Differential host utilisation by different life history stages of the fish ectoparasite Argulus foliaceus (Crustacea: Branchiura).

In this study we examine differences in the occurrence of life history stages of the destructive fish ectoparasite Argulus foliaceus (L., 1758) on eight fish species (stickleback, rudd, roach, gudgeon, bream, tench, crucian carp and common carp) sampled from a mixed-species recreational fishing lake on nine occasions during late spring and summer. Total numbers ofA. foliaceus, as well as the number of larval, juvenile and adult parasite stages, from each fish were recorded along with the fish species. Lice generally exhibited an aggregated distribution approximating a negative binomial distribution. Significant differences in the prevalence, intensity and intensity frequency distribution were observed between life history stages and between host species. In general, all life history stages of A. foliaceus exhibited an over-dispersed distribution. However, larval lice did show some degree of aggregation particularly within the stickleback samples. Infection data for parasite larval stages suggested that sticklebacks are more likely to be infected than other host species. For adult lice, however, carp appeared to be the main host. We propose that A. foliaceus infection characteristics are predominantly determined by the level of host exposure to the parasite and its life history stages (larval, juvenile and adult) rather than by an innate difference in host susceptibility related to individual host factors such as immune responses. We conclude that host exposure is determined by the parasite-host behavioural interplay related to species-specific ecology and behavioural traits such as microhabitat preference and normal swimming speed.

Secretory immunoglobulin A reactivity to acute and cumulative acute multi-tasking stress: relationships between reactivity and perceived workload.

The effects of an acute stressor upon secretory immunoglobulin A (S-IgA) were assessed using a task that requires participants to attend and respond to several stimuli simultaneously and is therefore analogous to a variety of working environments. In two studies, the task was administered for periods of 5 min to healthy samples of men and women at two sessions 24 h apart (n = 49) and three times in succession within one session (n = 20). Multi-tasking stress was, at all sessions, associated with increases in S-IgA secretion. Inter and intra-session reliability of pre and post-stress S-IgA measures was observed, although the reliability of stress reactivity data was reduced. Classification of participants as either high or low S-IgA reactors revealed differences in their perceptions of task workload. Low S-IgA reactors consistently perceived the task to be more demanding and frustrating than did those who demonstrated high S-IgA reactivity. We conclude that S-IgA reactivity to stressful situations depends not just upon the task, but also upon individual perceptions of the stressor.