Mari Pölkki

Transgenerational effects of parental larval diet on offspring development time, adult body size and pathogen resistance in Drosophila melanogaster.

Environmental conditions experienced by parents are increasingly recognized to affect offspring performance. We set out to investigate the effect of parental larval diet on offspring development time, adult body size and adult resistance to the bacterium Serratia marcescens in Drosophila melanogaster. Flies for the parental generation were raised on either poor or standard diet and then mated in the four possible sex-by-parental diet crosses. Females that were raised on poor food produced larger offspring than females that were raised on standard food. Furthermore, male progeny sired by fathers that were raised on poor food were larger than male progeny sired by males raised on standard food. Development times were shortest for offspring whose one parent (mother or the father) was raised on standard and the other parent on poor food and longest for offspring whose parents both were raised on poor food. No evidence for transgenerational effects of parental diet on offspring disease resistance was found. Although paternal effects have been previously demonstrated in D. melanogaster, no earlier studies have investigated male-mediated transgenerational effects of diet in this species. The results highlight the importance of not only considering the relative contribution each parental sex has on progeny performance but also the combined effects that the two sexes may have on offspring performance.

Inbreeding affects sexual signalling in males but not females of Tenebrio molitor

In many species of animals, individuals advertise their quality with sexual signals to obtain mates. Chemical signals such as volatile pheromones are species specific, and their primary purpose is to influence mate choice by carrying information about the phenotypic and genetic quality of the sender. The deleterious effects of consanguineous mating on individual quality are generally known, whereas the effect of inbreeding on sexual signalling is poorly understood. Here, we tested whether inbreeding reduces the attractiveness of sexual signalling in the mealworm beetle, Tenebrio molitor, by testing the preferences for odours of inbred and outbred (control) individuals of the opposite sex. Females were more attracted to the odours produced by outbred males than the odours produced by inbred males, suggesting that inbreeding reduces the attractiveness of male sexual signalling. However, we did not find any difference between the attractiveness of inbred and outbred female odours, which may indicate that the quality of females is either irrelevant for T. molitor males or quality is not revealed through female odours.

Transgenerational Effects of Heavy Metal Pollution on Immune Defense of the Blow Fly Protophormia terraenovae

Recently environmental conditions during early parental development have been found to have transgenerational effects on immunity and other condition-dependent traits. However, potential transgenerational effects of heavy metal pollution have not previously been studied. Here we show that direct exposure to heavy metal (copper) upregulates the immune system of the blow fly, Protophormia terraenovae, reared in copper contaminated food. In the second experiment, to test transgenerational effects of heavy metal, the parental generation of the P. terraenovae was reared in food supplemented with copper, and the immunocompetence of their offspring, reared on uncontaminated food, was measured. Copper concentration used in this study was, in the preliminary test, found to have no effect on mortality of the flies. Immunity was tested on the imago stage by measuring encapsulation response against an artificial antigen, nylon monofilament. We found that exposure to copper during the parental development stages through the larval diet resulted in immune responses that were still apparent in the next generation that was not exposed to the heavy metal. We found that individuals reared on copper-contaminated food developed more slowly compared with those reared on uncontaminated food. The treatment groups did not differ in their dry body mass. However, parental exposure to copper did not have an effect on the development time or body mass of their offspring. Our study suggests that heavy metal pollution has positive feedback effect on encapsulation response through generations which multiplies the harmful effects of heavy metal pollution in following generations.

Prenatal Influences on Sexual Orientation: Digit Ratio (2D:4D) and Number of Older Siblings:

Prenatal androgen levels are suggested to influence sexual orientation in both sexes. The 2D:4D digit ratio has been found to associate with sexual orientation, but published findings have often been contradictory, which may partly be due to the large ethnic diversity between and within studied populations. In men, number of older brothers has been found to correlate positively with homosexuality. This phenomenon has been explained with a maternal immune reaction, which is provoked only by male fetuses and which gets stronger after each pregnancy. Here we assessed the relationship of sexual orientation to 2D:4D ratios and number of older siblings in Finland, where the population is found to be genetically relatively homogeneous. As in many previous studies, heterosexual men had lower 2D:4D than non-heterosexual men, which supports the notion that non-heterosexual men experience higher androgen levels in utero than population norms. Contrary to previous reports, non-heterosexual women had higher 2D:4D than heterosexual women. Non-heterosexual men had more older brothers and older sisters than heterosexual men. The greater number of older sisters in non-heterosexual men indicates that there are other factors that contribute to the higher birth order of homosexual men than the maternal immunization.

Intra- and trans-generational effects of larval diet on susceptibility to an entomopathogenic fungus, Beauveria bassiana, in the greater wax moth, Galleria mellonella

In addition to nutritional conditions experienced by individuals themselves, those experienced by their parents can affect their immune function. Here, we studied the intra‐ and trans‐generational effects of larval diet on susceptibility to an entomopathogenic fungus, Beauveria bassiana, in the greater wax moth, Galleria mellonella. In the first part of the study, a split‐brood design was used to compare the susceptibility of full sibs raised either on low‐ or on high‐nutrition larval diet. In the second part of the study, a similar experimental design was employed to investigate the effects of maternal and paternal diet as well as their interaction on offsprings susceptibility. In the first part of the study, we found that individuals fed with high‐nutrition diet had higher mortality from infection than individuals fed with low‐nutrition diet. However, diet did not affect post‐infection survival time. Conversely, in the second part of the study, maternal diet was found to have no significant effect on final mortality rate of offspring, but it affected survival time: larvae with high‐nutrition maternal diet survived fewer days after infection than larvae with low‐nutrition maternal diet. Paternal diet had no significant effect on offsprings susceptibility to the fungus, indicating that paternal effects are not as important as maternal effects in influencing immune function in this species. Our findings provide further indication that maternal nutrition affects immune function in insects, and suggest that the direct effects of nutrition on immunity may be different, yet parallel, to those caused by parental nutrition.

Dominance is not always an honest signal of male quality, but females may be able to detect the dishonesty

Females prefer dominant males as mating partners in numerous species. Male dominance rank is considered as an honest signal of male quality, because only healthy males in good condition are thought to be able to win fights with other males. Here, we tested whether activation of the immune system influences the success of males in male–male competition and mating in the field cricket, Gryllus integer. We activated the immune system of males with a nylon monofilament (to mimic a parasitoid larva), and arranged fights between male pairs to assess male dominance and associated mating success. Activation of the immune system with nylon monofilament substantially enhanced the fighting success of males during male–male competition but had no effect on mating success. However, sham-manipulation (a wound only) did not have any effect on fighting success although females mated more often with dominant males. Our study suggests that when male crickets meet an apparent survival threat they may behave more dominantly, probably owing to terminal investment. Male success during male–male competition is not always an honest signal of males’ quality, but females may be able to detect this dishonesty.

Immune Challenge has a Negative Effect on Cuticular Darkness in the Mealworm Beetle, Tenebrio molitor

Insect cuticle hardens and darkens during the processes of cuticular melanization and sclerotization, and it provides an effective physicochemical barrier against parasites and pathogens. If an invader manages to breach this barrier defense, it is attacked by immune mechanisms in the hemocoel. In this study, we set out to investigate the association between these two lines of defense in the mealworm beetle, Tenebrio molitor. The immune response of freshly emerged beetles was induced with nylon monofilament implants, and later the darkness of their cuticle was assessed. Our study shows that immune challenge has a negative effect on cuticular darkness in T. molitor, which is likely to reflect a trade-off in the allocation of resources between two important components of insect defense system — the protective cuticle and the encapsulation response. The putative trade-off was not affected by the availability of energy resources.

Effects of Interaction between Temperature Conditions and Copper Exposure on Immune Defense and Other Life-History Traits of the Blow Fly Protophormia terraenovae

Environmental pollution is considered one of the major threats to organisms. Direct effects of heavy metal pollution on various life-history traits are well recognized, while the effects of potential interactions between two distinct environmental conditions on different traits are poorly understood. Here, we have tested the effects of interactions between temperature conditions and heavy metal exposure on innate immunity and other life-history traits. Maggots of the blow fly Protophormia terraenovae were reared on either copper-contaminated or uncontaminated food, under three different temperature environments. Encapsulation response, body mass, and development time were measured for adult flies that were not directly exposed to copper. We found that the effects of copper exposure on immunity and other traits are temperature-dependent, suggesting that the ability to regulate toxic compounds in body tissues might depend on temperature conditions. Furthermore, we found that temperature has an effect on sex differences in immune defense. Males had an encapsulation response at higher temperatures stronger than that of females. Our results indicate that the effects of environmental conditions on different traits are much more intricate than what can be predicted. This is something that should be considered when conducting immunological experiments or comparing results of previous studies.

Independent and interactive effects of immune activation and larval diet on adult immune function, growth and development in the greater wax moth (Galleria mellonella)

Organisms in the wild are likely to face multiple immune challenges as well as additional ecological stressors, yet their interactive effects on immune function are poorly understood. Insects are found to respond to cues of increased infection risk by enhancing their immune capacity. However, such adaptive plasticity in immune function may be limited by physiological and environmental constraints. Here, we investigated the effects of two environmental stressors – poor larval diet and an artificial parasite‐like immune challenge at the pupal stage – on adult immune function, growth and development in the greater wax moth (Galleria mellonella). Males whose immune system was activated with an artificial parasite‐like immune challenge had weaker immune response – measured as strength of encapsulation response – as adults compared to the control groups, but only when reared on high‐nutrition larval diet. Immune activation did not negatively affect adult immune response in males reared on low‐nutrition larval diet, indicating that poor larval diet improved the capacity of the insects to respond to repeated immune challenges. Low‐nutrition larval diet also had a positive independent effect on immune capacity in females, yet it negatively affected development time and adult body mass in both sexes. As in the nature immune challenges are rarely isolated, and adverse nutritional environment may indicate an elevated risk of infection, resilience to repeated immune challenges as a response to poor nutritional conditions could provide a significant fitness advantage. This study highlights the importance of considering environmental context when investigating the effects of immune activation in insects.