Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

International Journal of Parasitology

Female Acomys cahirinus with pups. Photograph courtesy Elizabeth Warburton.

Corresponding Author: Elizabeth Warburton, ewarburton@uga.edu

Summary by Ethan Hackmeyer

Parasitism can impose significant fitness costs on host organisms, and it is thought that parasitism could possibly cause host reproductive failure, possibly through increased stress. A new study led by CEID member Elizabeth Warburton explores how parasites could affect maternal stress in vertebrates. Egyptian spiny mice (Acomys cahirinus), rodents native to deserts in the Middle East, and their principal flea (Parapulex chephrenis) were studied to better understand the stress of parasitism as it relates maternal and offspring outcomes.

Pregnant mice were separated into a control group with no parasites and a treatment group infested with parasitic fleas. To measure the amount of stress levels of the pregnant mice, researchers recorded the level of glucocorticoids, hormones produced at relatively high amounts under stress, in their droppings at 5 different intervals during the experiment. Fleas were introduced and maintained at consistent levels to the treatment group of mice before and during pregnancy, and then removed immediately prior to birth in order to prevent infestation of the pups.

Infested and non-infested mice had similar litter sizes and sex ratios, though the levels of glucocorticoids displayed significant differences during mid-pregnancy and post-parturition. Infested mothers had lower glucocorticoid levels at mid-pregnancy but higher ones post-parturition while non-infested mothers showed the opposite trend.  Additionally, mothers infected with fleas showed a significantly increased change in mass from before and after pregnancy compared to the non-infested mice. However, infested mothers with poor body condition produced significantly male-biased litters while infested mothers with good body condition produced significantly female-biased litters. Notably, pups from uninfected and infected mothers displayed similar birth mass, weaning mass and mass gain but only when mothers did not experience significant changes in mass. This indicates that stress caused by flea parasitism is likely not enough to significantly impact host reproduction by itself but rather are moderated by maternal body condition. Thus, the level of investment put into pups by the mothers did result in differing effects of parasitism related to enhanced glucocorticoid production.

Warburton, E.M., Khokhlova, I.S., Palme, R., Surkova, E.N., Krasnov, B.R., Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system. International Journal for Parasitology (2021), doi: https://doi.org/10.1016/j.ijpara.2020.12.005