Maintaining the current Dacetini: any need to correct the correctors?

Barry Bolton

     It is obvious that Baroni Urbani and de Andrade are striving to resurrect their 1994 classification of the Dacetini so that at least the Basicerotini and probably also the Phalacromyrmecini will be absorbed into Dacetini; and according to an earlier manuscript the Agroecomyrmecinae should also go in there. To achieve this they need to discredit or discard every character that would contradict their interpretation. Their note “Correcting our correctors” displays their approach very nicely. Their technique is to find a species or two from a whole tribe that shows some character in reduced or aberrant form and then claim that this annuls the character’s validity entirely.

     In Bolton’s (2000) classification the presence of a basimandibular process is considered diagnostic of Dacetini and a character that does not occur elsewhere in Myrmicinae. He clearly stated that the process is an extrusion of the mandible and not merely a modified basal tooth. This excludes those very few basicerotine species with a flattened and expanded basal tooth and also excludes the phalacromyrmecines, where the basal tooth tends to be the largest on the masticatory margin but has no basal process present.

     In Baroni Urbani & de Andrade’s note they make much of the fact that in Pyramica argiola the basal process is supposed to be “invisible or absent” and promise other examples “in a forthcoming paper”. As revelations go, this is not much of one as Bolton (2000) has already documented the enormous variation in shape and size of the process throughout the various species groups of Pyramica, and noted extreme reduction in the argiola, murphyi, mnemosyne and extemena groups. For the argiola group he states that the basal process is “small, dentiform to low triangular and inconspicuous, very widely separated from the basalmost tooth”. Which is just what can be seen in the picture of the mandible of argiola supplied by Baroni Urbani and de Andrade in their note, where the process is the bit that sticks out as a prebasal low triangular ridge on the inner margin.

     The point is that extreme reduction of a variable character in a very few specialised species does not annul the phylogenetic value of the character. There are currently more than 325 species in Pyramica, distributed through about 66 species groups, and variation in a character as important as this in the ants’ predatory behaviour must be expected through such a huge genus. If the absence of the process is considered by Baroni Urbani & de Andrade to be ancestral, rather than the result of a reduction sequence, then it must be assumed that all the species groups within the genus that have a distinct basimandibular process must each have evolved it independently. It would also imply that all other genera of Dacetini (sensu Bolton, 2000) where presence of the basimandibular process is universal, have also each evolved the condition independently. While this is theoretically possible, it seems highly improbable. I predict many more examples of this trick, at all systematic levels, in Baroni Urbani & de Andrade’s “forthcoming paper already submitted”, to support the reinstatement of their 1994 classification.

    Like the basimandibular process the labral impression varies considerably in shape, extent and depth across the Dacetini. Its function is to accommodate the basimandibular processes when the mandibles are fully closed and to lock them in place. It is absent only in Acanthognathus, where the labrum is extremely reduced and plays no part in the jaw closing mechanism (Bolton, 1999: 1652), but is hypertrophied in Epopostruma. Baroni Urbani & de Andrade, as usual highly selective in their quotes, are correct in asserting that I did not use the character in 2000, but if they care to check Bolton, 2003: 54 they will find it included.

     Baroni Urbani & de Andrade conclude by saying they are “unable to recall the existence of other commonly recognised ant tribes so ill defined as the above Dacetini.” I can think of plenty. How about Formicoxenini, Pheidolini, Solenopsidini, Camponotini and Lasiini? There are many more.

Additional reference
Bolton, B. 2003. Synopsis and classification of Formicidae. Memoirs of the American Entomological Institute 71: 1 – 370.