Metabolic rate and ecological traits of ectoparasites: a case study with seven flea species from the Negev Desert

We studied the relationship between fleas' metabolic rate and their ecological traits, using data on standard metabolic rate (SMR), mean abundance, host specificity, and geographic range size in males and females of seven desert flea species. SMR was measured via mass-specific CO² emission, whereas host specificity was measured as (a) the mean number of host species used by a flea per region in regions where this flea was recorded; (b) the total number of host species a flea exploited across its geographic range; and (c) the phylogenetic diversity of the flea's hosts. To control for confounding effects of phylogeny when analysing data on multiple species, we applied the Phylogenetic Generalised Least Squares (PGLS) model. We found that the only ecological trait significantly correlating with flea SMR was the phylogenetic diversity of hosts utilized by a flea across its geographic range. The strength of the association between SMR and host phylogenetic diversity was higher in male than in female fleas. We explain the relationship between flea SMR and their host specificity by the necessity of host-opportunistic species to compensate for the high energetic cost of neutralizing multiple defences from multiple hosts by increased SMR.