Upper thermal tolerance and oxygen limitation in terrestrial arthropods

Abstract

declined with declining oxygen concentration, this was not the case in the beetle. Efficient oxygen delivery via a tracheal system makes oxygen limitation of thermal tolerance, at a whole organism level, unlikely in insects. By contrast, oxygen limitation of thermal tolerances is expected to apply to species, like the isopod, in which the circulatory system contributes significantly to oxygen delivery. Because insects dominate terrestrial systems, oxygen limitation of thermal tolerance cannot be considered pervasive in this habitat, although it is a characteristic of marine species.

Differences in critical thermal maxima and mortality across life stages of the mealworm beetle Tenebrio molitor

“…The dramatic reduction in V CO2 variance that occurs during the mortal fall phase signifies the loss of spiracular control, and therefore CT max . This seven-phase pattern has been described in a variety of insects, including harvester ants (Lighton and Turner, 2004), drosophilid flies (Folk et al, 2007;Lighton, 2007) and tenebrionid beetles (Klok et al, 2004;Stevens et al, 2010). Only isopods have shown a different pattern of CO 2 release, which may result from differences in respiratory morphology between isopods and insects (Klok et al, 2004;Stevens et al, 2010).…”

“…The technique employs flow-through respirometry to measure CO 2 output from the animal during increasing temperature, typically with simultaneous infrared activity detection to monitor locomotor activity (Lighton and Turner, 2004;Klok et al, 2004;Folk et al, 2007;Lighton, 2007;Stevens et al, 2010). Prior studies have shown that these two independent measures of thermal limitation, spiracular and motor failure, occur simultaneously in adult insects tested under normoxic conditions, and thus represent statistically equivalent estimates of CT max (Lighton and Turner, 2004;Klok et al, 2004;Folk et al, 2007;Stevens et al, 2010).…”

The effects of temperature on aerobic metabolism: towards a mechanistic understanding of the responses of ectotherms to a changing environment

“…This linkage has been convincingly demonstrated for a number of fish and marine invertebrate species (Pörtner, 2001(Pörtner, , 2010Eliason et al, 2011). However, there is limited support for aerobic scope limiting maximum thermal tolerance in air-breathing ectotherms (Fobian et al, 2014) and particularly in taxa such as insects (Klok et al, 2004;Stevens et al, 2010). In addition, recent work in a variety of species of fishes has indicated that, at least in some species, aerobic scope can still be high at temperatures at which growth and reproduction are compromised, suggesting that thermal limitations on aerobic capacity cannot be the direct cause of fitness limitations in these species (Healy and Schulte, 2012;Clark et al, 2013a;Gräns et al, 2014;Norin et al, 2014).…”

Oxygen safety margins set thermal limits in an insect model system

“…Differences in breathing apparatus (gills versus occludible tracheae), and in the complexity of gas exchange systems (e.g. two-stage gas exchange, discussed in Klok et al, 2004), the respiratory milieu (e.g. Giomi et al, 2014;reviewed in Hsia et al, 2013) and the degree to which an animal is capable of regulating its gas exchange at rest, especially in the face of changing oxygen availability, may explain the difference between marine invertebrates that show support for OCLTT and air-breathing invertebrates that generally do not (Verberk and Bilton, 2013).…”

“…While hypoxia often decreases CT max (e.g. Klok et al, 2004, reviewed in W. C. E. P. Verberk, J. Overgaard, R. Ern, M. Bayley, T. Wang, L.B. and J.S.T., submitted), hyperoxia has only been documented to increase heat tolerance in aquatic, gill-breathing stonefly Dinocras cephalotes nymphs (Verberk and Bilton, 2011).…”