Microhabitat preference, body size, and egg allocation in the gill parasite Naobranchia lizae (Copepoda).

The relationships between microhabitat preference, body size, and egg allocation were examined in the copepod Naobranchia lizae, which establishes on the gills of striped mullet Mugil cephalus. A total of 297 individual N. lizae (mean intensity = 5.0 ± 4.8 SD) were recovered from 60 infected hosts collected from the Charleston Harbor Estuarine System, South Carolina USA. For each mullet, we identified 16 microhabitats per gill arch, which yielded 128 microhabitats per host that could potentially be occupied. On average, only 5% of these microhabitats were occupied per host. The distribution pattern of the copepods on the gills revealed that microhabitat preferences occurred both among and within gill arches. For the microhabitats occupied, there was no effect of preference on body size, egg number, or egg size. Similarly, microhabitat sharing, which was more likely to occur at higher infection intensities, was not costly in terms of the copepod body size and egg allocation and there was no detectable trade-off between egg number and egg size. However, results also revealed that about half (48%) of the available microhabitats were never occupied by the copepods. We suggest that the occupancy of these potentially poor quality sites could carry fitness costs not realized in nature since numerous high quality sites are available per host. The findings are consistent with the interpretation that female N. lizae occupy a resource-rich habitat on the gill arches of striped mullet that provides conditions for optimal growth and reproduction.

Egg fibrils and transmission in the acanthocephalan Acanthocephalus dirus.

Acanthocephalans have multi-host life cycles that include arthropods as intermediate hosts and vertebrates as definitive hosts. Eggs are dispersed into the habitat from definitive hosts and in some species eggs possess fibrils, which have been proposed to facilitate transmission to intermediate hosts. We examined the potential role of fibrils in transmission of the acanthocephalan Acanthocephalus dirus to its intermediate host Caecidotea intermedius, a stream-dwelling isopod. We identify three properties of fibrils that could favor transmission. First, there was a slow rate of fibril release, which was dependent on the actions of stream microorganisms. Second, eggs with fibrils were more likely to adhere to the substrate than those without fibrils. Third, in feeding trials, isopods exposed to eggs with fibrils had a higher infection prevalence than isopods exposed to eggs without fibrils. These properties could favor transmission by increasing the likelihood that eggs sink to the sediment occupied by their target hosts before adhering to items on the substrate (e.g., leaves) and by increasing recruitment after the eggs have been consumed.

Competitive growth, energy allocation, and host modification in the acanthocephalan Acanthocephalus dirus: field data.

The acanthocephalan Acanthocephalus dirus is a trophically transmitted parasite that modifies both the physiology and behavior of its intermediate host (isopod) prior to transmission to its definitive host (fish). Infected isopods often contain multiple A. dirus individuals and we examined the relationships between host sharing, body size, energy content, and host modification to determine if host sharing was costly and if these costs could influence the modification of host behavior (mating behavior). Using field-based measures of parasite energy content (glycogen, lipid) and parasite body size (volume), we showed that host sharing was costly in terms of energy content but not in terms of body size. Analysis of the predictors of host behavior revealed that energy content, and body size, were not predictors of host behavior. Of the variables examined, parasite intensity was the only predictor of host behavior. Hosts that contained more parasites were less likely to be modified (i.e., less likely to undergo mating suppression). We suggest that intraspecific competition influenced parasite energy content and that the costs associated with competition are likely to shape the strategy of growth and energy allocation adopted by the parasites. These costs did not appear to have a direct effect on the modification of host mating behavior.

Polysorbate 80 and polymyxin B inhibit Stenotrophomonas maltophilia biofilm.

Stenotrophomonas maltophilia is an opportunistic multiple-drug-resistant human pathogen that forms biofilms on implanted medical devices. We examined the potential inhibitory activity of polysorbate 80 and polymyxin B against S. maltophilia. A combination of subMIC polymyxin B and polysorbate 80 was the most effective inhibitor of growth and biofilm formation.

Acanthocephalan-related variation in the pattern of energy storage of a behaviorally and physiologically modified host: field data.

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Transmission to the definitive host occurs after the parasite has reached the cystacanth stage, and development into this stage is associated with changes in several behavioral and physiological traits of the host. Given the potential importance of host energy availability to trait modification, we examined the relationship between cystacanth-stage infection and energy storage of adult isopods. Six samples of infected and uninfected male C. intermedius were collected from a population in March, April, and May during which time cystacanth-stage A. dirus dominate infections and modification of behavior and physiology occurs in nature. Biochemical assays revealed that infected male C. intermedius contained more glycogen and more lipid than uninfected males and that this difference was present throughout the sampling period, which represents the entire adult phase of the host's life. Additional analysis revealed that infected and uninfected males differed in their pattern of allocation to each energy source and that host lipid levels were negatively correlated with parasite intensity. We propose that the typical pattern of allocation and storage of host energy appears to be disrupted by A. dirus infection and that the changes are more likely to favor the parasite than the host.

Intra-population variation in behavior modification by the acanthocephalan Acanthocephalus dirus: are differences mediated by host condition?

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Male C. intermedius infected by A. dirus parasites are less likely to engage in mating behavior than uninfected males but there is a significant intra-population variation in the occurrence of this behavioral change. Previous studies on uninfected isopods have shown that glycogen content is a predictor of male mating behavior and we examined whether the intra-population variation in the mating behavior of infected male C. intermedius could be explained by this relationship. A field-based behavioral experiment was used to quantify intra-population variation in male mating behavior, which showed that 50% of infected males were responsive to females and 50% were not responsive. Biochemical analysis of responsive and non-responsive males revealed that glycogen content was a predictor of the mating behavior for uninfected males but was not a predictor of mating behavior for infected males. For infected males, parasite intensity was a predictor of mating behavior. Males that contained more A. dirus parasites were less likely to undergo modification of mating behavior. We propose that the intra-population variation in the mating behavior of infected C. intermedius identified in nature was not mediated by host condition.

Dispersal in the acanthocephalan Acanthocephalus dirus.

In acanthocephalans, dispersal typically occurs when eggs that have been released in the intestines of definitive hosts are expelled with the feces. We examined whether the acanthocephalan Acanthocephalus dirus adopts a strategy of dispersal in which eggs are carried into the environment by gravid females. Using a combination of field surveys and lab-based experiments, we showed that the A. dirus female retained eggs as they passed out of the intestines and that these eggs could develop in intermediate hosts (sediment-dwelling isopods). Lab-based behavioral experiments revealed that the bodies of gravid females were attractive to foraging isopods. We propose that a strategy of egg dispersal could occur in A. dirus in which eggs are carried into the environment by females. This strategy could increase transmission success by dispersing eggs closer to the sediment, rather than in the water column, and by directing the feeding behavior of target hosts.

Parasite-related pairing success in an intermediate host, Caecidotea intermedius (Isopoda): effects of male behavior and reproductive physiology.

The acanthocephalan parasite Acanthocephalus dirus develops from the egg to the cystacanth stage inside the freshwater isopod Caecidotea intermedius. We have shown previously that cystacanth-infected male C. intermedius are less likely to initiate mating attempts with females than uninfected males in competitive situations. Here, we used a field-based experiment to examine whether cystacanth-infected males were also less likely to initiate mating attempts with females in noncompetitive situations. We found that infected males were less responsive to females than uninfected males, and we propose that the cystacanth-related change in male mating behavior is mediated by a change in the mating response of males to females rather than male-male competition. We then examined whether cystacanth-related changes in reproductive function, i.e., sperm content and fertilization ability, could explain this variation in male mating behavior. We found that cystacanth-infected males contained both developing and mature sperm and fertilized as many eggs as uninfected males. Thus, we propose that changes in reproductive function are unlikely to explain cystacanth-related variation in male mating behavior in C. intermedius.

Effects of predation risk on population variation in adult size in a stream-dwelling isopod.

I used a combination of laboratory experiments and field surveys to examine the role that population-specific predation risk may play in shaping the life history strategy of a stream-dwelling isopod Lirceus fontinalis. Two focal populations were identified that were exposed to different predator types. The first population was exposed to larvae of the streamside salamander (Ambystoma barbouri) and the second to banded sculpin (Cottus carolinae). A laboratory experiment, in which different size classes of prey were offered simultaneously to individual predators, revealed that L. fontinalis suffered greatest mortality risk at small sizes with A. barbouri. Alternatively, with C. carolinae the risk of mortality was independent of size. Life history theory predicts that L. fontinalis from populations exposed to the gape-limited salamander larvae should be larger at maturity relative to individuals from populations exposed to C. carolinae. Field surveys on the two focal populations both within 1 year and across 4 years supported this prediction. Four other populations, two exposed to streamside salamander larvae and two to fish, provided additional support for the prediction. I concluded that L. fontinalis exhibited an adaptive response in size at maturity in response to population-specific predation risk. I then used gut content assays of the major predators to assess whether the population-specific life history strategies adopted by L. fontinalis were successful in avoiding predation.

Energetic costs of mate guarding behavior in male stream-dwelling isopods.

In the stream-dwelling isopod Lirceus fontinalis, males and females engage in a precopulatory mate guarding phase prior to mating. We examined the energetic costs of mate guarding behavior in males by separately assaying glycogen and lipid content at different time increments following mating. We found that males that had recently mated possessed reduced glycogen reserves and that these reserves were fully replenished within 36 h. Conversely, we found that male lipid reserves were unaffected by time since mating. We concluded that precopulatory mate guarding behavior is energetically costly to males and that glycogen is the energy source utilized to pay that cost. We also examined whether food deprivation during the mate guarding phase affected male energy reserves (glycogen) at the end of that phase. We found that males that were held in the laboratory and starved during mate guarding possessed reduced glycogen at the termination of the phase when compared to fed males. This reduced quantity was equivalent to the glycogen reserves of recently mated males collected from the field. We propose that food deprivation during the mate guarding phase explains the reduction in glycogen reserves at the termination of that phase. We discuss these results with reference to patterns of refuge use behavior during the mate guarding phase.