| چکیده انگلیسی مقاله |
This study aimed to compare the morphological characteristics of northern Caucasian bleak (Alburnus hohenackeri) populations in the Caspian basin using geometric morphometrics. Geometric morphometrics in fishes examines the changes in their appearance among different groups or under different environmental conditions by using anatomical reference points on their body. The data encompassed 487 fish samples from the Caspian Basin, including the Aras, Shalmanrud, Mazoboon, Noor, Sorkhrud, Goharrud, Kaparbordrud 1, Kaparbordrud 2, Gorganrud 1, Gorganrud 2, Lamir, and Hajibakandeh rivers. Photographs were taken from the left side of the lateral surface of these samples, and then 13 landmarks were digitized using tpsDig2 software. The data obtained from Procrustes analysis were analyzed with multivariate statistical methods such as PCA, CVA, and cluster analysis. The comparison of geometric morphometrics revealed a significant difference between the Aras River population and the other populations. The main differences were related to the shape of the body, the size and shape of the head, the position of the mouth, the position of the fins, the height of the body, and the length of the tail stem. This difference between the Aras River population and other rivers may be due to variations in habitat and geographical separation. Alternatively, it is possible that the observed differences indicate distinct species. On the other hand, the other populations overlapped with each other, and no significant difference was observed between them. This similarity in morphometrics could be attributed to similar habitat conditions.
Keywords: Geometric morphometric, Principal Component Analysis, Canonical Variate Analysis, Procrustes Analysis.
Introduction
The Caucasian bleak (Alburnus hohenackeri), belonging to the Leuciscidae family, is commonly found among aquatic plants in the lower parts of rivers and freshwater lakes. It can tolerate brackish water to some extent and is most abundant in river estuaries. This species inhabits all ecosystems of the Caspian Sea, although human activities have inadvertently introduced it to other water bodies like Zarivar, Maraveh, Hamun, and Sistan. Habitat and river differences significantly impact fish species, making morphological studies of Caucasian sprat across various rivers and water bodies important.
Morphological characteristics are essential for differentiating populations within a species and can provide insights into evolution, behavior, conservation, and resource utilization (Nacua et al. 2010; Su et al. 2019). The geometric morphometric method based on landmarks is widely applicable in biological studies and is effective in analyzing morphological changes over time and space (Klingenberg 2017; Adams et al. 2004). This method allows for comparisons between biological forms based on landmark coordinates, which can be visualized in a deformation network.
Understanding fish in aquatic ecosystems is crucial from ecological, behavioral, evolutionary, and resource management perspectives (Razavipoor et al. 2014). The primary aim of this study is to investigate the geometric morphological differences of Caucasian sprat within the Caspian Sea basin, which is the largest lake globally, housing around 115 fish species, including economically and ecologically significant species like sturgeon, mullet, carp, and trout (Ghojoghi et al. 2018).
Materials and Methods
In this study, 487 specimens of Caucasian sprat (from a total of 12 populations across 12 rivers) were collected from the Caspian Sea basin between 2009 and 2010. The identification was based on the 2020 checklist (Jouladeh-Roudbar et al. 2020). The fish studied were not mature, making sex determination impossible; therefore, they were analyzed as a mixed group. However, the samples were sufficiently grown for identification. Some samples were excluded from the study due to inadequate growth for identification, and only recognizable specimens were included. The fish mature at a size of 12 cm, while the specimens studied ranged from 8 to 11 cm.
After selecting the target rivers for sampling, Caucasian sprat specimens were captured using a seine net and an electrofishing device. The samples were then fixed in 10% neutral buffered formalin and transferred to the Ichthyology Laboratory of the Faculty of Natural Resources at Isfahan University of Technology, where they were preserved in 70% alcohol.
Geometric morphometric data were extracted using a 14-megapixel Canon digital camera (made in Japan). Landmarks were placed on the images using TpsDig2 software (version 2.10). Morphometric data for the studied species were compared using Tps series software (version 2). Procrustes analysis was used to eliminate non-shape variations, followed by analysis using PAST software (version 2.17). The average shape changes of populations were derived from the overall mean shape. Geometric morphometric data were analyzed using principal component analysis and canonical variable analysis. Figure 2 illustrates a fish sample for landmark determination.
Research Findings
The results of principal component analysis (PCA) indicated that the first three components were selected as the main factors distinguishing the populations, accounting for approximately 53% of the total variance. The distribution of the studied populations and changes in body shape along the first two principal components were analyzed.
The analysis revealed that eleven populations overlapped, indicating no significant differences among them. However, the Aras River population did not overlap with the others, showing significant differences. Changes in body shape patterns indicated that movement in the positive direction of the first principal component was associated with alterations in mouth position, shifts in eye positions, and significant changes in dorsal fin positions, pelvic and anal fin positions, as well as increases in body height and caudal peduncle length.
In the positive direction of the second principal component, similar changes were observed, including downward movement of the mouth, shifts in the head end position, alterations in dorsal and anal fin positions, and increases in body height and caudal peduncle length.
Canonical correlation analysis demonstrated that nearly all populations overlapped with no significant differences, except for the Aras River population, which was distinct from the others. Cluster analysis indicated that the Aras River population formed a separate branch, showing the greatest distinction from other populations. Two main groups emerged: one including the Aras River and another with the remaining populations. Within the second group, the Marzbon population was notably distinct, while the pairs of populations Golestanrud1 and Haji-Bakandeh, as well as Koper-Bardrud1 and Noor, were identified as sister populations with minimal distance between them.
Discussion of Results & Conclusion
Fish populations in different habitats exhibit distinct forms due to environmental conditions. Among vertebrates, fish show a high degree of morphological diversity and sensitivity to environmental changes (Mouludi-Saleh et al. 2018). While shape variations were once thought to be primarily genetic, it is now recognized that environmental factors play a crucial role.
Numerous studies have demonstrated that body shape correlates with specific environmental conditions, leading to notable adaptations. For instance, research in the southern Caspian Sea basin identified traits such as head size, body depth, and fin positions as key factors distinguishing fish populations (Mouludi-Saleh & Keivany 2019). Similarly, studies on narrow-nosed mullet and stream catfish revealed significant morphological variations influenced by their habitats (Abassi et al. 2023a; Sharifinia & Mousavi 2016).
Morphological changes are significant when linked to functional aspects, such as foraging behavior and movement efficiency in aquatic ecosystems (Abassi et al. 2023b). For example, a downward mouth position in the Aras population may indicate feeding from deeper waters, while reduced body height may aid in navigating currents (Hawkins & Quinn 1996).
Overall, the evolutionary changes leading to morphological differences in the Aras population appear to be influenced by habitat characteristics and geographical isolation. The distinct shape of the Aras population likely relates to its dietary habits and environmental adaptations, impacting its feeding success and predator avoidance (Langerhans et al. 2003). |