3,120 research outputs found
Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (Gobiomorphus cotidianus) – implications for incipient speciation in island freshwater fish species
No full textBackground: Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.
Results: Microchemical analyses of otolith isotopes (Sr-88, Ba-137 and Ca-43) differentiated migratory and non-migratory stocks of the New Zealand endemic Gobiomorphus cotidianus McDowall (Eleotridae). Samples were taken from two rivers, one lake and two geographically-separated outgroup locations. Meristic analyses of oculoscapular lateral line canals documented a gradual reduction of these structures in the non-migratory populations. Amplified fragment length polymorphism (AFLP) fingerprints revealed considerable genetic isolation between migratory and non-migratory populations. Temporal differences in reproductive timing (migratory = winter spawners, non-migratory = summer spawners; as inferred from gonadosomatic indices) provide a prezygotic reproductive isolation mechanism between the two ecotypes.
Conclusion: This study provides a holistic look at the role of diadromy in incipient speciation of island freshwater fish species. All four analytical approaches (otolith microchemistry, morphology, spawning timing, population genetics) yield congruent results, and provide clear and independent evidence for the existence of distinct migratory and non-migratory ecotypes within a river in a geographically confined range. The morphological changes within the non-migratory populations parallel interspecific patterns observed in all non-migratory New Zealand endemic Gobiomorphus species and other derived gobiid taxa, a pattern suggesting parallel evolution. This study indicates, for the first time, that distinct ecotypes of island freshwater fish species may be formed as a consequence of loss of migration and subsequent diversification. Therefore, if reproductive isolation persists, these processes may provide a mechanism to facilitate speciation
Freshwater Turtles of Belize
No full textBelize, a country rich in natural resources and diverse wildlife, is home to nine species of freshwater turtles. Among these is the critically endangered hicatee, which has been eliminated in most of its range as a result of hunting and habitat loss. Freshwater turtles live in rivers, creeks, and lagoons, and build their nests on the banks. They eat a variety of plants, aquatic vegetation, and fruits. However, little is known about Belize’s unique turtle species. This 2-page fact sheet will help people identify, understand, and conserve these treasured resources. Written by Venetia Briggs, Lauren Watine, Dustin Smith, Robin Bijlani, Rebecca Harvey, William Giuliano, and Frank Mazzotti, and published by the UF Department of Wildlife Ecology and Conservation, January 2013.
http://edis.ifas.ufl.edu/uw373
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Electrical conductance – a versatile guide in freshwater science
No full textAttention is directed to the many potential uses of specific electrical conductance (‘conductivity’) in the study of inland waters. Its measurement is capable of a precision useful in the detection of differences in a standing or flowing water-mass, but cannot be translated into measures of chemical concentration with equivalent absolute accuracy. Reasons – not infrequently neglected – include approximations in temperature correction, in allowance for a depression effect at higher ionic strength (salinity), and especially in the differences of specific conductance of chemically different ions. The last can be reduced by treating ionic concentration in chemical equivalents (e.g. meq l-1) rather than the usual units of mass (e.g. mg l-1) or molarity (e.g. mmol l-1); also by making allowance for the exceptionally high equivalent conductance of H+ and OH- ions in markedly acid and alkaline waters.Measurement in the field has been helped by the development of small portable instruments with inbuilt temperature compensation, flow-through electrode systems and electrical output. Examples of both field and laboratory measurements, for the charting and interpretation of various field situations, are illustrated chiefly from the author’s experience. They include broad chemical surveys; interrelation with normal chemical analysis; longitudinal change, water travel and nutrient uptake in river and stream systems; ionic ↔ particulate conversion; horizontal and vertical differentiation in lakes; and ionic changes induced by photosynthesis
Habitat associations of freshwater sawfish (Pristis microdon) and Northern River sharks (Glyphis sp. C): including genetic analysis of P. microdon across northern Australia
No full textThis study investigated the ecology, morphology, habitat utilisation and population genetics of the vulnerable (Environment Protection and Biodiversity Conservation Act (EPBC) 1999) or critically endangered (IUCN) Freshwater Sawfish (Pristis microdon). It also examined the distribution and utility of satellite tags in tracking the movements of the endangered (EPBC Act 1999) or critically endangered (IUCN) Northern River Shark (Glyphis sp. C) in the Kimberley
Funding flows for freshwater: the role of philanthropy in market-based freshwater conservation
No full textAs freshwater development progresses around the world, institutions must shift from the paradigm of exploiting water resources towards managing water scarcity in a way that maintains adequate environmental flows to support the riverâs functioning, biodiversity, and many ecosystem services. Amidst the rise of market environmentalism, market-based solutions have gained popularity as a promising approach to reallocate water from existing uses to in-stream environmental purposes. Successful water transactions require a number of enabling conditions; this dissertation explores these conditions, the ways in which they are created, and the role of different actors in facilitating institutional change. The results indicate that philanthropic funders play a major role by enabling collective action, encouraging collaboration and efficiency in creating the necessary preconditions for successful transactions. This is connected to literature on philanthrocapitalism and the role that foundations play in shaping conservation discourse.</p
Relative sensitivities of common freshwater fish and invertebrates to acute hypoxia
No full textThe acute lethality of low dissolved oxygen (DO) was examined in laboratory studies using several New Zealand freshwater fish and two invertebrates at 15 degree C. The 48-h LC sub(50) value was used as the endpoint for acute DO sensitivity as, owing to rapid mortality, this was found to best approximate the threshold lethal concentration. Median lethal time to death did not provide a reliable endpoint for comparing sensitivities. Fish LC sub(50) values varied from 0.54 to 2.65 mg litre super(-1), with inanga whitebait (Galaxias maculatus; 2.65 plus or minus 0.19 mg litre super(-1), mean plus or minus SEM) being the most sensitive species tested. Common smelt (Retropinna retropinna; 1.83 plus or minus 0.08 mg litre super(-1)) and rainbow trout (Oncorhynchus mykiss; 1.61 plus or minus 0.06 mg litre super(-1)) were similar in their sensitivities, whereas common bully (Gobiomorphus cotidianus; 0.91 plus or minus 0.06 mg litre super(-1)) and shortfin eel elvers (Anguilla australis; 0.54 plus or minus 0.03 mg litre super(-1)) were the most tolerant fish. The shrimp (Paratya curvirostris; 0.82 plus or minus 0.09 mg litre super(-1)) and freshwater crayfish (Koura, Paranephrops planifrons; 0.77 plus or minus 0.06 mg litre super(-1)) were also tolerant to low DO. A subset of experiments to determine the relative sensitivities of larval and juvenile trout and bully indicated no significant differences between these life stages.TR: CS0612494Source type: Electronic(1
The response of two South African east coast estuaries to altered river flow regimes.
No full text1. Major reductions in catchment run-off, a result of frequent and prolonged drought conditions, together with extensive impoundment of rivers and streams, has led to concern about the possible negative effects on downstream estuaries. Preliminary studies have shown that changes in river flow and associated nutrient inputs have had a predominantly negative impact on the aquatic biota of Eastern Cape estuaries. Natural successions now have human imposed trajectories which are reducing variability and forcing both freshwater ‘deprived’ and freshwater ‘enriched’ systems into artificial cycles. 2. The Kariega and Great Fish estuaries in the Eastern Cape Province are used in a comparative manner to illustrate how differences in riverine inflow can influence the structure and functioning of selected biotic components in permanently open systems. Maximum chlorophyll a values in the freshwater deprived Kariega Estuary were 1 μg L-1, whereas maximum values in the freshwater enriched Great Fish Estuary were 22 μg L-1. Mean zooplankton biomass in the lower, middle and upper reaches of the Kariega Estuary was always below 50 mg m-3, whereas in the same reaches of the Great Fish Estuary, these values ranged from 256 to 4253 mg m-3. Similarly, mean ichthyonekton densities in the mouth region of the Kariega Estuary were 49 individuals per 100 m2 compared with 279 per 100 m2 in the Great Fish Estuary. 3. Temporal changes of riverine flow reinforce the importance of allochthonous inputs to the functioning of Eastern Cape estuaries. A comparison between a dry and wet period in the Kariega Estuary revealed mean nitrate and phosphate concentrations increasing from 5 to 101 μmol L-1 and from 1 to 5 μmol L-1, respectively. Phytoplankton stocks responded positively to freshettes in both the Kariega and Great Fish estuaries. Similarly, peaks in zooplankton biomass in the Great Fish Estuary increased rapidly in response to high food resource availability resulting from elevated river discharge. The higher ichthyoplankton and ichthyonekton densities in the Great Fish Estuary, when compared with the Kariega Estuary, were attributed to a combination of stronger olfactory cues for larval immigrants from the sea and elevated food stocks in the former system. Copyright © 2000 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]Peer reviewedfinal article publishedestuarine ecosystem integrityfishzooplanktonphytoplanktonnutrient
Evidence that viral abundance across oceans and lakes is driven by different biological factors
No full text1. Samples from 16 lakes in central ( n = 145) and western ( n = 12) North America, the coastal northeast Pacific ( n = 302) and the western Canadian Arctic Oceans ( n = 142) were collected and analysed for viral, bacterial and cyanobacterial abundances and chlorophyll- a concentration. 2. Viral abundance was significantly different among the environments. It was highest in the coastal Pacific Ocean and lowest in the coastal Arctic Ocean. The abundances of bacteria and cyanobacteria as well as chlorophyll- a concentrations also differed significantly among the environments, with both bacterial abundance and chlorophyll- a concentration highest in lakes. As a consequence, the association of these variables with viral abundance varied among the environments. 3. Discriminant analyses with the abundance data indicated that the marine and freshwater environments were predictably different from each other. Multiple-regression analysis included bacterial and cyanobacterial abundances, and chlorophyll- a concentration as significant variables in explaining viral abundance in lakes. In regression models for the coastal Pacific Ocean, bacterial and cyanobacterial abundances were significant variables, and for the coastal Arctic Ocean viral abundance was predicted by bacterial abundance and chlorophyll- a concentration. 4. The relationship of viral and bacterial abundance differed between the investigated freshwater and marine environments, probably because of differences in viral production and loss rates. However, freshwaters had fewer viruses compared to bacteria, despite previously documented higher burst sizes and frequencies of infected cells, suggesting that loss rates may be more important in lakes. 5. Together, these findings suggest that there are different drivers of viral abundance in different aquatic environments, including lakes and oceans. [ABSTRACT FROM AUTHOR]Peer reviewedfinal article publishedVirusesmarinefreshwaterchlorophyll-abacteri
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