Altitudinal variation in behavioural thermoregulation: local adaptation vs. plasticity in California grasshoppers

Abstract

We investigated the adaptive significance of behavioural thermoregulation in univoltine populations of the grasshopper Melanoplus sanguinipes along an altitudinal gradient in California using laboratory tests of animals raised under different temperatures. Trials consisted of continuous body temperature measurements with semi‐implanted microprobes in a test arena, and observation and simultaneous recording of behavioural responses. These responses included mobility, basking and orientation of the body axes (aspect angle) towards a radiation source. Mobility and basking are determined by the altitudinal origin of the parental generation and not by the temperature treatments. With increasing altitude, individuals tend increasingly to raise body temperatures via mobility and increased basking. In contrast, body orientation towards the radiation source is influenced by the temperature treatments but not by the altitude of origin. Individuals experiencing higher temperatures during rearing show a lower tendency to lateral flanking. We conclude that body orientation responses are not adapted locally. In contrast other components of the behavioural syndrome that increase body temperature, such as mobility and basking, are adaptive in response to local selection pressure. The thermoregulatory syndrome of these grasshoppers is an important contribution to life‐history adaptations that appropriately match season lengths.

Body temperature and basking behaviour of Nile crocodiles (Crocodylus niloticus) during winter

“…Generally, animals regulate T b to a set point ideal or optimum temperature (Cabanac, 2006). It has been suggested that preferred T b 's have co-evolved with performance optima, particularly those performances that are temperature sensitive (Samietz et al, 2005;Glanville and Seebacher, 2006). In crocodiles many of their behaviours are in water when T b is usually lower than when they are out of the water (Grigg et al, 1998).…”

Compensation for environmental change by complementary shifts of thermal sensitivity and thermoregulatory behaviour in an ectotherm

“…The behavioural mechanisms of thermoregulation are similar among terrestrial ectotherms (Muth, 1977;Seebacher, 1999;Samietz et al, 2005), although actual body temperature is determined by the thermal sensitivities of the biochemical components, particularly enzyme activities, of the organisms (Somero, 1995). The regulated or preferred body temperature of terrestrial ectotherms is thought to have co-evolved with performance optima in response to the dominant thermal signal in the environment (Huey and Bennett, 1987;Samietz et al, 2005). The current view is that temperature-performance curves are non-reversibly centred around the mean (preferred) body temperature of individuals (Angilletta et al, 2002).…”

“…Body temperature set-points are controlled by temperature-sensitive neurons that link the animal core and periphery via the hypothalamus (Hammel, 1965;Boulant, 2006;Wechselberger et al, 2006), and thermoregulation may be influenced by endocrine factors that act on a daily or seasonal basis (Lutterschmidt et al, 2003). The behavioural mechanisms of thermoregulation are similar among terrestrial ectotherms (Muth, 1977;Seebacher, 1999;Samietz et al, 2005), although actual body temperature is determined by the thermal sensitivities of the biochemical components, particularly enzyme activities, of the organisms (Somero, 1995). The regulated or preferred body temperature of terrestrial ectotherms is thought to have co-evolved with performance optima in response to the dominant thermal signal in the environment (Huey and Bennett, 1987;Samietz et al, 2005).…”

The effectiveness of common thermo-regulatory behaviours in a cool temperate grasshopper

“…As has been found in other studies (Samietz et al, 2005), grasshoppers from higher altitudes actively increased their body temperatures more by sun seeking and basking.…”

“…Gillis and Smeigh, 1987;Willott, 1997) relating them to the operative temperature of non-thermoregulating models (Hertz et al, 1993). Field studies on grasshoppers have demonstrated that the proportion of individuals exhibiting behaviours such as basking, stilting or crouching is related to surface temperatures (Chappell, 1983;Gilman et al, 2008;O'Neill and Rolston, 2007;Samietz et al, 2005), but few studies have attempted to measure the change in body temperature accompanying particular behaviours. Basking has been shown to lead to increases in body temperature under exposure to solar radiation, but the effects of passive warming and active thermoregulation are not always distinguished (Carruthers et al, 1992).…”