Browsing by Subject "Selachii"

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    Comparative anatomy of Selachian vertebrae and the correlations with ecological and behavioural traits
    (2026) Arendse, Amy Hannah; Attwood, Colin
    Diversity in habitat use and ecological niche seen in sharks should be reflected in the vertebral column. The mechanical constraints of different environments and swimming modes should affect the morphology of vertebral centra allowing sharks to optimally function in their respective habitats. There are few comparative anatomy studies of Chondrichthyan vertebral morphology. Most work on Chondrichthyan vertebrae concerned their use for age and growth studies. This study aims to investigate centra morphology and its relationship with ecological aspects of Selachian species, which includes habitat use, vagility and swimming style. A comparative analysis of vertebrae shape across 12 families (Alopiidae, Carcharhinidae, Carchariidae, Etmopteridae, Galeocerdidae, Lamnidae, Pentanchidae, Pristiophoridae, Pseudocarchariidae, Scyliorhinidae, Sphyrnidae, Squalidae and Trikidae) and 30 species was conducted. Species were compared according to a designated ecological environment of either pelagic (n=13) or benthic (n=17). Vertebrae centra were isolated by removing transverse processes, muscle and other tissue. Centra were bleached for approximately 30 minutes before rinsing in deionized water and left to completely dry on paper towel overnight. Six measurements of the dried centra were measured with digital vernier callipers (mm). A fineness ratio (FR) between the cranial-caudal length and the dorsal-ventral height was used to quantify morphology to compare across shark orders. It was hypothesised that benthic sharks have a larger cranial-caudal length and a smaller dorsal-ventral height in contrast to pelagic sharks. Secondly it was hypothesised that the FR will be greater for benthic sharks resulting in block-shaped centra and lower for pelagic sharks resulting in disc-shaped centra. Benthic sharks had a mean (±SE) FR of 0.98 (±0.05). Pelagic sharks had a mean (±SE) FR of 0.56 (±0.02). A general linear model exposed significant differences between shark orders (F-value = 4.215, R2 = 0.24, p-value = 0.015). FR differed between Squaliformes and Lamniformes and between Squaliforms and Carcharhiniforms. The FR differed between pelagic and benthic sharks (t = 5.09, df = 29, p-value < 0.05). Multiple Gaussian general linear models showed that swimming mode, centra shape, migration and environment had significant effects on the fineness ratio (F-value = 25.91, R2 = 0.88, p-value<0.05; F-value = 36.53, R2 = 0.88, p-value<0.05; F-value = 20.7, R2 = 0.87, p-value<0.05;). Factor of Mixed Analysis (FAMD) plots formed distinct two distinct clusters of pelagic species with associated pelagic ecological variables and benthic species with associated benthic ecological variables. Species, fineness ratio and centra shape were the largest contributors in explaining the dimensions. The second moment of area (I ) was calculated to quantify the stiffness of vertebrae. Values for I differed for benthic and pelagic sharks (t = -2.36, df = 28, p-value = 0.03). Following beam theory, large fineness ratios were was associated with longer cranial-caudal lengths, fluted cylinder and hourglass vertebral shapes, anguilliform swimming, small second moment of area values, and a flexible vertebral column. Smaller fineness ratios were associated with smaller fineness ratios, shorter cranial-caudal lengths, cylinder vertebral shape, carangiform swimming, large second moment of area values, and a rigid vertebral column. Centra shape is an adaption to different environments and swimming modes and could be used to infer ecological and behavioural traits. These relationships could form a foundation for tools to infer the ecological characteristics of unobserved and extinct species.