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Thermal variations due to global climate change are expected to modify the distributions of marine ectotherms, with potential pathogen translocations. This is of particular concern at high latitudes where cold-adapted stenothermal fish such as the Notothenioids occur. However, little is known about the combined effects of thermal fluctuations and immune challenges on the balance between cell damage and repair processes in these fish. The aim of this study was to determine the effect of thermal variation on specific genes involved in the ubiquitination and apoptosis pathways in two congeneric Notothenioid species, subjected to simulated bacterial and viral infections. Adult fish of Harpagifer bispinis and Harpagifer antarcticus were collected from Punta Arenas (Chile) and King George Island (Antarctica), respectively, and distributed as follows: injected with PBS (control), LPS (2.5 mg/kg) or Poly I:C (2 mg/kg) and then submitted to 2, 5 and 8 °C. After 1 week, samples of gills, liver and spleen were taken to evaluate the expression by real-time PCR of specific genes involved in ubiquitination (E3-ligase enzyme) and apoptosis (BAX and SMAC/DIABLO). Gene expression was tissue-dependent and increased with increasing temperature in the gills and liver while showing an opposite pattern in the spleen. Studying a pair of sister species that occur across the Antarctic Polar Front can help us understand the particular pressures of intertidal lifestyles and the effect of temperature in combination with biological stressors on cell damage and repair capacity in a changing environment.

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Human settlements within the Antarctic continent have caused significant coastal pollution by littering plastic. The present study assessed the potential presence of microplastics in the gastrointestinal tract of the Antarctic fish Harpagifer antarcticus, endemic to the polar region, and in the sub-Antarctic fish Harpagifer bispinis. H. antarcticus. A total of 358 microfibers of multiple colors were found in 89 % of H. antarcticus and 73 % of H. bispinis gastrointestinal track. A Micro-FTIR analysis characterized a sub-group (n = 42) of microfibers. It revealed that most of the fibers were cellulose (69 %). Manmade fibers such as microplastics polyethylene terephtalate, acrylics, and semisynthetic/natural cellulosic fibers were present in the fish samples. All the microfibers extracted were textile fibers of blue, black, red, green, and violet color. Our results suggest that laundry greywater discharges of human settlements near coastal waters in Antarctica are a major source of these pollutants in the Antarctic fish.

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Reproduction involves high energetic costs which are related to behaviour and gamete production. In females energy allocation to gamete production has been well documented. However, estimations of male investment in seminal material are scarce. The present study aims to assess and compare male investment in four brachyuran species by determining biochemical substrates present in the vasa deferentia to subsequently estimate energetic investment during the reproductive cycle. We identified two groups with contrasting energy investments. Two species, Homalaspis plana and Romaleon setosum, showed high investment due to significant quantities of proteins and lipids. Both species are characterised by large and complex vasa deferentia, and the formation of a remarkably large sperm plug deposited to the female after copulation as a sperm competition avoidance strategy. In contrast, Metacarcinus edwardsii and Taliepus dentatus invested little energy in their smaller-sized and simpler vasa deferentia. Morpho-functional traits may play a key role in determining the investment, which may also be influenced by mechanisms (i.e. mating tactics) to prevent sperm competition and the intensity of polygyny. This study emphasises the high amount of energy males invest in seminal material and highlights the diversity of mating strategies in Brachyura, which are reflected even on the physiological level.

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Dissolved oxygen (DO) and water temperature vary in coastal environments. In tropical regions, the ability of aquatic ectotherms to cope with hypoxia and high-temperature interactive effects is fundamental for their survival. The mechanisms underlying both hypoxia and thermal tolerance are known to be interconnected, therefore, the idea of cross-tolerance between both environmental stressors has been put forward. We investigated the combined role of hypoxia and temperature changes on the physiological responses of blue crab Callinectes sapidus living in the southern Gulf of Mexico. We measured oxygen consumption, plasmatic biochemical indicators, total hemocyte count (THC), and antioxidant activity biomarkers in muscle and gill tissues of blue crab acclimated to moderate hypoxia or normoxia and exposed to a thermal fluctuation or a constant temperature, the former including a temperature beyond the optimum range. Animals recovered their routine metabolic rate (RMR) after experiencing thermal stress in normoxia, reflecting physiological plasticity to temperature changes. In hypoxia, the effect of increasing temperature was modulated as reflected in the RMR and plasmatic biochemical indicators concentration, and the THC did not suggest significant alterations in the health status. In both DO, the antioxidant defense system was active against oxidative (OX) damage to lipids and proteins. However, hypoxia was associated with an increase in the amelioration of OX damage. These results show that C. sapidus can modulate its thermal response in a stringent dependency with DO, supporting the idea of local acclimatization to tropical conditions, and providing insights into its potential as invasive species.

RESUMO

The blue crab Callinectes sapidus is a widespread ectothermic species that supports large fisheries. Physiology of temperate and subtropical populations of blue crabs are well studied; however, a lack of information exists on tropical populations. Given the low locomotion capabilities of C. sapidus adult blue crabs, natural selection should favor traits that shape a particular thermal niche reflected through tolerance modulation to dissolved oxygen (DO). This study was designed to evaluate the thermal window and hypoxia sensitivity of the blue crab population in the southern Gulf of Mexico. The effect of acclimation temperatures from 20 °C to 34 °C on thermal preference (TP), critical thermal limits (CT), and thermal metabolic scope (TMS) was assessed in normoxia. Metabolic rate regulation over oxygen partial pressure (pO2) gradient was evaluated through oxygen consumption measurements at different degrees of acute hypoxia. Callinectes sapidus was observed tending to specialize towards higher temperatures, showing a mean TP from 26 °C to 33 °C. The lowest performance of aerobic pathways was observed at the coldest regimes and the highest at the warmest ones with mean TMS value being 35 % greater at 34 °C than 20 °C. Patterns for metabolic regulation were dependent on the interaction between environmental temperature and DO, in which the interval from 29 °C to 34 °C provoked a 50 % reduction in oxygen consumption when exposed to ∼20% air saturation levels. The results obtained showed that blue crabs distributed in the southern Gulf of Mexico could be close to their oxygen-temperature tolerance limits, which has important implications when climate change effects on species re-distribution is considered.

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The potential for biological colonization of Antarctic shores is an increasingly important topic in the context of anthropogenic warming. Successful Antarctic invasions to date have been recorded exclusively from terrestrial habitats. While non-native marine species such as crabs, mussels and tunicates have already been reported from Antarctic coasts, none have as yet established there. Among the potential marine invaders of Antarctic shallow waters is Halicarcinus planatus (Fabricius, 1775), a crab with a circum-Subantarctic distribution and substantial larval dispersal capacity. An ovigerous female of this species was found in shallow waters of Deception Island, South Shetland Islands in 2010. A combination of physiological experiments and ecological modelling was used to assess the potential niche of H. planatus and estimate its future southward boundaries under climate change scenarios. We show that H. planatus has a minimum thermal limit of 1°C, and that its current distribution (assessed by sampling and niche modelling) is physiologically restricted to the Subantarctic region. While this species is presently unable to survive in Antarctica, future warming under both 'strong mitigation' and 'no mitigation' greenhouse gas emission scenarios will favour its niche expansion to the Western Antarctic Peninsula (WAP) by 2100. Future human activity also has potential to increase the probability of anthropogenic translocation of this species into Antarctic ecosystems.

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Thermal and saline variations of the Southern Ocean are important signs of climate change which can alter the physiological responses of stenotic species residing at high latitudes. Our study aimed to evaluate the cellular stress response (CSR) of Harpagifer antarcticus subjected to increased ambient temperature and decreased salinity. The fish were distributed in different thermal (2, 5, 8, 11, and 14 °C) and saline (23, 28, and 33 psu) combinations for 10 days. We used qPCR analysis to evaluate the transcription of genes involved in the thermal shock response (HSP70, HSC70, HSP90, and GRP78), ubiquitination (E2, E3, ubiquitin, and CHIP), 26S proteasome complex (PSMA2, PSMB7, and PSMC1), and apoptosis (SMAC/Diablo and BAX) in the liver and gill. The expression profiles were tissue-specific and mainly dependent on temperature rather than salinity in the gill; meanwhile, in the liver, both conditions modulated the expression of these genes. Transcription of markers involved in the heat shock response was much higher in the liver than in the gill and was higher when salinity decreased and the temperature increased. Similarly, the genes involved in the ubiquitination pathway, 26S complex of the proteasome, and the apoptotic pathway showed the same pattern, being mainly induced in the liver rather than in the gill. This is the first study to show that this Antarctic fish can induce the cellular stress response in their tissues when subjected to these thermal/saline combinations.

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Global warming is having a significant impact around the world, modifying environmental conditions in many areas, including in zones that have been thermally stable for thousands of years, such as Antarctica. Stenothermal sedentary intertidal fish species may suffer due to warming, notably if this causes water freshening from increased freshwater inputs. Acute decreases in salinity, from 33 down to 5, were used to assess osmotic responses to environmental salinity fluctuations in Antarctic spiny plunderfish Harpagifer antarcticus, in particular to evaluate if H. antarcticus is able to cope with freshening and to describe osmoregulatory responses at different levels (haematological variables, muscle water content, gene expression, NKA activity). H. antarcticus were acclimated to a range of salinities (33 as control, 20, 15, 10 and 5) for 1 week. At 5, plasma osmolality and calcium concentration were both at their lowest, while plasma cortisol and percentage muscle water content were at their highest. At the same salinity, gill and intestine Na+ -K+ -ATPase (NKA) activities were at their lowest and highest, respectively. In kidney, NKA activity was highest at intermediate salinities (15 and 10). The salinity-dependent NKA mRNA expression patterns differed depending on the tissue. Marked changes were also observed in the expression of genes coding membrane proteins associated with ion and water transport, such as NKCC2, CFTR and AQP8, and in the expression of mRNA for the regulatory hormone prolactin (PRL) and its receptor (PRLr). Our results demonstrate that freshening causes osmotic imbalances in H. antarcticus, apparently due to reduced capacity of both transport and regulatory mechanisms of key organs to maintain homeostasis. This has implications for fish species that have evolved in stable environmental conditions in the Antarctic, now threatened by climate change.

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The information available on structures and function of reproductive systems are female-biased in many animal groups and crabs are not an exception. However, knowledge about the male reproductive system can help us to understand evolutionary and ecological processes such as the mating system and mating behavior. This study focuses on an integrative description of the principal regions of the male reproductive system of the purple crab, Homalaspis plana, a commercially exploited crab from the southeastern Pacific. For this description a combination of morphological observation, gravimetric records, histological and histochemical techniques and biochemical analysis were used. Also, a gross description of the seminal receptacle of the female was performed. The male reproductive system of H. plana was highly extended and complex, with a great capacity to produce and store spermatophores and secrete, at least, two kinds of seminal fluids. Sperm production, sperm packaging in spermatophores, storage of spermatophores and seminal liquid secretion were functions localized in specific regions. The vasosomatic index was the highest recorded to date in crabs, symptomatic of a high investment in reproduction. All these traits allow identification of H. plana as an internal sperm plug producer, which matches well with the highly extensible seminal receptacle of females. The great quantity of seminal material transferred to females during mating indicates that males may be able to mate only one time in the reproductive season and thus this species could be vulnerable to sperm depletion in males and sperm limitation in females if the fishery substantively reduced the abundance of males in the populations.

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Male-biased fishery management can provoke depletion of seminal reserves, which is the primary cause of sperm limitation. Therefore, identifying factors which contribute to the vulnerability to depletion of seminal reserves is a priority. The present study aimed to determine the effect of temperature on the recovery rate of sperm and seminal reserves after their depletion in Lithodes santolla, an important fishery resource in southern Chile. Sperm and seminal reserves were not fully recovered within 30 days. Temperature significantly affected seminal recovery: after 30 days the recovery index increased to 40% and 21% at 9°C and 12°C, respectively. The twice as fast seminal recovery at 9°C may be explained by the zone of origin of the individuals in this study (northern distributional limit), and 12°C may be close to the threshold of temperature tolerance. Lithodes santolla populations subject to intense male-only fisheries may be vulnerable to depletion of seminal reserves and a climate change scenario could additionally aggravate the risk of seminal depletion in L. santolla in its northern distributional limit.