A genetically distinct hybrid zone occurs for two globally invasive mosquito fish species with striking phenotypic resemblance

Hybrid zones allow for the investigation of incipient speciation and related evolutionary processes of selection, gene flow, and migration. Interspecific dynamics, like competition, can impact the size, shape, and directional movement of species in hybrid zones. Hybrid zones contribute to a paradox for the biological species concept because interbreeding between species occurs while parental forms remain distinct. A long‐standing zone of intergradation or introgression exists for eastern and western mosquito fish (Gambusia holbrooki and G. affinis) around Mobile Bay, AL. The region has been studied episodically, over decades, making it perfect for addressing temporal dynamics and for providing a deeper understanding of the genetics of these periodically reclassified fishes (as species or subspecies). We used six microsatellite markers to assess the current population structure and gene flow patterns across 19 populations of mosquito fish and then compared our results with historical data. Genetic evidence demonstrates that the current hybrid zone is located in a similar geographic region as the historical one, even after three decades. Hybrid fish, however, demonstrate relatively low heterozygosity and are genetically distinct from western and eastern mosquito fish populations. Fin ray counts, sometimes used to distinguish the two species from one another, demonstrate more eastern (G. holbrooki) phenotype fish within the molecular genetic hybrid zone today. Mosquito fish are globally invasive, often found on the leading edge of flooded waters that they colonize, so the impact of hurricanes in the wake of climate change was also evaluated. An increase in the frequency and intensity of hurricanes in the hybrid region has occurred, and this point warrants further attention since hurricanes are known to move these aggressive, invasive species into novel territory. This work contributes to our classical understanding of hybrid zone temporal dynamics, refines our understanding of mosquito fish genetics in their native range, evaluates important genotype–phenotype relationships, and identifies a potential new impact of climate change.     

DNA damage in the kidney tissue cells of the fish Rhamdia quelen after trophic contamination with aluminum sulfate

Even though aluminum is the third most common element present in the earth''s crust, information regarding its toxicity remains scarce. It is known that in certain cases, aluminum is neurotoxic, but its effect in other tissues is unknown. The aim of this work was to analyze the genotoxic potential of aluminum sulfate in kidney tissue of the fish Rhamdia quelen after trophic contamination for 60 days. Sixty four fish were subdivided into the following groups: negative control, 5 mg, 50 mg and 500 mg of aluminum sulfate per kg of fish. Samples of the posterior kidney were taken and prepared to obtain mitotic metaphase, as well as the comet assay. The three types of chromosomal abnormalities (CA) found were categorized as chromatid breaks, decondensation of telomeric region, and early separation of sister chromatids. The tests for CA showed that the 5 mg/kg and 50 mg/kg doses of aluminum sulfate had genotoxic potential. Under these treatments, early separation of the sister chromatids was observed more frequently and decondensation of the telomeric region tended to increase in frequency. We suggest that structural changes in the proteins involved in DNA compaction may have led to the decondensation of the telomeric region, making the DNA susceptible to breaks. Moreover, early separation of the sister chromatids may have occurred due to changes in the mobility of chromosomes or proteins that keep the sister chromatids together. The comet assay confirmed the genotoxicity of aluminum sulfate in the kidney tissue of Rhamdia quelen at the three doses of exposure.     

Ecological genomics in full colour

Colour patterns in animals have long offered an opportunity to observe adaptive traits in natural populations. Colour plays myriad roles in interactions within and among species, from reproductive signalling to predator avoidance, leading to multiple targets of natural and sexual selection and opportunities for diversification. Understanding the genetic and developmental underpinnings of variation in colour promises a fuller understanding of these evolutionary processes, but the path to unravelling these connections can be arduous. The advent of genomic techniques suitable for nonmodel organisms is now beginning to light the way. Two new studies in this issue of Molecular Ecology use genomic sequencing of laboratory crosses to map colour traits in cichlid fishes, a remarkably diverse group in which coloration has played a major role in diversification. They illustrate how genomic approaches, specifically RAD sequencing, can rapidly identify both simple and more complex genetic variation underlying ecologically important traits. In the first, Henning et al. ( 2014 ) detect a single locus that appears to control in a Mendelian fashion the presence of horizontal stripes, a trait that has evolved in numerous cichlid lineages. In the second, Albertson et al. ( 2014 ) identify several genes and epistatic interactions affecting multiple colour traits, as well as a novel metric describing integration across colour traits. Albertson et al. ( 2014 ) go further, by quantifying differential expression of parental alleles at a candidate locus and by relating differentiation among natural populations at mapped loci to trait divergence. Herein lies the promise of ecological genomics – efficiently integrating genetic mapping of phenotypes with population genomic data to both identify functional genes and unravel their evolutionary history. These studies offer guidance on how genomic techniques can be tailored to a research question or study system, and they also add to the growing body of empirical examples addressing basic questions about how ecologically important traits evolve in natural populations.     

Introductions, spread and colonization of new localities by fish helminth and crustacean parasites in the British Isles: a perspective and appraisal

Most parasites are disseminated by movements of infected hosts. The increasing extent and rapidity of anthropochore fish movements are causing increased concern related to awareness of their potential and known capacity for disseminating parasites. This paper puts these data in perspective by examining examples of actual and potential translocations of fish helminthes and crustaceans by anthropochore movements offish into and throughout the British Isles, and by distinguishing the processes of dissemination and invasiveness from those of colonization and establishment. An investigation of the British fish and helminth parasite fauna suggests that: (1) the range of many species is not well known, many are local in distribution and appearances beyond the range may reflect detection and patchiness, not translocation; (2) taxonomic problems in many groups hinder detection and determination of range; (3) most parasites possess the attributes of good colonizers so the natural expansion and contraction of ranges are often not noticed or recognized as such and the importance of parasite introductions by natural movements of fish or avian hosts is generally underestimated; (4) invasions are far commoner than colonizations, since conditions for establishment may be very restricted and transmission windows very narrow in time and space; (5) successful colonizations and translocations tend to be documented and attract attention whereas invasions resulting in failed colonizations are seldom observed and more seldom documented, thus biasing our perception. Given the extensive history of fish introductions to, and translocations within, the British Isles it is surprising how few fish helminths and crustaceans have invaded the country successfully (16 species: 11·4%) and how many still show restricted distributions. The majority (68·7%) of introduced helminths are associated with fish having ornamental varieties. Barriers of colonization are more effective than those to invasion and it is clear that most translocations and invasions fail. It is right to be concerned about the dangers, but it is also important to put anthropochore factors in perspective.     

Annotated list of demersal fishes occurring at Sedlo Seamount, Azores north-east central Atlantic Ocean

Several fish surveys were carried out in recent years at Sedlo Seamount, Azores, north-eastern central Atlantic Ocean. An objective of the surveys was to determine the species composition of the demersal fish species living in the area. Four types of sampling gears (bottom trawl and three types of longline) were used at Sedlo Seamount resulting in very different species composition by gear and a very complete coverage of the fish fauna of the area. A list of fishes caught with these sampling methods is presented, along with other specific auxiliary information. Altogether 78 species from 43 families were listed for Sedlo Seamount, and as far as is known, 15 species were recorded for the first time for Azorean waters.     

Sulphur, thiols, and disulphides in the fish epidermis, with remarks on keratinization

Energy dispersive x-ray (EDX) analysis and qualitative and quantitative histochemistry were applied to study the distribution and contents of sulphur, thiols and disulphides in the epidermis of the river lamprey Lampetra fluviatilis , the lesser spotted dogfish Scyliorhinus canicula and the brown trout Salmo trutta fario . Thiols generally reacted weakly throughout the entire epidermis, whereas disulphide reactions were more distinct and differentiated. In the river lamprey, the concentrations of -S-S- groups clearly increased in the developing mucous cells from the stratum basale to the stratum superficiale; skein cells and granular cells reacted negatively to weakly. In the lesser spotted dogfish, amounts of disulphides appeared at moderate concentrations, and only goblet cells displayed a strong reaction. In the brown trout, filament cells showed low concentrations or weak reactions of disulphides, goblet cells and the most outer superficial cells stained strongly. Sulphur distribution and contents generally supported the histochemical observations in normal epidermis cells (absolute sulphur contents: 41–59 mM), only the brown trout showed high amounts of sulphur in the stratum basale (81 mM). The findings corroborate the view that there is an inverse correlation between keratinization and mucous secretion in normal fish epidermis. The sometimes distinct contents of disulphides in the outer mucous layer indicate that this system could endure higher mechanical stress than predictable from its large amounts of neutral glycoproteins.     

Intranasal HB-EGF administration favors adult SVZ cell mobilization to demyelinated lesions in mouse corpus callosum

In the adult rodent brain, the subventricular zone (SVZ) represents a special niche for neural stem cells; these cells proliferate and generate neural progenitors. Most of these migrate along the rostral migratory stream to the olfactory bulb, where they differentiate into interneurons. SVZ-derived progenitors can also be recruited spontaneously to damaged brain areas to replace lost cells, including oligodendrocytes in demyelinated lesions. In this study, we searched for factors able to enhance this spontaneous recruitment of endogenous progenitors. Previous studies have suggested that epidermal growth factor (EGF) could stimulate proliferation, migration, and glial differentiation of SVZ progenitors. In the present study we examined EGF influence on endogenous SVZ cell participation to brain repair in the context of demyelinated lesions. We induced a focal demyelinated lesion in the corpus callosum by lysolecithin injection and showed that intranasal heparin-binding epidermal growth factor (HB-EGF) administration induces a significant increase in SVZ cell proliferation together with a stronger SVZ cell mobilization toward the lesions. Besides, HB-EGF causes a shift of SVZ-derived progenitor cell differentiation toward the astrocytic lineage. However, due to the threefold increase in cell recruitment by EGF treatment, the absolute number of SVZ-derived oligodendrocytes in the lesion of treated mice is higher than in controls. These results suggest that enhancing SVZ cell proliferation could be part of future strategies to promote SVZ progenitor cell mobilization toward brain lesions.     

No short‐ or long‐term effects of geolocator attachment detected in Pied Flycatchers Ficedula hypoleuca

Tracking small passerines using miniaturized location tags is a rapidly expanding field of study. In a 1‐year study, we tested whether there were any short‐ or longer‐term effects of fitting geolocators weighing 3% of body mass on male Pied Flycatchers Ficedula hypoleuca. In the deployment year, we compared adult provisioning rates to nestlings, nestling growth and nest success between nesting attempts in which adult males were fitted with a geolocator, with control nests where males had the same capture history but were not tagged. We found no difference between treatments in provisioning effort by males or their associated female 2 days after geolocator fitting, in terms of nestling growth, subsequent brood reduction or nest success. Return rate, arrival date on territories, nest timing and breeding parameters were compared between tagged and untagged males in the following breeding season. We found no difference in return rate or arrival date, and no difference in nest timing, fecundity or outcome. Our study suggests that fitting lightweight tags to small passerines need not affect behaviour, breeding or apparent between‐year survival. However, tagging new species should still require assessment and comparison with well‐matched control cohorts, and it should be recognized that tag effects could vary between years and populations, mediated by environmental conditions.     

The biogeography of trophic cascades on US oyster reefs

Predators can indirectly benefit prey populations by suppressing mid‐trophic level consumers, but often the strength and outcome of trophic cascades are uncertain. We manipulated oyster reef communities to test the generality of potential causal factors across a 1000‐km region. Densities of oyster consumers were weakly influenced by predators at all sites. In contrast, consumer foraging behaviour in the presence of predators varied considerably, and these behavioural effects altered the trophic cascade across space. Variability in the behavioural cascade was linked to regional gradients in oyster recruitment to and sediment accumulation on reefs. Specifically, asynchronous gradients in these factors influenced whether the benefits of suppressed consumer foraging on oyster recruits exceeded costs of sediment accumulation resulting from decreased consumer activity. Thus, although predation on consumers remains consistent, predator influences on behaviour do not; rather, they interact with environmental gradients to cause biogeographic variability in the net strength of trophic cascades.