While interspecific hybridization is a recognized key driver of plant diversification in recently diverged lineages, the resulting introgression can generate complex patterns of genetic and morphological variation that often challenge the recognition of species boundaries. In Paepalanthus (Eriocaulaceae), interspecific hybridization has long been hypothesized but remains largely underexplored, particularly from a genetic perspective. Here, we investigate the evolutionary dynamics of hybridization between two sympatric species of Paepalanthus in Central Brazil by integrating morphological and population genomic analyses. Our morphological assessments revealed that hybrids generally exhibited intermediate or asymmetric trait expression and a lack of gynoecium development, suggesting reduced female fertility. Genomic analyses identified an absence of contemporary F1 hybrids, with most individuals assigned to advanced-generation hybrid classes. Furthermore, we detected bidirectional and asymmetric introgression, characterized by contrasting patterns of allele sharing, while morphological traits were decoupled from genomic ancestry, highlighting the mosaic nature of hybrid genomes. These results provide the first integrative evidence of natural hybridization in Paepalanthus, suggesting incomplete reproductive isolation and recurrent introgression between divergent lineages, thereby emphasizing the role of reticulate evolution in shaping diversification and species boundaries within this group.
Cryptic speciation is common among marine bivalves; however, it remains largely unexplored in symbiotic bivalve groups. Planktomya amamiensis (Galeommatidae) is a commensal bivalve that lives on the body surface of sipunculan worms and is characterized by its exceptionally large prodissoconch II (PII). In this study, we investigated the cryptic species diversity within the Pl. amamiensis complex in the Japanese Archipelago based on morphological, ecological, and genetic data. Our molecular assessment based on the COI and ITS2 genes indicates that Pl. amamiensis in Japan is genetically separated into three distinct species (Planktomya spp. 1–3). Planktomya spp. 1 and 3 were both collected from the subtropical Amami Islands in the Ryukyu Archipelago, southern Japan, and partly shared the same Siphonosoma species as hosts, whereas Planktomya sp. 2 was collected with different Siphonosoma species from the temperate Kii Peninsula on Honshu Island, Japan. Planktomya sp. 2 was genetically close to Planktomya sp. 1, showing 9.6
This study investigated the variability within populations of the copepod Eurytemora velox. Integrative taxonomy confirmed significant genetic heterogeneity among the studied populations supported the hypothesis of E. velox being a species complex. To assess morphological variability, morphometric traits and ordination analyses were utilized. For molecular assessment, the mitochondrial cytochrome c oxidase subunit 1 (COI) and cytochrome b (cyt b) and the nuclear 18S ribosomal DNA (18S) and the internal transcribed spacer 2 (ITS2) were employed. Both morphological and molecular data facilitated the identification of at least two species: E. velox s. str. and a new cryptic species, E. nilsseni sp. nov. The former one, E. velox s. str. is an expansive, widely distributed species that inhabits diverse water bodies, including transformed river systems, particularly those with altered water parameters such as high salinity. Within this species, no population-specific morphological differences were observed; however, COI data revealed clear genetic structuring in E. velox s. str., with distinct mitochondrial haplotype clades associated with different drainage basins, whereas nuclear markers showed only limited differentiation among populations. In contrast, E. nilsseni sp. nov. is an endemic and likely relict species recorded exclusively in ponds on the Skagerrak coast islands.
Acoela are a group of microscopic worms that remains poorly known despite their high abundance and world-wide distribution. Within Acoela, the family Dakuidae has undergone several taxonomic changes in recent decades, yet its internal phylogeny remains unclear. Herein, we describe seven new species of Dakuidae from Croatia, Germany, Italy, Panama, and Sweden: Philactinoposthia brunopunctata sp. nov., Philactinoposthia centrofusca sp. nov., Philactinoposthia raikovae sp. nov., Philactinoposthia gracilia sp. nov., Philactinoposthia parvipenis sp. nov., Philocelis leasae sp. nov. and Philocelis dunensis sp. nov. Mitochondrial (COI) and nuclear (18 S, 28 S) sequences were used to assess the phylogenetic relationships within the family, supporting the presence of two sister groups: the first comprising species of the genus Philocelis along with Philactinoposthia saliens, Philactinoposthia rhammifera and Daku woorimensis, and the second consisting of other species of the genus Philactinoposthia. P. saliens and P. rhammifera are transferred from Philactinoposthia to Philocelis. The genus Daku is synonymised with Philocelis. Finally, we assessed the diagnostic relevance of the morphological characters traditionally used in the taxonomy of Dakuidae, proposing emended diagnoses for the genera Philocelis and Philactinoposthia.
Phylogenetic inference aims to propose hypotheses that explain the evolutionary history of a group of organisms, typically represented as phylogenetic trees. These trees are constructed by analysing morphological, molecular, or other types of evolutionary data and applying optimisation methods. However, different topologies often yield equally optimal solutions for the same group under study, complicating the interpretation of a single evolutionary scenario. Consensus techniques are commonly employed to summarise agreement among these optimal trees. However, because consensus trees collapse conflicting relationships, they do not preserve the fully resolved structure of any optimal topology, which restricts analyses that require a single resolved tree with a defined parsimony score. Additionally, the polytomies arising from node collapse complicate the estimation of morphological rate of change and hinder the incorporation of temporal information into phylogenetic hypotheses. We present a pipeline that applies medoid selection and clustering techniques to characterise the topological diversity among most-parsimonious trees and to identify a fully resolved representative topology that preserves parsimony optimality. Rather than replacing consensus approaches, this method provides a complementary summary that retains a single optimal tree while making the structure of the broader phylogenetic landscape explicit. As case studies, we applied the pipeline to the phylogenetic analyses of Burkesuchus mallingrandensis and Arackar licanantay, two fossil taxa from Chile. In both cases, the pipeline recovered representative optimal trees that complement the interpretations of the original studies. The approach also supports analyses that require a resolved topology, including estimating morphological change rates and incorporating temporal information via time-scaling.
