In a changing environment, learning and memory are essential for an animal's survival and reproduction. The role played by the environment in shaping learning and memory is now attracting considerable attention. Until now, studies have tended to compare the behaviour of two, or at best a few species, but interspeci¢c comparisons can be misleading as many life history variables other than environment may di¡er between species. Here we report on an experiment designed to determine how learning varies between di¡erent populations of the same species, the three-spined stickleback. We found di¡erences between the populations in their ability to solve a spatial task and also in the spatial strategies they used. A second simple learning task showed that these di¡erences were not the result of gross di¡erences in learning ability or adaptation to laboratory conditions. We discuss these results and suggest that the behavioural di¡erences may relate to features of the respective habitats from which the ¢sh were sampled.
Experiments were designed to investigate whether three-spined sticklebacks Gasterosteus aculeatus can use direction of water flow as an orientation cue. The fish had to learn the location of a food patch in a channel where water flow direction was the only reliable indicator of the food patch position. Fish from two ponds and two rivers were trained and tested in the spatial task to determine whether river three-spined sticklebacks are more adept at using water flow as a spatial cue than fish from ponds. All fish were able to use water flow to locate the food patch but one of the two river groups was significantly faster at learning the patch location. When the task was reversed so that fish that had formerly been trained to swim downstream now had to learn to swim upstream and vice versa both river groups learned the reversed task faster than the two pond groups. In a second experiment, to investigate whether fish from ponds or rivers vary in the type of spatial cue that they prefer to use, fish from one pond and one river were given a choice between two different types of spatial cue: flow direction or visual landmarks. A test trial in which these two cues were put into conflict revealed that the river population showed a strong preference for flow direction whilst the pond population preferred to use visual landmarks.
To investigate the mechanisms underlying preferred spatial information use in Three-spined sticklebacks we reared fish derived from contrasting habitats (pond and river populations) under a range of conditions. The rearing conditions were designed to determine whether the spatial information used by sticklebacks is population specific, whether it is learned or whether it is produced by an interaction between these two factors. Fish reared under different conditions were trained to solve two experimental tasks to determine what spatial information they preferred to use. The results indicate that the fish learned spatial cues relevant to the environment that they were raised in but there was also evidence of a gene by environment interaction that influenced which spatial cues were learned.
The Irish Pollan Coregonus autumnalis Pallas is unique in western Europe, with its current known distribution being limited to four lakes in Ireland; Lough Neagh and Lower Lough Erne in Northern Ireland and Lough Ree and Lough Derg in the Republic of Ireland. In this paper we report the fi rst authenticated record of pollan in a fi fth Irish lake-Lough Allen, County Leitrim. Using hydroacoustic technology, combined with a ground-truth gill netting survey, abundance estimates show that the population is relatively small, numbering in the region of several thousand individuals. Captured fi sh ranged in age from 1+ to 4+, indicating reproductive success in each year over the previous four years. Threats to sensitive species such as pollan include eutrophication, competition with introduced species, land drainage and the resulting siltation of downstream lakes. Further detailed investigations on the status of this newly discovered population, including location of spawning sites, recruitment success and genetic relationship with other Irish populations, are crucial in informing management decisions with a view to protecting this unique and threatened fi sh species.
ABSTRACT1. Mesotrophic lakes are a threatened habitat in the United Kingdom (UK), and are specified within the UK Biodiversity Action Plan (UKBAP) as requiring protection. Lough Melvin is a large mesotrophic lake that is of particular interest owing to the genetic diversity of its brown trout, but it is currently showing signs of nutrient enrichment.2. In 1990, average lake total phosphorus (TP) was less than 19 mg P L À1 but increased to 29.5 mg P L À1 by July 2001. Inflow TP also increased from 34 mg P L À1 to 41 mg P L À1 over the same period. Neither phosphorus nor nitrogen appeared to be limiting.3. Despite higher lake TP, annual chlorophyll a did not increase, remaining less than 5 mg L À1 . The phytoplankton was dominated by cyanobacteria and seems to have remained unchanged since the 1950s. Rotifer numbers increased significantly after 2001 but the macro-zooplankton did not. The absence of a phytoplankton response to P enrichment is attributed to light limitation caused by peat staining and thorough mixing.4. In the catchment, an accelerated programme of clear-felling began in 1999. Recent changes in the lake are consistent with the known impacts of clear-felling conifers on peat soils, namely larger P and dissolved organic carbon (DOC) losses. The latter was reflected in a lower Secchi depth and an enhanced microbial food-web supporting a larger rotifer population.5. It is suggested that, for the purposes of the Water Framework Directive (WFD), Lough Melvin and other large, alkaline but peat-stained lakes may be treated as a distinct lake type as they do not fit easily into the conventional classifications of dystrophic or mesotrophic lakes.
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