We compared time spent at cleaning stations and ectoparasite loads for adult and subadult yellowtail damselfish Microspathodon chrysurus on nearshore fringing reefs in Barbados. In a preliminary study on 2 reefs in summer 1997, both time spent at cleaning stations and frequency of chafing were inversely correlated with distance from shore. A subsequent study in spring 1998 of fish at the shore-and seaward ends of 8 reefs revealed a strong sex by habitat association, with males predominating at the seaward end and females predominating at the shore end. Females and combined fish at the shore end of reefs had access to fewer cleaners but spent more time visiting cleaners than males and combined fish at the seaward end of reefs. Chafing showed the same relatlve difference but was not significant. Ectoparasites included gnathiid isopod larvae, parasitic copepods, and dactylogyrid monogeneans. Total crustacean loads, but not monogenean loads, increased with body size. With the effects of body size statistically removed, crustacean loads were significantly higher in females and fish at the shore end of reefs. Monogeneans showed a similar but marginally non-significant trend. These data indicate an association between ectoparasite loads and amount of time spent at cleaners, and thus appear consistent with adaptive, mutualistic hypotheses of client-cleaner interactions. However, the causal relationships between them, habitat, and sex remain to be determined.

Few experimental studies have documented the negative effect of parasites on fitness of hosts under natural or seminatural conditions. We studied the effect of Eimeria arizonensis (Protozoa) on recruitment, winter survival, and change in body mass in deer mice (Peromyscus maniculatus). In field observations, the presence of E. arizonensis was negatively related to recruitment in females and to over—winter survival in males. Experimental manipulation of E. arizonensis in large field enclosures also showed that infection negatively affected over—winter survival of males. There was no relationship between the body mass of deer mice and the presence of either natural or experimental infection. Thus, the mechanism through which E. arizonensis affects survival remains unclear.

We hypothesized that flooding represents an environmental stressor that might affect the corticosterone levels, parasite prevalence, and life history of small mammals living in floodplain environments. We compared populations of white-footed mice (Peromyscus leucopus (Rafinesque, 1818)) on floodplains and dry areas. We found more males on floodplains (p = 0.008) and more females on dry areas (p = 0.005). There were no differences in mass (p > 0.05) or intestinal parasite prevalence (p = 0.665) between dry and floodplain habitats, but bot fly larvae were significantly more prevalent in males living on floodplains (p = 0.043). Floodplain animals had significantly higher levels of corticosterone than dry-area animals in fall, and lower levels in summer (F[1,20] = 4.483, p = 0.047). In addition, we found that animals with intestinal parasites had higher levels of corticosterone than those that were without parasites (p = 0.014) or that harbored bot fly larvae (p = 0.001). Floodplains seem to be harsher environments than dry areas, but this may be a result of differences in habitat rather than a direct result of flooding.Résumé : Nous émettons l'hypothèse selon laquelle les inondations représentent des facteurs environnementaux de stress qui peuvent affecter les concentrations de corticostérone, la prévalence des parasites et le cycle biologique chez de petits mammifères qui habitent dans les milieux de plaines de débordement. Nous comparons les populations de souris à pieds blancs (Peromyscus leucopus (Rafinesque, 1818)) dans des plaines de débordement et des zones sèches. Nous trouvons plus de mâles dans les plaines de débordement (p = 0,008) et plus de femelles dans les régions sèches (p = 0,005). Il n'y a pas de différence de masse (p > 0,05), ni de prévalence de parasites intestinaux (p = 0,665) entre les habitats de plaine de débordement et de région sèche; cependant, les larves d'oestres ont une prévalence significativement plus grande chez les mâles habitant les plaines de débordement (p = 0,043). Les animaux de la plaine de débordement ont des concentrations significativement plus élevées de corticostérone que les animaux des régions sèches en automne et des concentrations plus faibles en été (F [1,20] = 4,483, p = 0,047). De plus, les animaux portant des parasites intestinaux ont des concentrations plus élevées de corticostérone que ceux qui sont sans parasites (p = 0,014) ou qui portent des larves d'oestres (p = 0,001). Les plaines de débordement semblent donc être des habitats plus rudes que les régions sèches, mais cela peut résulter de différences entre les habitats plutôt qu'être un effet direct des inondations.[Traduit par la Rédaction]

1. Little is known about interactions between environmental conditions surrounding insects and their immune responses.2. The environment in and around termite colonies, including temperature, relative humidity, soil pH, and light was analysed using principal components analysis (PCA).3. The relationship between these abiotic parameters and two aspects of termite immunity (phenoloxidase activity and lipid content) was examined in field-caught workers of Nasutitermes acajutlae Holmgren. Finally, termites from warm/dry and cool/moist habitats were exposed to Metarhizium anisopliae to determine their susceptibility to mycosis.4. PCA indicated that environmental components external to the nest [ambient temperature, ambient relative humidity (RH), soil temperature and light] comprised the majority (PC1 = 37.5%) of variation. Internal variables (nest temperature and RH) and nest volume accounted for 19.6% (PC2) of the variation with pH comprising 12.9% (PC3).5. AIC and regression models suggested that ambient temperature was most strongly and positively associated with immune variables and that relative humidity may also play a role. Termites from warm/dry colonies were less susceptible to M. anisopliae than termites from cool/moist colonies.6. Thus, termites nesting in warmer habitats may exhibit increased immune-related measures and reduced susceptibility to mycosis compared with termites from cooler habitats.

I investigated whether biotic factors (competitive exclusion between parasites and host immunity), abiotic factors (high temperature, low temperature, and rainfall), or a combination of the 2 affected the population dynamics of Eimeria arizonensis and Eimeria delicata in naturally infected deer mice (Peromyscus maniculatus). There was no evidence of competitive exclusion between E. arizonensis and E. delicata, nor were E. arizonensis population dynamics affected by host immunity (young deer mice were not infected significantly more frequently than adults). However, high temperatures were negatively associated with the prevalence of observed infections (r = -0.725, P < 0.001), suggesting sporulation of oocysts might be affected. In contrast, juvenile deer mice were infected with E. delicata more frequently than adults (z = 2.05, P < 0.02), suggesting that host immunity plays a role in the population dynamics of E. delicata. Temperature and rainfall during oocyst sporulation were not significantly associated with the prevalence of observed E. delicata infections. Finally, there was no evidence that a combination of biotic and abiotic factors was important in the population dynamics of either eimerian. Thus, the population dynamics of E. arizonensis seem to be controlled by abiotic factors, whereas those of E. delicata seem to be affected by biotic factors.