Moving targets: collective decisions and flexible choices in house-hunting ants

Many decisions involve a trade-off between commitment and flexibility. We show here that the collective decisions ants make over new nest sites are sometimes sufficiently flexible that the ants can change targets even after an emigration has begun. Our findings suggest that, in this context, the ants’ procedures are such that they can sometimes avoid ‘negative information cascades’ which might lock them into a poor choice. The ants are more responsive to belated good news of a higher quality nest than they are when the nest they had initially chosen degraded to become worse than an alternative. Our study confirms, in a new way, that ant colonies can be very powerful “search engines”.     

Evaluating reproductive decisions as discrete choices under social influence

Discrete choice, coupled with social influence, plays a significant role in evolutionary studies of human fertility, as investigators explore how and why reproductive decisions are made. We have previously proposed that the relative magnitude of social influence can be compared against the transparency of pay-off, also known as the transparency of a decision, through a heuristic diagram that maps decision-making along two axes. The horizontal axis represents the degree to which an agent makes a decision individually versus one that is socially influenced, and the vertical axis represents the degree to which there is transparency in the pay-offs and risks associated with the decision the agent makes. Having previously parametrized the functions that underlie the diagram, we detail here how our estimation methods can be applied to real-world datasets concerning sexual health and contraception.     

New species and unexpected diversity of socially parasitic bees in the genus Inquilina Michener (Hymenoptera: Apoidea: Apidae)

Abstract  Allodapine bees present particular problems for taxonomy due to a high level of morphological conservatism in adults, even between genera. However, this tribe of bees also presents a unique opportunity to explore the evolution of social parasitism because of the comparatively large number of origins of socially parasitic species. Morphological differences presented here, along with DNA sequence data and molecular phylogenetic analyses, indicate a much larger number of Australian social parasite species in the genus Inquilina than previously anticipated, and suggest that the final number of socially parasitic species may be considerable. We describe five new species and present sequence data that will help elucidate the delineation of further new species. Inquilina provides a unique opportunity to study the evolution of social parasitism in social insects, but further studies will need to encompass both population genetic and phylogenetic approaches.     

Polymorphic microsatellite loci in Allodapine bees for investigating the evolution of social behaviour

Allodapine bees provide extraordinary systems for investigating the evolution of cooperation and particularly the division of reproduction in animal societies. We present the first microsatellite primers for two native Australian species (Exoneura nigrescens and E. robusta; Hymenoptera: Apidae: Xylocopinae) which allow the accurate determination of pedigrees, reproductive skew and relatedness in colonies. Up to 55 different alleles were observed per locus.     

Honey bee colony collapse disorder is possibly caused by a dietary pyrethrum deficiency

Industrialized farming relies on bee keepers transporting hives to the vicinity of large areas of mono-crops for crop pollination. Hives are typically moved multiple times per growing season to satisfy the pollination need. A phenomenon wherein colonies of honey bees collapse in large numbers has been threatening crops in North America. Honey bees are hosts to at least two pathogenic mites; Varroa destructor and Acarapis woodi (a tracheal mite). Pyrethrums are a group of flowering plants which include Chrysanthemum coccineum, Chrysanthemum cinerariifolium, Chrysanthemum marschallii, and related species. These plants produce potent insecticides, also named pyrethrums, which are powerful mite toxins. We believe that a honey bee dietary deficiency of pyrethrums and other micro-nutrients from pyrethrum producing plants allows parasitic mites to either kill the honey bees directly or reduce honey bee resistance to other pathogens. Intermittent feeding of honey bees on pyrethrum producing plants might reverse or prevent colony collapse disorder.     

Decisions,decisions, decisions: choosing a biological science of choice

Behavioral ecologists argue that evolution drives animal behavior to efficiently solve the problems animals face in their environmental niches. The ultimate evolutionary causes of decision making, they contend, can be found in economic analyses of organisms and their environments. Neurobiologists interested in how animals make decisions have, in contrast, focused their efforts on understanding the neurobiological hardware that serves as a more proximal cause of that same behavior. Describing the flow of information within the nervous system without regard to these larger goals has been their focus. Recent work in a number of laboratories has begun to suggest that these two approaches are beginning to fuse. It may soon be possible to view the nervous system as a representational process that solves the mathematically defined economic problems animals face by making efficient decisions. These developments in the neurobiological theory of choice, and the new schema they imply, form the subject of this article.     

Habitat-related microgeographic variation of worker size and colony size in the ant Cataglyphis cursor

In social insects, colony size is a crucial life-history trait thought to have major implications for the evolution of social complexity, especially in relation to worker size polymorphism. Yet, little is known about how ecological factors can affect and constrain colony. Here, we explored the pattern of colony-size and worker-size variation in the Mediterranean ant Cataglyphis cursor, in relation to the type of habitats colonized (seaside vs. vineyard). The high level of the water table in the seaside habitat could constrain the depth of C. cursor underground nests and directly constrain its colony size. If worker size increases with colony size, as observed in other ant species, larger colony size and larger workers should be found in the vineyard populations. By comparing worker size among 16 populations, we verified that workers were significantly larger in the vineyard populations. We further determined that the morphological similarities detected among populations from the same habitat type were not due to geographic or genetic proximity. In two populations from each habitat type, the depth of nests was positively correlated with colony size and colony size with worker size. Using a type II regression approach, we further showed that the difference between the two populations in the depth of nest was sufficient to explain the difference in colony size, and similarly, variation in colony size was sufficient to explain variation in worker size. Our results suggest that a single proximate ecological factor could lead to significant variation in major life-history parameters.     

Origins of social parasitism: the importance of divergence ages in phylogenetic studies

Phylogenetic studies on insect social parasites have found very close host-parasite relationships, and these have often been interpreted as providing evidence for sympatric speciation. However, such phylogenetic inferences are problematic because events occurring after the origin of parasitism, such as extinction, host switching and subsequent speciation, or an incomplete sampling of taxa, could all confound the interpretation of phylogenetic relationships. Using a tribe of bees where social parasitism has repeatedly evolved over a wide time-scale, we show the problems associated with phylogenetic inference of sympatric speciation. Host-parasite relationships of more ancient species appear to support sympatric speciation, whereas in a case where parasitism has evolved very recently, sympatric speciation can be ruled out. However, in this latter case, a single extinction event would have lead to relationships that support sympatric speciation, indicating the importance of considering divergence ages when analysing the modes of social parasite evolution.     

Climate,host phylogeny and the connectivity of host communities govern regional parasite assembly

Aim

Identifying barriers that govern parasite community assembly and parasite invasion risk is critical to understand how shifting host ranges impact disease emergence. We studied regional variation in the phylogenetic compositions of bird species and their blood parasites (Plasmodium and Haemoproteus spp.) to identify barriers that shape parasite community assembly.

Location

Australasia and Oceania.

Methods

We used a data set of parasite infections from >10,000 host individuals sampled across 29 bioregions. Hierarchical models and matrix regressions were used to assess the relative influences of interspecies (host community connectivity and local phylogenetic distinctiveness), climate and geographic barriers on parasite local distinctiveness and composition.

Results

Parasites were more locally distinct (co‐occurred with distantly related parasites) when infecting locally distinct hosts, but less distinct (co‐occurred with closely related parasites) in areas with increased host diversity and community connectivity (a proxy for parasite dispersal potential). Turnover and the phylogenetic symmetry of parasite communities were jointly driven by host turnover, climate similarity and geographic distance.

Main conclusions

Interspecies barriers linked to host phylogeny and dispersal shape parasite assembly, perhaps by limiting parasite establishment or local diversification. Infecting hosts that co‐occur with few related species decreases a parasite's likelihood of encountering related competitors, perhaps increasing invasion potential but decreasing diversification opportunity. While climate partially constrains parasite distributions, future host range expansions that spread distinct parasites and diminish barriers to host shifting will likely be key drivers of parasite invasions.     

Impact of a social parasite on ant host populations depends on host species,habitat and year

Parasites often affect the abundance and life‐history traits of their hosts. We studied the impact of a social parasite – a slavemaking ant – on host ant communities using two complementary field manipulations. In the first experiment, we analysed the effect of social parasite presence on host populations in one habitat. In a second experiment, conducted in two habitats, we used a cross‐fostering design, analysing the effect of sympatric and allopatric social parasites. In the first experiment, host colonies benefited to some extent from residing in parasite‐free areas, showing increased total production. Yet, in the second experiment, host colonies in plots containing social parasites were more productive, and this effect was most evident in response to allopatric social parasites. We propose several explanations for these inconsistent results, which are related to environmental variability. The discrepancies between the two habitats can be explained well by ecological variation as a result of differences in altitudes and climate. For example, ant colonies in the colder habitat were larger and, for one host species, colonies were more often polygynous. In addition, our long‐term documentation – a total of four measurements of community structure in 6 years – showed temporal variation in abundance and life‐history traits of ant colonies, unrelated to the manipulations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 559–570.     

Changes in the patterning of a hydroid colony

It is a widely held view that colonial hydroids (Cnidaria, Hydroidomedusae) are formed on the basis of a repetition of uniform elements. The dominant opinion is that the equal spatial organisation of the colony exists during all stages of its development except the primary polyp, which develops from the settled larva. However, the complex structure and large dimensions of shoots in certain thecate species (subcl. Leptomedusae) suggest that the organisation of the primary shoot differs strongly from that of established colonies. The present study based on a thorough collection and examination of the collected material allowed to describe the entire sequence of the colony ontogeny in Hydrallmania falcata (Sertulariidae). The established shoots of this species are characterised by relatively large size, spiral arrangement of pinnate branches over the shoot stem, and hydranths arranged in one row along the upper side of branches. We showed that the primary shoot developing from the larva has much smaller dimensions and an alternate arrangement of hydranths. During further colony development the shoot organisation undergoes a gradual transformation ending with the emergence of large shoots with 'characteristic' species-specific features. The discovered sequence of changes in shoot patterning shows certain correlations with alterations of the growing tip dimensions. The dimensions of the growing tip seem to determine the patterning in accordance with the particular spatial location of the tip. This finding implies the necessity of a detailed reinvestigation of the entire colony development in thecate hydroids, which would make a significant contribution to the understanding of the morphogenetic evolution and patterning mechanisms within this group of colonial organisms.     

The relationship between population size,amount of brood,and individual foraging behaviour in the honey bee,Apis mellifera L.

This study experimentally examines the relationship between colony state and the behaviour of individual pollen and nectar foragers in the honey bee, Apis mellifera L. In the first experiment we test the prediction that individual pollen foragers from colonies with higher brood quantities should exhibit a greater work effort for pollen resources than individual pollen foragers from colonies with low brood quantities. Eight colonies were assigned into two treatment groups; HIGH brood colonies were manipulated to contain 9600±480 cm² brood area; LOW brood colonies were manipulated to contain 1600±80 cm² brood area. We measured colony brood levels over the course of the experiment and collected individual pollen loads from returning pollen foragers. We found that, while colonies remained significantly different in brood levels, individual pollen foragers from HIGH brood colonies collected larger loads than individuals from LOW brood colonies. In the second experiment we investigated the influence of colony size on the behaviour of individual nectar foragers. We assigned eight colonies to two treatment groups; LARGE colonies were manipulated to contain 35000±1700 adult workers with 3500±175 cm² brood area, and SMALL colonies were manipulated to contain 10000±500 adult workers with 1000±50 cm² brood area. We observed foraging trips of individually marked workers and found that individuals from LARGE colonies made longer foraging trips than those from SMALL colonies (LARGE: 1666.7±126.4 seconds, SMALL: 1210.8±157.6 seconds), and collected larter nectar loads (LARGE: 19.2±1.0 l, SMALL: 14.6±0.8 l). These results indicate that individual nectar foragers from LARGE colonies tend to work harder than individuals from SMALL colonies. Both experiments indicate that the values of nectar and pollen resources to a colony change depend on colony state, and that individual foragers modify their behaviour accordingly.     

The social biology of domiciliary cockroaches: colony structure, kin recognition and collective decisions

A substantial body of research on eusocial insects seen in the last decades has gone hand-in-hand with the development of social evolution theory. In contrast, little attention has been given to the non-eusocial insect species that nevertheless exhibit a rich spectrum of social behaviours, thus effectively skewing our vision of insect sociality. Recent studies on the behaviour, ecology and genetic of “gregarious” cockroaches (Blattodea) have revealed a diversity of social structures and group dynamics unique among insects, providing an important comparative model for the broader understanding of insect social evolution. Here, we present an overview of the social biology of the domiciliary cockroaches (ca. 25 species adapted to human habitats) based on research on two model species, Blattella germanica and Periplaneta americana. We discuss the evolution of these domiciliary cockroaches, considering them in the context of “social herds” within the insect sociality framework.     

Avoid mistakes when choosing a new home: Nest choice and adoption of Leptothorax ant queens

In ants, mating and colony founding are critical steps in the life of ant queens. Outside of their nests, young queens are exposed to intense predation. Therefore, they are expected to have evolved behavior to accurately and quickly locate a nesting place. However, data on the early life history of female reproductives are still lacking. Leptothorax gredleri is a suitable model organism to study the behavior of young queens. Reproductives can be reared under artificial conditions and readily mate in the laboratory. After mating, L. gredleri queens have the options to found solitarily, seek adoption into another colony, or return into their natal nest. In this study, we investigated the decision-making processes of female sexuals before and after mating. In particular, we tested whether female sexuals use chemical cues to find their way back to the nest, studied if they prefer their own nest over other nesting sites and followed the adoption dynamics of mated queens over 8 weeks (plus hibernation and spring). We showed that female sexuals and freshly mated queens spent more time on substrate previously used by workers from their own colony and from another colony than on a blank substrate. This discriminatory capability of queens appears to be lost in old, reproductive queens. Nest choice experiments showed that female sexuals and freshly mated queens can distinguish their own nest while old mated queens’ do not. When reintroduced in their maternal colony, young queens were readily adopted, but a few weeks later aggression against young queens led to their emigration from the maternal nest and eventually also death.     

Rates of brood development in a social wasp: effects of colony size and parasite infection

Summary Colonies of eusocial insect species are most vulnerable during the founding stage. Many species have evolved means to minimize the length of the founding, or pre-emergence, stage by accelerating the rate of development of the first worker offspring. Other things being equal, the sooner a colony can begin producing workers, the less the risk of colony failure, the steeper the growth curve of the colony during the ergonomic stage, and the larger the colony will be at reproductive maturity. Swarm-founding species, whose founding units consist of hundreds or thousands of workers, may face less selection pressure to minimize the duration of the founding stage than independent-founding species. However, swarm size varies within species, and small swarms face greater risk of extinction during the founding stage than large swarms. This consideration predicts that within a species, small swarms should have shorter founding stages than large swarms, likely by rearing a small group of precocious brood. On the other hand, evidence that large social groups organize colony labor more efficiently, gather resources more predictably, and homeostatically maintain physical conditions inside the nest within narrower ranges, predicts that larger groups should rear all brood more rapidly and therefore have shorter founding stages. To test whether small or large swarms have shorter founding stages in colonies of Polybia occidentalis, a Neotropical swarm-founding wasp, we measured brood development rates in colonies collected after 28 days of development, just short of the minimum egg-to-adult development time. We found that as size increased across colonies, pre-emergence times decreased, mean age of pupae in the nest increased, and median age of the brood (larvae + pupae) increased. That is, brood developed significantly faster in large colonies than in small ones. Using these same measures, we also found that infection by a gregarine parasite increased brood development time, independently of colony size.Received 10 April 2003; revised 29 October 2003; accepted 21 November 2003.     

Serial passage of the parasite Crithidia bombi within a colony of its host, Bombus terrestris, reduces success in unrelated hosts

In the wild, Bombus spp. bees may contract infections of the trypanosome parasite Crithidia bombi from their nestmates or from others while foraging on contaminated flowers. We expected that as C. bombi is transmitted repeatedly among related workers within a colony, the parasite population would become more successful in this relatively homogeneous host population and less successful in individuals from unrelated colonies of the same or different species. To test our prediction, we serially passaged cocktails of C. bombi strains through workers from the same colony, taking the intensity of infection in related versus unrelated workers as a measure of parasite success at each step in the serial transfer. Using a repeated measures ANOVA, we found the ability of C. bombi to exploit Bombus spp. hosts did not increase within a colony, but did decrease for infections in workers from unrelated colonies. This reduction in success is most likely due to a gradual loss of appropriate C. bombi strains from the infecting the population as the cocktail is 'filtered' during the serial passage within a given colony, without a corresponding increase in overall intensity of the surviving strains.     

Colony development and social structure in a subtropical paper wasp,Ropalidia fasciata (F.) (Hymenoptera: Vespidae)

More than 50% of nests of Ropalidia fasciata were founded by association of foundresses (multifemale nests). The multifemale nests were generally initiated earlier and grew faster than the single-female nests. The survival rate of the multifemale nests was significantly higher than that of single-female nests, and the productivity as measured by the number of cells produced per foundress had a peak at a foundress-group size from 6 to 10. The number of marked foundresses which were seen on their original nest decreased as the colony cycle proceeded, but some of them continued to coexist on the original nests after emergency of many female progeny. Except in the case where a large number of foundresses attended a young nest so that some foundresses could not sit on the nest, the dominance interactions among cofoundresses were mild. More than twothirds (71.4%) of nests (including those at the post-emergence stage) had multiple egg-layers. The foundress association in this species is considered to be beneficial for every foundress because it raises ability to avoid predation or to reconstruct their nests when the nests are destroyed by typhoons.     

Mimetic host shifts in an endangered social parasite of ants

An emerging problem in conservation is whether listed morpho-species with broad distributions, yet specialized lifestyles, consist of more than one cryptic species or functionally distinct forms that have different ecological requirements. We describe extreme regional divergence within an iconic endangered butterfly, whose socially parasitic young stages use non-visual, non-tactile cues to infiltrate and supplant the brood in ant societies. Although indistinguishable morphologically or when using current mitochondrial and nuclear sequence-, or microsatellite data, Maculinea rebeli from Spain and southeast Poland exploit different Myrmica ant species and experience 100 per cent mortality with each other''s hosts. This reflects major differences in the hydrocarbons synthesized from each region by the larvae, which so closely mimic the recognition profiles of their respective hosts that nurse ants afford each parasite a social status above that of their own kin larvae. The two host ants occupy separate niches within grassland; thus, conservation management must differ in each region. Similar cryptic differentiation may be common, yet equally hard to detect, among the approximately 10 000 unstudied morpho-species of social parasite that are estimated to exist, many of which are Red Data Book listed.