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Understanding the eco‐evolutionary processes which drive phenotypic variability in non‐native species is crucial to predicting impact and informing spatially explicit management models. Invasive redclaw crayfish, Cherax quadricarinatus, are spreading rapidly through the ecologically and economically important Upper and Middle Zambezi system in south‐central Africa.We tested whether there was an invasion front effect in the Barotse floodplain and disentangle whether these effects were related to environmental filtering, spatial sorting, or density‐dependent processes along a nonlinear 200 km invasion gradient over seasonal hydrological periods.Crayfish spread up‐ and down‐stream indicated an expanding population compared to the former invasion front in 2019, facilitated by both sexes. Wet season detection probability and relative abundance were lower than in the dry season. No signals of environmental filtering were detected as a result of high connectivity of habitats in the wet season.The invasion front population was characterised by lower relative abundance, lower body condition, larger overall body and chelae size, and longer front leg length. There was no effect on sex ratio. This indicated that spatial sorting, density‐dependent processes and predation pressure are acting as selective forces on phenotypic variability across the invasion gradient.Better understanding of the effects of flood regime and trophic interactions on phenotypic variability and dispersal is urgently needed. Population suppression to reduce spatial sorting and conspecific competition could be a viable management option at the invasion front. [ABSTRACT FROM AUTHOR]

Global amphibian populations are declining, and invasive fish are known to impact many threatened species. South Africa has both a biodiverse amphibian fauna and a rich history of invasive fish introductions with high establishment success. Studies have identified some preliminary evidence for negative impacts of invasive salmonids on two ghost frog species (Anura: Heleophrynidae). This study aims to investigate whether these negative impacts previously reported are reflected across a broader scale. Tadpoles of two species, Heleophryne regis and H. purcelli were sampled in the presence and absence of invasive fish at 111 sites across 26 streams in the Western Cape province of South Africa. A generalised linear mixed model showed invasive fish to have the most significant negative effect explaining tadpole abundance. Mean tadpole abundance decreases by 18 times in the presence of invasive fish. Environmental variables with significant effects on tadpole abundance include pH, oxygen saturation, temperature, stream depth and non-native riparian vegetation type. We also define an environmental niche of ghost frog tadpoles which does not differ between species. We conclude that invasive fish have significant negative impacts on ghost frog tadpole abundance, but the effect of the environment should not be overlooked in amphibian conservation planning and invasive species management decisions. This study supports the removal of invasive fish and alien vegetation to improve the conservation of ghost frogs. [ABSTRACT FROM AUTHOR]

The morphology of animal body structures influences their function; intrapopulation plasticity in diet composition can occur where head morphology limits gape size. The European eel, Anguilla anguilla, a critically endangered catadromous fish, shows significant intrapopulation variations in head width, with broader headed individuals being more piscivorous., Infection of eels during their freshwater phase by Anguillicoloides crassus, an invasive nematode parasite, involves paratenic fish hosts. We tested the relationships between their infection status, head functional morphology (as head width/total length ratio; HW: TL) and the proportion of fish in diet (estimated by stable isotope mixing models) across three populations., The extent of piscivory in the diets of individual eels increased significantly as their HW: TL ratios increased. There were no significant differences between infected and uninfected eels in their total lengths and hepatic-somatic indices. However, the HW: TL ratios of infected eels were significantly higher than those of uninfected eels and, correspondingly, their diet comprised a higher proportion of fish., Logistic regression revealed that head morphology and diet were significant predictors of infection status, with models correctly assigning up to 78% of eels to their infection status. Thus, eel head functional morphology significantly influenced their probability of being infected by invasive A. crassus, most likely through increased exposure to fish paratenic hosts. Accordingly, the detrimental consequences of infections are likely to be focussed on those individuals in freshwater populations whose functional morphology enables greater specialisation in piscivory. [ABSTRACT FROM AUTHOR]

The European barbel Barbus barbus is threatened in areas of its range because of its sensitivity to anthropogenic disturbance in riverine habitats and, in the UK, is indigenous to a relatively small number of east-flowing rivers, with nonindigenous populations present in other rivers following introductions for angling enhancement. Fish stock assessment surveys completed between 2002 and 2010 collated age and growth data from 20 rivers across their indigenous and nonindigenous UK range. Analyses revealed that individuals present in samples are of 21 years old, with growth rates highly variable between rivers. There was no relationship between growth rates and the maximum age of fish per river, and there was no difference in growth rates between their indigenous and nonindigenous ranges. A range of abiotic data were collated and analysed against the growth data; these analyses suggested higher mean growth rates were evident in rivers of higher biological water quality (expressed as British Monitoring Working Party Score) and higher mean air temperatures (used as a surrogate of water temperature). That growth of B. barbus was significantly and positively enhanced by increased biological water quality was in contrast to cyprinid fishes such as roach Rutilus rutilus and suggests that as river water quality continues to improve through reduced nutrient inputs, further ecological changes are likely in riverine fish communities. [ABSTRACT FROM AUTHOR]

Simple Summary: Superficial Digital Flexor Tendon (SDFT) injuries are the most common musculoskeletal injury reported in equestrian jumping disciplines. In an attempt to reduce incidences of injuries in elite event horses, Ridden Water Submersion Training (RWST) is a form of condition training that involves submerging the horse up to sternum height in water and trotting for set intervals. It is used by a small number of trainers to increase cardiovascular fitness whilst potentially minimising tendon temperature increase, which is typically reported during traditional condition training sessions. The results of this study suggest that RWST acted as a moderate sub-maximal intensity level of exercise in a group of elite international event horses whilst preventing the accompanying increase of distal limb temperature commonly associated with condition training on land. RWST could thus be a useful adjunct to current condition training protocols, particularly for horses that compete in disciplines that have high incidence rates of tendon injury. However, further research is required to provide a more comprehensive understanding of the workload imposed during RWST training. This observational study aimed to elucidate the effects of RWST on the cardiovascular and musculoskeletal systems of horses and concurrently determine whether RWST limits distal limb temperature increases previously reported during gallop training on land. A group of 15 clinically sound international event horses were recruited, and heart rate (HR), speed (km/h) and thermal images of the distal limb were analysed at set intervals during RWST training. Intervals of RWST produced a total mean HRmax value of 65.18 ± 3.76%, which is within the parameters for increased aerobic stamina. Mean HR increased significantly (p < 0.01) while mean distal limb temperature decreased significantly (p < 0.01) between warm-up and RWST, which contrasts with positive correlations previously reported during gallop training on land. These preliminary results suggest that RWST can be classed as a moderate submaximal intensity exercise in elite international event horses whilst restricting an increase in temperature of the distal limb that is commonly associated with tendon rupture. Horses competing at very elite levels of eventing only represent a small percentage of the total performance population; therefore, further research is needed to ascertain the physiological effects of RWST in non-elite performance horses, as well as horses competing across various equestrian disciplines. [ABSTRACT FROM AUTHOR]