Phenotypic plasticity and local adaptations to dissolved oxygen in larvae fire salamander (Salamandra infraimmaculata).

A key environmental factor that varies both spatially and temporally in surface waters is dissolved oxygen (DO). In stagnant ephemeral freshwater ponds, DO can fluctuate diurnally and seasonally, while the constant mixing of water in streams typically maintain DO levels close to saturation with only minor fluctuations. Larvae of the Near Eastern fire salamander (Salamandra infraimmaculata) develop in a range of waterbodies that vary in flow and permanence. To study inter-population variation in larval response to environmental change, we translocated larvae between stream and pond habitats and exposed larvae sampled from different habitat types to hypoxic and normoxic conditions in the laboratory. Larvae transferred from stream to pond retain gill size, while larvae transferred from pond to stream show a reduction in gill size. Larvae that were caged within their native habitat, either stream or pond, display a decrease in gill size similar to larvae transferred from pond to stream. When exposed to experimentally manipulated levels of DO in the laboratory larvae, respectively, increase and decrease gill size under hypoxic and normoxic conditions. Habitat-type origin had a significant effect on the degree of change in gill size with larvae from permanent streams demonstrating the lowest absolute variation in gill size. There was no interaction between DO level (hypoxic/normoxic) and the larvae habitat-type origin. These results suggest that S. infraimmaculata larvae are locally adapted to their aquatic breeding habitat through the plastic ability to respond to the prevailing respiratory conditions by rapidly decreasing or increasing gill size.