Beetle Lineage Research Articles

Transoceanic Stepping–stones between Cretaceous waterfalls? The enigmatic biogeography of pantropical Oocyclus cascade beetles

Beetles have colonized freshwater habitats multiple times throughout their evolutionary history. Some of these aquatic lineages are associated exclusively with waterfall–like habitats, often with modified morphologies to cope with their unusual way of life. The historical biogeography of such cascade beetle lineages has been shown to strongly reflect ancient tectonic events. We focus on the pantropical genus Oocyclus of which species dwell in waterfalls and associated habitats. We infer the first molecular phylogeny of Oocyclus using a dataset of seven gene fragments. We recover a well resolved phylogenetic hypothesis, with a monophyletic Oocyclus divided in three genetically well–differentiated subclades which correspond to geography. Comparative dating analyses across Hydrophilidae based on ten fossil calibrations recover a Cretaceous origin for the genus. Based on a comprehensive suite of ancestral range analyses, we suggest a unique pattern with an origin in Southeast Asia followed by the successive colonization of India and the Neotropics via transoceanic stepping–stone dispersal. Diversification rate analyses support a scenario in which old Oocyclus lineages diversified slowly with a homogeneous rate regime. Waterfall beetle radiations are ancient and remarkably track Earth’s paleogeological history, shedding light on intricate patterns of macroevolution.

Whirling in the late Permian: ancestral Gyrinidae show early radiation of beetles before Permian-Triassic mass extinction

BackgroundGyrinidae are a charismatic group of highly specialized beetles, adapted for a unique lifestyle of swimming on the water surface. They prey on drowning insects and other small arthropods caught in the surface film. Studies based on morphological and molecular data suggest that gyrinids were the first branch splitting off in Adephaga, the second largest suborder of beetles. Despite its basal position within this lineage and a very peculiar morphology, earliest Gyrinidae were recorded not earlier than from the Upper Triassic.ResultsTunguskagyrus. with the single species Tunguskagyrus planus is described from Late Permian deposits of the Anakit area in Middle Siberia. The genus is assigned to the stemgroup of Gyrinidae, thus shifting back the minimum age of this taxon considerably: Tunguskagyrus demonstrates 250 million years of evolutionary stability for a very specialized lifestyle, with a number of key apomorphies characteristic for these epineuston predators and scavengers, but also with some preserved ancestral features not found in extant members of the family. It also implies that major splitting events in this suborder and in crown group Coleoptera had already occurred in the Permian. Gyrinidae and especially aquatic groups of Dytiscoidea flourished in the Mesozoic (for example Coptoclavidae and Dytiscidae) and most survive until the present day, despite the dramatic “Great Dying” – Permian-Triassic mass extinction, which took place shortly (in geological terms) after the time when Tunguskagyrus lived.ConclusionsTunguskagyrus confirms a Permian origin of Adephaga, which was recently suggested by phylogenetic “tip-dating” analysis including both fossil and Recent gyrinids. This also confirms that main splitting events leading to the “modern” lineages of beetles took place before the Permian-Triassic mass extinction. Tunguskagyrus shows that Gyrinidae became adapted to swimming on the water surface long before Mesozoic invasions of the aquatic environment took place (Dytiscoidea). The Permian origin of Gyrinidae is consistent with a placement of this highly derived family as the sister group of all remaining adephagan groups, as suggested based on morphological features of larvae and adults and recent analyses of molecular data.

Speciation below ground: Tempo and mode of diversification in a radiation of endogean ground beetles.

Dispersal is a critical factor determining the spatial scale of speciation, which is constrained by the ecological characteristics and distribution of a species' habitat and the intrinsic traits of species. Endogean taxa are strongly affected by the unique qualities of the below-ground environment and its effect on dispersal, and contrasting reports indicate either high dispersal capabilities favoured by small body size and mediated by passive mechanisms, or low dispersal due to restricted movement and confinement inside the soil. We studied a species-rich endogean ground beetle lineage, Typhlocharina, including three genera and more than 60 species, as a model for the evolutionary biology of dispersal and speciation in the deep soil. A time-calibrated molecular phylogeny generated from >400 individuals was used to delimit candidate species, to study the accumulation of lineages through space and time by species-area-age relationships and to determine the geographical structure of the diversification using the relationship between phylogenetic and geographic distances across the phylogeny. Our results indicated a small spatial scale of speciation in Typhlocharina and low dispersal capacity combined with sporadic long distance, presumably passive dispersal events that fuelled the speciation process. Analysis of lineage growth within Typhlocharina revealed a richness plateau correlated with the range of distribution of lineages, suggesting a long-term species richness equilibrium mediated by density dependence through limits of habitat availability. The interplay of area- and age-dependent processes ruling the lineage diversification in Typhlocharina may serve as a general model for the evolution of high species diversity in endogean mesofauna.

Landscape-scale genetic differentiation of a mycangial fungus associated with the ambrosia beetle, Xylosandrus germanus (Blandford) (Curculionidae:Scolytinae) in Japan.

In this study, we examined the genetic structures of the ambrosia fungus isolated from mycangia of the scolytine beetle, Xylosandrus germanus to understand their co‐evolutionary relationships. We analyzed datasets of three ambrosia fungus loci (18S rDNA, 28S rDNA, and the β‐tubulin gene) and a X. germanus locus dataset (cytochrome c oxidase subunit 1 (COI) mitochondrial DNA). The ambrosia fungi were separated into three cultural morphptypes, and their haplotypes were distinguished by phylogenetic analysis on the basis of the three loci. The COI phylogenetic analysis revealed three distinct genetic lineages (clades A, B, and C) within X. germanus, each of which corresponded to specific ambrosia fungus cultural morphptypes. The fungal symbiont phylogeny was not concordant with that of the beetle. Our results suggest that X. germanus may be unable to exchange its mycangial fungi, but extraordinary horizontal transmission of symbiotic fungi between the beetle's lineages occurred at least once during the evolutionary history of this symbiosis.

The chicken or the egg? Adaptation to desiccation and salinity tolerance in a lineage of water beetles.

Transitions from fresh to saline habitats are restricted to a handful of insect lineages, as the colonization of saline waters requires specialized mechanisms to deal with osmotic stress. Previous studies have suggested that tolerance to salinity and desiccation could be mechanistically and evolutionarily linked, but the temporal sequence of these adaptations is not well established for individual lineages. We combined molecular, physiological and ecological data to explore the evolution of desiccation resistance, hyporegulation ability (i.e., the ability to osmoregulate in hyperosmotic media) and habitat transitions in the water beetle genus Enochrus subgenus Lumetus (Hydrophilidae). We tested whether enhanced desiccation resistance evolved before increases in hyporegulation ability or vice versa, or whether the two mechanisms evolved in parallel. The most recent ancestor of Lumetus was inferred to have high desiccation resistance and moderate hyporegulation ability. There were repeated shifts between habitats with differing levels of salinity in the radiation of the group, those to the most saline habitats generally occurring more rapidly than those to less saline ones. Significant and accelerated changes in hyporegulation ability evolved in parallel with smaller and more progressive increases in desiccation resistance across the phylogeny, associated with the colonization of meso- and hypersaline waters during global aridification events. All species with high hyporegulation ability were also desiccation-resistant, but not vice versa. Overall, results are consistent with the hypothesis that desiccation resistance mechanisms evolved first and provided the physiological basis for the development of hyporegulation ability, allowing these insects to colonize and diversify across meso- and hypersaline habitats.

Different processing of CAPA and pyrokinin precursors in the giant mealworm beetle Zophobas atratus (Tenebrionidae) and the boll weevil Anthonomus grandis grandis (Curculionidae)

Capa and pyrokinin (pk) genes in hexapods share a common evolutionary origin. Using transcriptomics and peptidomics, we analyzed products of these genes in two beetles, the giant mealworm beetle (Zophobas atratus; Tenebrionidae) and the boll weevil (Anthonomus grandis grandis; Curculionidae). Our data revealed that even within Coleoptera, which represents a very well-defined group of insects, highly different evolutionary developments occurred in the neuropeptidergic system. These differences, however, primarily affect the general structure of the precursors and differential processing of mature peptides and, to a lesser degree, the sequences of the active core motifs. With the differential processing of the CAPA-precursor in Z. atratus we found a perfect example of completely different products cleaved from a single neuropeptide precursor in different cells. The CAPA precursor in abdominal ganglia of this species yields primarily periviscerokinins (PVKs) whereas processing of the same precursor in neurosecretory cells of the subesophageal ganglion results in CAPA-tryptoPK and a novel CAPA-PK. Particularly important was the detection of that CAPA-PK which has never been observed in the CNS of insects before. The three different types of CAPA peptides (CAPA-tryptoPK, CAPA-PK, PVK) each represent potential ligands which activate different receptors. In contrast to the processing of the CAPA precursor from Z. atratus, no indications of a differential processing of the CAPA precursor were found in A. g. grandis. These data suggest that rapid evolutionary changes regarding the processing of CAPA precursors were still going on when the different beetle lineages diverged. The sequence of the single known PVK of A. g. grandis occupies a special position within the known PVKs of insects and might serve asa basis to develop lineage-specific peptidomimetics capable of disrupting physiological processes regulated by PVKs.

Pleistocene range shifts, refugia and the origin of widespread species in western Palaearctic water beetles

Quaternary glacial cycles drove major shifts in both the extent and location of the geographical ranges of many organisms. During glacial maxima, large areas of central and northern Europe were inhospitable to temperate species, and these areas are generally assumed to have been recolonized during interglacials by range expansions from Mediterranean refugia. An alternative is that this recolonization was from non-Mediterranean refugia, in central Europe or western Asia, but data on the origin of widespread central and north European species remain fragmentary, especially for insects. We studied three widely distributed lineages of freshwater beetles (the Platambus maculatus complex, the Hydraena gracilis complex, and the genus Oreodytes), all restricted to running waters and including both narrowly distributed southern endemics and widespread European species, some with distributions spanning the Palearctic. Our main goal was to determine the role of the Pleistocene glaciations in shaping the diversification and current distribution of these lineages. We sequenced four mitochondrial and two nuclear genes in populations drawn from across the ranges of these taxa, and used Bayesian probabilities and Maximum Likelihood to reconstruct their phylogenetic relationships, age and geographical origin. Our results suggest that all extant species in these groups are of Pleistocene origin. In the H. gracilis complex, the widespread European H. gracilis has experienced a rapid, recent range expansion from northern Anatolia, to occupy almost the whole of Europe. However, in the other two groups widespread central and northern European taxa appear to originate from central Asia, rather than the Mediterranean. These widespread species of eastern origin typically have peripherally isolated forms in the southern Mediterranean peninsulas, which may be remnants of earlier expansion-diversification cycles or result from incipient isolation of populations during the most recent Holocene expansion. The accumulation of narrow endemics of such lineages in the Mediterranean may result from successive cycles of range expansion, with subsequent speciation (and local extinction in glaciated areas) through multiple Pleistocene climatic cycles.

Hidden biodiversity: total evidence phylogenetics and evolution of morphological traits in a highly diverse lineage of endogean ground beetles, Typhlocharis Dieck, 1869 (Carabidae, Trechinae, Anillini).

Typhlocharis is the most diverse eyeless endogean ground beetle genus known to date, with 62 species all endemic to the West Mediterranean region. The lineage is characterized by a conservative and singular body plan within Carabidae that contrasts with a high morphological diversity in many traits. We provide an exhaustive phylogeny of the lineage through the study of 92 morphological characters from all 62 described species and 45 potential new species from 70 additional populations, and the combination of morphological and available molecular data, in the first total evidence phylogenetic approach for a highly diverse endogean lineage. We tracked the evolution of morphological traits over the obtained phylogenies. Results suggest eight morphologically distinct clades, which do not correspond to the species groups proposed formerly. Ancestral state reconstructions and phylogenetic signal analyses of morphological traits revealed that some of the previously key characters to the classification of Typhlocharis, such as the umbilicate series or the apical denticles of elytra, are highly homoplasic, whereas other characters show stronger phylogenetic signal, including structures in the antennae, gula, pronotum and last abdominal ventrite. This evidence supports the split of Typhlocharis into three genera: Lusotyphlus gen. nov.; Typhlocharis Dieck, 1869 and Microcharidius Coiffait, 1969 (revalidated), forming the subtribe Typhlocharina Jeanne, 1973.

Using phylogenies to trace the geographical signal of diversification

AbstractAimCurrent geographical distributions in conjunction with species‐level phylogenies have been viewed as offering an enormous potential for investigating the causes of speciation. However, many authors have concluded that species ranges are too dynamic to retain the historical signal of the speciation processes. We develop an approach to explore the extent to which range changes have erased the geographical signal of speciation in the current distribution of species lineages, and whether phylogenetic relationships among species and their current distributions can provide information regarding the geography of diversification. As case studies we used different lineages of aquatic Coleoptera.LocationWestern Palaearctic.MethodsWe first assessed the persistence of a geographical signal in the current distribution of a clade from the association between evolutionary relationships and geography using Mantel tests. We then tested two potential scenarios of diversification using bivariate plots of the geographical distance between the centroids of the species ranges and phylogenetic distances, and an assessment of the match between the observed geographical distribution and the phylogenetic topology. We used as a study system a set of 10 monophyletic lineages of water beetles with different ecological characteristics (either standing water, running water or a mixture of both habitat types).ResultsOur results point to a common pattern of geographically conserved ranges where current species seem to have originated through range fragmentation of formerly more widespread species. Exclusive standing water clades showed a much weaker signal, as expected from their higher mobility, which erases the geographical signal at much shorter temporal scales.Main conclusionsOverall, our findings show that for at least some lineages it is possible to obtain strong evidence of stasis of the geographical ranges of species, as well as information regarding the diversification process, through the study of their current distributions and phylogenetic relationships.

Deep-Time Convergence in Rove Beetle Symbionts of Army Ants

Recent adaptive radiations provide striking examples of convergence [1-4], but the predictability of evolution over much deeper timescales is controversial, with a scarcity of ancient clades exhibiting repetitive patterns of phenotypic evolution [5, 6]. Army ants areecologically dominant arthropod predators of theworld's tropics, with large nomadic colonies housing diverse communities of socially parasitic myrmecophiles [7]. Remarkable among these are many speciesof rove beetle (Staphylinidae) that exhibit ant-mimicking "myrmecoid" body forms and are behaviorally accepted into their aggressive hosts' societies: emigrating with colonies and inhabiting temporary nest bivouacs, grooming and feeding with workers, but also consuming the brood [8-11]. Here, we demonstrate that myrmecoid rove beetles are strongly polyphyletic, with this adaptive morphological and behavioral syndrome having evolved at least12 times during the evolution of a single staphylinid subfamily, Aleocharinae. Each independent myrmecoid clade is restricted to one zoogeographic region and highly host specific on a single army ant genus. Dating estimates reveal that myrmecoid cladesare separated by substantial phylogenetic distances-as much as 105 million years. All such groups arose in parallel during the Cenozoic, when army ants diversified into modern genera [12] and rose to ecological dominance [13, 14]. This work uncovers arare example of an ancient system of complex morphological and behavioral convergence, with replicate beetle lineages following a predictable phenotypic trajectory during their parasitic adaptation to host colonies.

Ambrosia beetle Premnobius cavipennis (Scolytinae: Ipini) carries highly divergent ascomycotan ambrosia fungus, Afroraffaelea ambrosiae gen. nov. et sp. nov. (Ophiostomatales)

Abstract Ambrosia beetles and fungi represent an interesting and economically important symbiosis, but the vast majority of ambrosia fungi remain unexplored, hindering research, management of pathogens, and mitigation of invasive species. Beetles in the subtribe Premnobiini are one example of an entire beetle lineage whose fungal symbionts have never been studied. Here, we identify one dominant fungal symbiont of Premnobius cavipennis by using fungus culturing, community sequencing, microtome sectioning and micro-CT scanning of mycangia. Phylogenetic analyses of combined 18S and 28S rDNA and β-tubulin sequences revealed a highly divergent fungal lineage within Ophiostomatales, Afroraffaelea ambrosiae gen. nov. et sp. nov. The newly described fungal lineage represents another origin of the symbiosis within the Kingdom Fungi, adding to our understanding of the geographic ancestry of ambrosia fungi. P. cavipennis possesses pharyngeal mycangia which appear restrictive in fungus selection. This ambrosia beetle-fungus association has remained stable even after invasions into non-native regions.

Ancient hastisetae of Cretaceous carrion beetles (Coleoptera: Dermestidae) in Myanmar amber

Hastisetae are extremely elaborate and intricate insect setae that occur solely on dermestid larvae (Coleoptera: Dermestidae). The present work characterizes hastisetae found in mid-Cretaceous amber from Myanmar and compares them to hastisetae found on extant dermestid larvae. The presence of hastisetae in Myanmar amber shows that lineages of dermestid beetles had already developed hastisetae by the mid-Cretaceous and their presence allows us to follow the evolutionary development of this particular arthropod structure over the past 100 million years. Hastisetae attached to a parasitic wasp in the same piece of amber indicates that ancient dermestid beetles used their hastisetae for defense, similar to their function today.

Strategies of chemical anti-predator defences in leaf beetles: is sequestration of plant toxins less costly than de novo synthesis?

The evolution of defensive traits is driven both by benefits gained from protection against enemies and by costs of defence production. We tested the hypothesis that specialisation of herbivores on toxic host plants, accompanied by the ability to acquire plant defensive compounds for herbivore defence, is favoured by the lower costs of sequestration compared to de novo synthesis of defensive compounds. We measured physiological costs of chemical defence as a reduction in larval performance in response to repeated removal of secretions (simulating predator attack) and compared these costs between five species synthesising defences de novo and three species sequestering salicylic glucosides (SGs) from their host plants. Experiments simulating low predator pressure revealed no physiological costs in terms of survival, weight and duration of development in any of study species. However, simulation of high predation caused reduction in relative growth rate in Chrysomela lapponica larvae producing autogenous defences more frequently, than in larvae sequestering SGs. Still meta-analysis of combined data showed no overall difference in costs of autogenous and sequestered defences. However, larvae synthesising their defences de novo demonstrated secretion-conserving behaviour, produced smaller amounts of secretions, replenished them at considerably lower rates and employed other types of defences (regurgitation, evasion) more frequently when compared to sequestering larvae. These latter results provide indirect evidence for biosynthetic constraints for amounts of defensive secretions produced de novo, resulting in low defence effectiveness. Lifting these constraints by sequestration may have driven some leaf beetle lineages toward sequestration of plant allelochemicals as the main defensive strategy.

Endocrine Control of Exaggerated Trait Growth in Rhinoceros Beetles.

Juvenile hormone (JH) is a key insect growth regulator frequently involved in modulating phenotypically plastic traits such as caste determination in eusocial species, wing polymorphisms in aphids, and mandible size in stag beetles. The jaw morphology of stag beetles is sexually-dimorphic and condition-dependent; males have larger jaws than females and those developing under optimum conditions are larger in overall body size and have disproportionately larger jaws than males raised under poor conditions. We have previously shown that large males have higher JH titers than small males during development, and ectopic application of fenoxycarb (JH analog) to small males can induce mandibular growth similar to that of larger males. What remains unknown is whether JH regulates condition-dependent trait growth in other insects with extreme sexually selected structures. In this study, we tested the hypothesis that JH mediates the condition-dependent expression of the elaborate horns of the Asian rhinoceros beetle, Trypoxylus dichotomus. The sexually dimorphic head horn of this beetle is sensitive to nutritional state during larval development. Like stag beetles, male rhinoceros beetles receiving copious food produce disproportionately large horns for their body size compared with males under restricted diets. We show that JH titers are correlated with body size during the late feeding and early prepupal periods, but this correlation disappears by the late prepupal period, the period of maximum horn growth. While ectopic application of fenoxycarb during the third larval instar significantly delayed pupation, it had no effect on adult horn size relative to body size. Fenoxycarb application to late prepupae also had at most a marginal effect on relative horn size. We discuss our results in context of other endocrine signals of condition-dependent trait exaggeration and suggest that different beetle lineages may have co-opted different physiological signaling mechanisms to achieve heightened nutrient-sensitive weapon growth.

A review and phylogeny of Scarabaeine dung beetle fossils (Coleoptera: Scarabaeidae: Scarabaeinae), with the description of two Canthochilum species from Dominican amber.

Despite the increasing rate of systematic research on scarabaeine dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae), their fossil record has remained largely unrevised. In this paper, we review all 33 named scarabaeine fossils and describe two new species from Dominican amber (Canthochilum alleni sp.n., Canthochilum philipsivieorum sp.n.). We provide a catalogue of all fossil Scarabaeinae and evaluate their assignment to this subfamily, based primarily on the original descriptions but also, where possible, by examining the type specimens. We suggest that only 21 fossil taxa can be reliably assigned to the Scarabaeinae, while the remaining 14 should be treated as doubtful Scarabaeinae. The doubtful scarabaeines include the two oldest dung beetle fossils known from the Cretaceous and we suggest excluding them from any assessments of the minimum age of scarabaeine dung beetles. The earliest reliably described scarabaeine fossil appears to be Lobateuchus parisii, known from Oise amber (France), which shifts the minimum age of the Scarabaeinae to the Eocene (53 Ma). We scored the best-preserved fossils, namely Lobateuchus and the two Canthochilum species described herein, into the character matrix used in a recent morphology-based study of dung beetles, and then inferred their phylogenetic relationships with Bayesian and parsimony methods. All analyses yielded consistent phylogenies where the two fossil Canthochilum are placed in a clade with the extant species of Canthochilum, and Lobateuchus is recovered in a clade with the extant genera Ateuchus and Aphengium. Additionally, we evaluated the distribution of dung beetle fossils in the light of current global dung beetle phylogenetic hypotheses, geological time and biogeography. The presence of only extant genera in the late Oligocene and all later records suggests that the main present-day dung beetle lineages had already been established by the late Oligocene–mid Miocene.

Thermal niche estimators and the capability of poor dispersal species to cope with climate change.

For management strategies in the context of global warming, accurate predictions of species response are mandatory. However, to date most predictions are based on niche (bioclimatic) models that usually overlook biotic interactions, behavioral adjustments or adaptive evolution, and assume that species can disperse freely without constraints. The deep subterranean environment minimises these uncertainties, as it is simple, homogeneous and with constant environmental conditions. It is thus an ideal model system to study the effect of global change in species with poor dispersal capabilities. We assess the potential fate of a lineage of troglobitic beetles under global change predictions using different approaches to estimate their thermal niche: bioclimatic models, rates of thermal niche change estimated from a molecular phylogeny, and data from physiological studies. Using bioclimatic models, at most 60% of the species were predicted to have suitable conditions in 2080. Considering the rates of thermal niche change did not improve this prediction. However, physiological data suggest that subterranean species have a broad thermal tolerance, allowing them to stand temperatures never experienced through their evolutionary history. These results stress the need of experimental approaches to assess the capability of poor dispersal species to cope with temperatures outside those they currently experience.

India-Madagascar vicariance explains cascade beetle biogeography

India and Madagascar drifted apart more than 80 Mya, yet few taxonomic groups currently found in these regions bear any signature of this split. When drifting in isolation, extensive volcanic activity covered almost half of India in lava flows, likely triggering widespread extinction on the island. Consequently, most of India's rich extant flora and fauna are considered to be the result of recent Cenozoic dispersal, and no lineages are conclusively a result of ancient vicariance. Many of Madagascar's lineages also stem from either Cenozoic diversification or dispersal events, with the latter being a result of the close proximity of the island with mainland Africa. In the present study, we focus on two remarkable lineages of cascade beetles in the genera Scoliopsis and Tritonus (Coleoptera, Hydrophilidae), respectively, dwelling in the mountains of south India and Sri Lanka, as well as in Madagascar. Based on a molecular phylogeny of the family Hydrophilidae dated with eight fossils, we show that these two lineages are sister taxa, and diverged when Madagascar and Greater India (India, Sri Lanka, Seychelles) separated, suggesting a pattern of Gondwanean vicariance. The results of the present study show that, despite geological upheaval, the present-day fauna of India still retains traces of its Gondwanan past.

How the rice weevil breaks down the pectin network: Enzymatic synergism and sub-functionalization

Pectin is the most complex polysaccharide in nature and highly abundant in plant cell walls and middle lamellae, where it functions in plant growth and development. Phytopathogens utilize plant pectin as an energy source through enzyme-mediated degradation. These pectolytic enzymes include polygalacturonases (PGs) of the GH28 family and pectin methylesterases (PMEs) of the CE8 family. Recently, PGs were also identified in herbivorous insects of the distantly related plant bug, stick insect and Phytophaga beetle lineages. Unlike all other insects, weevils possess PMEs in addition to PGs. To investigate pectin digestion in insects and the role of PMEs in weevils, all PME and PG family members of the rice weevil Sitophilus oryzae were heterologously expressed and functionally characterized. Enzymatically active and inactive PG and PME family members were identified. The loss of activity can be explained by a lack of substrate binding correlating with substitutions of functionally important amino acid residues. We found subfunctionalization in both enzyme families, supported by expression pattern and substrate specificities as well as evidence for synergistic pectin breakdown. Our data suggest that the rice weevil might be able to use pectin as an energy source, and illustrates the potential of both PG and PME enzyme families to functionally diversify after horizontal gene transfer.

Comparative developmental analysis of Drosophila and Tribolium reveals conserved and diverged roles of abrupt in insect wing evolution

Morphological innovation is a fundamental process in evolution, yet its molecular basis is still elusive. Acquisition of elytra, highly modified beetle forewings, is an important innovation that has driven the successful radiation of beetles. Our RNAi screening for candidate genes has identified abrupt (ab) as a potential key player in elytron evolution. In this study, we performed a series of RNA interference (RNAi) experiments in both Tribolium and Drosophila to understand the contributions of ab to the evolution of beetle elytra. We found that (i) ab is essential for proper wing vein patterning both in Tribolium and Drosophila, (ii) ab has gained a novel function in determining the unique elytron shape in the beetle lineage, (iii) unlike Hippo and Insulin, other shape determining pathways, the shape determining function of ab is specific to the elytron and not required in the hindwing, (iv) ab has a previously undescribed role in the Notch signal-associated wing formation processes, which appears to be conserved between beetles and flies. These data suggest that ab has gained a new function during elytron evolution in beetles without compromising the conserved wing-related functions. Gaining a new function without losing evolutionarily conserved functions may be a key theme in the evolution of morphologically novel structures.

Wolbachia distribution in selected beetle taxa characterized by PCR screens and MLST data.

Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia's effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia-arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages.