Eric Baxter

The Das Contas river basin in Eastern Brazil drains over 55,000 sq km (21,000 sq mi), about the area of Massachusetts and Belgium combined. Yet despite its neighbors have endemic species, no species of native killifish (Rivulidae) has ever been sampled. researchgate.net/publication/40…

The Malili Lake system on Sulawesi Island represents a classic natural laboratory for studying freshwater fish evolution and harbours multiple endemic 𝑂𝑟𝑦𝑧𝑖𝑎𝑠 species (ricefishes) that diversified under repeated hydrological reorganisations. Here, researchers present a revised taxonomy for the ricefishes from this ancient lake system, demonstrating that introgression from the 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 lineage into 𝑂. 𝑝𝑟𝑜𝑓𝑢𝑛𝑑𝑖𝑐𝑜𝑙𝑎 and 𝑂. 𝑙𝑜𝑥𝑜𝑙𝑒𝑝𝑖𝑠 was not a single ancient event, but rather a more sustained process. 🔓 link.springer.com/article/10.118… 𝗥𝗲𝘀𝗲𝗮𝗿𝗰𝗵 𝗧𝗶𝘁𝗹𝗲 Revised taxonomy reveals sustained introgression and secondary contact in ancient lake ricefishes 𝗖𝗶𝘁𝗮𝘁𝗶𝗼𝗻 Yashima, Y., Nofrianto, A.B., Nuryadi, H. et al. Revised taxonomy reveals sustained introgression and secondary contact in ancient lake ricefishes. BMC Ecol Evo 26, 46 (2026). doi.org/10.1186/s12862… 𝗔𝗯𝘀𝘁𝗿𝗮𝗰𝘁 Background Biotic diversification in ancient lakes is shaped by complex geological histories and genetic exchange among populations. The Malili Lake system on Sulawesi Island represents a classic natural laboratory for studying freshwater fish evolution and harbors multiple endemic 𝑂𝑟𝑦𝑧𝑖𝑎𝑠 species that diversified under repeated hydrological reorganizations. Previous genomic analyses inferred that two sympatric species in Lake Towuti (𝑂. 𝑝𝑟𝑜𝑓𝑢𝑛𝑑𝑖𝑐𝑜𝑙𝑎 and 𝑂. 𝑙𝑜𝑥𝑜𝑙𝑒𝑝𝑖𝑠) experienced a single ancient introgression event from a “ghost lineage” derived from 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 inhabiting another lake. However, recent taxonomic re-evaluation has revealed the presence of an extant 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 population within Lake Towuti itself. This finding suggests that the putative ghost lineage may in fact represent a living population co-occurring in the lake, calling for a re-examination of the introgression history and speciation mode in Lake Towuti. Results By incorporating newly generated ddRAD-seq data from the true 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 in Lake Towuti, we reanalyzed phylogenetic relationships and population genetic structure among Malili Lake Oryzias. Previously reported major phylogenetic relationships and inter-lake introgression patterns were largely reproduced. In contrast, TreeMix and f4-statistic analyses revealed that introgression signals previously attributed to a “ghost lineage” into 𝑂. 𝑝𝑟𝑜𝑓𝑢𝑛𝑑𝑖𝑐𝑜𝑙𝑎 and 𝑂. 𝑙𝑜𝑥𝑜𝑙𝑒𝑝𝑖𝑠 instead originated from the extant 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 population coexisting within Lake Towuti. Demographic model comparisons explicitly incorporating within-lake gene flow further supported a scenario in which 𝑂. 𝑝𝑟𝑜𝑓𝑢𝑛𝑑𝑖𝑐𝑜𝑙𝑎 and 𝑂. 𝑙𝑜𝑥𝑜𝑙𝑒𝑝𝑖𝑠 diverged in allopatry, subsequently came into secondary contact within Lake Towuti, and later experienced additional gene flow following secondary contact with 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 that entered the lake. Conclusion Our results demonstrate that introgression from the 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 lineage into 𝑂. 𝑝𝑟𝑜𝑓𝑢𝑛𝑑𝑖𝑐𝑜𝑙𝑎 and 𝑂. 𝑙𝑜𝑥𝑜𝑙𝑒𝑝𝑖𝑠 was not a single ancient event, but rather a more sustained process. This finding highlights the critical importance of taxonomic resolution for accurately inferring introgression and divergence history. Comparative studies across other ancient lakes on Sulawesi will be valuable for understanding how the timing and nature of gene flow from third lineages influence patterns of population divergence and the strength of reproductive isolation. 𝗣𝗵𝗼𝘁𝗼 𝗖𝗿𝗲𝗱𝗶𝘁 Left - ( A ) A map of the Malili Lake system and the collection site of 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 in Lake Towuti (red circle). The drainage system of the Malili Lakes is shown in blue. The map was provided by Thomas von Rintelen and modified. ( B ) The demographic model proposed by Mandagi et al. (2021), which assumes ancient introgression from a ghost lineage into Lake Towuti. ( C ) A demographic model expected in the case that the ghost lineage in Mandagi et al. (2021) actually corresponds to 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠 in Lake Towuti. This model assumes continuous gene flow following secondary contact with 𝑂. 𝑚𝑎𝑟𝑚𝑜𝑟𝑎𝑡𝑢𝑠. Right - Maximum-likelihood phylogeny of 𝑂𝑟𝑦𝑧𝑖𝑎𝑠 in the Malili Lake system based on 3,457 genome-wide SNPs. © 2026 the Author(s). Published in the journal BMC Ecology and Evolution. This paper is released under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. creativecommons.org/licenses/by-nc… #Ricefish #Ricefishes #Ichthyology #Taxonomy #Biodiversity #AquariumHobby #Fishkeeping #Aquarist #TropicalFish #Sulawesi #Indonesia #AncientLakes #MaliliLake #LakeTowuti #Oryzias #Biogeography #Introgression