Sex-Specific Differences in Shoaling Affect Parasite Transmission in Guppies

Background: Individuals have to trade-off the costs and benefits of group membership during shoaling behaviour. Shoaling can increase the risk of parasite transmission, but this cost has rarely been quantified experimentally. Guppies (Poecilia reticulata) are a model system for behavioural studies, and they are commonly infected by gyrodactylid parasites, notorious fish pathogens that are directly transmitted between guppy hosts. Methodology/Principal Findings:Parasite transmission in single sex shoals of male and female guppies were observed using an experimental infection of Gyrodactylus turnbulli. Parasite transmission was affected by sex-specific differences in host behaviour, and significantly more parasites were transmitted when fish had more frequent and more prolonged contact with each other. Females shoaled significantly more than males and had a four times higher risk to contract an infection. Conclusions/Significance: Intersexual differences in host behaviours such as shoaling are driven by differences in natural and sexual selection experienced by both sexes. Here we show that the potential benefits of an increased shoaling tendency are traded off against increased risks of contracting an infectious parasite in a group-living species

Proportion (mean ±SE) of non-focal male and female guppies contracting a <i>Gyrodactylus turnbulli</i> infection.

<p>Proportion (mean ±SE) of non-focal male and female guppies contracting a <i>Gyrodactylus turnbulli</i> infection.</p

Female guppies exhibit increased shoaling behaviour compared to males.

<p>(A) Mean ±SE nearest neighbour distance of non-focal female and male guppies, pooled for Days 1–6. (B) Mean ±SE time spent shoaling by non-focal female and male guppies pooled for Days 1–6.</p

Relationship between shoaling behaviour and parasite load.

<p>Nearest neighbour distance and parasite load for female (A) and male (B) guppies. Shown are the mean and standard deviation for both nearest neighbour distance and parasite load, averaged across the individuals within a tank.</p

Contingency table with counts of clean (non-infected) and infected non-focal female and male guppies, at the end of the 3-day infection period.

<p>Contingency table with counts of clean (non-infected) and infected non-focal female and male guppies, at the end of the 3-day infection period.</p

Correlation between shoaling behaviours separated by sex.

<p>Correlation between the nearest neighbour distance and (A) the number of guppies per shoal, and (B) the time spent shoaling for female guppies. (C) and (D) represent the same correlations respectively for male guppies. Shown are the mean and standard deviation.</p