Research Article |
Corresponding author: Nasreen Peer ( peer.nasreen@gmail.com ) Academic editor: Célio Magalhães
© 2023 Nasreen Peer, Gavin Gouws, Lazola Maliwa, Nigel Barker, Paul Juby, Renzo Perissinotto.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Peer N, Gouws G, Maliwa L, Barker N, Juby P, Perissinotto R (2023) Description of a new montane freshwater crab (Arthropoda, Malacostraca, Decapoda, Potamonautidae) from the Eastern Cape, South Africa. ZooKeys 1160: 89-108. https://doi.org/10.3897/zookeys.1160.100844
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A new species of freshwater crab, Potamonautes amathole sp. nov., is described from the Winterberg-Amathole mountain range in the Eastern Cape Province, South Africa. Morphologically, P. amathole Peer & Gouws, sp. nov. most closely resembles P. tuerkayi but can be distinguished by key morphological characters including the variation in the shape of the subterminal segment of gonopod 2 between both species. Genetically, P. amathole Peer & Gouws, sp. nov. is placed within the clade of small-bodied, mountain-dwelling crabs including P. parvispina, P. parvicorpus, P. brincki, P. tuerkayi, P. baziya, and P. depressus. The new species is found in slow-moving mountain streams and pools at high altitudes. The continued discovery and description of new freshwater crab species reinforces the need for ongoing research, especially in under-sampled regions.
Afrotropical Region, Brachyura, high altitude streams, molecular analyses, morphology, taxonomy
In South Africa, the genera Potamonautes and Maritimonautes represent the freshwater crabs with a total of 26 described species since the last published descriptions (
Recently, several new species have been described from natural forest habitats (
Aside from high forest biodiversity, the Amathole Mountain Range, forming part of the escarpment between the Sneeuberg range in the west and the Drakensberg range in the east, is considered to display great diversity across habitat types, as well as high levels of endemism in terms of flora (
In this paper, we describe P. amathole sp. nov. from the Hogsback and Katberg Forests in the Amathole Mountains of the Eastern Cape. NP and GG wrote the taxonomic part of this study, including the description of the new species, while the contribution of the other authors dealt with genetic analyses, natural history, and ecological observations.
Crabs were collected from three localities (Table
Map showing the location of the Amathole Mountain Range sampling sites (black markers) in relation to nearby towns and villages (white points). South Africa National Land Cover (SANLC) 2018 map layer shows land cover to be predominantly indigenous forest and plantations with residential area nearby.
Site name | Coordinates |
---|---|
Katberg State Forest | 32°28.43'S, 26°40.10'E |
Hogsback Arboretum | 32°35.42'S, 26°56.05'E |
Hogsback Waterfall | 32°36.40'S, 26°57.80'E |
Crabs were collected by hand or net and preserved in 70% ethanol.
The genetic placement and relationships of the proposed new species were examined using data generated in two sequential studies.
For the first study, total genomic DNA was extracted from 0.5–1 mg of pereiopod muscle tissue from specimens collected from Hogsback and Katberg during 2013. Tissue was rinsed in sterile water and DNA was extracted using an Invisorb Spin Tissue Mini Kit (Invitek Molecular, Berlin), following the manufacturer’s protocol.
A fragment of the large ribosomal subunit 16S mitochondrial marker was amplified by Polymerase Chain Reaction, using the primers of
In the second study, DNA was extracted from specimens collected from Hogsback during 2018, using a PureLink Miniprep kit (Invitrogen, Carlsbad, California). A fragment of the protein-coding mtDNA cytochrome c oxidase subunit I (COI) gene was amplified and sequenced using the approach described by
Data sets for each of the 16S and COI fragments included data generated in the present study and published data for all described southern African Potamonautes species, as compiled previously (
ClustalX2 (
Morphological variables were measured using a pair of Vernier callipers. A Canon Powershot G12 digital camera was used to photograph carapaces and appendages, while a Nikon SMZ25 microscope fitted with a Nikon Digital Sight DS-Fi2 camera was used for macro-examination and to take photos of gonopods and mouthparts.
EC Eastern Cape;
WC Western Cape;
KZN KwaZulu–Natal.
Abbreviations for all morphological and morphometric characters (following
AW6 Width of sixth abdominal segment;
CH Carapace height;
CL Carapace length;
CLDL Left cheliped, dactyl length;
CRDL Right cheliped, dactyl length;
CRPL Right cheliped, propodus length;
CRPW Right cheliped, propodus width;
CWA Distance between exorbital teeth;
CWW Carapace widest width;
CWP Carapace posterior width;
ED Distance between orbits;
MCPL Major cheliped propodus length;
MCPW Major cheliped propodus width;
ML Merus length;
MW Merus width;
PFCD Distance between postfrontal crest and anterior margin;
P2ML Pereopod 2, merus length;
P2MW Pereopod 2, merus width;
s2/s3 First sternal groove (suture between the second and third sulci);
s3/s4 Second sternal groove (suture between the third and fourth sulci).
New sequences generated in the present study were lodged in GenBank (16S: accession numbers OQ559329–OQ559337; COI: OQ558909–OQ558911). The 16S alignment was 549 nucleotides in length. The ML analysis, using the parameters of the optimal model (base frequencies: A = 0.369, C = 0.122, G = 0.163 and T = 0.346; rate matrix: RA↔C = 0.571, RA↔G = 5.756, RA↔T = RG↔T = 1.000, RC↔G = RC↔T = 2.251; α = 0.341 for the gamma distribution of rate variation), produced the topology (-lnL = 3754.743) presented in Fig.
The most likely topology (-lnL = 3754.743) obtained in the Maximum-Likelihood analysis of a 549 nucleotide 16S rRNA alignment, depicting relationships between potamonautid freshwater crabs sampled from Hogsback and Katberg (Eastern Cape, South Africa) and known southern African Potamonautes species. Nodal support in the form of Bayesian Posterior Probabilities (BPPs) are indicated above the branches, with only BPPs > 0.95 shown. Species of Maritimonautes are included as outgroups.
The COI alignment was 660 nucleotides in length. The optimal model had base frequencies of A = 0.292, C = 0.184, G = 0.154 and T = 0.371, a rate matrix of RA↔C = 4.203, RA↔G = 10.249, RA↔T = 2.385, RC↔G = RG↔T = 1.000, RC↔T = 31.047, a proportion of invariant sites (I = 0.549) and a gamma distribution of rate variation (α = 1.280). The tree produced by the ML analysis is shown as Fig.
The most likely topology (-lnL = 5093.453) obtained in the Maximum-Likelihood analysis of a 660 nucleotide mtDNA cytochrome c oxidase subunit I (COI) alignment, depicting relationships between potamonautid freshwater crabs sampled from Hogsback (Eastern Cape, South Africa) and known southern African Potamonautes species. Nodal support in the form of Bayesian Posterior Probabilities (BPPs) are indicated above the branches, with only BPPs > 0.95 shown. Species of Maritimonautes are included as outgroups.
The topologies produced by the analyses of the 16S and COI data were congruent with respect to, and reflected, the major phylogenetic divisions reported previously for the southern African Potamonautes radiation (e.g.,
Of relevance to the current study, the crabs sampled from Hogsback and Katberg were placed in two separate clades. In the 16S topology, samples from Hogsback and Katberg were placed within the clade of small-bodied, mountain-dwelling species, sister to P. parvispina, in a larger well-supported clade (BPP = 0.98) of mountain-dwelling species from the Western Cape (P. parvicorpus, P. parvispina, and P. tuerkayi), which was sister to a clade containing those (P. baziya, P. clarus, and P. depressus) from the Drakensberg in the Eastern Cape and KwaZulu-Natal. Other samples from Hogsback, including one collected sympatrically with the aforementioned at the Hogsback Arboretum, were allied to P. danielsi within the clade of IOCB forest-dwelling species with high support (BPP 1.00). In the COI topology, where only samples from Hogsback were included, these were placed similarly within the clade of mountain-dwelling species. These results suggest the presence of two distinct species among the crabs sampled from Hogsback and Katberg.
Uncorrected sequence divergences among individuals are presented in Suppl. material
For the COI data, where the only specimens included from Hogsback belonged to the clade of mountain-dwelling species, uncorrected sequence divergences between these specimens and other species in that clade ranged from 7.4 to 10.9%. With the exception of the comparison between P. barbarai and P. granularis (0.5%), previously described species were 2.4 to 18.4% divergent. Comparatively, these divergences again support the taxonomic distinctiveness of the Hogsback (and, by extension, Katberg) specimens.
Genus Potamonautes
Holotype
: male, CL = 25.3 mm (Table
Ranges of measurements (mm) for 12 morphometric variables of the Potamonautes amathole sp. nov. holotype and paratypes collected from Katberg and Hogsback, as well as P. brincki, P. tuerkayi, P. parvispina, and P. parvicorpus from published sources.
Variable | Potamonautes amathole sp. nov. | Potamonautes brincki Stewart, 1997 | Potamonautes tuerkayi Wood & Daniels, 2016 | Potamonautes parvispina Stewart, 1997 | Potamonautes parvicorpus Daniels, Stewart & Burmeister, 2001 | |||||
---|---|---|---|---|---|---|---|---|---|---|
Holotype | Males (n = 11) | Females (n = 8) | Males | Females | Holotype | Males | Females | Males | Females | |
CL | 25.3 | 19.5–25.3 | 19.3–25.5 | 15.5–26.9 | 9.1–25.3 | 20 | 20.8–28.7 | 22.7–28.4 | 11.85–24.08 | 9.13–24.71 |
CWW | 37.3 | 27.8–37.5 | 26.8–35.5 | 20.4–38.2 | 11.4–35.1 | 30 | 28.9–42.0 | 31.5–41.3 | 15.9–36.24 | 11.41–34.99 |
CWP | 12.5 | 10.0–14.3 | 10.5–15.0 | 16.8–28.6 | 9.8–27.7 | 10 | 23.3–32.6 | 25.6–32.8 | 12.75–26.38 | 9.84–27.95 |
CH | 12.8 | 9.0–12.8 | 8.5–12.0 | 4.5–7.7 | 4.5–13.6 | 10 | 10.3–16.4 | 12.4–15.3 | 5.68–13.48 | 4.47–13.12 |
PFCD | 3.8 | 3.0–3.8 | 2.5–3.8 | 2.6–3.9 | 1.4–3.6 | 4 | 3.2–4.6 | 3.7–4.5 | 2.06–4.27 | 1.42–3.82 |
ED | 13.5 | 9.5–13.8 | 9.0–12.5 | 7.7–13.4 | 4.7–12.4 | - | 10.7–15.3 | 11.7–14.5 | 7.03–13.28 | 4.73–14.07 |
CWA | 25 | 18.5–24.5 | 17.8–23.8 | 15.1–26.5 | 9.3–24.6 | 10 | 21.7–29.2 | 22.2–27.6 | 12.57–24.09 | 9.27–23.84 |
AW6 | 8 | 6.0–7.8 | 15.0–21.8 | 13.1–42.7 | 6.6–22.7 | - | 5.6–8.1 | 13.5–24.7 | 3.62–7.63 | 3.10–21.57 |
MCPL | 39 | 22.0–37.0 | 15.0–21.5 | 5.1–17.7 | 2.4–8.4 | 32 | 19.8–42.1 | 19.2–24.2 | 9.60–25.08 | 6.59–19.15 |
MCPW | 16.1 | 9.0–15.3 | 5.0–7.3 | 8.2–17 | 4.5–13.9 | 12 | 8.0–19.4 | 7.3–9.1 | 3.34–12.81 | 2.41–10.84 |
P2ML | 15 | 11.0–15.5 | 8.8–12.5 | 7.8–14.9 | 3.1–23.2 | 12 | 11.2–18.5 | 12.7–14.8 | 6.21–14.20 | 1.92–12.62 |
P2MW | 4 | 3.0–4.0 | 3.0–4.3 | 3.6–5.9 | 1.9–5.6 | 3 | 4.4–5.5 | 5.2–5.4 | 2.76–4.77 | 1.92–4.44 |
Potamonautes amathole sp. nov. exhibits a smooth carapace, flank and epibranchial region, with a rounded anterolateral margin and a narrow posterior end. Postfrontal crest complete. Dactyl of major cheliped highly arched. Pereopod 4 is longest. Bi-lobed maxillary palp with no flange.
Carapace
(Fig.
Sternites
(Fig.
Third maxilliped
(Figs
Mandibular palp
(Fig.
Potamonautes amathole sp. nov. male holotype (MB-A094813) a major cheliped b minor cheliped c right mandibular palp posterior view d right mandibular palp anterior view e 3rd maxilliped f left gonopod 1 anterior view g left gonopod 1 posterior view h left gonopod 2 posterior view, and i left gonopod 2 anterior view. Scale bars: 10 mm (a, b); 1 mm (c, d); 5 mm (e–i).
Pereopods
(Figs
Pleon
(Fig.
Pleopods
(Fig.
The major cheliped is not always distinctly arched, especially in females and juveniles.
Colouration varies between orange-brown to a darker purple-brown when alive. Tips of the dactyli may be paler in colour, displaying as orange or paler brown/purple.
Currently known only from the Katberg State Forest, the Hogsback State Forest, Madonna and Child Falls and the Hogsback Arboretum, all situated in the Amathole Mountain Range in the Eastern Cape province of South Africa.
The species is named after the Amathole Mountains, part of the Winterberg-Amathole mountain range complex, located on the Great Escarpment in the Eastern Cape. It is currently thought to be endemic to this region. The isiXhosa name ‘Amathole’ translates to ‘calves’ in English and refers to the mountain range, the forest, and the municipal district.
Potamonautes amathole sp. nov. is genetically and morphologically most similar to the Western Cape small-bodied montane freshwater crabs, i.e., P. brincki (Bott, 1960), P. parvispina Stewart, 1997, P. parvicorpus Daniels, Stewart & Burmeister, 2001, and P. tuerkayi Wood & Daniels, 2016. Morphologically, the species can be most easily distinguished from P. parvispina by the latter’s small but pronounced epibranchial tooth. Potamonautes parvicorpus bears slightly arched chelipeds, an arched carapace, and a poorly developed postfrontal crest, while the new species has highly arched major chelipeds, a flattened carapace and a distinct postfrontal crest. Potamonautes brincki also has an arched carapace as well as a partitioned terminal segment of the mandibular palp with a setae-covered flange. Potamonautes amathole sp. nov. has a unilobed terminal segment of the mandibular palp with no flange. Of all the Western Cape montane freshwater crabs, P. tuerkayi is the most similar to P. amathole sp. nov. However, P. tuerkayi has a sharply tapering subterminal segment of gonopod 2, forming a rounded subterminal base, while in P. amathole sp. nov. this tapering is gradual, forming a sloping instead of a rounded base. Geographically, the above-mentioned species are all confined to the Cape Fold Mountain region, with P. amathole sp. nov. being the first described small-bodied montane freshwater crab from the Eastern Cape part of the Great Escarpment.
Potamonautes depressus and P. clarus are two species of highland river crabs in the Drakensberg Mountain range. Although superficially similar to P. amathole sp. nov. in terms of a flattened carapace and slender limbs, morphological differences do exist in the structure of the mandibular palp and carapace depression. In P. clarus, a bright orange species, the mandibular palp has a flange on the terminal segment, while this is absent in P. amathole. Potamonautes depressus has an extremely flattened carapace, with CH/CL ranging from 0.38–0.43. In P. amathole sp. nov., this depression of the carapace is less extreme with a ratio ranging from 0.43–0.51. Both of these species are confined to fast-flowing rivers in the Drakensberg highlands. In most other Potamonautes spp., pereopod 3 is the longest. However, in P. amathole sp. nov., pereopod 4 appears to be the longest.
Hogsback and Katberg are both situated in the Keiskamma River catchment. Both sites consist of Southern Mistbelt Forest (FoZ 3), known to be tall, multi-layered, species-rich forests dominated by Afrocarpus falcatus, Celtis africana, Calodendrum capense, Vepris lanceolata, and Zanthoxylum davyi (
The Hogsback (Madonna and Child) Waterfall site is situated inside the Hogsback State Forest. The habitat is represented by a tall, high-flowing stream with different biotopes and pools rich in macro-invertebrate diversity, i.e., Ephemeroptera, Coleoptera, Hemiptera, Diptera, Trichoptera, Odonata, and Plecoptera (
The second site is situated inside the Hogsback Arboretum Park, downstream from the 39 Steps Waterfall. The habitat is represented by a small stream with pools and the substrate is largely sand with rocks. The edge of the stream is represented by marginal vegetation (i.e., Pseudoschoenus inanis) with tree canopy cover and burrows (
The Katberg site is situated in the montane Katberg State Forest. This habitat is comprised of a trickling stream on a very steep slope. The habitat is represented by low and clean water with some other macro-invertebrate diversity, i.e., Ephemeroptera, Coleoptera, Hemiptera, Diptera, Trichoptera, and Odonata (
At the Hogsback Arboretum site, P. amathole sp. nov. co-occurs with P. danielsi. Potamonautes danielsi is also found at the nearby Municipal Dam.
Resolving the distribution of southern African potamonautids is often difficult due to the general cryptic nature of this genus (
16S Sequence divergences among previously known species ranged from 2.1 to 16.9%; the exception being the comparison between P. dentatus and P. mhlophe (1.5%). The indication of the P. danielsi Hogsback population, alongside the morphological identification of the specimen used in a study by
Although South African freshwater crabs have been extensively researched, we continue to find and describe new species (
Dr NAF Miranda is thanked for his invaluable efforts in the field. This work is based on the research supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa. Any opinion, finding, and conclusion or recommendation expressed in this material is that of the author(s) and the NRF does not accept any liability in this regard. The genetic study presented here was partly supported by a Competitive Programme for Rated Researchers (CPRR13082029507) grant from the National Research Foundation.
Supplementary infromation
Data type: phylogenetic
Explanation note: table S1: Representatives of valid southern African Potamonautes species included in the phylogenetic analysis used to contextualise divergences and confirm the affinities of specimens included in the current study. Four species of Maritomonautes were included as outgroup taxa. GenBank accession numbers for the 16S rRNA and cytochrome c oxidase subunit I (COI) included and the data sources are provided; table S2: Uncorrected sequence divergences, expressed as percentages, as calculated from a 549 nucleotide alignment of 16S rRNA mtDNA sequences (below diagonal) and a 660 nucleotide alignment of the protein-coding mtDNA cytochrome c oxidase subunit I (COI) fragment (above diagonal), between representative of Potamonautes included in the present study. Newly-sampled specimens are identified as Potamonautes danielsi and P. amathole sp. nov.