Research

Bacteria are involved in intimate and often complicated interactions with their hosts. In mutualistic associations, the bacteria and hosts benefit each other, in commensalistic associations, the host benefit the bacteria with no reciprocal effect, whereas in parasitic associations, the bacteria damage their host. Most interestingly, the nature of association between bacteria and their hosts may vary over time and space. Which ecological factors will determine the nature of association between bacteria and their hosts and the bacterial composition within a host? Which factors determine the level of specificity between the bacteria and their hosts? And how host specificity is determined? We address these questions and more by integrating field surveys, natural field experiments, lab manipulations, and molecular approaches.

Our research projects, although diverse follow, the same principles: 1) a focus on the organisms in natural settings; 2) a strong emphasis on an experimental approach; 3) interdisciplinary research integrating ecological and evolutionary theory, behavioral ecology, physiology, population dynamics, and molecular tools; and 4) simultaneous examination of species interactions from the perspectives of the different “players” involved in it, with a consideration of the broader community.

Current Projects (click to expand)

1. A community perspective on the ‘dilution’ effect hypothesis
Most evidence regarding specific pathogens supports the dilution effect, i.e. negative relationships between host species diversity and disease risk. However, recent syntheses argue that biodiversity-disease relationships are more complex and can be negative, positive, or neutral in nature, depending on the ecological context. In this project we are testing different hypotheses for universal conditions in which an added host species would either increase or decrease microbial prevalence. Rodent-flea-bacterial communities in the Negev desert offer a living laboratory ideal for studying the relationships between host and bacteria species diversities. In this desert, there are three regions that are each numerically dominated by a different rodent species, but within each region, there are defined areas in close proximity to one another with different species compositions. All rodent species in a given region are infested by fleas of the same species, which are likely to transmit bacteria from one rodent host species to another. The bacteria, which are transmitted via blood feeding, can be transmitted between conspecific hosts; such transmission can be simulated in the laboratory in passage experiments. This work is part of collaboration with Dr. Evelyn Toh from Indiana University and Dr. Qunfeng Dong and Daniel Munro from University of North Texas.
 
2. Effects of vertebrate host age on the community structure of its symbionts
A large body of evidence suggest that with host maturation the prevalence of some host symbionts increases while the prevalence of other symbionts decreases. In this project we look at the effect of the host age on the symbiont community composition and on the interactions between the different species within such communities. We conducted a longitudinal field survey, in which we quantified the composition of ectoparasites (fleas, ticks, and mites) and bacterial communities in blood and ectoparasite samples taken from the same host individual over a maturation timeline. We are now testing experimentally for the mechanisms underlying the age-patterns we observed in the field.
 
3. The effects of human disturbance on host-vector-bacteria networks
Understanding the impact of natural and human disturbances on host-vector-microbes networks can help reducing the spread of vector-borne diseases. We captured rodents at different distances from outdoor clubs in either burned plots or control plots, collected their ectoparasites and characterized the bacteria lineages inside them using a 454 pyrosequencing approach. We combine path analysis with model selection approaches to quantify the direct and indirect effects that disturbances have on vector-borne bacterial community composition. This work is part of collaboration with Prof. Tamar Dayan and Aviv Avisar from Tel-Aviv University.
 
4. Causes and consequences of the natural bacterial community composition in hedgehogs and their ectoparasites
Different ecological factors including vertebrate host-related, arthropod vector-related and environmental variables are expected to have major effects on bacterial species composition. The main goal of this project is to unveil the causes for the bacterial community compositions in hosts and vectors, and explore the possible consequences of the bacterial community composition on the vector fitness-related traits. The hedgehog- tick- flea-bacteria model system is convenient to test this question because it is a multi- species system (two species of hosts and two species of vectors) and includes bacterial species with zoonotic importance.