Abstract
Changes to calcium carbonate (CaCO3) biomineralization in aquatic organisms is among the many predicted effects of climate change. Because otolith (hearing/orientation structures in fish) CaCO3 precipitation and polymorph composition are controlled by genetic and environmental factors, climate change may be predicted to affect the phenotypic plasticity of otoliths. We examined precipitation of otolith polymorphs (aragonite, vaterite, calcite) during early life history in two species of sturgeon, Lake Sturgeon, (Acipenser fulvescens) and White Sturgeon (A. transmontanus), using quantitative X-ray microdiffraction. Both species showed similar fluctuations in otolith polymorphs with a significant shift in the proportions of vaterite and aragonite in sagittal otoliths coinciding with the transition to fully exogenous feeding. We also examined the effect of the environment on otolith morphology and polymorph composition during early life history in Lake Sturgeon larvae reared in varying temperature (16/22 °C) and pCO2 (1000/2500 µatm) environments for 5 months. Fish raised in elevated temperature had significantly increased otolith size and precipitation of large single calcite crystals. Interestingly, pCO2 had no statistically significant effect on size or polymorph composition of otoliths despite blood pH exhibiting a mild alkalosis, which is contrary to what has been observed in several studies on marine fishes. These results suggest climate change may influence otolith polymorph composition during early life history in Lake Sturgeon.
Highlights
Changes to calcium carbonate (CaCO3) biomineralization in aquatic organisms is among the many predicted effects of climate change
Following techniques developed in Loeppky et al.[15], both left sagittal and lapilli otoliths were dissected (Supplementary Information 1.2) and transported to Oak Ridge National Laboratory (ORNL) in Tennessee, USA for quantification of otolith polymorph composition via X-ray microdiffraction
Developmental stage had a significant effect on both sagittal and lapilli otolith polymorph composition with peak aragonite precipitation in sagittal otoliths occurring at 20 dph in both species (Fig. 1)
Summary
Changes to calcium carbonate (CaCO3) biomineralization in aquatic organisms is among the many predicted effects of climate change. PCO2 had no statistically significant effect on size or polymorph composition of otoliths despite blood pH exhibiting a mild alkalosis, which is contrary to what has been observed in several studies on marine fishes These results suggest climate change may influence otolith polymorph composition during early life history in Lake Sturgeon. Otoliths of age-0 Lake Sturgeon have been shown to be primarily composed of aragonite (> 60%) along with vaterite[15] These results indicate that species in the earliest branch of Actinopterygii have the capacity to precipitate any form of C aCO3 polymorph, a mechanism of otolith biomineralization in fishes that previously was thought to only have evolved after the separation of teleosts from chondrostean (i.e., sturgeons, paddlefish) and holostean (i.e., gars, bowfins) lineages[13,16]. The induced downregulation of starmaker, a gene responsible for regulating crystal growth, resulted in a switch from aragonite to calcite precipitation in zebrafish, Danio rerio[21], suggesting the molecular control over matrix forming proteins, which can change throughout ontogeny, is an important factor in determining otolith polymorph composition[18]
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