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P Poneroid Ants Ponerinae, which included the current poneroid subfamilies as well as Leptanillinae, the formicoid Roberto A. Keller1 and Christian Peeters2 subfamilies Ectatomminae and Heteroponerinae, 1Museu Nacional de História Natural e da Ciência and all the ▶ Dorylinae that do not display army- & cE3c-FCUL, Universidade de Lisboa, Lisbon, ant behavior (formerly included in the now obso- Portugal lete subfamily Cerapachyinae). Ponerinae sensu 2CNRS, Institute of Ecology and Environmental lato was defined by putative ancestral traits Sciences, Sorbonne Université, Paris, France exhibited by its members rather than the existence of shared derived characteristics. William Morton Wheeler remarked that “the Ponerinae comprises Poneroid ants are a clade composed of six well- unmistakably primitive and generalized forms and defined subfamilies that are morphologically het- therefore constitutes a group of twofold interest, erogeneous (Agroecomyrmecinae, first, as the ancestral stock of the higher subfamilies, Amblyoponinae, Apomyrminae, Paraponerinae, and second, as the oldest existing expression of Ponerinae and Proceratiinae) (Fig. 1). Poneroids social life among the Formicidae” [13]. Wheeler’s include just 11% of extant ant species, and molec- view persisted for a century, with subsequent ular data [4] recognize it as the sister group of the authors explicitly treating Ponerinae sensu lato as formicoids [12], the clade with the bulk of species an all-encompassing taxon from which the other diversity (Fig. 2). Not included in either of the subfamilies arose [5]. poneroids or formicoids are ▶ Leptanillinae and The twenty-first century has already brought Martialinae, two diminutive subfamilies com- major changes to the higher classification as sub- posed of highly specialized tiny subterranean families were redefined [2], morphological charac- workers. Their relationship to other extant ants ters were formalized in a phylogenetic framework remains inconclusive. The now obsolete term [5], and internal phylogeny was revealed by DNA “poneromorph” [2] should not be confused with data ([4] and included references). The current “poneroid.” The various “-morphs” were tentative scheme (Fig. 2) recognizes poneroids not as a groups of similar-looking subfamilies without any collection of primitive or ancestral ants, but as an claim of phylogenetic relationships or formal tax- evolutionary radiation that occurred independent onomic status. from and simultaneous to formicoids [4]. Prior to quantitative phylogenetic analyses, The poneroid radiation resulted in a set of there was a long taxonomic history of treating morphologically distinct subfamilies, several of ants that are superficially similar to wasp ances- which have only one or two extant species, tors as a large and heterogeneous subfamily suggesting a high degree of past extinction events. © Springer Nature Switzerland AG 2020 C. Starr (ed.), Encyclopedia of Social Insects, https://doi.org/10.1007/978-3-319-90306-4_99-1 2 Poneroid Ants Poneroid Ants, Fig. 1 Poneroid ants are almost all mixta (Proceratiinae) predate specifically on spider eggs ground predators (solitary or in a group; generalists or (yellowish, mixed with white ant eggs); (c) Bothroponera highly prey-specific), with colonies seldom reaching soror (Ponerinae) shows the archetypal limited size diver- more than hundreds of workers: (a) Adetomyrma goblin gence between queens (dealate queen is bottom left) and (subfamily Amblyoponinae) workers are minute and blind workers (male is top left); (d) Neoponera commutata cooperative hunters of linear arthropods; (b) Discothyrea (Ponerinae) colonies have a few thousand workers that Poneroid Ants 3 Amblyoponinae is peculiar because most of its spe- between the two to understand the possible causes cies lack the diagnostic petiole of ants (Fig. 1a). This of their greater ecological success. alone led to the idea that amblyoponines represented In light of the current phylogeny, it is tempting the transition between wasps and “higher” ants, to focus on Leptanillinae and Martialinae for clues strengthening the view that poneroids as a whole about early stages in ant evolution, as this clade were ancestral, but this atypical petiole is better lies outside the formicoids and poneroids (Fig. 2). considered a reversal. Apomyrminae (one species) However, we cannot assume that, relative to a was initially placed within Amblyoponinae, then sister clade that is morphologically diverse and Leptanillinae due to its similar underground habitus, highly speciose, a small clade (69 species) repre- and is now the sister clade to Amblyoponinae (Fig. sents the ancestral condition [6]. Rather, lone 2). Proceratiinae (Fig. 1b)and▶ Paraponerinae (Fig. branches are often evolutionary “experiments” in 1e) were historically associated with Ectatomminae adaptation for a particular niche that were not very as a tribe within Ponerinae sensu lato and considered successful and an evolutionary dead end due to the link to subfamily Myrmicinae. Indeed, their mor- morphological specialization. A better interpreta- phology includes a mixture of primitive traits shared tion is that the larger sister clade is a lineage that with other poneroids and derived traits common remained generalized, thus giving rise to greater among formicoids. The poorly-known diversity in the long run but also retaining species Agroecomyrmecinae has two extant monotypic gen- that more likely reflect ancestral conditions. Not era previously placed in Myrmicinae. Amid these only is it unlikely that ants radiated from a highly clades sits Ponerinae sensu stricto (Fig. 1c, d), specialized subterranean clade with reduced mor- containing the bulk of the poneroid species and phology [7], but the Cretaceous fossil record is exhibiting a broad range of morphologies, particu- rich with unspecialized forms that lived above larly in their mandibles that reflect diverse feeding ground [1]. habits [11]: generalist to highly specialist predators, hunting exclusively underground or above ground. The impact from the shift of viewing poneroids How to Assess Social Complexity in as an ancestral stock to recognizing them as one of Ants? two main independent ant radiations cannot be overstated. Because ponerines-as-basal ants was Sociality is always a composite of interconnecting the dominant paradigm, authors turned to traits including age structure, genetic composi- poneroids for clues about putative ancestral states tion, group size, communication mechanisms, for everything from morphology to behavior, division of labor, and degree of task specificity. “ ” while formicoids were held as the higher ants In ants these interacting traits can be magnified by and their traits considered advanced. Poneroids as marked morphological differences among adult an independent parallel radiation to formicoids, nestmates (queens and workers) and often however, require reassessment of social complex- supplemented by enduring mutualisms with ity across different lineages. Traits uniquely pre- plants, bacteria, fungi, or sap-sucking insects. sent among poneroids might not represent The diversity in ant diets and ecology is unparal- examples of early stages in ant evolution, but leled among insects, but commonalities across rather advanced states. Likewise, the formicoids lineages are easier to grasp by focusing on the as a whole exhibit a mix of ancestral and advanced fundamental dichotomy in colony characteristics traits, and it is important to carefully discern (modified from Ref. [3]): (A) foraging strategies, i.e., how resources are acquired, and (B) how ä ä Poneroid Ants, Fig. 1 (continued) are column raiders on of the very few arboreal hunters (solitary generalists). termites; (e) Paraponera clavata (Paraponerinae) are one Body sizes range from 3 to 25 mm. (Photos © Alex Wild) 4 Poneroid Ants Poneroid Ants, Fig. 2 Evolutionary relationships among extant subfamilies of ants. Area of triangles represents relative numbers of species (phylogeny after Ref. [4]; species count after AntCat.org [March 2020]) resources are allocated to produce new adults, i.e., hunting, mass raiding, scavenging dispersed car- body size of queens and workers, their degree of casses, collection of honeydew, or assembly-line dimorphism, and the number of workers (colony tasks like fungus-farming. Mature colony size is size) and gynes reared annually. Both worker determined by queen fecundity (queen number morphology (including body size) and colony also), the degree of caste dimorphism, and the size have likely coevolved with foraging strate- amount of resources extracted from the environ- gies across ants, while queen morphology (includ- ment. An increased dimorphism is mostly linked ing body size and ovariole numbers) has to a reduction in size of the workers, with the coevolved with the hazards of colony foundation consequence that more individuals can be and selection for optimal size and longevity of manufactured with finite colony resources colonies. Hence, social complexity in an organi- (¼ food intake) [9]. Increased caste dimorphism zational sense can be assessed by comparing also allows “claustral” ▶ colony foundation, i.e., degrees of dimorphism between workers and founding queens are able to raise the first workers queens. Unlike social wasps and bees that are using internal metabolic reserves only if the constrained by the need to fly for both castes, ant queen-worker size difference is sufficient. workers can evolve to be 10–20 times as small as Because claustrality requires gynes that are costly