Ecological predictors of lateral line asymmetry in stickleback (Gasterosteus aculeatus)

Abstract

Threespine stickleback exhibit a row of superficial neuromasts that project through the bony plates on each side of the trunk and which constitute an important sensory modality for detection of near-field water motion. Previously, we have shown that numbers of neuromasts on each structural plate are highly variable among populations. In the current paper, we expand this study to evaluate the extent of deviation from bilateral symmetry of 4344 fish in 57 natural and three transplant populations of threespine stickleback from lakes, streams and oceanic habitats of coastal British Columbia, predicting that neuromasts would be largely bilaterally symmetrical for optimal detection of external stimuli. In contrast, we found asymmetry in all populations, the greatest amount occurring on the anterior buttressing lateral plates and on populations with the fewest neuromasts. We found no consistent trends of signed (directional) asymmetry (SA) among the populations while relative absolute asymmetry (RAA) is lower in dystrophic (stained) habitats than in clearwater habitats (p < 0.001), except for fish with few neuromasts. Sexual dimorphism in RAA is also greater in dystrophic habitats (p < 0.001). Transplants from stained lakes to unstained ponds resulted in a 0.1% to 14% difference in RAA from the source population in less than 12 generations but varied in direction among experiments. Our data suggest a widespread tendency for populations exposed to reduced photic information to exhibit reduced asymmetry in their lateral line system, which can change rapidly in response to a new environment.

Sensory evolution in a cavefish radiation: patterns of neuromast distribution and associated behaviour inSinocyclocheilus(Cypriniformes: Cyprinidae)

“…= 0.079 ± 0.031). This finding consistent with prior work suggesting asymmetry facilitates navigation in darkness [52,53], food-foraging success [54] and the ability to maximize sensory information [37,51]. We note, however, that there was modest within-species variation for some Clades (see bar lengths in Clade A, figure 4), but substantial within-species variation for others (see bar lengths in Clade D, figure 4).…”

“…In other cave-dwelling species, neuromast asymmetry demonstrates a consistent left-side bias (e.g. A. mexicanus cave-adapted morphs from North America) or a right-side bias ( Gasterosteus aculeatus from Central America) [37,51]. Neuromast distributions in our analysis revealed asymmetry was present across the left-right axis, and this variation was present within and across species.…”

“…The lower density of neuromast distribution may be an optimization to provide the lower resolution of information for living in stable environment (distinguishing a wall or a ceiling, as opposed to a predator). At present, however, it remains unclear precisely what is the functional relevance of this pattern in the cave microenvironment [37].…”

“…which side of the head harboured more neuromast organs). This lateral bias trait was scored by calculating a signed asymmetry rate (SAR), SAR=(R−L)/(normalR+normalL)∗100%; [37]. This analysis yielded two morphological categories: ‘right-biased’ (SAR > 0), in which more neuromasts are on the right-side and ‘left-biased’ (SAR < 0) in which more neuromasts are on the left side of the head (figure 3; electronic supplementary material, table S1 and figure S2).…”

“…In other cave-dwelling species, neuromast asymmetry demonstrates a consistent left-side bias (e.g. A. mexicanus cave-adapted morphs from North America) or a right-side bias (Gasterosteus aculeatus from Central America) [37,51].…”