We all have our favourite meals, and parasites are no different, preferring to dine and reside on one particular host – although they will infest and feed off others if their host of preference is not available. However, Boris Krasnov and colleagues from Israel and the USA explain that the more distant the evolutionary relationship between the principal host and second choice dining opportunities, the fewer parasites tend to take up residence. Intrigued by the relationship between parasites and their hosts, Krasnov and his team decided to find out whether the parasites preferences were affected by the dining opportunities presented by their host (p. 1259).
Suspecting that fleas would be more likely to dine, consume more and spend less energy digesting blood extracted from their preferred host than more distantly related hosts, the team collected newly hatched Parapulex chephreis and Xenopsylla ramesis fleas to infest rodents ranging from the fleas’ preferred hosts to more distantly related species. Then, after allowing the fleas to feast, the team measured how many of the fleas had dined, how much they had consumed and their metabolic rate as they tackled digesting the meal, to find out if the relatedness of the hosts impacted the parasites’ dining preferences.
The team was surprised to find that the fleas did not always do better when dining on their preferred host. Having expected that the fleas would consume most when sucking blood from their host of choice and spend the least energy digesting that meal, the team actually found the opposite: that fleas drank more from hosts that were only distantly related to their first choice and spent less energy digesting the meal. Also, X. ramesis fleas always consumed more than P. chephreis and used less energy processing the meal.
Analysing the unexpected consumption patterns, the team suspects that fleas used less energy digesting the blood of distantly related hosts because the victims rarely encounter the fleas; hence their immune response is weaker, making the blood easier to digest.
The team also suspects that X. ramesis’ lifestyle could account for their efficient digestion. Explaining that X. ramesis only reside briefly on the bodies of their hosts, whereas P. chephreis remain in residence for lengthy periods, the team suggests that X. ramesis fleas are opportunists, consuming large meals and digesting them efficiently to make the most of their infrequent dining opportunities.