Specimen identification in the absence of diagnostic morphological characters (e.g., larvae) can be problematic even for experts. The goal of the present study was to assess the performance of COI in discriminating specimens of the fish family Cyprinidae in Africa, and to explore whether COI-phylogeny can be reliably used for phylogenetic comparative analysis. The main objective was to analyse a matrix of COI sequences for 315 specimens from 15 genera of African Cyprinidae using various distance-based identification methods alongside multiple tests of DNA barcode efficacy (barcode gap, species monophyly on NJ tree). Some morphological and biological characters were also mapped on a COI-phylogeny reconstructed using Maximum Parsimony. First, the results indicated the existence of barcode gaps, a discriminatory power of COI ranging from 79 % to 92 %, and that most nodes form well-supported monophyletic clades on an NJ tree. Second, it was found that some morphological and biological characters are clustered on the COI-phylogeny, and this indicates the reliability of these characters for taxonomic discrimination within the family. Put together, our results provide not only an additional support for the COI as a good barcode marker for the African Cyprinidae but it also indicate the utility of COI-based phylogenies for a wide spectrum of ecological questions related to African Cyprinidae.

BRONX algorithm, character variations, COI, specimen identification

Cyprinidae is the most diverse family of freshwater fishes (Nelson et al. 2006; Imoto et al. 2013) with 377 genera and over 3000 described species (Eschmeyer and Fong 2015; Froese and Pauly 2017). Species of this family are mostly found in Africa, Europe, Asia, and North America (Thai et al. 2007). In Africa, recent studies of the family have identified 24 genera and 539 species (Yang et al. 2015; Vreven et al. 2016). Some species of the family are of economic importance in aquaculture, angling, fisheries, aquarium trade and many serve as an essential source of protein for humans in addition to their high values in recreational fisheries (Skelton 2001; Thai et al. 2007; Collins et al. 2012).

Traditionally, external morphological and osteological characteristics have been used to differentiate species within the subfamilies Cyprininae and Danioninae (Zhou 1989; Chen et al. 2009; Yang et al. 2010; Liao et al. 2011; Nelson et al. 2016). For example, diagnostic characters such as a spinous anal-fin ray in some Cyprininae (Yang et al. 2010), interhyal not ossified (Liao et al. 2011) and an extended anal fin in mature males of some Danioninae (Stiassny et al. 2006) are used for specimen identification in both subfamilies. Additionally, there are key morphological features that distinguish the males from the females, including a brighter breeding colour, longer fins and presence of the tubercles on the body and head in some African genera (Skelton 2001). Similarly, morphological features such as the presence/absence of barbels, the number of barbels, as well as barbel type, pattern of innervation, and barbel position have been used to differentiate species within and between genera of the subfamilies Cyprininae sensu lato and Danioninae sensu lato (Howes 1991; Skelton 2001).

The taxonomy of the family has been a topic debated in several studies (e.g., Howes 1991; Cavender and Coburn 1992; Briolay et al. 1998; Zardoya and Doadrio 1999; Gilles et al. 2001; Yang et al. 2015; Ren and Mayden 2016). Some studies have explored the phylogeny of this family at subfamily and genus levels using both mitochondrial and nuclear genes (Zardoya and Doadrio 1999; Simons et al. 2003; Stiassny and Getahun 2007; Tang et al. 2010; Yang et al. 2010; Zheng et al. 2012; Yang et al. 2015). Specifically in Africa, most cyprinid species were previously assigned to the subfamily Cyprininae (Tsigenopoulos et al. 2002). The former genus Barbus forms a large polyphyletic group of more than 800 species across the world and 300 species across Africa (Skelton et al. 1991). Early studies used, in addition to morphological characteristics, the ploidy level to reorganise the genus Barbus sensu lato in Africa (Agnèse et al. 1990; Oellermann and Skelton 1990; Güegan et al. 1995; Berrebi et al. 1996; Machordom and Doadrio 2001; Tsigenopoulos et al. 2002). As a result, some African Barbus from northern and southern Africa have been regrouped into genera such as Luciobarbusand Pseudobarbus (Swartz et al. 2009; Tsigenopoulos et al. 2010) and other species now belong to genus Labeobarbus (Oellermann and Skelton 1990; Berrebi et al. 1996; Machordom and Doadrio 2001).

Similarly, the recent molecular and morphological work of Yang et al. (2015) on subfamily Cyprininae had led to a major reclassification and name changes in the global Cyprinidae. This reclassification has since been adopted in some recent works (Armbruster et al. 2016; Decru et al. 2016; Skelton 2016; Vreven et al. 2016). As a result, some genera within the African Cyprinidae are now subfamilies (e.g., Cyprininae, Danioninae and Leuscininae) with few species belonging to non-specified subfamilies (Suppl. material 1). Presently, the African Cyprininae is grouped into four tribes including Barbini, Smiliogastrini, Torini and Labeonini (Yang et al. 2015). The tribe Barbini includes genera such as Luciobarbus, Barbopsis, Caecobarbus and Coptostomabarbus and the Smiliogastrini includes the genera Barbodes, Barboides, Clypeobarbus, Enteromius and Pseudobarbus. The former African diploid ‘Barbus’ is now reclassified within the genus Enteromius (Yang et al. 2015; Armbruster et al. 2016) and the South African tetraploid Barbus has been elevated to genus ‘Pseudobarbus’ (Yang et al. 2015; Skelton 2016), although Schmidt and Bart (2015) suggested a revision for genus Pseudobarbus to clarify those with inverted comma. Additionally, the former African Varicorhinus was reassigned to Labeobarbus in the tribe Torini (Beshera et al. 2016; Skelton 2016; Vreven et al. 2016). Yang et al. (2015) also suggested Sanagia velifera Holly, 1926 to be grouped with the genus Labeobarbus. The tribe Labeonini includes the genera Labeo, Garra and Prolabeo (Rainboth et al. 2012; Yang et al. 2012, 2015). In such context of taxonomic debate around the family Cyprinidae (Yang et al. 2015), it becomes necessary to question whether the ongoing global campaign of DNA barcoding can play a role at least in assigning specimen to their corresponding taxa. The DNA barcoding approach has been employed to complement or refine morphological species identification (Kochzius et al. 2010; Pereira et al. 2011; Chen et al. 2015). DNA barcoding is based on the use of a short standardised cytochrome c oxidase subunit I (COI) sequence to distinguish between animal species (Hebert et al. 2003; 2004). It has gained worldwide support because it is rapid, cost-effective (but see Stein et al. 2014), and applicable to species identification across the animal kingdom (e.g., Hebert et al. 2003; Ward et al. 2005; Van der Bank et al. 2013; Sethusa et al. 2014; Decru et al. 2016; Nigro et al. 2016). In particular, Decru et al. (2016) clearly demonstrated, using DNA barcoding, how knowledge of the African fish species diversity can be greatly improved, but they focused only on the Congo Basin region in Central Africa.

The present study uses a broader sampling of the African Cyprinidae and integrates morphology and ploidy data to further assess the effectiveness of DNA barcoding in discriminating specimens within the family. Specifically, the aim was to: (i) test the reliability of COI as a DNA barcode for the African Cyprinidae based on barcode gap, various distance methods, and the Rosenberg test of species monophyly; and (ii) map six traits including five morphological characters and ploidy level onto a COI-based phylogeny of the African Cyprinidae.

The length of the aligned COI matrix was 652 bp with the following base composition: A: 25.9 %, C: 26.8 %, G: 18.2 % and T: 29.1 %. The interspecific genetic distances (K2P) ranged from 0 to 0.30 (median = 0.15) and are larger than the intraspecific genetic distances (range: 0 – 0.02; median = 0.001; p < 0.001; Figure 1). This is indicative of a barcode gap in the COI dataset of the studied Cyprinidae. The existence of a barcode gap is further confirmed when we compared the lowest interspecific versus the furthest intraspecific distance (Figure 2). We found the optimised distance d = 0.015 suitable for species discrimination in the studied African Cyprinidae (Figure 3). Based on this threshold, the performance of COI varies with the method used (Table 1). The near neighbour method shows a discriminatory power of 92.1 %. The other two methods provide a lower performance of 88.2 % for the best close match (278 specimens out of 315) and 79.4 % with the BOLD method.

Figure 1. 

Evaluation of barcode gap in the dataset. Boxplot of the interspecific (inter) and intraspecific genetic (intra) distances, indicating the existence of a barcode gap, i.e., interspecific distance is larger than intraspecific distance. The median is indicated by the horizontal line and the range as the vertical dashed lines and outliers by bold vertical lines.

Figure 2. 

Evaluation of barcode gap in the dataset. Line plot of the barcode gap for the 315 Cyprinidae individuals. The black lines indicate where the smallest interspecific distance is longer than the longest intraspecific distance (bottom of line value), thus showing the existence of a barcode gap. The red lines show where this pattern is reversed.

Figure 3. 

Determination of the threshold genetic distance for species identification. False positive (grey) and false negative (black) identification error rates summed across a range of distance thresholds from 0.01 to 1.9 %. The cumulative error plot indicates the transition between intraspecific and interspecific distances, the genetic distance corresponding to the least cumulative error (1.51 %) showing the appropriate threshold value for the dataset.

In addition, the result presented in Figure 4 shows that most nodes form robust monophyletic clades (red-coded nodes in Figure 4). The level of monophyly is further confirmed on Figure 5 which clearly indicates two distinct subfamilies (Cyprininae and Danioninae) and five tribes in the subfamily Cyprininae (Figure 5). The mapping of morphological characters and ploidy level on the phylogeny indicates that some characters are clearly clustered [e.g., number of anal soft rays and presence/absence of barbels for the tribe Smiliogastrini, the fish length (21–40 cm) for the tribe Labeonini and the tetraploidy for Barbinini; fig. 5].

Figure 4. 

Neighbour-joining tree analysis using Rosenberg’s (2007) test. Nodes in red are strongly supported nodes, indicating species monophyly.

Figure 5. 

Parsimonious phylogenetic tree showing some plotted morphological characters, such as anal soft rays, barbels, dorsal soft rays, length, lip types, and ploidy status of 86 African Cyprinidae species.

Although COI is a universally accepted DNA barcode for animal groups (Hebert et al. 2003), its efficacy has also been questioned for some clades (Vences et al. 2005a; Chen et al. 2012; Murphy et al. 2013), and this prompts the need to assess its reliability for any particular group of interest (Collins et al. 2012).

The results presented in this work confirm that COI can be reliably used from a barcode perspective to distinguish between specimens of the African Cyprinidae in a dataset of 315 specimens representing 14 out of the 24 (58 %) recognised genera in Africa. For example, a significant barcode gap was found irrespective of the methods used, and this has also been reported for Cyprinidae of other geographic regions (e.g., Batishchevaa et al. 2011). Our results (79.4 %–92.1 %) from the distance-based method showed a pattern similar to the 90 % to 99 % discriminatory power reported for ornamental cyprinid fish species also mostly from Cyprininae and Danioninae and a catostomid (Collins et al. 2012). Irrespective of some drawbacks associated with the use of DNA barcoding and highlighted by some authors for some taxonomic groups (Vences et al. 2005a, b; Nielsen and Matz 2006; Valentini et al. 2008; Laskar et al. 2013) as well as the recent development of new generation sequencing techniques (e.g., Taylor and Harris 2012), the marker COI still remains useful for identification purposes (Batishchevaa et al. 2011; Collins et al. 2012; Van der Bank et al. 2013).

For example, the high level of COI discrimination is further supported by the test of species monophyly, a test that resulted in strongly supported clades based on Rosenberg (2007)’s probability of reciprocal monophyly on the NJ tree (see also Collins et al. 2012). Even our Maximum Parsimony tree provides additional support to the COI’s power of discriminating between clades of the African Cyprinidae. Specifically, our phylogenetic analysis retrieved 14 monophyletic genera clearly grouped into two subfamilies (Cyprininae and Danioninae). Within the Cyprininae, five tribes are distinctly recovered: Barbini, Cyprinini, Labeonini, Smiliogastrini, and Torini as in Yang et al. (2015). The subfamily Danioninae was represented in our material by the tribe Chedrini which is well supported and includes Chelaethiops, Engraulicyprus, Leptocypris, Mesobola, Opsaridium, and Raiamas (see also Tang et al. 2010).

This evidence of monophyly accords with the morphology-based taxa delimitation as we found that some morphological characters and ploidy levels clustered within some clades along the phylogeny. Such characters that clustered within clades include, for example, the number of anal soft rays and presence/absence of barbels for the tribe Smiliogastrini, the fish length (21–40 cm) for the tribe Labeonini and the tetraploidy for Barbinini. Such clustering on the COI-phylogeny is evidence not only for COI as DNA barcoding of some African Cyprinidae 11 a good barcode for the family Cyprinidae but also that COI-phylogeny can be used for a comparative phylogenetic analysis. Only the tribe Labeonini sensu Rainboth 1991 (Yang and Mayden 2010) was retrieved non-monophyletic in our dataset.

Overall, the existence of DNA barcode gap and a high discriminatory power, as well as the high level of monophyly give support to the use of COI as a reliable DNA barcode for African Cyprininae and Danioninae. Several studies have examined the phylogeny of this family at subfamily and genus levels using both mitochondrial and nuclear genes (Simons et al. 2003; Stiassny and Getahun 2007; Swartz et al. 2009; Tsigenopoulos et al. 2010; Yang et al. 2010; Zheng et al. 2012). Our study provides additional evidence for the effectiveness of DNA barcode data as a complementary tool to morphology-based identification of some African Cyprinidae, and our findings indicate that a COI-based phylogenetic tree for the African Cyprinidae can be used in comparative phylogenetic analyses and important applied problems (e.g., conservation) for this group of fish.

Kowiyou Yessoufou acknowledges the South Africa’s National Research Foundation (NRF) for funding (Grant No: 103944) as well as La Société Botanique de France. He also acknowledges a start-up grant from the University of Johannesburg (URC Grant: 073450). We also thank the editor and anonymous reviewers for their comments.