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Flea fitness is reduced by high fractional concentrations of CO2 that simulate levels found in their hosts' burrows

ABSTRACT Nidicolous ectoparasites such as fleas and gamasid mites that feed on small and medium-sized mammals spend much of their time in their hosts' burrows, which provide an environment for living, and often feeding, to their pre-imaginal and/or adult stages. Thus, these ectoparasites should be adapted to environmental conditions in burrows, including high fractional concentrations of CO2 (FCO2). We examined how a high FCO2 (0.04) affected survival and reproductive success of a hematophagous ectoparasite of burrowing rodents using fleas Xenopsylla ramesis and Sundevall's jirds Meriones crassus. In the first experiment, fleas fed on hosts housed in high-CO2 (FCO2=0.04) or atmospheric-CO2 (FCO2≈0.0004) air, and were allowed to breed. In a second experiment, fleas were maintained in high CO2 or CO2-free air with no hosts to determine how CO2 levels affect survival and activity levels. We found that at high FCO2 fleas laid fewer eggs, reducing reproductive success. In addition, at high FCO2, activity levels and survival of fleas were reduced. Our results indicate that fleas do not perform well in the FCO2 used in this experiment. Previous research indicated that the type and intensity of the effects of CO2 concentration on the fitness of an insect depend on the FCO2 used, so we advise caution when generalizing inferences drawn to insects exposed to other FCO2. If, however, FCO2 found in natural mammal burrows brings about reduced fitness in fleas in general, then burrowing hosts may benefit from reduced parasite infestation if burrow air FCO2 is high. Highlighted Article: Fleas living in high fractional concentrations of CO2 have reduced survival and reproduction.