Phd. defense of Nicolas Larranaga
Ecological correlates of diel activity in stream-dwelling Arctic charr Salvelinus alpinus
Diel activity, the partitioning of time between periods of activity and rest, gives insights into how organisms compete for resources in time. Some species show plasticity in the rate and timing of their activity,which enables to study associations with ecological factors. Streamdwelling fishes like salmonids are a textbook example of animals with variable activity patterns. During this Ph.D., I studied the diel activity of individually tagged juvenile Arctic charr in several field experiments and studies, focusing on critical factors for salmonids ecology. I found that Arctic charr increased activity (i) with rising temperature, (ii) when shelters are limited, (iii) in fast current, (iv) under relatively stable waterflow and (v) at high population density. The distribution of activity in time was also affected by ecological conditions in all studies. Flexible activity patterns coincided with modifications of other behaviors (aggregation, foraging mode, habitat selection). Arctic charr sometimes appear to maintain growth under suboptimal conditions by modifying their activity (e.g. limited shelters), whereas in other situations they increase activity under conditions that yield higher growth (high current velocity). In all but one experiment, more active fish grew faster. This relationship depended on the environment. It was stronger in faster currents, and under stable waterflow. These results have important implications for biological fields such as behavioral ecology, by estimating behavioral flexibility, salmonids ecology via food intake and growth under different ecological scenarii, and conservation biology by using behavior to assess the effect of future changes in the physical habitat of stream fishes
Parasitic freshwater pearl mussel larvae impair foraging, activity, and dominance performance in juvenile brown trout (Salmo trutta L.)
The life cycle of the freshwater pearl mussel includes a parasitic larval phase (glochidia) on the gills of a salmonid host. This phenomenon has been evolved over a very long time and Infestation in juvenile salmonids has traditionally been assumed to be more or less benign to the host fish. Here I will present some recent work where we have investigated the relationship between glochidia encystment and behavioral parameters such as foraging activity and agonistic behaviour in brown trout. Our findings suggest that high loads of glochidiae larvae had significant effects on foraging, activity and behavior. In addition, glochidia encystment also imposed a physiological effect on the trout reflected in an increased metabolism and haematocrit in infested fish. Preliminary results also suggest that glochidia infestation is non-random and that the behaviour of the host fish can influence the likelihood of glochidia infestation where active fish were more likely to get infested. Hence, for management of mussel populations in the streams it is important to acknowledge that activity of the fish both may affect the infestation rate as well as the dispersal of the mussel. Heavy glochidia loads, may also negatively influence host fitness due to reduced competitive ability. Captive breeding programs where artificially infested fish are translocated into streams should therefore avoid high infestation rates. Instead, low levels of infestation on host fish which do not affect trout behavior but maintains mussel populations, may be optimal in these cases.
Dr. Neil B. Metcalfe professor at the University of Glasgow will talk about:
Why does metabolic rate vary between individuals?
In all species studied to date both minimal and maximal rates of metabolism show pronounced variation among individuals, even if they are the same size, sex and nutritional state, and look identical to the human eye. In this talk I will explore the causes of this variation (delving into the mitochondria, and even the position of an egg in the ovary), and its behavioural and ecological consequences. The topic will be illustrated using examples drawn from our recent work on salmonid fishes.
Both speakers are in Iceland for the examination of the Ph.D. thesis of Nicolas Larranaga – Ecological correlates of diel activity in stream-dwelling Arctic charr Salvelinus alpinus on November 21st.
Chair for these talks will be Stefán Ó. Steingrímsson.