False Infection & Species Recognition
Due to parasite-host specificity, false signals of infection could
evolve as means of reinforcing species recognition. Hybrid zones and
hybrid reproduction by allopatric species are common phenomena (Harrison
1993). Often hybrids are at a fitness disadvantage compared to
non-hybrid individuals of either species (Sage et al. 1986;
Bleeker & Matthies 2005). This favors reliable mechanisms of species
recognition (Andersson 1994). Parasites are often highly
species-specific, even when closely related species occur sympatrically
(Van As & Basson 1987; Bittencourt & Rocha 2003; Dick 2007). As
parasites are obliged to identify their correct hosts, and do so by
directly sampling the host’s physiology, the presence of visible
infection, or symptoms of a host-specific parasitic infection, could be
used to increase the reliability of conspecific recognition.
Females tend to be especially attentive to reliable indicators of
species identity, because the costs of mistakenly mating with
heterospecifics are typically greater for females (Parker, 1979; Parker
1983; Parker & Partridge 1998). Thus, attending to cues of
species-specific infection could provide indirect benefits to females
via increased offspring vigour, and direct benefits due to reduced mate
searching costs. Signals to emphasize or exaggerate, or even “imitate”
being infected could then be advantageous for increasing male
reproductive success. Over time, a runaway process could cause these
signals emphasizing or imitating species-specific cues of parasitism to
become species-identifying sexual signals and possibly spread to
fixation if costs are low (Fisher 1930). In this hypothetical, infection
mimicry is likely not to be dishonest as such, because males displaying
false infection would do best to be most attractive to their own species
to avoid reduced hybrid fitness in their offspring.