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Parasite Intensities (parasite + intensity)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Experimental evidence for costs of parasitism for a threatened species, White Sands pupfish (Cyprinodon tularosa)

JOURNAL OF ANIMAL ECOLOGY, Issue 5 2004
MICHAEL L. COLLYER
Summary 1We used field and experimental data to test if white grub parasites (Diplostomatidae) are costly to White Sands pupfish (Cyprinodon tularosa), a threatened species restricted to four sites in the Chihuahuan desert, New Mexico. 2Of the four populations of C. tularosa, two are native and two are introduced. The two native populations (Malpais Spring and Salt Creek) are genetically distinct and have been isolated historically in dissimilar aquatic habitats (brackish spring and saline river, respectively). Two populations were established c. 1970 from translocation of Salt Creek fish to another saline river (Lost River) and another brackish spring (Mound Spring). 3Physid snails (Physidae) occur in the two brackish spring habitats but not the saline river habitats. These snails are first intermediate hosts for white grubs (Diplostomatidae). Therefore, the two freshwater populations are infected by diplostomatids. For the Mound Spring population, the ecological relationship of C. tularosa and diplostomatids has only recently occurred. 4In 1995, a population crash occurred for C. tularosa at Mound Spring, associated with a parasite outbreak. Diplostomatids were the presumptive cause of this crash, but this was inferred from observation of infection in collected fish. 5Two years of seasonal sampling of the two populations revealed that all collected fish were infected. Parasite intensities were significantly lower in winter compared to summer, suggesting that heavily infected fish were lost from the population on a seasonal basis. 6We conducted an artificial infection experiment to assess the costs of parasitism for previously uninfected C. tularosa females for various life-history traits. Under experimental conditions, diplostomatid infection caused increases in C. tularosa mortality and decreases in growth and fat storage. Individual-level costs of parasitism may translate to population-level patterns of parasitism for C. tularosa populations. Results from this study suggest that parasites may impact host overwinter survival, which is consistent with lower parasite intensities found during winters in wild populations. [source]

Host sex and ectoparasites choice: preference for, and higher survival on female hosts

JOURNAL OF ANIMAL ECOLOGY, Issue 4 2007
PHILIPPE CHRISTE
Summary 1Sex differences in levels of parasite infection are a common rule in a wide range of mammals, with males usually more susceptible than females. Sex-specific exposure to parasites, e.g. mediated through distinct modes of social aggregation between and within genders, as well as negative relationships between androgen levels and immune defences are thought to play a major role in this pattern. 2Reproductive female bats live in close association within clusters at maternity roosts, whereas nonbreeding females and males generally occupy solitary roosts. Bats represent therefore an ideal model to study the consequences of sex-specific social and spatial aggregation on parasites' infection strategies. 3We first compared prevalence and parasite intensities in a host,parasite system comprising closely related species of ectoparasitic mites (Spinturnix spp.) and their hosts, five European bat species. We then compared the level of parasitism between juvenile males and females in mixed colonies of greater and lesser mouse-eared bats Myotis myotis and M. blythii. Prevalence was higher in adult females than in adult males stemming from colonial aggregations in all five studied species. Parasite intensity was significantly higher in females in three of the five species studied. No difference in prevalence and mite numbers was found between male and female juveniles in colonial roosts. 4To assess whether observed sex-biased parasitism results from differences in host exposure only, or, alternatively, from an active, selected choice made by the parasite, we performed lab experiments on short-term preferences and long-term survival of parasites on male and female Myotis daubentoni. When confronted with adult males and females, parasites preferentially selected female hosts, whereas no choice differences were observed between adult females and subadult males. Finally, we found significantly higher parasite survival on adult females compared with adult males. 5Our study shows that social and spatial aggregation favours sex-biased parasitism that could be a mere consequence of an active and adaptive parasite choice for the more profitable host. [source]

Experimental evidence for costs of parasitism for a threatened species, White Sands pupfish (Cyprinodon tularosa)

Effect of tick parasitism on the health status of a passerine bird

FUNCTIONAL ECOLOGY, Issue 6 2008
D. J. A. Heylen
Summary 1Little information is available on the ecological interactions between ticks and their hosts under natural conditions, and particularly so for avian hosts. To understand this host,parasite interaction it is necessary to assess the physiological harm ticks can do to their host. 2We combined observational and experimental (field and laboratory) data to examine the effects of a common tick species with major economic importance, the sheep tick (Ixodes ricinus), on the health status of a common passerine bird, the great tit (Parus major). 3In the laboratory experiment a parallel group design was carried out in which the birds of the experimental group were infested with 3,10 nymphs, whereas the birds of the control group were kept free of ticks and received a sham treatment. Both groups were stratified according to age and sex. Health parameters were measured the day before and 3 days after infestation or sham treatment: haematocrit level, erythrocyte sedimentation rate, leucocyte concentration and general body condition (body mass corrected for body size). 4No effects of age were observed on any of the health parameters. The decrease in haematocrit level in the experimental group was significantly greater than in the control group. Moreover, infested males suffered more blood depletion than infested females. The increase in sedimentation rate was greater in the experimental group than in the control group. Surprisingly, no treatment effects were found on leucocyte concentrations, which may indicate immunoregulation by the ticks on components of the birds' cellular immune response. Also no difference in general body condition between the treatment groups was found. None of the infested birds died during infestation. 5Lower haematocrit levels in infested birds, but unaffected leucocyte concentrations and general body condition are confirmed by field data (experimental and observational) of adult birds during breeding season. 6Neither haematocrit level nor general body condition was associated with parasite intensity among infested birds, suggesting that immature Ixodes ricinus are not resource limited at high natural densities. Still, the measurable direct harm caused by sheep tick infestations calls for further study on its importance for the evolutionary ecology of passerine hosts. [source]

Parasitism and developmental plasticity in Alpine swift nestlings

JOURNAL OF ANIMAL ECOLOGY, Issue 4 2003
Pierre Bize
Summary 1Development plasticity is a common evolutionary and phenotypic response to poor growth condition, in particular in organisms with determinate growth such as most birds and mammals. Because various body structures can contribute differently to overall fitness, natural selection will adjust the degree of plasticity of each structure to its proportionate contribution to fitness at a given life stage. 2Two non-mutually exclusive mechanisms can account for plasticity in the growth of offspring to compensate for the effect of parasites. First, if parasite infestation levels fluctuate over the nestling period, parasitized young may show reduced growth until peak parasite infestation, and accelerated growth once the conditions improve (the accelerated growth hypothesis). Secondly, if the period of tissue maturation is not fixed in time, hosts may grow slower than parasite-free hosts but for a longer period of time (the delayed maturation hypothesis). 3To test whether hosts compensate for the effects of parasites on their development, the load of the blood-sucking louse-fly Crataerina melbae Rondani in the nests of Alpine swifts, Apus melba Linnaeus, was increased or decreased experimentally. Parasite prevalence was 100% in both treatments, but intensity (no. of parasites per nestling) was significantly lower for deparasitized nestlings. In both treatments, parasite intensity increased up to halfway through the rearing period (i.e. 30 days of age) and decreased afterwards. 4In line with the accelerated growth hypothesis, wings of parasitized nestlings grew at a lower rate than those of deparasitized ones before the peak of parasite infestation, but at a greater rate after the peak. Louse-flies had no significant effect on the growth of body mass. In agreement with the delayed-maturation hypothesis, wings of parasitized nestlings grew for 3 additional days and were of similar size at fledging as in deparasitized birds. 5In summary, the present study shows in a wild bird population that nestling hosts can compensate for the effect of parasitism on their phenotype. It emphasizes the need to take the dynamics of parasite populations into account in studies of host,parasite relationships, and to investigate the effect of parasites on host development over the entire growing period rather than only at fledging, as employed traditionally. [source]