Lake Towuti sits at the center of the Malili Lakes complex, an ancient chain of interconnected waterways that includes the large lakes Towuti, Matano, and Mahalona along with the satellite lakes Masapi and Lontoa. This system lies within Wallacea, the famous transitional biogeographic zone bounded by Huxley’s Line to the west and Lydekker’s Line to the east, where the faunas of Asia and Australia blend and blur. Lake Towuti itself is a tectonic giant, plunging to a maximum depth of 203 meters, with oxygen-rich surface waters extending down to roughly 70 meters and permanent anoxic conditions below 130 meters. A dynamic network of rivers, including the Larona, Tiinampoeoe, Tokolimboe, Babasalo, Lengke, and Katawang, feeds into the lake, which serves as the primary discharge point for the entire system. This hydrological complexity has long been suspected of nurturing endemic populations within a geographically constrained setting, creating what conservationists call Wallace’s Dreamponds.

Four species of Glossogobius gobies are endemic to the Malili Lakes: G. flavipinnis confined to Lake Towuti, G. mahalonensis to Lake Mahalona, G. matanensis to Lake Matano, and G. intermedius occurring in both Matano and Towuti. Despite their protected status on paper, these fish had never been characterized with the combination of modern morphometrics and DNA sequencing that contemporary taxonomy demands. Before this study, knowledge of G. flavipinnis rested primarily on descriptions from 1938 and a handful of partial genetic sequences of uncertain provenance derived from environmental samples. The researchers set out to close this gap by accomplishing three goals: a thorough characterization of the species’ morphometric and meristic features, the first mitochondrial cytochrome c oxidase subunit I sequences obtained from morphologically verified specimens, and a phylogenetic placement of the species within its genus using curated data from GenBank.

The fieldwork took place on March 12, 2025, when the team collected ten specimens, five males and five females, from three sampling stations roughly two kilometers apart along the shallow littoral zone of Lake Towuti. Using an oval dip net at depths of around two meters, the researchers targeted the hard sandy and rocky substrates, between roughly one and two meters deep, where the species preferentially lives among rocks 15 to 20 centimeters in diameter. Specimens were anesthetized and euthanized with 2-phenoxyethanol, preserved in 75 percent ethanol, assigned unique identification codes, and deposited as voucher specimens at Indonesian Muslim University. This voucher-based approach matters enormously: many DNA sequences in global databases were submitted without proper morphological validation, creating so-called ghost sequences that undermine reliable species identification. By anchoring every genetic result to a physically preserved, expertly identified specimen, the study provides a reproducible reference point for future taxonomic work.

The morphological analysis revealed a suite of diagnostic characters that make G. flavipinnis unmistakable. The species displays a velvety brownish-black body coloration, a moderately dorsoventrally depressed head, a dwarf body size, and the complete absence of cephalic sensory pores, a trait it shares with other dwarf Glossogobius of the Malili Lakes. Its most striking feature is the first dorsal fin, which bears black fin rays set against distinctly bright yellow membranes, the character that gives the species its name and makes it the most popular ornamental fish among the endemic Malili gobies, with individual specimens valued at approximately 12 to 40 US dollars. Males carry an elongated second spine of the first dorsal fin that extends as a filament beyond the posterior end of the second dorsal fin, a trait absent in females and thought to function in sexual signaling or reproductive behavior. Total length of examined specimens ranged from 33.0 to 54.2 millimeters, confirming the species’ diminutive stature.

Detailed comparisons against the syntype specimen ZMH 419 held in Hamburg, Germany, and against published measurements of the species’ three endemic congeners revealed broad consistency with only minor variations in proportions such as head length, body depth, and eye diameter, differences the authors attribute to normal intra-specific variability. Critically, the species can be told apart from its relatives by measurable traits: a shorter snout and smaller eye than G. intermedius, proportionally smaller head and eye dimensions than G. matanensis, and a dramatically darker coloration than G. mahalonensis, whose light brown body, whitish belly, and faint reddish-brown spotting contrast sharply with the deep velvet-black of G. flavipinnis. A multivariate Principal Component Analysis of 21 morphometric variables produced a striking result: the first two components together accounted for 96.65 percent of total variance, with PC1 alone explaining 87.38 percent, and the ordination with 95 percent confidence ellipses showed clear separation between males and females, providing formal statistical evidence of sexual dimorphism.

On the molecular side, the team extracted genomic DNA from dorsal muscle tissue of three randomly selected specimens, one from each sampling locality, and amplified mitochondrial COI barcode fragments using the established FishF1 and FishR1 primer pair. Rigorous quality control followed: bidirectional Sanger sequencing, trimming to a quality threshold above 40, validation through local and global nucleotide BLAST, and translation checks to confirm the correct reading frame, all guarding against nuclear mitochondrial pseudogenes. The resulting sequences, deposited in GenBank under accession numbers PV702231 to PV702233, were compared against a carefully curated dataset of 36 sequences representing 19 other Glossogobius species, roughly 46.5 percent of all recognized species in the genus, with the sleepy goby Psammogobius biocellatus serving as the outgroup.

The genetic results were unambiguous. Aligning to a uniform length of 538 base pairs, the dataset revealed 38.10 percent variable nucleotide sites and a mean inter-specific divergence of 18.1 percent uncorrected p-distance across the 20 Glossogobius taxa analyzed. G. flavipinnis showed substantial genetic distances from all compared congeners, ranging from a minimum of 14.15 percent uncorrected p-distance against G. sparsipapillus to a maximum of 21.99 percent against G. olivaceus, with Kimura two-parameter distances spanning 0.16 to 0.26. Within the species itself, divergence was minimal, at just 0.2 percent uncorrected p-distance, indicating a coherent, genetically homogeneous population in the sampled area. Phylogenetic reconstructions using both Bayesian inference and maximum-likelihood methods consistently placed G. flavipinnis in a well-supported distinct clade within the genus, with a posterior probability of 1.00 and 99 percent bootstrap support, cementing its status as an independently evolving lineage.

The broader evolutionary picture that emerges is one of historical geographic isolation driving diversification. Although the Malili Lakes are hydrologically connected, with Lake Matano draining into Mahalona via the Petea River and Mahalona into Towuti via the Tominanga River, the strict single-lake endemism of each Glossogobius species suggests that past isolation within individual basins restricted gene flow and permitted allopatric speciation, a pattern echoed in the adaptive radiations of sailfin silversides, gastropods, and shrimp in the same system. The authors are careful to note limitations: the sampling was limited to ten specimens from one lake, the mtCOI marker is a single maternally inherited locus that cannot fully resolve deep phylogenetic relationships, and genetic data for the three endemic congeners remain absent from public databases. Expanded sampling and nuclear markers will be needed to complete the picture.

What is not in doubt is the urgency of conservation. G. flavipinnis is classified as Near Threatened on the IUCN Red List, and its tiny range exposes it to unregulated harvesting for the ornamental trade, surface mining, water pollution, hydropower-driven alterations to waterways, and a growing roster of introduced fishes, from tilapia and common carp to flowerhorn cichlids and suckermouth catfish. By confirming the species’ identity through a rigorous integration of anatomy and genetics anchored to preserved vouchers, the study delivers exactly the evidence base that conservation planning requires. The team hopes its approach will be extended to the other endemic gobies and freshwater taxa of the Malili Lakes, ensuring that the remarkable evolutionary treasures of Wallace’s Dreamponds are catalogued accurately before human pressures erase them.

Subject of Research: Integrative morphological and mitochondrial DNA analysis validating the species status of the endemic goby Glossogobius flavipinnis in Lake Towuti, Sulawesi

Article Title: Integrative morphogenetics validates the distinctiveness of Glossogobius flavipinnis (Aurich 1938) from lake Towuti in the Wallacea biodiversity hotspot

Article References: Muslimin, M. M., Putra, A., Aini, S., Hadijah, S., Jayadi, Suriadin, H., Kim, H.-W., & Kundu, S. (2026). Integrative morphogenetics validates the distinctiveness of Glossogobius flavipinnis (Aurich 1938) from lake Towuti in the Wallacea biodiversity hotspot. Discover Conservation, 3(1), Article 29. https://doi.org/10.1007/s44353-026-00101-2

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00101-2

Keywords: Glossogobius flavipinnis, Lake Towuti, Malili Lakes, Wallacea, freshwater goby, DNA barcoding, mtCOI, species delimitation, phylogeny, endemism, Sulawesi, biodiversity conservation

In research published in BMC Genomics, Tomasz Grzyb, Małgorzata Wlaźlak and Justyna Szulc took six bacterial strains isolated from soils in post-maize cultivation fields and subjected them to a battery of genome-based species assignment methods. Their targets belonged to the order Caryophanales, a group that includes the enormously consequential genera Bacillus, Priestia and Paenibacillus, organisms used in agriculture, industry and biotechnology, and close relatives of dangerous pathogens. What they found was a taxonomic landscape riddled with contradiction: species boundaries that shift depending on which metric you trust, genomes that intermix across supposedly distinct species names, and a widely used identity threshold that may be significantly miscalibrated.

The team compared several complementary approaches. Average Nucleotide Identity, or ANI, was computed with two different tools, FastANI and skani, which estimate the overall similarity between two genomes by aligning shared DNA sequence. Digital DNA-DNA hybridization, dDDH, a computational descendant of the wet-laboratory hybridization experiments that once defined bacterial species, was calculated using formula 2. The researchers also employed tetranucleotide Z-score distance, TZMD, which measures differences in short-word DNA composition, and single-copy gene phylogenomics, reconstructing evolutionary trees from sets of genes present exactly once in each genome. Crucially, rather than comparing each strain against only its nearest named neighbors, the authors performed comprehensive pairwise comparisons among all available RefSeq genomes at both complete and chromosome assembly levels for each taxonomic neighborhood, an unusually thorough sweep designed to reveal the true structure of variation around each strain.

For two of the six strains, the answer came back clean. Both could be assigned without ambiguity, one to Bacillus subtilis and one to Bacillus licheniformis, with every ANI comparison against their respective species exceeding the conventional 95 percent threshold and with clear phylogenomic separation from neighboring taxa. These cases show that the classical framework still works when species boundaries are genuinely well separated. The complications began with the remaining four strains, each of which landed in a different taxonomic minefield.

Strain Bac2 fell within the Operational Group Bacillus amyloliquefaciens, and here the analysis documented what the authors call fundamental boundary inconsistency. ANI values measured between recognized species within this group exceeded the ANI values measured among genomes assigned to Bacillus amyloliquefaciens itself. In other words, genomes bearing different species names were more similar to each other than genomes carrying the same name, a direct inversion of what a coherent species concept requires. Single-copy gene phylogenomics confirmed the chaos, revealing extensive intermixing of named species across the tree. A name assigned under these conditions conveys little about evolutionary relatedness.

Strain zielonkawy was assigned to the Bacillus cereus sensu stricto genomospecies, but its placement highlighted a familiar and stubborn problem: the deep intermixing of Bacillus cereus sensu stricto and Bacillus thuringiensis. These two names describe bacteria with dramatically different ecological roles, one an opportunistic pathogen and the other an insecticidal biocontrol agent, yet their genomes remain so entangled that no genomic metric reliably separates them. The new data add one more well-documented instance to a debate that has persisted since whole genomes first became available.

The two remaining strains, assigned to Priestia megaterium and Paenibacillus amylolyticus, produced perhaps the most novel findings. Both ANI multi-comparison analysis and single-copy gene phylogenomics suggested possible species intermixing or mislabelling within the public reference databases themselves. To the authors’ knowledge, this is the first study to quantitatively document species delimitation problems between Priestia megaterium and Priestia aryabhattai, and between Paenibacillus amylolyticus and Paenibacillus xylanexedens. The Paenibacillus analysis carried the caveat of a small available sample size, but the Priestia result points to a quietly widespread issue: reference databases, which thousands of labs treat as ground truth, may contain genomes whose species labels do not survive close genomic scrutiny.

Beyond the individual assignments, the study delivers a quantitative contribution to the methodology of bacterial taxonomy itself. Concordance analysis between FastANI and dDDH formula 2 revealed a non-linear relationship, well described by a quadratic fit with an R-squared of 0.991. From this relationship, the researchers derived a striking number: the traditional 70 percent dDDH species threshold, inherited from the pre-genomic era of DNA reassociation experiments, corresponds not to the conventionally assumed 95 percent ANI but to approximately 96.16 percent ANI. In practical terms, dDDH formula 2 is the more conservative of the two metrics, meaning that genomes judged to be the same species by the 95 percent ANI rule could still fail the dDDH test. Laboratories relying on ANI alone may be lumping together organisms that a stricter standard would split.

The comparison between alignment-free and tree-based approaches added further nuance. Correlations between skani genomic distances and single-copy gene phylogenomic patristic distances, the branch-length distances separating genomes on the reconstructed trees, were high across all datasets, with R-squared values ranging from 0.900 to 0.997. Overall genomic structure, in other words, is consistent between methods. But Spearman rank correlations, while still strong, were consistently lower, at 0.780 to 0.916, indicating that the precise identity of a genome’s closest neighbors can shift depending on whether you measure raw sequence similarity or reconstructed evolutionary distance. For taxonomists deciding whether a strain belongs to one species or its nearest rival, that rank-order disagreement is exactly where decisions get made.

As a constructive response, the authors propose a complementary diagnostic tool: within- and between-species ANI multi-comparison analysis paired with PERMANOVA, a non-parametric statistical test for differences among groups, followed by post-hoc pairwise testing. The idea is to treat species boundaries not as a single threshold but as a statistical question: do the ANI distributions within a named species differ significantly from the distributions between it and its relatives? Applied alongside single-copy gene phylogenomics, this framework could flag boundary inconsistencies that single-threshold assignment silently passes over, giving taxonomists an explicit, reproducible way to test whether a species name still carves nature at its joints.

The broader significance of the work extends well beyond six soil isolates from Polish maize fields. The Caryophanales taxa examined here anchor industries from probiotics to pest control and include the closest relatives of the anthrax bacillus. If species boundaries in these groups are inconsistent, then everything built on top of those names, from safety assessments of biocontrol strains to regulatory definitions of pathogenic species, inherits the uncertainty. The study also lands amid an ongoing, sometimes contentious community effort to redefine prokaryotic species entirely, with competing proposals for genome-based circumscriptions. By showing that even gold-standard tools disagree at the margins, and that the canonical thresholds themselves encode hidden conservatism, the Lodz team’s results argue for pluralism: no single number can settle species questions in difficult groups, but a disciplined combination of metrics, statistics and phylogenetics can at least make the disagreements visible, quantifiable and, ultimately, resolvable.

Subject of Research: Genome-based species delimitation and taxonomic boundary evaluation in Caryophanales bacteria using ANI, dDDH and phylogenomics

Article Title: Challenges in Caryophanales species delimitation: comparative evaluation of genomic similarity metrics and phylogenomics based on six environmental strains

Article References: Grzyb, T., Wlaźlak, M., & Szulc, J. (2026). Challenges in Caryophanales species delimitation: comparative evaluation of genomic similarity metrics and phylogenomics based on six environmental strains. BMC Genomics. https://doi.org/10.1186/s12864-026-13320-7

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13320-7

Keywords: Caryophanales, species delimitation, phylogenomics, Average Nucleotide Identity, digital DNA-DNA hybridization, Bacillus subtilis group, Bacillus cereus group, Priestia, Paenibacillus, bacterial taxonomy, BMC Genomics, environmental strains