Larval size in acanthocephalan parasites: Influence of intraspecific competition and effects on intermediate host behavioural changes

In extensive livestock production, high densities may inhibit regulation processes, maintaining high levels of intraspecific competition over time. During competition, individuals typically modify their behaviours, particularly feeding and bite rates, which can therefore be used as indicators of competition. Over eight consecutive seasons, we investigated if variation in herd density, food availability, and the presence of a potential competitor, the guanaco (Lama guanicoe), was related with behavioural changes in domestic sheep in Chilean Patagonia. Focal sampling, instantaneous scan sampling, measures of bite and movement rates were used to quantify behavioural changes in domestic sheep. We found that food availability increased time spent feeding, while herd density was associated with an increase in vigilant behaviour and a decrease in bite rate, but only when food availability was low. Guanaco presence appeared to have no impact on sheep behaviour. Our results suggest that the observed behavioural changes in domestic sheep are more likely due to intraspecific competition rather than interspecific competition. Consideration of intraspecific competition where guanaco and sheep co-graze on pastures could allow management strategies to focus on herd density, according to rangeland carrying capacity.

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Acanthocephalan size and sex affect the modification of intermediate host colouration

Parasitology ◽

10.1017/s0031182009006180 ◽

2009 ◽

Vol 136 (8) ◽

pp. 847-854 ◽

Cited By ~ 14

Author(s):

D. P. BENESH ◽

O. SEPPÄLÄ ◽

E. T. VALTONEN

Keyword(s):

Intermediate Host ◽

Adaptive Strategy ◽

Female Size ◽

Larval Size ◽

Male And Female ◽

Establishment Success ◽

Acanthocephalus Lucii ◽

Host Mortality ◽

Male Parasite ◽

The Relationship

SUMMARYFor trophically transmitted parasites, transitional larval size is often related to fitness. Larger parasites may have higher establishment success and/or adult fecundity, but prolonged growth in the intermediate host increases the risk of failed transmission via natural host mortality. We investigated the relationship between the larval size of an acanthocephalan (Acanthocephalus lucii) and a trait presumably related to transmission, i.e. altered colouration in the isopod intermediate host. In natural collections, big isopods harboured larger worms and had more modified (darker) abdominal colouration than small hosts. Small isopods infected with a male parasite tended to have darker abdominal pigmentation than those infected with a female, but this difference was absent in larger hosts. Female size increases rapidly with host size, so females may have more to gain than males by remaining in and growing mutually with small hosts. In experimental infections, a large total parasite volume was associated with darker host respiratory operculae, especially when it was distributed among fewer worms. Our results suggest that host pigment alteration increases with parasite size, albeit differently for male and female worms. This may be an adaptive strategy if, as parasites grow, the potential for additional growth decreases and the likelihood of host mortality increases.

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Changes induced by Hymenolepis diminuta (Cestoda) in the behaviour of the intermediate host Tenebrio molitor (Coleoptera)

Canadian Journal of Zoology ◽

10.1139/z91-321 ◽

1991 ◽

Vol 69 (9) ◽

pp. 2291-2294 ◽

Cited By ~ 26

Author(s):

Hilary Hurd ◽

Sharon Fogo

Keyword(s):

Intermediate Host ◽

Aggregation Pheromone ◽

Tenebrio Molitor ◽

Significant Loss ◽

Hymenolepis Diminuta ◽

Male And Female ◽

Behavioural Changes ◽

Loss Of Response ◽

Host Behaviour ◽

Dose Dependent

Metacestodes of the rat tapeworm, Hymenolepis diminuta, have been shown to induce behavioural changes in the intermediate host Tenebrio molitor (Coleoptera). Male and female beetles, examined 11–12 days postinfection, were shown to exhibit a significant decrease in activity and photophobic behaviour. In addition, a significant loss of response to aggregation pheromone occurred in both sexes. No differences in host behaviour were detected 4–5 days postinfection. It thus appears that behavioural changes are associated with parasite maturity. We were unable to demonstrate a dose-dependent loss of photophobic behaviour.

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Parasite-induced changes in the behaviour of cestode-infected beetles: adaptation or simple pathology?

Canadian Journal of Zoology ◽

10.1139/z96-141 ◽

1996 ◽

Vol 74 (7) ◽

pp. 1268-1274 ◽

Cited By ~ 27

Author(s):

Tonia Robb ◽

Mary L. Reid

Keyword(s):

Intermediate Host ◽

Post Infection ◽

Tribolium Confusum ◽

Hymenolepis Diminuta ◽

Intermediate Hosts ◽

Larval Form ◽

Infected Female ◽

Behavioural Changes ◽

Male Pheromones ◽

Induced Changes

Although the cause is often unclear, many parasites alter the behaviour of their intermediate hosts. The larval form of the rat tapeworm, Hymenolepis diminuta, has previously been shown to modify the behaviour of its intermediate host, the flour beetle, Tribolium confusum, in a manner that may be adaptive to the parasite. To test this explanation we observed host behaviours including activity, concealment, and the response to and production of pheromones. Infected female beetles examined both 4–5 and 11–12 days post infection were slower moving and slower to conceal themselves than uninfected conspecifics; however, they did not differ from uninfected individuals in staying concealed. Infection of T. confusum did not affect the production of pheromones by mated and virgin females or the response of females to male pheromones. A second hypothesis for altered behaviours may be that modified behaviours result from pathology. The survivorship of mated infected female beetles was significantly lower than that of infected virgin beetles and uninfected beetles. Thus, both mated status and infection were important factors in survivorship, but only infection had significant effects on the altered behaviours. In this system, therefore, the hypothesis that behavioural changes are due to adaptive manipulation of the host by the parasite is supported.

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The physiology of wandering behaviour in Manduca sexta. I. Temporal organization and the influence of the internal and external environments

Journal of Experimental Biology ◽

10.1242/jeb.110.1.35 ◽

1984 ◽

Vol 110 (1) ◽

pp. 35-51 ◽

Cited By ~ 1

Author(s):

O. S. Dominick ◽

J. W. Truman

Keyword(s):

Juvenile Hormone ◽

Manduca Sexta ◽

Temporal Organization ◽

Gland Secretion ◽

Major Influence ◽

Labial Gland ◽

Larval Size ◽

Prothoracicotropic Hormone ◽

Behavioural Changes ◽

Labial Gland Secretion

A stereotyped series of behavioural changes occurs in preparation for pupation in Manduca sexta. Feeding declines over an 8-h period, after which the larva coats its body with a labial gland secretion. The animal then begins a 10- to 30-h wandering behaviour during which it constructs a pupation chamber underground. Wandering behaviour starts during a specific temporal gate which is determined by an internal circadian timer. The scotophase of the day prior to wandering has the major influence on the timing of internal processes which activate the behaviour. Wandering duration is correlated with larval size, reflecting a possible influence of juvenile hormone. The larva appears to be irrevocably committed to begin wandering by an event that occurs about 15 h previously, a time that corresponds to the second of three prothoracicotropic hormone (PTTH) pulses and the accompanying elevation of ecdysteroids as measured by Gilbert et al. (1981). We conclude that both the initiation and duration of wandering behaviour are governed primarily by processes which are internal to the larva.

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