Underestimated diversity in Characidium (Characiformes: Crenuchidae) from Neotropical rivers revealed by an integrative approach

Abstract

Characidium represents the most widely distributed and species-rich fish genus within the family Crenuchidae in the Neotropical region, with numerous species described over the last decade. Despite this taxonomic progress, the understanding of species boundaries and population variation within the genus remains limited. In response, an integrative study was undertaken, utilizing both morphological and molecular data from neotropical freshwater ecoregions with rivers that drain the Brazilian northeastern. The primary objective of this investigation was to elucidate taxonomic delimitations and, where relevant, propose new species hypotheses. Our results propose the existence of 15 operational taxonomic units (OTUs) as species hypotheses. Among these, 10 were identified as valid species, four represented morphotypes that hold the potential of constituting new species, and one OTU was determined as a new species, corroborated by all proposed delimitation methods. Our results demonstrated discrepancies between morphological and molecular data, highlighting the challenges in defining taxonomic boundaries within Characidium. Moreover, our findings provided insights into the intricate diversification history of Characidium species, applied to the species that occur in northeastern Brazilian drainages. We proposed that historical events, such as river connections and barriers, have played a significant role in shaping the current distribution patterns of the genus.

Key words:

• Brazilian Shield
• Characidiinae
• COI marker
• freshwater ecoregions
• molecular systematics

Acknowledgements

We thank Osvaldo Oyakawa (MZUSP), Carla Pavanelli (UEM), Carlos Lucena (MCP), Cláudio de Oliveira (UNESP), Marcelo Britto (MNRJ), Ricardo Rosa (UFPB), Sérgio Lima (UFRN), and Tiago Pessali (MCNIP) for loaning comparative material and/or donating tissue samples. We are also grateful to Rafael Burger (UFBA), Tiago Quadros (UFBA), Silvia Yasmin (UEPB), Telton Ramos (UEPB), and Antônio Sobral for their support in the fieldwork. We thank Elaine Cardoso (UFBA) and Silvia B. Brito (UFPA) for their initial support with technical procedures for obtaining DNA samples. We also acknowledge the sequencing performed by the Laboratory and Sequencing Platform of the Gonçalo Moniz Research Center (Fiocruz).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772000.2024.2346510.

Supplemental Appendix S1: Taxa, vouchers, locality, source, and GenBank or BOLD accession number of Characidium specimens used in the mitochondrial DNA analysis.

Supplemental Appendix S2: Examined material of Characidium in morphological analyses.

Supplemental Appendix S3: Pairwise distance matrix (uncorrected p-distance) between lineages/species.

Associate Editor: Dr Kevin Conway

Additional information

Funding

This work was partially funded by the Coodenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Funding Code 001. LOS received a doctoral scholarship from the CAPES Foundation [Proc. No. 88882.156834/2017-01 and 88887.506287/2020-00] and postdoctoral scholarship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) [Proc. No. 151061/2022-0] and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) [Proc. No. 2023/09871-6; current]. AMZ and PC acknowledge funding from the CNPq [Proc. No. 420557/2016-4 and Proc. No. 423760/2018-1, respectively), and AMZ acknowledges funding from the Bahia State Research Support Foundation (FAPESB) [Proc. No. APP0031/2016]. HBF acknowledges the CNPq Research Productivity Fellowships [310673/2021-6].