Ecology and Evolution of the Grass-Endophyte Symbiosis

Profundae diversitas: the uncharted genetic diversity in a newly studied group of fungal root endophytes

“…Endophytes can have several functions and/or may change function during their life cycle (Murphy et al 2013, 2014a). Benefits to crop plants infected with endophytic fungi include an increase in seed yield (Achatz et al 2010; Murphy et al 2014b, 2015), enhanced resistance to pathogens and herbivores (Cheplick and Faeth 2009; Murphy et al 2015a) and increased stress tolerance (Waller et al 2005; Rodriguez et al 2009). …”

“…Some of these endophytes are localised to specific tissue types and some are found systemically. The leaf endophytes of many grassy plant species, including barley ( Hordeum vulgare ) have been well studied and characterised (Arnold and Lutzoni 2007; Cheplick and Faeth 2009; Wang et al 2009; Torres et al 2012; de Souza Leite et al 2013). The endophytes of wild barley species have been less studied, particularly root endophytes.…”

Niche Differentiation in the Dynamics of Host-Symbiont Interactions: Symbiont Prevalence as a Coexistence Problem

“…There has been much discussion over whether heritable microbes such as fungal endophytes function as mutualists or parasites of their hosts, fueled in part by their often variable and intermediate frequencies of occurrence (Faeth 2002;Cheplick and Faeth 2009). The idea that vertically transmitted symbionts with beneficial fitness effects should be maintained at high frequency in host populations is intuitively appealing.…”

“…Counterintuitively, strong host-symbiont mutualism may actually facilitate persistence of symbiont-free hosts if it is also associated with niche differentiation. Imperfect transmission (Gundel et al 2008) and migration (Saikkonen et al 2002) could further cloud connections between fitness effects of symbionts and local symbiont frequency, as others have recognized (Cheplick and Faeth 2009), and modeling their influence can provide additional insights. Thus, observed symbiont frequencies are, at best, incomplete information about the fitness effects of symbionts on hosts and, at worst, completely mute on the issue.…”

“…For example, the population-level frequency of the vertically transmitted bacterium Wolbachia follows a bimodal distribution across species of arthropod host, with peaks at 0% and 100% but a broad range of infection levels between these extremes (Hilgenboecker et al 2008). Similarly, for the vertically transmitted fungal endophytes of many grasses, intermediate symbiont frequencies seem to be more the rule than the exception (reviewed in Cheplick and Faeth 2009;Rudgers et al 2009). Variable and often intermediate symbiont frequencies have contributed to confusion over whether vertically transmitted symbionts function primarily as mutualists, as predicted by evolutionary theory, or as parasites (Faeth 2002;Faeth et al 2004).…”