Demographic and reproductive associations with nematode infection in a long-lived mammal

Carly L Lynsdale,Nay Oo Mon,Diogo J Franco Dos Santos,Virpi Lummaa,Win Htut,Htoo Htoo Aung,Dylan Childs,U Kyaw Nyein

doi:10.1038/s41598-020-66075-w

Abstract

Infection by macroparasites, such as nematodes, varies within vertebrate host systems; elevated infection is commonly observed in juveniles and males, and, for females, with different reproductive states. However, while such patterns are widely recognized in short-lived model systems, how they apply to long-lived hosts is comparatively understudied. Here, we investigated how infection varies with host age, sex, and female reproduction in a semi-captive population of individually marked Asian elephants Elephas maximus. We carried out 1,977 faecal egg counts (FECs) across five years to estimate nematode loads for 324 hosts. Infection patterns followed an established age-infection curve, whereby calves (5 years) exhibited the highest FECs and adults (45 years) the lowest. However, males and females had similar FECs across their long lifespan, despite distinct differences in life-history strategy and clear sexual dimorphism. Additionally, although mothers invest two years in pregnancy and a further three to five years into lactation, nematode load did not vary with four different measures of female reproduction. Our results provide a much-needed insight into the host-parasite dynamics of a long-lived host; determining host-specific associations with infection in such systems is important for broadening our knowledge of parasite ecology and provides practical applications for wildlife medicine and management.

Highlights

Infection by macroparasites, such as nematodes, varies within vertebrate host systems; elevated infection is commonly observed in juveniles and males, and, for females, with different reproductive states
Host age has a pivotal role in influencing patterns of macroparasite infection, but the patterns observed depend on the host system, occupant parasite(s), and measure of infection used
We determined how infection by gastro-intestinal nematodes was associated with individual age, sex, and female reproduction, in a long-lived host living in natural forest www.nature.com/scientificreports habitat

Summary

Introduction

Infection by macroparasites, such as nematodes, varies within vertebrate host systems; elevated infection is commonly observed in juveniles and males, and, for females, with different reproductive states. Females bear high metabolic and physiological costs following reproduction, for example during pregnancy, with parturition and throughout lactation, and from other post-partum care[29] It follows that variation in host reproductive state may influence the success rate of establishing parasite fauna and allow infection to expand under reduced host immunity, which is concordant with empirical evidence of higher parasite loads in mothers and pregnant females than in non-reproductive females[30,31]. This is a longstanding finding in veterinary and agricultural studies, which outline periparturient lapses in resistance, which is relaxed following parturition, even in lines bred for genetic resistance[32]

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