Thermoregulatory strategy may shape immune investment inDrosophila melanogaster

Abstract

As temperatures change, insects alter the amount of melanin in their cuticle to improve thermoregulation. However, melanin is also central to insect immunity, suggesting that thermoregulatory strategy may indirectly impact immune defense by altering the abundance of melanin pathway components (a hypothesis we refer to as thermoregulatory-dependent immune investment). This may be the case in the cricket Allonemobius socius, where warm environments (both seasonal and geographical) produced crickets with lighter cuticles and increased pathogen susceptibility. Unfortunately, the potential for thermoregulatory strategy to influence insect immunity has not been widely explored. Here we address the relationships between temperature, thermoregulatory strategy and immunity in the fruit fly Drosophila melanogaster. To this end, flies from two separate Canadian populations were reared in either a summer-or autumnlike environment. Shortly after adult eclosion, flies were moved to a common environment where their cuticle color and susceptibility to a bacterial pathogen (Pseudomonas aeruginosa) were measured. As with A. socius, individuals from summer-like environments exhibited lighter cuticles and increased pathogen susceptibility, suggesting that the thermoregulatory-immunity relationship is evolutionarily conserved across the hemimetabolous and holometabolous clades. If global temperatures continue to rise as expected, then thermoregulation might play an important role in host infection and mortality rates in systems that provide critical ecosystem services (e.g. pollination), or influence the prevalence of insect-vectored disease (e.g. malaria).

Temperature and population density: interactional effects of environmental factors on phenotypic plasticity, immune defenses, and disease resistance in an insect pest

“…2013; Kutch et al. 2014). Moreover, environmental cooling or warming may affect the likelihood of transmission or impact of disease at both organism and population levels.…”

“…While changes in the thermal environment may trigger direct physiological and behavioral responses at the organism level, it may also indirectly trigger such responses through alternative pathways. In insects, for example, a greater resistance to a pathogenic challenge can be reached via changes in cuticular melanization, which enhances the immune investment pleiotropically (Fedorka et al 2013;Kutch et al 2014). Moreover, environmental cooling or warming may affect the likelihood of transmission or impact of disease at both organism and population levels.…”

Temperature Dramatically Shapes Mosquito Gene Expression with Consequences for Mosquito-Zika Virus Interactions

“…Studies in both butterflies and Anopheles stephensi demonstrated that phenoloxidase activity was higher at cool temperatures and becomes less efficient at warmer temperatures (Suwanchaichinda and Paskewitz, 1998; Murdock et al, 2012b). The production of melanin is also essential for other physiological processes such as cold acclimization in insects (Crill et al, 1996; Kutch et al, 2014) the formation of the hard protective layer around eggs, and wound healing (Lai et al, 2009). Our data also reveal that c-type lectin, reported to participate in activation of the melanization cascade (Yu and Kanost, 2000; Christensen et al, 2005) was also up-regulated.…”

Effect of long-term cold storage on trehalose metabolism of pre-wintering Harmonia axyridis adults and changes in morphological diversity before and after wintering

“…Melanic forms of H. axyridis are thought to have a fitness advantage at low temperatures because their dark colour may enable them to absorb heat and increase body temperature more rapidly than non-melanic forms [5,51,54]. Besides, previous studies have shown that a darker cuticle can reduce rates of water loss [55][56][57], and increase immune function [58][59].…”