COS 270-5 - When whodunit matters: Species identity often drives cross-species transmission in multihost-multiparasite Daphnia communities

Background/Question/Methods

Most host species harbor multiple parasite species and many parasite species infect multiple host species. As such, common manipulative approaches focusing on single host-parasite species interactions miss important community effects, like cross-species transmission, which have the potential to impact larger scale community infection dynamics. This leaves a need for greater understanding of how the composition of a community influences disease transmission.

We used 3 years of time series field sampling data from a Daphnia host-parasite system of 8 host species and 7 parasite species to investigate which parasite species showed the most cross-species transmission and which host species contributed most significantly to cross-species transmission. We applied a network modeling approach to estimate plausible cross-species transmission, to find patterns of transmission by host and parasite species, and to identify host or parasite species that disproportionately contributed to cross-species transmission within their communities.

Results/Conclusions

Parasite species varied in their ability to infect multiple host species and their capacity to transmit from one host species to another. For example, for the bacterial parasite Pasteuria ramosa, two host species, Daphnia dentifera and Daphnia retrocurva, drove potential cross-species transmission and another, Ceriodaphnia dubia, acted as a potential sink. Thus, this work provides further evidence that community composition modifies disease in these systems, with some host species acting as potential amplifiers and some acting as potential diluters of disease.

Additionally, we found variability among pathogens, not only in the importance of specific host species but in the overall pattern of cross-species transmission. For our three most common multihost parasites, we found three different patterns: one host, two host, or no host potentially acted as important drivers of cross-species transmission. This indicates that cross-species transmission may depend on host species for some pathogens, but, for others, host identity may not be an important factor. The variability in these results among pathogens within the same host communities highlights the importance of understanding underlying patterns of cross-species transmission for both conservation and epidemiology.