Eurythermal Species Research Articles

Transcriptomic Analysis Reveals Dynamics of Gene Expression in Liver Tissue of Spotted Sea Bass Under Acute Thermal Stress.

The spotted sea bass (Lateolabrax maculatus), a eurythermal species, exhibits strong adaptability to temperature variations and presents an ideal model for studying heat stress-responsive mechanisms in fish. This study examined the liver transcriptome of spotted sea bass over a 24-h period following exposure to elevated temperatures, rising from 25 to 32°C. The results revealed significant alterations in gene expression in response to this thermal stress. Specifically, we identified 1702, 1199, 3128, and 2636 differentially expressed genes at 3, 6, 12, and 24h post-stress, respectively. Weighted Gene Co-expression Network Analysis (WGCNA) was used to identify specific gene modules responsive to heat stress, containing hub genes such as aco2, eci2, h6pd, suclg1, fgg, fga, fgb, f2, and apoba, which play central roles in the heat stress response. Enrichment analyses via KEGG and GSEA indicated that upregulated differentially expressed genes (DEGs) are predominantly involved in protein processing in the endoplasmic reticulum, while downregulated genes are primarily associated with the AGE-RAGE signaling pathways. Additionally, 272 genes exhibited differential alternative splicing, primarily through exon skipping, underscoring the complexity of transcriptomic adaptations. These findings provide deeper insights into the molecular responses to thermal stress and are crucial for advancing the breeding of heat-resistant strains of spotted sea bass.

New data on the species composition of freshwater algae and cyanobacteria of Kotelny Island, New Siberian Islands, Russian Federation

New data are obtained on the species composition of algae (excluding diatoms and silicascaled chrysophytes) and cyanobacteria in water bodies of Kotelny Island of the New Siberian Archipelago. A species list is provided for the 12 studied water bodies of the island, including 124 species and varieties. A taxonomic revision of the previously existing species list based on collections carried out on the island in 1947 is accomplished and combined with new data. The general species list contains 233 taxa, including 93 new species and varieties. A relatively high diversity of desmid algae has been established. The studied communities are characterized by a large number of cosmopolitan forms, a predominance of attached organisms and eurythermal species, as well as species indiff erent to the water fl ow speed. The trophic status of the studied water bodies of the island, the degree of their mineralization and the pH level of the environment are characterized using algal indication.

Assessment of the ecological state of the middle Irtysh based on the development of zooplankton at the present stage

Observations in 2021–2022 showed that the zooplankton community of the Irtysh River was formed by 33 species and two forms from three systematic groups: rotifers — 19, Cladocerans were represented by 12, copepods by 2 species from the order Cyclopoida and 2 species from the orders Harpactiformes and Calaniformes. The planktofauna of the river is represented by species common to water bodies of Western Siberia. The main part of rotifers belonged to typically planktonic eurythermal species. Among the cladocerans, along with planktonic species, there were also phytophilic and benthic forms. Average zooplankton indicators for the growing season of 2021 reached 3646 specimens/m3 in numbers and 70.7 mg/m3 in biomass. In 2022, the quantitative values were slightly lower: 2237 specimens/m3 and 40.4 mg/m3. Asplanchna priodonta Gosse and Mesocyclops leuckarti Claus were dominating species in spring, Bosmina longirostris O.F. Müller in summer, Alona intermedia Sars and Ceriodaphnia affinis Lillijeborg in autumn of both years accordingly. Waters of the Irtysh River is characterized mainly by the values of indicators corresponding to the α-mesosaprobic zone. The saprobity index in spring was 1.5, in summer and autumn — 1.6, which corresponds to moderately polluted waters. In terms of a set of zooplankton indicators, the water of the Irtysh River at the present stage is somewhat different from the previous low-water period in the beginning of this century. Currently, the number of species has increased, the structure of the community has changed, in which the dominance of branchous crustaceans has been noted, the biomass has significantly increased and the saprobity index has decreased, that is, the purity of water has increased. Qualitative and quantitative indicators of zooplankton, as well as the level of saprobity, are more consistent with the period of the second half of the last century.

Response of phytoplankton community structure to environmental changes in the coastal areas of northern China

In this study, we analyzed high-frequency data pertaining to phytoplankton and environmental factors in Jiaozhou Bay from December 10, 2004, to December 10, 2005 and from July 26, 2020, to August 1, 2021. Compared with 2004–2005, the abundance of phytoplankton during 2020–2021 presented a “two-peak pattern” of annual variation, and the number of species decreased significantly. The ecological types were dominated by eurythermal species, while cold-water species declined. The overall abundance showed a downward trend, and the peak period moved to a time with lower water temperature. This could be attributed to the increase in sea surface temperature. The increase in water temperature and intensification of eutrophication made the emergence of dominant species more inclined to be single; the diversity and stability of the community structure decreased. Generalized additive model (GAM) and network analysis showed that temperature was the main driving factor influencing the phytoplankton community structure, especially during the peak period. In addition, nitrogen and phosphorus were important factors influencing species composition and competitive advantage of phytoplankton.

Taxonomic diversity and biomass of the invertebrate fauna of nine drinking water treatment plants and their non-chlorinated distribution systems

Invertebrates such as Asellus aquaticus, halacarid mites, copepods and cladocerans are known to regularly occur in drinking water distribution systems (DWDS). An eight-year study investigated the biomass and taxonomic composition of invertebrates in the finished water of nine Dutch drinking water treatment plants (using surface water, ground water or dune-infiltrated water) and their non-chlorinated distribution systems. The main aims of the study were to examine the source waters’ influence on invertebrate biomass and composition in the distribution networks and to describe invertebrate ecology in relation to the habitat of filters and the DWDS.Invertebrate biomass of the finished drinking waters of the surface water treatment plants was significantly higher than in the finished waters of the other treatment plants. This difference was due to the higher nutrient levels of the source water. The main part of the biomass in the finished water of the treatment plants consisted of rotifers, harpacticoid copepods, copepod larvae, cladocerans and oligochaetes, which are small-sized, euryoecious and tolerate broad environmental conditions. Most of them reproduce asexually.Most species found in the DWDS are known to be detritivores, but all are benthic and euryoecious organisms, many of which have a cosmopolitan distribution. The euryoeciousness of these freshwater species was also shown by their occurrence in brackish waters and ground or hyporheic waters and the ability of many eurythermic species to overwinter in the DWDS habitat. These species are preadapted to the oligotrophic environment of the DWDS and can develop stable populations there. Most species can reproduce asexually and the sexually reproducing invertebrates (Asellus aquaticus, cyclopoids and probably also halacarids) have obviously overcome the potential problem of finding a mating partner. This study also showed a significant correlation of DOC in the drinking water with the invertebrate biomass. A. aquaticus was the dominant biomass component in six out of nine locations and was highly correlated with the Aeromonas counts in the DWDS. Thus, invertebrate monitoring in DWDS is an important additional parameter in understanding biological stability conditions in non-chlorinated DWDS.

First record of two urotsylid ciliates (Protozoa: Ciliophora: Spirotrichea) from Japan expanding the circumscription of species

ABSTRACT Two urostylid ciliates, Trichototaxis marina Lu et al., 2014 and Uncinata bradburyae (Gong et al., 2001) Luo et al., 2015, new to Japan, were collected from coastal water in Nagasaki. Both were identified based on live and protargol-stained specimens. Morphologically, two new populations of T. marina correspond well with the type population in the live morphology and ciliature, especially a very flexible body having a long elliptical shape, and reddish cell colour caused by irregularly shaped pigments, multiple left marginal rows and marine habitat. A few morphological features were supplemented for the species. The Japanese population of Uncinata bradburyae presents the diagnostic features, especially the presence of an anterior snout-like procession and the elongated membranelles in the proximal portion of adoral zone, orientation of the anterior portion of the left marginal row, highly developed transverse cirri, and high number of dorsal kineties derived from two unique, de novo formed anlagen. Additionally, greenish pigments were first documented for the species. The new record suggests U. bradburyae might be a eurythermal species. The overall pattern of the divisional events resembles that of the Qingdao population described previously. Part of the reorganisation was also first revealed for U. bradburyae, which corresponds to the divisional processes in the opisthe. The present study corroborates the wide distribution of both species, and contributes to circumscribe the species by expanding the range of some morphometric data.

Deer and climate change: impacts and perspectives

Climate change is one of the most important threats to biodiversity both for the relevance of the impacts and the speed of the process. Deer are widely affected by climate change even if the outcomes of the interaction with a given species are equivocal. Cold-adapted species are in general more susceptible to climate-change impacts, but even eurythermic species such as roe deer can be affected in their population dynamics. Both indirect effects, such as the mismatch between vegetation flushing and birth date, or the reduction of food accessibility, and direct ones, such as the impact of temperature causing heat stress, on activity rhythms, habitat selection and ultimately food intake, can have important consequences. In deer species, the ability to cope with these changes is dependent on the timing of resource acquisition, being different in capital and income breeder, but also on the breeding biology with special reference to the ability to shift reproduction in time. A number of consequences are caused by the impact of climate change on populations and individuals; notably, relevant shifts in species distribution have been described in different parts of the world. Moreover, changes in young and adult body size, in juvenile survival, in population dynamics and in the timing of biological cycles, such as rutting time or birth season, have been observed in a number of species. Changes in hunting regulations and management or conservation actions may be necessary to buffer the impacts of climate change, and some species or populations may be threatened with extinction or extirpation if proper measures of conservation are not adopted.

Response of the Black Sea Zooplankton to the Marine Heat Wave 2010: Case of the Sevastopol Bay

Global warming is increasing the frequency and severity of the marine heat waves, which poses a serious threat to the marine ecosystem. This study analyzes seasonal and interannual dynamics in the abundance and structure of the mesozooplankton community in Sevastopol Bay based on bi-monthly routine observations over 2003–2014. The focus is on the impact of the summer 2010 marine heat wave (MHW2010) on crustaceans belonging to different ecological groups. As a response to the MHW2010, three warm-water species (O. davisae, A. tonsa and P. avirostris) exhibiting the maximum seasonal density in latter summer showed a sharp increase in the annual abundance and their share in the mesozooplankton community. The increase in the annual abundance in 2010 of the eurythermal species P. parvus and P. polyphemoides exhibiting seasonal peaks in spring and autumn is not related to the MHW2010 but can be explained by a rise of temperature in the first part of the year. O. davisae and A. tonsa showed the most pronounced response among the species to the MHW2010, confirming that non-native species exhibited great flexibility as an adaptive response to environmental changes, especially in the case of climate warming. Among crustaceans observed in this study, O. davisae can be considered as an indicator of the environmental conditions associated with the warming of the Black Sea and the Mediterranean basin as a whole.

Sub‐seasonal correlation between growth and survival in three sympatric aquatic ectotherms

Animals experience seasonally changing conditions in temperate regions, thus population vital rates change seasonally. However, knowledge is lacking on patterns of seasonal correlation between growth and survival in sympatric ectotherms, and this knowledge gap limits our understanding of environmental change impacts on animal populations and communities. Here, we investigated sub‐seasonal (two‐month intervals) correlation between growth and survival in three stream fishes (bluehead chubNocomis leptocephalus, creek chubSemotilus atromaculatusand mottled sculpinCottus bairdii) in South Carolina, USA, via a mark–recapture survey over 28 months. We found that patterns of temporal correlation between the population vital rates differed among the sympatric species. Growth increased and survival decreased with water temperature in two eurythermal species, resulting in negative correlation between growth and survival. Growth peaked in sub‐seasons with an intermediate water temperature range in a third stenothermal species, while survival decreased with water temperature for this species too. Consequently, there was not significant negative or positive correlation between sub‐seasonal growth and survival in the stenothermal species. Body condition (weight at given length) decreased from May through November in all three species, providing a potential physiological explanation for why survival rates were lower during this period. Negative correlation among population vital rates stabilizes population size over time and buffers animal populations from environmental change because the vital rates are not affected simultaneously in the same direction, indicating some degree of resiliency in the face of climate changes in the two eurythermal species. However, such a demographic mechanism of resiliency could be maintained so long as climate warming does not exceed optimal growth temperature, above which negative correlation between growth and survival may no longer be maintained.

Distribution of zooplankton in Lake Aslikul (South Urals, Russian Federation)

Fauna of aquatic invertebrates from various biotopes of the mineralized Lake Aslikul of the Asly-Kul natural park was studied. Lake Aslikul is the largest body of water in the Republic of Bashkortostan, one of the largest lakes in the Middle Volga region. Crustaceans dominated (67%) in the zooplankton in terms of the number of species. Typical eurythermal species such as Keratella quadrata (Müller, 1786), Eudiaptomus gracilis (Sars, 1863), and E. graciloides (Lilljeborg, 1888) were recorded in the zooplankton, that thrived throughout the summer and autumn. Typical brackish-water species were encountered, for example, Hemidiaptomus ignatovi Sars, 1903. A specific community of zooplankters was formed in different biotopes of the lake: Daphnia galeata and Bosmina (E.) cf longispina (Leydig, 1860) were found in the pelagial; Pleuroxus aduncus (Jurne, 1820) and Eucyclops macruroides (Lilljborg, 1901) in macrophyte beds. The species inhabiting the deep-water part of the water body may be considered as indicators of oligo- and mesotrophic waters (Diaphanasoma brachyurum (Lievin, 1848), Bosmina (Eubosmina) cf. longispina Ley dig, 1860, and Bilpalpus hudsoni (Imhof, 1891)). Two rotifer species Rotaria rotatoria (Pallas, 1766) and Lecane (s. Str.) luna (Müller, 1776) were found only in macrophyte beds indicating mesotrophic conditions. In June and September 2010, the abundance of zooplankton throughout the entire lake varied from 1200 to 196 (on average, 484.3 ± 166.4) thousand individuals/m³, and the biomass from 13.6 to 0.9 (on average, 8.5 ± 2.5) g/m³. Crustaceans (78%) have also made the main contribution to the formation of quantitative indicators of zooplankton in various biotopes of the lake.

Thermal responses of two sub-Antarctic notothenioid fishes, the black southern cod Patagonotothen tessellata (Richardson, 1845) and the Magellan plunderfish Harpagifer bispinis (Forster, 1801), from southern South America

The Notothenioidei are a typical example of stenothermal fishes since most species have evolved and lived in Antarctic waters, where the water temperature is low and stable. This fact enabled them to evolve physiological characteristics related to cold. Nevertheless, some species came out of Antarctic waters a few million years ago and coped with more variable thermal regimes. This work aims to determine the thermal tolerance and preference of two sub-Antarctic notothenioid species found in Southern South America, Patagonotothen tessellata and Harpagifer bispinis, adding valuable information about thermal adaptation mechanisms. Experiments were conducted after exposing their juveniles for three weeks at 4, 7, 10 and 12 °C. Their thermal tolerance limits were established using the Critical Thermal Methodology and their acute thermal preferenda, employing a horizontal thermal gradient tank. Fishes acclimated to different exposure temperatures had small to intermediate thermal tolerance polygons (P. tessellata: 593.85°C2, H. bispinis: 475.40 °C2) and positive relationships between preferred and acclimation temperatures. The Final Temperature Preferenda were estimated to be 14.25 °C for P. tessellata and 13.05 °C for H. bispinis, allowing to characterize them as cold eurythermal species, with P. tessellata more tolerant to heat and H. bispinis more tolerant to cold. Their different thermal sensitivities are in agreement with their different thermal histories and distributions. In a climate change context, the increase of sea surface temperatures is likely to reduce the northern boundaries of their distributions. Conversely, it can potentially enhance both species’ performances at their southernmost distribution limits since those environments are cooler than their maximum thermal tolerances.

Effects of rearing temperature on egg incubation, growth, standard metabolic rate, and thermal tolerance of chocolate mahseer, Neolissochilus hexagonolepis.

The present study was aimed to assess the effect of temperatures on egg incubation, growth, standard metabolic rate (SMR), and thermal tolerance of a near threatened Himalayan hill stream chocolate mahseer (Neolissochilus hexagonolepis). For the hatching study, eggs were incubated in four temperatures (17, 20, 23, and 26°C). The total hatching and free-swimming larvae percentage were higher at 23°C (p<0.05). Experiment I (for validation of the CTmax method) was carried out by incubating eggs at 17°C and 23°C. The CTmax was estimated in response to different warming rates (1-18°C h-1), acclimation temperatures (17 and 23°C), and the age of fishes (8, 15, 35 dph). The results suggested that a warming rate of 18°C h-1 could be used for the thermal tolerance study of yolk-sac larvae (8 dph) and 35 dph larvae, but for free-swimming larvae (15 dph) up to 3°C h-1 is suitable. Experiment II (for growth, SMR and thermal tolerance) was carried by acclimatizing 15 dph larvae in five temperatures (15, 19, 23, 27, and 31°C) for 60 days. The mean growth rate increased with the increase in temperature from 15°C to 27°C (1.30-3.58% day-1) and decreased at 31°C. The mean SMR of the chocolate mahseer in the above acclimation temperatures was ranged from 1.14±0.36 to 2.81±0.15 μgO2h-1mg-1 and were significantly different (p<0.01). The Q10 with the SMR of the fish suggested the preferred temperature ranged between 23 and 27°C, and the optimum temperature for growth (ToptG) was estimated to be 25°C. Chocolate mahseer is an eurythermal species which is advantageous for aquaculture practices due to its wide thermal tolerance zone (411.68°C2 in 15 to 31°C acclimation temperature range) and high ARR values (0.49 - 0.54).

Current state and long-term changes in the mesozooplankton community of the Ukrainian and Georgian parts of the Black Sea as indicators of its ecological status

Water quality assessment is a key task of any measures in the field of water use, environmental management and protection. Thus, it is necessary to conduct systematic monitoring to assess the ecological state in the marine waters and to develop a strategy for its recovery. Anthropogenic impacts of various types leading to eutrophication and pollution of the Black Sea are changing the main characteristics of all components of the aquatic ecosystem. Zooplankton plays a key role in the pelagic food web. This article presents the results of the research on the state of zooplankton which was conducted during the Ukrainian-Georgian expedition in the framework of the international project “Emblas-plus” during 2016, 2017 and 2019. The ecological quality class of the investigated Black Sea waters was determined by the zooplankton integrated index (IZI). In Ukrainian waters in total, 49 taxa of zooplankton were registered. In 2017 taxonomic composition of zooplankton was more diverse (36 taxa in 2016, 35 in 2019). In Georgian waters in 2019, 40 taxa of mesozooplankton were registered, most of them are widespread forms in the Black Sea. The most diverse group is Crustacea (Cladocera and Copepoda).The most prevalent crustaceans were the eurythermic species, an important representative of forage zooplankton – Acartia (Acartiura) clausi Giesbrecht, 1889 and two thermophilic species of Calanoida – Acartia (Acanthacartia) tonsa Dana, 1849 and Centropages ponticus Karavaev, 1895. In Ukrainian waters average abundance and biomass of zooplankton in 2019 was similar to those in 2016 and much higher than in 2017. Dominant taxa and spatial distribution of zooplankton in 2019 were similar to those in 2016 and 2017. Average biomass of forage zooplankton in 2019 was approximately 10 times higher than in 2016 and 2017. In the Georgian coastal waters annual average abundance and biomass of mesozooplankton decreased, due to a sharp decline in the abundance of Noctiluca scintillans (Macartney) Kofoid &amp; Swezy, 1921. It was found that at most of the stations the dominant role in the formation of zooplankton biomass was played by the organisms of forage zooplankton. By the IZI index, the subdivision Northwestern Black Sea Bays had “Good”, “Poor” and “Moderate” water quality in spring, summer and autumn respectively. The subdivision’s deepwater shelf and shallow shelf had “Bad” water quality. The subdivision Danube-Dnieper interfluve coastal waters had “High” water quality. The Danube Avandelta area had “High”, “Good” and “High” water quality in spring, summer and autumn respectively. The best ecological class status was in 2019 and the worst – in 2016. The main tendencies in changes in the mesozooplankton community in the Black Sea are decrease in the percentage of N. scintillans in the total zooplankton biomass and increase in the percentage of Copepoda. Those tendencies indicate decrease in the pressure of the negative eutrophication factor and show positive changes in the forage base of commercial planktophagous fish and the ecological status of the Black Sea waters.

The upward elevational shifts of pond breeding amphibians following climate warming

While poorly dispersing taxa such as amphibians may have limited scope to track recent and rapid climate change by means of large range shifts, they may follow their climate envelope with short elevational shifts in mountain areas. Such elevational shifts are poorly documented by empirical data for amphibians. In this study, we analysed a 15-year data series on the distribution of three amphibian species (Bufo bufo, Triturus carnifex and Rana temporaria) inhabiting a mountain pond network in the southern Italian Alps, where temperatures have increased significantly over the last decades. By using multi-season occupancy models, we estimated the occupancy trend of each species over the study period and tested the occurrence of an actual elevational shift after accounting for the probability of false absence. The upper elevational limit of the two eurythermal species (B. bufo and T. carnifex) underwent a significant and progressive upward shift of ca. 200 m. Our results provide evidence of the ability of amphibians to perform rapid elevational shifts, great enough to track predicted rates of climate warming. Preserving and improving habitat connectivity between lowlands and highlands could safeguard the opportunity for such elevational migrations, but mountain aquatic habitats must be preserved in order to provide a safe refuge for amphibians escaping climate warming.

Improved mitochondrial function in salmon (Salmo salar) following high temperature acclimation suggests that there are cracks in the proverbial \u2018ceiling\u2019

Mitochondrial function can provide key insights into how fish will respond to climate change, due to its important role in heart performance, energy metabolism and oxidative stress. However, whether warm acclimation can maintain or improve the energetic status of the fish heart when exposed to short-term heat stress is not well understood. We acclimated Atlantic salmon, a highly aerobic eurythermal species, to 12 and 20 °C, then measured cardiac mitochondrial functionality and integrity at 20 °C and at 24, 26 and 28 °C (this species’ critical thermal maximum ± 2 °C). Acclimation to 20 °C vs. 12 °C enhanced many aspects of mitochondrial respiratory capacity and efficiency up to 24 °C, and preserved outer mitochondrial membrane integrity up to 26 °C. Further, reactive oxygen species (ROS) production was dramatically decreased at all temperatures. These data suggest that salmon acclimated to ‘normal’ maximum summer temperatures are capable of surviving all but the most extreme ocean heat waves, and that there is no ‘tradeoff’ in heart mitochondrial function when Atlantic salmon are acclimated to high temperatures (i.e., increased oxidative phosphorylation does not result in heightened ROS production). This study suggests that fish species may show quite different acclimatory responses when exposed to prolonged high temperatures, and thus, susceptibility to climate warming.

Фитоперифитон водотоков бассейна Белого моря (Мурманская область, Республика Карелия, Россия)

The results of phytoperiphyton studies in 92 watercourses of the White Sea basin are summarized and analyzed. Totally 540 taxa with a rank below the genus were identified. They belong to six divisions: Cyanophyta – 76, Ochrophyta – 374, Euglenophyta – 3, Dinophyta – 4, Rhodophyta – 8 and Chlorophyta – 75. Diatoms, cyanobacteria and chlorophytes form the basis of the species diversity (&gt; 90%) in all studied rivers. The predominance of these groups reflects the specificity of the phytoperiphyton in the river systems of the boreal and subarctic zones. Leading families are Naviculaceae (174 species), Achnanthaceae (45), Desmidiaceae (43) and Fragilaceaceae (36). Together they cover 337 species or 65% of the total number of species found. The group of leading genera (187 species, 35%) includes Eunotia – 36 species, Achnanthes – 33, Navicula – 48, Pinnularia – 39, and Cymbella – 31 species. The heterogeneity of the climatic regime in the study area determines the simultaneous presence in the algae flora of widespread eurythermic species characteristic of the taiga zone, stenothermic rheophiles of alpine origin and the boreal complex typical of wetlands. The dominant complex is represented by a small number of species resistant to dynamic water loading. It is noted that the ecological-geographical spectra of algae are dominated by widespread oligogalobic species, acidophilic or indifferent to the pH of the medium. The relative importance of indicator species in the formation of groupings allows to refer the waters of the studied watercourses and reservoirs to the second class of purity.

Comparative thermal ecology parameters of the mexican dusky rattlesnake (Crotalus triseriatus).

Montane habitats exhibit a high degree of thermal heterogeneity, and thus provide considerable thermoregulatory challenges for ectotherms. Comparative analyses provide an opportunity to understand how variation in abiotic factors (e.g., operative temperatures, thermal quality) can affect life history traits within species. We studied the thermal ecology of three populations of the rattlesnake Crotalus triseriatus inhabiting different volcanoes in the central region of Mexico using the Hertz et al. (1993) protocol. The average body temperature of dusky rattlesnakes from the three study sites was 22.4°C; mean active body temperature was higher in site 2 than in sites 1 and 3, but no differences between females, males and juveniles nor an interaction among site and sex was found. The thermal quality was low in the three sites, particularly in sites 1 and 3. Thermoregulation accuracy statistically differed among populations: individuals from site 2 were more accurate thermoregulating, while individuals from site 1 were the least accurate. Compared to other snakes, dusky rattlesnakes can be considered as a eurythermic species, which can often be active at relatively low body temperatures.

Generation studies on benthic amphipod-Quadrivisio bengalensis, Stebbing (Gammaridae) from the Kochin Estuary, Southwest coast of India.

Quadrivisio bengalensis (Stebbing Records of Indian Museum, 1, 159-161, 1907), a eurythermal (26.5-32.2 °C) and euryhaline (0.10-26.2 psu) tropical species, makes a profound contribution as a fodder organism to the benthic biomass of tropical backwaters. Studies on life span, variations in broods, fecundity, sex ratio, brooding behaviour, brood stock assessment, growth rate, antennal segments as an index of growth, moulting frequency, mortality and starvation resistance of Q. bengalensis were made for the first time under controlled laboratory conditions of 12-h photo period for 252 days on 8 pairs of specimens (male and female) collected from the field and their successive broods. The life span of females was found to be higher (maximum 220 days) than males (maximum 175 days). Number of broods varied between 5 and 15, depending on the "status of the brood" (early or late). The maximum number of juveniles in a single brood was 24 and that by a single female over the entire life span was 211. The incubation time varied between 6 and 9 days and the duration of moults (8-18 days) was found to increase with the age of the animals. Maximum growth is usually attained by the offspring arising from the 5th to 7th broods. The 4th to 7th broods were the optimal broods for the maximum number of females attaining maturity. For broods 3 to 7 of the parental set, probability of extinction (ξ) calculated on applying stochastic branching process to generation studies for the first time showed an increasing trend with number of broods while a decreasing trend for ξ for 8th and 9th broods, with least ξ for broods 5 to 7 of the 5th, 6th and 7th generations, suggesting life span and fecundity rates as functions of the "brood status" (early or late). Whether it is true with higher crustaceans remains to be explored.

SPATIAL DISTRIBUTION AND ECOLOGY OF EELPOUT LYCODES BRASHNIKOVI (ZOARCIDAE) AT THE WESTERN COAST OF KAMCHATKA IN SUMMER SEASON

Eelpout Lycodes brashnikovi is a common species of bottom ichthyofauna in the waters at West Kamchatka. It distributes through the whole surveyed area, with sporadic dense aggregations at the depths of 50–150 and 200–300 m. It is an eurythermic species. Adult fish with the length 36–45 cm prevail in its trawl catches (on average 59.3 %); its maximum length is 52 cm. Catches of other species from the family Zoarcidae are insignificant on the shelf of West Kamchatka in summer, so Lycodes brashnikovi is considered as the most numerous representative of this family in this season.

Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species

Mitochondrial respiration is a multi-step pathway that involves matrix and membrane-associated enzymes and plays a key role in acclimation to variable environmental conditions, but until now it has not been clear which of these steps would be most important in acclimation to changing temperatures and CO2 levels. Considering scenarios of ocean warming and acidification we assessed the role and limitation to phenotypic plasticity in the hearts of two Gadoid species adapted to different thermal ranges: the polar cod (Boreogadus saida), an Arctic stenotherm, and the Northeast Arctic population of Atlantic cod (NEAC, Gadus morhua), a cold eurytherm. We analysed the capacity of single enzymes involved in mitochondrial respiration [citrate synthase (CS), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO)], the capacity of the electron transport system and the lipid class composition of the cellular membranes. Juveniles of the two species were held for four months at four temperatures (0, 3, 6, 8 °C for polar cod and 3, 8, 12, 16 °C for NEAC), at both ambient and elevated $$P_{{{\text{CO}}_{2} }}$$ (400 µatm and 1170 µatm, respectively). Polar cod showed no changes in mitochondrial enzyme capacities and in the relative lipid class composition in response to altered temperature or elevated $$P_{{{\text{CO}}_{2} }} .$$ The lack of cardiac cellular plasticity together with evidence at the whole-animal level coming from other studies is indicative of little or no ability to overcome stenothermy, in particular during acclimation to 8 °C. In contrast, eurythermal NEAC exhibited modifications of membrane composition towards a more rigid structure and altered enzyme capacities to preserve functionality at higher temperatures. Furthermore, in NEAC, the capacities of SDH, CCO and CS were increased by high levels of CO2 if combined with high temperatures (12 and 16 °C), suggesting the compensation of an inhibitory effect. These results indicate that the cold eurythermal species (NEAC) is able to alter its mitochondrial function to a far greater extent than the Arctic stenotherm (polar cod), indicating greater resilience to variable environmental conditions. This difference in plasticity may underpin differences in the resilience to climate change and affect future species distributions and, eventually, survival.