Research Article |
Corresponding author: Piscart Christophe ( christophe.piscart@univ-rennes1.fr ) Academic editor: Damia Jaume
© 2021 Pountougnigni Oumarou Farikou, Piscart Christophe, Sob Nangou Paul Bertrand, Zebaze Togouet Serge Hubert.
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:
Farikou PO, Christophe P, Bertrand SNP, Hubert ZTS (2021) Distribution of Stenasellidae in Africa and description of a new species of Metastenasellus from Cameroonian groundwaters. Subterranean Biology 40: 175-194. https://doi.org/10.3897/subtbiol.40.76301
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During recent investigations of the groundwater fauna of Cameroon, specimens of a new species of the stygobitic genus Metastenasellus, M. boutini sp. nov. were collected in wells of the city of Douala. The new species can be easily distinguished from the other species of the genus by its relatively large size (up to 11 mm), pleonite 1 and 2 half the length of pereonite 7, the shape of pleopod 2 in males (presence of an external lobe on the protopodite, distal part of the spermatic duct slightly protruding out of the second article, lack of a distal seta on the exopodite), and uropod half the length of the pleotelson. Ecological data and a key to Metastenasellus species are provided. We also performed an exhaustive analysis of the literature on Stenasellidae in Africa to study the geographical distribution of the family in this continent and discuss some hypotheses about the origin of African species.
biogeography, integrative taxonomy, Isopoda, stygofauna, tropical Africa
Over the last decades, investigations of groundwaters around the world have highlighted an unexpectedly high diversity of organisms forming the so-called stygobitic fauna. Stygobitic diversity even exceeds epigean diversity for some groups (
Among the stygobitic species living in Africa, the order Isopoda, with at least 80 species, represents around 30% of the total number of groundwater species of the continent (
In this context, the goal of our study was to complete existing knowledge on the diversity and distribution of stenasellid isopods in Africa. We performed extensive sampling campaigns in Central Africa, in particular in Cameroon, starting in 2010. These campaigns revealed the presence of a new species, Metastenasellus camerounensis Zebaze Togouet, Boulanouar, Njiné & Boutin 2013 – but also of several other new species of Metastenasellus in Cameroon (
Between 2019 and 2021, 5 sampling campaigns (3 during the rainy season and 2 during the dry season) were carried out in 41 wells in the city of Douala. The wells were located in alluvial sediments near the Atlantic coast (maximum distance from the ocean 16 km) with an elevation lower than 65 m a.s.l., and a maximum depth of 9 m. The city of Douala has warm and humid climate conditions, with an average annual temperature of 27.0 °C and an average humidity level of 83%, with around 4,000 mm of precipitation per year (
Faunal samples were collected from the bottom of the wells using a modified phreatic net sampler (30 cm diameter aperture and 64 μm mesh size:
Water samples were collected in each well at each sampling date. Temperature, pH, electrical conductivity, and dissolved oxygen were measured directly in the field with a mercury thermometer, a portable pH-meter (CG 818, Schott instruments), and a portable conductivity meter and optical dissolved oxygen meter (HQ30d, Hach Lange), respectively. . The water was transported directly to the laboratory using polyethylene bottles under cool storage for additional analyses: alkalinity, dissolved carbon dioxide, calcium, magnesium, chemical (CDO) and biological (BDO5) oxygen demand, turbidity, and nutrient contents. The differences in physico-chemical parameters of water in wells with or without the new species were assessed using non-parametric Mann-Whitney U Tests using the STATISTICA v12 (StatSoft) software.
The specimens were dissected and mounted on microscopic slides in Faure’s mounting medium, after maceration +in lactic acid and staining with pink lignin. Body parts were digitally drawn using a Wacom tablet and the Adobe Illustrator software package (Adobe).
Total genomic DNA was extracted from a part of an animal using NucleoSpin Tissue Kits (Machery-Nagel) following the manufacturer’s instructions (Düren, Germany). A fragment of the mitochondrial COI gene was amplified using LCO1490/HCO2198 (
The PCR results were checked by gel electrophoresis, then the PCR products were purified and sequenced in both directions by the Eurofins sequencing facility or with an Applied Biosystem 3130 XL sequencer in the DNA sequencing facility of the Institute of Genetics and Development of the University of Rennes (https://igdr.univ-rennes1.fr/en). All COI sequences obtained in four wells are deposited on Genbank (assession numbers OL514108; OL514109; OL514110; OL51411 and OL51412) and on the Barcode of Life Data systems (BOLD) (BOLD process id: METAF001-21, METAF002-21, METAF003-21, METAF004-21 and METAF005-21).
The new COI sequences were supplemented by COI sequences downloaded from Genbank: two sequences of Metastenasellus species from Benin (accession numbers KY623773.1 and KY623774.1); four from M. camerounensis from Cameroon (accession numbers KY623769.1; KY623770.1; KY623771.1; KY623772.1), and two from an unknown Metastenasellus species from Cameroon (accession numbers KY623775.1; KY623776.1). All sequences were aligned with the MUSCLE algorithm (
For final visualization with already sequenced species of Metastenasellus, the neighbor-joining tree of all COI sequences, using the Kimura two-parameter (K2P) model of evolution (
An exhaustive survey of the literature on Stenasellidae (species descriptions, identification keys, monography, PhD theses, books, papers) was carried out for all the species known in continental Africa. All maps were drawn with Arcgis Desktop 10.4 software (Esri) and using GIS data available on DIVA website (http://www.diva-gis.org) in WGS 84 datum.
Suborder Asellota Latreille, 1802
Superfamily Aselloidea Latreille, 1802
Family Stenasellidae Dudich, 1924
Genus Metastenasellus Magniez, 1966
Metastenasellus boutini n.sp. is characterized by pleonites 1 and 2 around 50% as long as pereonite 7, the presence of sternal spine on each dactylus of pereopods 2–7 and endopodite of pleopod 2 in males long and large with a helicoidal spermatic duct.
Type-specimen: Holotype ♂ (9.8 mm), mounted on 2 slides and deposited at the Muséum national d’Histoire Naturelle de Paris (
Cameroon, in PK21 quarter, Douala city, 04°07'16"N; 09°49'41.4"E, in a well at 60 m a.s.l. and 8 m depth, 24 April 2021. Paratypes: 5 ♂♂ in vials; same data as for holotype;
22 specimens collected in seven wells around the type locality (Table
The epithet boutini refers to the name of Dr. Claude Boutin who initiated many studies on stygofauna in northern and central Africa.
M. boutini sp. nov is a relatively medium-sized stenasellid, length up to 11 mm in males. Cephalon short and rounded with a concave rostral margin and convex distally. Pereonites 1 to 7 well developed, the 6th and 7th being the longest. Pleonites 1 and 2 free and as long as 50% of the length of the pereonite 7. Pleotelson subrectangular with a pointed caudal margin and partially covering the protopodite of the uropod.
Antenna 1 (Fig.
Gnathopod (pereopod 1) (Fig.
Pereopods 2 to 7 (Fig.
Pleopod 1 (Fig.
Female. Females are very similar to males with a reduced chaetotaxis on uropods. They are slightly longer than males, size up to 12 mm. Pleopod 2 (Fig.
The new species differs from most of species of Metastenasellus by the presence of an external lobe on the protopodite of pleopod 2 which is known only in Metastenasellus leysi Magniez, 1985. However, M. boutini differs from M. leysi by many other characteristics such as the total length (< 3.5 mm for M. leysi); the number of articles on flagellum of antenna 1 and 2 (2 and 13, respectively) much reduced for M. leysi in comparison with M. boutini (15 and 48, respectively); pleonites 1 and 2 as long as pereonite 7 for M. leysi (as long as 0.5 fold pereonite 7 for M. boutini). The shape of the endopodite of pleopod 2 of M. boutini is also characterized by a distal part of spermatic duct slightly protruding out the second article. By these characteristics, the new species strongly differs from M. camerounensis, M. leleupi (Chappuis 1951), M. dartivellei (Chappuis 1952), M. congolensis (Chappuis 1951), and M. powelli
We sequenced and analyzed DNA from five individuals from four wells, including the type locality at Douala. Based on the Folmer’s fragment of COI marker, the new species is clearly distinct from the other species sequenced in Cameroon and in Benin. The pairwise genetic distances between M. boutini and all other species varied between 22.4 and 27.8% for Cameroonian species and even 28.2% for the species in Benin (Fig.
Neighbor-joining tree of the identified COI gene haplotypes. The evolutionary distances were computed using the Kimura two-parameter (K2P) model. Numbers between brackets in front of the nodes indicate bootstrap support (1,000 replicates). Boxes on the right indicate the best partition of species using ASAP, ABGD, mPTP and GMYC delimitation methods.
Pleopods 2 of males Metastenasellus as drawn in original descriptions (A) M. leleupi (scale 1) (B) M. camerounensis (scale 1) (C) M. dartivellei (scale 2) (D) M. powelli (scale 3) (E) M. congolensis (scale 1) (F) M. boutini (scale 2) (G) M. leysi (scale 3) (H) M. wikkiensis (scale 2) (I) M. tarrissei (scale 3).
Distribution map of Stenasellidae in Africa: Acanthastenasellus (A. forficuloides); Johanella (J. purpurea); Magniezia (Ma1: M. africana, Ma2: M. gardei, Ma3: M. guinensis, Ma4: M. laticarpa, Ma5: M. studiosorum); Metastenasellus (Me1: M. boutini, Me2: M. camerounensis, Me3: M. congolensis, Me4: M. dartvellei, Me5: M. leleupi, Me6: M. leysi, Me7: M. powelli, Me8: M. tarrissei, Me9: M. wikkiensis, Me10: Metastenasellus sp1, Me11: Metastenasellus sp2, Me12: Metastenasellus sp3, Me13: Metastenasellus sp. 4, Me14: Metastenasellus sp5); Parastenasellus (P. chappuisi); Stenasellus (St1: S. agiuranicus, St2: S. costai, St3: S. kenyensis, St4: S. migiurtinicus, St5: S. pardii, St6: S. ruffoi, St7: S. simonsi).
The new species M. boutini was collected in 7 of the 10 wells sampled in quarter PK21 of Douala (Table
Wells | Latitude, Longitude | M. boutini |
---|---|---|
P1 | 4.124111, 9.826861 | Yes |
P2 | 4.124083, 9.827056 | No |
P3 | 4.121444, 9.828333 | Yes |
P4 | 4.121111, 9.828167 | Yes |
P5 | 4.120694, 9.827278 | Yes |
P6 | 4.120639, 9.826028 | No |
P7 | 4.119528, 9.826389 | Yes |
P8 | 4.119056, 9.826528 | No |
P9 | 4.118778, 9.827111 | Yes |
P10 | 4.119083, 9.825917 | Yes |
The water chemistry of phreatic water in this part of the city was very acidic (pH = 4.2 ± 0.4), relatively warm, and well oxygenated with relatively low concentrations of calcium and magnesium (Table
Mean (min–max) values of physico-chemical parameters of wells sampled in quarter PK21 where M. boutini were found at Douala.
Wells with M. boutini | Wells without isopod | |
---|---|---|
Depth (m) | 7.4 (6 – 9) | 7.8 (7.6 – 8) |
Water layer (cm) | 157.7 (30 – 310) | 116.2 (30 – 245) |
Temperature (°C) | 26.2 (22.4 – 29.5) | 26.2 (22.7 – 28.7) |
pH (IU) | 4.2 (3.4 – 5.1) | 4.23 (3.92 – 4.92) |
O2 (mg/L) | 5.3 (3.8 – 8.2) | 5.31 (3.3 – 7.4) |
Electrical Conductivity (µS/Cm) | 587 (155 – 822) | 646 (192 – 947) |
N03- (mg/L) | 1.3 (0 – 3.5) | 1.0 (0 – 3.1) |
PO43- (mg/L) | 0.95 (0 – 3.1) | 0.8 (0 – 2.9) |
Ca2+ (mg/L) | 2.0 (0.2 – 4) | 2.1 (1.1 – 2.6) |
Mg2+ (mg/L) | 4.4 (0.3 – 11.4) | 8.3 (1.3 – 14) |
The known distribution of Stenasellidae in Africa is very patchy (most of the species are known only from their type localities). Genera belong to three main geographic groups (Fig.
The first stenasellid isopods were found for the first time in France in 1896 and later described as Stenasellus virei Dolfus, 1897. This first species was followed by successive discoveries in southern and central Europe in the early 1900’s (
Despite the geographical proximity of M. camerounensis and M. boutini, their morphology differs strongly. The two species have a relatively large size among Metastenasellus and a similar pleonites/pereonite 7 ratio, but the shape of pleopod 2 strongly differs. In M. boutini, the endopodite of pleopod 2 is evolved, with a distal part of the spermatic duct almost fully inside the second article of the endopodite. This specificity is considered as the ultimate evolution of pleopod 2 in the genus Metastenasellus (
As suggested by previous studies, the second male pleopod exhibits several significant differences among Metastenasellus species (
The stygobitic family Stenasellidae is widely distributed in southwestern Europe, the Middle East, Asia, and even Central America (
Stenasellids can also colonize all kinds of groundwaters (karst, interstitial and phreatic waters) (
This identification key concerns males of the nine currently known species of the genus Metastenasellus: M. leleupi (Chappuis, 1951); M. congolensis (Chappuis, 1951); M. dartivellei (Chappuis, 1952); M. wikkiensis Lincoln, 1972; M. powelli Magniez, 1979; M. tarrissei Magniez, 1979; M. leysi Magniez, 1986; M. camerounensis Zebaze Togouet, Boulanouar, Njiné & Boutin, 2013, M. boutini Pountougnigni, Piscart & Zebaze (present study).
Like the key proposed by
1 | Pleopod 2, distal part of spermatic duct clearly protruding out of the main part of the second article of endopodite (Fig. |
2 |
– | Pleopod 2, distal part of spermatic duct slightly protruding out or fully inside the second article of endopodite (Fig. |
6 |
2 | Pleopod 2, external part of spermatic duct strongly protruding out (≥ 50%) of the second article of endopodite (Fig. |
3 |
– | Pleopod 2, external part of spermatic duct slightly protruding out (≈ 20%) of the second article of endopodite (Fig. |
4 |
3 | Pleopod 2, second article of endopodite subrectangular, external part of spermatic duct half the length of second article of endopodite with a row of chitinous teeth along the last 2 whorls, second article of exopodite with 4 marginal and subterminal setae but without a terminal seta; total body length > 10 mm; (Fig. |
M. camerounensis [Yaoundé, Cameroon] |
– | Pleopod 2, second article of endopodite conical, external part of spermatic duct of the same length as the second article of endopodite with a row of chitinous teeth only at the apex, second article of exopodite with 2 or 3 setae with a terminal seta at the apex; total body length < 8 mm (Fig. |
M. leleupi [Kinshasa Province, Democratic Republic of the Congo] |
4 | Pleopod 2, first segment of endopodite clearly delimited, second article of exopodite with 6 to 8 setae (Fig. |
5 |
– | Pleopod 2, first segment of endopodite not clearly delimited, second article of the exopodite with 5 setae (Fig. |
M. dartivellei [Équateur province, northwestern Democratic Republic of the Congo] |
5 | Pleopod 2 protopodite longer than wide (Fig. |
M. powelli [Port Harcourt, southeastern Nigeria] |
– | Pleopod 2 protopodite longer than wide (Fig. |
M. congolensis [Congo Central Province, eastern Democratic Republic of the Congo] |
6 | Pleonites 1 and 2 as long as pereonite 7; flagellum of antenna 1 with less than 8 articles; flagellum of antenna 2 with less than 25 articles; total body length ≤ 5 mm | 7 |
– | Pleonites 1 and 2 as long as 50% of pereonite 7; flagellum of antenna 1 with 8 articles; flagellum of antenna 2 with more than 25 articles; total body length ≥ 8 mm | 8 |
7 | Pleopods 2 exopodite wider than endopodite; exopodite and endopodite not clearly separated (Fig. |
M. leysi [Naâma Province, northeastern Algeria] |
– | Pleopod 2 endopodite wider than exopodite; exopodite and endopodite well separated (Fig. |
M. tarrissei [Lake District, central Ivory Coast] |
8 | Pleopod 2 protopodite with an external lobe, second article without terminal setae (Fig. |
M. boutini [Douala, southwestern Cameroon] |
– | Pleopods 2 protopodite without an external lobe, second article with a terminal seta (Fig. |
M. wikkiensis [Plateau State, northeastern Nigeria] |
This study was supported by the University Yaoundé 1 (Cameroon) and the financial support of the Agence Universitaire de la Francophonie (AUF) and the French Embassy (SCAC 2021) that permitted the work of O.F. Pountougnigni in France.
List ot sampling sites with ot without Metastenasellus boutini in the area arround the type locality
Data type: occurrences