Kissing cousins: a review of the African genus Limnophis Günther, 1865 (Colubridae: Natricinae), with the description of a new species from north-eastern Angola

ABSTRACT

The African natricine genus Limnophis is represented by two species: Limnophis bicolor Günther, 1865 and Limnophis bangweolicus (Mertens, 1936). They are stout-bodied, semi-aquatic snakes that mostly feed on fish and amphibians, and occur from Botswana and Namibia in the south throughout most of Zambia and Angola to the Democratic Republic of the Congo in the north. We gathered new material from the ranges of both species in Angola and Zambia in order to examine their taxonomic status and identify any overlooked diversity. We constructed a phylogenetic tree, based on three mitochondrial genes (16S, cytb, ND4) and one nuclear gene (cmos), which includes the first DNA sequence data for Limnophis. Three well-supported lineages were identified, each representing separate species. The taxonomic status of the two currently recognised species is validated, and we describe a new species of Limnophis from north-eastern Angola. The new species is distinguished from the others by the combination of distinct ventral and lateral head colouration and patterning, differences in head and ventral scalation, and uncorrected pairwise genetic distances to both L. bicolor and L. bangweolicus of 5.4–8.1% in cytb, 6.1–8.4% in ND4 and 2.7–8.3% in 16S.

RESUMO

O género africano de natricíneos Limnophis contém duas espécies: Limnophis bicolor Günther, 1865 e Limnophis bangweolicus (Mertens, 1936). Estas cobras semi-aquáticas de corpo robusto alimentam-se principalmente de peixes e anfíbios, e ocorrem no sul de África entre o Botswana e a Namíbia, para norte em grande parte da Zâmbia e Angola até à República Democrática do Congo. Nós colhemos material da área de distribuição de ambas as espécies em Angola e na Zâmbia para examinar o seu estatuto taxonómico, e para identificar se existia alguma diversidade oculta. Construímos uma árvore filogenética baseada em três genes mitocondriais (16S, cytb, ND4) e um gene nuclear (cmos), incluindo os primeiros dados de sequências genéticas para o género Limnophis. Foram identificadas três linhagens bem suportadas, cada uma representando uma espécie distinta. Assim, validámos o estatuto taxonómico das duas espécies já conhecidas, e descrevemos uma nova espécie de Limnophis do nordeste de Angola. Esta nova espécie pode ser distinguida das outras pela combinação de padrões de coloração ventral e lateral da cabeça, e diferenças nas escamas da cabeça e escamas ventrais. As distâncias genéticas não corrigidas entre esta espécie e L. bicolor e L. bangweolicus são de 5.4–8.1% para o gene cytb, 6.1–8.4% para o ND4 e 2.7–8.3% para o 16S.

KEYWORDS:

• Africa
• cryptic species
• geometric morphometrics
• integrative taxonomy
• Serpentes
• swamp snake

PALAVRAS-CHAVE:

• África
• morfometria geométrica
• taxonomia integrativa
• Serpentes
• cobra-dos-pântanos

Acknowledgments

We particularly want to thank Brian Huntley for organising the Lagoa Carumbo Expedition in 2011, which was supported logistically by De Beers Angola Prospecting and permitting by the Angolan Ministry of Environment (MINAMB). A National Geographic Society grant #891-11) provided financial support for the 2011 Lagoa Carumbo Expedition. Chris Brooks is thanked for organising the Southern Africa Regional Environmental Program’s (SAREP) Aquatic Biodiversity Survey of the lower Cuito and Cuando Rivers in Angola in 2013 in collaboration with the Angolan Ministry of Environment’s (MINAMB) Institute of Biodiversity and the Angola Ministry of Agriculture’s National Institute of Fish Research (INIP). The National Geographic Okavango Wilderness Project (National Geographic Society grant number EC0715-15) funded fieldwork to Angola from 2015 to 2019. VD’s contribution was supported in part, by an EU Marie Skłodowska Curie fellowship (no. 751567) cohosted by DJG and Natalie Cooper. VD thanks Gabriela Bittencourt for practical assistance. We thank Alan Resetar (Field Museum of Natural History, USA) and Lauren Scheinberg (California Academy of Sciences, USA) making available samples for some of the outgroups used in the study. We thank Patrick Campbell at Natural History Museum, London and Gunther Köhler, Linda Mogk and Martin Jansen at the Senckenberg Research Institute for curatorial support and loans. We thank Luke Verburgt, James Harvey, Pedro Vaz Pinto, Ninda Baptista, Sendi Baptista, Alex Rebelo, Ben van der Waal, Roger Bills and Anton Bok for assistance in the field or collecting specimens. We would also like to thank Taryn Bodill (South African Aquatic Biodiversity Institute) for assisting in generating sequences, Adriaan Jordaan for providing data for (TM) material, Luke Kemp for making the line drawing of the holotype and Ninda Baptista for translating the abstract into Portuguese. Ninda Baptista (Instituto Superior de Ciências da Educação da Huíla, Angola), Pedro Vaz Pinto (Kissama Foundation Collection, Angola), and Luis Ceríaco (Instituto de Investigação Científica Tropical, Lisbon) made available photographs of unpublished records to verify identifications to be include in this study.