Hybridization in the Anthropocene - how pollution and climate change disrupt mate selection in freshwater fish.

Chemical pollutants and/or climate change have the potential to break down reproductive barriers between species and facilitate hybridization. Hybrid zones may arise in response to environmental gradients and secondary contact between formerly allopatric populations, or due to the introduction of non-native species. In freshwater ecosystems, field observations indicate that changes in water quality and chemistry, due to pollution and climate change, are correlated with an increased frequency of hybridization. Physical and chemical disturbances of water quality can alter the sensory environment, thereby affecting chemical and visual communication among fish. Moreover, multiple chemical compounds (e.g. pharmaceuticals, metals, pesticides, and industrial contaminants) may impair fish physiology, potentially affecting phenotypic traits relevant for mate selection (e.g. pheromone production, courtship, and coloration). Although warming waters have led to documented range shifts, and chemical pollution is ubiquitous in freshwater ecosystems, few studies have tested hypotheses about how these stressors may facilitate hybridization and what this means for biodiversity and species conservation. Through a systematic literature review across disciplines (i.e. ecotoxicology and evolutionary biology), we evaluate the biological interactions, toxic mechanisms, and roles of physical and chemical environmental stressors (i.e. chemical pollution and climate change) in disrupting mate preferences and inducing interspecific hybridization in freshwater fish. Our study indicates that climate change-driven changes in water quality and chemical pollution may impact visual and chemical communication crucial for mate choice and thus could facilitate hybridization among fishes in freshwater ecosystems. To inform future studies and conservation management, we emphasize the importance of further research to identify the chemical and physical stressors affecting mate choice, understand the mechanisms behind these interactions, determine the concentrations at which they occur, and assess their impact on individuals, populations, species, and biological diversity in the Anthropocene.

Complex hybridization between deeply diverged fish species in a disturbed ecosystem.

Over the past two decades researchers have documented the extent of natural hybridization between closely related species using genomic tools. Many species across the tree of life show evidence of past hybridization with their evolutionary relatives. In some cases, this hybridization is complex-involving gene flow between more than two species. While hybridization is common over evolutionary timescales, some researchers have proposed that it may be even more common in contemporary populations where anthropogenic disturbance has modified a myriad of aspects of the environments in which organisms live and reproduce. Here, we develop a flexible tool for local ancestry inference in hybrids derived from three source populations and describe a complex, recent hybridization event between distantly related swordtail fish lineages (Xiphophorus) and its potential links to anthropogenic disturbance.

The health and condition responses of Delta Smelt to fasting: A time series experiment.

There is an extensive literature establishing, validating, and quantifying a wide range of responses of fishes to fasting. Our study complements this work by comparing fed and unfed treatments of hatchery-raised Delta Smelt (Hypomesus transpacificus)-an imperiled fish that is endemic to the San Francisco Estuary and its tributaries in California, USA-across a diverse suite of endpoints over a two-month time series. The experiment was conducted at 15.9°C, and individuals were sampled at 12 time points as starvation became increasingly severe. We found that hepatosomatic index and condition factor were relatively sensitive to starvation, becoming significantly depressed at Day 4 and 7, respectively. Histological analysis of liver showed elevated cytoplasmic inclusion bodies at Day 7, followed by increased glycogen depletion, single cell necrosis, and hydropic vacuolar degeneration at Day 14, 21, and 28, respectively. Of four antioxidants measured, glutathione decreased at Day 4, superoxide dismutase increased at Day 14, catalase increased at Day 56, and glutathione peroxidase was not affected by starvation. The net result was a ~2-fold increase in lipid peroxidation (malondialdehyde) in fasted fish that was highly inconsistent through time. RNA to DNA ratio and triglycerides in muscle were relatively insensitive to starvation, only consistently decreasing with fasting after mortality began increasing in the 'No Feeding' treatment, at Day 21. Together, these results suggest that Delta Smelt mobilize hepatic energy stores far more rapidly than lipids in muscle when subjected to fasting, leading to rapid atrophy of liver and the development of cytoplasmic inclusion bodies-possibly autophagosomes-in hepatocytes.

Sub-lethal effects of herbicides penoxsulam, imazamox, fluridone and glyphosate on Delta Smelt (Hypomesus transpacificus).

Concerns regarding non-target toxicity of new herbicides used to control invasive aquatic weeds in the San Francisco Estuary led us to compare sub-lethal toxicity of four herbicides (penoxsulam, imazamox, fluridone, and glyphosate) on an endangered fish species Delta Smelt (Hypomesus transpacificus). We measured 17ß-estradiol (E2) and glutathione (GSH) concentrations in liver, and acetylcholinesterase (AChE) activity in brain of female and male fish after 6 h of exposure to each of the four herbicides. Our results indicate that fluridone and glyphosate disrupted the E2 concentration and decreased glutathione concentration in liver, whereas penoxsulam, imazamox, and fluridone inhibited brain AChE activity. E2 concentrations were significantly increased in female and male fish exposed to 0.21 µM of fluridone and in male fish exposed to 0.46, 4.2, and 5300 µM of glyphosate. GSH concentrations decreased in males exposed to fluridone at 2.8 µM and higher, and glyphosate at 4.2 µM. AChE activity was significantly inhibited in both sexes exposed to penoxsulam, imazamox, and fluridone, and more pronounced inhibition was observed in females. The present study demonstrates the potential detrimental effects of these commonly used herbicides on Delta Smelt.

Effects of low levels of ultraviolet radiation on antioxidant mechanisms of Japanese Medaka (Oryzias latipes).

Extreme weather events like drought are expected to increase with climate change, which will increase exposure of freshwater fish to ultraviolet (UV) radiation. Compared to fully grown adult fish, fish in early life stages are more susceptible to UV radiation due to the lack of well-developed pigmentation. Even though several studies have described affectation of fish health after exposure to UV radiation, most of the studies have used intensities that are only found on the surface of the earth crust or at shallow depths in water bodies, and little is known about impacts of weaker UV radiation, which can be found in deep water. This study showed effects on the antioxidant system of Japanese Medaka after 7 days of exposure to very low intensities of UV radiation, levels that can be found at deep locations in lakes and rivers. Exposure to UV radiation (UVA: 360.1 ± 18.4 µW cm-2 for a dose of 21.6 ± 1.2 mJ cm-2 min-1, and UVB: 6.3 ± 0.5 µW cm-2 for a dose of 0.38 ± 0.03 mJ cm-2 min-1) caused a reduction in the catalase activity (over 50%) and enhanced oxidative damage to lipids. Results of this study showed that environmentally relevant, low levels of UV radiation affect mechanisms by which fish deal with enhanced production of reactive oxygen species and oxidative damage. The results raise concerns about early life stages of fish under scenarios of increased exposure to solar light, such as in tropic regions or during summer in temperate regions.

Impairment of antioxidant mechanisms in Japanese Medaka (Oryzias latipes) by acute exposure to aluminum.

Increasing aluminum (Al) concentrations in aquatic habitats as a result of anthropogenic acidification and industrialization is a global issue. Moreover, in extensive areas of the humid tropics and subtropics, high Al concentrations in freshwater are observed because of both naturally low pH and high Al concentrations in soil. Al increases production of reactive oxygen species and enhances oxidative damage in mammals. However, no studies have examined the effect of environmentally relevant concentrations of Al at low pH on oxidative stress in fish. This study assessed Al-induced effects on enzymatic and non-enzymatic antioxidants, lipid peroxidation, and on expression of oxidative stress-related genes at low pH using Japanese Medaka (Oryzias latipes). Larval fish were exposed to dissolved Al concentrations of 0, 1.7, 6.2 and 16.7µgL-1 for 4days at pH5.3 in soft water. Al caused a significant reduction in activity of glutathione peroxidase at 6.2 and 16.7µgL-1, and of glutathione reductase at 16.7µgL-1 in whole body homogenates. No changes were observed in the expression of the glutathione peroxidase gene, and expression levels of the glutathione reductase gene were too low to be quantitated. Even though there was an overall decrease in the activity of catalase and in the concentration of glutathione, differences were not significant compared to the control. Changes in lipid peroxidation were not found. This study showed that exposure to environmentally relevant concentrations of Al at low pH impairs antioxidant defense mechanisms of Medaka.

Effects of prolonged exposure to low pH on enzymatic and non-enzymatic antioxidants in Japanese Medaka (Oryzias latipes).

Acidification in aquatic ecosystems is a major concern worldwide. In freshwater, although there are several publications reporting acute toxicity and adverse effects due to low pH, little is known about adverse effects on antioxidant mechanisms in fish after prolonged exposure. This study aimed to investigate how antioxidants are affected by raising larval Japanese Medaka (Oryzias latipes) in soft water at pH5.5, 6.0, and 6.5. After 18days of exposure, glutathione concentration and glutathione peroxidase activity in whole body homogenates increased as pH decreased, without changes in lipid peroxidation measured as thiobarbituric acid reactive substances. This study showed that prolonged exposure to low pH increased reactive oxygen species production and that fish cope with it by increasing levels of enzymatic and non-enzymatic antioxidants.

Use of sodium chloride and zeolite during shipment of Ancistrus triradiatus under high temperature

The use of sodium chloride (0.5 g/L and 1 g/L) and zeolite (22.7 g/L) during shipment (48 h) of Ancistrus triradiatus at high temperatures (between 24.5 and 34ºC) were evaluated. Several water quality parameters (dissolved oxygen, pH, conductivity, and total ammonia) were measured before and after shipment. Glycemia was measured before shipment and at 24 and 48 h after shipment. After shipment, a resistance test was carried out in a high concentration of sodium chloride, and mortality was recorded after shipment, and 7 days post-shipment. While the two evaluated substances increased survival of A. triradiatus challenged by high temperatures during shipment, the best result was obtained with 1 g/L of sodium chloride.

O uso de cloreto de sódio (0,5 g/L e 1 g/L) e zeolita (22,7 g/L) foram avaliados durante o transporte (48 h) de Ancistrus triradiatus em altas temperaturas (entre 24,5 e 34ºC). Os seguintes parâmetros foram monitorados: pH, oxigênio dissolvido, condutividade e amônia antes e depois do transporte. Também foi mensurada a concentração de glicose no sangue antes do transporte e 0, 24 e 48 h após o transporte. Foi realizado um teste de resistência a altas concentrações de cloreto de sódio após o transporte, sendo registrada a mortalidade no final do transporte e após 7 dias. As duas substâncias testadas aumentam a sobrevivência de A. triradiatus a altas temperaturas durante o transporte, porém o melhor resultado foi obtido com o uso de 1 g/L cloreto de sódio.

Acute toxicity and histopathological alterations of Roundup® herbicide on "cachama blanca" (Piaractus brachypomus) / Toxicidade aguda e alterações histopatológicas induzidas pelo herbicida Roundup® em pirapitinga (Piaractus brachypomus)

Acute toxicity of the glyphosate -N (phosphonomethyl) glycine- herbicide, Roundup®, in juveniles of cachama blanca, (Piaractus brachypomus), was evaluated and the histopathological lesions were assessed. The 96 h lethal concentration 50 was 97.47mg.L-1 (P<0.05). In the gill, necrotic and proliferative lesions were detected. In the liver, congestion, degenerative foci, hyaline droplets and lipidic vacuolization of the hepatocytes were observed. In the stomach mild hyperplasia of mucous cells was detected, which was also observed in the skin. In this latter tissue, a large increase in the thickness of the epidermis with necrotic lesions, infiltration of leukocytes and melanin pigment were observed. In the brain, degenerative foci of neuronal bodies in the telencephalon associated with gliosis and infiltration of eosinophilic granule cells/mast cells were shown. In conclusion, gills, liver, skin and brain are susceptible to Roundup®. Moreover, effects on the central nervous system could affect olfaction as well as individual and group behavior, the reproductive performance of the fish and hence have repercussions at the population level.

Este estudo avaliou a toxicidade aguda e as alterações histopatológicas induzidas pelo glifosato -N (fosfometil) glicina, na formulação Roundup® em juvenis de pirapitinga (Piaractus brachypomus) expostos durante 96 horas. A concentração letal 50 foi de 97.47mg.L-1 (P<0.05). Nas brânquias foram achadas lesões proliferativas e necróticas. No fígado foi observada congestão, processos degenerativos, gotas hialinas e presença de vacúolos lipídicos nos hepatócitos. No estomago e na pele foi detectada hiperplasia ligeira das células de moco. Nesta ultima, adicionalmente foi observado engrossamento da epidermes com lesões necróticas, infiltração de células leucocitárias e acumulação de melanina. No cérebro foram observados focos de degeneração de somas neurais na região do telencéfalo junto com gliose e infiltração de células granulais eosinofilicas/células mast. Concluindo, as brânquias, o fígado, a pele e o cérebro são órgãos suscetíveis ao Roundup®. Adicionalmente, os efeitos sobre o sistema nervoso central poderiam reduzir a olfação nos peixes, tanto como o comportamento grupal e individual, a performance reprodutivo e desta forma, repercutir no nível populacional.

Evaluación de los efectos tóxicos y concentración letal 50 del surfactante Cosmoflux® 411F sobre juveniles de cachama blanca (Piaractus brachypomus) / Assessment of toxic effects and lethal concentration 50 of surfactant Cosmoflux® 411F on juveniles of cachama blanca (Piaractus brachypomus)

En Colombia, el surfactante Cosmoflux® 411F es usado en fumigaciones de cultivos ilícitos para mejorar la efectividad del glifosato. El uso del Cosmoflux® 411F no está soportado por estudios toxicológicos. Los objetivos del presente trabajo fueron determinar las lesiones anatomopatológicas derivadas de la exposición al Cosmoflux® 411F y establecer la concentración letal 50 (CL50) a 96 horas en cachama blanca (Piaractus brachypomus). Se utilizaron juveniles de cachama blanca (40 g) en dos experimentos: 1) toxicidad subletal (n =126) y, 2) determinación de la CL50 (n =84). Las concentraciones del ensayo de toxicidad subletal fueron: 0 mg/l (Tratamiento 0), 0.17 mg/l (Tratamiento 1), 0.34 mg/l (Tratamiento 2), 0.68 mg/l (Tratamiento 3), 1.36 mg/l (Tratamiento 4), y 2.72 mg/l (Tratamiento 5), en sistema semiestático. Para determinar la CL50 las dosis fueron: 3000, 3450, 3900, 4350 y 4800 mg/l de Cosmoflux® 411F. La CL50 obtenida fue de 4417.99 mg/l. En los peces se evidenció leve disminución de la actividad de nado. A la necropsia se halló palidez del hígado y acumulación de material mucoso en las branquias. Por histopatología se halló: vacuolización de hepatocitos, hiperplasia de células epiteliales, de cloro y caliciformes branquiales, vacuolización de enterocitos, aumento de centros melanomacrófagos renales, gliosis, degeneración neuronal e infiltración de células granulares eosinofílicas/células mastocitos en telencéfalo. Los hallazgos concuerdan con lo reportado en peces expuestos a surfactantes, exceptuando las lesiones del sistema nervioso central que pueden tener consecuencias sobre interacciones sociales, de alimentación y reproducción de la especie; siendo necesario profundizar la investigación sobre dicho efecto. El hígado, branquias y piel constituyen órganos blanco de la acción tóxica. La CL50 hallada (4417.99 mg/l) es alta comparada con lo reportado en surfactantes no-iónicos.

In Colombia, surfactant Cosmoflux® 411F is used for the fumigation of illicit crops in order to improve the glyphosate herbicide activity. The use of Cosmoflux® 411F is not supported by toxicological surveys. The aims of this study were to determinate the anatomopathological lesions due to the exposure to Cosmoflux® 411F and to establish lethal concentration 50 (LC50) to 96 hours in cachama blanca (Piaractus brachypomus). Juveniles of cachama blanca (40 g) in two assays were used: 1) sublethal toxicity (n= 126) and 2) determination of LC50 (n=84). Sublethal toxicity assay concentrations were: 0 mg/l (Treatment 0) 0.17 mg/l (Treatment 1), 0.34 mg/l (Treatment 2), 0.68 mg/l (Treatment 3), 1.36 mg/l (Treatment 4), and 2.72 mg/l (Treatment 5); through semi-static system. For the determination of LC50 of Cosmoflux® 411F 3000, 3450, 3900, 4350 y 4800 mg/l concentrations were used. LC50 was 4417.99 mg/l. Animals showed slight decrease in swimming activity. At necropsy examination were found paleness in liver and whitish material accumulation in top of gill filament. Histopathologically, it was found fatty degeneration and hepatocyte vacuolization, epithelial cells, chloride cells and mucous cells hyperplasia, enterocyte vacuolization, increase in the expression of melanomacrophage centres in kidney, gliosis, neuronal degeneration and infiltration of eosinophilic granule cells/mast cells in telencephalon. With exception of central nervous system lesions, the findings are according to the reported in literature about surfactant exposure in fish. Central nervous system effects can have consequences on feeding, reproductive and social interactions, due to close telencephalon/olfactory system relationship, being necessary to deep in research to these processes. In same way, liver, gills and skin are target organs of toxic action of this xenobiotic. LC50 is high (4417.99 mg/l) compared with that reported for other nonionic surfactants.