The first fossil Microweiseini (Coleoptera: Coccinellidae) from the Eocene of Europe and its significance for the reconstruction of the evolution of ladybird beetles

Molecular studies on the evolution of ladybird beetles date their origin somewhere in the Cretaceous, but no fossils are known from that period. The oldest representatives come from the Eocene, with the richest diversity found in Baltic amber. Until now, representatives of only three tribes (from around 40 known) have been recognized. Recent investigation of Baltic amber have revealed representatives of the fourth tribe (Microweiseini), which are described here as Baltosidis gen. nov. with three new species: B. damgaardi sp. nov., B. damzeni sp. nov. and B. szadziewskii sp. nov. In order to test the systematic placement of this extinct genus, a phylogenetic analysis of Microweiseinae was conducted. The results place Baltosidis in a cluster with four modern genera of Microweiseini distributed exclusively in the New World. Such a distribution pattern is surprising because no close relatives of the newly described fossil genus are known from Europe or even from the Palaearctic region. Analysis of the distribution of Microweiseini genera leads to the conclusion of a possible Gondwanan origin of the tribe. Further comparison of the diversity of the ladybird beetles from modern ecosystems with those known from Baltic amber suggests substantial differences between these communities and a recent radiation of modern fauna.

Revision of the genus Coccidula Kugelann (Coleoptera, Coccinellidae)

The genus Coccidula Kugelann includes five species distributed in the Holarctic, with one species in North America and four in Palearctic region. Coccidula belongs to the tribe Coccidulini which historically was treated as a separate subfamily within ladybird beetles, but recent studies confirmed its placement as a tribe within the broadly defined subfamily Coccinellinae. All species are revised and a new synonymy of Lithophilusnaviauxi Duverger with C.litophiloides Reitter is proposed. Light and electron microscopy pictures support morphological descriptions. An identification key to all species is also provided.

Horizontally acquired antibacterial genes associated with adaptive radiation of ladybird beetles

BACKGROUND

Horizontal gene transfer (HGT) has been documented in many herbivorous insects, conferring the ability to digest plant material and promoting their remarkable ecological diversification. Previous reports suggest HGT of antibacterial enzymes may have contributed to the insect immune response and limit bacterial growth. Carnivorous insects also display many evolutionary successful lineages, but in contrast to the plant feeders, the potential role of HGTs has been less well-studied.

RESULTS

Using genomic and transcriptomic data from 38 species of ladybird beetles, we identified a set of bacterial cell wall hydrolase (cwh) genes acquired by this group of beetles. Infection with Bacillus subtilis led to upregulated expression of these ladybird cwh genes, and their recombinantly produced proteins limited bacterial proliferation. Moreover, RNAi-mediated cwh knockdown led to downregulation of other antibacterial genes, indicating a role in antibacterial immune defense. cwh genes are rare in eukaryotes, but have been maintained in all tested Coccinellinae species, suggesting that this putative immune-related HGT event played a role in the evolution of this speciose subfamily of predominant predatory ladybirds.

CONCLUSION

Our work demonstrates that, in a manner analogous to HGT-facilitated plant feeding, enhanced immunity through HGT might have played a key role in the prey adaptation and niche expansion that promoted the diversification of carnivorous beetle lineages. We believe that this represents the first example of immune-related HGT in carnivorous insects with an association with a subsequent successful species radiation.

New insights into the phylogeny and evolution of lady beetles (Coleoptera: Coccinellidae) by extensive sampling of genes and species

Ladybirds (family Coccinellidae) are one of the most diverse groups of beetles and globally comprise over 6000 species. Despite their scientific and economic significance, the taxonomy of Coccinellidae remains unstable, and we still know little about their evolutionary history. By using a small number of genes, previous phylogenetic analyses have not reliably resolved the relationships among major ladybird lineages. In this study, we sequenced 94 nuclear protein-coding genes for 214 species of Coccinellidae and 14 outgroups, covering 90 genera and 35 tribes. We found that nucleotide compositional heterogeneity is present among ladybird tribes so that phylogenetic inference at the amino acid level is more reliable than at the DNA level. Based on the maximum likelihood analyses of the amino acid dataset, we recognize three subfamilies in Coccinellidae: Microweiseinae, Monocoryninae stat. nov., and Coccinellinae. The subfamily relationships are strongly supported as (Microweiseinae, (Monocoryninae stat. nov., Coccinellinae)). The tribes of ladybirds are mostly monophyletic, except Ortaliini, Sticholotidini, Scymnini, and Coccidulini. The phylogenetic relationships among tribes of Coccinellinae are still not well resolved, with many nodes weakly supported. Our divergence time analysis suggests that the crown group of extant lady beetles arose in the Early Cretaceous ~ 143 million years ago (Mya) and experienced a rapid diversification during the Late Cretaceous (120-70 Mya). We hypothesize that the boom of angiosperms in the Late Cretaceous promoted the diversification of herbivorous Sternorrhyncha insects, especially aphids, which in turn drove the rapid radiation of predatory lady beetles. In summary, our work provides a comprehensive time-calibrated phylogeny of Coccinellidae that provides a sound framework for revising their classification and understanding the origin of their biodiversity.

Optimizing the widely used nuclear protein-coding gene primers in beetle phylogenies and their application in the genus Sasajiscymnus Vandenberg (Coleoptera: Coccinellidae)

Advances in genomic biology and the increasing availability of genomic resources allow developing hundreds of nuclear protein-coding (NPC) markers, which can be used in phylogenetic research. However, for low taxonomic levels, it may be more practical to select a handful of suitable molecular loci for phylogenetic inference. Unfortunately, the presence of degenerate primers of NPC markers can be a major impediment, as the amplification success rate is low and they tend to amplify nontargeted regions. In this study, we optimized five NPC fragments widely used in beetle phylogenetics (i.e., two parts of carbamoyl-phosphate synthetase: CADXM and CADMC, Topoisomerase, Wingless and Pepck) by reducing the degenerate site of primers and the length of target genes slightly. These five NPC fragments and 6 other molecular loci were amplified to test the monophyly of the coccinellid genus Sasajiscymnus Vandenberg. The analysis of our molecular data set clearly supported the genus Sasajiscymnus may be monophyletic but confirmation with an extended sampling is required. A fossil-calibrated chronogram was generated by BEAST, indicating an origin of the genus at the end of the Cretaceous (77.87 Myr). Furthermore, a phylogenetic informativeness profile was generated to compare the phylogenetic properties of each gene more explicitly. The results showed that COI provides the strongest phylogenetic signal among all the genes, but Pepck, Topoisomerase, CADXM and CADMC are also relatively informative. Our results provide insight into the evolution of the genus Sasajiscymnus, and also enrich the molecular data resources for further study.