Temperature surpasses the effects of velocity and turbulence on swimming performance of two invasive non-native fish species.

Global climate change continues to impact fish habitat quality and biodiversity, especially in regard to the dynamics of invasive non-native species. Using individual aquaria and an open channel flume, this study evaluated the effects of water temperature, flow velocity and turbulence interactions on swimming performance of two lentic, invasive non-native fish in the UK, pumpkinseed (Lepomis gibbosus) and topmouth gudgeon (Pseudorasbora parva). Burst and sustained swimming tests were conducted at 15, 20 and 25°C. Acoustic Doppler velocimetry was used to measure the flume hydrodynamic flow characteristics. Both L. gibbosus and P. parva occupied the near-bed regions of the flume, conserving energy and seeking refuge in the low mean velocities flow areas despite the relatively elevated turbulent fluctuations, a behaviour which depended on temperature. Burst swimming performance and sustained swimming increased by up to 53% as temperature increased from 15 to 20°C and 71% between 15 and 25°C. Furthermore, fish test area occupancy was dependent on thermal conditions, as well as on time-averaged velocities and turbulent fluctuations. This study suggests that invasive species can benefit from the raised temperatures predicted under climate change forecasts by improving swimming performance in flowing water potentially facilitating their further dispersal and subsequent establishment in lotic environments.

Influence of host reproductive state on Sphaerothecum destruens prevalence and infection level.

Sphaerothecum destruens is an obligate intracellular parasite with the potential to cause high mortalities and spawning inhibition in the endangered cyprinid Leucaspius delineatus. We investigated the influence of L. delineatus's reproductive state on the prevalence and infection level of S. destruens. A novel real time quantitative polymerarse chain reaction (qPCR) was developed to determine S. destruens' prevalence and infection level. These parameters were quantified and compared in reproductive and non-reproductive L. delineatus. The detection limit of the S. destruens specific qPCR was determined to be 1 pg of purified S. destruens genomic DNA. Following cohabitation in the lab, reproductive L. delineatus had a significantly higher S. destruens prevalence (P<0.05) and infection levels (P<0.01) compared to non-reproductive L. delineatus. S. destruens prevalence was 19% (n=40) in non-reproductive L. delineatus and 41% (n=32) in reproductive L. delineatus. However, there was no difference in S. destruens prevalence in reproductive and non-reproductive fish under field conditions. Mean infection levels were 18 and 99 pg S. destruens DNA per 250 ng L. delineatus DNA for non-reproductive and reproductive L. delineatus respectively. The present work indicates that S. destruens infection in L. delineatus can be influenced by the latter's reproductive state and provides further support for the potential adverse impact of S. destruens on the conservation of L. delineatus populations.

Interactions between riparian shading and food supply: a seasonal comparison of effects on time budgets, space use and growth in Atlantic salmon Salmo salar.

This study examines seasonal (winter v. summer) differences in space-time budgets, food intake and growth of Atlantic salmon Salmo salar parr in a controlled, large-scale stream environment, to examine the direction and magnitude of shifts in behaviour patterns as influenced by the availability of overhead cover and food supply. Salmo salar parr tested in the presence of overhead cover were significantly more nocturnal and occupied more peripheral positions than those tested in the absence of overhead cover. This increase in nocturnal activity was driven primarily by increased activity at night, accompanied by a reduction in daytime activity during winter. The presence of overhead cover had no effect on rates of food intake or growth for a given food supply in a given season. Growth rates were significantly higher for fish subjected to a high food supply than those subjected to a low food supply. Food supply did not affect the extent to which S. salar parr were nocturnal. These results were consistent between winter and summer. The use of riparian shading as a management technique to mitigate the effects of warming allows the adoption of more risk-averse foraging behaviour and may be particularly beneficial in circumstances where it serves also to increase the availability of food.

Deposition of Atlantic salmon Salmo salar carcasses in a Scottish upland catchment.

Radio telemetry was utilized to track 38 Atlantic salmon Salmo salar across space and time during and following their spawning run on the Conon system, Scotland. The data collected were used to assess the proportion of S. salar able to migrate successfully from an upland oligotrophic area of the catchment and the distribution of the carcasses of those fish that remained. Of these fish, 35% successfully migrated from the study area after the spawning period. The fish that remained were distributed approximately equally between riverine and lacustrine areas, but with a strong tendency to accumulate in regions of relatively slow water flows.

Individual MHC class I and MHC class IIB diversities are associated with male and female reproductive traits in the three-spined stickleback.

Genes of the major histocompatibility complex (MHC) are indispensable for pathogen defence in vertebrates. With wild-caught three-spined sticklebacks (Gasterosteus aculeatus) we conducted the first study to relate individual reproductive parameters to both MHC class I and II diversities. An optimal MHC class IIB diversity was found for male nest quality. However, male breeding colouration was most intense at a maximal MHC class I diversity. One MHC class I allele was associated with male redness. Similarly, one MHC class IIB allele was associated with continuous rather than early female reproduction, possibly extending the reproductive period. Both alleles occurred more frequently with increasing individual allele diversity. We suggest that if an allele is currently not part of the optimum, it had not been propagated by choosy females. The parasite against which this allele provides resistance is therefore unlikely to have been predominant the previous year - a step to negative frequency-dependent selection.

Coping with divided attention: the advantage of familiarity.

The ability of an animal to perform a task successfully is limited by the amount of attention being simultaneously focused on other activities. One way in which individuals might reduce the cost of divided attention is by preferentially focusing on the most beneficial tasks. In territorial animals where aggression is lower among familiar individuals, the decision to associate preferentially with familiar conspecifics may therefore confer advantages by allowing attention to be switched from aggression to predator vigilance and feeding. Wild juvenile brown trout were used to test the prediction that familiar fishes respond more quickly than unfamiliar fishes to a simulated predator attack. Our results confirm this prediction by demonstrating that familiar trout respond 14% faster than unfamiliar individuals to a predator attack. The results also show that familiar fishes consume a greater number of food items, foraging at more than twice the rate of unfamiliar conspecifics. To the best of our knowledge, these results provide the first evidence that familiarity-biased association confers advantages through the immediate fitness benefits afforded by faster predator-evasion responses and the long-term benefits provided by increased feeding opportunities.

The benefits of genetic diversity outweigh those of kin association in a territorial animal.

The theories of kin selection and heterogeneous advantage have been central to studies of altruistic behaviour and the evolution of sex over the last 35 years. Yet they predict diametrically opposite effects of genetic diversity on population density. Close relatives gain inclusive fitness advantages by preferentially associating with and behaving altruistically towards one another. However, heterogeneous advantage, which predicts competition to be highest when genetic diversity is low, suggests that benefits will be greater for individuals in groups of non-kin. Here we test how these two processes balance and affect the productivity of populations of animals in natural habitats. We report from a study of juvenile Atlantic salmon in the wild that heterogeneous advantage outweighs the benefits of kin-biased behaviour, resulting in a 1.8-fold higher population biomass and significantly better condition of individual fish.