Aculeata
Encyclopedia
The name Aculeata is used to refer to a monophyletic lineage of Hymenoptera
. The word "Aculeata" is a reference to the defining feature of the group, which is the modification of the ovipositor
into a stinger
(thus, the group could be called stinging wasps). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom
. Not all members of the group can sting; in fact, a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether. This group includes the bee
s and ant
s and all of the eusocial Hymenopterans; it is, in fact, commonly believed that the possession of a venomous sting was one of the important features promoting the evolution of social behavior, as it confers a level of anti-predator defense rarely approached by other invertebrate
s.
that the higher classifications of insects (and other organisms) have come to reject artificial (paraphyletic) grouping categories. While the Aculeata is a good natural group, containing all the descendants of a single common ancestor, the supposed "other infraorder" of the Apocrita - the "Parasitica" or "Terebrantia" - is not a natural group, just as the "sawflies", the basal lineages of Hymenoptera, are not.
The Aculeata are therefore maintained as a taxon
, either at infraorder or division rank or as an unranked clade
. However, the "Parasitica" must be considered a paraphyletic assemblage; the taxon "Parasitica" is discarded and their interrelationships are subject of further study. Provisionally, they all can be treated as superfamilies incertae sedis
in the Apocrita, without being placed in an infraorder. It is highly likely that at least some of these parasitic wasps - for example the Stephanoidea - are as closely related to the Aculeata as to other "Parasitica".
On the other hand, among the parasitic wasps the Ichneumonoidea seem particularly closely related to the Aculeata. If taxonomic ranks are used, it may therefore be best to treat the latter as a division and divide the Apocrita into some 6 infraorders representing lineages of about equal standing, one of which would unite the Aculeata and the Ichneumonoidea.
Note that having the same taxonomic rank does not imply equal evolutionary standing, whereas placement in the same higher-ranked taxon ideally does, or at least implies that regardless of what specific rank they have, the lower-ranked taxa are all part of the same evolutionary radiation
. Therefore, would the Aculeata and the Ichneumonoidea be placed in an infraorder, the former would still be considered a division and the latter a superfamily. Despite having different ranks, they would be members of the same taxon and sister lineages.
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
. The word "Aculeata" is a reference to the defining feature of the group, which is the modification of the ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
into a stinger
Stinger (organ)
A sting, sometimes called a stinger in the US, is a sharp organ or body part found in various animals that delivers some kind of venom . A true sting differs from other piercing structures in that it pierces by its own action and injects venom, as opposed to teeth, which pierce by the force of...
(thus, the group could be called stinging wasps). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
. Not all members of the group can sting; in fact, a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether. This group includes the bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s and ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s and all of the eusocial Hymenopterans; it is, in fact, commonly believed that the possession of a venomous sting was one of the important features promoting the evolution of social behavior, as it confers a level of anti-predator defense rarely approached by other invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s.
Classification
The use of the name Aculeata has a long history at the rank of infraorder or division, and it is only with the advent of modern phylogeneticsPhylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
that the higher classifications of insects (and other organisms) have come to reject artificial (paraphyletic) grouping categories. While the Aculeata is a good natural group, containing all the descendants of a single common ancestor, the supposed "other infraorder" of the Apocrita - the "Parasitica" or "Terebrantia" - is not a natural group, just as the "sawflies", the basal lineages of Hymenoptera, are not.
The Aculeata are therefore maintained as a taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, either at infraorder or division rank or as an unranked clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. However, the "Parasitica" must be considered a paraphyletic assemblage; the taxon "Parasitica" is discarded and their interrelationships are subject of further study. Provisionally, they all can be treated as superfamilies incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
in the Apocrita, without being placed in an infraorder. It is highly likely that at least some of these parasitic wasps - for example the Stephanoidea - are as closely related to the Aculeata as to other "Parasitica".
On the other hand, among the parasitic wasps the Ichneumonoidea seem particularly closely related to the Aculeata. If taxonomic ranks are used, it may therefore be best to treat the latter as a division and divide the Apocrita into some 6 infraorders representing lineages of about equal standing, one of which would unite the Aculeata and the Ichneumonoidea.
Note that having the same taxonomic rank does not imply equal evolutionary standing, whereas placement in the same higher-ranked taxon ideally does, or at least implies that regardless of what specific rank they have, the lower-ranked taxa are all part of the same evolutionary radiation
Evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
. Therefore, would the Aculeata and the Ichneumonoidea be placed in an infraorder, the former would still be considered a division and the latter a superfamily. Despite having different ranks, they would be members of the same taxon and sister lineages.