title: Time budget, oxygen consumption and body mass responses to parasites in juvenile and adult wild rodents.
abstract: BACKGROUND
  The study of changes in a host's energy allocation in response to parasites is crucial for understanding parasite impact on both individual- and population-level processes. Experimental studies have explored such responses mainly in a single subsample of hosts per study, primarily adult males, and have only assessed either the overall energy acquisition or expenditure, rather than their different components simultaneously, or the behavioral responses. Accordingly, two fundamental questions arise: why have multiple host strategies evolved to cope with increased energy expenditure? and, which factors determine this variation (e.g. host species, identity, age)? This study provides an important step towards addressing both questions by experimentally disentangling the short-term physiological and behavioral responses of juvenile and non-reproductive adult rodents to natural levels of flea infestation. These two cohorts represent extreme cases of the energy demand continuum, as the former, in contrast to the latter, is involved in growth--a highly energy-demanding process--and may not be able to operate far below its upper limit of energy expenditure, and thus should reduce its energy expenses upon the occurrence of extra demands (e.g. due to parasitic pressure). Accordingly, we hypothesized that the response to fleas is age-dependent and varies according to the age-specific energy requirements and constraints.
  
  
  METHODS
  We monitored the behavior and physiology of juvenile and non-reproductive adult rodents before and after experimental flea infestation. First, we used a model selection approach to search for the factors that best explained the variability in the time budget, oxygen consumption, and body mass change in response to fleas. Then, using a path analysis approach, we quantified the different pathways connecting the important associations revealed at stage 1.
  
  
  RESULTS
  Compared to their flea-free counterparts, flea-infested adults groomed longer and had a higher oxygen consumption rate, but did not lose body mass. Infested juveniles also groomed longer but grew slower and had a similar rate of oxygen consumption.
  
  
  CONCLUSIONS
  Results suggest that both juvenile and adult rodents suffer from natural flea infestation levels. However, the comparison between the responses of juveniles and adults to experimental infestation, also suggests that juveniles may reallocate their energy expenditure from growth to maintenance, while non-reproductive adults increase their energy acquisition. Such age-dependent responses suggest that juveniles may be constrained by their higher need to rest for full functioning or by an upper limit in energy expenditure. Taken together, our study provides experimental evidence that hosts can compensate for the costs incurred by parasitism through physiological and behavioral plasticity, depending on their age, which probably determines their requirements and constraints. These compensatory responses may have important implications for the population dynamics of hosts and their parasites.
authors.affiliation: Mitrani Department of Desert Ecology, Swiss Institute for Dryland Environmental and Energy Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel. gaadio@post.bgu.ac.il.
authors.forename: Mario
authors.initials: M
authors.lastname: Garrido
authors.affiliation: Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. valeriabgu@gmail.com.
authors.forename: Valeria Hochman
authors.initials: VH
authors.lastname: Adler
authors.affiliation: Department of Zoology, Tel Aviv University, Tel Aviv, Israel. yogevmei@gmail.com.
authors.forename: Meital
authors.initials: M
authors.lastname: Pnini
authors.affiliation: Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. zvika@bgu.ac.il.
authors.forename: Zvika
authors.initials: Z
authors.lastname: Abramsky
authors.affiliation: Mitrani Department of Desert Ecology, Swiss Institute for Dryland Environmental and Energy Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel. krasnov@bgu.ac.il.
authors.forename: Boris R
authors.initials: BR
authors.lastname: Krasnov
authors.affiliation: Departments of Animal Science and Nutritional Sciences, Faculty of Sciences and Technology, Tel-Hai College, Upper Galilee, Israel. roeeg@migal.org.il.|Unit of Integrative Physiology (LIP), Laboratory of Human Health and Nutrition Sciences, MIGAL - Galilee Research institute, Kiryat Shmona, Israel. roeeg@migal.org.il.
authors.forename: Roee
authors.initials: R
authors.lastname: Gutman
authors.affiliation: Department of Zoology, Tel Aviv University, Tel Aviv, Israel. nogaks@tauex.tau.ac.il.
authors.forename: Noga
authors.initials: N
authors.lastname: Kronfeld-Schor
authors.affiliation: Mitrani Department of Desert Ecology, Swiss Institute for Dryland Environmental and Energy Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel. hadashaw@bgu.ac.il.|Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. hadashaw@bgu.ac.il.
authors.forename: Hadas
authors.initials: H
authors.lastname: Hawlena
mesh_terms: D000818:Animals; D000835:Animals, Wild; D001522:Behavior, Animal; D015992:Body Mass Index; D058267:Flea Infestations / Q000469:parasitology / Q000503:physiopathology / Q000662:veterinary*; D010101:Oxygen Consumption; D010273:Parasitic Diseases, Animal / Q000469:parasitology / Q000503:physiopathology*; D012376:Rodent Diseases / Q000469:parasitology / Q000503:physiopathology*; D012377:Rodentia