Adephaga are a suborder of beetles and the second-largest suborder of the Coleoptera order, with around 45,000 recorded species. The members of these species are chiefly predators in various terrestrial and aquatic ecosystems, and some of them, such as ground beetles (Carabidae), serve as agricultural pests’ prominent natural enemies. According to Gustafson et al. (2020), the suborder has traditionally been divided into two groups due to the significant differences in the adephagan families’ macroecology: Geadephaga for terrestrial lineages and Hydradephaga for aquatic ones. The suborder’s monophyly is clearly established regarding Geadephaga, the terrestrial group. However, when it comes to Hydradephaga, the aquatic one, its monophyly remains questionable and there is no consensus yet among researchers on the relationships between the constituent families. Gustafson et al. (2020) note that most studies based on molecular data support the theory of a monophyletic Hydradephaga, frequently mutually monophyletic to Geadephaga. Conversely, most studies based on morphology support the theory of a paraphyletic Hydradephaga, including the most recent ones using phylogenomic data and over 90 protein-coding genes (Gustafson et al., 2020). This paper explores the current works of researchers on the issue, takes a look at their methods, and compares results.
It is so difficult to reconstruct Adephaga’s evolutionary relationships likely because of the diversity of the group as well as its comparatively old age. Adephaga’s fossils record can be traced back to as far as the Triassic, and the Trachypachidae, their extant family, possibly had fossil members even earlier, in the Permian (Gustafson et al., 2020). The time of the phylogenetic divergence calculated with the use of a node-dating method supports the deviation of Adefaga from its closest relatives during the period of the late Carboniferous. The deepest lineages in the crown of Adefaga are related to branching events that took place somewhere in the Triassic. The age of these events can be compared to the estimated age of the events between archosaurs and turtles, which is similarly difficult to determine.
Different researchers used different methods to explore the issue of the phylogeny of Adephaga on their studies. For one, López-López and Vogler (2017) were particularly interested in the position of Cicindelidae (tiger beetles) in the Adephaga families, and used Cicindelidae’s and Carabidae’s mitogenomes to conduct phylogenetic analyses. The mitogenomes were elicited and congregated from the mixed-species DNA readers, which, in their turn, were congregated into contigs using a variety of software packages for genome congregation, including Celera Assembler, IDBA-UD and Newbler (López-López and Vogler, 2017). Gene sequences were concatinated to create a matrix of almost 14,000 bp, and the AliGROVE software was employed to estimate bias in evolutionary rates and nucleotide composition. Then there is Gustafson et al. (2020), who pursued to perform a complex phylogenomic analysis of the Adephaga suborder applying ultraconserved elements (UCEs). The researchers evaluated the practicality of a specifically designed UCE probe set tailored for Adephaga use, and compared the customized and generalized probes separately for the reconstruction of evolutionary relationships (Gustafson et al., 2020). For this study, the reads utilized were Raw Illumina, and the software pipelines for UCE datasets assembly were by Phyluce.
The third study among the four ones analyzed in this paper resorted to a phylogenetic analyses of Adephaga’s amino-acid sequence. Cai et al. (2020) used the amino acid transcriptome alignment employed by other researchers and concentrated on three MENDELEY DATA supermatrices to test their hypotheses about the phylogeny of Dytiscoidea, the Adephagan superfamily. For the compositional heterogeneity among sites to be reduced and for the convergence of runs to be facilitated, Cai et al. (2020) applied data block mapping and gathering using entropy (BMGE). To assess competing phylogenetic hypotheses between the main Dytiscoidea groups, the researchers used both site-homogeneous and site-heterogeneous models. Finally, in their study, Beutel et al. (2020) resorted to microtome sectioning to dissect specimen of many Adephaga species to make phylogenetic conclusions. The selected specimen were immersed in araldite CY 212® and cut with the help of a microtome HM360. Winclada was used for the data to be entered in a matrix, and NONA and TNT were used to conduct parsimony analyses. Mesquite was employed for the character evolution reconstruction with enforced topologies.
When it comes to results, all of the studies, like most morphology-based ones, support the theory of Geadephaga and Hydradephaga being sister groups. López-López and Vogler (2017) corroborate the basal split of two groups, and report that Cicindelidae and Trachypachidae are sisters to other Geadephaga, which substantiates their status of family. Analyses of Gustafson et al. (2020) provided a strong argument for Hydradephaga’s paraphyly, and allowed the researchers to place Gyrinidae as sister to other Adephaga families. Additionally, Cai et al. (2020) report that their results are congruent with the views of other morphology-based studies on dytiscoid relationships: Adephaga’s aquatic families are sisters to one another and to its terrestrial families. Beutel et al. (2020) echo that: in their research, as is in others based on morphology, a family of water beetles was sister to all other Adephaga ones. In this regard, the current perspective on the issue among researchers resorting to analysis of morphological data in their studies can be deemed unanimous.
However, the remaining issue is exactly that: the one-sidedness of the approach. Perhaps, if more researchers decided to base their studies on molecular data, the results would be of a widening variety, and, consequently, of an increasing value. Specialists who intend to explore the issue basing their research on morphology will either contribute to the body of literature supporting the existing hypothesis, or challenge this hypothesis by coming to different conclusions. For the latter to happen, however, different methods and techniques need to applied; otherwise, there is a high possibility nothing new will be discovered.
References
Beutel, R. G., Ribera, I., Fikáček, M., Vasilikopoulos, A., Misof, B., & Balke, M. (2020). The morphological evolution of the Adephaga (Coleoptera). Systematic Entomology, 45(2), 378-395.
Cai, C., Tihelka, E., Pisani, D., & Donoghue, P. C. (2020). Data curation and modeling of compositional heterogeneity in insect phylogenomics: A case study of the phylogeny of Dytiscoidea (Coleoptera: Adephaga). Molecular Phylogenetics and Evolution, 147, 1-7.
Gustafson, G. T., Baca, S. M., Alexander, A. M., & Short, A. E. (2020). Phylogenomic analysis of the beetle suborder Adephaga with comparison of tailored and generalized ultraconserved element probe performance. Systematic Entomology, 45(3), 552-570.
López-López, A., & Vogler, A. P. (2017). The mitogenome phylogeny of Adephaga (Coleoptera). Molecular Phylogenetics and Evolution, 114, 166-174.