Didzis Elferts

Age and spatial structure of natural Pinus sylvestris stands in Latvia

Abstract The age and spatial structure of six natural old growth Pinus sylvestris stands in Latvia were investigated, to attempt to identify retrospectively the past features of development. In each stand, one or two plots of size 200–900 m2 were established. Tree locations were mapped, stem diameter was measured, and tree age was determined from cores or by counting branch whorls. Tree distribution was assessed by Ripleys K function. A clumped spatial pattern was shown for P. sylvestris younger than 100 years. The temporal patterns of establishment could be partly linked to favourable climatic periods. The major disturbance affecting pine stands along the coast was windblown sand, which partly buried some stems and probably affected the patterns of seedling recruitment and mortality. Disturbance caused by fire had a major role in determining the past regimens of mortality and establishment in dry stands located inland. The successful invasion during the last century of spruce in more mesic plots with a pine overstorey may be due to fire suppression.

Influence of the initial acidification step on biogas production and composition

Laboratory‐scale experiments were carried out to evaluate the effect of initial acidification of feedstock consisting of different components on biogas production and composition. Feedstock containing different agricultural wastes, biomass, and microorganisms was collected from five full‐scale biogas plants. Two continuously stirred tank reactors were used. The fermentation temperature was 37 °C. The pH value was adjusted to 6.0 in the first reactor at the beginning of the experiment, and an initial pH value of 7.0 was implemented after 48 H. The second reactor was used as a control reactor with a constant pH of 7.0. The experiment lasted a total of 7 days. In the reactors, the gas phase was dominated by CH4, CO2, and N2. The results showed that acidification increased biogas and carbon dioxide production in five cases, increased methane production and reduced nitrogen production in four cases, and reduced methane content in biogas in four of five cases. Only feedstock composed of 74% of different manures and 26% of plant material reduced the production of methane and increased the production of nitrogen after acidification. Other feedstock contained 47% to 96% plant material. An initial pH value of 6 could be recommended for mesophilic single‐phase methanogenesis with a prevalence of plant material.

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

ABSTRACT 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 rRNA V3 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 organisms 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. Summary: Having high numbers of midgut symbionts may bring costs to a host organism, which is a crucial finding for understanding the evolution of host–symbiont interactions.

Reproduction compromises adaptive immunity in a cyprinid fish

Vertebrates differ in their ability to mount an adaptive immune response to novel antigens. Bioenergetic resources available to an organism are finite; investment in reproduction compromises immune function and may therefore affect critical life history trade-offs. We tested whether reproduction impairs the ability to produce an antibody response against a novel antigen in roach (Rutilus rutilus). The antigen approach has rarely been used in fish studies, and the ability to produce an antibody response during reproductive season has never been tested in cyprinid fish before. The fish in an experimental group were injected with a Brucella abortus (BA) antigen, while the fish in a control group were injected with an isotonic saline solution. Blood samples were extracted from all the fish to obtain the total number and proportion of blood cells such as lymphocytes, neutrophils and antioxidant glutathione. The groups were tested during the spawning season and one week after it had ended. The roach were unable to mount an immune response during spawning but produced a robust response after it. We conclude that reproduction is costly in roach, as indicated by the increased concentration of neutrophils in fish injected with BA during spawning, as well as the negative associations between neutrophil counts and glutathione levels. This study demonstrates the potential of BA antigen as a research tool in experimental research on fish ecological immunology.

Comparison of telomere length between population-specific mitochondrial haplogroups among different age groups in a Latvian population

Population studies have demonstrated that telomere length (TL) displays great diversity among different populations. Previously described controversial findings associated longevity with specific mitochondrial DNA haplogroups (hgs) (e.g., J and U). These observations may be influenced by population diversity, geographic location, and/or specific historic background. The aims of this study were to identify a specific hg which correlates with aging in a Latvian populating and to evaluate the possible association of TL variability with specific mitochondrial hgs. The results show no significant correlation between TL, mitochondrial DNA hgs and longevity. A slight increase in frequency was observed among centenarians of hg H; however, these findings were not statistically significant. TL did not show any statically significant difference, only hg W had slightly longer telomeres among others. An insignificant increase in TL was observed in the 55-89 age group of hg W but in the <90 age group for hg J which also had the longest TL in the 20-45 age group. In conclusion this study indicates that specific mitochondrial DNA hgs do not have a significant, if any, influence on the variation of TL in Latvians.

Effect of water level and climatic factors on the radial growth of black alder

Effect of water level and climatic factors on the radial growth of black alder Black alder (Alnus glutinosa (L.) Gaertn.) is a widespread tree species in Europe and the western part of the temperate climate zone. The area of forest in Latvia dominated by this tree species has substantially decreased due to wide-spread forest drainage. To predict future changes due to environmental change, it is extremely important to understand the function of ecosystems with black alder and their dynamics. Tree rings can be used as a proxy of past environmental factors. The aim of the study was to determine the effects of meteorological and hydrological factors on radial growth of black alder at two study sites (Dursupe and Raķupe) in Latvia. The response of black alder trees to the influence of climatic and hydrological factors was found to depend on site conditions, i.e. a climatic effect was observed in conditions when the water level was low. Spatial variation in the strength of the relationship of black alder growth to temperature, precipitation, and river level suggests that alder growth is more susceptible to drought stress on higher river banks, where the water table is deeper. Black alder trees growing on low river banks can potentially be used to reconstruct past water-levels. Ūdens līmeņa un klimatisko faktoru ietekme uz melnalkšņa radiālo augšanu Melnalksnis (Alnus glutinosa (L.) Gaertn.) ir plaši izplatīta koku suga Eiropā un mērenās klimata zonas rietumu daļā. Latvijā melnalkšņu mežu daudzums ir ievērojami krities sakarā ar mežu nosusināšanu. Lai prognozētu nākotnes izmaiņas saistībā ar vides izmaiņām, ir ļoti svarīgi saprast ekosistēmu ar melnalksni funkcionēšanu un dinamiku. Koku gadskārtas var izmantot kā informācijas avotu par pagātnes vides faktoriem. Šī pētījuma mērķis bija noskaidrot meteorologisko un hidrologisko faktoru ietekmi uz melnalkšņa radiālo augšanu divās teritorijās Latvijā (Dursupe un Raķupe). Tika noskaidrots, ka melnalkšņa atbilde uz klimatisko un hidrologisko faktoru ietekmi ir atkarīga no vietas apstākļiem, tas ir, klimata ietekmes efekts novērojams apstākļos, kad ūdens līmenis bija zems. Sakarības starp melnalkšņa augšanu un temperatūru, nokrišņiem un ūdens līmeni telpiskā variācija norāda, ka melnalkšņa augšana ir vairāk pakļauta sausuma ietekmei uz augstākiem upju krastiem, kur ūdens līmenis ir zemāks. Melnalkšņi, kas auga uz zemiem upju krastiem, potenciāli var būt izmantojami ūdens līmeņu rekonstrukcijai par senākiem laika periodiem.

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.

Linking organismal growth, coping styles, stress reactivity, and metabolism via responses against a selective serotonin reuptake inhibitor in an insect

Evidence suggests that brain serotonin (5-HT) is one of the central mediators of different types of animal personality. We tested this assumption in field crickets Gryllus integer using a selective serotonin reuptake inhibitor (SSRI). Crickets were selected for slow and rapid development and tested for their coping styles under non-stressful conditions (time spent exploring a novel object). Resting metabolic rate, maximum metabolic rate and latency to resume activity were measured under stressful conditions (stress reactivity). Measurements were taken (i) before and (ii) during the SSRI treatment. Before the SSRI treatment, a strong negative correlation was observed between coping style and stress reactivity, which suggests the existence of a behavioral syndrome. After the SSRI treatment, the syndrome was no longer evident. The results of this study show that 5-HT may be involved in regulating behavior not only along a stress reactivity gradient but also along a coping styles axis. The relationship between personality and the strength and direction of 5-HT treatment on observed behaviors indicates trait-like individual differences in 5-HT signaling. Overall, these findings do not support recent ideas arising from the pace-of-life syndrome (POLS) hypothesis, which predict higher exploration and metabolic rates in rapidly developing bold animals.

Population Genetics of Latvians in the Context of Admixture between North-Eastern European Ethnic Groups

Abstract This article presents a review on population genetics of Latvians, which alongside Lithuanians are the two extant Baltic speaking populations. The article provides a description of genome-wide single nucleotide polymorphism (SNP) data and contains a comparative analysis of the results of studies performed on classical autosomal genetic markers, mitochondrial DNA (mtDNA) and the non-recombining part of the Y chromosome (NRY), with data on neighbouring populations. The study also covers data of recently performed ancient DNA (aDNA) studies carried out on samples from the territory of today’s Latvia. The results of population genetic studies have shown a mixture of eastern and western genetic traits in present-day Latvians with only small differences between Latvian subpopulations. Studies of the Baltic “tribal gene” LWb, as well as the gene’s SERPINA1 allele PIZ have indicated the presence of a considerable Baltic admixture in the neighbouring Finno-Ugric and Slavic populations. Although mtDNA analyses have shown that Latvians genetically in general belong to the same common gene pool as most of the Europeans, the Y-chromosomal lineage composition suggests that they are most similar to Northern and Eastern European populations of Lithuanians, Estonians, and Eastern-Slavic populations, which are ethnogenetically closest to them. The analysis of aDNA from the Early and Middle Neolithic did not present any genomic evidence of gene-flow from Central European farmers or any mitochondrial or Y-chromosomal haplogroups that are typical for them in the hunter-gatherers from the territory of today’s Latvia and Lithuania.

Macrophyte assessment in European lakes: Diverse approaches but convergent views of ‘good’ ecological status

Graphical abstract