Abstract
Distichodus notospilus was described from the Ogooué River and is considered to occur throughout the Lower Guinea ichthyofaunal province and the western tributaries of the middle and lower Congo River. Recent expeditions in Equatorial Guinea collected D. notospilus specimens in the Mbini River drainage and the Mbia River; a small coastal river that is located between the Ntem and Mbini river drainages. Detailed morphological analyses and multilocus molecular analyses confirm that these two populations are distinct from one another. Topotypic populations of D. notospilus were included in the analyses and demonstrated that populations in the Mbini and Mbia rivers are distinct and these two new species are described herein. Distichodus microps sp. nov. is endemic to the Mbia River drainage and is distinguished from D. notospilus in having more scales along the lateral line (41, rarely 40 versus 37–39, rarely 40), a nearly inferior mouth versus subterminal in D. notospilus, a curved posterolateral margin of the opercle versus straight in D. notospilus, a smaller eye (56.7–80.4 versus 70.1–104.3 % of snout length), and a less prominent elongated spot at the base of the caudal fin. Distichodus mbiniensis sp. nov. is endemic to the upper Mbini River drainage and distinguished from D. notospilus in having more scales along the lateral line (41–42, rarely 40 versus 37–39, rarely 40), a much less prominent elongated dark spot at the base of the caudal fin, and a shorter dorsal fin (21.4–27.2 versus 22.7–34.2% standard length). Distichodus microps is distinguished from D. mbiniensis in having a shallower body (usually six scales from lateral line to the pelvic fin versus seven), fewer anal-fin rays (usually 12 total rays versus 13 or 14), a more inferior mouth, a deeper and longer caudal peduncle, a smaller eye, and differences in several features associated with the head. In addition to the two new species described this study also revealed potential undescribed diversity in the D. notospilus species complex in the Ntem River and Dja River (Congo R. basin) in Cameroon. The biogeography of these fishes in the rivers of Lower Guinea suggests that the Mbini River and smaller coastal rivers are overlooked areas of endemism. Studies of other reported widespread species will likely reveal additional diversity and further elucidate the processes promoting and maintaining freshwater diversity in Central Africa.
References
Abwe, E., Snoeks, J., Chocha Manda, A. & Vreven, E. (2019) Distichodus polli, a new distichodontid species (Teleostei: Characiformes) from the southern Congo basin. Ichthyological Exploration of Freshwaters, 1067, 1–18.
Arroyave, J. & Stiassny, M.L. (2011) Phylogenetic relationships and the temporal context for the diversification of African characins of the family Alestidae (Ostariophysi: Characiformes): Evidence from DNA sequence data. Molecular Phylogenetics and Evolution, 60 (3), 385–397.
https://doi.org/10.1016/j.ympev.2011.04.016
Arroyave, J., Denton, J.S. & Stiassny, M.L. (2020) Pattern and timing of diversification in the African freshwater fish genus Distichodus (Characiformes: Distichodontidae). BMC Evolutionary Biology, 20, 1–28.
https://doi.org/10.1186/s12862-020-01615-6
Calcagnotto, D., Schaefer, S.A. & DeSalle R. (2005) Relationships among characiform fishes inferred from analysis of nuclear and mitochondrial gene sequences. Molecular Phylogenetics and Evolution, 36 (1), 135–153.
https://doi.org/10.1016/j.ympev.2005.01.004
Chakona, A., Swartz, E.R. & Gouws, G. (2013) Evolutionary drivers of diversification and distribution of a southern temperate stream fish assemblage: Testing the role of historical isolation and spatial range expansion. PLoS ONE, 8 (8), e70953. https://doi.org/10.1371/journal.pone.0070953
Cutler, J.S., Mvé-Beh, J.H., Sullivan, J.P., Fermon, Y., Sidlauskas, B.L. (2019) Fish fauna in and around the Rapids of Mboungou Badouma and Doumé Ramsar site, Gabon, Check List 15: 997–1029.
https://doi.org/10.15560/15.6.997
Darwall, W., Bremerich, V., De Wever, A., Dell, A. I., Freyhof, J., Gessner, M. O., ... & Jeschke, J. M. (2018) The Alliance for Freshwater Life: A global call to unite efforts for freshwater biodiversity science and conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 28 (4), 1015–1022.
https://doi.org/10.1002/aqc.2958
Decru, E., Vreven, E. & Snoeks, J. (2013) A revision of the Lower Guinean Hepsetus species (Characiformes; Hepsetidae) with the description of Hepsetus kingsleyae sp. nov. Journal of Fish Biology, 82 (4), 1351–1375.
https://doi.org/10.1111/jfb.12079
Decru, E., Snoeks, J. & Vreven, E. (2015) Taxonomic evaluation of the Hepsetus from the Congo basin with the revalidation of H. microlepis (Teleostei: Hepsetidae). Ichthyological Exploration of Freshwaters, 26 (3), 273–287.
Dudgeon, D., Arthington, A.H., Gessner, M.O., Kawabata, Z.I., Knowler, D.J., Lévêque, C. Naiman, R.J., Prieur-Richard, A.H., Soto, D., Stiassny, M.L.J. & Sullivan, C.A. (2006) Freshwater biodiversity: importance, threats, status and conservation challenges. Biological reviews, 81 (2), 163–182.
https://doi.org/10.1017/S1464793105006950
Eisenberg, J. (2012) Geomorphic evolution of the Nyong and Ntem River basins in Southern Cameroon considering neo-tectonic influences. In: Landscape Evolution, Neotectonics and Quaternary Environmental Change in Southern Cameroon: Palaeoecology of Africa. Vol. 31. An International Yearbook of Landscape Evolution and Palaeoenvironments. CRC Press, Boca Raton, Florida, 302 pp.
Fouchy, K., McClain, M.E., Conallin, J. & O’Brien, G. (2019) Multiple Stressors in African Freshwater Systems. Multiple Stressors in River Ecosystems, 2019, pp. 179–191.
https://doi.org/10.1016/B978-0-12-811713-2.00010-8
Fricke, R., Eschmeyer, W. N. & Van der Laan, R. (Eds.) (2020) Eschmeyer’s Catalog Of Fishes: Genera, Species, References. Available from: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp (accessed 15 May 2020)
Friel, J.P. & Sullivan J.P. (2008) Synodontis woleuensis (Siluriformes: Mochokidae), a new species of catfish from Gabon and Equatorial Guinea, Africa. Proceedings of the Academy of Natural Sciences of Philadelphia, 157, 3–12.
https://doi.org/10.1635/0097-3157(2008)157[3:SWSMAN]2.0.CO;2
Goodier, S.A., Cotterill, F.P., O’Ryan, C., Skelton, P.H. & de Wit, M.J. (2011) Cryptic diversity of African tigerfish (Genus Hydrocynus) reveals palaeogeographic signatures of linked Neogene geotectonic events. PloS one, 6 (12), e28775.
https://doi.org/10.1371/journal.pone.0028775
Günther, A.C.L.G. (1867) XV.—New fishes from the Gaboon and Gold Coast. Annals and Magazine of natural History, Series 3, 20 (116), 110–117.
https://doi.org/10.1080/00222936708562735
Lanfear, R., Frandsen, P.B., Wright, A.M., Senfeld, T. & Calcott, B. (2017) PartitionFinder 2: new methods for selecting partitioned models of evolution for molecular and morphological phylogenetic analyses. Molecular biology and evolution, 34 (3), 772–773.
https://doi.org/10.1093/molbev/msw260
Lévêque, C. (1997) Biodiversity dynamics and conservation: the freshwater fish of tropical Africa. Cambridge University Press, Cambridge, 451 pp.
Mamonekene, V. & Vreven, E. (2008) Distichodus teugelsi a new distichodontid from the middle Congo River basin, Africa (Characiformes: Distichodontidae). Ichthyological exploration of freshwaters, 19 (2), 97–98.
Markwick, P.J. (2019) Palaeogeography in exploration. Geological Magazine, 156 (2), 366–407.
https://doi.org/10.1017/S0016756818000468
Miller, M.A., Pfeiffer, W. & Schwartz, T. (2010) Creating the CIPRES Science Gateway for inference of large phylogenetic trees. 2010 gateway computing environments workshop, GCE, 2010, pp. 1–8.
https://doi.org/10.1109/GCE.2010.5676129
Mipounga, H.K., Cutler, J., Mve Beh, J.H., Adam, B. & Sidlauskas, B.L. (2019) Enteromius pinnimaculatus sp. nov. (Cypriniformes: Cyprinidae) from southern Gabon. Journal of fish biology, 2019, 1–16.
https://doi.org/10.1111/jfb.13995
Moelants, T., Mbadu Zebe, V., Snoeks, J. & Vreven, E. (2014) A review of the Distichodus antonii assemblage (Characiformes: Distichodontidae) from the Congo basin. Journal of Natural History, 48 (27–28), 1707–1735.
https://doi.org/10.1080/00222933.2013.862312
Moelants, T., Snoeks, J. & Vreven, E. (2018) Distichodus kasaiensis and D. ingae, two new distichodontid species (Characiformes: Distichodontidae) from the Congo basin. Ichthyological Exploration of Freshwaters, 28 (2), 177–192.
Roberts, T.R. (1975) Geographical distribution of African freshwater fishes. Zoological Journal of the Linnean Society, 57 (4), 249–319.
https://doi.org/10.1111/j.1096-3642.1975.tb01893.x
Román, B. (1971) Peces de Río Muni, Guinea Ecuatorial: (Aguas dulces y salobres). Fundacion La Salle de Ciencias Naturales, Barcelona, 295 pp
https://doi.org/10.2307/1442809
Ronquist, F., Teslenko, M., van der Mark, P., Ayres, D.L., Darling, A., Höhna, S., Larget, B., Liu, L., Suchard, M.A. & Huelsenbeck, J.P. (2012) MrBayes 3.2: efficient Bayesian phylogenetic inference and model choice across a large model space. Systematic biology, 61 (3), 539–542.
https://doi.org/10.1093/sysbio/sys029
Runge, J., Eisenberg, J. & Sangen, M. (2006) Geomorphic evolution of the Ntem alluvial basin and physiogeographic evidence for Holocene environmental changes in the rain forest of SW Cameroon (Central Africa)—preliminary results. Zeitschrift fur Geomorphologie, 145, 63–79.
Sabaj, M.H. (2016) Standard symbolic codes for institutional resource collections in herpetology and ichthyology: an Online Reference. Version 6.5. American Society of Ichthyologists and Herpetologists, Washington, D.C. Available from: http://www.asih.org/ (accessed 20 May 2020)
Schmidt, R.C., Bart Jr, H.L. & Pezold, F. (2016) High levels of endemism in suckermouth catfishes (Mochokidae: Chiloglanis) from the Upper Guinean forests of West Africa. Molecular Phylogenetics and evolution, 100, 199–205.
https://doi.org/10.1016/j.ympev.2016.04.018
Schmidt, R.C., Bart Jr., H.L. & Nyingi, W.D. (2017) Multi-locus phylogeny reveals instances of mitochondrial introgression and unrecognized diversity in Kenyan barbs (Cyprininae: Smiliogastrini). Molecular Phylogenetics and Evolution, 111, 35–43. https://doi.org/10.1016/j.ympev.2017.03.015
Schmidt, R.C. & Barrientos, C. (2019) A new species of suckermouth catfish (Mochokidae: Chiloglanis) from the Rio Mongo in Equatorial Guinea. Zootaxa, 4652 (3), 507–519.
https://doi.org/10.11646/zootaxa.4652.3.7
Schmidt, R.C., Dillon, M.N., Kuhn, N.M., Bart Jr, H.L. & Pezold, F. (2019) Unrecognized and imperilled diversity in an endemic barb (Smiliogastrini, Enteromius) from the Fouta Djallon highlands. Zoologica Scripta, 48 (5), 605–613.
https://doi.org/10.1111/zsc.12362
Schmidt, R.C., Knobloch, E.C., Barrientos, C. (2020a) Distichodus sp. nov. ‘microps’. The IUCN Red List of Threatened Species, 2020, e.T177754310A177754313.
https://doi.org/10.2305/IUCN.UK.2020-3.RLTS.T177754310A177754313.en
Schmidt, R.C., Knobloch, E.C. & Barrientos, C. (2020b) Distichodus sp. nov. ‘mbiniensis’. The IUCN Red List of Threatened Species, 2020, e.T177754327A177754338.
https://doi.org/10.2305/IUCN.UK.2020-3.RLTS.T177754327A177754338.en
Sidlauskas, B.L., Mol, J.H. & Vari, R.P. (2011) Dealing with allometry in linear and geometric morphometrics: a taxonomic case study in the Leporinus cylindriformis group (Characiformes: Anostomidae) with description of a new species from Suriname. Zoological Journal of the Linnean Society, 162 (1), 103–130.
https://doi.org/10.1111/j.1096-3642.2010.00677.x
Sonet, G., Snoeks, J., Nagy, Z. T., Vreven, E., Boden, G., Breman, F. C., Decru, E., Hanssens, M., Ibala Zamba, A., Jordaens, K., Mamonekene, V., Musschoot, T., Van Houdt, J., Van Steenberge, M., Lunkayilakio Wamuini, S. & Verheyen, E. (2019) DNA barcoding fishes from the Congo and the Lower Guinean provinces: Assembling a reference library for poorly inventoried fauna. Molecular ecology resources, 19 (3), 728–743.
https://doi.org/10.1111/1755-0998.12983
Stiassny, M.L., Teugels, G.G. & Hopkins, C.D. (2007) Fresh and brackish water fishes of Lower Guinea, West-Central Africa. Vol. 42. IRD Editions, Paris. 800 pp.
Thys van den Audenaerde, D.F.T. (1966) Les Tilapia (Pisces, Cichlidae) du sud-Cameroun et du Gabon: étude systématique. Musée royal de l’Afrique centrale, Tervuren, 153 pp.
Walker, R.B.N. (1865) Letter from Mr. RBN Walker from the Gaboon. Proceedings of the Royal Geographical Society of London, 10 (3), 128–129.
https://doi.org/10.2307/1799661
Warton, D.I., Wright, I.J., Falster, D.S. & Westoby, M. (2006) Bivariate line-fitting methods for allometry. Biological Reviews, 81 (2), 259–291.
https://doi.org/10.1017/S1464793106007007
Vari, R.P. (2007) Distichodontidae. In: The Fresh and Brackish Water fishes of Lower Guinea, West Central Africa. Poissons d’eaux douces et saumâtres de Basee Guinée, l’Afrique Ouest-Central, Paris, 1, pp. 412–465.