Pheidole oculata

Fischer et al. (2020) found 13 unusual species, which they call the Pheidole lucida group (for the first of its two described species, Pheidole lucida, Pheidole oculata being the other), all of which are associated with other Pheidole species in Madagascar. Although the full biology of these species is not yet known, multiple lines of evidence suggest that they are inquilines (residing inside the nest of another species), and likely social parasites. First, they were frequently observed and collected as part of a nest series of other Pheidole species (i.e., the putative hosts). Second, they have a suite of morphological traits that are typically observed in other inquiline species. The minor worker caste has reduced mandibles and loss of cuticular pigmentation, whereas the queens show modifications found in many other inquiline species that are often referred to as part of a ‘‘parasitic syndrome’’ (e.g., rounded head shape, elongated antennae, broadened postpetiole, etc. (Wilson, 1971; Wilson, 1984)). Third, the major worker subcaste, a hallmark of the genus and present in all 1,000+ non-parasitic Pheidole species, is entirely absent in the P. lucida group. In this genus, the partial loss of the worker caste is a strong indication of a socially parasitic lifestyle, where reproductive allocation to the worker caste is often reduced or lost entirely (Buschinger, 2009; Wilson, 1971; Wilson, 1984; Hoelldobler & Wilson, 1990; Maschwitz et al., 2000; Sumner et al., 2003). Only one of the 13 inquiline species (an undescribed species, Pheidole gf010) seems to be entirely workerless, with the queen itself showing a very reduced, worker-like morphology. Sumner et al. (2003) suggested that workers of incipient social parasites (inquilines) may help the parasitic queen suppress host reproduction and redirect host resources toward the production of parasite queens and males. We refer to this group as ‘‘social parasites’’ because of the evidence above but, without direct observation, the strength of this parasitism in the P. lucida group is uncertain and we cannot rule out weak or even no costs to the host (i.e., commensalism). However, the important point for the following study is that if the workers in the P. lucida group are symbiotic with the host colonies, we should expect their phenotypes to be subject to scrutiny by the host workers in everyday social interactions.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  oculata. Aphaenogaster oculata Emery, 1899f: 276 (q.) MADAGASCAR. Combination in Parapheidole: Emery, 1915d: 68; in Pheidole: Smith, D.R. 1979: 1366.

References based on Global Ant Biodiversity Informatics

 * Fisher B. L. 1997. Biogeography and ecology of the ant fauna of Madagascar (Hymenoptera: Formicidae). Journal of Natural History 31: 269-302.
 * Fisher B. L. 2003. Formicidae, ants. Pp. 811-819 in: Goodman, S. M.; Benstead, J. P. (eds.) 2003. The natural history of Madagascar. Chicago: University of Chicago Press, xxi + 1709 pp.
 * Wheeler W. M. 1922. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. IX. A synonymic list of the ants of the Malagasy region. Bulletin of the American Museum of Natural History 45: 1005-1055