Relatedness facilitates cooperation in the subsocial spider, Stegodyphus tentoriicola

<p>Abstract</p> <p>Background</p> <p>Cooperative hunting and foraging in spiders is rare and prone to cheating such that the actions of selfish individuals negatively affect the whole group. The resulting social dilemma may be mitigated by kin selection since related individuals lose indirect fitness benefits by acting selfishly. Indeed, cooperation with genetic kin reduces the disadvantages of within-group competition in the subsocial spider <it>Stegodyphus lineatus</it>, supporting the hypothesis that high relatedness is an important pre-adaptation in the transition to sociality in spiders. In this study we examined the consequences of group size and relatedness on cooperative feeding in the subsocial spider <it>S. tentoriicola</it>, a species suggested to be at the transition to permanent sociality.</p> <p>Results</p> <p>We formed groups of 3 and 6 spiders that were either siblings or non-siblings. We found that increasing group size negatively affected feeding efficiency but that these negative effects were reduced in sib-groups. Sib groups were more likely to feed cooperatively and all group members grew more homogenously than groups of unrelated spiders. The measured differences did not translate into differential growth or mortality during the experimental period of 8 weeks.</p> <p>Conclusion</p> <p>The combination of our results with those from previous studies indicates that the conflict between individual interests and group interests may be reduced by nepotism and that the latter promote the maintenance of the social community.</p

Ecosia – Who Cares About a Green Search Engine?

The environmental impact of IT is facing increasing public attention. The search engine Ecosia takes advantage of thissituation by pursuing a Social Business model. Search engines need electricity to provide their services and indirectlyproduce CO2. The estimation of greenhouse gas emissions for the average search query using the market leader Googlefluctuate between 0.2 g and 10.0 g of CO2. The search engine Ecosia tries to compensate the emissions by donating most ofits revenues to the World Wildlife Fund (WWF) and save rainforest from deforestation. Rainforests process CO2 throughphotosynthesis and store it as carbon. The question arises if Social Business models in general possess potential for success inthe search engine market. To investigate this question we apply case study research. Additionally, we use a survey to evaluatewhat is important to users and which aspects of search engines influence the customer’s attitude towards social business

Evolution and maintenance of sociality in crab spiders (Thomisidae)

Thesis by publication."Thesis presented for the Doctor of Philosophy/Doctor rerum naturalium to be jointly awarded by Macquarie University and University of Hamburg."Includes bibliographical references.1. General introduction -- 2. Re-description of Xysticus bimaculatus Koch, 1867 (Araneae, Thomisidae) and characterization of its subsocial lifestyle -- 3. Multiple origins of subsociality in crab spiders (Thomisidae) -- 4. Mating behaviour and natural mating rates in a subsocial spider -- 5. Offspring dynamics affect food provisioning, growth and mortality in a brood-caring spider -- 6. Families hunt more successfully: effect of group composition on hunting and communal feeding -- 7. Hunted hunters? Effect of group size on predation risk and growth in the Australian subscocial crab spider Diaea ergandros -- 8. General discussion -- Appendix 1. Cuticular antifungals in spiders: density- and condition dependence.In this thesis I investigated factors that may explain the evolution and maintenance of sociality in crab spiders (Thomisidae). Group-living crab spiders differ from most other social spiders because they lack a capture web, a factor considered to be very important for the evolution of sociality in spiders. Colonies of subsocial and social spiders are usually comprised of family members, and thus another unusual trait of subsocial crab spiders is the regular acceptance of unrelated conspecifics into their groups. Previous work on the subsocial crab spider Diaea ergandros has demonstrated that maternal care as well as the construction and occupation of nests as protective retreats are important factors that may explain group-living in this species. Furthermore, it has been shown that these spiders are able to recognize kin, which offers an excellent opportunity to study group dynamics between relatives and immigrants. Building up on this knowledge, I examined potential costs and benefits of group living with a focus on the effect of unrelated spiderlings. Moreover, I estimated the genetic relatedness within family groups, and studied the broader natural history as well as phylogenetic relationships of subsocial and social crab spiders.With a detailed natural history description of the crab spider Xysticus bimaculatus I have demonstrated that lifestyle and demographics are very similar to the subsocial Diaea ergandros (chapter 2). This new discovery of subsocial behaviour outside the genus Diaea indicated that subsociality may have evolved multiple times independently within Thomisidae. Testing this hypothesis, I investigated the evolutionary history of social behaviour in crab spiders in a molecular-phylogenetic context. The results suggest that subsociality has at least two independent origins confirming that X. bimaculatus is not closely related to any of the other group-living thomisid species (chapter 3).The evolution of sociality in spiders is accompanied by a switch from outbreeding to inbreeding. D. ergandros has been suggested to be at a particularly advanced transitory stage from subsocial to social behaviour, and a previous study has shown that populations are inbred. Considering that low mating rates and inbreeding favour offspring cooperation of highly related individuals, females may benefit from monogamous or even incestuous mating. I studied the mating behaviour of D. ergandros and investigated natural mating rates with microsatellite markers (chapter 4). However, mating trials did not provide evidence for female choice. Accordingly, the genetic analyses did not support the existence of a monogamous mating system but rather supported relatively low mating rates, which may still sufficiently secure offspring cooperation while simultaneously providing some degree of outbreeding.Genetic relatedness has been identified as an important factor promoting cooperation in many subsocial spiders and other organisms studied to date. With two laboratory experiments (chapter 5 & 6) I confirmed that siblings of Diaea ergandros had an advantage over mixed groups that included immigrants. The latter were generally accepted but negatively affected female-offspring and offspring-offspring foraging interactions. Nevertheless, accepting immigrants may have benefits as well. In another experiment, larger groups of D. ergandros outperformed small groups in that they built larger protective retreats and had a lower mortality as well as higher individual growth (chapter 7). Group size varies considerably under natural conditions and small groups may thus benefit from accepting immigrants.Mode of access: World wide web1 online resource (130 pages) illustration

Supplementary material 1 from: Ruch J, Riehl T, Michalik P (2014) Re-description of Xysticus bimaculatus L. Koch, 1867 (Araneae, Thomisidae) and characterization of its subsocial lifestyle. ZooKeys 427: 1-19. https://doi.org/10.3897/zookeys.427.7450

List of species examined: Explanation note: The table shows a list of all species examined as well as the location of the material. Sex (male, female or juvenile) and whether the material was type material (yes/no) is shown as well

Re-description of Xysticus bimaculatus L. Koch, 1867 (Araneae, Thomisidae) and characterization of its subsocial lifestyle

Spiders have become an important model to study the evolution of sociality, but a lack of their detailed natural history and taxonomy hinders broader comparative studies. Group-living crab spiders (Thomisidae) provide an excellent contrast to other social spiders since they lack a communal capture web, which was thought to be a critical factor in the evolution of sociality. Only three non-webbuilding crab-spider species are known to be subsocial or social, all of which belong to the genus Diaea Thorell, 1869. The aim of this study is to describe the social lifestyle of Xysticus bimaculatus L. Koch, 1867 for the first time. Furthermore, we present a detailed re-description of this species and discuss its taxonomic implications. Like other subsocial crab spiders, X. bimaculatus builds nests from tree leaves. Nests contain up to 38 spiders and sometimes several adult females, indicating the species may be at a transitory stage between subsociality and permanent sociality

Social network structure in group-feeding spiders

In group-living animals, an individual’s fitness is predicted by non-random interactions with other group members and social network analysis has become a powerful tool to study these interactions. We experimentally studied the social network structure in group-foraging subsocial spiders that naturally live in kin groups but accept immigrants. Spiderlings were individually marked and we observed interactions during six foraging trials in groups comprising (i) siblings, (ii) siblings with two non-siblings, and (iii) assorted spiderlings. In this foraging context, we found a higher social network structure in sibling groups compared with assorted groups or sibling groups containing two non-siblings. We asked whether non-siblings in the treatment containing mostly siblings and two immigrants are excluded or less connected, which would explain the overall reduced social network structure of the whole group. We found that non-siblings were not generally excluded but that their presence negatively affected the network structure of the whole group. The connectivity of foreign individuals in this treatment was moreover predicted by their size relative to the other group members with very small and very large spiderlings being well connected. Our findings support the idea that siblings have an advantage over unrelated individuals and that the social network structure may play a role in the evolution of social behaviour in spiders.8 page(s

Offspring dynamics affect food provisioning, growth and mortality in a brood-caring spider

In brood-caring species, family members are faced with a conflict over resource distribution. While parents are selected to adapt the amount of care according to their offspring's needs, offspring might be selected to demand more care than optimal for parents. Recent studies on birds have shown that the social network structure of offspring affects the amount of care and thus the fitness of families. Such a network structure of repeated interactions is probably influenced by within-brood relatedness.We experimentally manipulated the group composition in a brood-caring spider to test howthe presence of unrelated spiderlings affects the dynamics between female and brood as well as within broods. Broods consisting of siblings grew better and had a lower mortality compared with mixed broods, no matter whether the caring female was a genetic or foster mother. Interestingly, we found that foster mothers lost weight when caring for sibling broods, whereas females caring for mixed broods gained weight. This indicates that females may be willing to share more prey when the brood contains exclusively siblings even if the entire brood is unrelated to the female. Resource distribution may thus be negotiated by offspring dynamics that could have a signalling function to females.7 page(s

Families hunt more successfully : effect of group composition on hunting and communal feeding

Group activities that require an initial investment are liable to be exploited. This situation can, for example, be found in group-hunting lions, but also in subsocial and social spiders, in which several individuals capture single large prey items. Individuals could save investment by contributing less to the hunt but also during feeding by saving their external digestive enzymes. Such dynamics have been partly explored in subsocial and social web-building spiders, but are likely to differ when groups hunt in the absence of a web. Subsocial crab spiders hunt without webs and forage communally. Their nests usually comprise related individuals, although groups accept immigrating spiderlings from foreign nests, which may affect competition among group members. We aimed to test whether hunting and communal feeding differ depending on spiderling group composition and formed experimental treatments consisting of either (1) family members, (2) family members including two foreigners or (3) assorted spiderlings. Group hunting was more frequently found among family members and was positively correlated with spiderling mass increase. Family groups fed in consistently larger numbers and grew better compared with the assorted groups, but also compared with family groups including only two foreigners. The latter finding suggests that even a few immigrants may negatively affect communal activities.8 page(s

Cuticular antifungals in spiders: density- and condition dependence.

Animals living in groups face a high risk of disease contagion. In many arthropod species, cuticular antimicrobials constitute the first protective barrier that prevents infections. Here we report that group-living spiders produce cuticular chemicals which inhibit fungal growth. Given that cuticular antifungals may be costly to produce, we explored whether they can be modulated according to the risk of contagion (i.e. under high densities). For this purpose, we quantified cuticular antifungal activity in the subsocial crab spider Diaea ergandros in both natural nests and experimentally manipulated nests of varying density. We quantified the body-condition of spiders to test whether antifungal activity is condition dependent, as well as the effect of spider density on body-condition. We predicted cuticular antifungal activity to increase and body-condition to decrease with high spider densities, and that antifungal activity would be inversely related to body-condition. Contrary to our predictions, antifungal activity was neither density- nor condition-dependent. However, body-condition decreased with density in natural nests, but increased in experimental nests. We suggest that pathogen pressure is so important in nature that it maintains high levels of cuticular antifungal activity in spiders, impacting negatively on individual energetic condition. Future studies should identify the chemical structure of the isolated antifungal compounds in order to understand the physiological basis of a trade-off between disease prevention and energetic condition caused by group living, and its consequences in the evolution of sociality in spiders

Hunted hunters? Effect of group size on predation risk and growth in the Australian subsocial crab spider Diaea ergandros

A reduced predation risk is considered to be a major adaptive advantage of sociality. While most studies are concerned with non-predatory prey species, group-living predators are likely to face similar threats from higher-order predators. We studied the relationship between group size and predation risk in the subsocial crab spider Diaea ergandros by testing predictions from theoretical models including attack abatement as well as the formation of protective retreats. In a field survey, we found predatory clubionid spiders in 35 % of the D. ergandros nests and as predicted, nest size did not correlate with predator presence. In a subsequent laboratory experiment, we observed survival probability, nest construction activity and feeding behaviour including weight development between groups of different sizes as well as in the absence or presence of a predator. Large groups had an advantage in terms of survival and growth compared to smaller groups or single individuals. They also built significantly larger nests than smaller groups, supporting the idea of protective retreat formation being an adaptive benefit to group living. Even though clubionids did attack D. ergandros, they did not significantly affect overall mortality of D. ergandros. The feeding experiment showed that spiders fed on a larger proportion of flies in the presence of a predator. However, these groups gained significantly less weight compared to the control groups, indicating that the potential predators not only act as predators but also as food competitors, constituting a twofold cost for D. ergandros.10 page(s