Social insects employ a range of behaviours to protect their colonies against disease, but little is known about how such collective behaviours are orchestrated. This is especially true for the social Blattodea (termites). We developed an experimental approach that allowed us to explore how the social response to disease is co-ordinated by multistep host-pathogen interactions. We infected the eastern subterranean termite Reticulitermes flavipes with the entomopathogenic fungus Metarhizium anisopliae, and then, at different stages of infection, reintroduced them to healthy nestmates and recorded behavioural responses. As expected, termites groomed pathogen-exposed individuals significantly more than controls; however, grooming was significantly elevated after fungal germination than before, demonstrating the importance of fungal status to hygienic behaviour. Significantly, we found that cannibalism became prevalent only after exposed termites became visibly ill, highlighting the importance of host condition as a cue for social hygienic behaviour. Our study reveals the presence of a coordinated social response to disease that depends on stage of infection. Specifically, we show how the host may play a key role in triggering its own sacrifice. Sacrificial self-flagging has been observed in other social insects: our results demonstrate that termites have independently evolved to both recognize and destructively respond to sickness.

Honeybee disappearance is one of the major environmental and economic challenges this century has to face. The ecto-parasitic mite Varroa destructor represents one of the main causes of the worldwide beehive losses. Although halting mite transmission among beehives is of primary importance to save honeybee colonies from further decline, the natural route used by mites to abandon a collapsing colony has not been extensively investigated so far. Here, we explored whether, with increasing mite abundance within the colony, mites change their behaviour to maximize the chances of leaving a highly infested colony. We show that, at low mite abundance, mites remain within the colony and promote their reproduction by riding nurses that they distinguish from foragers by different chemical cuticular signatures. When mite abundance increases, the chemical profile of nurses and foragers tends to overlap, promoting mite departure from exploited colonies by riding pollen foragers.

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This is an author version of the contribution published on:Questa è la versione dell'autore dell'opera: Journal of Experimental Marine Biology and Ecology, 453, 2014, doi:10.1016/j.jembe.2014 The definitive version is available at: La versione definitiva è disponibile alla URL: ABSTRACTMating opportunities fluctuate in the wild and hermaphrodites have the chance of partitioning reproductive resources between their two sexual functions accordingly, i.e., they have a plastic sex allocation. Plasticity is usually promoted by environmental fluctuations butmay be affected by species-specific factors, which may be revealed by comparisons between related species.We testedwhether polychaeteworms of three related species of simultaneous hermaphrodites, Ophryotrocha diadema, Ophryotrocha adherens and Ophryotrocha gracilis, had plastic male and female allocation. We measured the costs of the female function and investigated whether the costs might affect the magnitude of plasticity in this function. To these aims, we exposed adult worms to three levels of mating opportunities and measured their female and male functions. In our experimental conditions, there was no adjustment in the male function, the cheapest function, whereas the three species differed in how they adjusted their allocation into the female function to mating opportunities. O. diadema and O. adherens worms exhibited highly plastic female allocation, and plasticitywas consistent across three measures of female function. In contrast, O. gracilis worms had a fixed female allocation, irrespective of mating opportunities. Additionally, when the sexual functions were relatively costly, their plasticity was greater than when they were relatively cheap. However, the magnitude of the plasticity did not depend solely on species-specific costs of the function, but also on the features of the mating system of each species.

Sex allocation theory predicts that simultaneous hermaphrodites evolve to an evolutionary stable resource allocation, whereby any increase in investment to male reproduction leads to a disproportionate cost on female reproduction and vice versa. However, empirical evidence for sexual trade-offs in hermaphroditic animals is still limited. Here, we tested how male and female reproductive traits evolved under conditions of reduced selection on either male or female reproduction for 40 generations in a hermaphroditic snail. This selection favors a reinvestment of resources from the sex function under relaxed selection toward the other function. We found no such evolutionary response. Instead, juvenile survival and male reproductive success significantly decreased in lines where selection on the male function (i.e., sexual selection) was relaxed, while relaxing selection on the female function had no effect. Our results suggest that most polymorphisms under selection in these lines were not sex-antagonistic. Rather, they were deleterious mutations affecting juvenile survival (thus reducing both male and female fitness) with strong pleiotropic effects on male success in a sexual selection context. These mutations accumulated when sexual selection was relaxed, which supports the idea that sexual selection in hermaphrodites contributes to purge the mutation load from the genome as in separate-sex organisms.

Assortative mating by size has been argued to be widespread in the animal kingdom. However, the strength of size-assortative mating is known to vary considerably between species and the underlying mechanisms promoting this inter-specific variation remain largely unexplored. Sizeassortative mating has been proposed to be particularly strong in simultaneous hermaphrodites, i.e. organisms that produce male and female gametes at the same time. Here, we build on this hypothesis by arguing that size-assortative mating mediated by sexual selection is generally stronger in reciprocally mating hermaphrodites compared with unilaterally mating species and separate-sexed organisms. We report a series of empirical tests suggesting that size-assortative mating in the unilaterally copulating freshwater snail Physa acuta is caused by spatial clustering of similar-sized individuals and not by mate choice. In addition, we present a meta-analysis testing, for the first time, the hypothesis that sexual selection-mediated size-assortative mating is stronger in reciprocally copulating simultaneous hermaphrodites. Overall, we found significant size-assortative mating across 18 tested species and substantial inter-specific variation. Importantly, part of this variation can be explained by mating type, providing support for the hypothesis that size-assortative mating is stronger in reciprocally mating hermaphrodites compared with unilaterally mating species. We highlight potential pitfalls when testing for sexual selection-mediated size-assortative mating and discuss the need for more experimental and comparative approaches in order to resolve the observed variation in the strength of size-assortative mating among species.

Social recognition has rarely received attention in the studies on annelids. This is not surprising since the biology of behavioral interactions in annelids is mostly unexplored. Only few pheromones have been identified, which function as cues in mate recognition and gamete release. Many annelids use chemical and visual cues to locate partners and classify them according to mating status, body size, or oocyte ripeness. In some hermaphroditic polychaete worms and leeches the ability to recognize the quality of potential partners seem to be very refined, especially in relation to the ability to assess the number of competitors over mating. These examples suggest that sexual selection might have favored individual ability to assess conspecific numerosity accurately and vary their male and female resource allocation (sex allocation) accordingly. Finally, annelids can estimate whether they are related to their potential partners and whether they belong to the same or a different population, which again result in adjustments of their reproductive allocation. We suggest that sexual selection is likely to be responsible for the evolution of the ability to assess mate quality and social group size because sex allocation adjustments are favored by sexual selection.

2This is an author version of the contribution published Abstract 35Labile sex expression is considered to play a key role in the evolution of breeding systems and in the 36 transition from hermaphroditism to dioecy, according to the evolutionary models proposed for plants. While in 37 hermaphrodites sex allocation within the individual can be plastically adjusted in response to social environment, 38 in dioecious species it is predicted to be fixed. However, labile sex expression in the form of gender plasticity 39can still be present in dioecious species of animals with environmental sex determination. It is still unclear how 40 gender plasticity is involved in the evolution of breeding systems and what its role is in the transition from 41 hermaphroditism to dioecy. We assessed the degree of plasticity in gender expression in three dioecious species 42 of polychaete worms of the genus Ophryotrocha. We found sexual polymorphism and plasticity in sex 43 expression during the juvenile phase to be a response to social environment. The majority of juveniles reared 44 with an adult female or male expressed the gender opposite of that of the partner, so as to form heterosexual 45 pairs. On the basis of these findings we outline a possible evolutionary pathway of the transition from 46 hermaphroditism to dioecy in the genus Ophryotrocha. 47 48 49