builds a complex picture of the archipelago's colonization history. The present reconstruction relies on submerged platforms to explain the early divergence of the young southern Isabela endemics or the Española or San Cristobal populations. Diversity is later built through inter-island divergence starting on older islands and continuing on two simultaneous tracks towards younger islands. The amount of diversity generated through intra-island processes is skewed towards older islands, suggesting that island age significantly influences diversity. Phylogenetic concordance between nuclear and mitochondrial datasets and well-supported monophyletic species in mitochondrial derived topologies appear to reject the possibility of inter-species hybridization. These clear species boundaries might be related to the tight host associations of adult weevils in discrete ecological zones. If shared hosts facilitate hybridization, then host- or habitat-promoted divergences could prevent it, even in the case of species that share islands, since the altitudinal partitioning of habitats minimizes range overlap.

Food resource access can mediate establishment success in invasive species, and generalist herbivorous insects are thought to rely on mechanisms of transcriptional plasticity to respond to dietary variation. While asexually reproducing invasives typically have low genetic variation, the twofold reproductive capacity of asexual organisms is a marked advantage for colonization. We studied host-related transcriptional acclimation in parthenogenetic, invasive, and polyphagous weevils: Naupactus cervinus and N. leucoloma. We analyzed patterns of gene expression in three gene categories that can mediate weevil-host plant interactions through identification of suitable host plants, short-term acclimation to host plant defenses, and long-term adaptation to host plant defenses and their pathogens. This approach employed comparative transcriptomic methods to investigate differentially expressed host detection, detoxification, immune defense genes, and pathway-level gene set enrichment. Our results show that weevil gene expression responses can be host plant-specific, and that elements of that response can be maintained in the offspring. Some host plant groups, such as legumes, appear to be more taxing as they elicit a complex gene expression response which is both strong in intensity and specific in identity. However, the weevil response to taxing host plants shares many differentially expressed genes with other stressful situations, such as host plant cultivation conditions and transition to novel host, suggesting that there is an evolutionarily favorable shared gene expression regime for responding to different types of stressful situations. Modulating gene expression in the absence of other avenues for phenotypic adaptation may be an important mechanism of successful colonization for these introduced insects.

The challenge of maintaining genetic diversity within populations can be exacerbated for island endemics if they display population dynamics and behavioral attributes that expose them to genetic drift without the benefits of gene flow. We assess patterns of the genetic structure and demographic history in 27 populations of 9 species of flightless endemic Galápagos weevils from 9 of the islands and 1 winged introduced close relative. Analysis of mitochondrial DNA reveals a significant population structure and moderately variable, though demographically stable, populations for lowland endemics (F_ST = 0.094–0.541; π: 0.014–0.042; Mismatch P = 0.003–0.026; and D_(Tajima) = −0.601 to 1.203), in contrast to signals of past contractions and expansions in highland specialists on 2 islands (Mismatch P = 0.003–0.026 and D_(Tajima) = −0.601 to 1.203). We interpret this series of variable and highly structured population groups as a system of long-established, independently founded island units, where structuring could be a signal of microallopatric differentiation due to patchy host plant distribution and poor dispersal abilities. We suggest that the severe reduction and subsequent increase of a suitably moist habitat that accompanied past climatic variation could have contributed to the observed population fluctuations in highland specialists. We propose the future exploration of hybridization between the introduced and highland endemic species on Santa Cruz, especially given the expansion of the introduced species into the highlands, the sensitivity to past climatic variation detected in highland populations, and the potentially threatened state of single-island endemics.