Effects of temperature and water turbulence on vertebral number and body shape in Astyanax mexicanus (Teleostei: Characidae)

Abstract

Environmental changes can modify the phenotypic characteristics of populations, which in turn can influence their evolutionary trajectories. In ectotherms like fishes, temperature is a particularly important environmental variable that is known to have significant impacts on the phenotype. Here, we raised specimens of the surface ecomorph of Astyanax mexicanus at temperatures of 20°C, 23°C, 25°C, and 28°C to examine how temperature influenced vertebral number and body shape. To increase biological realism, specimens were also subjected to two water turbulence regimes. Vertebral number was counted from x-rays and body shape variation was analysed using geometric morphometric methods. Temperature significantly impacted mean total vertebral number, which increased at the lowest and highest temperatures. Fish reared at lower temperatures had relatively more precaudal vertebrae while fish reared at higher temperatures had relatively more caudal vertebrae. Vertebral anomalies, especially vertebral fusions, were most frequent at the extreme temperature treatments. Temperature significantly impacted body shape as well, with fish reared at 20°C being particularly divergent. Water turbulence also impacted body shape in a generally predictable manner, with specimens reared in high turbulence environments being more streamlined and having extended dorsal and anal fin bases. Variation in environmental variables thus resulted in significant changes in morphological traits known to impact fish fitness, indicating that A . mexicanus has the capacity to exhibit a range of phenotypic plasticity when challenged by environmental change. Understanding the biochemical mechanisms underlying this plasticity and whether adaptive plasticity has influenced the evolutionary radiation of the Characidae, are major directions for future research.

Body shape and fin size in juvenile Atlantic salmon (Salmo salar): effects of temperature during embryogenesis

“…We did not measure the number of skeletal elements, but assuming body shape and fin area are related to the number of vertebrae and fin rays, respectively, it seems likely that a slenderer body shape and a larger fin area would indicate a larger number of vertebrae and fin rays (cf. Aguirre et al 2019;Corral and Aguirre 2019), but this remains to be examined in the present case.…”

“…More recently, it was shown that counts of vertebrae and number of fin rays influence body shape and fin sizes as revealed for the genus Rhoadsia Fowler, 1911, which is endemic to western Ecuador and northwestern Peru (Aguirre et al 2019). Similarly, Mexican tetra (Astyanax mexicanus (De Filippi, 1853)) raised in 20 and 28°C water had a higher number of vertebrae and a more elongated body shape than fish raised at temperatures in between (Corral and Aguirre 2019). Environmental influence on body shape has also been shown for Chinook salmon (Oncorhynchus tshawytscha (Walbaum in Artedi, 1792)), where those from an ephemeral stream had deeper bodies than those that came from continuously Note: B is the regression coefficient; SE is the standard error; exp(B) is the odds ratio.…”

“…These authors also revealed that there were close associations between body shape and number of vertebrae (see even Corral and Aguirre 2019), which also vary as predicted by Jordan's rule (McDowall 2008). There is very little known, however, if thermal conditions before egg hatching influence body shape and fin size of fishes (but see Corral and Aguirre 2019).…”

“…Since the mid-1900s, it has been well documented for fishes and other ectotherms that temperature conditions during embryogenesis not only influence the number of vertebrae but also other skeletal features, such as the number of fin rays of teleost fishes (Tåning 1952;Billerbeck et al 1997 ; McBride and Horodysky 2004). Recent studies have also linked the number of vertebrae and body shape, where more vertebrae tend to be associated with an elongated body shape (Aguirre et al 2019;Corral and Aguirre 2019). Moreover, there is an association between early rearing temperature and body shape.…”

Monsters with a shortened vertebral column: A population phenomenon in radiating fish Labeobarbus (Cyprinidae)

“…Various body and skeletal deformities in fish have been reviewed in many publications [7][8][9][10][11][12][13][14][15][16]; earlier reports can also be found in Dawson's bibliographies [17][18][19][20]. Many of these deformities apparently can be treated as monstrosities, particularly when the vertebral column is shortened without pronounced curvature, resulting in an altered body form that is extremely short and deep.…”