Daily ageing to delineate population dynamics of the invasive fish Gambusia holbrooki: implications for management and control

Biological Invasions - Despite the high global invasion profile of Gambusia holbrooki, there is limited knowledge of its population dynamics, especially biological parameters for fine-scale...     

A comparison of mosquito predation by the fish Pseudomugil signifier Kner and Gambusia holbrooki (Girard) in laboratory trials.

Using larval Cx. annulirostris mosquitoes, this study compared the predation rate of Pseudomugil signifer and Gambusia holbrooki for four larval instars, three prey densities, and three vegetation densities. There was no significant difference in the quantity of first, second, and third instar larvae consumed by the two fish species after 24 h. There was a significant negative relationship between the predation rate and both larval instar and prey density for both fish species. In simulated vegetation trials, P. signifer performed marginally better than G. holbrooki in medium to high density vegetation (0.3 stems/cm 2 and 0.6 stems/cm2, respectively).     

Life history and parasites of the invasive mosquitofish (Gambusia holbrooki) along a latitudinal gradient

The eastern mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide and yet, while very abundant in most Mediterranean countries, it is unable to tolerate the colder winters of northern and central Europe. Understanding the effects of latitude on its life-history traits is essential to predict the potential for its invasion of central Europe in current scenarios of climate change. We studied the variation of life-history traits and parasite load in the eastern mosquitofish along a latitudinal gradient from southern France to southern Spain, sampling mosquitofish populations in eight Mediterranean river mouths ranging 5° in latitude. Southern mosquitofish populations displayed higher catch rates, allocated more energy to reproduction (gonadosomatic index and gonadal weight after accounting for fish size) and had a lower condition (total weight and eviscerated weight after accounting for fish size) than in northern populations. Despite variability among populations, size-at-maturity (L₅₀) significantly varied with latitude and northern individuals matured at smaller size (lower L₅₀). Parasite prevalence ranged from 0.0 to 26.7% but parasite richness was very low; all the parasites identified were larvae of pleurocercoid cestodes belonging to the order Pseudophyllidea. The abundance of mosquitofish parasites decreased with latitude and the presence and number of parasites infecting the mosquitofish had a significant negative effect on fish condition. The significant effects of latitude on the catch rates, life history and parasites of mosquitofish highlight the importance of latitudinal studies of invasive species to understand the interactive mechanisms of climate change and biological invasions.     

Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress

Wample, R. L. and Thornton, R. K. 1984. Differences in the response of sunflower ( Helianthus annuus ) subjected to flooding and drought stress.
Comparison of drought- and flood-stressed sunflower plants ( Helianthus annuus L. hybrid 894) showed some similarities in response but differences in the mechanisms responsible for the responses to stress. Drought–stressed plants showed typical reductions in leaf water potential with increasing stress accompanied by increased leaf resistance. Photosynthesis declined while photorespiration increased after 48 and 96 h of drought stress. A primary reason for reduced photosynthesis in drought-stressed plants was increased stomatal resistance. No significant 0change in leaf water potential or in leaf resistance in flooded plants was found in this study. However, photosynthesis declined in a manner similar to that in drought-stressed plants and photorespiration showed only a transient increase at 48 h. Dark respiration was significantly higher at 48 and 96 h but the magnitude of the increase cannot account for the reduction in photosynthesis. Since the photosynthetic rate of flooded plants declined while stomata remained open, an effect at a more fundamental level is suggested and is thought to be related to disruption of carbohydrate transport.     

Genetic variation in populations of the endangered fish Ladigesocypris ghigii and its implications for conservation

1. The genetic variation of the endangered freshwater fish Ladigesocypris ghigii, endemic to the island of Rhodes (Greece), was investigated for nine populations, originating from seven different stream systems and a reservoir, both at the mtDNA and nuclear level, in order to suggest conservation actions. 2. Both restriction fragment length polymorphism analysis of five segments of mitochondrial DNA (ND‐5/6, COI and 12S‐16S rRNA) amplified by polymerase chain reaction, and random amplified polymorphic DNA analysis, revealed extremely low levels of intra‐population polymorphism. It is highly likely that the low intra‐population variability is the result of successive bottleneck events evident in shrinkage and expansion of the populations year after year, which may have led to a complete loss of several genotypes and haplotypes, and an increased degree of inbreeding. 3. Inter‐population genetic structuring was high, with fixation of haplotypes within six of the nine populations and fixation of alleles within populations originating from different waterbodies. It is probable that all haplotypes and/or alleles found were initially represented in all populations. However, because of the long time of isolation coupled with successive bottleneck and subsequent genetic drift, common mtDNA haplotypes and alleles among the populations may have become rare or extinct through stochastic lineage loss. 4. Although nucleotide divergence among haplotypes was very shallow, half of the haplotypes recorded (three of six), resulted from nucleotide changes on the 12S–16S rRNA segments, which are the most conserved part of the mitochondrial genome. This fact may indicate that the observed genetic variation did not necessarily result only from the retention of ancestral polymorphism, but may have arisen through mutation and complete lineage sorting over a relatively small number of generations, once the populations had become isolated from one another. 5. Our data suggest that two of the L. ghigii populations may be on independent evolutionary trajectories. Considering that each population appears so far well adapted within each site, all populations should be managed and conserved separately.     

Surf zone fish community and species response to a wave energy gradient

Analysis of seine netting data for Algoa Bay, South Africa reveals that species richness and relative abundances of surf zone fishes differ at three beach sites, despite their close proximity. A gradient in species compositional and abundance response to spatially varying wave exposure is proposed as the principle cause. Implications are considered in the context of trophic interaction and impact of individuals and species assemblages upon energy and other resources of the habitat.     

Noradrenaline, dopamine, 5-hydroxytryptamine and tryptophan concentrations in the brains of four cohabiting species of fish

1. The concentrations of the neurotransmitters noradrenaline, dopamine and 5-hydroxy-tryptamine and the amino acid tryptophan were determined in the telencephalon, optic lobes and rest of the brains of four species of fish collected from a stream in central Saskatchewan. 2. The species investigated were white sucker (Catostomus commersoni), longnose sucker (Catostomus catostomus), longnosed dace (Rhinichthys cataractae) and northern pike (Esox lucius). 3. Significant differences were found in the concentrations of amines in different regions of the brain within species and within the same brain region between species. 4. These results may be related to the phylogenetic differences or to patterns in brain development evolved by fish species to adapt to particular lifestyles.     

Characterization and use of the total head soluble cholinesterases from mosquitofish (Gambusia holbrooki) for screening of anticholinesterase activity

Inhibition of cholinesterases (ChE) has been widely used as an environmental biomarker of exposure to organophosphates (OP) and carbamate (CB) pesticides. Different ChE isoforms may be present in the same tissue and may present distinct sensitivities towards environmental contaminants. The present work characterises the soluble ChE present in mosquitofish (Gambusia holbrooki) total head homogenates, through the use of different substrates and selective inhibitors of cholinesterasic activity. Furthermore, the effects of sodium dodecylsulphate (SDS) on the enzymatic activity were investigated, both in vivo and in vitro. These results showed that acetylcholinesterase (AChE) seemed to be the predominant form present in head homogenates of G. holbrooki, despite the inhibition by tetraisopropylpyrophosphoramide (iso-OMPA) found at high concentrations. SDS was responsible for in vitro, but not in vivo, inhibitory effects. The in vitro AChE inhibitory effects of SDS was partially prevented by the use of increasing amounts of ethanol, suggesting that the inhibition was induced by an emulsion effect, which may explain the lack of effect in vivo.     

Differential response to soil salinity in endangered key tree cactus: implications for survival in a changing climate

Understanding reasons for biodiversity loss is essential for developing conservation and management strategies and is becoming increasingly urgent with climate change. Growing at elevations <1.4 m in the Florida Keys, USA, the endangered Key tree cactus (Pilosocereus robinii) experienced 84 percent loss of total stems from 1994 to 2007. The most severe losses of 99 and 88 percent stems occurred in the largest populations in the Lower Keys, where nine storms with high wind velocities and storm surges, occurred during this period. In contrast, three populations had substantial stem proliferation. To evaluate possible mortality factors related to changes in climate or forest structure, we examined habitat variables: soil salinity, elevation, canopy cover, and habitat structure near 16 dying or dead and 18 living plants growing in the Lower Keys. Soil salinity and elevation were the preliminary factors that discriminated live and dead plants. Soil salinity was 1.5 times greater, but elevation was 12 cm higher near dead plants than near live plants. However, distribution-wide stem loss was not significantly related to salinity or elevation. Controlled salinity trials indicated that salt tolerance to levels above 40 mM NaCl was related to maternal origin. Salt sensitive plants from the Lower Keys had less stem growth, lower root:shoot ratios, lower potassium: sodium ratios and lower recovery rate, but higher δ (13)C than a salt tolerant lineage of unknown origin. Unraveling the genetic structure of salt tolerant and salt sensitive lineages in the Florida Keys will require further genetic tests. Worldwide rare species restricted to fragmented, low-elevation island habitats, with little or no connection to higher ground will face challenges from climate change-related factors. These great conservation challenges will require traditional conservation actions and possibly managed relocation that must be informed by studies such as these.     

Environmental and biological factors influence the relationship between a predator fish,Gambusia holbrooki,and its main prey in rice fields of the Lower Mondego River Valley (Portugal)

We studied the relationships between a predator fish, Gambusia holbrooki, and its main food prey, within the content of a rice field food web. The influence of some environmental and biological factors on these trophic interactions, in combination with existent quantitative information, allowed us to evaluate the ecological viability of using a non-ionic surfactant, Genapol OXD-080, to control a plague caused by crayfish (Procambarus clarkii) populations in the rice fields. In the Lower Mondego River Valley, Portugal, G. holbrooki is abundant in rice fields. It feeds mainly on copepods, cladocerans and rotifers. Surface insects, such as aphids, collembolans, adult (imago) chironomids and other dipterans, are additional food. Large G. holbrooki consumed greater amounts of cladocerans and adult chironomids than other smaller size groups, while small fish prefered rotifers. Gravid females ate copepods, cladocerans, and adult chironomids and other dipterans in significantly greater amounts than immatures, males, and non-gravid females. Non-gravid females ate collembolans in significantly greater quantities than any other fish group. The population density of copepods, cladocerans, adult chironomids, and other dipterans, the area covered by aquatic vegetation, and water temperature all had significant effects on the total number of prey caught by G. holbrooki. In contrast, a negative correlation was found with rotifers, collembolans, aphids in higher densities, and of increased water volume, dissolved oxygen and pH. G. holbrooki holds a key intermediate position in the rice field food chain, feeding in large amounts of aquatic invertebrates and being eaten, in turn, by piscivores. With regard to the toxicity of Genapol OXD-080 on non-target organisms, LC₅₀ values for G. holbrooki and some of its main prey were several times lower than the concentration necessary to decrease the activity of crayfish populations in the rice fields. Thus, Genapol OXD-080 could potentially cause greater damage to the local populations of non-target species and should not be used without taking precautions not to contaminate other important biological reservoirs, such as the rice field irrigation channels. This revised version was published online in July 2006 with corrections to the Cover Date.     

物种濒危等级划分与物种保护

介绍了国际与国内濒危物种等级最新标准。探讨了濒危物处等级的划分标准存在的问题和物种的保护优先序。介绍了确定物种保护优先序时的两种不同观点。     

Limits to the niche and range margins of alien species

We discuss the apparent paradox that while introduced populations often adapt rapidly to conditions in the new range, it is normally assumed that the species’ niche remains unchanged. Focusing on plants, we argue that studies of the niche dynamics of alien species are useful for understanding the constraints acting on species in their native ranges, and vice versa. Most hypotheses about species ecological range margins are more consistent with there being a niche shift than niche stasis in the new range. After reviewing the evidence for niche shifts in alien species, we suggest that the probability of a shift occurring depends primarily upon the ecological and genetic processes limiting the species in its native range. For example, a fundamental niche shift might occur if introduced individuals are released from maladaptive gene flow from central populations, or if genetic diversity is increased by the mixing of individuals from different sources. In addition, other factors such as species characteristics, introduction history and conditions in the new range may also influence whether a niche shift occurs. Based on these considerations, we propose conditions under which niche shifts are most likely. Such understanding is important for predicting and mitigating current and future anthropogenic impacts on species ranges.     

Captive breeding of endangered fish Chitala chitala (Hamilton-Buchanan) for species conservation and sustainable utilization

Over the last few decades wild population of Chitala chitala (HamiltonBuchanan) has been declined more than 50% due to various reasons and is presently listed under endangered (EN) category due to reduced abundance. In the present communication wild C. chitala were collected from natural habitats and induced to spawn under captivity during July 2002 by injecting three different doses of synthetic hormone Ovaprim. Intramuscular injections were administered to fishes using three different doses (1.5, 1.0 and 0.5 ml/kg body weight). Artificial breeding pool was prepared for each set by encircling area (20 × 5 m) with mosquito net, where wooden country boat (8 × 4 × 2.5 feet with surface area 48.5 sq. feet) was placed inside the breeding pool. Distinct spawning behavior was noticed in the experimental sets with different hormonal dose whereas no spawning activity was noticed in control set. The fertilization rate varied from 48.8680.2% and total numbers of spawned eggs in two sets of experiments were estimated to be 81,034. The average number of eggs deposited 15 ± 2.1/square inches. The fertilized eggs were large in size (4.5 ± 0.05 mm), adhesive and attached to the hard substratum. The eggs hatch out between 168192 h after fertilization and about 33,639 hatchlings were produced. Newly hatched larvae measured 10.23 ± 0.03 mm and 0.031± 0.008 gm in weight and the mean diameter of yolk sac was 4.1 ± 0.08 mm. The yolk sac remains attached up to a week. The percentage survival of hatchlings varied from 42.2 to 65.60. Statistical analysis was worked out to determine the relation between the hormone dosage with different breeding parameters like latency period, fertilization rate, egg output, hatching rate and hatchling production.     

Genetic diversity of the endangered species Rosa rugosa Thunb. in China and implications for conservation strategies

Rosa rugosa Thunb. is one of the dominant and important shrub species in estuary dunes and shingle beaches of northern China. However, its area of distribution, the number of populations, and the size of each population have decreased rapidly in the past two decades because of habitat degradation and loss. Random amplified polymorphic DNA markers were used to determine the genetic diversity of four remaining large natural populations of R. rugosa and to discuss an effective conservation strategy for this endangered species in China. High genetic variations were detected in R. rugosa populations in China. The mean percentage of polymorphic loci （P%） within four local populations was 57.99%, with the P% of the total population being 75.30%. Mean Shannon＇s information index （H0） was 0.2826, whereas total Ho was 0.3513. The genetic differentiation among populations was 0.1878, which indicates that most genetic diversity occurs within populations. Population Tumenjiang （TMJ） showed the highest genetic diversity （P% = 66.27%; H0 = 0.3117） and contained two exclusive bands. Population Changshandao （CSD） showed higher genetic diversity （P% =59.04%; H0 = 0.3065）. Populations TMJ and CSD contained 95.33% and 99.33%, respectively, of loci with moderate to high frequency （P〉0.05） of the total population. These results indicate that populations TMJ and CSD should be given priority for in situ conservation and regarded as seed or propagule sources for ex situ conservation. The results of the present study also suggest that R. rugosa in China has become endangered as a result of human actions rather than genetic depression of populations; thus, human interference should be absolutely forbidden in R. rugosa habitats.     

Anthropogenic changes in the freshwater fish fauna of Italy, with reference to the central region and Barbus graellsii, a newly established alien species of Iberian origin

In a survey of the west-central Italian rivers Ombrone, Fiora, Albegna and Bruna, among established exotic species, the Iberian barbel Barbus graellsti was recorded in Italian fresh waters for the first time. Morphological identification was supported by comparison of cytochrome b sequences with those from related barbel species. Other exotics of particular note were Barbus barbus, Pseudorasbora parva and Leuciscus cephalus , together with the Padano-Venetian Chondrostoma genei and Padogobius bonelli. Native species still present included Leuciscus lucumonis, Telestes muticellus, Rutilus rubilio and Padogobius nigricans , but were now more restricted to upper reaches and smaller watercourses. The deleterious effect of alien species on native forms is discussed with particular reference to probable competition between C. genei and L. lucumonis , and between the two gobies. The checklist of species introduced to the fresh waters of Italy is now updated to 34. For the Italian freshwater fish fauna in general, the conservation status of three native species ( Acipenser naccari, Salmo marmoratus and Knipowitschia punctatissima ) has been improved but five species are believed to be at risk ( Salmo carpio, L. lucumonis, Scardinius scardafa, Gobio benacensis and P. nigricans ) and four anadromous species ( Petromyzon marinus, Lampetra fluviatilis, Acipenser sturio and Huso huso ) no longer breed in Italian fresh waters. The processes of change in the composition of the Italian freshwater fish fauna as a whole may be summarized as successively 'padanization', 'danubization' and now 'globalization'.