Marcel Vermeulen BSc

Phenotypic divergence across a flow regime in the Blackspot barb Dawkinsia filamentosa (Valenciennes 1844) (Teleostei: Cyprinidae) from Sri Lanka

Advisor: Harald Ahnelt

Master's Defensio - Tuesday, April 2nd 2024, 10:30
SR 5.1, UBB
Djerassiplatz 1, 1030 Vienna


Adaptation to different environmental factors, influenced by different selective pressures, typically serves as the basis for morphological differentiation. Fish often exhibit habitat-related morphological divergence as populations living in different environments experience different abiotic and biotic factors. These factors include a range of biotic and abiotic elements such as water flow, temperature, light availability, food resources or predation pressure, which shape the overall structure. The relationship between body shape and hydrodynamics in aquatic ecosystems is well established, especially considering that a fish's ability to navigate efficiently through water is highly dependent on its morphology. Recent research suggests that individuals in lentic environments tend to develop a deeper body shape, whereas those in lotic habitats develop a more streamlined shape. However, the benefits associated with specific phenotypic traits, often linked with improved swimming performance, may be overshadowed by the morphological influences of other environmental factors. In this study, two populations of Dawkinsia filamentosa were tested for phenotypic divergence inhabiting lentic and lotic habitats respectively using traditional morphometric and meristic analyses. The results revealed distinct patterns of morphological differentiation among populations in these different habitats, i.e., in body shape, relative fin characteristics and head morphology. In addition, sexual dimorphism, which was primarily linked to fin characteristics, was examined. The observed results contradict the swimming-performance theory in some points, as individuals from low-flow habitats showed more streamlined body shapes than individuals from high-flow habitats. More research would be needed to understand how different evolutionary processes lead to diverse body shapes in fish.