Revision of the Schistura cincticauda species group (Teleostei, Nemacheilidae) using molecular and morphological markers

Abstract

To approach the taxonomy of large and complex animal groups it is of advantage to focus on species groups with shared derived character state. We investigate the composition, morphological characteristics and relationships of and within the Schistura cincticauda species group, whose members are small freshwater fishes that inhabit streams and rivers in eastern Myanmar and western and southern Thailand. A phylogenetic analysis using molecular genetic markers demonstrated the monophyly of this group; a combined genetic and morphological analysis revealed the inclusion of at least twelve species. They share the presence of a pair of black marks on the lower lip, one on each side of the median interruption (these marks may be reduced to few melanophores or even missing in some individuals). Additionally, all species share a small body size (max. 60 mm SL), an incomplete lateral line reaching at most to vertical through anal-fin base, and the absence of sexual dimorphism. Each of the 12 species is diagnosed by a unique combination of character states in fin ray numbers, anus position, presence/absence of an axillary pelvic lobe, and colour pattern. The distribution areas of several species overlap and five cases of syntopic occurrence are known. Five unnamed species are described herein.

Figure 1

Bayesian tree of the concatenated dataset (mitochondrial cytochrome b plus nuclear IRBP 2 genes) showing the phylogenetic relationships of the species of the Schistura cincticauda species group and the proposed position of S. paucifasciata as concluded from its shared rare pigmentation element with S. balteata. The Bayesian (BAY) and maximum likelihood (ML) analyses revealed congruent topologies; the rectangles at the nodes indicate the posterior probabilities and bootstrap support. The map indicates the geographic origin of the analysed samples of the species. Colours in the tree correspond to colours in map; the values at the nodes represent the posterior possibilities.

Figure 2

Maximum Likelihood phylogenetic tree showing the monophyly of the Schistura cincticauda species group (indicated by red arrow). Besides the 11 species of the Schistura cincticauda group for which genetic data are available (underlaid with yellow colour), the analysis covered 54 additional species of the genus Schistura (species names and branches in black) and 23 species of other nemacheilid genera (species names and branches in red). The tree was rooted with Cobitis taenia. The values at the nodes represent relevant statistical supports in percentages of 5000 bootstrap replicates. Values lower than 70% are not shown.

Figure 3

Ventral view of the mouth of the twelve species presently assigned to the Schistura cincticauda species group. Red arrows indicate the characteristic pair of black blotches on the lower lip, blue arrows indicate an additional pair of black blotches on the lower lip. (A) S. ataranensis, ZRC 61579, holotype, 43.8 mm SL; (B) S. aurantiaca, IAPG A11272-11,274, 27.0 mm SL; (C) S. balteata, IAPG A2554, 32.2 mm SL; (D) S. cincticauda, IAPG A8313, 30.0 mm SL; (E) S. crocotula, IAPG A10513-10,517, 35.5 mm SL; (F) S. hartli, CMK 28810, paratype, 36.6 mm SL, blue outline depicts the diagnostic black mark posterior of the median incision; (G) S. kuehnei, ZRC 61582, holotype, 37.1 mm SL; (H) S. myaekanbawensis, CMK 24993, paratype, 29.4 mm SL; (I) S. paucifasciata, BMNH 930.3.3.4, paratype, 46.6 mm SL, blue dotted line shows anterior margin of lower lip; (J) S. peninsulae, IAPG A11506, 33.8 mm SL; (K) S. robertsi, IAPG A10967, 31.4 mm SL; (L) S. tenebrosa, UF 181418, paratype, 33.2 mm SL.

Figure 4

Species of the cincticauda species group described before 2023: (A) Schistura aurantiaca, CMK 14530, 45.8 mm SL; Thailand: Kanchanaburi province: Mae Khlong basin; (B) Schistura balteata, CMK 17236, 53.5 mm SL; Thailand: Kanchanaburi province: Mae Khlong basin: Pilok stream; (C) Schistura cincticauda, ZRC 38458, neotype, 29.3 mm SL; Thailand: Tak province: Salween basin: Moei River; (D) Schistura crocotula, CMK 16458, 30.4 mm SL; Thailand: Prachuap Khiri Khan province; (E) Schistura paucifasciata, BMNH 1930.3.3:4, paratype, 46.6 mm SL: Myanmar: Monglong; (f) Schistura robertsi, CMK 5346, paratype, 30.0 mm SL; Thailand: Phang Nga province: Phang Nga basin; (G) Schistura tenebrosa, UF 181417, holotype, 45.1 mm SL: Thailand: Kanchanaburi province: Mae Khlong drainage. (from Kangrang et al. 2012).

Figure 5

The new species described in the present study. (A) Schistura ataranensis, ZRC 61579, holotype, 43.5 mm SL; Myanmar: Kayin province: Ataran drainage; (B) Schistura hartli, ZRC 61581, holotype, 41.0 mm SL; Thailand: Surat Thani Province: Khao Sok; (C) Schistura myaekanbawensis, MHNG 2790.081, holotype, 29.8 mm SL; Myanmar: Tanintharyi Region: Tanintharyi drainage; (D) Schistura kuehnei, ZRC 61582, holotype, 37.1 mm SL; Thailand: Surat Thani Province: Tapi drainage, Khlong Sok watershed;. (E) Schistura peninsulae, ZRC 61584, holotype, 35.6 mm SL; Malaysia: Kedah province: Langkawi Island.

Figure 6

Cladogram based on species tree resulting from multi-species coalescence analyses in *BEAST plus morphocode of the twelve species currently included into the Schistura cincticauda species group. The position of S. paucifasciata is putative, since no DNA of this species was available. Characters and their states in the morphocode are: (A)—number of pectoral-fin rays (0 = 9, 1 = 10–11, 2 = 8); (B)—number of branched caudal-fin rays (0 = 9 + 8, 1 = 8 + 8, 2 = 7 + 8, 3 = 8 + 7); (C)—length of lateral line (0 = long [ending behind dorsal fin base], 1 = intermediate, 2 = short [ending before middistance from pectoral to pelvic-fin base]); (D)—position of anus (0 = half distance between pelvic to anal fin, 1 = closer to pelvic fin, 2 = closer to anal fin); (E)—black dots on lower lip (0 = present, 1 = variable); (F)—axillary pelvic lobe (0 = absent, 1 = present); (G)—black bar on base of caudal fin (0 = present, 1 = absent, 2 = irregular); (H)—black blotch posterior of median incision of lower lip (0 = absent, 1 = present) (I)—second pair of black dots on lower lip (0 = absent, 1 = present); (J)—black dot on base of dorsal fin (0 = present, 1 = absent); (K)—black bars on dorsal fin (0 = absent, 1 = present); (L)—bars of body (0 = bars numerous, broad or grey, 1 = 2 to 4 very thin black contrasting bars in middle of flank, 2 = all bars fused into plain brown body, 3 = most bars fused leaving few interspaces in middle of flank.

Figure 7

Detailed geographic origin of samples of the southernmost species of the Schistura cincticauda species group.