Introduction
Parasitic life strategies dominate biological systems and can profoundly
influence several aspects of host biology, ecology, and community
structure (Windsor 1989; Jones et al. 1994; Thomas et al. 1999; Moore
2002; Thomas et al. 2005; Peay et al. 2008; Anderson et al. 2009;
Pontoppidan et al. 2009). Several studies have demonstrated a propensity
for certain fungal lineages to actively manipulate their hosts through
complex changes in behavior and body plan, and these results have
captured the attention and imagination of evolutionary ecologists in
recent years (Moore 2002; Thomas et al. 2005; Anderson et al. 2009;
Pontoppidan et al. 2009; Goodman and Johnson 2011; Hughes et al. 2011;
Hughes et al. 2016). The majority of these studies have focused
primarily on myrmecophilous Ophiocordyceps species, namelyO. unilateralis , for their particularly spectacular influence on
their ant-hosts (Anderson et al. 2009; Hughes et al. 2011). Parasite
induced changes in host physiology force ants infected with O.
unilateralis to permanently secure themselves in locations specifically
suited to fungal development and dispersal via irreversible
“death-grip” behavior (Andersen et al. 2009; Hughes et al. 2011;
Weinersmith and Faulkes 2014; Thomas et. al. 2005, 2010). Scores of ants
killed in this way tend to aggregate into so-called “graveyards”, a
phenomenon thought to represent an “extended phenotype” of parasite
gene expression (Dawkins 1982; Anderson et al. 2009; Pontoppidan et al.
2009). In the context of parasitic manipulation of host behavior, an
extended phenotype refers to the influence of parasite gene expression
on host phenotype, particularly when this behavioral manipulation serves
to increases parasite transmission and fitness (Dawkins 1982; Hughes et
al. 2011; Bailey 2012). Such dramatic examples of extended phenotypes
are not limited to Ophiocordyceps species, however, and empirical
evidence suggests that the same phenomena may occur among certain
specialized fungal parasites of spiders.