C Colony Foundation Two Alternative Founding Strategies Christian Peeters In independent colony founding (ICF), a lone Institute of Ecology and Environmental Sciences, queen (founding pair in termites) needs to raise Sorbonne Université, Paris, France the first brood of offspring without the help of nestmates. Following aerial dispersal and mating with one or more foreign males, the queen exca- Efficient cooperation and division of tasks among vates, builds, or takes over an existing shelter and nestmates are the strength of insect societies, yet lays a first batch of eggs. During the next few in most species this cooperation is absent while weeks or months, she must guard and feed the new colonies are beginning. For several weeks, a first larvae. In social bees and wasps, as well as in lone founding queen (queen and king in termites) a minority of ants, ICF necessitates risky foraging faces the same challenges as solitary insects to trips away from the brood that is temporarily produce her offspring. Although her brood sur- undefended. In many unrelated lineages, ICF has vives better in the safety of a rudimentary nest, been replaced by a strikingly different founding foraging is always associated with high mortality mode whereby queens are never alone. This is risk. A proportion of social Hymenoptera have known as dependent colony founding (DCF) or reduced risks by evolving two very distinct adap- swarm founding. In DCF species, existing colo- tations: (i) in three large subfamilies of ants (80% nies divide into two or more daughter groups, of all species), solitary founding queens no longer which soon become autonomous. This allows forage, because the first larvae can develop on the queen(s) to be continuously protected by their mother’s internal metabolic reserves, or nestmate workers that take all the risks involved food obtained from mutualistic fungi or scale in foraging. insects, or food obtained from parasitism of for- The evolution of DCF was an evolutionary eign ant colonies; (ii) in many species across all breakthrough, allowing the benefits of social life lineages, established colonies can split into to be retained at all stages of the ▶ colony cycle daughter colonies, so that founding queens are [2]. DCF evolved in many social wasps and bees, helped by nestmate workers who feed and protect but it is particularly suited to the biology of ants, the brood. since the eggs, larvae, and pupae are mobile items that are easily carried to a new nest. This contrasts © Springer Nature Switzerland AG 2020 C. Starr (ed.), Encyclopedia of Social Insects, https://doi.org/10.1007/978-3-319-90306-4_26-1 2 Colony Foundation with bees and wasps in which brood develops in the rule. Risky foraging trips are not needed when fixed cells of wax or paper, so that nest emigration dead wood provides both a nest and cellulose for implies that all existing brood must be abandoned. food [14], although most species of Termitidae do Accordingly, new daughter colonies begin not nest in their food supply. Importantly, hemi- without any brood, and as the older foragers die, metabolous development in termites results in colony size tends toward a minimum. autonomous immatures (nymphs) that do not In several lineages of social Hymenoptera, rely on the founding queen and king for a number of foundresses cooperate in building nourishment. the nest and producing the first workers (pleometrosis). As a rule, once the first workers emerge, only one queen survives since the Winglessness in Ant Workers Impacts others are expelled or executed. In various spe- Both ICF and DCF cies, pleometrosis is a facultative strategy influenced by the local density of dispersing Ant workers are permanently wingless, and one of queens [12]. the many consequences is that queens spend Unlike ant queens, independent foundresses in almost all of their lives on the ground. Indeed, social bees and wasps must retain the ability to fly queens fly only briefly to disperse from the mater- and so cannot metabolize their wing muscles as a nal nest. They break off and discard their wings source of brood food. They must forage inten- shortly after mating, and wing muscles are sively to rear the first brood of daughters, increas- converted to amino acids to feed the first larvae. ing the probability of mortality. In various Two major trends in ants are a striking queen- ▶ Polistes species showing ICF, 42–84% of incip- worker dimorphism in body size and the evolution ient colonies fail before the emergence of the first of permanently wingless queens. Both are associ- offspring [15]. Such a low success rate is likely ated with a diversity of founding strategies to account for the broad distribution of DCF in (Table 1) that greatly exceeds that found in social social wasps and bees [6, 11, 13]. Nonetheless, bees and wasps. ICF occurs in most polistine wasps, as well as all ▶ stenogastrine and ▶ vespine wasps (Provespa (1) Non-claustral ICF is the ancestral strategy in excepted) as well as ▶ Bombus bees. Among ants, resembling the behavior of solitary para- polistine wasps, Belonogaster, ▶ Mischocyttarus, sitoid wasps. In these, a mother provisions Polistes, and many ▶ Ropalidia species show each offspring with paralyzed insects. Simi- ICF [3], but other genera (e.g., Polybia and larly, dealate ant queens hunt on the ground Metapolybia) reproduce by DCF. Polistine spe- just like workers. This unspecialized ICF pre- cies that show colony fission are polygynous, dominates in the ▶ poneroid subfamilies and mean colony sizes range from a few dozen Amblyoponinae and Ponerinae, as well as in to a few thousand females. Provespa wasps, all three formicoid subfamilies (Ectatomminae, ▶ stingless bees, and ▶ Apis are monogynous and Myrmeciinae, and ▶ Pseudomyrmecinae) show DCF. An interesting difference is that the (Table 1). In Formicinae and Myrmicinae, old queen flies away in Apis, but this is almost the few non-claustral species (scattered in, impossible in stingless bees, because queens e.g., ▶ Cataglyphis and ▶ Pogonomyrmex) become physogastric, hence it is the young queens represent an adaptive response to local envi- that disperse with nestmate workers. Colony divi- ronmental conditions, hence a secondary sion is abrupt in Apis, but more gradual in sting- modification from claustral ICF [10]. less bees, as workers from the daughter colony (2) A majority of ICF species in ants have temporarily return to the mother colony for build- evolved the ability to found colonies ing materials and food supplies. claustrally, i.e., without relying on food In termites, evidence for colony fission is obtained outside the nest. In most species scanty or ambiguous [2] and ICF appears to be of Dolichoderinae, Formicinae, and Colony Foundation 3 Colony Foundation, Table 1 Patterns of colony-founding strategies across the different ant subfamilies (47 genera for which founding behavior is known). Evidence for DCF is either direct (e.g., field observations) or indirect (e.g., absence of winged queens, genetic differentiation data [10]). The first five subfamilies are poneroids, while others are formicoids Myrmicinae, dispersing young queens carry that show claustral ICF make up almost 80% large metabolic reserves (fat and specialized of known species, and claustrality is arguably storage proteins) that are accumulated before a contributing factor to their evolutionary leaving the natal nest; the wing muscles are success. hypertrophied to carry this extra load [4]. (3) In a small number of genera, claustral ICF is Hence young queens can feed their first off- possible due to a mutualism with sap-feed- spring without taking any of the risks ing insects or with fungi. During the mating involved in foraging outside (Fig. 1). In flight of Acropyga and Tetraponera, these lineages, the significance of metabolic foundresses carry a gravid pseudococcid reserves is amplified by the large size differ- (scale insect) to the stem cavity where they ence relative to the worker caste. This makes settle. Being clonal, the sap-suckers multiply it possible for a founding queen to produce rapidly and supply sufficient ▶ honeydew to many small offspring. Moreover, these first feed the first worker brood. In attine species, workers are often smaller than average dispersing queens carry hyphae of the mutu- (nanitics), another adaptation for claustral alistic fungus in their infrabuccal pocket, and ICF. None of the social bees or wasps this will be the nucleus of future ▶ fungus show claustral ICF, which is a true novelty gardens. Similarly, ▶ Azteca foundresses of the ants. The three ant subfamilies bring an ascomycete fungus to the Cecropia (Dolichoderinae, Formicinae, Myrmicinae) domatium in which they settle. Parenchyma 4 Colony Foundation (4) Social parasitism is an independent founding strategy. In several ant lineages, newly mated queens attempt to enter existing colonies of their own or other species, follow- ing which their offspring are fed and raised by host workers. ▶ Social parasitism is a form of ICF, because queens are not helped by nestmate workers [10]. Founding queens dis- perse alone and take considerable risks in trying to enter the host colonies. The latter are nothing more than a resource of the envi- Colony Foundation, Fig. 1 A claustral Lasius foundress ronment to be exploited, similar to insect prey. queen raises her first crop of workers sealed in an under- Many authors have considered parasitism to ground chamber. She feeds the developing larvae with be DCF because queens depend on their host reserves from her own body. (Photo ©Alex Wild) colonies, but claustral queens depend just as much on their metabolic reserves, while non- tissue is scraped from the walls and processed claustral queens depend on the food they by the fungus that is then used as food for the gather outside. What is crucial in DCF species fi rst larvae, so the foundress does not need to is that queens rely on nestmate workers, and forage outside.