Iain Barber

BEHAVIOURAL RESPONSES TO SIMULATED AVIAN PREDATION IN FEMALE THREE SPINED STICKLEBACKS: THE EFFECT OF EXPERIMENTAL SCHISTOCEPHALUS SOLIDUS INFECTIONS

Barber, I., Walker, P., Svensson, P. A. (2004). Behavioural responses to simulated avian predation in three-spined sticklebacks: the effect of experimental Schistocephalus infections. Behaviour, 141,(11-12),1425-1440.

Split-clutch IVF: a technique to examine indirect fitness consequences of mate preferences in sticklebacks.

Although laboratory mate choice experiments and field studies often reveal certain traits of male three-spined sticklebacks (as well as other model species) to be attractive to mate searching females, evidence that mating with males possessing such traits improves offspring survival and performance is scarce. In particular, there is a lack of unambiguous data linking preferred male traits with inherited genetic viability, which are essential for good genes models of sexual selection. In this paper, we provide a protocol for performing half-sibling crosses in three-spined sticklebacks using a split-clutch in vitro fertilisation (SC-IVF) technique. This approach controls for variable maternal investment and standardises parental care - two confounding variables that frequently distort the relationship between sire trait and offspring performance - allowing the detection of offspring viability characteristics linked to specific sire traits such as sexual coloration, body size or condition.

Effects of experimental Schistocephalus solidus infections on growth, morphology and sexual development of female three-spined sticklebacks, Gasterosteus aculeatus

The use of naturally infected hosts in studies attempting to identify parasite-induced changes in host biology is problematical because it does not eliminate the possibility that infection may be a consequence, rather than a cause, of host trait variation. In addition, uncontrolled concomitant infections may confound results. In this study we experimentally infected individual laboratory-bred female three-spined sticklebacks Gasterosteus aculeatus L. with the pseudophyllidean cestode Schistocephalus solidus [Müller], and compared the morphology and growth patterns of infected females with sham-exposed controls over a 16-week period. Fish were fed a ration of 8% body weight per day. Non-invasive image analysis techniques allowed the growth of individual plerocercoids to be tracked in vivo throughout the course of infection, and patterns of host and parasite growth were determined. Females that developed infections diverged morphometrically from unexposed control females and exposed-uninfected females at 6 weeks post-infection, with the width of the body at the pectoral fins giving the earliest indication of infection success. When including the plerocercoid, infected females gained weight more quickly than controls, but when plerocercoid weight was removed this trend was reversed. There was no effect of infection on the increase in fish length. Plerocercoids grew at different rates in individual hosts, and exhibited measurable sustained weight increases of up to 10% per day. Final estimates of plerocercoid weight from morphometric analysis prior to autopsy were accurate to within +/- 17% of actual plerocercoid weight. At autopsy, infected female sticklebacks had significantly lower perivisceral fat reserves but had developed significantly larger ovaries than controls. The results are discussed in relation to previous studies examining natural infections, and the value of utilizing experimental infections to examine ecological aspects of host-parasite interactions is discussed.

Shoaling behaviour of sticklebacks infected with the microsporidian parasite, Glugea anomala

We compared the shoaling behaviour of three-spined sticklebacks, Gasterosteus aculeatus, infected with the microsporidian, Glugea anomala, to that of non-infected conspecifics. Infected fish lost significantly more weight than non-infected fish during a period of food deprivation, suggesting a metabolic cost to parasitism. In binary shoal choice tests, non-infected test fish showed an association preference for a shoal of non-infected over a shoal of infected conspecifics; infected test fish displayed no preference. Infected fish, however, showed a higher overall tendency to shoal than non-parasitised fish. Furthermore, infected fish occupied front positions within a mixed school. We consider the behavioural differences between infected and uninfected fish in the context of their potential benefits to the fish hosts and the parasites.