The paraphyly controversy

Highlighting the articles written by Ward et al. and  Seifert et al. in Insectes Sociaux

Written by Insectes Sociaux Editor in Chief, Michael Breed

Should we change a commonly used and widely understood name when bringing classification into alignment with phylogeny? This is not a new question; it has plagued generations of systematists (e.g., Michener 1964). The Linnean system of classifying and naming organisms is a foundational tool in biological sciences. Yet not all scientists agree about how and when information about phylogeny should be embedded into classification. A particularly sticky point comes when well-accepted names for organisms conflict with newly understood phylogenetic information. The second of a pair of commentaries dealing with phylogeny, classification and scientific names appears in this month’s issue of Insectes Sociaux (Ward et al. 2016; Seifert et al. 2016).

Particularly vexsome in the social insect world have been classifications involving social parasites. Are there clear synapomorphies-traits that distinguish the social parasite from its hosts? Alternatively, is each socially parasitic species within a clade an evolutionary offshoot from shared ancestors with its host species? Or is it a distinct clade within a clade? Are parasitic characteristics, which often involve loss of foraging morphology, arrived at by convergence? The answers to these questions often affect a species’ name, in particular its placement in a genus.

The two commentaries address the question of whether, when new data reveals that genera are paraphyletic, should their naming reflect the current phylogeny. In ants, there are several examples of groups of parasitic species for which new data has caused placement within a host genus, when previously the parasites had generic status. The renaming of species has been controversial and lies at the core of the disagreement between the two groups of authors.

The much-studied relationship between bumblebees, Bombus, and their social parasites, Psithyrus, exemplifies the fascinating difficulties posed by social parasites. Psithyrus differ substantially in morphology and behavior from their hosts so much that the early literature (e.g., Plath 1922) considers Psithyrus as a distinct genus. At points in the past, Psithyrus species have also been argued to have evolved pairwise from their hosts. The contemporary understanding (Cameron et al. 2007) is that Psithyrus comprises a single clade within Bombus, and it is recognized as a subgenus. Thus, in this case the name reflects the currently supported phylogenetic hypothesis, and most bee biologists have come to accept Psithyrus as a part of Bombus.

The readers of Insectes Sociaux are very much affected by controversies over naming social parasites, as many non- taxonomic studies focus on the behavior, ecology and evolution of these insects. It is possible that a student, new to the field, might find that changed names make it difficult to connect older literature with newer work. Importantly, though, to the extent that the naming system is a hypothesis about evolutionary relationships, names that do not embody current phylogenetic knowledge could also mislead a student about evolution. Knowing that new hypotheses about phylogeny will appear in the future and, perhaps affect names, adds tension to the situation.

Name changes make things inconvenient and awkward at times; in my own work on halictid bees I have seen that the shifts between Dialictus and Lasioglossum as the genus name for the same bee¹ have been confusing to biologists outside the inner circle of halictid biologists. On the other hand, the removal of the ant genus Paraponera from the tribe Ectatommini as well as from the subfamily Ponerinae greatly informed my thinking about the evolution of Paraponera behavior, a definite positive outcome of the current reworking of ant systematics.

Why should a journal publish commentaries on an issue like this? The role of scientific journals is to document an extended conversation about theory, hypotheses and facts. My view is that it is far better for scientists to have open, and one would hope civil exchanges about controversial topics. This ensures scientific progress and helps workers outside the immediate field understand seeming contradictions. My personal agreement, or disagreement, with the point of view of either Ward et al. (2016) or Seifert et al. (2016) is much less important than the discussion of the issue within the scientific community. Additionally, one constant concern of journal editors is that the peer review system can be used to suppress work in ways that are difficult to ferret out in the editorial process. Having the conversation in a transparent way should help to advance science and maintain the integrity of editorial processes.

¹ Thus, Lasioglussum zephyrum = Dialictus zephyrus, because the Latin ending of the species epithet changes to match the ending of the genus name. I think this name mismatch inhibits non-specialists from accessing the comparative value of the literature on halictid bee behavior, but the present usage, L. zephyrum, is well justified on systematic grounds. This is a different naming issue than the question about social parasites, but it has many of the same potential outcomes and conflicts in terms of utility.

References

Cameron SA, Hines HM, Williams PH (2007) A comprehensive phylogeny of the bumble bees (Bombus). Biol J Linn Soc 91:161–188

Michener CD (1964) The possible use of uninominal nomenclature to increase the stability of names in biology. Syst Zool 13:182–190 Plath OE (1922) Notes on Psithyrus, with records of two new American hosts. Biol Bull 43:23–44

Seifert B, Buschinger A, Aldawood A, Antonova V, Bharti H, Borowiec L, Dekoninck W, Dubovikoff D, Espadaler X, Flegr J, Georgiadis C, Heinze J, Neumeyer R, Ødegaard F, Oettler J, Radchenko A, Schultz R, Sharaf M, Trager J, Vesnic A, Wiezik M, Zettel H (2016) Banning paraphylies and executing Linnaean taxonomy is discordant and reduces the evolutionary and semantic information content of biological nomenclature. Insect Soc 63:237–242. doi:10.1007/s00040-016-0467-1

Ward PS, Brady SG, Fisher BL, Schultz TR (2016) Phylogenetic classifications are informative, stable, and pragmatic: the case for monophyletic taxa. Insect Soc doi:10.1007/s00040-016-0516-9

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