Immune function responds to selection for cuticular colour in Tenebrio molitor

Abstract

Cuticular colour in the mealworm beetle (Tenebrio molitor) is a quantitative trait, varying from tan to black. Population level variation in cuticular colour has been linked to pathogen resistance in this species and in several other insects: darker individuals are more resistant to pathogens. Given that cuticular colour has a heritable component, we have taken an experimental evolution approach: we selected 10 lines for black and 10 lines for tan adult cuticular phenotypes over at least six generations and measured the correlated responses to selection in a range of immune effector systems. Our results show that two immune parameters related to resistance (haemocyte density and pre-immune challenge activity of phenoloxidase (PO)) were significantly higher in selection lines of black beetles compared to tan lines. This may help to explain increased resistance to pathogens in darker individuals. Cuticular colour is dependent upon melanin production, which requires the enzyme PO that is present in its inactive form inside haemocytes. Thus, the observed correlated response to selection upon cuticular colour and immune variables probably results from these traits' shared dependence on melanin production. Heredity (2005) 94, 650-656.

Intralocus Sexual Conflict and the Tragedy of the Commons in Seed Beetles

“…The link between SD in color pigmentation and IeSC is also consistent with male harassment of females being pronounced in this species and causing significant reductions in female life span (e.g., Maklakov and Bonduriansky 2009), as well as with the male genitalia, by successive remating, causing potentially severe damage to the female reproductive tract (Hotzy and Arnqvist 2009). Alternatively, the result may be a consequence of competing demands: lighter (more male-like) coloration may be associated with increased allocation to reproduction in females, since increased melanization is known to be positively genetically correlated with allocation to important aspects of immune function and negatively related to fecundity in other insects (e.g., Armitage et al 2003;Armitage and Siva-Jothy 2005;Wittkopp and Beldade 2009).…”

Quantitative genetics of immunity and life history under different photoperiods

“…Enzyme activity was determined by examining the slope of the linear phase of the reaction. As the rate during the linear phase of the reaction is proportional to the amount of enzyme present in the sample, the value given by the Softmax PRO software's autoslope function was used as the unit for the activity of enzyme concentration (Armitage and Siva-Jothy, 2005). Reactions were performed in sterile 96-well culture plates.…”

A standardised protocol for measuring phenoloxidase and prophenoloxidase in the honey bee, Apis mellifera

“…Nevertheless, contradictory evidence exists that increasing PO concentrations are indeed correlated with an increased resistance to pathogens, and the use of PO activity assays as a good measure of the immune response of an individual is not without controversy (Adamo, 2004;Mucklow et al, 2004;Cerenius et al, 2008). Whilst some studies have shown no correlation between PO concentration and pathogen susceptibility (Adamo, 2004;Mucklow et al, 2004;Leclerc et al, 2006;Schwarzenbach and Ward, 2007), others provide compelling evidence to suggest otherwise (Nigam et al, 1997;Braun et al, 1998;Barnes and Siva-Jothy, 2000;Brown et al, 2003;Armitage and Siva-Jothy, 2005;Cerenius et al, 2008;Eleftherianos et al, 2008). Subsequent studies infecting bees with bacterial derivatives found a negative effect of immune challenge on PO and ProPO activity, suggesting that phenoloxidase does play an important role in the immune response in honey bees (Laughton, 2008).…”

“…With the role that immunity plays in honey bee health recently coming under scrutiny due to the phenomenon termed Colony Collapse Disorder (Oldroyd, 2007;Cox-Foster et al, 2007), developing an accurate, reliable and cost-effective assay of immune function in honey bees is vital. Quantification of PO/ProPO activity offers the potential for assaying 'health', as increased activity correlates with higher levels of pathogen resistance in several study systems (Tenebrio molitor (Barnes and SivaJothy, 2000;Armitage and Siva-Jothy, 2005), Drosophila (Braun et al, 1998), Glossina sp. (Nigam et al, 1997) and Manduca sexta (Eleftherianos et al, 2006)).…”