The evolution of transmission mode

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.This article reviews research on the evolutionary mechanisms leading to different transmission modes. Such modes are often under genetic control of the host or the pathogen, and often in conflict with each other via trade-offs. Transmission modes may vary among pathogen strains and among host populations. Evolutionary changes in transmission mode have been inferred through experimental and phylogenetic studies, including changes in transmission associated with host shifts and with evolution of the unusually complex life cycles of many parasites. Understanding the forces that determine the evolution of particular transmission modes presents a fascinating medley of problems for which there is a lack of good data and often a lack of conceptual understanding or appropriate methodologies. Our best information comes from studies that have been focused on the vertical versus horizontal transmission dichotomy. With other kinds of transitions, theoretical approaches combining epidemiology and population genetics are providing guidelines for determining when and how rapidly new transmission modes may evolve, but these are still in need of empirical investigation and application to particular cases. Obtaining such knowledge is a matter of urgency in relation to extant disease threats.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.J.A is supported by grants NSF DEB1115895 and NIH R01GM122061 as part of the joint NSF-NIH-USDA Ecology and Evolution of Infectious Diseases program. A.J.W. is supported by UK’s Biotechnology and Biological Sciences Research Council grant BBS/ E/I/00002066. M.R.F. is supported by Natural Sciences and Engineering Research Council of Canada Discovery Grant. H.C.H. is supported by Fondazione E. Mach and the Autonomous Province of Trento under the ‘Trentino programme of research, training and mobility of post-doctoral researchers’ Incoming Team project ECOBIOME (EU FP7 Marie Curie actions COFUND: 2011 Call). E.R.K. is supported by Academy of Finland, grant 250524. H.C.L. is supported by Royal Commission for the Exhibition of 1851. B.L. is supported by NERC grant (NE/L004232/1) and a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (grant no. 109356/Z/15/Z). B.O. is supported by NERC grant (NE/N005902/1). S.M.S. is supported by NERC grant (NE/ H021256/1). J.P.W. is supported by ZELS research grant (combined BBSRC, MRC, ESRC, NERC, DSTL and DFID: BB/L018985/1)