| چکیده انگلیسی مقاله |
This study investigated the morphological diversity of the Euphrates stone loach, Oxynoemacheilus euphraticus, in the Persian Gulf basin. For this purpose, samples were collected from the Khorram River (Karkhe River Sub-basin, Iran), Sirvan (the Iranian section of the Tigris Sub-basin), and the Euphrates River (tributaries of the Sultanyu River in Malatya (the type locality) and the Karasu River, Turkey), transferred to the laboratory, and 25 morphometric characteristics were measured. To investigate the morphological diversity between the studied populations, the measured traits were analyzed after standardization using one-way analysis of variance and Duncan's grouping, principal component analysis, and canonical variate analysis, with p-values obtained from the NPMANOVA test. The results showed significant differences between the studied populations in most of the measured traits, including predorsal length, preventral length, distance between the anus and the origin of the anal fin, height of the caudal peduncle, depth of the dorsal fin, length of the dorsal fin base, body depth at the head and at the origin of the dorsal fin, head width, eye diameter, and length of the barbels. PCA and CVA analyses distinguished the studied populations from each other. The population of the Sultansu River in Turkey showed greater differentiation than the other populations. According to the results, the Euphrates stone loach can adapt to various environmental characteristics by altering the aforementioned morphological traits to thrive in different habitats, indicating its high phenotypic plasticity across diverse habitats. Also, since different populations of this species cannot be distinguished from one another based on morphological characteristics, the aforementioned traits, which relate to the morphological phenotypic plasticity of this species, should be avoided when describing a new species.
Keywords: Freshwater fishes, Tigris, Morphology, Multivariate analysis, Adaptation.
Introduction
The genus Oxynoemacheilus is widely distributed in Iranian inland waters. So far, 62 species have been described in this genus worldwide (van der Laan, 2021), of which 17 species are found in Iranian inland waters (Eagderi et al., 2022). The wide distribution range of the members of this genus has resulted in the description of many new species, creating numerous taxonomic challenges. The Euphrates stone loach, Oxynoemacheilus euphraticus, has a wide distribution range in the Euphrates–Tigris river system within the Persian Gulf basin (Freyhof & Özuluĝ, 2017) and, in recent years, has been reported from the Tigris River drainage in the Lesser and Greater Zab and Sirvan sub-basins (Mouludi-Saleh et al., 2022). This species is also found in the Tigris River drainage in Iraq (Çiçek et al., 2023). Despite some studies on the distribution of this species, the morphological mechanisms associated with its adaptation to diverse habitats remain largely unknown. Therefore, this study aims to fill this gap by analyzing morphometric data from different populations. For this purpose, the present study was conducted to investigate the morphological patterns of the Euphrates stone loach in the Persian Gulf basin.
Materials and methods
To investigate the morphological adaptation patterns of the Euphrates stone loach, 48 specimens were collected from rivers in three sub-basins of the Persian Gulf, including Khorramrud (Karkhe sub-basin, 15 specimens), Sirvan (the Iranian section of the Tigris sub-basin, 15 specimens), and the Euphrates River (Turkey, Sultansu tributaries in Malatya, the type locality of the species) and Karasu in Erzincan, comprising 18 specimens, using an electrofishing device (Samus MP750) (Table 1). After anesthesia, the samples were fixed in a 4% buffered formalin solution and then transported to the laboratory. In the laboratory, 25 morphological characteristics were measured using a digital caliper with an accuracy of 0.1 mm, according to Armbruster (2012). After photography and biometry of the fish samples, their abdomens were opened, and the sex of the samples was determined. To eliminate the effects of allometric growth, raw morphometric data were standardized based on the allometric method (allometric vs. standard algorithm). The efficiency of the corrected data was assessed by testing the significance of the correlation between the variables and the standard length. To investigate the patterns and possible morphological differences between the studied populations, one-way analysis of variance, Duncan's range, Principal Component Analysis (PCA), and Canonical Variate Analysis (CVA) were used based on the p-value obtained from the NPMANOVA test. Standardization and all statistical analyses were performed using PAST-2.17b, SPSS 19, and Excel 2016 software. The significance level in this study was set at 0.05.
Research Findings
Due to the non-normality of the data, the Kruskal–Wallis test was used to compare each morphological trait separately between the studied populations. The results revealed significant differences in many morphological traits. Specifically, the findings indicated that significant differences were observed in the predorsal length, preanal length, distance between the anus and the origin of the anal fin, caudal peduncle height, dorsal fin depth, dorsal fin base length, body depth at the head and at the origin of the dorsal fin, head width, eye diameter, and barbel length (Table 2). In the PCA, to investigate potential morphological patterns between the studied populations, the first component emerged as the most influential component. The PCA plot based on the two components, PC1 and PC2, distinctly separated all populations (Fig. 1). In the CVA analysis, all populations were thoroughly distinguished from one another, with the Sultansu River population in Turkey significantly separated from the others (Fig. 2). The results of the CVA test of body shape indicated a significant difference in the morphometric characteristics of the Euphrates stone loach, based on the p-value obtained from the NPMANOVA test.
Discussion of Results & Conclusion
Intraspecific variation exists both within each population of a species and between different populations due to geographical variation. Therefore, the formation of a new species signifies the transformation of variation within a species into differences between two species (Ridley, 1996). However, geographical isolation does not necessarily serve as an isolating barrier to the creation of a new species, because geographical variation in species can arise from adaptation to their habitat conditions. Consequently, the morphological differences and color patterns observed between the studied populations of the Euphrates stone loach can be regarded as morphological differences stemming from geographical separation. In conclusion, it can be stated that, given that different populations of this species are indistinguishable from each other in terms of morphological characteristics, one should not limit the description of a taxon to only morphological traits that reflect the flexibility of the species.
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