Biomedical subjects

Carla E Cáceres

Publications and source records attributed to Carla E Cáceres.

5 recordsLinked to original sources

PubMed2006

Segregating variation in the transcriptome: cis regulation and additivity of effects.

Properties of genes underlying variation in complex traits are largely unknown, especially for variation that segregates within populations. Here, we evaluate allelic effects, cis and trans regulation, and dominance patterns of transcripts that are genetically variable in a natural population of Drosophila melanogaster. Our results indicate that genetic variation due to the third chromosome causes mainly additive and nearly additive effects on gene expression, that cis and trans effects on gene expression are numerically about equal, and that cis effects account for more genetic variation than do trans effects. We also evaluated patterns of variation in different functional categories and determined that genes involved in metabolic processes are overrepresented among variable transcripts, but those involved in development, transcription regulation, and signal transduction are underrepresented. However, transcripts for proteins known to be involved in protein-protein interactions are proportionally represented among variable transcripts.

Animals↗

PubMed2006

Warmer does not have to mean sicker: temperature and predators can jointly drive timing of epidemics.

Ecologists and epidemiologists worry that global warming will increase disease prevalence. These fears arise because several direct and indirect mechanisms link warming to disease, and because parasite outbreaks are increasing in many taxa. However, this outcome is not a foregone conclusion, as physiological and community-interaction-based mechanisms may inhibit epidemics at warmer temperatures. Here, we explore this thermal-community-ecology-based mechanism, centering on fish predators that selectively prey upon Daphnia infected with a fungal parasite. We used an interplay between a simple model built around this system's biology and laboratory experiments designed to parameterize the model. Through this data-model interaction, we found that a given density of predators can inhibit epidemics as temperatures rise when thermal physiology of the predator scales more steeply than that of the host. This case is met in our fish-Daphnia-fungus system. Furthermore, the combination of steeply scaling parasite physiology and predation-induced mortality can inhibit epidemics at lower temperatures. This effect may terminate fungal epidemics of Daphnia as lakes cool in autumn. Thus, predation and physiology could constrain epidemics to intermediate temperatures (a pattern that we see in our system). More generally, these results accentuate the possibility that warmer temperatures might actually enhance predator control of parasites.

Animals↗

PubMed2005

Spatial heterogeneity of daphniid parasitism within lakes.

Spatially explicit models show that local interactions of hosts and parasites can strongly influence invasion and persistence of parasites and can create lasting spatial patchiness of parasite distributions. These predictions have been supported by experiments conducted in two-dimensional landscapes. Yet, three-dimensional systems, such as lakes, ponds, and oceans, have received comparatively little attention from epidemiologists. Freshwater zooplankton hosts often aggregate horizontally and vertically in lakes, potentially leading to local host-parasite interactions in one-, two-, or three-dimensions. To evaluate the potential spatial component of daphniid parasitism driven by these local interactions (patchiness), we surveyed vertical and horizontal heterogeneity of pelagic Daphnia infected with multiple microparasites in several north temperate lakes. These surveys uncovered little evidence for persistent vertical patchiness of parasitism, since the prevalence of two parasites showed little consistent trend with depth in four lakes (but more heterogeneity during day than at night). On a horizontal scale of tens of meters, we found little systematic evidence of strong aggregation and spatial patterning of daphniid hosts and parasites. Yet, we observed broad-scale, basin-wide patterns of parasite prevalence. These patterns suggest that nearshore offshore gradients, rather than local-scale interactions, could play a role in governing epidemiology of this open water host-parasite system.

Animals↗

PubMed2004

Selective predation and productivity jointly drive complex behavior in host-parasite systems.

Successful invasion of a parasite into a host population and resulting host-parasite dynamics can depend crucially on other members of a host's community such as predators. We do not fully understand how predation intensity and selectivity shape host-parasite dynamics because the interplay between predator density, predator foraging behavior, and ecosystem productivity remains incompletely explored. By modifying a standard susceptible-infected model, we show how productivity can modulate complex behavior induced by saturating and selective foraging behavior of predators in an otherwise stable host-parasite system. When predators strongly prefer parasitized hosts, the host-parasite system can oscillate, but predators can also create alternative stable states, Allee effects, and catastrophic extinction of parasites. In the latter three cases, parasites have difficulty invading and/or persisting in ecosystems. When predators are intermediately selective, these more complex behaviors become less important, but the host-parasite system can switch from stable to oscillating and then back to stable states along a gradient of predator control. Surprisingly, at higher productivity, predators that neutrally select or avoid parasitized hosts can catalyze extinction of both hosts and parasites. Thus, synergy between two enemies can end disastrously for the host. Such diverse outcomes underscore the crucial importance of the community and ecosystem context in which host-parasite interactions occur.

Animals↗

PubMed2004

Incidence of diapause varies among populations of Daphnia pulicaria.

Dormancy is a common way in which organisms survive environmental conditions that would be lethal to the active individual. However, while dormant, individuals forego reproduction. Hence theory suggests an optimal time in which to enter dormancy, depending on risks associated with both remaining active and entering dormancy. When these relative risks differ among habitats, dormancy strategies are predicted to vary as well. For freshwater zooplankton, it has been suggested that sensitivity to the cues that initiate dormancy should be selected against when females have the opportunity to remain in the water column year round. We tested this prediction with 12 populations of lake-dwelling Daphnia pulicaria (Crustacea: Cladocera). Differences among lakes in basin morphometry, predators and resources create a gradient of risk for Daphnia in the water column. Some populations persist in high numbers year round while others are abundant only in spring. We used this difference in persistence ability as an estimate of risk in the water-column. For 3 years of field sampling we found consistent differences among the lake populations in the incidence of dormancy. In some populations, only a small fraction of females switched to producing dormant eggs each year whereas in others the majority of eggs produced in the late spring were dormant. In general, populations that experienced predictably low abundances in the active form exhibited higher incidence of dormancy than did populations that persisted in high abundance year round, but there were exceptions. Our results confirm that the incidence of dormancy varies considerably among populations in a fashion consistent with general theory, but suggest that persistence in the water column is not the sole predictor of the diapause strategy found in any particular lake.

Adaptation, Physiological↗