The evolution of morphospace in phytophagous scarab chafers: no competition--no divergence?

Evolutionary radiation strategy revealed in the Scarabaeidae with evidence of continuous spatiotemporal morphology and phylogenesis

Evolutionary biology faces the important challenge of determining how to interpret the relationship between selection pressures and evolutionary radiation. The lack of morphological evidence on cross-species research adds to difficulty of this challenge. We proposed a new paradigm for evaluating the evolution of branches through changes in characters on continuous spatiotemporal scales, for better interpreting the impact of biotic/abiotic drivers on the evolutionary radiation. It reveals a causal link between morphological changes and selective pressures: consistent deformation signals for all tested characters on timeline, which provided strong support for the evolutionary hypothesis of relationship between scarabs and biotic/abiotic drivers; the evolutionary strategies under niche differentiation, which were manifested in the responsiveness degree of functional morphological characters with different selection pressure. This morphological information-driven integrative approach sheds light on the mechanism of macroevolution under different selection pressures and is applicable to more biodiversity research.

A new species and new records of Sericini chafers from the Lower Gangetic Plains in India (Coleoptera: Scarabaeidae: Sericinae)

Here, we investigated the diversity of Sericini in the faunistically rather unknown Lower Gangetic plains in North India, based on material from the collection of the Zoological Survey of India. We discovered one new species from West Bengal, Maladerakolkataensis Bhunia, Gupta, Sarkar & Ahrens, and provide further records of an additional 23 species belonging to five genera from the lowlands of the states Bihar and West Bengal. Out of these, 21 species represent new state records: 12 for Bihar and nine for West Bengal. All recorded species are briefly documented by diagnostic illustrations.

Local stochastics and ecoclimatic situation shape phytophagous chafer assemblage composition

Very little is known about factors determining the assemblage structure of megadiverse polyphagous-herbivore scarab chafers in the tropics (Coleoptera: Scarabaeidae). Here, we examined the composition of Sri Lankan chafer assemblages and investigated whether it is influenced more by the general ecoclimatic situation, macrohabitat, or indetermined stochastic biotic and abiotic factors of each locality. We also explored the influence of the latter on separate lineages and general body size. Based on dedicated field surveys conducted during the dry and wet seasons, we examined 4847 chafer individuals of 105 species sampled using multiple UV-light traps in 11 localities covering different forest types and altitudinal zones. Assemblages were assessed for compositional similarity, species diversity, and abundance within four major eco-spatial partitions: forest types, elevational zones, localities, and macrohabitats. Our results revealed that assemblages were shaped mainly by locality stochastics (i.e., multi-factor ensemble of all biotic and abiotic environmental conditions at local scale), and to a minor extent by ecoclimatic conditions. Macrohabitat had little effect on the assemblage composition. This was true for the entire chafer assemblage as well as for all single lineages or different body size classes. However, in medium and large species the contrasts between localities were less pronounced, which was not the case for individual lineages of the assemblage. Contrasts of assemblage similarity between localities were much more evident than those for forest types and elevation zones. Significant correlation between species composition and geographic distance was found only for the assemblage of small-bodied specimens. Seasonal change (dry-wet) in species composition was minor and only measurable in a few localities. The strong turnover between examined localities corroborates with the high degree of endemism in many phytophagous chafers, particularly in Sericini. Connected with their hypothetic poor habitat specificity and polyphagy, this might also explain why so many chafer crop pests in the Asian tropics are endemics.

Mitochondrial phylogenomics reveals deep relationships of scarab beetles (Coleoptera, Scarabaeidae)

In this study, we newly sequenced the complete mitochondrial genomes (mitogenomes) of two phytophagous scarab beetles, and investigated the deep level relationships within Scarabaeidae combined with other published beetle mitogenome sequences. The complete mitogenomes of Dicronocephalus adamsi Pascoe (Cetoniinae) and Amphimallon sp. (Melolonthinae) are 15,563 bp and 17,433 bp in size, respectively. Both mitogenomes have the typical set of 37 genes (13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes) and an A+T-rich region, with the same gene arrangement found in the majority of beetles. The secondary structures for ribosomal RNA genes (rrnL and rrnS) were inferred by comparative analysis method. Results from phylogenetic analyses provide support for major lineages and current classification of Scarabaeidae. Amino acid data recovered Scarabaeidae as monophyletic. The Scarabaeidae was split into two clades. One clade contained the subfamilies Scarabaeinae and Aphodiinae. The other major clade contained the subfamilies Dynastinae, Rutelinae, Cetoniinae, Melolonthinae and Sericini. The monophyly of Scarabaeinae, Aphodiinae, Dynastinae, Cetoniinae and Sericini were strongly supported. The Scarabaeinae was the sister group of Aphodiinae. The Cetoniinae was sister to the Dynastinae + Rutelinae clade. The Melolonthinae was a non-monophyletic group. The removal of fast-evolving sites from nucleotide dataset using a pattern sorting method (OV-sorting) supported the family Scarabaeidae as a monophyletic group. At the tribe level, the Onthophagini was non-monophyletic with respect to Oniticellini. Ateuchini was sister to a large clade comprising the tribes Onthophagini, Oniticellini and Onitini. Eurysternini was a sister group of the Phanaeini + Ateuchini clade.

Revisiting trends in morphology of antennal sensilla in scarabaeoid beetles

Phytophagous scarab beetles associated with angiosperms have characteristically enlarged lamellate antennae and exhibit a striking morphological variation of sensilla. In this study, we compared the morphology of antennal surface of 62 species Scarabaeoidea using SEM microscopy, particularly also in light of their evolution in association with angiosperms. We investigated the correlation of antennal sensilla morphology, i.e., their structure and distribution, with species diversity and lineage diversification rates. A high diversity of sensilla was observed but also multiple transitional forms, even on the same antennomere. We interpreted this as evidence for a high evolutionary plasticity. We recognized clear patterns of convergence and repeated evolution of certain types of placoid sensilla. One main tendency found in the phytophagous Pleurostict chafers was a shift from sensilla trichodea to placoid-like sensilla, apparently also enhanced by the increase of the lamellate antennal surface, either by size or number of the lamellae. This trend occurred not only in the Pleurosticts, but also in Glaphyridae, a second angiosperm-associated lineage of Scarabaeoidea. However, our results suggest no direct relation between species diversity or the rate of diversification and general sensilla morphology, i.e., the origin of placoid sensilla. This could be explained not only by species-poor lineages also possessing placoid sensilla but also by otherwise successful and species rich groups having sensilla trichodea (e.g., dung beetles). Results further reveal the need to refine current phylogenetic hypotheses by more comprehensive taxon sampling and to expand the molecular characterization of pheromones and odor binding proteins to better understand the role of chemical communication in scarab diversification.

The Mitochondrial Genomes of 18 New Pleurosticti (Coleoptera: Scarabaeidae) Exhibit a Novel trnQ-NCR-trnI-trnM Gene Rearrangement and Clarify Phylogenetic Relationships of Subfamilies within Scarabaeidae

The availability of next-generation sequencing (NGS) in recent years has facilitated a revolution in the availability of mitochondrial (mt) genome sequences. The mt genome is a powerful tool for comparative studies and resolving the phylogenetic relationships among insect lineages. The mt genomes of phytophagous scarabs of the subfamilies Cetoniinae and Dynastinae were under-represented in GenBank. Previous research found that the subfamily Rutelinae was recovered as a paraphyletic group because the few representatives of the subfamily Dynastinae clustered into Rutelinae, but the subfamily position of Dynastinae was still unclear. In the present study, we sequenced 18 mt genomes from Dynastinae and Cetoniinae using next-generation sequencing (NGS) to re-assess the phylogenetic relationships within Scarabaeidae. All sequenced mt genomes contained 37 sets of genes (13 protein-coding genes, 22 tRNAs, and two ribosomal RNAs), with one long control region, but the gene order was not the same between Cetoniinae and Dynastinae species. All mt genomes of Dynastinae species showed the same gene rearrangement of trnQ-NCR-trnI-trnM, whereas all mt genomes of Cetoniinae species showed the ancestral insect gene order of trnI-trnQ-trnM. Phylogenetic analyses (IQ-tree and MrBayes) were conducted using 13 protein-coding genes based on nucleotide and amino acid datasets. In the ML and BI trees, we recovered the monophyly of Rutelinae, Cetoniinae, Dynastinae, and Sericinae, and the non-monophyly of Melolonthinae. Cetoniinae was shown to be a sister clade to (Dynastinae + Rutelinae).

Comparative analysis of morphospace of Neotropical Sericini (Coleoptera: Scarabaeidae): disparity in the light of species diversity and activity patterns

The striking diversity among herbivorous Scarabaeoidea is still poorly understood. Therefore, we compare in these work linear measurements of body features of Neotropical and Old World linages of Sericini chafers to uncover patterns possibly linked to foraging behavior (day or night activity) or to the success of their diversification in terms of diversity. If diversity in Sericini chafers would be linked to morphological disparity, we would expect in the much less diverse Neotropical lineage a very clear drop of morphological disparity. Comparing the two major sister clades, Old World and Neotropical Sericini, in terms of their disparity and diversity, the here elaborated distance data do not support the hypothesis that morphological disparity could be a driver for the diversity of Sericini in the Old World. The influence of the metacoxal length on morphological disparity appears to represent a possible key for a better understanding of the evolution of Sericini in the Neotropical region (including their lower diversity) and answers the question of why they are so much less diverse than their sister lineage in the Old World. The increasing length of the metacoxal plate appears to be a result of the presence of a secondary metacoxal joint in Old World Sericini, which has a crucial impact on hind leg mobility and digging behavior. General body shape and single morphological characters appear under similar general evolutionary pressure: high morphometric disparity between nocturnal and diurnal Neotropical species was also corroborated by disparity estimated from discrete morphological characters.

Intraspecific variation in the Cambrian: new observations on the morphology of the Chengjiang euarthropod Sinoburius lunaris

Background

The Chengjiang biota from southwest China (518-million-years old, early Cambrian) has yielded nearly 300 species, of which more than 80 species represent early chelicerates, crustaceans and relatives. The application of µCT-techniques combined with 3D software (e.g., Drishti), has been shown to be a powerful tool in revealing and analyzing 3D features of the Chengjiang euarthropods. In order to address several open questions that remained from previous studies on the morphology of the xandarellid euarthropod Sinoburius lunaris, we reinvestigated the µCT data with Amira to obtain a different approach of visualization and to generate new volume-rendered models. Furthermore, we used Blender to design 3D models showing aspects of intraspecific variation.

Results

New findings are: (1) antennulae consist of additional proximal articles that have not been detected before; (2) compared to other appendages, the second post-antennular appendage has a unique shape, and its endopod is comprised of only five articles (instead of seven); (3) the pygidium bears four pairs of appendages which are observed in all specimens. On the other hand, differences between specimens also have been detected. These include the presence/absence of diplotergites resulting in different numbers of post-antennular appendages and tergites and different distances between the tip of the hypostome and the anterior margin of the head shield.

Conclusions

Those new observations reveal intraspecific variation among Chengjiang euarthropods not observed before and encourage considerations about possible sexual dimorphic pairs or ontogenetic stages. Sinoburius lunaris is a variable species with respect to its morphological characters, cautioning that taxon-specific variabilities need to be considered when exploring new species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01854-1.

Comparative morphology of antennal surface structures in pleurostict scarab beetles (Coleoptera)

The diverse pleurostict (phytophagous) scarab beetles with characteristically clubbed antennae exhibit striking morphological variation and a variety of different antennal sensilla. Here we compare the morphology of the antennal surface between major pleurostict lineages, including Cetoniinae, Dynastinae, Melolonthinae, Rutelinae, and a few outgroups, including Scarabaeinae and Hybosoridae. We identified various types of antennal sensilla morphologically and searched for phylogenetic patterns of sensilla within the Scarabaeidae. Sensilla were examined using SEM micrographs of 36 species and the occurrence of the different types of antennal sensilla was studied for each species. We observed a high diversity of sensilla, including multiple transitional forms. There were also a number of other interesting structures on the antennal surface with adaptive value, such as elongate elevations, serial bags, and fields of setae. Our results confirm earlier findings that within pleurostict scarabs there has occurred a clear differentiation of sensilla composition and patterns.

A mathematical model explores the contributions of bending and stretching forces to shoot gravitropism in Arabidopsis

Plant shoot gravitropism is a complex phenomenon resulting from gravity sensing, curvature sensing (proprioception), the ability to uphold self-weight and growth. Although recent data analysis and modelling have revealed the detailed morphology of shoot bending, the relative contribution of bending force (derived from the gravi-proprioceptive response) and stretching force (derived from shoot axial growth) behind gravitropism remains poorly understood. To address this gap, we combined morphological data with a theoretical model to analyze shoot bending in wild-type and lazy1-like 1 mutant Arabidopsis thaliana. Using data from actual bending events, we searched for model parameters that minimized discrepancies between the data and mathematical model. The resulting model suggests that both the bending force and the stretching force differ significantly between the wild type and mutant. We discuss the implications of the mechanical forces associated with differential cell growth and present a plausible mechanical explanation of shoot gravitropism.

A new calmanostracan crustacean species from the Cretaceous Yixian Formation and a simple approach for differentiating fossil tadpole shrimps and their relatives

BACKGROUND

Calmanostraca is a group of branchiopod eucrustaceans, with Triops cancriformis and Lepidurus apus as most prominent representatives. Both are regularly addressed with the inaccurate tag "living fossil", suggesting that the morphology has remained stable for several millions of years. Yet, T. cancriformis and L. apus represent only a fraction of the morphological diversity occurring in Calmanostraca, comprising the two groups Notostraca and Kazacharthra. Notostracans, commonly called tadpole shrimps, comprise the two groups Lepidurus and Triops with their elongated and rather narrow (in dorsal view) head shields. Kazacharthrans are exclusively fossil calmanostracans with broad and rather short shields, known from the Jurassic and Triassic period. One formation where fossil calmanostracans have been found is the Yixian Formation of northeastern China (Lower Cretaceous, 125-121 million years). It is part of the Jehol Group, an ecosystem known for its exceptionally well-preserved fossils, including vertebrates and plants, but also diverse arthropods. Two calmanostracan species have to date been described from the Yixian Formation, Jeholops hongi and Chenops yixianensis.

RESULTS

We describe here a new calmanostracan crustacean from the Yixian Formation, Notostraca oleseni, and additionally a simple tool using a morphospace analysis to delineate different species. Measurements characterising the shield and trunk proportions of different calmanostracan species were performed, data were size-corrected, and used for this morphospace analysis to compare the different morphologies. As sclerotised body parts are more likely to be preserved in fossils than soft tissue, shields and parts of the trunk are in many cases the only morphological structures available for study. Therefore, the present analysis represents a simple tool for distinguishing between different species, as well as allowing the inclusion of specimens that are only preserved fragmentarily. Additionally, it provides a tool to demarcate the kazacharthran-like specimen described, but not formally named, by Wagner et al. (Paleontol Res. 22:57-63, 2018). Hence, we amended the description and name the species Calmanostraca hassbergella.

CONCLUSION

Our results indicate a large diversity in shield and trunk morphology in calmanostracans, in contrast to their often claimed highly conserved and uniform morphology. Especially extinct forms such as Notostraca oleseni add up to this result and point to the species richness and morphological diversity within Calmanostraca.

Running in circles in phylomorphospace: host environment constrains morphological diversification in parasitic wasps

Understanding phenotypic diversification and the conditions that spur morphological novelty or constraint is a major theme in evolutionary biology. Unequal morphological diversity between sister clades can result from either differences in the rate of morphological change or in the ability of clades to explore novel phenotype ranges. We combine an existing phylogenetic framework with new phylogenomic data and geometric morphometrics to explore the relative roles of rate versus mode of morphological evolution for a hyperdiverse group: cryptine ichneumonid wasps. Data from genomic ultraconserved elements confirm that cryptines are divided into two large clades: one specialized in the use of hosts that are deeply concealed under hard substrates, and another with a much more diversified host range. Using a phylomorphospace approach, we show that both clades have experienced similar rates of morphological evolution. Nonetheless, the more specialized group is much more restricted in morphospace occupation, indicating that it repeatedly evolved morphological change through the same morphospace regions. This is in agreement with our prediction that host use imposes constraints in the morphospace available to lineages, and reinforces an important distinction between evolutionary stasis as opposed to a scenario of continual morphological change restricted to a certain range of morphotypes.

The Mitochondrial Genomes of Phytophagous Scarab Beetles and Systematic Implications

In this study, we newly sequenced five mitogenomes of representatives of phytophagous scarab beetles (Coleoptera: Scarabaeidae) by using next-generation sequencing technology. Two species have complete (or nearly complete) mitogenome sequences, namely Popillia mutans Newman (Coleoptera: Scarabaeidae) and Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae). The remaining three species have the partial mitogenomes, and the missing genes are mainly located adjacent to the control region. The complete (or nearly complete) mitogenomes have the same genome structure as most of the existing Scarabaeidae mitogenomes. We conducted phylogenetic analyses together with 24 published mitogenomes of Scarabaeoidea. The results supported a basal split of coprophagous and phytophagous Scarabaeidae. The subfamily Sericinae was recovered as sister to all other phytophagous scarab beetles. All analyses supported a non-monophyletic Melolonthinae, which included two different non-sister clades. The Cetoniinae was recovered as sister to a clade including Rutelinae and Dynastinae. Although the Rutelinae was rendered paraphyletic by Dynastinae in the Bayesian trees inferred under the site-heterogeneous CAT-GTR or CAT-MTART model, discordant patterns were given in some of ML trees estimated using the homogeneous GTR model.

A continuous morphological approach to study the evolution of pollen in a phylogenetic context: An example with the order Myrtales

The study of pollen morphology has historically allowed evolutionary biologists to assess phylogenetic relationships among Angiosperms, as well as to better understand the fossil record. During this process, pollen has mainly been studied by discretizing some of its main characteristics such as size, shape, and exine ornamentation. One large plant clade in which pollen has been used this way for phylogenetic inference and character mapping is the order Myrtales, composed by the small families Alzateaceae, Crypteroniaceae, and Penaeaceae (collectively the "CAP clade"), as well as the large families Combretaceae, Lythraceae, Melastomataceae, Myrtaceae, Onagraceae and Vochysiaceae. In this study, we present a novel way to study pollen evolution by using quantitative size and shape variables. We use morphometric and morphospace methods to evaluate pollen change in the order Myrtales using a time-calibrated, supermatrix phylogeny. We then test for conservatism, divergence, and morphological convergence of pollen and for correlation between the latitudinal gradient and pollen size and shape. To obtain an estimate of shape, Myrtales pollen images were extracted from the literature, and their outlines analyzed using elliptic Fourier methods. Shape and size variables were then analyzed in a phylogenetic framework under an Ornstein-Uhlenbeck process to test for shifts in size and shape during the evolutionary history of Myrtales. Few shifts in Myrtales pollen morphology were found which indicates morphological conservatism. Heterocolpate, small pollen is ancestral with largest pollen in Onagraceae. Convergent shifts in shape but not size occurred in Myrtaceae and Onagraceae and are correlated to shifts in latitude and biogeography. A quantitative approach was applied for the first time to examine pollen evolution across a large time scale. Using phylogenetic based morphometrics and an OU process, hypotheses of pollen size and shape were tested across Myrtales. Convergent pollen shifts and position in the latitudinal gradient support the selective role of harmomegathy, the mechanism by which pollen grains accommodate their volume in response to water loss.

Short-range phenotypic divergence among genetically distinct parapatric populations of an Australian funnel-web spider

Speciation involves divergence at genetic and phenotypic levels. Where substantial genetic differentiation exists among populations, examining variation in multiple phenotypic characters may elucidate the mechanisms by which divergence and speciation unfold. Previous work on the Australian funnel-web spider Atrax sutherlandi Gray (2010; Records of the Australian Museum62, 285-392; Mygalomorphae: Hexathelidae: Atracinae) has revealed a marked genetic structure along a 110-kilometer transect, with six genetically distinct, parapatric populations attributable to past glacial cycles. In the present study, we explore variation in three classes of phenotypic characters (metabolic rate, water loss, and morphological traits) within the context of this phylogeographic structuring. Variation in metabolic and water loss rates shows no detectable association with genetic structure; the little variation observed in these rates may be due to the spiders' behavioral adaptations (i.e., burrowing), which buffer the effects of climatic gradients across the landscape. However, of 17 morphological traits measured, 10 show significant variation among genetic populations, in a disjunct manner that is clearly not latitudinal. Moreover, patterns of variation observed for morphological traits serving different organismic functions (e.g., prey capture, burrowing, and locomotion) are dissimilar. In contrast, a previous study of an ecologically similar sympatric spider with little genetic structure indicated a strong latitudinal response in 10 traits over the same range. The congruence of morphological variation with deep phylogeographic structure in Tallaganda's A. sutherlandi populations, as well as the inconsistent patterns of variation across separate functional traits, suggest that the spiders are likely in early stages of speciation, with parapatric populations independently responding to local selective forces.

A molecular phylogeny of rose chafers (Coleoptera: Scarabaeidae: Cetoniinae) reveals a complex and concerted morphological evolution related to their flight mode

Rose chafers (Cetoniinae) are a large group of flower visitors within the pleurostict Scarabaeidae that are characterized by their distinctive flight mode with nearly closed forewings. Despite their popularity, this is the first study to use molecular data to infer their phylogenetic relationships. We used partial gene sequences for 28S rRNA, cytochrome oxidase I (cox1) and 16S rRNA (rrnL) for 299 species, representing most recognized subfamilies of Scarabaeidae, including 125 species of Cetoniinae. Combined analyses using maximum parsimony, maximum likelihood and Bayesian inferences recovered Cetoniinae as monophyletic in all analyses, with the sister clade composed of Rutelinae and Dynastinae. Rutelinae was always recovered as paraphyletic with respect to Dynastinae. Trichiini sensu lato (s.l.) was recovered as a polyphyletic clade, while Cetoniini s.l. was recovered as paraphyletic. The inferred topologies were also supported by site bootstrapping of the ML trees. With the exception of Cremastochelini, most tribes of Cetoniinae were poly- or paraphyletic, indicating the critical need for a careful revision of rose chafer classification. Analysis of elytral base structure (including 11 scored characters) in the context of phylogeny, revealed a complex, concerted and rapid transformation of the single trait elements linked to a modified flight mode with closed elytra. This appears to be unlinked to the lateral sinuation of the elytra, which originated independently several times at later stages in the evolution of the group.