Seasonal depth distribution and thermal experience of the non-indigenous round goby Neogobius melanostomus in the Baltic Sea: implications to key trophic relations

Biological Invasions - Native to the Ponto-Caspian region, the benthic round goby (Neogobius melanostomus) has invaded several European inland waterbodies as well as the North American Great Lakes...     

Structures determining bryophyte species richness in a managed forest landscape in boreo-nemoral Europe

Forest patches with high biological value are protected as woodland key habitats (WKH), which are identified by the presence of forest structures and indicator species. However, management for conservation needs to consider also managed forests as habitats for species. In this respect, there is a need to set quantitative targets for species and structures at different landscape scales. Due to non-intensive methods of forest management used prior to 1940 in Latvia, it might be expected that large areas of forest have developed structures that can support many species characteristic of natural forests. The aim of the study was to create a model that best described the richness of bryophyte species that are characteristic of natural forests, using forest structures as explanatory factors. The structures and bryophyte communities on living trees and coarse woody debris (CWD) were described in plots along transects blindly placed in areas dominated by State forests under commercial management. Explanatory variables related to tree species composition and tree size explained 54% of the variation in WKH indicator species richness on living trees. The best explanatory factors were maximum diameter of deciduous tree species and CWD. Low richness of total bryophyte and indicator species was found on dead wood, and the amount of variation in bryophyte species richness on CWD explained by explanatory variables was low. The study indicates the importance of deciduous tree substrate in managed forests in maintaining the spatial continuity of epiphytic species diversity. However, the forests in the managed forest landscape did not support high diversity of epixylic species, even in the WKHs, due to low diversity of suitable dead wood substrate.     

Pointer years in tree-ring width and earlywood-vessel area time series of Quercus robur—Relation with climate factors near its northern distribution limit

For a long time, radial growth of pedunculate oak (Quercus robur) in relation to environmental factors has been studied in Central Europe. However, there is insufficient information on oak growth in the Baltic region. Climate–growth interactions have been mostly investigated by correlation/response analysis between ring width and climatic factors. Other wood anatomical proxies, and also pointer year analysis, which focuses on weather extremes, can be sources of additional information. Wood samples were taken from 40 sites across Latvia. Tree-ring width (TRW) and mean area of earlywood vessels (EVA) were measured. To assess differences in wood formation among sites, a PCA was performed based on pointer year series of TRW and EVA per site. The relation with climate was assessed by Pearson's correlation. Patterns of wood formation differed along west/east gradient, so that two regions (western and eastern) of Latvia were distinguished. Pointer year values were higher for TRW than for EVA and higher in the eastern than in the western region. However, the pointer year values were moderate, suggesting that there was no strict limiting factor for their formation. Pointer years of EVA were strongly related with temperature during the dormant period in both regions; June precipitation had a significant effect in the eastern region. Pointer years of TRW were correlated with spring and summer temperature in the western region and with February temperature in the eastern region; precipitation in autumn showed a negative effect. These differences can be explained by a gradient from maritime to continental climate, leading to shifts in the growth limiting factors. Extremely cold winters resulted in most of the negative pointer years of TRW and EVA.     

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.     

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.