Testing male immunocompetence in two hymenopterans with different levels of social organization: ‘live hard, die young?’

Abstract

Males are under different selective pressures than females, which results in differences in the physiology of the two sexes to maximize their fitness. In terms of immunity, males are typically considered as the 'sicker sex', where immunocompetence is reduced to favour increased reproductive output. However, male social Hymenoptera are also haploid and therefore lack allelic variation at the individual level, which can also lead to reduced immunocompetence. Over the last decade, several studies have provided evidence for a higher susceptibility to disease in males of social Hymenoptera, without clarifying whether this susceptibility was a direct consequence of their haploid condition or the result of a 'live hard, die young' overall evolutionary strategy. In the present study, we used an experimental approach of bacterial challenge to test the immune response of males and females in two species of social Hymenoptera (honey bees, Apis mellifera; paper wasps, Polistes dominula), where males show very different life-history traits. Drones benefit from colony protection for most of their life, whereas P. dominula males leave their colonies and have to survive for weeks at leks. If the haploid condition is responsible for a higher susceptibility in males, we should expect a lower immune response in males of both species compared to females. Conversely, if the immunocompetence depends on the life-history traits of males, an opposite trend is expected in males of the two species. Our results do not support the 'haploid susceptibility hypothesis' but are in accordance with the different life history of males from the two species.

Competition between the native and the introduced hornets Vespa crabro and Vespa velutina: a comparison of potentially relevant life‐history traits

“…bacterial clearance), workers belonging to each species were injected with the Gram-negative bacteria Escherichia coli, an immune elicitor commonly used to test antibacterial activity in insects (Yang & Cox-Foster, 2005;Manfredini et al, 2010Manfredini et al, , 2013Gätschenberger et al, 2013;Cappa et al, 2015;Polykretis et al, 2016). bacterial clearance), workers belonging to each species were injected with the Gram-negative bacteria Escherichia coli, an immune elicitor commonly used to test antibacterial activity in insects (Yang & Cox-Foster, 2005;Manfredini et al, 2010Manfredini et al, , 2013Gätschenberger et al, 2013;Cappa et al, 2015;Polykretis et al, 2016).…”

“…To compare the ability of hornet workers of the two species to remove bacterial cells from their haemolymph (i.e. bacterial clearance), workers belonging to each species were injected with the Gram-negative bacteria Escherichia coli, an immune elicitor commonly used to test antibacterial activity in insects (Yang & Cox-Foster, 2005;Manfredini et al, 2010Manfredini et al, , 2013Gätschenberger et al, 2013;Cappa et al, 2015;Polykretis et al, 2016).…”

Subtle effect of Xenos vesparum (Xenidae, Strepsiptera) on the reproductive apparatus of its male host: Parasite or parasitoid?

“…In social Hymenoptera it has also been proposed that males should be more sensitive to diseases because of their haploid condition that reduces the availability of genetic combinations capable to provide resistance against parasites (O'Donnell and Beshers, 2004). However, recent results produced by our research group do not provide support for a fundamental role of ploidy in the determination of male immunocompetence: P. dominula males, who survive for weeks far from the protection of their nest, show a higher immune competence in terms of bacterial clearance with respect to female workers of the same age (Cappa et al, 2015). The different effect of host gender in the PolistesXenos system could be explained with a more parsimonious approach, i.e.…”

“…From the point of view of the immune system, males of social insects seem to represent the weakest part of the colony (see Cappa et al, 2015). It has been hypothesized that because of their haploid condition, males should be more susceptible to parasites and pathogens than diploid females, as they possess a smaller repertoire of genetic combinations that enable them to effectively fight infections (O'Donnell and Beshers, 2004;Baer and Schmid Hempel, 2006;Retschnig et al, 2014).…”

“…It has been hypothesized that because of their haploid condition, males should be more susceptible to parasites and pathogens than diploid females, as they possess a smaller repertoire of genetic combinations that enable them to effectively fight infections (O'Donnell and Beshers, 2004;Baer and Schmid Hempel, 2006;Retschnig et al, 2014). The "haploid susceptibility hypothesis", however, does not apply to every system and several studies suggest that not only genetic condition, but also male life history traits can affect male resistance to parasites and pathogens (Ruiz-Gonzàlez and Brown, 2006;Cappa et al, 2015).…”