Cannibalism and conflict in Formica ants

In complex societies like ant colonies individuals cooperate in the aim of maximizing offspring production. But cooperation is only flawless from afar. In fact, because adults can differ in their relatedness to brood they often have contrasting inclusive fitness interests, which may lead to outbreaks of social conflict. However, although conflicts in ant colonies typically arise over offspring production, the role of offspring as actors in social conflict has received little attention. The primary aim of this thesis was to investigate the role of larvae in ant societies, with particular emphasis on selfish larval behavior in the form of egg cannibalism. This thesis demonstrates that Formica ant larvae readily engage in egg cannibalism. Egg consumption allows larvae to increase survival and positively affects the expression of key growth-related genes. Levels of cannibalism across species decrease when relatedness between larvae and eggs is high, which suggests that cannibalism is a selfish trait that can underlie social control. Cannibalism appears to be plastic in F. aquilonia, where levels increase when larvae are presented with foreign eggs compared to sibling eggs. In addition, cannibalism intensity is highly dependent on larvae sex and size across eight species. I conclude that ant larvae are far from powerless. Instead, cannibalism may allow larvae to influence important determinants of individual fitness such as caste fate or size. By consuming eggs, larvae may furthermore affect overall colony fitness. For the first time, this thesis identifies larvae as individuals with selfish interests that have the power to act in social conflict, thus adding a new dimension to our understanding of colony dynamics in social insects. In order to understand how relatedness between individuals potentially impacts conflict in ant societies on a larger scale, this thesis furthermore focuses on the genetic network of native wood ant populations. The societies of these ants consist of many interconnected nests with hundreds of reproductive queens, where individuals move freely between nests and cooperate across nest boundaries. The combination of high queen numbers and free mixing of individuals results in extremely low relatedness within these so-called supercolonies. Here, cooperative worker behavior appears maladaptive because it may aid random individuals instead of relatives. I use network analysis to test for spatial and temporal variation in genetic structure, in order to provide a comprehensive picture of genetic substructure in native wood ant populations. I find that relatedness within supercolonies is low but positive when viewed on a population level, which may be due to limited dispersal range of individuals and ecological factors such as nest site limitation and competition against conspecifics. Genetic network analysis thus provides novel evidence that ant supercolonies can exhibit fine-scale genetic substructure, which may explain the maintenance of cooperation in these low-relatedness societies. Overall, these results offer a new perspective on the stability of cooperation in ant societies, and will hopefully contribute to our understanding of the evolutionary forces governing the balance between cooperation and conflict in other complex social systems.Monimutkaisissa yhteiskunnissa sukulaisuuden aste määrää yksilöiden välisten konfliktien voimakkuuden. Muurahaisten suuri lajienvälinen ja sisäinen vaihtelevuus yhteiskuntien sukulaisuusrakenteessa tekee niistä oivallisen itsekkyyden ja konfliktien tutkimuksen kohteen. Vaikka konfliktit yleensä liittyvät jälkeläisten kasvattamiseen, ei kehittyvien toukkien roolia konfliktin aktiivisina osapuolina ole juuri tutkittu. Väitöskirjassani keskityn toukkien rooliin muurahaisten yhteiskunnissa yleisesti, ja erityisesti toukkien itsekkääseen kannibalistiseen munien syöntiin. Ymmärtääkseni laajemmin sukulaisuuden vaikutukset konflikteihin muurahaisyhteiskunnissa, tutkin lisäksi Formica aquilonia kekomuurahaislajin pesäverkostojen geneettistä rakennetta. Kaikenkaikkiaan väitöskirjani lisää tietämystämme yhteistyön ja konfliktien välisestä tasapainottelusta monimutkaisissa sosiaalisissa yhteisöissä

Social environment affects sensory gene expression in ant larvae

Social insects depend on communication to regulate social behaviour. This also applies to their larvae, which are commonly exposed to social interactions and can react to social stimulation. However, how social insect larvae sense their environment is not known. Using RNAseq, we characterized expression of sensory-related genes in larvae of the ant Formica fusca, upon exposure to two social environments: isolation without contact to other individuals, and stimulation via the presence of other developing individuals. Expression of key sensory-related genes was higher following social stimulation, and larvae expressed many of the same sensory-related genes as adult ants and larvae of other insects, including genes belonging to the major insect chemosensory gene families. Our study provides first insights into the molecular changes associated with social information perception in social insect larvae.Peer reviewe

Development, reproductive capacity and diet of the Mediterranean grasshopper Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Caelifera: Acrididae: Gomphocerinae)

Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Acrididae) is a rare grasshopper native to Mediterranean grassland habitats in the Languedoc-Roussillon region of southern France. Changes in land-use have modified these unique habitats, thus threatening the survival of A. b. vicheti populations. To improve the conservation of this species this study aimed to describe important aspects of its biology and ecology. Development of nymphs passed through five instars after hatching and was closely associated with the Mediterranean spring season. A prominent sexual size dimorphism is highlighted, but the larger females developed in the same number of instars as males. Hind femur length and number of antenna segments were useful characters when distinguishing between nymphal instars. All individuals were brachypterous, indicating that A. b. vicheti is unable to fly. Adult females laid 15 eggs on average and deposited no more than two egg pods in their lifetime. Grass debris made up 93% of faecal content of both sexes. Our results provide valuable information for the conservation of this highly endangered grasshopper species.Peer reviewe

Development, reproductive capacity and diet of the Mediterranean grasshopper Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Caelifera: Acrididae: Gomphocerinae)

Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Acrididae) is a rare grasshopper native to Mediterranean grassland habitats in the Languedoc-Roussillon region of southern France. Changes in land-use have modified these unique habitats, thus threatening the survival of A. b. vicheti populations. To improve the conservation of this species this study aimed to describe important aspects of its biology and ecology. Development of nymphs passed through five instars after hatching and was closely associated with the Mediterranean spring season. A prominent sexual size dimorphism is highlighted, but the larger females developed in the same number of instars as males. Hind femur length and number of antenna segments were useful characters when distinguishing between nymphal instars. All individuals were brachypterous, indicating that A. b. vicheti is unable to fly. Adult females laid 15 eggs on average and deposited no more than two egg pods in their lifetime. Grass debris made up 93% of faecal content of both sexes. Our results provide valuable information for the conservation of this highly endangered grasshopper species.Peer reviewe

Honesty of Larval Begging Signals Covaries With Colony Kin Structure in Formica Ants

Social insects live in highly complex societies with efficient communication systems. Begging is one display commonly used by offspring to signal their nutritional state, however begging behavior has received very little attention in social insects. Theory predicts that begging can be either an honest (i.e., honest-signaling strategy) or a dishonest (i.e., scrambling competition) signal of need, with dishonest signals expected to be more likely when relatedness within the group is low. To investigate the presence and honesty of begging, as well as the nature of the involved signals, we used a comparative approach with four species of the ant genus Formica known to differ in the degree of intra-colony relatedness. We investigated the behavior of starved and non-starved larvae of F. aquilonia, F. pressilabris (both low intra-colony relatedness), F. exsecta (intermediate relatedness), and F. fusca (high relatedness). In addition, we assessed the attraction of conspecific workers toward odors extracted from these two classes of larvae and analyzed the larval cuticular hydrocarbon profiles. We found that in F. fusca and F. exsecta, larvae signaled significantly more when starved. In contrast, larvae of F. aquilonia signaled significantly more when they were non-starved, while there was no significant difference in the behavior of starved vs. non-starved larvae in F. pressilabris. Our results show that workers were not preferentially attracted to the odor of starved larvae, and we also did not detect any differences between the cuticular hydrocarbon profiles of starved and non-starved larvae. Overall, this study demonstrates among species variation in larval hunger signaling in Formica ants, and encourages further studies to confirm the link between kin structure variation and the honesty of begging signals.Peer reviewe

Endosymbionts mediate the effects of antibiotic exposure in the tramp ant Cardiocondyla obscurior

1. Bacterial endosymbionts play a fundamental role in insect ecology. Ants host a large diversity of bacterial symbionts, but comparably little is known about how the loss or reduction of symbionts affects ant fitness. 2. We investigated the effects of the rifampicin, a commonly used antibiotic, on colonies from several populations of the globally distributed tramp ant Cardiocondyla obscurior, which differ in their endosymbiont communities. 3. We found that rifampicin treatment negatively affected queen fecundity and colony productivity, even when there was a delay of 3 months between treatment and productivity assessment. In addition, the viability of sperm from males produced in rifampicin-treated colonies was significantly reduced, pointing towards a trans-generational effect of antibiotics on male ant fitness. As expected, rifampicin treatment also led to a significant decrease in the titres of Candidatus Westeberhardia cardiocondylae and Wolbachia sp., the main bacterial endosymbionts of this ant. 4. The negative effects of antibiotic exposure on ant and symbiont fitness were modulated by the presence and strain of symbiotic bacteria, revealing a complex relationship between the microbiome and ant fitness

Behavioural interactions between co‐habiting females and their impact on productivity and offspring sex ratios in the coffee berry borer, Hypothenemus hampei

The coffee berry borer (CBB) Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae) has invaded all coffee-producing regions of the world and causes substantial economic losses every year. A single female beetle typically infests one coffee berry, which her offspring consume over the course of development. Offspring then engage in sib-mating before daughters fly off to infest new berries. We assessed infestation rates across different locations in Jamaica and found a strong positive correlation between double infestation and overall infestation rate, suggesting that females prefer to breed alone but will tolerate sharing a berry under resource constraints. Using an artificial habitat to study productivity and behaviour in the laboratory, we found that single females produced significantly more offspring per capita than two females, suggesting that co-habitation is costly. Accordingly, co-habiting females spent a significant proportion of their time engaged in antagonistic interactive behaviours such as pushing. When daughter beetles were given the opportunity to stay with their mothers or to infest a new berry, they tended to leave. In contrast to some related beetle species, which exhibit gregariousness and even cooperative behaviour, beneficial social interactions in the CBB appear to be limited to parental care

Evolution of Social Insect Polyphenism Facilitated by the Sex Differentiation Cascade

The major transition to eusociality required the evolution of a switch to canalize development into either a reproductive or a helper, the nature of which is currently unknown. Following predictions from the 'theory of facilitated variation', we identify sex differentiation pathways as promising candidates because of their pre-adaptation to regulating development of complex phenotypes. We show that conserved core genes, including the juvenile hormone-sensitive master sex differentiation gene doublesex (dsx) and a kruppel homolog 2 (kr-h2) with putative regulatory function, exhibit both sex and morph-specific expression across life stages in the ant Cardiocondyla obscurior. We hypothesize that genes in the sex differentiation cascade evolved perception of alternative input signals for caste differentiation (i.e. environmental or genetic cues), and that their inherent switch-like and epistatic behavior facilitated signal transfer to downstream targets, thus allowing them to control differential development into morphological castes.Peer reviewe