Modification of the "acute" method for calculating the final preferred temperatures: As applied to Daphnia longispina (Crustacea: Cladocera).

Given the global temperature anomalies observed in recent years, knowing the temperature preferences of ectotherms is very important. The purpose of this study was to determine the final preferred temperature (FPT) and the preferred temperature (PT) range in non-acclimated animals in comparison with acclimated animals, as well as with data obtained by the gravitational method using the example of Cladocera Daphnia longispina. For the first time, the FPT in D. longispina was determined by the "acute" and gravitational methods (18.4 and 18.8 ± 1.7 °C, respectively). We showed that it is possible to calculate the PT range from the standard deviations and/or confidence intervals of PT linear regression that cross the line of equality. The range of PT for acclimated D. longispina obtained by the "acute" method was 17.5-19.4 °C and 16-22 °C as calculated by the gravitational method. The ranges of pejus (7-15 and 23-24 °C) and avoided (3-6 and 25-27 °C) temperatures were also determined. The possibility of using the "acute" method for determining FPT in animals selected from natural habitats without prior acclimation has been shown.

Biomarkers in bivalve mollusks and amphipods for assessment of effects linked to cyanobacteria and elodea: Mesocosm study.

The effects of cyanobacteria (Aphanizomenon flos-aquae (90%), Microcystis aeruginosa) and dense Elodea canadensis beds on the health endpoints of the amphipod Gmelinoides fasciatus and bivalve mollusc Unio pictorum were examined in mesocosms with simulated summer conditions (July-August 2018) in the environment of the Rybinsk Reservoir (Volga River Basin, Russia). Four treatments were conducted, including one control and three treatments with influencing factors, cyanobacteria and dense elodea beds (separately and combined). After 20 days of exposure, we evaluated the frequency of malformed and dead embryos in amphipods, heart rate (HR) and its recovery (HRR) after stress tests in molluscs as well as heat tolerance (critical thermal maximum or CTMax) in both amphipods and molluscs. The significant effect, such as elevated number of malformed embryos, was recorded after exposure with cyanobacteria (separately and combined with elodea) and presence of microcystins (MC) in water (0.17 µg/l, 40% of the most toxic MC-LR contribution). This study provided evidence that an elevated number (>5% of the total number per female) of malformed embryos in amphipods showed noticeable toxicity effects in the presence of cyanobacteria. The decreased oxygen under the influence of dense elodea beds led to a decrease in HR (and an increase in HRR) in molluscs. The notable effects on all studied biomarkers, embryo malformation frequency and heat tolerance in the amphipod G. fasciatus, as well as the heat tolerance and heart rate in the mollusc U. pictorum, were found when both factors (elodea and cyanobacteria) were combined. The applied endpoints could be further developed for environmental monitoring, but the obtained results support the importance of the combined use of several biomarkers and species, especially in the case of multi-factor environmental stress.

Thermal tolerance of Cyclops kolensis lilljeborg, 1901 (Copepoda: Cyclopoida) and its relationships with pessimal to optimal performance.

Cyclops kolensis Lilljeborg, 1901 belongs to the Arctic complex of Palaeoarctic species, yet in the past 20 years, its occurrence has extended to the summer months in waterbodies with high water temperatures. This species is considered one of the most active migrants from the northern waterbodies in the Volga reservoir cascade to the Volga delta. Here, we explored the ranges of the preferred and avoidance temperatures of C. kolensis from two geographically isolated populations. Thermal tolerance was measured in a thermogradient installation and compared to the temperatures at which members of these populations occurred in their source waterbodies. Temperature preference was determined using the "chronic" method. Individuals of C. kolensis possessed a bimodal final temperature preferendum of 2-6 °C and 13-21 °C, which corresponds to the optimal thermal conditions of the species in a pond. These ranges were the same for individuals of both populations irrespective of the geographical location and water temperature of their source waterbodies. The temperature range of normal performance was 2-4 to 21-25 °C, and the pessimal temperature ranges were from 1 - 2 to 3-4 °C and from 22-25 °C to 26-30°Ð¡. These temperature ranges coincide with field observations over a recent 20-year period of temperature conditions under which the species develops in nature. Our results allow us to characterize C. kolensis as an ecologically plastic species, which, despite its strong association with the cold-water Complex species, is adapting to a wider temperature range as global warming occurs.

The preferred and avoidance temperatures of Thermocyclops crassus (Fischer, 1853) and their relation to the temperature of optimal, pessimal and normal performance of the species.

The ranges of the preferred and avoided temperatures in representatives of Thermocyclops crassus (Fischer, 1853) were determined by the results of experimental testing in a thermogradient aparatus and comparison of the obtained values with field observations of the optimal, pessimal and tolerated temperature conditions of development of these populations in nature. Copepods were sampled from pond located near Borok, Yaroslavl region, Russia (58o02'57'' N; 38o14'56'' E). The ambient water temperature was 15.0°Ð¡. Temperature preference was determined by the "chronic" method. The phenology of development of Th. crassus was observed in the field of water bodies in Central and Volga Federal Districts of Russia. The final thermal preferendum (FTP) achievement occurred with an increase in the preferred temperature: when animals were placed at a temperature in the thermal gradient (14.0-15.0°C) that approximated the temperature of the source pond, they moved to warmer water until they chose FTP (26.7°C). Obtained the values of FTP (25-30°C), temperature of normal performance (21-32°C) and pessimal temperatures of 9-20 and 33°Ð¡ well coincide with numerous field observations for temperature conditions of development of species in northern waterbodies of Holarctic and with the temperatures at which populations of Th. crassus thrive in southern waterbodies of Holarctic and in tropical lakes. It is concluded that, despite the historically long existence of the species in the reservoirs of the temperate climatic zone, the northern populations of Th. crassus retained the temperature responses characteristic of their southern sister populations. And although the species has adapted to life in northern reservoirs at lower temperatures, when it becomes possible to choose, cyclops prefer temperatures above 25°C, which are optimal for southern populations living in tropical waters. These data once again confirm that the horizontal thermal gradient method can be used to infer temperature tolerance of freshwater cyclopoid copepods in nature.