In 1909, the entomologist
Carlo Emery noted that
social parasites among insects (e.g.,
kleptoparasite
Kleptoparasitism (etymologically, parasitism by theft) is a form of feeding in which one animal deliberately takes food from another. The strategy is evolutionarily stable when stealing is less costly than direct feeding, which can mean when f ...
s) tend to be
parasites of species or genera to which they are closely related.
[Emery, C. "Über den Ursprung der dulotischen, parasitischen und myrmekophilen Ameisen". ''Biologisches Centralblatt'' 29, 352–362 (1909)] Over time, this pattern has been recognized in many additional cases, and generalized to what is now known as Emery's rule.
The pattern is best known for various
taxa of
Hymenoptera. For example, the
social wasp ''
Dolichovespula adulterina
''Dolichovespula adulterina'' is a species of parasitic social wasp found in the Palearctic region. ''D. adulterina'' feeds on a variety of foods, including insects, spiders, arthropods, meat, molluscs, fruit, nectar, and larval secretions. ''D ...
''parasitizes other members of its genus such as ''
Dolichovespula norwegica'' and ''
Dolichovespula arenaria''. Emery's rule is also applicable to members of other kingdoms such as
fungi
A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
,
red algae, and
mistletoe. The significance and general relevance of this pattern are still a matter of some debate, as a great many exceptions exist, though a common explanation for the phenomenon when it occurs is that the parasites may have started as
facultative parasites within the host species itself (such forms of intraspecific parasitism are well-known, even in some species of
bee
Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...
s
), but later became reproductively isolated and split off from the ancestral species, a form of
sympatric speciation.
When a parasitic species is a sister taxon to its host in a
phylogenetic sense, the relationship is considered to be in "strict" adherence to Emery's rule. When the parasite is a close relative of the host but not its sister species, the relationship is in "loose" adherence to the rule.
[Hines, H. M., & Cameron, S. A. (2010)]
The phylogenetic position of the bumble bee inquiline ''Bombus inexspectatus'' and implications for the evolution of social parasitism.
''Insectes Sociaux'', 57(4), 379–383.
References
{{Biological rules
Parasitology
1909 introductions
Biological rules
1909 in biology