Incorporating the process of vertical transmission into understanding of host-symbiont dynamics

GUNDEL, P.E.; RUDGERS JA; GHERSA CM

OIKOS

WILEY-BLACKWELL PUBLISHING, INC

Año: 2011 vol. 120 p. 1121 - 1128

0030-1299

Variation exists in the frequency of obligate, vertically transmitted symbiotic organisms within and among host populations; however, these patterns have not been adequately explained by variable fi tness eff ects of symbionts on their hosts. In this forum, we call attention to another equally important, but overlooked mechanism to maintain variation in the frequency of symbioses in nature: the rate of vertical transmission. On ecological time scales, vertical transmission can aff ectthe equilibrium frequencies of symbionts in host populations, with potential consequences for population and community dynamics. In addition, vertical transmission has the potential to infl uence the evolution of symbiosis, by affecting the probability of fi xation of symbiosis (and therefore the evolution of complexity) and by allowing hosts to sanction against costly symbionts. Here we use grass ? epichloae symbioses as a model system to explore the causes and consequences of variation in vertical transmission rates. We identify critical points for symbiont transmission that emerge from considering the host growth cycle devoted to reproduction (asexual vs sexual) and the host capability to maintain homeostasis. We also use information on the process of transmission to predict the environmental factors that would most likely aff ect transmissionrates. Altogether, we aim to highlight the vertical transmission rate as an important process for understanding the ecology and evolution of symbiosis, using grass ? epichloae interactions as a case study.