What are the factors determining the probability of discovering a flea species (Siphonaptera)?

Our aim was to determine which of four variables (number of host species exploited by the parasite, taxonomic distinctness of these hosts, geographic range of the principal host, and year of description of this host) was the best predictor of description date of fleas. The study used previously published data on 297 flea species parasitic on 197 species of small mammals from 34 different regions of the Holarctic and one region from the Neotropics. We used both simple linear and multiple regressions to evaluate the relationships between the four predictor variables and the year of flea description, on species values as well as on phylogenetically independent contrasts. Whether or not the analyses controlled for flea phylogeny, all predictor variables correlated significantly with year of flea description when tested separately. In multiple regressions, however, the number of exploited host species was the best predictor of the date of flea description, with the geographic range of the principal host species as well as the date of its description having a lesser, though significant, influence. Overall, our results indicate that a flea species is more likely to be discovered and described early if its biological characteristics (exploitation of many host species) and those of its hosts (long-known to science, broad geographic distributions) increase its chances of being included in a collection. Because the variables we investigated only explained about 10-11% of the variation in year of description among flea species, other factors must be important, such as temporal variability in the activity of flea taxonomists.