Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life‐history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean‐type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico‐chemical factors and phytoplankton availability in freshwater habitats. These life‐history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r‐ to K‐strategy in freshwater decapods are traded‐off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio‐temporal alteration of their socio‐ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.     

Climate change and freshwater biodiversity: detected patterns, future trends and adaptations in northern regions

Current rates of climate change are unprecedented, and biological responses to these changes have also been rapid at the levels of ecosystems, communities, and species. Most research on climate change effects on biodiversity has concentrated on the terrestrial realm, and considerable changes in terrestrial biodiversity and species’ distributions have already been detected in response to climate change. The studies that have considered organisms in the freshwater realm have also shown that freshwater biodiversity is highly vulnerable to climate change, with extinction rates and extirpations of freshwater species matching or exceeding those suggested for better‐known terrestrial taxa. There is some evidence that freshwater species have exhibited range shifts in response to climate change in the last millennia, centuries, and decades. However, the effects are typically species‐specific, with cold‐water organisms being generally negatively affected and warm‐water organisms positively affected. However, detected range shifts are based on findings from a relatively low number of taxonomic groups, samples from few freshwater ecosystems, and few regions. The lack of a wider knowledge hinders predictions of the responses of much of freshwater biodiversity to climate change and other major anthropogenic stressors. Due to the lack of detailed distributional information for most freshwater taxonomic groups and the absence of distribution‐climate models, future studies should aim at furthering our knowledge about these aspects of the ecology of freshwater organisms. Such information is not only important with regard to the basic ecological issue of predicting the responses of freshwater species to climate variables, but also when assessing the applied issue of the capacity of protected areas to accommodate future changes in the distributions of freshwater species. This is a huge challenge, because most current protected areas have not been delineated based on the requirements of freshwater organisms. Thus, the requirements of freshwater organisms should be taken into account in the future delineation of protected areas and in the estimation of the degree to which protected areas accommodate freshwater biodiversity in the changing climate and associated environmental changes.     

Cadmium,chromium, and lead accumulation in aquatic plants and animals near a municipal landfill

This research was conducted to assess the contamination of heavy metals in the water, sediment, aquatic plants and animals around a municipal landfill. The heavy metals were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). The concentrations of cadmium (Cd), chromium (Cr), and lead (Pb) in water and sediment were Not detected (ND), 0.05 ± 0.98, and 0.02 ± 0.01 mg/L; and 0.47 ± 0.23, 18.65 ± 11.39, and 5.36 ± 2.08 mg/kg, respectively. A total of 24 aquatic plants from 4 species were collected from the municipal landfill. Cd concentrations in all plant species were within the standard, while Cr and Pb exceeded the standard. Forty-four fish from 4 species, 29 freshwater snails from 3 species, 10 freshwater prawns from 1 species, and 9 freshwater crabs from 1 species were collected. Cd and Cr concentrations in 2 species of fish samples exceeded the standard and Pb concentration in all fish species exceeded the standard. Cd and Pb concentrations in all freshwater snails were within the standard, except Cr. Meanwhile, Cd and Pb in freshwater prawns and snails were within the standard, except Cr. Five species of frogs were collected. Cd and Cr concentrations in 2 species exceeded the standard. Pb concentrations in all frog species exceeded the standard. The pattern of metal accumulation was fish > frogs > freshwater snails > freshwater prawns = freshwater crab (Cd), freshwater prawn > frogs > freshwater crab = freshwater snail > fish (Cr), and freshwater prawn > fish > frogs > freshwater snail > freshwater crab (Pb).     

Progress and opportunities in advancing near-term forecasting of freshwater quality

Near-term freshwater forecasts, defined as sub-daily to decadal future predictions of a freshwater variable with quantified uncertainty, are urgently needed to improve water quality management as freshwater ecosystems exhibit greater variability due to global change. Shifting baselines in freshwater ecosystems due to land use and climate change prevent managers from relying on historical averages for predicting future conditions, necessitating near-term forecasts to mitigate freshwater risks to human health and safety (e.g., flash floods, harmful algal blooms) and ecosystem services (e.g., water-related recreation and tourism). To assess the current state of freshwater forecasting and identify opportunities for future progress, we synthesized freshwater forecasting papers published in the past 5 years. We found that freshwater forecasting is currently dominated by near-term forecasts of water quantity and that near-term water quality forecasts are fewer in number and in the early stages of development (i.e., non-operational) despite their potential as important preemptive decision support tools. We contend that more freshwater quality forecasts are critically needed and that near-term water quality forecasting is poised to make substantial advances based on examples of recent progress in forecasting methodology, workflows, and end-user engagement. For example, current water quality forecasting systems can predict water temperature, dissolved oxygen, and algal bloom/toxin events 5 days ahead with reasonable accuracy. Continued progress in freshwater quality forecasting will be greatly accelerated by adapting tools and approaches from freshwater quantity forecasting (e.g., machine learning modeling methods). In addition, future development of effective operational freshwater quality forecasts will require substantive engagement of end users throughout the forecast process, funding, and training opportunities. Looking ahead, near-term forecasting provides a hopeful future for freshwater management in the face of increased variability and risk due to global change, and we encourage the freshwater scientific community to incorporate forecasting approaches in water quality research and management.     

Analysing freshwater fish biodiversity records and respective conservation areas in Spain

The number of threatened freshwater fish species in Spain is among the highest recorded in Europe and includes a high percentage of endemic taxa. Investigated were the distribution of Spanish freshwater fish to identify priority areas for conservation and assess the extent to which freshwater fish are included in the existing network of protected areas. Considered were those threatened species recorded in the Spanish National inventories. From these data, several biodiversity indices were calculated and analysed. The results reveal important discrepancies between the national and international assessments of conservation status, whereby the current Spanish national catalogue needs updating to reconcile these inconsistencies. Several important areas for the conservation of freshwater fish lie outside protected areas. The results encourage the establishment of protected areas specifically for freshwater environments. An extensive database of Spanish freshwater fish species is needed to redefine priority areas and to maintain freshwater biodiversity.     

Eocene–Oligocene sea-level fall drove amphipod habitat shift from marine to freshwater in the Far East

The Eocene–Oligocene sea-level fall has been viewed as a primary driver of biological succession. We used Anisogammaridae living in both marine and freshwater habitats to test the hypothesis that Eocene–Oligocene sea-level fall can explain the marine–freshwater habitat shift in the Far East. We obtained three mitochondrial and two nuclear fragments for 138 samples representing 31 species, covering marine and freshwater habitats from latitudes 24 to 50°N. The phylogenetic analyses revealed that freshwater Anisogammaridae is monophyletic. Divergence-time estimation and ancestral range reconstruction indicate that the family originated from a marine habitat in the North Pacific region during the Eocene and separated between marine and freshwater lineages at 38 Ma. The freshwater lineage diversified at 27 Ma, and further diverged into lotic and lentic clades. Our results suggest that the Eocene–Oligocene sea-level fall provided an opportunity for marine-derived Anisogammaridae to shift to new freshwater habitats. The freshwater anisogammarids dispersed from north to south, resulting in the restriction of current marine species restricted to the latitudes 35–50°N and the range of freshwater species in latitudes 24–40°N. Deep divergences within the freshwater lineage were related to the separation of lotic and lentic environments and the opening of the Japan Sea.     

Freshwater nemerteans

The freshwater hoplonemertean genus Prostoma is critically reviewed and revised and a new species Prostoma kolasai sp. nov., is described. All the freshwater nemerteans of the world are compared and contrasted, with reference to those common morphological characters which may be related to the colonization of freshwater habitats. A key to the world freshwater nemerteans is provided.     

Spatiotemporal Variation in Shallow-Water Freshwater Fish Distribution and Abundance in a Large Subtropical Coastal Lagoon

Patos Lagoon is located off the southern Brazilian coast and represents one of the largest coastal lagoons in the world. We estimated hydrological and physicochemical conditions associated with spatial variation in the abundance and diversity of freshwater fishes along the lagoon, and inter-annual variability in abundances of freshwater fishes occurring in its estuarine zone. During our study, the region experienced two periods of average rainfall and two periods with above-average rainfall. The characids Astyanax eigenmaniorum and Oligosarcus jenynsii and the siluriform Parapimelodus nigribarbis were the most abundant freshwater fishes in the estuary during wet periods when water levels were higher and salinity was lower. Increases in abundance of these species in the estuarine area, all of which members of primary-division freshwater families, apparently were associated with pulses of reproduction and passive transport from freshwater habitats located near middle and upper lagoon reaches. Abundance of species from secondary freshwater families, such as poeciliids and cichlids, were less correlated with hydrological conditions, and their patterns of occurrence in the estuary suggest active migration from nearby freshwater habitats draining into this area. Findings indicate that freshwater discharge in the basin and expansion/retraction of freshwaters in the middle-upper lagoon determined patterns of freshwater fish abundance and species richness in the estuarine zone.     

Comparison of freshwater discrimination ability in three species of sea kraits (Laticauda semifasciata, L. laticaudata and L. colubrina)

Three species of amphibious sea kraits (Laticauda spp.) require drinking freshwater to regulate water balance. The extent of terrestriality is known to differ among them. Species with higher extent of terrestriality would drink freshwater accumulated on land, whereas less terrestrial species would rely totally on freshwater that runs into the sea. Consequently, we predicted that the latter species might have a better ability to follow the flow of freshwater or lower salinity water in the sea than the former. We investigated the freshwater discrimination ability of three sea krait species, using a Y-maze apparatus. We found that Laticauda semifasciata and Laticauda laticaudata, less terrestrial species, followed freshwater significantly more frequently than seawater, whereas Laticauda colubrina, more terrestrial species, unbiasedly selected freshwater and seawater. This result supports our prediction and suggests that less terrestrial sea kraits more efficiently access freshwater sources in the sea than highly terrestrial sea kraits. It is likely that behavioral rehydration systems vary among sea kraits in relation to their terrestrial tendency.     

Freshwater Reserves in Australia: Directions and Challenges for the Development of a Comprehensive,Adequate and Representative System of Protected Areas

The establishment of a system of protected areas that samples all ecosystems, including freshwater environments, in a comprehensive, adequate and representative (CAR) manner is regarded as a cornerstone for the conservation of biodiversity. There have been few quantitative assessments of the comprehensiveness, adequacy and representativeness of freshwater reserves in Australia. This paper reviews and quantifies the effect of classification of freshwater ecosystems for conservation planning, the importance of reservation status and protection measures for developing a CAR reserve system, and aspects of reserve design for freshwater ecosystems. We propose a strategic and iterative process that incorporates these measures to assist in the efficient and effective development of freshwater reserve systems worldwide. However, the provision of suitable water regimes for freshwater reserves presents further ecological and political challenges, and even adequate reservation of freshwater ecosystems may not conserve constituent biodiversity without effective management.     

Freshwater habitat use by a moray eel species,Gymnothorax polyuranodon,in Fiji shown by otolith microchemistry

Freshwater eels of the Anguillidae are diadromous because they migrate between ocean and freshwater environments, but other anguilliform fishes are generally considered to be strictly marine species. A few marine eels of the Muraenidae and Ophichthidae have occasionally been found in freshwater or estuaries, indicating that anguillids are not the only anguilliform eels that can use freshwater in some parts of the world. The moray eel Gymnothorax polyuranodon is one species that is known to be present in freshwater in the Indo-Pacific, but its life history is unknown. One way to evaluate what types of habitats are used by fishes is to determine the ratio of strontium (Sr) to calcium (Ca) in their otoliths, because this can show if they have used freshwater or saltwater environments. To evaluate the patterns of freshwater use by this unusual species of marine eel, the otolith Sr/Ca ratios of four G. polyuranodon (275–344 mm) caught in a freshwater stream of Fiji were analyzed. The consistently low Sr/Ca values (0–4) indicated upstream movement after settlement and freshwater or estuarine residence of all four individuals. These eels did not appear to have entered freshwater just for a short time period, which is consistent with other reports that this species is present in estuarine and freshwater habitats. This suggests that G. polyuranodon may be a catadromous species of marine eel. The similarities and differences between the life histories of anguillid eels and the few marine eels that have evolved the ability to invade freshwater habitats is discussed in relation to the evolutionary origin of diadromy in anguilliform fishes that originated in the marine environment.     

An assessment of animal species diversity in continental waters

There is a need for monitoring the status and trends of freshwater biodiversity in order to quantify the impacts of human actions on freshwater systems and to improve freshwater biodiversity conservation. Current projects carrying assessment of freshwater biodiversity focus mainly on leading-better-known groups such as fish, or identify keystone species and/or endemic freshwater systems for conservation purposes. Our purpose is to complete these existing projects by providing quantitative estimates of species number for all freshwater groups on each continent and/or major eco-regions. This article present the results of the first implementation phase carried out from September 2002 to June 2003 and which addressed only freshwater animal species. The project consisted of: (1) compiling existing data from literature, web sites and museum collections; (2) contacting scientific experts of each group to provide a ‘to the best of their knowledge, estimates of species numbers. In this study, we consider as true freshwater species, those that complete part or all of their life cycle in freshwater, and water-dependant species those that need freshwater for food or that permanently use freshwater habitats. The current order of magnitude for known freshwater animal species world wide is 100 000, of which half are insects. Among other groups, there are some 20 000 vertebrate species; 10 000 crustacean species and 5000 mollusc species that are either true freshwater or water-dependant species. The study highlighted gaps in the basic knowledge of species richness at continental and global scales: (1) Some groups such as Protozoa, nematodes or annelids have been less studied and data on their diversity and distribution is scarce. Because current richness estimates for these groups are greatly biased by knowledge availability, we can expect that real species numbers might be much higher. (2) Continents are not equal in the face of scientific studies: South America and Asia are especially lacking global estimates of species richness for many groups, even for some usually well-known ones such as molluscs or insects. The second phase of the project will address freshwater plants and algae. The present status should be considered as a first sketch of the global picture of freshwater biodiversity. We hope that this project will initiate interactive exchange of data to complete and update this first assessment.     

Renal water and solute excretion in the Atlantic stingray in fresh water

Freshwater, male Atlantic stingrays Dasyatis sabina , from Lake Jesup, Florida, U·S·A·, excreted a dilute urine similar in composition to freshwater teleosts and lampreys with the exception that urea was the primary osmolyte. Urine flow rate was 2·5 to 10 fold higher than that reported for freshwater teleosts resulting in high free-water clearance. Mass-specific free-water clearance values from euryhaline elasmobranchs inhabiting freshwater environments greatly exceed those for freshwater teleosts and are nearly equivalent to those of freshwater lampreys.     

海南岛淡水蟹类分布格局与多样性保护

热带岛屿生物多样性是全球生物多样性保护研究的热点之一。海南岛是中国面积最大的热带岛屿, 丰富独特的淡水蟹类是维持岛内淡水生态系统功能完整性的关键类群。本文通过多年野外调查, 综合历史及最新文献资料, 对海南岛淡水蟹类物种多样性及其现状进行调查和评估, 并对淡水蟹类物种多样性保护现状进行了分析讨论。研究发现, 海南岛淡水蟹类物种多样性分布中心位于中南部山地, 主要集中于中部的霸王岭、鹦哥岭和猕猴岭, 南部的五指山和吊罗山, 以及西南部的尖峰岭一带。其物种多样性整体上呈现中南部山地高、平原台地低的特点。根据《IUCN物种红色名录濒危等级和标准》对海南岛淡水蟹类物种现状的评估结果显示, 全岛受威胁淡水蟹类物种的占比为16.7%。基于分布区预测, 以海南热带雨林国家公园为主体的保护地对淡水蟹类潜在适宜分布区的覆盖度明显优于此前碎片化的各级保护区。本文研究结果显示, 海南岛淡水蟹类的总体生存状况良好, 但一部分山地或平原种类处于受胁状态。国家公园体制的建立有望为岛内淡水蟹类物种多样性保护提供前所未有的机遇。基于物种多样性分布格局开展淡水蟹类等淡水生物多样性监测, 有助于促进海南岛淡水生态系统完整性的长效保护与可持续发展。     

Rapid evolution of body fluid regulation following independent invasions into freshwater habitats

Colonizations from marine to freshwater environments constitute among the most dramatic evolutionary transitions in the history of life. Colonizing dilute environments poses great challenges for acquiring essential ions against steep concentration gradients. This study explored the evolution of body fluid regulation following freshwater invasions by the copepod Eurytemora affinis. The goals of this study were to determine (1) whether invasions from saline to freshwater habitats were accompanied by evolutionary shifts in body fluid regulation (hemolymph osmolality) and (2) whether parallel shifts occurred during independent invasions. We measured hemolymph osmolality for ancestral saline and freshwater invading populations reared across a range of common-garden salinities (0.2-25 PSU). Our results revealed the evolution of increased hemolymph osmolality (by 16-31%) at lower salinities in freshwater populations of E. affinis relative to their saline ancestors. Moreover, we observed the same evolutionary shifts across two independent freshwater invasions. Such increases in hemolymph osmolality are consistent with evidence of increased ion uptake in freshwater populations at low salinity, found in a previous study, and are likely to entail increased energetic costs upon invading freshwater habitats. Our findings are consistent with the evolution of increased physiological regulation accompanying transitions into stressful environments.     

Locomotory capacity of Baltic Sea and freshwater populations of the threespine stickleback (Gasterosteus aculeatus)

Two freshwater populations and one marine population (Baltic Sea) of threespine stickeback (Gasterosteus aculeatus) from Northeastern Germany were studied with regard to locomotory capacity: sustained swimming performance, activities of key enzymes in axial muscle, pectoral fin muscle and heart, and morphology. We postulated that life history differences between migratory Baltic Sea and resident freshwater populations could have led to a divergence in their locomotory capacity. The activity of citrate synthase (CS) in pectoral muscle correlated with critical swimming speed. Critical swimming speed, aerobic and anaerobic capacity of the pectoral fin muscle were population-specific. The Baltic Sea sticklebacks had a higher locomotory capacity (activity of CS in pectoral muscle, critical swimming speed) than sticklebacks of one freshwater population. However, another freshwater population expressed a similar locomotory capacity as the Baltic Sea population. In addition, Baltic Sea sticklebacks had a greater mass and lower anaerobic capacity of the pectoral fin muscle than the freshwater sticklebacks. The results are interpreted as an indication of a proceeding divergence between marine and resident freshwater populations and between freshwater populations of G. aculeatus originating from marine ancestors. The migratory Baltic Sea sticklebacks had better morphological prerequisites for sustained swimming than both freshwater populations, but there was no general difference in the locomotory capacity between marine and freshwater sticklebacks. However, their morphology could favour a more effective locomotion in the Baltic Sea sticklebacks.     

Should I stay or should I go? The Ectodysplasin locus is associated with behavioural differences in threespine stickleback

Adaptive divergence may be facilitated if morphological and behavioural traits associated with local adaptation share the same genetic basis. It is therefore important to determine whether genes underlying adaptive morphological traits are associated with variation in behaviour in natural populations. Positive selection on low-armour alleles at the Ectodysplasin (Eda) locus in threespine stickleback has led to the repeated evolution of reduced armour, following freshwater colonization by fully armoured marine sticklebacks. This adaptive divergence in armour between marine and freshwater populations would be facilitated if the low allele conferred a behavioural preference for freshwater environments. We experimentally tested whether the low allele is associated with preference for freshwater by measuring the preference of each Eda genotype for freshwater versus saltwater after acclimation to either salinity. We found no association between the Eda low allele and preference for freshwater. Instead, the low allele was significantly associated with a reduced preference for the acclimation environment. This behaviour may facilitate the colonization of freshwater habitats from the sea, but could also hinder local adaptation by promoting migration of low alleles between marine and freshwater environments.     

Genetic differentiation of freshwater and marine sticklebacks, (Gasterosteus aculeatus) of Eastern Europe

Electrophoretic variation of 13 presumptive enzymatic loci was studied in sticklebacks (Gasterosteus aculeatus) at 6 marine (Baltic) and 13 freshwater sites from Poland. Marine samples are significantly more variable (proportion of polymorphic loci, p # 0.38) than freshwater Samles (p # 0.12). Also the mean number of alleles per locus is significantly higher in the marine samples (n # 1.54) than in freshwater samples (n # 1.14). There is however no significant difference in values of mean heterozygosity between marine and freshwater sticklebacks. Some alleles are found in Baltic sticklebacks only, but all these occur in very low frequencies. Genetic distance between samples is low ranging from D = 0.000053 to 0.031410. However D is significant smaller between marine samples than between freshwater Samles. We suggest than this probaily is the result of larger genetic subdivision of freshwater populations. The low genetic divergence of marine and freshwater populations of the stickleback from poland might be expfained by the recent postglacial colonization of this area from a common refugium.     

Declining freshwater mussel diversity in the middle and lower reaches of the Xin River Basin: Threat and conservation

Freshwater mussels provide important functions and services for aquatic ecosystems, but populations of many species have been extirpated. Information on biodiversity plays an important role in the conservation and management of freshwater mussels. The Xin River Basin is a biodiversity hotspot for freshwater mussels in China, with more than 43 species known, but populations of which are decreasing. Here, we quantify the diversity of freshwater mussels in the middle and lower reaches of the Xin River Basin and study the correlation of habitat characteristics and freshwater mussel diversity. Compared to the historical period, the number of species, density, and biomass of freshwater mussels decreased 33%, 83%, and 82% in the current period, respectively. Fifty two percent of recorded species were empty shells, and 14 native freshwater mussels were not found in the study area. Four species are currently listed as vulnerable species using IUCN criteria and their global status. The assemblage structure of freshwater mussels exhibits significant spatial differences, and there was a correlation with substrate and physicochemical parameters. The main tributary of the Xin River with higher freshwater mussel diversity should be established as one large protected area because the nestedness component was the main pattern of beta diversity. These results indicated freshwater mussel diversity was declining rapidly, which can help focus conservation effort for freshwater mussel biodiversity.