Social organization in a flatworm: trematode parasites form soldier and reproductive castes

In some of the most complex animal societies, individuals exhibit a cooperative division of labour to form castes. The most pronounced types of caste formation involve reproductive and non-reproductive forms that are morphologically distinct. In colonies comprising separate or mobile individuals, this type of caste formation has been recognized only among the arthropods, sea anemones and mole-rats. Here, we document physical and behavioural caste formation in a flatworm. Trematode flatworm parasites undergo repeated clonal reproduction of ‘parthenitae’ within their molluscan hosts forming colonies. We present experimental and observational data demonstrating specialization among trematode parthenitae to form distinct soldier and reproductive castes. Soldiers do not reproduce, have relatively large mouthparts, and are much smaller and thinner than reproductives. Soldiers are also more active, and are disproportionally common in areas of the host where invasions occur. Further, only soldiers readily and consistently attack heterospecifics and conspecifics from other colonies. The division of labour described here for trematodes is strongly analogous to that characterizing other social systems with a soldier caste. The parallel caste formation in these systems, despite varying reproductive mode and taxonomic affiliation, indicates the general importance of ecological factors in influencing the evolution of social behaviour. Further, the ‘recognition of self’ and the defence of the infected host body from invading parasites are comparable to aspects of immune defence. A division of labour is probably widespread among trematodes and trematode species encompass considerable taxonomic, life history and environmental diversity. Trematodes should therefore provide new, fruitful systems to investigate the ecology and evolution of sociality.     

Improvements on colony morphology identification towards bacterial profiling

Colony morphology may be an indicator of phenotypic variation, this being an important adaptive process adopted by bacteria to overcome environmental stressors. Furthermore, alterations in colony traits may reflect increased virulence and antimicrobial resistance. Despite the potential relevance of using colony morphological traits, the influence of experimental conditions on colony morphogenesis has been scarcely studied in detail. This study aims to clearly and systematically demonstrate the impact of some variables, such as colony growth time, plate colony density, culture medium, planktonic or biofilm mode of growth and strain genetic background, on bacterial colony morphology features using two Pseudomonas aeruginosa strains. Results, based on 5-replicate experiments, demonstrated that all variables influenced colony morphogenesis and 18 different morphotypes were identified, showing different sizes, forms, colours, textures and margins. Colony growth time and composition of the medium were the variables that caused the highest impact on colony differentiation both derived from planktonic and biofilm cultures. Colony morphology characterization before 45 h of incubation was considered inadequate and TSA, a non-selective medium, provided more colony diversity in contrast to P. aeruginosa selective media. In conclusion, data obtained emphasized the need to perform comparisons between colony morphologies in equivalent experimental conditions to avoid misinterpretation of microbial diagnostics and biomedical studies. Since colony morphotyping showed to be a reliable method to evaluate phenotypic switching and also to infer about bacterial diversity in biofilms, these unambiguous comparisons between morphotypes may offer a quite valuable input to clinical diagnosis, aiding the decision-making towards the selection of the most suitable antibiotic and supportive treatments.     

The police are not the army: context-dependent aggressiveness in a clonal ant

Animals often exhibit particular ‘personalities’, i.e. their behaviour is correlated across different situations. Recent studies suggest that this limitation of behavioural plasticity may be adaptive, since continuous adjustment of one''s behaviour may be time-consuming and costly. In social insects, particularly aggressive workers might efficiently take over fighting in the contexts of both nest defence and ‘policing’, i.e. the regulation of kin conflict in the society. Here, we examine whether workers who engage in aggressive policing in the ant Platythyrea punctata play a prominent role also in nest defence against intruders. The participation of individuals in policing and nest defence was highly skewed and a minority of workers exhibited most of the aggression. Workers who attacked reproductives after experimental colony fusion were less active during nest defence and vice versa. This suggests that workers show situation-dependent behavioural plasticity rather than consistently aggressive personalities.     

Fractal bird nest distribution produces scale-free colony sizes

The spatial distribution of organisms often differs across scales. For instance, colonial bird populations could be described, from large to small scale, as scattered clumps of otherwise regularly distributed breeding pairs. We analysed the distribution of nests of a large colonial population of white storks (Ciconia ciconia) and found a fractal pattern in each of the 4 study years. Moreover, we found that the often-observed, long-tailed frequency distribution of colony sizes was well described by a power law, regardless of the cut-off used to define colonies (from 16 to 1024 m). Thus, although storks were locally highly clumped even with tens of nests in a single tree, the population was not structured in colonies (a simple clustered distribution) as previously thought. Rather, they were distributed in a continuous hierarchical set of clusters within clusters across scales, clusters lacking the commonly assumed characteristic mean size. These quantitative solutions to previously perceived scaling problems will potentially improve our understanding of the ecology and evolution of bird coloniality and animal spacing patterns and group living in general.     

Growth dynamics of Bacillus circulans colony

We have investigated the growth dynamics of Bacillus circulans colony exhibiting the knotted-branching pattern by swarming on a hard agar medium. The knotted-branching pattern consists of many circular clusters, so-called subcolonies, and their trajectories. We analysed the processes of a subcolony because they are presumably the key elements for the formation of knotted-branching pattern. It was found that a subcolony has three processes, i.e. "generation", "growth", and "migration" by microscopic and time-resolved observations. An embryonic small subcolony (child subcolony) formed around an existing subcolony (parent subcolony) grows larger and migrates away from the parent subcolony. We proposed a simple model to explain the migration and the growth processes. It is assumed that the internal part of the subcolony is unfavorable for the bacteria and that the motion of the child subcolony on the agar medium can be modeled using a frictional force. The experimental data were quantitatively analysed in order to compare with models. Our models are consistent with the experimental results on following three points: (1) the radius of a subcolony increases linearly with the incubation time, (2) a subcolony stops just after formation and then starts to migrate suddenly, and (3) the trajectory of a subcolony predicted by the model agrees with the experimental one.     

Polymorphic social organization in an ant

Identifying species exhibiting variation in social organization is an important step towards explaining the genetic and environmental factors underlying social evolution. In most studied populations of the ant Leptothorax acervorum, reproduction is shared among queens in multiple queen colonies (polygyny). By contrast, reports from other populations, but based on weaker evidence, suggest a single queen may monopolize all reproduction in multiple queen colonies (functional monogyny). Here we identify a marked polymorphism in social organization in this species, by conclusively showing that functional monogyny is exhibited in a Spanish population, showing that the social organization is stable and not purely a consequence of daughter queens overwintering, that daughter queen re-adoption is frequent and queen turnover is low. Importantly, we show that polygynous and functionally monogynous populations are not genetically distinct from one another based on mtDNA and nDNA. This suggests a recent evolutionary divergence between social phenotypes. Finally, when functionally monogynous and polygynous colonies were kept under identical laboratory conditions, social organization did not change, suggesting a genetic basis for the polymorphism. We discuss the implications of these findings to the study of reproductive skew.     

Regulation of cuticular and postpharyngeal hydrocarbons in the slave-making ant Polyergus rufescens: effect of Formica rufibarbis slaves

The purpose of this study was to compare cuticular hydrocarbon profiles of slave-making Polyergus rufescens ants reared alone or with their Formica rufibarbis slaves. Chemical analyses showed that due to the close contacts occurring when the Formica were tending the Polyergus, the synthesis of the cuticular hydrocarbons carried by the slaves was enhanced in the slave-makers. The postpharyngeal hydrocarbon levels increased during the first 15 days of life, whether or not the Polyergus were exposed to Formica. Our findings suggest that Polyergus is able to secrete all components of their cuticular hydrocarbon blend and that none are acquired through contact with Formica. In addition to presenting our experimental evidence, several hypotheses are proposed to explain the synthesis and regulation of hydrocarbon blends borne when these two species cohabitate within a single colony.     

A new platform for ultra-high density Staphylococcus aureus transposon libraries

Background

Staphylococcus aureus readily develops resistance to antibiotics and achieving effective therapies to overcome resistance requires in-depth understanding of S. aureus biology. High throughput, parallel-sequencing methods for analyzing transposon mutant libraries have the potential to revolutionize studies of S. aureus, but the genetic tools to take advantage of the power of next generation sequencing have not been fully developed.

Results

Here we report a phage-based transposition system to make ultra-high density transposon libraries for genome-wide analysis of mutant fitness in any Φ11-transducible S. aureus strain. The high efficiency of the delivery system has made it possible to multiplex transposon cassettes containing different regulatory elements in order to make libraries in which genes are over- or under-expressed as well as deleted. By incorporating transposon-specific barcodes into the cassettes, we can evaluate how null mutations and changes in gene expression levels affect fitness in a single sequencing data set. Demonstrating the power of the system, we have prepared a library containing more than 690,000 unique insertions. Because one unique feature of the phage-based approach is that temperature-sensitive mutants are retained, we have carried out a genome-wide study of S. aureus genes involved in withstanding temperature stress. We find that many genes previously identified as essential are temperature sensitive and also identify a number of genes that, when disrupted, confer a growth advantage at elevated temperatures.

Conclusions

The platform described here reliably provides mutant collections of unparalleled genotypic diversity and will enable a wide range of functional genomic studies in S. aureus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1361-3) contains supplementary material, which is available to authorized users.     

Morphogenetic evolution of hydroid colony pattern

A scheme of evolution of hydrozoan colony pattern is proposed based upon the consideration of macro-morphogenesis. Four main processes play decisive roles(1) hard skeleton formation by soft tissues, (2) changes in duration of the growth phase relative to the transition to differentiation in interdependent zones of growth, (3) ratio in growth rates between adjacent zones of growth within the rudiment, the shoot, or the whole colony, and (4) spatial relationships among growth zones. The main tendency in morphological evolution of the hydroids is an increasing integration of the colony as revealed by increasing complexity of its structure. That is from a temporary colony towards the permanent one with highly organised shoots, as hydranths and branches are localised in a strictly arranged manner. An analysis of diverse data allows one to state that the main morphogenetic mechanism of increasing complexity in the hydroid colony is convergence, then fusion, of adjacent growth zones, a variant of heterochrony.     

Colony pattering ofAspergillus oryzae on agar media

To clarity the effects of nutrient concentration and diffusion on the pattern formation of fungal colonies, the colony patterning ofAspergillus oryzae at various nutrient and agar levels was studied experimentally and was summarized in a colony morphology diagram. Roles of the nutrient content and the relaxation of nutrient distribution on the colony patterning were discussed based on a computer model of the mycelial growth. The colony morphology changed from compact to ramified as the nutrient and agar levels were lowered. No clear boundary was found between these two morphologies. The deterioration of substrate around the growing colony was detected when the morphic switching from homogeneous into splitting patterns emerged in the growth of ramified colonies. In the mycelial growth model, dense compact colonies developed at low growth rates and high nutrient influx into the colonized area. Under low nutrient levels, splitting colonies appeared at high growth rates as compared with the nutrient influx.