No evidence of sickness behavior in immune‐challenged field crickets

Abstract

Sickness behavior is a taxonomically widespread coordinated set of behavioral changes that increases shelter‐seeking while reducing levels of general activity, as well as food (anorexia) and water (adipsia) consumption, when fighting infection by pathogens and disease. The leading hypothesis explaining such sickness‐related shifts in behavior is the energy conservation hypothesis. This hypothesis argues that sick (i.e., immune‐challenged) animals reduce energetic expenditure in order have more energy to fuel an immune response, which in some vertebrates, also includes producing an energetically expensive physiological fever. We experimentally tested the hypothesis that an immune challenge with lipopolysaccharide (LPS) will cause Gryllus firmus field crickets to reduce their activity, increase shelter use and avoid foods that interfere with an immune response (i.e., fat) while preferring a diet that fuels an immune response (i.e., protein). We found little evidence of sickness behavior in Gryllus firmus as immune‐challenged individuals did not reduce their activity or increase their shelter‐seeking. Neither did we observe changes in feeding or drinking behavior nor a preference for protein or avoidance of lipids. Males tended to use shelters less than females but no other behaviors differed between the sexes. The lack of sickness behavior in our study might reflect the fact that invertebrates do not possess energetically expensive physiological fever as part of their immune response. Therefore, there is little reason to conserve energy via reduced activity or increased shelter use when immune‐challenged.

Sickness and the Social Brain: How the Immune System Regulates Behavior across Species

“…While sickness behaviors have historically been studied in the context of vertebrate physiology, more work has been done to identify their presence and importance in invertebrates. As mentioned previously, these behaviors confer advantage for survival, and thus have evolved to be present in many species, including field crickets [Jacot et al, 2004;Kelly and Leroux, 2020], honeybees [Kazlauskas et al, 2016], caterpillars [Adamo et al, 2007], fruit flies Jardine, 2015, 2017;Surendran et al, 2017], Caenorhabditis elegans [Singh and Aballay, 2019], and many others.…”

“…In addition to humans, changes in social motivation in response to sickness have been described in many other animals. Social vocalizations in passerine birds [Garamszegi et al, 2004], field crickets [Jacot et al, 2004;Kelly and Leroux, 2020], and vampire bats [Stockmaier et al, 2020] have all been studied in the context of immune challenge. In all cases, infection causes a decrease in social contacts, which can be interpreted as social withdrawal.…”

The developmental high wire: Balancing resource investment in immunity and reproduction

“…Interestingly, although mating grants females an immune advantage and there is little evidence of sickness behavior in field crickets (Kelly & Mc Cabe Leroux, 2020 ; Sullivan et al, 2016 ), we found that immune‐challenged adults exhibited decreased rates of mating and consequently lower egg viability compared to healthy females. These findings confirm that illness just prior to a mating opportunity can have significant negative impacts on female fitness beyond those predicted by resource constraints alone.…”