Molecular systematics and time-scale for the evolution of Timarcha, a leaf-beetle genus with a disjunct Holarctic distribution

Higher-level phylogeny of Chrysomelidae based on expanded sampling of mitogenomes

Chrysomelidae is one of the most diverse lineages of beetles. The classification and phylogeny of Chrysomelidae have been contentious. In this study, we obtained 16 new mitogenome sequences by using next-generation sequencing. Combined with the published mitogenomes, we inferred the phylogenetic relationships of Chrysomelidae. Different data recoding strategies and substitution models were applied to phylogenetic reconstruction. In the Maximum likelihood analyses under the homogeneous model, Dayhoff recoding allowed for the improved phylogenetic resolution due to the decreased level of heterogeneous sequence divergence. Bayesian inference under the heterogeneous model yielded generally well resolved subfamily relationships. The present mitogenome data strongly supported Chrysomelidae as a monophyletic group. Consistent with previous work, we found three major subfamily clades within Chrysomelidae. However, the pattern of the "sagrine" clade plus the "eumolpine" clade being sister to the "chrysomeline" clade contrasted with the prior study. The placement of the genus Syneta with regards to these three clades was ambiguous. Relationships recovered suggested several major chrysomelid lineages, including: (1) Bruchinae in the "sagrine" clade; (2) Donaciinae + Criocerinae; (3) Spilopyrinae + (Cassidinae + (Eumolpinae + (Lamprosomatinae + Cryptocephalinae))); (4) Chrysomelinae + (Alticinae + Galerucinae). Results also suggested the placement of Timarcha outside the major Chrysomelinae.

The species of Timarcha Samouelle, 1819 described by Linnaeus (Coleoptera, Chrysomelidae)

Linnaeus described five species presently included in the genus Timarcha: Chrysomela goettingensis, Tenebrio caeruleus, Tenebrio laevigatus, Tenebrio latipes, and Tenebrio rugosus. After a study of the relevant material, the identity of these species has been established. The following synonyms are proposed or confirmed: Timarcha goettingensis (Linnaeus, 1758) = T. latipes (Linnaeus, 1767), syn. nov.; Timarcha caerulea (Linnaeus, 1758), comb. nov. = T. balearica Gory, 1833, syn. nov. = T. balearica Pérez Arcas, 1865, syn. nov.; Timarcha rugosa (Linnaeus, 1767) = T. scabra (Olivier, 1807), syn. conf. = T. generosa Erichson, 1841, syn. conf.; Timarcha laevigata (Linnaeus, 1767) = T. tenebricosa (Fabricius, 1775), syn. conf.. The type of Tenebrio caeruleus is a Chrysomelidae currently belonging to genus Timarcha and therefore can no longer be considered a Tenebrionidae (Helops caeruleus) nor the type species of genus Helops. For the sake of nomenclatural stability, an application to the International Commission on Zoological Nomenclature to change the relative precedence of Timarcha caerulea and retain usage of T. balearica will be made. An application to change the relative precedence of Timarcha laevigata has been submitted, which would lead to the conservation of usage of T. tenebricosa as valid. Lectotypes are designated for Chrysomela goettingensis, Tenebrio latipes, Tenebrio caeruleus, Timarcha balearica Gory, T. balearica Pérez Arcas, Tenebrio rugosus, Chrysomela scabra, Timarcha generosa, Tenebrio laevigatus, and Chrysomela tenebricosa. For each of the valid species the diagnosis, distribution, and host-plant data are reported.

Timarcha Latreille: A strange beetle and a living fossil

The genus Timarcha seems unique among Chrysomelidae: Chrysomelinae by having plesiomorphic characters such as genitalia with a ring-like tegmen, covered with a setose parameral cap, together with apomorphic characters, including apterism and fused elytra. The distribution of this genus is also very peculiar: circum Mediterranean and northwestern American. Food selection also seems rather stict, comprising 8 families and 20 genera of plants. Two of the subgenera (Metallotimarcha and Americanotimarcha) share one plant family, the Ericaceae. The plant family Rubiaceae is also shared between three subgenera: Timarcha, Timarchostoma and Metallotimarcha. Reflex bleeding among diurnal species, aposematism, thanatosis, stomatic regurgitation are means of defense against predators, but not against parasites and commensals. A very archaic genus, probably originating in early Mesozoic, with around 100 taxa, and 50 subspecies. Mutations remain very common in the group and new species are possibly still emerging.

Cytogenetics, cytotaxonomy and chromosomal evolution of Chrysomelinae revisited (Coleoptera, Chrysomelidae)

Nearly 260 taxa and chromosomal races of subfamily Chrysomelinae have been chromosomally analyzed showing a wide range of diploid numbers from 2n = 12 to 2n = 50, and four types of male sex-chromosome systems. with the parachute-like ones Xy(p) and XY(p) clearly prevailing (79.0%), but with the XO well represented too (19.75%). The modal haploid number for chrysomelines is n = 12 (34.2%) although it is not probably the presumed most plesiomorph for the whole subfamily, because in tribe Timarchini the modal number is n = 10 (53.6%) and in subtribe Chrysomelina n = 17 (65.7%). Some well sampled genera, such as Timarcha, Chrysolina and Cyrtonus, are variable in diploid numbers, whereas others, like Chrysomela, Paropsisterna, Oreina and Leptinotarsa, are conservative and these differences are discussed. The main shifts in the chromosomal evolution of Chrysomelinae seems to be centric fissions and pericentric inversions but other changes as centric fusions are also clearly demonstrated. The biarmed chromosome shape is the prevalent condition, as found in most Coleoptera, although a fair number of species hold a few uniarmed chromosomes at least. A significant negative correlation between the haploid numbers and the asymmetry in size of karyotypes (r = -0.74) has been found from a large sample of 63 checked species of ten different genera. Therefore, the increases in haploid number are generally associated with a higher karyotype symmetry.

Molecular phylogeny of reed beetles (Col., Chrysomelidae, Donaciinae): the signature of ecological specialization and geographical isolation

The Donaciinae consist of approximately 165 species predominantly occurring in the northern hemisphere. We analysed mitochondrial and nuclear DNA (COI, EF-1alpha) of 46 species to investigate their phylogeny and to discuss general topics in the context of insect herbivory (generalists versus specialists, ecological speciation). Phylogenetic reconstructions from various methodical approaches yielded very similar results. Clades corresponding to the traditional tribes/genera were recovered. Within the genus Donacia, species groups with characteristic host plant preference were identified. Estimated divergence times are discussed on the background of geological events. The origin of the Donaciinae is dated to 75-100 million years before present, after which they quickly diversified into the main groups. An initial split of those groups occurred in the Palaeocene. In the Eocene and Oligocene, major lineages specialized on certain host plants, where they radiated in the Miocene. This radiation was enforced by geographic isolation brought about by the final separation of America and Europe, after which there arose continental lineages within three larger species groups. In their evolution based on ecological specialization with a recently superimposed geographic isolation, the Donaciinae follow a pattern of specialists arising from generalists. Host plant shifts show that such a specialization is not necessarily an 'evolutionary dead-end'.

Living on the edge: demographic and phylogeographical patterns in the woodlouse-hunter spiderDysdera lancerotensisSimon, 1907 on the eastern volcanic ridge of the Canary Islands

The Eastern Canary Islands are the emerged tips of a continuous volcanic ridge running parallel to the northeastern African coast, originated by episodic volcanic eruptions that can be traced back to the Miocene and that, following a major period of quiescence and erosion, continued from the Pliocene to the present day. The islands have been periodically connected by eustatic sea-level changes resulting from Pleistocene glacial cycles. The ground-dwelling spider Dysdera lancerotensis Simon, 1907 occurs along the entire ridge, except on recent barren lavas and sand dunes, and is therefore an ideal model for studying the effect of episodic geological processes on terrestrial organisms. Nested clade and population genetic analyses using 39 haplotypes from 605 base pairs of mitochondrial DNA cytochrome c oxidase I sequence data, along with phylogenetic analyses including two additional mitochondrial genes, uncover complex phylogeographical and demographic patterns. Our results indicate that D. lancerotensis colonized the ridge from north to south, in contrast to what had been expected given the SSW-NNE trend of volcanism and to what had been reported for other terrestrial arthropods. The occurrence of several episodes of extinction, recolonization and expansion are hypothesized for this species, and areas that act as refugia during volcanic cycles are identified. Relaxed molecular clock methods reveal divergence times between main haplotype lineages that suggest an older origin of the northern islets than anticipated based on geological evidence. This study supports the key role of volcanism in shaping the distribution of terrestrial organisms on oceanic islands and generates phylogeographical predictions that warrant further research into other terrestrial endemisms of this fascinating region.

Recalibrated tree of leaf beetles (Chrysomelidae) indicates independent diversification of angiosperms and their insect herbivores

BACKGROUND

The great diversity of the "Phytophaga" (weevils, longhorn beetles and leaf beetles) has been attributed to their co-radiation with the angiosperms based on matching age estimates for both groups, but phylogenetic information and molecular clock calibrations remain insufficient for this conclusion.

METHODOLOGY

A phylogenetic analysis of the leaf beetles (Chrysomelidae) was conducted based on three partial ribosomal gene markers (mitochondrial rrnL, nuclear small and large subunit rRNA) including over 3000 bp for 167 taxa representing most major chrysomelid lineages and outgroups. Molecular clock calibrations and confidence intervals were based on paleontological data from the oldest (K-T boundary) leaf beetle fossil, ancient feeding traces ascribed to hispoid Cassidinae, and the vicariant split of Nearctic and Palearctic members of the Timarchini.

PRINCIPAL FINDINGS

The origin of the Chrysomelidae was dated to 73-79 Mya (confidence interval 63-86 Mya), and most subfamilies were post-Cretaceous, consistent with the ages of all confirmed body fossils. Two major monocot feeding chrysomelid lineages formed widely separated clades, demonstrating independent colonization of this ancient (early Cretaceous) angiosperm lineage.

CONCLUSIONS

Previous calibrations proposing a much older origin of Chrysomelidae were not supported. Therefore, chrysomelid beetles likely radiated long after the origin of their host lineages and their diversification was driven by repeated radiaton on a pre-existing diverse resource, rather than ancient host associations.

Molecular systematics of Eumolpinae and the relationships with Spilopyrinae (Coleoptera, Chrysomelidae)

The 3400 species of Eumolpinae constitute one of the largest subfamilies of leaf beetles (Chrysomelidae). Their systematics is still largely based on late 19th century monographs and remains highly unsatisfactory. Only recently, some plesiomorphic lineages have been split out as separate subfamilies, including the southern hemisphere Spilopyrinae and the ambiguously placed Synetinae. Here we provide insight into the internal systematics of the Eumolpinae based on molecular phylogenetic analyses of three ribosomal genes, including partial mitochondrial 16S and nuclear 28S and complete nuclear 18S rRNA gene sequences. Sixteen morphological characters considered important in the higher-level systematics of Eumolpinae were also included in a combined analysis with the molecular characters. All phylogenetic analyses were performed using parsimony by optimizing length variation directly on the tree, as implemented in the POY software. The data support the monophyly of the Spilopyrinae outside the clade including all sampled Eumolpinae, corroborating their treatment as a separate subfamily within the Chrysomelidae. The systematic placement of the Synetinae remains ambiguous but consistent with considering it a different subfamily as well, since the phylogenetic analyses using all the available evidence show the representative sequence of the subfamily also unrelated to the Eumolpinae. The Megascelini, traditionally considered a separate subfamily, falls within the Eumolpinae. Several recognized taxonomic groupings within Eumolpinae, including the tribes Adoxini or Typophorini, are not confirmed by molecular data; others like Eumolpini seem well supported. Among the morphological characters analyzed, the presence of a characteristic groove on the pygidium (a synapomorphy of the Eumolpini) and the shape of tarsal claws (simple, appendiculate or bifid) stand out as potentially useful characters for taxonomic classification in the Eumolpinae.