Individual stress-resistance in the ant Formica exsecta

Compared to solitary insects, the social organization and interactions in eusocial insects are expected to render them more vulnerable to parasitic exploitation. As a consequence, eusocial insects in turn evolved social immune defenses – sophisticated behaviors that complement the individual immune defenses and increase their resistance against parasitic exploitation. Thus, within the network of the eusocial community, host-parasite interactions occur not only between a single host and its parasites,but among all individuals in the network. Yet, although in eusocial insects host-parasite interactions and other ecological stresses affect the entire community, the individuals provide the basic physiological responses in the defense against external influences. Thus, individual stress responses are an important factor in mediating the variation within the colony to ecological stresses. In this thesis I investigated the physiological stress responses of the ant F. exsecta in the light of host-parasite interactions. I found that oral exposure to bacteria can have a beneficial effect on the survival of food deprivation. Yet, the response to the infection in combination with starvation showed temporal variation. Furthermore, I found striking similarities in the immune responses of young males and foraging workers,as compared to young queens and nursing workers. This suggests that the residual life expectancy may have a role in mediating immune defenses among the castes of F. exsecta. Stress responses not only varied among the castes, but also between two natural populations. I found different reaction norms to temperature and humidity, possibly due to the different environmental conditions that the ants experience in their natural habitat. Given that these reaction norms also affected the expression of immune genes, it is likely that variation in the environmental conditions can affect the immune defenses, and thus, may influence host-parasite interactions. In conclusion, this thesis provides insight into the impact of ecological factors on the resistance and responses to stress in a social insect. I show that individual stress responses are tightly linked to immune defenses, which in turn may affect the stress response of the entire community. As a consequence, variation in the environmental conditions, and thus, exposure to different ecological stresses, may result in different evolutionary trajectories among populations, and even among colonies.Sosiaalisten hyönteisten oletetaan olevan yksin eläviä hyönteisiä alttiimpia loisille niiden yhteiskuntarakenteen ja sosiaalisen vuorovaikutuksen vuoksi. Siksi sosiaalisille hyönteisille on kehittynyt sosiaalista immuunipuolustusta – erityisiä käyttäytymismalleja jotka täydentävät yksilön varsinaista immuunipuolustusta ja lisäävät niiden vastustuskykyä loisia vastaan. Täten lois-isäntä –suhteet eivät rajoitu vain yksittäisen lois-isäntä –parin välille vaan vaikuttavat laajemmin koko eusosiaalisen yhteiskunnan verkostossa, kaikkien sen yksilöiden välillä. Huolimatta siitä, että eusosiaalisilla hyönteisillä lois-isäntäsuhteet ja muut ekologiset stressitekijät vaikuttavat koko yhteiskuntaan, näihin ulkoisiin tekijöihin vastaavat fysiologiset perustoiminnot tapahtuvat kuitenkin yksilötasolla. Tässä väitöskirjassa tarkastelen loviniskamuurahaisen (F. exsecta) fysiologisia stressivasteita lois-isäntäsuhteen yhteydessä. Havaitsin, että bakteereille altistuminen suun kautta saattaa parantaa ravinnonpuutteesta selviämistä, vaikkakin infektiovaste yhdessä nälkiintymisen kanssa vaihteli eri ajanjaksoina. Havaitsin myös selkeitä samankaltaisuuksia immuunivasteessa nuorten koiraiden ja pesän ulkopuolella liikkuvien työläisten kesken verrattuna nuoriin kuningattariin ja jälkeläisiä hoivaaviin työläisiin. Tämä viittaisi siihen, että yksilön odotettavissa oleva elinikä vaikuttaisi immuunivasteisiin loviniskamuurahaisen eri kasteissa. Stressivasteet vaihtelivat kastien lisäksi myös kahden eri populaation välillä. Havaitsin erilaiset reaktionormit lämpötilaan ja kosteuteen, mahdollisesti liittyen populaatioiden luonnossa kokemiin erilaisiin ympäristöoloihin. Koska reaktionormit vaikuttivat myös immuunigeenien ilmenemiseen, on todennäköistä, että ympäristöolojen vaihtelu vaikuttaa immuunipuolustukseen ja voi täten vaikuttaa myös lois-isäntä –suhteisiin. Tämä väitöskirja valottaa ympäristötekijöiden vaikutusta stressinsietokykyyn ja stressivasteisiin sosiaalisilla hyönteisillä. Osoitan, että yksilöiden stressivasteet ovat tiukasti kytköksissä immuunipuolustukseen, mikä puolestaan voi vaikuttaa koko yhteiskunnan stressivasteeseen. Tämän seurauksena ympäristöolojen vaihtelu ja erilaisille ekologisille stressitekijöille altistuminen voi johtaa erilaisiin evolutiivisiin polkuihin eri populaatioissa, mahdollisesti jopa eri kolonioissa

Survival and gene expression under different temperature and humidity regimes in ants

Short term variation in environmental conditions requires individuals to adapt via changes in behavior and/or physiology. In particular variation in temperature and humidity are common, and the physiological adaptation to changes in temperature and humidity often involves alterations in gene expression, in particular that of heat-shock proteins. However, not only traits involved in the resistance to environmental stresses, but also other traits, such as immune defenses, may be influenced indirectly by changes in temperature and humidity. Here we investigated the response of the ant F. exsecta to two temperature regimes (20 degrees C & 25 degrees C), and two humidity regimes (50% & 75%), for two populations. We measured the survival and the expression of six metabolism- and immunity-related genes, and furthermore compared the expression levels in each condition with the pre-experiment expression levels. Both populations survived equally well at the two humidities, but one population showed higher mortality at 25 degrees C than 20 degrees, at 50% humidity. Similarly, the two populations showed striking differences in their gene expression before the experiment, and in their responses to the environmental conditions. Surprisingly, instead of converging to similar expression levels in the same environmental conditions, gene expression diverged further apart. This indicates different reaction norms to both temperature and humidity for the two populations. Furthermore, our results suggest that also immune defenses are indirectly affected by environmental conditions.Peer reviewe

Stress responses upon starvation and exposure to bacteria in the ant Formica exsecta

Organisms are simultaneously exposed to multiple stresses, which requires regulation of the resistance to each stress. Starvation is one of the most severe stresses organisms encounter, yet nutritional state is also one of the most crucial conditions on which other stress resistances depend. Concomitantly, organisms often deploy lower immune defenses when deprived of resources. This indicates that the investment into starvation resistance and immune defenses is likely to be subject to trade-offs. Here, we investigated the impact of starvation and oral exposure to bacteria on survival and gene expression in the ant Formica exsecta. Of the three bacteria used in this study, only Serratia marcescens increased the mortality of the ants, whereas exposure to Escherichia coli and Pseudomonas entomophila alleviated the effects of starvation. Both exposure to bacteria and starvation induced changes in gene expression, but in different directions depending on the species of bacteria used, as well as on the nutritional state of the ants.Peer reviewe

Comparison of Twelve Ant Species and Their Susceptibility to Fungal Infection

Eusocial insects, such as ants, have access to complex disease defenses both at the individual, and at the colony level. However, different species may be exposed to different diseases, and/or deploy different methods of coping with disease. Here, we studied and compared survival after fungal exposure in 12 species of ants, all of which inhabit similar habitats. We exposed the ants to two entomopathogenic fungi (Beauveria bassiana and Metarhizium brunneum), and measured how exposure to these fungi influenced survival. We furthermore recorded hygienic behaviors, such as autogrooming, allogrooming and trophallaxis, during the days after exposure. We found strong differences in autogrooming behavior between the species, but none of the study species performed extensive allogrooming or trophallaxis under the experimental conditions. Furthermore, we discuss the possible importance of the metapleural gland, and how the secondary loss of this gland in the genus Camponotus could favor a stronger behavioral response against pathogen threats

Induced immune responses in Formica fusca (Hymenoptera: Formicidae)

Parental immune experience can enhance offspring defence mechanisms towards prevalent pathogens in the surrounding environment. This process of inherited resistance from one generation to another is known as trans-generational immune priming (TGIP) in invertebrates. In sedentary and dense insect societies, such as ant colonies, TGIP can influence colony survival and fitness upon pathogen outbreaks. However, TGIP appears to depend on species and environmental stressors and therefore can vary in intensity, as well as in the molecular mechanisms leading to resistance. Here, we stimulated the immune system of queens of the ant Formica fusca (LINNAEUS, 1758) by wounding or injecting dead conidia of the entomopathogenic fungus Beauveria bassiana (BALS.-CRIV.) VUILL. (1912). The offspring were subsequently infected with B. bassiana, and the effect of this priming on survival was evaluated. Furthermore, we investigated whether immune challenge of the mother queen induces changes in the expression of immunity-related genes in queens themselves and their brood. We combined this information with measurements of offspring size and number. Larvae produced by untreated queens had a significantly higher mortality after infection with B. bassiana, whereas those produced by immune-primed queens survived no worse than unexposed ones. Adult worker offspring from sham-control mothers showed a protective effect of queen treatment, consistent with transgenerational immune priming. Thus, the effects of queen priming appear to manifest themselves slightly differently in larval and adult offspring. No differences were detected in offspring number or size, but immune gene expression levels showed changes, both in queens and their offspring.Peer reviewe

The relationship between common data-based indicators and the welfare of Swiss dairy herds.

The assessment of dairy cow welfare has become increasingly important in recent years. Welfare assessments that use animal-based indicators, which are considered the most direct indicators, are time consuming and therefore not feasible for assessments on a large number of farms. One approach to reducing this effort is the use of data-based indicators (DBIs) calculated from routine herd data. The aim of this study was to explore the relationship between common DBIs and the welfare of 35 dairy herds to evaluate the feasibility of a data-based welfare prediction method. For this purpose, the WelfareQuality® (WQ) protocol was used to assess the welfare of dairy cows on 35 Swiss farms, for each of which 10 commonly used DBIs were calculated from herd data. Spearman's rank correlations were used to investigate the relationship between DBIs and WQ criteria and measurements. The study found only a few statistically weak associations between DBIs and animal welfare, with no associations for measurements or criteria of resting comfort and appropriate behavior. Thus, the multidimensional welfare definition is insufficiently covered, and the present publication does not support the approach of a purely data-based prediction of dairy welfare status at the farm level. Instead, the regular calculation of DBIs that are indicative of isolated animal welfare problems or metrics of animal health could allow monitoring of these specific areas of animal welfare

Prevalence and antimicrobial resistance of Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7) in Swiss sheep flocks.

Salmonella (S.) enterica subspecies diarizonae (IIIb) serovar 61:k:1,5,(7) (S. IIIb 61:k:1,5,(7)) is considered to be sheep-associated, as it can be found in the intestine, tonsils and nose of clinically healthy sheep, but it has also been described in separate clinical disorders in sheep. In particular, S. IIIb 61:k:1,5,(7) is described as the causative agent of chronic proliferative rhinitis (CPR) in sheep. In Switzerland, CPR in sheep due to S. IIIb 61:k:1,5,(7) was first described in 2017 in a flock of Texel sheep. Therefore, we assessed the prevalence of S. IIIb 61:k:1,5,(7) within the Swiss sheep population using a representative sampling strategy. From May 2017 to June 2018 a total of 681 nasal swabs from individual clinically healthy sheep of 141 different flocks throughout Switzerland were taken. Swabs were analysed by selective enrichment for the presence of S. IIIb 61:k:1,5,(7). Additionally, antimicrobial resistance of the isolates was determined by broth microdilution. A total of 146 out of 681 nasal swabs tested positive for S. IIIb 61:k:1,5,(7), which corresponds to a prevalence on animal level of 21% (95%CI 18%-25%). In 73 out of 141 flocks tested, at least one sheep tested positive for S. IIIb 61:k:1.5,(7), resulting in a minimal prevalence on flock level of 52% (95%CI 43%-60%). Positive flocks were found in all cantons except the canton of Jura. Adults were significantly more affected than sheep under one year/lambs and positive sheep were found in several breeds. No microbiologically resistant isolates were detected, except for one isolate showing resistance against ampicillin. Because of its widespread occurrence in the Swiss sheep population, further research should focus on the pathogenic impact of S. IIIb 61:k:1,5,(7) on the health status of sheep

Associations of antimicrobial use with antimicrobial susceptibility at the calf level in bacteria isolated from the respiratory and digestive tracts of veal calves before slaughter.

OBJECTIVES Antimicrobial drugs are frequently administered in veal calves, but investigations on associations with antimicrobial susceptibility of bacteria are scarce and convey partly contradictory findings. The aim of this study was to investigate associations of antimicrobial use (AMU) during the fattening period with antimicrobial susceptibility shortly before slaughter. METHODS Detailed treatment data of 1905 veal calves from 38 farms were collected prospectively during monthly farm visits for 1 year (n = 1864 treatments, n = 535 visits); 1582 Escherichia coli, 1059 Pasteurella multocida and 315 Mannheimia haemolytica were isolated from rectal and nasopharyngeal swabs collected before slaughter and subjected to antimicrobial susceptibility testing by microdilution. Associations of antimicrobial treatments with resistant isolates were investigated at the calf level. RESULTS Associations of AMU with antimicrobial resistance were observed using generalized linear models. For E. coli, the odds of being resistant were increased with increased AMU (OR 1.36 when number of treatments >1, P = 0.066). Use of tetracyclines was associated with resistance to tetracycline (OR 1.86, P < 0.001) and use of penicillins was associated with resistance to ampicillin (OR 1.66, P = 0.014). No significant associations were observed for P. multocida (use of aminoglycosides: OR 3.66 for resistance to spectinomycin, P = 0.074). For M. haemolytica, the odds of being resistant were increased with increased AMU (OR 4.63, P < 0.001), and use of tetracyclines was associated with resistance to tetracycline (OR 6.49, P < 0.001). CONCLUSIONS Occurrence of resistant bacteria shortly before slaughter was associated with AMU in veal calves. Prudent and appropriate use may contribute to limit the selection of resistant bacteria on veal farms

One clutch or two clutches? Fitness correlates of coexisting alternative female life-histories in the European earwig

Whether to reproduce once or multiple times (semelparity vs. iteroparity) is a major life-history decision that organisms have to take. Mode of parity is usually considered a species characteristic. However, recent models suggested that population properties or condition-dependent fitness payoffs could help to maintain both life-history tactics within populations. In arthropods, semelparity was also hypothesised to be a critical pre-adaptation for the evolution of maternal care, semelparous females being predicted to provide more care due to the absence of costs on future reproduction. The aim of this study was to characterize potential fitness payoffs and levels of maternal care in semel- and itero-parous females of the European earwig Forficula auricularia. Based on 15 traits measured in 494 females and their nymphs, our results revealed that iteroparous females laid their first clutch earlier, had more eggs in their first clutch, gained more weight during the 2weeks following hatching of the first clutch, but produced eggs that developed more slowly than semelparous females. Among iteroparous females, the sizes of first and second clutches were significantly and positively correlated, indicating no investment trade-off between reproductive events. Iteroparous females also provided more food than semelparous ones, a result contrasting with predictions that iteroparity is incompatible with the evolution of maternal care. Finally, a controlled breeding experiment reported full mating compatibility among offspring from females of the two modes of parity, confirming that both types of females belong to one single species. Overall, these results indicate that alternative modes of parity represent coexisting life-history tactics that are likely to be condition-dependent and associated with offspring development and specific levels of maternal care in earwig