Biology
The Influence of Parasite Load on Sexual Ornamentation in Lizard Species
Quick fact
In some lizard species, males with heavier parasite loads display duller ornaments, and females prefer the brighter males—a pattern consistent with the parasite-mediated sexual selection hypothesis.
Why this is interesting
Male lizards flash brilliant colors to attract mates, but parasites may be dimming their shine. Could the parasites be the hidden puppet masters of lizard courtship?
Read the full explanation
Understanding The Influence of Parasite Load on Sexual Ornamentation in Lizard Species
Imagine a male lizard trying to impress a female with a bright red throat or a colorful patch. These ornaments aren't just decoration—they're signals of his health and vigor. Parasites, like mites, worms, or blood parasites, drain a lizard's energy and nutrients. When a lizard is fighting off parasites, it has less energy to produce and maintain elaborate ornaments. So the brightness or size of an ornament can honestly signal how well a male copes with parasites. In many lizard species, researchers catch males, measure their ornamentation (like color intensity or patch size), and count the number of parasites (parasite load). They often find that males with more parasites have duller or smaller ornaments. Females use these cues to pick mates with fewer parasites, thereby gaining indirect benefits like 'good genes' for their offspring.
A deeper explanation
The key mechanism is condition-dependent signaling. Ornament production and maintenance are costly—they require carotenoids (pigments), energy, and may increase predation risk. Parasites impose an additional physiological burden, reducing the male's overall condition. Therefore, only males in good condition (i.e., low parasite load) can produce and display bright ornaments. This makes the ornament an honest indicator of parasite resistance, which is heritable. Females choosing the most ornamented males are choosing genes that confer resistance to parasites, thereby increasing offspring fitness. This process, termed parasite-mediated sexual selection, reinforces the coevolution between host immunity and parasite virulence and helps maintain genetic variation in resistance. In lizards, examples include colorful throat patches in rock lizards and vivid blue spots in common lizards, where intensity correlates with fewer blood parasites.