The parasite's long arm: a tapeworm parasite induces behavioural changes in uninfected group members of its social host

Parasites can induce alterations in host phenotypes in order to enhance their own survival and transmission. Parasites of social insects might not only benefit from altering their individual hosts, but also from inducing changes in uninfected group members. Temnothorax nylanderi ant workers infected with the tapeworm Anomotaenia brevis are known to be chemically distinct from nest-mates and do not contribute to colony fitness, but are tolerated in their colonies and well cared for. Here, we investigated how tapeworm- infected workers affect colony aggression by manipulating their presence in ant colonies and analysing whether their absence or presence resulted in behavioural alterations in their nest-mates. We report a parasite-induced shift in colony aggression, shown by lower aggression of uninfected nest-mates from parasitized colonies towards conspecifics, potentially explaining the tolerance towards infected ants. We also demonstrate that tapeworm-infected workers showed a reduced flight response and higher survival, while their presence caused a decrease in survival of uninfected nest-mates. This anomalous behaviour of infected ants, coupled with their increased survival, could facilitate the parasites'' transmission to its definitive hosts, woodpeckers. We conclude that parasites exploiting individuals that are part of a society not only induce phenotypic changes within their individual hosts, but in uninfected group members as well.     

A social insect fertility signal is dependent on chemical context

Identifying group members and individuals'' status within a group are fundamental tasks in animal societies. For ants, this information is coded in the cuticular hydrocarbon profile. We manipulated profiles of the ant Odontomachus brunneus to examine whether the releaser and primer effects of fertility signals are dependent on chemical context. Fertility status is signalled through increased abundance of (Z)-9-nonacosene (Z9 : C₂₉). Across the ant''s distribution, populations have distinct hydrocarbon profiles but the fertility signal is conserved. Foreign queens and fertility-signal-treated workers from the same population, sharing a similar chemical background, elicited releaser effects from workers, whereas queens and fertility-signal-treated workers from different populations did not. Z9 : C₂₉ presented without chemical background did not elicit releaser effects. A primer-effect experiment found that Z9 : C₂₉, presented without a chemical background, did not inhibit worker reproduction. Our results demonstrate that a familiar chemical background is necessary for appropriate responses to fertility signals.     

Trophallaxis and prophylaxis: social immunity in the carpenter ant Camponotus pennsylvanicus

In social insects, group behaviour can increase disease resistance among nest-mates and generate social prophylaxis. Stomodeal trophallaxis, or mutual feeding through regurgitation, may boost colony-level immunocompetence. We provide evidence for increased trophallactic behaviour among immunized workers of the carpenter ant Camponotus pennsylvanicus, which, together with increased antimicrobial activity of the regurgitate droplet, help explain the improved survival of droplet recipient ants relative to controls following an immune challenge. We have identified a protein related to cathepsin D, a lysosomal protease, as a potential contributor to the antimicrobial activity. The combined behavioural and immunological responses to infection in these ants probably represent an effective mechanism underlying the social facilitation of disease resistance, which could potentially produce socially mediated colony-wide prophylaxis. The externalization and sharing of an individual''s immune responses via trophallaxis could be an important component of social immunity, allowing insect colonies to thrive under high pathogenic pressures.     

Ants recognize foes and not friends

Discriminating among individuals and rejecting non-group members is essential for the evolution and stability of animal societies. Ants are good models for studying recognition mechanisms, because they are typically very efficient in discriminating ‘friends’ (nest-mates) from ‘foes’ (non-nest-mates). Recognition in ants involves multicomponent cues encoded in cuticular hydrocarbon profiles. Here, we tested whether workers of the carpenter ant Camponotus herculeanus use the presence and/or absence of cuticular hydrocarbons to discriminate between nest-mates and non-nest-mates. We supplemented the cuticular profile with synthetic hydrocarbons mixed to liquid food and then assessed behavioural responses using two different bioassays. Our results show that (i) the presence, but not the absence, of an additional hydrocarbon elicited aggression and that (ii) among the three classes of hydrocarbons tested (unbranched, mono-methylated and dimethylated alkanes; for mono-methylated alkanes, we present a new synthetic pathway), only the dimethylated alkane was effective in eliciting aggression. Our results suggest that carpenter ants use a fundamentally different mechanism for nest-mate recognition than previously thought. They do not specifically recognize nest-mates, but rather recognize and reject non-nest-mates bearing odour cues that are novel to their own colony cuticular hydrocarbon profile. This begs for a reappraisal of the mechanisms underlying recognition systems in social insects.     

A Gaussian-3 theoretical study of the alkylthio radicals and their anions: structures, thermochemistry, and electron affinities

The optimized geometries, electron affinities, and dissociation energies of the alkylthio radicals have been determined with the higher level of the Gaussian-3(G3) theory. The geometries are fully optimized and discussed. The reliable adiabatic electron affinities with ZPVE correction have been predicted to be 1.860 eV for the methylthio radical, 1.960 eV for the ethylthio radical, 1.980 and 2.074 eV for the two isomers (n-C₃H₇S and i-C₃H₇S) of the propylthio radical, 1.991, 2.133 and 2.013 eV for the three isomers (n-C₄H₉S, t-C₄H₉S, and i-C₄H₉S) of the butylthio radical, and 1.999, 2.147, 2.164, and 2.059 eV for the four isomers (n-C₅H₁₁S, b-C₅H₁₁S, c-C₅H₁₁S, and d-C₅H₁₁S) of the pentylthio radical, respectively. These corrected EA_ad values for the alkylthio radicals are in good agreement with available experiments, and the average absolute error of the G3 method is 0.041 eV. The dissociation energies of S atom from neutral C_nH_2n+1S (n?=?1–5) and S^- from corresponding anions C_nH_2n+1S^- species have also been estimated respectively to examine their relative stabilities.     

Worker policing limits the number of reproductives in a ponerine ant

Reproductive division of labour is an essential feature of insect sociality, but the regulation of sterility among colony members remains incompletely understood. Ant workers and queens are morphologically divergent and workers are only capable of producing males in a colony, although they usually do not do so. Worker policing is one mechanism proposed for their infertility and it can be expressed as either aggressive inhibition of ovarian activity among workers or destruction of worker-laid eggs. A few studies have shown that workers with developed ovaries are preferentially attacked by nest-mates, but adequate demonstration of worker policing also requires evidence that these attacks result in the suppression of ovarian activity or death. We investigated worker policing in the ponerine ant Harpegnathos saltator in which workers are able to mate and replace the founding queen. Five colonies were each divided into two groups, one of which consisted exclusively of infertile workers. Some individuals in the orphaned groups began laying eggs during the three-week separation and upon reunification these were vigorously attacked by infertile workers of the other groups. The ovarian activity of these new egg layers became inhibited, as revealed by subsequent dissection of marked individuals. Worker policing in H. saltator appears to function primarily in preventing an excess of reproductive workers.     

Interaction between Workers during a Short Time Window Is Required for Bacterial Symbiont Transmission in Acromyrmex Leaf-Cutting Ants

Stable associations between partners over time are critical for the evolution of mutualism. Hosts employ a variety of mechanisms to maintain specificity with bacterial associates. Acromyrmex leaf-cutting ants farm a fungal cultivar as their primary nutrient source. These ants also carry a Pseudonocardia Actinobacteria exosymbiont on their bodies that produces antifungal compounds that help inhibit specialized parasites of the ants'' fungal garden. Major workers emerge from their pupal cases (eclose) symbiont-free, but exhibit visible Actinobacterial coverage within 14 days post-eclosion. Using subcolony experiments, we investigate exosymbiont transmission within Acromyrmex colonies. We found successful transmission to newly eclosed major workers fostered by major workers with visible Actinobacteria in all cases (100% acquiring, n = 19). In contrast, newly eclosed major workers reared without exosymbiont-carrying major workers did not acquire visible Actinobacteria (0% acquiring, n = 73). We further show that the majority of ants exposed to major workers with exosymbionts within 2 hours of eclosion acquired bacteria (60.7% acquiring, n = 28), while normal acquisition did not occur when exposure occurred later than 2 hours post-eclosion (0% acquiring, n = 18). Our findings show that transmission of exosymbionts to newly eclosed major workers occurs through interactions with exosymbiont-covered workers within a narrow time window after eclosion. This mode of transmission likely helps ensure the defensive function within colonies, as well as specificity and partner fidelity in the ant-bacterium association.     

Symbiont Interactions in a Tripartite Mutualism: Exploring the Presence and Impact of Antagonism between Two Fungus-Growing Ant Mutualists

Mutualistic associations are shaped by the interplay of cooperation and conflict among the partners involved, and it is becoming increasingly clear that within many mutualisms multiple partners simultaneously engage in beneficial interactions. Consequently, a more complete understanding of the dynamics within multipartite mutualism communities is essential for understanding the origin, specificity, and stability of mutualisms. Fungus-growing ants cultivate fungi for food and maintain antibiotic-producing Pseudonocardia actinobacteria on their cuticle that help defend the cultivar fungus from specialized parasites. Within both ant-fungus and ant-bacterium mutualisms, mixing of genetically distinct strains can lead to antagonistic interactions (i.e., competitive conflict), which may prevent the ants from rearing multiple strains of either of the mutualistic symbionts within individual colonies. The success of different ant-cultivar-bacterium combinations could ultimately be governed by antagonistic interactions between the two mutualists, either as inhibition of the cultivar by Pseudonocardia or vice versa. Here we explore cultivar-Pseudonocardia antagonism by evaluating in vitro interactions between strains of the two mutualists, and find frequent antagonistic interactions both from cultivars towards Pseudonocardia and vice versa. To test whether such in vitro antagonistic interactions affect ant colonies in vivo, we performed sub-colony experiments using species of Acromyrmex leaf-cutting ants. We created novel ant-fungus-bacterium pairings in which there was antagonism from one, both, or neither of the ants'' microbial mutualists, and evaluated the effect of directional antagonism on cultivar biomass and Pseudonocardia abundance on the cuticle of workers within sub-colonies. Despite the presence of frequent in vitro growth suppression between cultivars and Pseudonocardia, antagonism from Pseudonocardia towards the cultivar did not reduce sub-colony fungus garden biomass, nor did cultivar antagonism towards Pseudonocardia reduce bacteria abundance on the cuticle of sub-colony workers. Our findings suggest that inter-mutualist antagonism does not limit what combinations of cultivar and Pseudonocardia strains Acromyrmex fungus-growing ants can maintain within nests.     

Natronosporangium hydrolyticum gen. nov., sp. nov., a haloalkaliphilic polyhydrolytic actinobacterium from a soda solonchak soil in Central Asia

During a cultural diversity survey on hydrolytic bacteria in saline alkaline soils, a hydrolytic actinobacterium strain ACPA39^T was enriched and isolated in pure culture from a soda solonchak soil in southwestern Siberia. It forms a substrate mycelium with rod-shaped sporangia containing 1–3 exospores. The isolate is obligately alkaliphilic, growing at pH 7.5–10.3 (optimum at 8.5–9.0) and moderately halophilic, tolerating up to 3 M total Na⁺ in the form of sodium carbonates. It is an obligately aerobic, organoheteroterophic, saccharolytic bacterium, utilizing various sugars and alpha/beta-glucans as growth substrates. According to the 16S rRNA gene-based phylogenetic analysis, strain ACPA39^T forms a distinct branch within the family Micromonosporaceae, with the sequence identities below 94.5% with type strains of other genera. This is confirmed by phylogenomic analysis based on the 120 conserved single copy protein-based markers and genomic indexes (ANI, AAI). The cell-wall of ACPA39^T contained meso-DAP, glycine, glutamic acid and alanine in a equimolar ratio, characteristic of the peptidoglycan type A1γ'. The whole-cell sugars include galactose and xylose. The major menaquinone is MK-10(H₄). The identified polar lipids consist of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The polar lipid fatty acids were dominated by anteiso-C_17:0, iso-C_16:0, iso-C_17:0, 10 Me-C_18:0 and C_18:1ω9. Based on the distinct phylogeny, the chemotaxonomy features and unique phenotypic properties, strain ACPA39^T (DSM 106523^T = VKM 2772^T) is classified into a new genus and species in the family Micromonosporaceae for which the name Natronosporangium hydrolitycum gen. nov., sp. nov. is proposed.     

Pavement Ant Workers (<Emphasis Type="Italic">Tetramorium caespitum</Emphasis>) Assess Cues Coded in Cuticular Hydrocarbons to Recognize Conspecific and Heterospecific Non-Nestmate Ants

Most ants live in closed societies from which non-members are excluded through fighting or ritualized displays to protect colony resources. Nestmate recognition is the process by which ants discriminate nestmate from non-nestmate ants. Ants use cues coded in mixtures of long-chain hydrocarbon compounds on the cuticle as nestmate recognition cues. Pavement ants (Tetramorium caespitum) form conspicuous wars between neighboring colonies that are organized after workers meet and make the decision to fight after assessing nestmate recognition cues. These wars involve thousands of individuals. Fighting is ritualized and few ants die in the process. We identified 24 cuticular hydrocarbon compounds, above 1% in relative abundance, in the profile of pavement ants with chain lengths ranging from 15 to 31 carbon atoms. Cuticular lipids contained, in order of abundance: mono-methyl alkanes (45–56%), n-alkanes (range: 16–40% relative abundance), and alkenes (10–20%), with small or trace amounts of di-methyl, tri-methyl alkanes and fatty acids. Results from behavioral tests show that pavement ants assess information in cuticular hydrocarbon profiles to recognize both conspecific and heterospecfic (Pogonomyrmex occidentalis and Camponotus modoc) non-nestmate ants and that the relative abundance of methyl-branched alkanes and alkenes codes for nestmate status, at least for conspecific interactions. Our data add to a growing body of knowledge about how ants use cuticular hydrocarbon based nestmate recognition cues to prevent the intrusion of non-nestmates in to colony space.     

Ant defence system: A mechanism organizing individual responses into efficient collective behavior

A colony of social insects is an excellent model for investigating the organization of responses of subunits (i.e. colony members) with limited skills into sophisticated collective behavior. The defence system of Lasius niger ant colonies is well organized in a context-dependent way. The proportion of fighting ants to fleeing ants changes gradually according to the importance of the area being defended, and was higher where ants tended honeydew-rich aphids and on trails for foraging with heavy traffic, than where ants were walking alone or on trails with light traffic. Although there were intrinsic differences in aggressiveness between individual ants, the differences in aggressive responses between defended areas was not due to the presence of highly aggressive or timid individuals in each area. Instead, it was due to a change in aggressiveness of individuals in response to external conditions. The cue that altered individual aggressiveness was the presence of surrounding nest-mates, rather than the presence of aphids. We concluded that the defence system of this ant species consists of three processes: (i) a recruiting system that allocates more workers to more valuable resources; (ii) individual ants following a simple decision rule to become more aggressive in response to increased numbers of nest-mates nearby (hence aggressive behavior reflecting the importance of each area to the colony); and (iii) variability in individual responses causing a gradual change in the proportion of fighting ants responding to a threat.     

The Effect of Diet and Opponent Size on Aggressive Interactions Involving Caribbean Crazy Ants (Nylanderia fulva)

Biotic interactions are often important in the establishment and spread of invasive species. In particular, competition between introduced and native species can strongly influence the distribution and spread of exotic species and in some cases competition among introduced species can be important. The Caribbean crazy ant, Nylanderia fulva, was recently introduced to the Gulf Coast of Texas, and appears to be spreading inland. It has been hypothesized that competition with the red imported fire ant, Solenopsis invicta, may be an important factor in the spread of crazy ants. We investigated the potential of interspecific competition among these two introduced ants by measuring interspecific aggression between Caribbean crazy ant workers and workers of Solenopsis invicta. Specifically, we examined the effect of body size and diet on individual-level aggressive interactions among crazy ant workers and fire ants. We found that differences in diet did not alter interactions between crazy ant workers from different nests, but carbohydrate level did play an important role in antagonistic interactions with fire ants: crazy ants on low sugar diets were more aggressive and less likely to be killed in aggressive encounters with fire ants. We found that large fire ants engaged in fewer fights with crazy ants than small fire ants, but fire ant size affected neither fire ant nor crazy ant mortality. Overall, crazy ants experienced higher mortality than fire ants after aggressive encounters. Our findings suggest that fire ant workers might outcompete crazy ant workers on an individual level, providing some biotic resistance to crazy ant range expansion. However, this resistance may be overcome by crazy ants that have a restricted sugar intake, which may occur when crazy ants are excluded from resources by fire ants.     

Monogyny and regulation of worker mating in the queenless antDinoponera quadriceps

The morphologically specialized queen caste has been lost in various ponerine ants, and mated workers (‘gamergates’) reproduce instead of queens. Unlike previous reports in the literature, we found only one gamergate in each colony ofDinoponera quadriceps. We documented monogyny by dissecting ovaries and spermathecae in 914 workers from 15 colonies, and by observing mating in the laboratory. In colonies without a gamergate, aggressive interactions among some of the unmated nestmates led to the behavioural differentiation of a top-ranking worker (‘alpha’), which laid almost all the eggs. Only the alpha went outside the nest at night, and mated if foreign males were present (N=11 tests), thus becoming a gamergate. The alpha was sexually attractive even when her ovaries were not yet active. After intromission, the male remained linked to the alpha while she severed the end of his abdomen. Pieces of the male genitalia remained attached to her genital tract, and she removed them after 30±18 min (X±sdN=9). We interpret this to be a mating plug, preventing other males from fathering her offspring. None of these newly inseminated gamergates continued to go outside the nest, and, when tested, they never re-mated (N=4). Thus, gamergates ofD. quadricepsprobably mate only once. In queenless ant species, comparative evidence indicates that worker mating is often regulated in monogynous species, while unrestricted mating of young individuals is typical of polygynous species (oviposition is regulated subsequently). Furthermore, the occurrence of either monogyny or polygyny influences the mating strategies of males, and mating plugs have been reported only in some monogynous species.     

Two fungal symbioses collide: endophytic fungi are not welcome in leaf-cutting ant gardens

Interactions among the component members of different symbioses are not well studied. For example, leaf-cutting ants maintain an obligate symbiosis with their fungal garden, while the leaf material they provide to their garden is usually filled with endophytic fungi. The ants and their cultivar may interact with hundreds of endophytic fungal species, yet little is known about these interactions. Experimental manipulations showed that (i) ants spend more time cutting leaves from a tropical vine, Merremia umbellata, with high versus low endophyte densities, (ii) ants reduce the amount of endophytic fungi in leaves before planting them in their gardens, (iii) the ants'' fungal cultivar inhibits the growth of most endophytes tested. Moreover, the inhibition by the ants'' cultivar was relatively greater for more rapidly growing endophyte strains that could potentially out-compete or overtake the garden. Our results suggest that endophytes are not welcome in the garden, and that the ants and their cultivar combine ant hygiene behaviour with fungal inhibition to reduce endophyte activity in the nest.     

Social Context and Reproductive Potential Affect Worker Reproductive Decisions in a Eusocial Insect

Context-dependent decision-making conditions individual plasticity and is an integrant part of alternative reproductive strategies. In eusocial Hymenoptera (ants, bees and wasps), the discovery of worker reproductive parasitism recently challenged the view of workers as a homogeneous collective entity and stressed the need to consider them as autonomous units capable of elaborate choices which influence their fitness returns. The reproductive decisions of individual workers thus need to be investigated and taken into account to understand the regulation of reproduction in insect societies. However, we know virtually nothing about the proximate mechanisms at the basis of worker reproductive decisions. Here, we test the hypothesis that the capacity of workers to reproduce in foreign colonies lies in their ability to react differently according to the colonial context and whether this reaction is influenced by a particular internal state. Using the bumble bee Bombus terrestris, we show that workers exhibit an extremely high reproductive plasticity which is conditioned by the social context they experience. Fertile workers reintroduced into their mother colony reverted to sterility, as expected. On the contrary, a high level of ovary activity persisted in fertile workers introduced into a foreign nest, and this despite more frequent direct contacts with the queen and the brood than control workers. Foreign workers'' reproductive decisions were not affected by the resident queen, their level of fertility being similar whether or not the queen was removed from the host colony. Workers'' physiological state at the time of introduction is also of crucial importance, since infertile workers failed to develop a reproductive phenotype in a foreign nest. Therefore, both internal and environmental factors appear to condition individual reproductive strategies in this species, suggesting that more complex decision-making mechanisms are involved in the regulation of worker reproduction than previously thought.     

Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants

Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens.     

Surface wax of Andreaea and Pogonatum species

The mosses Andreaea rupestris, Pogonatum aloides and P. urnigerum contain surface waxes in amounts of 0.05–0.12% dry wt. The waxes consisted of esters (C₃₈-C₅₄), primary alcohols (C₂₀-C₃₂), free fatty acids (C₁₆-C₃₀), and alkanes (C₂₁-C₃₁). Additionally, aldehydes (C₂₂-C₃₀) were major constituents in the wax of P. urnigerum. The classes and their chain length distributions in the surface waxes of these mosses are comparable to those of epicuticular waxes of higher plants.     

The Caucaso-Anatolian slave-making ant Myrmoxenus tamarae (Arnoldi, 1968) and its more widely distributed congener Myrmoxenus ravouxi (André, 1896): a multidisciplinary comparison (Hymenoptera: Formicidae)

A small minority of the presently recognized ～12,500 species of ants are slave-makers, which permanently depend on the help of “slave workers,” that is workers of other ant species, which they pillage as brood from their nests in well-organized slave raids. The genus Myrmoxenus is one of the most species-rich taxa of slave-making ants, but individual species are often not well-delimited. Here, we compare behavior, morphometry, and nuclear and mtDNA sequences between two taxa of Myrmoxenus: Myrmoxenus tamarae (Arnoldi, 1968), known only from its type locality in Georgia, and the wide-spread M. ravouxi (André, 1896) to determine if the former might simply represent a Caucasian variant of the latter. Workers of the two taxa differed clearly in locomotor activity and slightly also in morphometry, while genetic investigations with nuclear and mitochondrial genes revealed only a weak differentiation. Given that Myrmoxenus appears to be a genus with a relatively recent radiation, we suggest to conservatively keep the present taxonomic situation with M. ravouxi and M. tamarae as separate species. The latter would then include specimens from Eastern Turkey and probably also Ukraine. Further studies, in particular in Greece and Turkey, might help to clarify the status of these endangered ants.     

Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant

In insect societies lacking morphologically specialized breedersand helpers, reproduction is often restricted to behaviorallydominant individuals. Such societies occur in about 100 speciesof ants that have secondarily lost the queen caste. All females,who are morphologically workers, can potentially mate and layeggs but only a few do so, and we demonstrate in Dinoponeraquadriceps that this is regulated by a dominance hierarchy.Six types of agonistic interactions allowed the ranking of 5-10workers in the hierarchy (n = 15 colonies). In particular, alphaand beta had characteristic behavioral profiles and were easily recognized.Only alpha mated, and workers ranking beta to delta sometimes producedunfertilized, male-destined eggs. Natural replacements (n = 19)and experimental removals (n = 15) of alpha demonstrated that betawas the individual most likely to replace alpha, although gammaand more rarely delta sometimes did, and we discuss the conflictthat occurs among high-ranking individuals over who should replacealpha. After such replacements, the new alpha behaved more aggressivelythan the overthrown alpha. Newly emerged workers tended to reachhigh ranks and displaced older high-ranking individuals downthe hierarchy. Low-ranking subordinates often prevented high-rankingindividuals from replacing alpha by biting and holding theirappendages (worker policing), which is consistent with the patternof relatedness associated with monogyny and monandry in D. quadriceps. Weinvestigated the relative importance of chemical communicationand dominance interactions to regulate reproduction. Alpha,beta, and sterile workers have different signatures of cuticularhydrocarbons, and these may provide honest information whichunderpins worker policing by low-ranking individuals.     

Theoretical investigation on the mechanism and kinetics of the ring-opening polymerization of ε-caprolactone initiated by tin(II) alkoxides

A theoretical investigation of the ring-opening polymerization (ROP) mechanism of ε-caprolactone (CL) with tin(II) alkoxide, Sn(OR)₂ initiators (R?=?n-C₄H₉, i-C₄H₉, t-C₄H₉, n-C₆H₁₃, n-C₈H₁₇) was studied. The density functional theory at B3LYP level was used to perform the modeled reactions. A coordination-insertion mechanism was found to occur via two transition states. Starting with a coordination of CL onto tin center led to a nucleophilic addition of the carbonyl group of CL, followed by the exchange of alkoxide ligand. The CL ring opening was completed through classical acyl-oxygen bond cleavage. The reaction barrier heights of ε-caprolactone with different initiators were calculated using potential energy profiles. The reaction of ε-caprolactone with Sn(OR)₂ having R?=?n-C₄H₉ has the least value of barrier height compared to other reactions. The rate constants for each reaction were calculated using the transition state theory with TheRATE program. The rate constants are in good agreement with available experimental data.