Inbreeding and extreme outbreeding cause sex differences in immune defence and life history traits in Epirrita autumnata

Abstract

Empirical studies in vertebrates support the hypothesis that inbreeding reduces resistance against parasites and pathogens. However, studies in insects have not found any evidence that inbreeding compromises immune defence. Here we tested whether one generation of brother-sister mating or extreme outbreeding (mating between two populations) have an effect on innate immunity and life history traits in the autumnal moth, Epirrita autumnata. We show that the effect of inbreeding on immune response differed between the sexes: whereas in females, inbreeding significantly reduced encapsulation response against nylon monofilament ability, it did not have a significant effect on male immune response. There were also differences in the correlation of the immune response with other traits: in females increased immune response was positively correlated with large size, whereas in males immune response increased with a reduction in development time. Immune response differed significantly among families in males but not in females, both for the inbreeding and extreme outbreeding experiments. In conjunction with the observed immune responses to inbreeding, these data suggest that in males genetic variation for immune response is largely additive or non-directional with respect to dominance, whereas in females variation is much reduced and consists of directional dominance variance. Further, we show that encapsulation response against nylon monofilament is associated with the resistance against real pathogens suggesting that this widely used method to measure the strength of immune defence in insects is also a biologically relevant method.

Genetic and phenotypic relationships between immune defense, melanism and life-history traits at different temperatures and sexes in Tenebrio molitor

“…Studies in insects testing sexual dimorphism in immune defense have resulted in mixed findings (for example, CordobaAguilar et al, 2006, Rantala andRoff, 2007). It has been found that there is sex difference in response to genetic (Rantala and Roff, 2007) and nutritional stress (McKean and Nunney, 2005;Ruuhola et al, 2007) that may cause between population and species variation in sex difference in immunity. In the present case, encapsulation ability was highest in females and the gender difference showed a modest or no change with temperature.…”

“…A standard method for initiating and measuring immune responses in insects is by inserting a small artificial object into the body of the insect, and then quantifying the degree of melanization on the object after a set time (Rantala et al, 2000). The ability of insects to encapsulate artificial objects is correlated with their ability to encapsulate parasites (Smilanich et al, 2009) and resist fungal pathogens (Rantala and Roff, 2007). Hence, it provides an index of the strength of an individual's ability to resist living parasites.…”

Predation selects for increased immune function in male damselflies,Calopteryx splendens

“…Damselflies defend themselves against infection by ectoparasitic water mites by encapsulating the feeding tubes of the mites [24,25]. The ability of insects to encapsulate abiotic material has shown to be related to their ability to encapsulate parasites [26,27] and to resist fungal pathogens [28], which suggests that the use of this method to measure an individual's immune function is biologically valid.…”

Variation in Resistance to the Invasive Crayfish Plague and Immune Defence in the Native Noble Crayfish

“…Yang et al 2007, van Ooik & Rantala 2010, Smilanich et al 2011, Wilson-Rich et al 2012. In addition to accurately quantifying immune capacity in arthropods, this method especially reveals the resistance of an individual against fungi (Gorman et al 1996, Rantala & Roff 2007, but see Rantala et al 2011). We inserted a nylon monofilament implant (6 mm long, 0.30 mm in diameter) in the crayfish to determine the strength of the encapsulation response according to Rantala and Kortet (2004).…”