Independent colony founding by ergatoid queens in the ant genus Pogonomyrmex: queen foraging provides an alternative to dependent colony founding

Ant queens exhibit two primary strategies to initiate nests, independent colony founding (ICF) by solitary queens and dependent colony founding (DCF) when the queen starts a nest with a group of workers that disperse on foot from the parent nest. Numerous ant species have wingless (ergatoid) queens, and it is generally assumed that these species exhibit obligate DCF because their lack of wing musculature provides them with few resources to divert towards producing their first brood of workers. Thus, ICF by ergatoid queens is viewed as maladaptive because these queens need to take additional dangerous foraging trips to garner sufficient food to rear their first brood of workers. Contrary to this prediction, I document ICF by ergatoid queens for three species of harvester ants in the genus Pogonomyrmex (subfamily Myrmicinae), P. cunicularius cunicularius, P. cunicularius pencosensis, and P. huachucanus. Queens of P. huachucanus were obligate foragers, i.e., no minim workers could be produced without external food, and one queen of P. cunicularius pencosensis was observed foraging in the field. Abundant and/or predictable food resources likely select for the evolution of semi-claustral nest founding and ICF by these ergatoid queens. Under these conditions, foraging time would be minimized and the number and size of minim workers would be maximized. These benefits should increase founding success, which could compensate for loss of long-range dispersal. Overall, this study demonstrates that care should be taken before concluding that ant colonies employ DCF based solely on queen morphology.     

How do workers of the primitively eusocial wasp Ropalidia marginata detect the presence of their queens?

Queens in primitively eusocial insect societies are morphologically indistinguishable from their workers, and occupy the highest position in the dominance hierarchy. Such queens are believed to use aggression to maintain worker activity and reproductive monopoly in the colony. However, in the primitively eusocial wasp Ropalidia marginata, the queen is a strikingly docile individual, who interacts rarely with her workers. If the queen is experimentally removed, one of the workers becomes extremely aggressive within minutes, and eventually becomes the new queen of the colony. We designate her as the potential queen. Experimental evidence suggests that the queen probably uses a non-volatile pheromone to signal her presence to her workers. Here we attempt to identify the mechanism by which the queen transmits information about her presence to the workers. We designate the time taken for the potential queen to realize the absence of the queen as the realization time and model the realization time as a function of the decay time of the queen's signal and the average signal age. We find that the realization time obtained from the model, considering only direct interactions (193.5 min) is too large compared to the experimentally observed value of 30 min. Hence we consider the possibility of signal transfer through relay. Using the Dijkstra's algorithm, we first establish the effectiveness of relay in such a system and then use experimental data to fit the model. We find that the realization time obtained from the model, considering relay (237.1 min) is also too large compared to the experimentally observed value of 30 min. We thus conclude that physical interactions, both direct and indirect (relay), are not sufficient to transfer the queen's signal in R. marginata. Finally, we discuss the possibility that the queen applies her pheromone on the nest material from where the workers can perceive it without having to physically interact with the queen.     

Social control of egg-laying rate in queens of the fire ant, Solenopsis invicta*

ABSTRACT Social control of egg-laying rate in queens of the fire ant (Solenopsis invicta Buren) was studied by experimental manipulation of the number of larvae, pupae and workers in colonies, and the age and size of larvae and workers. Workers and pupae do not stimulate oviposition by queens. The number of fourth instar larvae, on the other hand, bears a positive log-log relationship to the queen's egg-laying rate. Such larvae are needed both to stimulate and maintain oviposition. Their withdrawal results, within 48 h, in a decline in queen oviposition almost to zero. Their addition to broodless nests results in peak laying in about 4 days. Larvae in the first three stadia and early in the fourth stadium have a much lower effect upon queen fecundity. Sexual larvae are only c. 5% as stimulating on a weight basis, but equivalent on an individual basis. Several associated measures are positively correlated to egg-laying rate: weight of the queen, the number of her vitellogenic follicles per ovariole, total vitellogenic follicles, the time she spends feeding and (usually) the number of workers in the retinue that cares for her. The egg volume is negatively correlated with laying rate, so that queens lay more eggs for the same expenditure of material as laying rate increases. As body size of workers increases, they become less effective in transmitting the larval stimulation to the queen, but worker age has no effect on this ability. For a given number of larvae, queens in small, naturally growing colonies lay fewer, larger eggs than do queens in experimental colonies, but their fecundity increases more rapidly in relation to number of larvae. When larvae are fed vital-dyed food in one experimental colony, and then transferred to an undyed colony, the dye is rapidly transferred to worker crops, and into the queen's eggs, indicating bulk movement of material from larvae to workers to the queen and eggs. Large larvae are more effective at this than small larvae. Fourth instar larvae may be a digestive and metabolic caste that processes protein for egg production by the queen. If that is the case, the queen and fourth instar larvae are linked in a positive feedback loop. Either the logarithmic relation of fecundity to larval numbers or physical limits of the queen may set the maximum egg-laying rate, and thus determine maximum colony size. The data do not allow a clear choice between these alternatives.     

QUEEN SIGNALING IN SOCIAL WASPS

Social Hymenoptera are characterized by a reproductive division of labor, whereby queens perform most of the reproduction and workers help to raise her offspring. A long‐lasting debate is whether queens maintain this reproductive dominance by manipulating their daughter workers into remaining sterile (queen control), or if instead queens honestly signal their fertility and workers reproduce according to their own evolutionary incentives (queen signaling). Here, we test these competing hypotheses using data from Vespine wasps. We show that in natural colonies of the Saxon wasp, Dolichovespula saxonica, queens emit reliable chemical cues of their true fertility and that these putative queen signals decrease as the colony develops and worker reproduction increases. Moreover, these putative pheromones of D. saxonica show significant conservation with those of Vespula vulgaris and other Vespinae, thereby arguing against fast evolution of signals as a result of a queen–worker arms race ensuing from queen control. Lastly, levels of worker reproduction in these species correspond well with their average colony kin structures, as predicted by the queen signaling hypothesis but not the queen control hypothesis. Altogether, this correlative yet comprehensive analysis provides compelling evidence that honest signaling explains levels of reproductive division of labor in social wasps.     

Evolution of wingless reproductives in ants: weakly specialized ergatoid queen instead of gamergates in Platythyrea conradti

Platythyrea conradti is the only species in this genus with ergatoid (= permanently wingless) queens. Colonies lack gamergates (unlike other species in this genus), yet aggressive interactions among queen and workers define a hierarchy. A single fertile queen has the top rank and highranking workers do not lay eggs, except when the queen dies. Colonial reproduction by both alate queens (independent foundation) and gamergates (fission) seems the ancestral state in Platythyrea. Independent foundation can be selected against in some species, causing the loss of alate queens for economic reasons. Thus gamergates become the only reproductives, except in P. conradti in which queens became ergatoid. Gamergates and ergatoid queens are two mutually redundant reproductive phenotypes that allow colonial reproduction by fission. Received 1 July 2005; revised 10 November 2005; accepted 16 November 2005.     

Unequal partitioning of reproduction and investment between cooperating queens in the fire ant,Solenopsis invicta,as revealed by microsatellites

Social insects provide ideal systems for investigating how kinship and ecological factors affect cooperation and conflict. In many ant species, unrelated queens cooperate to initiate new colonies. However, fights between queens break out after the eclosion of the first workers, leading to the death of all but one queen. Queens within associations potentially face a trade-off. On one hand, a queen should restrain her investment in brood production and care if this helps her to maintain fighting ability. On the other hand, a queen may benefit by increasing her contribution to brood production if having more daughter workers than her cofoundresses enhances her chances of taking over the colony. Increased investment is also beneficial because a large brood enhances colony survival. Using microsatellites, we determined the maternity of workers (adults and larvae) at the time of queen execution in the fire ant, Solenopsis invicta. Differential mass loss by initially equal nestmates affected survival, with the queen losing less body mass being more likely to survive. Surprisingly, the queen which lost less body mass, that is the one which provided the lowest energy investment, was the one which achieved higher maternity. A control experiment indicated that interactions among queens are responsible for this differential partitioning of reproductive and investment tasks between nestmates. The finding that the queen most likely to win the fights is the one with above-average maternity may explain why workers apparently do not attempt to influence the outcome of fights.     

Production of winged and wingless males in the ant, <Emphasis Type="Italic">Cardiocondyla minutior</Emphasis>

Summary Wingless (ergatoid) males of the tramp ant Cardiocondyla minutior attack and kill their young ergatoid rivals and thus attempt to monopolize mating with female sexuals reared in the colony. Because of the different strength of local mate competition in colonies with one or several reproductive queens, we expected the production of new ergatoid males to vary with queen number. Sex ratios were mostly female-biased, but in contrast to the sympatric species C. obscurior (Cremer and Heinze, 2002) neither the percentage of ergatoid males nor of female sexuals among the first 20 sexuals produced varied considerably with queen number. As in C. obscurior, experimental colony fragmentation led to the production of winged males, whereas in unfragmented control colonies only ergatoid males eclosed.Received 3 December 2003; revised 20 February 2004; accepted 23 February 2004.     

Road to Royalty – Transition of Potential Queen to Queen in the Primitively Eusocial Wasp Ropalidia marginata

Ropalidia marginata, a primitively eusocial wasp, is different from typical primitively eusocial species in having docile queens who cannot be using dominance to maintain reproductive monopoly and instead appear to use a pheromone from the Dufour's gland to do so. When a docile queen is removed from her colony, one of the workers (potential queen, PQ) becomes highly aggressive, and if the queen is not returned, gradually loses her aggression and becomes the new docile queen within a few days. We hypothesized that the decrease in aggression of the PQ with time since queen removal should be correlated with her change in ovaries and pheromone profile. Because the Dufour's gland hydrocarbon composition in R. marginata can be correlated with fertility, this also gave us an opportunity to test whether PQ is different from workers in her Dufour's gland hydrocarbons. In this study, we therefore trace the road to royalty in R. marginata, that is, the transition of the PQ during queen establishment, in terms of her ovaries, aggression, and Dufour's gland hydrocarbons. Our study focuses on queen establishment, which is important for understanding how reproductive conflict can be manifested and resolved.     

Workers of the primitively eusocial wasp <Emphasis Type="Italic">Ropalidia marginata</Emphasis> do not perceive their queen across a wire mesh partition

Queens of primitively eusocial wasps generally have active and behaviourally dominant queens who use physical aggression to suppress worker reproduction. Although a Ropalidia marginata queen is strikingly docile and behaviourally non-dominant, she is completely successful in maintaining reproductive monopoly. R. marginata queens must achieve such reproductive monopoly by some means other than overt physical aggression. Upon loss or removal of the queen, one of the workers (referred to as the potential queen) becomes extremely aggressive and will eventually go on to become the next queen of the colony, if the original queen is not returned. The fact that potential queens are not discernible in the presence of the queen but become obvious within minutes after removal of the queen raises the question of how workers in general and the potential queens in particular, perceive the presence or absence of their queens. Here, we have conducted experiments in which we separate half of the workers from their queen by a wire mesh screen and study their behavioural response to such separation. We demonstrate that the presence of the queen is not perceived across the wire mesh screen, which suggests that if the queen uses a pheromone to signal her presence, then that pheromone is not very volatile.     

THE EVOLUTION OF WORKER STERILITY IN HONEY BEES: AN INVESTIGATION INTO A BEHAVIORAL MUTANT CAUSING FAILURE OF WORKER POLICING

Normally, worker honey bees (Apis mellifera) only lay eggs when their colony is queenless. When a queen is present, worker egg-laying is controlled by mutual “policing” behavior in which any rare worker-laid eggs are eaten by other workers. However, an extremely rare behavioral phenotype arises in which workers develop functional ovaries and lay large numbers of eggs despite the presence of the queen. In this study, microsatellite analysis was used to determine the maternity of drones produced in such a colony under various conditions. One subfamily was found to account for about 90% of drone progeny, with the remainder being laid by other subfamilies or the queen. No evidence of queen policing was found. After a one-month period of extreme worker oviposition in spring, the colony studied reverted to normal behavior and showed no signs of worker oviposition. However, upon removal of the queen, workers commenced oviposition very quickly. Significantly, the subfamily that laid eggs when the queen was present did not contribute to the drone production when the colony was queenless. However, another subfamily contributed a disproportionately large number of drones. The frequency of worker oviposition appears to be determined by opposing selective forces. Individual bees benefit from personal reproduction, whereas other bees and the colony are disadvantaged by it. Thus a behavioral polymorphism can be maintained in the population in which some workers can escape worker policing, with balancing selection at the colony level to detect and eliminate these mutations.     

Worker dominance and policing in the ant Temnothorax unifasciatus

In many species of eusocial Hymenoptera, conflict about the production of males is resolved through “policing.” Recent studies in wasps and the ant Temnothorax unifasciatus suggest that in these species policing workers are dominant themselves and selfishly increase their own chances of later becoming fertile. Policing may therefore to some extent be associated with dominance and selfishness, and dominance and policing behaviour are indeed difficult to distinguish and often not mutually exclusive. Moreover, selfish policing requires that workers form rank orders already in the presence of the queen. Here, we try to allocate aggressiveness by workers towards policing and/or dominance behaviour and investigate whether hierarchies based on subtle, non-aggressive interactions exist in queenright colonies of the ant T. unifasciatus. We either split colonies into a queenright and queenless halve or temporarily removed the queen from complete colonies, which in both cases allows a few dominant workers to lay eggs in the queenless colony. Reunification of colony halves and return of the queen to orphaned colonies led to aggression against those workers that had become fertile during the absence of the queen. Dominant workers in reunited, split colonies were more severely attacked than those in orphaned colonies after return of the queen. Furthermore, we observed that workers, which later became dominant egg layers under queenless conditions, have more contact with the queen than other workers. Both results corroborate the existence of rank relationships among workers in queenright colonies and show that results from policing experiments may be affected by the disturbance of pre-existing hierarchies through colony splitting.     

Shift from independent to dependent colony foundation and evolution of 'multi-purpose' ergatoid queens in Mystrium ants (subfamily Amblyoponinae)

Division of labour improves fitness in animal societies. In ants, queens reproduce, whereas workers perform all other tasks. However, during independent colony founding, queens live as solitary insects and must be totipotent, especially in species where they need to forage. In many ants, solitary founding has been replaced by dependent founding, where queens are continuously helped by nestmate workers. Little is known about the details of this evolutionary transition. Mystrium rogeri from Madagascar and Mystrium camillae from Southeast Asia (subfamily Amblyoponinae) have winged queens, but three congeneric species from Madagascar reproduce with permanently wingless queens instead. We show that this 'ergatoid' caste has distinct body proportions in all three species, expressing a mixture of both queen and worker traits. Ergatoid queens have functional ovaries and spermatheca, and tiny wing rudiments. They can be as numerous as workers within a colony, but only a few mate and reproduce, whereas most behave as sterile helpers. The shape of their mandibles makes them unsuited for hunting and, together with a lack of metabolic reserves (i.e. in the form of wing muscles), this means that ergatoid queens cannot be solitary foundresses. In comparison with winged queens, ergatoid queens are less costly per capita and they experience lower mortality. They remain in their natal colonies where they can either reproduce or function as helpers, making them a 'multi-purpose' caste. Within the Amblyoponinae, ergatoid queens replace winged queens in Onychomyrmex as well. However, in this genus, ergatoid queens are 'sole-purpose', few are produced each year and they reproduce but do not work. Hence, different types of ergatoid queens evolved to replace winged queens in ants.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 198–207.     

Regulation of worker activity in a primitively eusocial wasp, Ropalidia marginata

Ropalidia marginala, a tropical, primitively eusocial, polistinewasp, is unusual in that the queen (the sole egg-layer) is neitherthe most behaviorally dominant nor the most active individualin the colony. The queen by herself rarely ever initiates interactionstoward her nest mates or unloads returning foragers. There arealways a few workers in the colony who are more dominant andactive than the queen. Absence of the queen from her colonydoes not affect colony maintenance activities such as foragingor brood care, but it always results in one individual becomingvery aggressive and dominant. The dominant worker becomes thenext queen if the original queen does not return. The queendoes not appear to play any significant role in colony activityregulation. Instead, colony activities appear to be regulatedby several mechanisms including dominance behavior toward foragers,feeding of larvae, and the unloading of returning foragers,all mediated by workers themselves. Regulation of colony maintenanceappears to be based on direct evaluation of the needs of thecolony by the workers themselves. The queen however has perfectreproductive control over all workers; workers never lay eggsin the presence of the queen. It appears therefore that themechanisms involved in regulation of worker activity and workerreproduction are separate in R marginata. These findings contrastwith other primitively eusocial species where the queen actsas a "central pacemaker" and controls both worker activity andworker reproduction.     

Brood development into sexual females depends on the presence of a queen but not on temperature in an ant dispersing by colony fission,Aphaenogaster senilis

Abstract. 1. In eusocial insects, colony fission is a mode of dispersal by which a young queen leaves her nest with some workers to found a new colony. In these species, adult females (workers and the queen) should allocate most resources to increasing their colony size, which constrains the possibility of fission. In contrast, developing diploid larvae should have a preference for becoming a queen and having their own offspring, rather than becoming workers and rearing the offspring of other females. 2. In the ant Aphaenogaster senilis, queens are produced in very small numbers, suggesting that adult females control larval development. We used a 6‐year series of data on more than 300 nests to determine the annual cycle of worker and queen production. Although both overlapped, the latter mostly occurred in the second half of the summer, after a major peak of worker emergence. Young queens were also often produced in nests whose reproductive queen had died, thus allowing her replacement. Overall, we estimate that only 0.07% of diploid larvae actually develop into gynes. 3. Laboratory experiments indicated that brood is bipotent until the second larval instar. Diploid larval development into queen was favoured by the removal of the mother queen, but was not affected by rearing temperature. 4. Our data suggest that most diploid broods are forced by the adults to develop into workers rather than into gynes. However, when the queen is not present due to death or after a fission event, a few larvae are allowed to develop into gynes. One way for workers to limit the development of larvae might be by controlling the amount of food they receive.     

Facultative use of thelytokous parthenogenesis for queen production in the polyandrous ant Cataglyphis cursor

The evolutionary paradox of sex remains one of the major debates in evolutionary biology. The study of species capable of both sexual and asexual reproduction can elucidate factors important in the evolution of sex. One such species is the ant Cataglyphis cursor, where the queen maximizes the transmission of her genes by producing new queens (gynes) asexually while simultaneously maintaining a genetically diverse workforce via the sexual production of workers. We show that the queen can also produce gynes sexually and may do so to offset the costs of asexual reproduction. We genotyped 235 gynes from 18 colonies and found that half were sexually produced. A few colonies contained both sexually and asexually produced gynes. Although workers in this species can also use thelytoky, we found no evidence of worker production of gynes based on genotypes of 471 workers from the six colonies producing sexual gynes. Gynes are thus mainly, and potentially exclusively, produced by the queen. Simulations of gynes inbreeding level following one to ten generations of automictic thelytoky suggest that the queen switches between or combines thelytoky and sex, which may reduce the costs of inbreeding. This is supported by the relatively small size of inbred gynes in one colony, although we found no relationship between the level of inbreeding and immune parameters. Such facultative use of sex and thelytoky by individual queens contrasts with other known forms of parthenogenesis in ants, which are typically characterized by distinct lineages specializing in one strategy or the other.     

A possible novel function of dominance behaviour in queen-less colonies of the primitively eusocial wasp Ropalidia marginata

Unlike the queens of other primitively eusocial species, Ropalidia marginata queens are strikingly docile and non-aggressive individuals, never at the top of the behavioural dominance hierarchy of their colonies. Nevertheless, these queens are completely successful at suppressing worker reproduction, suggesting that they do not use aggression but employ some other mechanism (e.g. pheromones) to do so. Upon removal of the queen from a colony, a single worker, the 'potential queen', immediately begins to display highly elevated levels of aggression towards her nest mates. This individual becomes the next docile queen if the original queen is not returned. We attempt to understand the function of the temporary and amplified dominance behaviour displayed by the potential queen. We find that the dominance behaviour shown by the potential queen is unrelated to the number of her nest mates, their dominance ranks or ovarian condition. This suggests that aggression may not be used to actively suppress other workers and counter threat. Instead we find evidence that dominance behaviour is required for the potential queen's rapid ovarian development, facilitating her speedy establishment as the sole reproductive individual in the colony.     

Dynamics of colony emigration in the ant Aphaenogaster senilis

In many social insect species, colonies frequently emigrate to a new nest. This requires the coordination of many individuals, and it puts the queen at risks of being lost or predated. We experimentally studied colony emigration in the ant Aphaenogaster senilis, who emigrates frequently and obligatorily reproduces by colony fission. As in other species, colony emigration was characterised by a synchronised relocation of workers. Foragers found the new nest site and triggered the relocation of the “inside” workers, which built up following a sigmoid curve. Unlike in Temnothorax, where workers are transported to the new nest, most individuals relocated by walking. The brood was transported around the middle of colony relocation, mostly by “inside” workers because they represent most of the workforce. The queen walked to the new nest at the middle of colony relocation, when the flow of ants to the new nest was maximal. Overall, this temporal dynamic of colony emigration is similar to that observed in other species. However, we argue that species-specific traits, such as whether workers are transported to the new nest or relocate by themselves, may affect parts of the process of colony emigration.     

Absence of Within‐Colony Kin Discrimination in a Multiple‐Queen Ant,Leptothorax acervorum

Inclusive fitness theory predicts that, other things equal, individuals within social groups should direct altruistic behaviour towards their most highly related group‐mates to maximise indirect fitness benefits. In the social insects, most previous studies have shown that within‐colony kin discrimination (nepotism) is absent or weak. However, the number of studies that have investigated within‐colony kin discrimination at the level of individual behaviour remains relatively small. We tested for within‐colony kin discrimination in the facultatively multiple‐queen (polygynous) ant, Leptothorax acervorum. Specifically, we tested whether workers within polygynous colonies treated queens differently as a function of their relatedness to them. Colonies containing two egg‐laying queens were filmed to measure the rate at which individually marked workers antennated and groomed or fed each queen. Relatedness between individual queens and workers was calculated from their genotypes at four microsatellite loci. The results showed there were no differences in the rates at which workers antennated or groomed/fed their more related queen and their less related queen. Workers interacted preferentially with their potential mother queen with respect to grooming/feeding but not with respect to antennation. However, because of high queen turnover, the frequency of adult workers with their potential mother queen still present within the colony was relatively low. Overall, therefore, we found no evidence for within‐colony kin discrimination in the context of the average worker's treatment of queens in polygynous L. acervorum colonies.     

Colony dynamics in a primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum (Hymenoptera: Halictidae)

Summary Proximate control of colony dynamics was studied in the primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum using allozyme markers. The results indicate that workers produce on average 15% of the male brood (range=0–50%) in small laboratory colonies made up of unrelated, single-generation, uninseminated females. This proportion is not influenced by colony size, but is influenced by the relative size of the queen. Large queens are more successful in dominating their workers than are small queens, the queen being defined as the female that is the mother of most of the brood produced in the colony. Older and larger females tend to become queens. Thus, while small differences in age (up to 4 days) influence which female becomes a queen, her ability to control her workers is primarily influenced by her relative size. The proportion of reproduction that is co-opted by the queen is negatively correlated with colony reproductivity (the number of males/day/female). Colony reproductivity is also negatively correlated with the standard deviation in size among females.     

Selection against Aerial Dispersal in Ants: Two Non-Flying Queen Phenotypes in Pogonomyrmex laticeps

The South American seed-harvester ant Pogonomyrmex laticeps has dimorphic queens: ergatoid (permanently wingless) and brachypterous (short, non-functional wings). Surveys in western Argentina indicated that colonies near Chilecito, La Rioja Province, produced only ergatoid queens, while those near Punta Balasto, Catamarca Province (263 km away), produced only brachypterous queens. Brachypterous queens were significantly larger than ergatoid queens for 10 of 11 external characters, but both phenotypes had comparable reproductive potential, i.e., a spermatheca and a similar number of ovarioles. Using normal winged queens of the closely related P. uruguayensis for comparison, we determined that both queen phenotypes in P. laticeps had a full set of dorsal thoracic sclerites, albeit each sclerite was much reduced, whereas workers had a thorax without distinct dorsal sclerites. Sclerites were fused and immobile in ergatoid queens, while they were separable and fully articulated in brachypterous queens. Both phenotypes lacked the big indirect flight muscles, but brachypterous queens retained the tiny direct flight muscles. Overall, this dimorphism across populations indicates that there are alternative solutions to selective pressures against flying queens. We lack field data about colony founding strategy (independent or dependent) for either queen phenotype, but colonies at both sites produced numerous gynes, and we infer that all foundresses initiate colonies independently and are obligate foragers.