We expect that natural selection should result in behavioural rules which perform well; however, animals (including humans) sometimes make bad decisions. Researchers account for these with a variety of explanations; we concentrate on two of them. One explanation is that the outcome is a side effect; what matters is how a rule performs (in terms of reproductive success). Several rules may perform well in the environment in which they have evolved, but their performance may differ in a ‘new’ environment (e.g. the laboratory). Some rules may perform very badly in this environment. We use the debate about whether animals follow the matching law rather than maximizing their gains as an illustration. Another possibility is that we were wrong about what is optimal. Here, the general idea is that the setting in which optimal decisions are investigated is too simple and may not include elements that add extra degrees of freedom to the situation.

We present a novel demonstration that violations of transitive choice can result from decision strategies that maximize fitness. Our results depend on how the available options, including options not currently chosen, influence a decision-maker's expectations about the future. In particular, they depend on how the presence of an option may act as an insurance against a run of bad luck in the future.

The European eel, Anguilla anguilla, is classified as critically endangered by the IUCN. To protect what remains of the European eel population, accurate monitoring methods for this species are important. Environmental DNA (eDNA) techniques are gaining popularity for ecological monitoring of aquatic organisms because they are sensitive and noninvasive. This study directly compared catch data from a standardized fyke‐net fishing survey with a single species A. anguilla eDNA survey in five freshwater lakes in Ireland. The eDNA was recovered by the filtration of water samples and amplified by quantitative real‐time polymerase chain reaction (qPCR). European eel eDNA was reliably determined in 83% (70/84) of surface water samples collected from lakes classified as having high, medium, and low eel populations. In addition, there was a positive association between the eDNA concentrations recovered and the eel population classification with lower eDNA concentrations in lakes classified as low eel population lakes. Similar amounts of A. anguilla eDNA were detected in water samples collected from open water and shore‐side, suggesting shore sampling is an adequate method for eel detection. Together, the results demonstrate that eDNA sampling is more sensitive for detecting eel presence in low eel population environments than standard survey methods and may be a useful noninvasive tool for monitoring A. anguilla species distribution.

The size and fecundity of parasitic nematodes are constrained by the host immune response. For the parasitic nematode of rats,Strongyloides ratti, parasitic females infecting immunized rats are smaller and less fecund than those infecting naïve rats. Here, we investigated whether these constraints on size and fecundity are life-long. This was done by comparison of worms from different immunization and immunosuppression regimes. It was found that theper capitafecundity of parasitic females ofS. rattiis fully reversed, but that their size is only partially reversed, if previously immunized hosts are subsequently immunosuppressed, suggesting that fecundity is not subject to life-long constraints. The host immune response also resulted in allometric changes in the parasitic females. The significance of these results with respect to the growth and control of nematode fecundity are discussed.

In August 2009 the Natural History Museum London, Hungarian Natural History Museum and Systematic Zoology Research group, Entomological Museum in Leon and The Society for Environmental Exploration, mounted the first earthworm collection expedition to Nicaragua. No native earthworm species had previously been recorded for this country. This paper lists 18 new species records for the Country with the description of two new taxa to science: Eutrigaster (Graffia) azul sp. n. and Eutrigaster (Graffia) nicaraoi sp. n. New data on the species Eutrigaster (Eutrigaster) oraedivitis Cognetti, 1904 is also presented here.