Indrikis Krams

University of Latvia | LU · Department of Zoology and Animal Ecology

Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose...

Body height and other body attributes of humans may be associated with a diverse range of social outcomes such as attractiveness to potential mates. Despite evidence that each parameter plays a role in mate choice, we have little understanding of the relative role of each, and relationships between indices of physical appearance and general health....

The resources available to an individual in any given environment are finite, and variation in life history traits reflect differential allocation of these resources to competing life functions. Nutritional quality of food is of particular importance in these life history decisions. In this study we tested trade-offs among growth, immunity and surv...

Cuticle melanism in insects is linked to a number of life history traits: a positive relationship is hypothesized between melanism, immune function, fecundity and lifespan. However, it is not clear how activation of the immune system affects trade-offs between life history traits in female mealworm beetles (Tenebrio molitor) differing in cuticle me...

Factors such as temperature, habitat, larval density, food availability and food quality substantially affect organismal development. In addition, risk of predation has a complex impact on the behavioural and morphological life history responses of prey. Responses to predation risk seem to be mediated by physiological stress, which is an adaptation...

Modification and deterioration of old‐growth forests by industrial forestry have seriously threatened species diversity worldwide. The loss of natural habitats increases the concentration of circulating glucocorticoids and incurs chronic stress in animals, influencing the immune system, growth, survival, and lifespan of animals inhabiting such area...

Male Tenebrio molitor enhance sex odor attractiveness when immunocompromised by an artificial implant that activates their immune system. We examined how females evaluate the health status of implanted (treatment) and control males based not only on their sex pheromones, but also on their fecal odors. Odor discs of three groups were collected from...

Modification and deterioration of old-growth forests by industrial forestry have seriously threatened species diversity worldwide. The loss of natural habitats increases the concentration of circulating glucocorticoids and incurs chronic stress in animals, influencing the immune system, growth, survival, and lifespan of animals inhabiting such area...

Historically, males have frequently been portrayed as the manipulative and deceptive gender, while females are often seen as adopting a coy and passive role. In this context, it is proposed that males use a terminal investment strategy, misleading females about their true poor condition, while females passively opt to mate with these deceptive male...

Introduction Although some findings indicate that yoga can reduce stress and anxiety, many studies present mixed results. The potential of yoga interventions to alleviate anxiety, including the mechanisms and boundary conditions by which it does so, is an under-researched topic. Anxiety is often divided into “state anxiety” and “trait anxiety,” the...

Stress caused by predator exposure can lead to various behavioural, physiological, stoichiometric, and biochemical changes in prey. Prior research has shown that growth under predation stress can cause the development of a diabetes-like biochemical phenotype in fruit flies. Exposure to predator risk during larval development decreases flies’ walkin...

In the terminal investment strategy, organisms allocate resources to maximize current reproduction when their future reproductive opportunities are uncertain due to a high risk of mortality. However, whether the role of time lapse between stress and reproductive investment (courtship vs. courtship and mating) triggers the terminal investment strate...

Group living has long been viewed as an adaptation to reduce predation risk. Earlier comparative analyses provided support for the hypothesis but typically ignored variation in group size at the local scale and included proxies of predation risk rather than more direct estimates. Here, we related variation in group size at the scale of a study site...

Predation can have both lethal and non-lethal effects on prey. The non-lethal effects of predation can instil changes in prey life history, behaviour, morphology and physiology, causing adaptive evolution. The chronic stress caused by sustained predation on prey is comparable to chronic stress conditions in humans. Conditions like anxiety, depressi...

Heritable microbes that exhibit reproductive parasitism are common in insects. One class of these are the male-killing bacteria, which are found in a broad range of insect hosts. Commonly, our knowledge of the incidence of these microbes is based on one or a few sampling sites, and the degree and causes of spatial variation are unclear. In this pap...

The development of high-throughput behavioral assays, where numerous individual animals can be analyzed in various experimental conditions, has facilitated the study of animal personality. Previous research showed that isogenic Drosophila melanogaster flies exhibit striking individual non-heritable locomotor handedness. The variability of this trai...

The optimal body mass hypothesis posits that the body reserves of wintering birds are balanced between the risk of starvation and predation. In this study, we tested whether the body mass of wintering Great Tits (Parus major) was higher under conditions of less predictable food resources. We compared body mass, body mass index, the speed at take-of...

Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average...

Animals adjust their use of alarm calls depending on social environments. We tested whether dominant (adult) and subordinate (juvenile non-kin) male crested tits ( Lophophanes cristatus ) warn each other and heterospecific willow tits ( Poecile montanus ) across the wintering season. Birds rarely alarm called when feeding alone. Both adult and juve...

Evolutionary approaches to human mating strategies have associated facial and physical attractiveness with cues of health, fertility, and personality traits both in men and women. In this study, we tested the hypothesis that these associations may be mediated by psychological flexibility (an indicator of mental health) and/or sociosexual orientatio...

Hormones are key factors in determining the response of organisms to their environment. For example, the juvenile hormone (JH) coordinates the insects' development, reproduction, and survival. However, it is still unclear how the impact of juvenile hormone on insect immunity varies depending on the sex and reproductive state of the individual, as w...

Invertebrates' immune priming or innate immune memory is an analogous response to the vertebrates' adaptive memory. We investigated if honey bees have immune memory. We compared survival and immune response between bees that were: 1) manipulated (Naïve), 2) challenged twice with the same pathogen Escherichia coli (Memory), 3) challenged twice with...

Schizophrenia has been an evolutionary paradox: it has high heritability, but it is associated with decreased reproductive success. The causal genetic variants underlying schizophrenia are thought to be under weak negative selection. To unravel this paradox, many evolutionary explanations have been suggested for schizophrenia. We critically discuss...

Objective Findings on the associations between sex hormones and immune function are scarce and mixed, especially in women. To contribute to the understanding on how sex hormones and immune function interact, we analyzed relationships between testosterone, estradiol, and immune responses in women.Methods Two doses of hepatitis B vaccine were adminis...

Blood parasites are considered to have strong negative effects on host fitness. Negative fitness consequences may be associated with proximity to areas where blood parasite vectors reproduce. This study tested for relationships between haemosporidian infection prevalence, parasitemia, and fitness parameters of breeding Pied Flycatchers (Ficedula hy...

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 e...

Free-living organisms face multiple stressors in their habitats, and habitat quality often affects development and life history traits. Increasing pressures of agricultural intensification have been shown to influence diversity and abundance of insect pollinators, and it may affect their elemental composition as well. We compared reproductive succe...

Avian species often use anti‐predator calls such that the costs and benefits of vigilance are distributed within the group. Some species respond differentially to graded risk by attending to relevant predator cues, such as head orientation and gaze direction. One benefit of graded‐risk sensitivity is fewer missed foraging opportunities. It is not k...

Significance In many monogamous species, a substantial proportion of offspring is sired by other males than the one providing care at the nest. Although females often solicit extra-pair mating, the benefits of extra-pair copulations to females are not fully understood. In this study on pied flycatchers, we tested whether extra-pair paternity in nei...

Bumblebees are key pollinators in agricultural landscapes. However, little is known about how gut microbial communities respond to anthropogenic changes. We used commercially produced colonies of buff-tailed bumblebees (Bombus terrestris) placed in three habitats. Whole guts (midgut, hindgut, and rectum) of B. terrestris specimens were dissected fr...

Objective Phenotypic markers associated with developmental stability such as fluctuating asymmetry, facial attractiveness, and reports of minor ailments can also act as indicators of overall physical health. However, few studies have assessed whether these markers might also be cues of mental health. We tested whether self- and other-perceived faci...

Modelling fertility decline in post-industrial populations in the context of life history theory has allowed us to better understand the environmental pressures that shape reduced family size. One such pressure, which has received relatively little attention from ecologists, is the movement of women into the labour market. Analyses of effects of em...

Ecological stoichiometry is important for revealing how the composition of chemical elements of organisms is influenced by their physiological functions and ecology. In this study, we investigated the elemental body composition of queens, workers, and males of the bumblebee Bombus terrestris, an important pollinator throughout Eurasia, North Americ...

Background The abundance of insects has decreased considerably during recent decades, resulting in current abundance showing 70–80% reductions in more than 15 studies across temperate climate zones. Dramatic reductions in the abundance of insects are likely to have consequences for other taxa at higher trophic levels such as predators and parasites...

The presence of pathogens has imposed constant threats to human survival and reproduction. Selective pressures exerted by pathogens have shaped our array of immune functions—including physiological, psychological, and behavioral immune systems. Pathogens and epidemics have plagued humankind and our ancestors from their dawn, yet despite advances in...

Habitat quality has direct effects on the evolutionary fitness of breeding organisms, which is why it is believed that animals tend to have an evolved preference for the best possible habitats. However, some animals may mistakenly choose to reproduce in habitats that decrease their fitness, resulting in ‘ecological traps’. In this study, we tested...

When organisms’ environmental conditions vary unpredictably in time, it can be advantageous for individuals to hedge their phenotypic bets. It has been shown that a bet-hedging strategy possibly underlies the high inter-individual diversity of phototactic choice in Drosophila melanogaster . This study shows that fruit flies from a population living...

The genes of the Major Histocompatibility Complex (MHC), which plays a fundamental role in the immune system, are some of the most diverse genes in vertebrates and have been connected to mate choice in several species, including humans. While studies suggest a positive relationship between MHC diversity and male facial attractiveness, the connectio...

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 T...

The development of costly traits such as immune function and secondary sexual traits is constrained by resource availability. The quality of developmental conditions and the availability of resources in ontogeny may therefore influence immune system functions and other biological traits. We analyzed causal pathways between family socioeconomic posi...

The immune response of animals, including insects, is overcome by some parasites. For example, dauer larvae (DL) of the obligate entomopathogenic nematodes (EPNs) Heterorhabditis and Steinernema can invade insects, evade their defenses, and cause death. Although DL were long assumed to be the only infective stage of nematodes, recent reports sugges...

While COVID-19 infection and mortality rates are soaring in Western countries, Southeast Asian countries have successfully avoided the second wave of the SARS-CoV-2 pandemic despite high population density. We provide a biochemical hypothesis for the connection between low COVID-19 incidence, mortality rates, and high visceral adiposity in Southeas...

Bipolar disorder is a mental health disorder characterized by extreme shifts in mood, high suicide rate, sleep problems, and dysfunction of psychological traits like self-esteem (feeling inferior when depressed and superior when manic). Bipolar disorder is rare among populations that have not adopted contemporary Western lifestyles, which supports...

Predation is an essential factor affecting prey populations, yet attacks are notoriously difficult to observe in real time. Here, we provide descriptive data about the attack behavior of Eurasian Sparrowhawks (Accipiter nisus) and the escape tactics of their prey in coniferous forests in Latvia during the non-breeding season. Over a period of 36 ye...

Juvenile hormone has been suggested to be a potential mediator in the trade-off between mating and insects' immunity. Studies on various insect taxons have found that juvenile hormone interferes with humoral and cellular immunity. Although this was shown experimentally, studies using highly virulent parasites or pathogens are lacking so far. In thi...

Abstract- Male mating signals are sexual traits that may provide females with information about the physiological quality of the individual. Males of the yellow mealworm beetle, Tenebrio molitor, use pheromones to attract mating partners. The level of pheromone production in males has been identified as a signal of the male condition. We tested wh...

Research Highlights: Studies on tree canopy dwelling species often require simple proxies of tree canopy volume estimated at a stand level. These include allometrically related tree crown parameters such as crown area and basal area, and canopy cover. Background and Objectives: In monoculture Scot's pine and mixed pine/Norway spruce forest, we aime...

Although obesity is known to be a risk factor for COVID-19 severity, there is an urgent need to distinguish between different kinds of fat – visceral and subcutaneous fat – and their inflammation status in COVID-19. These different fat types have partially diverging biochemical roles in the human body, and they are differentially associated with SA...

Male mating signals are sexual traits that may provide females with information about the physiological quality of the individual. Males of the yellow mealworm beetle, Tenebrio molitor, use pheromones to attract mating partners. The level of pheromone production in males has been identified as a signal of the male condition. We tested whether male...

We studied the relationship between temperature and the coexistence of great tit Parus major and blue tit Cyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a...

The elemental composition of organisms belongs to a suite of functional traits that change during development in response to environmental conditions. However, associations between adaptive variations in developmental speed and elemental body composition are not well understood. We compared body mass, elemental body composition, food uptake and fat...

Immune function, height and resource accumulation comprise important life history traits in humans. Resource availability models arising from life history theory suggest that socioeconomic conditions influence immune function, growth and health status. In this study, we tested whether there are associations between family income during ontogeny, ad...

We investigated the intra- and trans-generational effects of larval diet on immune function, body size and development time of the greater wax moth, Galleria mellonella (Lepidoptera : Pyralidae). We found that moths reared on a diet diluted with cellulose (a low-nutrition diet) were about one-third smaller, had about one-fifth longer development ti...

Only dominant individuals have unrestricted access to contested resources in group-living animals. in birds, subordinates with restricted access to resources may respond to intragroup contests by acquiring extra body reserves to avoid periods of food shortage. In turn, higher body mass reduces agility and increases predation and mortality risk to s...

Mixed-species animal groups (MSGs) are widely acknowledged to increase predator avoidance and foraging efficiency, among other benefits, and thereby increase participants' fitness. Diversity in MSG composition ranges from two to 70 species of very similar or completely different phenotypes. Yet consistency in organization is also observable in that...

We present data from 122 nations showing that Baumard’s argument on the ecological predictors of life history strategies and innovation is incomplete. Our analyses indicate that wealth, parasite stress, and cold climate impose orthogonal effects on life histories, innovation, and industrialization. Baumard also overlooks the historical exploitation...

Before a population becomes extinct, there are hidden costs in the physiology at the individual level that provide valuable insights into their condition. Here, we study two dams with one species in common (Argia anceps Garrison, 1996) to evaluate whether their physiological condition differed (total protein quantity, prophenoloxidase (proPO) and p...