Escaping to the Surface: A Phylogenetically Independent Analysis of Hypoxia‐Induced Respiratory Behaviors in Sculpins

Behavioral responses to progressive hypoxia exposure were assessed in several species of fish from the family Cottidae (sculpins), which are distributed along the near‐shore marine environment and differ in their hypoxia tolerance. The use of aquatic surface respiration (ASR) and aerial emergence as a response to progressive decreases in environmental O2differed between intertidal and subtidal sculpins. Intertidal sculpins consistently displayed ASR followed by emergence behaviors, while the subtidal species performed these behaviors at low frequency or not at all. There was a significant negative correlation between the O2thresholds for the onset of ASR and critical O2tensions (Pcrit, a measure of hypoxia tolerance), such that the hypoxia‐tolerant species performed ASR at higher O2tensions than the more hypoxia‐sensitive species. There was no relationship between the O2thresholds for emergence and Pcrit. When restricted from accessing the water surface during progressive decreases in O2, all species of sculpin displayed the same sequence of behaviors including agitation, attempts to escape, quiescence, and unresponsiveness. The only behavior from this suite that correlated with Pcritwas the first sign of agitation, which occurred at a lower O2tension in the most hypoxia‐tolerant species. With the application of phylogenetically independent contrasts, all the relationships between behavior and Pcritwere nonsignificant, which limits our capacity to separate selection‐driven changes in behavior from the phylogenetic signal.