Defining comparative physiology: results from an online survey and systematic review.

August Krogh's 1929 principle is referenced as the cornerstone of comparative physiology (CP). However, there are diverse views as to what type of research falls under the CP approach. This study had three aims: 1) determine how CP is defined through an online survey (OS) of physiologists and a systematic review (SR), 2) put forth an updated definition of CP by summarizing OS and SR results, and 3) outline the numerous CP research approaches. Professional physiology societies (n = 54) were invited to share the OS with their members, and a SR was conducted, which yielded 197 and 70 definitions, respectively. The three most common words in descending order in the OS definitions were "different," "animals," and "species" and in the SR definitions, "animals," "species," and "organisms." The three most prevalent themes from the OS and SR definitions were comparing/differences/diversity across species (78% and 51%, respectively), response to the environment/ecology (28% and 43%, respectively), and included evolution or adaptation (24% and 60%, respectively). Ten research approaches were identified, which include broad comparison (i.e., many species generalization), specific comparison (e.g., 2 species; for traits that are different, exaggerated, extreme, missing, or not induced), or comparison while considering evolution (i.e., evolutionary physiology), ecology (i.e., ecophysiology), or human physiology/medicine. Only 5% and 33% of OS and SR definitions described or mentioned Krogh's principle. In conclusion, CP can best be defined as a compilation of research approaches that utilize different types of comparisons to elucidate physiological mechanisms and not simply comparing physiologies as the name implies.

Mite not make it home: tracheal mites reduce the safety margin for oxygen delivery of flying honeybees.

Many physiological systems appear to have safety margins, with excess capacity relative to normal functional needs, but the significance of such excess capacity remains controversial. In this study, we investigate the effects of parasitic tracheal mites (Acarapis woodi) on the safety margin for oxygen delivery and flight performance of honeybees. Tracheal mites did not affect the flight metabolic rate of honeybees in normoxic (21% oxygen) or hyperoxic (40% oxygen) air, but did reduce their metabolic rate relative to uninfected bees when flying in hypoxic air (5 or 10% oxygen), demonstrating that mites reduced the safety margin for tracheal oxygen delivery. The negative effects of mites on flight metabolic rate in hypoxic atmospheres were graded with the number of mites per trachea. For example, in 10% oxygen atmospheres, flight metabolic rate was reduced by 20% by moderate mite infection and by 40% by severe mite infection. Thus, the safety margin for oxygen delivery in honeybees allows them to retain normal flight metabolic rate and behavior despite tracheal mite infection under most conditions. However, the reduction in tracheal gas-exchange capacity may constrain activities requiring the highest metabolic rates, such as flying in cool weather. In support of this hypothesis, bees that were unable to return to the hive during late-winter flights showed significantly higher levels of mite infection than bees that returned safely.