Both theoretical and laboratory research suggests that many prey animals should live in a solitary, dispersed distribution unless they lack repellent defences such as toxins, venoms and stings. Chemically defended prey may, by contrast, benefit substantially from aggregation because spatial localization may cause rapid predator satiation on prey toxins, protecting many individuals from attack. If repellent defences promote aggregation of prey, they also provide opportunities for new social interactions; hence the consequences of defence may be far reaching for the behavioural biology of the animal species. There is an absence of field data to support predictions about the relative costs and benefits of aggregation. We show here for the first time using wild predators that edible, undefended artificial prey do indeed suffer heightened death rates if they are aggregated; whereas chemically defended prey may benefit substantially by grouping. We argue that since many chemical defences are costly to prey, aggregation may be favoured because it makes expensive defences much more effective, and perhaps allows grouped individuals to invest less in chemical defences.

1. The aim of this study was to assess the extent to which the behavioural traits of freshwater mussels provide suitable indicators of stress in individuals, towards the advancement of non-invasive, remote monitoring techniques to examine population condition.2. Variation in the expression of particular behavioural metrics was examined in accordance with measurements of oxygen consumption, across environmental stressors (aerial exposure and high concentrations of total suspended solids), and between two freshwater mussel species (Margaritifera margaritifera and Anodonta anatina)3. Aerobic metabolic rate was quantified using intermittent respirometry, and behaviour was observed using time-lapse footage. Comparisons of metabolic response and the occurrence of behavioural traits, across the two stressors, focused on differences between the 24 h pre-exposure period (pre-exposure), the first 3 h of post-exposure (immediate post-exposure), and the time following the initial 3 h of post-exposure until the end of the experimental run (extended postexposure).4. The results of this study demonstrated a relationship between the frequency of occurrence of behavioural responses to stress exposure, associated with valve activity, and significant changes in the metabolic functioning of A. anatina and M. margaritifera mussels. The findings from the study also highlighted substantial intraspecific variation across species and stressors.

No abstract

Alterations to water management practices, in response to a growing demand to maximize energy production from renewable sources, threaten to exacerbate anticipated future water shortages caused by severe drought episodes, brought on by climate change. Across Scotland, many highly managed systems are inhabited by some of the last remaining reproductively viable populations of the freshwater pearl mussel, Margaritifera margaritifera. A lack of empirical evidence concerning mussel responses to alterations in flow is inhibiting the development of effective conservation management practices to prolonged drought. This study addressed this knowledge gap by examining the response of M. margaritifera to controlled water level drawdowns in laboratory and field settings. Using a laboratory flume, the responses of M. margaritifera from two different populations (a regulated system versus an unregulated system) were compared across rates of drawdown and density treatments. An analogous field trial was undertaken to examine the responses of M. margaritifera in a regulated system, with a hydroelectric dam facilitating a controlled drawdown. The study showed that M. margaritifera can detect alterations in flow depth, which culminate in the emersion of mussel beds, and respond by undertaking vertical and horizontal movements to mitigate the risk of prolonged aerial exposure. Results from the field trial corroborated findings from the flume experiments, with 80% of mussels shown to avoid emersion successfully by tracking receding water levels. Findings from this study support the role of controlled drawdowns in regulated rivers to reduce mortalities associated with receding water levels during prolonged low‐flow episodes. Differences between populations in response highlight a need to adopt a context‐dependent approach to conservation efforts.

<p>Whilst there is encouragement to be taken from the fact that Scotland remains a stronghold for M. margaritifera populations, a trend of continued population decline persists. Our understanding of the hydraulic characteristics associated with successful M. margaritifera proliferation in the wild is poor. Additionally, evidence to suggest how M. margaritifera respond to variation in the associated parameters, is limited. The primary motif of this research project is to address the knowledge gap. Initial experimental analysis sought to establish a non-invasive method of quantifying acute mussel stress; using behavioural response indicators, coupled with measures of physiological condition. Results from this work have provided a foundation for investigating mussels as biosensors to remotely track alterations in chemical, hydraulic, and geomorphological parameters. Further research has investigated the response of live mussels to alterations in flow depth, with consideration of riverbed geomorphology, in both a laboratory flume and regulated river. Current experimental work in a laboratory flume is utilising remote sensor technology to understand the impact of flow velocity on mussel behaviour; examining how flow velocity may impact habitat selection, and how a mussel’s behaviour may in turn affect the surrounding hydrodynamics. The results emanating from this research will be novel and will ultimately provide urgently needed empirical data to drive future conservation strategies implemented by government (SNH, SEPA) and utilized by the hydroelectric industry (SSE).</p>