Are Toxoplasma-infected subjects more attractive, symmetrical, or healthier than non-infected ones? Evidence from subjective and objective measurements

Background: Parasites are among the main factors that negatively impact the health and reproductive success of organisms. However, if parasites diminish a host's health and attractiveness to such an extent that finding a mate becomes almost impossible, the parasite would decrease its odds of reproducing and passing to the next generation. There is evidence that Toxoplasma gondii (T. gondii) manipulates phenotypic characteristics of its intermediate hosts to increase its spread. However, whether T. gondii manipulates phenotypic characteristics in humans remains poorly studied. Therefore, the present research had two main aims: (1) To compare traits associated with health and parasite resistance in Toxoplasma- infected and non-infected subjects. (2) To investigate whether other people perceive differences in attractiveness and health between Toxoplasma-infected and non-infected subjects of both sexes.Methods: For the first aim, Toxoplasma-infected (n = 35) and non-infected subjects (n = 178) were compared for self-perceived attractiveness, number of sexual partners, number of minor ailments, body mass index, mate value, handgrip strength, facial fluctuating asymmetry, and facial width-to-height ratio. For the second aim, an independent group of 205 raters (59 men and 146 women) evaluated the attractiveness and perceived health of facial pictures of Toxoplasma-infected and non-infected subjects.Results: First, we found that infected men had lower facial fluctuating asymmetry whereas infected women had lower body mass, lower body mass index, a tendency for lower facial fluctuating asymmetry, higher self-perceived attractiveness, and a higher number of sexual partners than non-infected ones. Then, we found that infected men and women were rated as more attractive and healthier than non-infected ones.Conclusions: Our results suggest that some sexually transmitted parasites, such as T. gondii, may produce changes in the appearance and behavior of the human host, either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts. Taken together, these results lay the foundation for future research on the manipulation of the human host by sexually transmitted pathogens and parasites.</p

Toxoplasma gondii and Psychopathology: Latent Infection Is Associated with Interpersonal Sensitivity, Psychoticism, and Higher Testosterone Levels in Men, but Not in Women

Objective The ability of parasites to hijack the nervous system, manipulating the host's physiology and behavior in ways that enhance the parasite's fitness while damaging host fitness, is a topic of ongoing research interest in evolutionary biology, but is largely overlooked in mental health research. Nevertheless, recent evidence has shown that Toxoplasma gondii infection can change host testosterone levels and influence the development of some psychiatric disorders. Here, we tested this hypothesis in a mixed sample of 213 non-clinical subjects.Methods Participants (n(males) = 108, n(females) = 105) provided 5 ml of blood to quantify testosterone levels and Toxoplasma gondii antibodies. The Symptom Checklist-90-Revised was used to assess psychopathological symptoms.Results The results showed that Toxoplasma-infected men had higher testosterone levels and scored higher in Interpersonal Sensitivity and Psychoticism symptoms than non-infected men. Toxoplasma-infected women did not differ from control women.Conclusions Framed in an evolutionary framework, the findings suggest that the elevated testosterone levels and the expression of psychopathological symptoms can be seen as the result of the manipulation exerted by Toxoplasma gondii either to reach its definitive host or to increase its spread. Future research can benefit from integrating insights from evolutionary biology and parasite-host interactions with physiology, immunology, and mental health to develop a better understanding of mental health etiology.</div

An exploratory, cross-cultural study on perception of putative cyclical changes in facial fertility cues

Although many researchers have argued that facial traits evolved as honest cues to women’s current fertility (possibly via changes in facial femininity), evidence that women’s facial attractiveness is significantly, positively related to probability of conception throughout menstrual cycle is mixed. These mixed results could reflect differences among studies in the methods used to assess facial attractiveness (i.e., forced choice versus rating-scale methods), differences in how fertility was assessed, differences in perceiver characteristics (e.g., their own attractiveness), and facial preferences possibly being moderated by the characteristics of the living environment. Consequently, the current study investigated the putative effect of cyclical changes in fertility on women’s facial attractiveness and femininity (1) using forced choice and rating-scale method, (2) conducting both ovulation tests and repeated daily measures of estradiol assessing the conception probability, (3) based on a culturally diverse sample of perceivers, while (4) controlling for inter-individual variation. Although we found some limited evidence that women’s faces became more attractive when conception probability increased, these effects differed depending on the methods used to assess both attractiveness and fertility. Moreover, where statistically significant effects were observed, the effect sizes were extremely small. Similarly, there was little robust evidence that perceivers’ characteristics reliably predicted preferences for fertility cues. Collectively, these results suggest that mixed results in previous studies examining cyclical fluctuation in women’s facial attractiveness are unlikely to reflect inter-cultural differences and are more likely to reflect differences in the methods used to assess facial attractiveness and fertility

Publisher correction : An exploratory, cross-cultural study on perception of putative cyclical changes in facial fertility cues

Correction to: Scientific Reports https://doi.org/10.1038/s41598-021-96454-w, published online 19 August 2021 The Funding section in the original version of this Article was omitted. The Funding section now reads: “This work was funded by the Polish National Science Center (grant number 2014/12/S/NZ8/00722), and the Polish-U.S. Fulbright Commission (grant number PL/2018/42/SR).” The original Article has been corrected

Food quality affects the expression of antimicrobial peptide genes upon simulated parasite attack in the larvae of greater wax moth

Predator-prey interactions are an important evolutionary force affecting the immunity of the prey. Parasitoids and mites pierce the cuticle of their prey, which respond by activating their immune system against predatory attacks. Immunity is a costly function for the organism, as it often competes with other life-history traits for limited nutrients. We tested whether the expression of antimicrobial peptides (AMP) of the larvae of the greater wax moth Galleria mellonella (L.) (Lepidoptera: Pyralidae) changes as a consequence of insertion of a nylon monofilament, which acts like a synthetic parasite. The treatment was done for larvae grown on a high-quality vs. a low-quality diet. The expression of Gloverin and 6-tox were upregulated in response to the insertion of the nylon monofilament. The expression of 6-tox, Cecropin-D, and Gallerimycin were significantly higher in the low-quality diet' group than in the high-quality diet' group. As food quality seems to affect AMP gene expression in G. mellonella larvae, it should always be controlled for in studies on bacterial and fungal infections in G. mellonella

Microbiome symbionts and diet diversity incur costs on the immune system of insect larvae.

Communities of symbiotic microorganisms that colonize the gastrointestinal tract play an important role in food digestion and protection against opportunistic microbes. Diet diversity increases the number of symbionts in the intestines, a benefit that is considered to impose no cost for the host organism. However, less is known about the possible immunological investments that hosts have to make in order to control the infections caused by symbiont populations that increase because of diet diversity. Using taxonomical composition analysis of the 16S rRNAV3 region, we show that enterococci are the dominating group of bacteria in the midgut of the larvae of the greater wax moth (Galleria mellonella). We found that the number of colony-forming units of enterococci and expressions of certain immunity-related antimicrobial peptide (AMP) genes such as Gallerimycin, Gloverin, 6-tox, Cecropin-D and Galiomicin increased in response to a more diverse diet, which in turn decreased the encapsulation response of the larvae. Treatment with antibiotics significantly lowered the expression of all AMP genes. Diet and antibiotic treatment interaction did not affect the expression of Gloverin and Galiomicin AMP genes, but significantly influenced the expression of Gallerimycin, 6-tox and Cecropin-D. Taken together, our results suggest that diet diversity influences microbiome diversity and AMP gene expression, ultimately affecting an organism's capacity to mount an immune response. Elevated basal levels of immunity-related genes (Gloverin and Galiomicin) might act as a prophylactic against opportunistic infections and as a mechanism that controls the gut symbionts. This would indicate that a diverse diet imposes higher immunity costs on organisms

Ecological Stoichiometry: A Link Between Developmental Speed and Physiological Stress in an Omnivorous Insect

The elemental composition of organisms belongs to a suite of functional traits that may adaptively respond to fluctuating selection pressures. Life history theory predicts that predation risk and resource limitations impose selection pressures on organisms' developmental time and are further associated with variability in energetic and behavioral traits. Individual differences in developmental speed, behaviors and physiology have been explained using the pace-of-life syndrome (POLS) hypothesis. However, how an organism's developmental speed is linked with elemental body composition, metabolism and behavior is not well understood. We compared elemental body composition, latency to resume activity and resting metabolic rate (RMR) of western stutter-trilling crickets (Gryllus integer) in three selection lines that differ in developmental speed. We found that slowly developing crickets had significantly higher body carbon, lower body nitrogen and higher carbon-to-nitrogen ratio than rapidly developing crickets. Slowly developing crickets had significantly higher RMR than rapidly developing crickets. Male crickets had higher RMR than females. Slowly developing crickets resumed activity faster in an unfamiliar relative to a familiar environment. The rapidly developing crickets did the opposite. The results highlight the tight association between life history, physiology and behavior. This study indicates that traditional methods used in POLS research should be complemented by those used in ecological stoichiometry, resulting in a synthetic approach that potentially advances the whole field of behavioral and physiological ecology

Women’s preferences for men’s facial masculinity are strongest under favorable ecological conditions

International audienceThe strength of sexual selection on secondary sexual traits varies depending on prevailing economic and ecological conditions. In humans, cross-cultural evidence suggests women's preferences for men's testosterone dependent masculine facial traits are stronger under conditions where health is compromised, male mortality rates are higher and economic development is higher. Here we use a sample of 4483 exclusively heterosexual women from 34 countries and employ mixed effects modelling to test how social, ecological and economic variables predict women's facial masculinity preferences. We report women's preferences for more masculine looking men are stronger in countries with higher sociosexuality and where national health indices and human development indices are higher, while no associations were found between preferences and indices of intra-sexual competition. Our results show that women's preferences for masculine faces are stronger under conditions where offspring survival is higher and economic conditions are more favorable

Mating plugs in polyandrous giants: Which sex produces them, when, how and why?

10.1371/journal.pone.0040939PLoS ONE77

Sex, War, and Disease: The Role of Parasite Infection on Weapon Development and Mating Success in a Horned Beetle (Gnatocerus cornutus)

While parasites and immunity are widely believed to play important roles in the evolution of male ornaments, their potential influence on systems where male weaponry is the object of sexual selection is poorly understood. We experimentally infect larval broad-horned flour beetles with a tapeworm and study the consequent effects on: 1) adult male morphology 2) male-male contests for mating opportunities, and 3) induction of the innate immune system. We find that infection significantly reduces adult male size in ways that are expected to reduce mating opportunities in nature. The sum of our morphological, competition, and immunological data indicate that during a life history stage where no new resources are acquired, males allocate their finite resources in a way that increases future mating potential