The effects of disturbance threat on leaf-cutting ant colonies: a laboratory study

The flexibility of organisms to respond plastically to their environment is fundamental to their fitness and evolutionary success. Social insects provide some of the most impressive examples of plasticity, with individuals exhibiting behavioural and sometimes morphological adaptations for their specific roles in the colony, such as large soldiers for nest defence. However, with the exception of the honey bee model organism, there has been little investigation of the nature and effects of environmental stimuli thought to instigate alternative phenotypes in social insects. Here we investigate the effect of repeated threat disturbance over a prolonged (17 month) period on both behavioural and morphological phenotypes, using phenotypically plastic leaf-cutting ants (Atta colombica) as a model system. We found a rapid impact of threat disturbance on the behavioural phenotype of individuals within threat-disturbed colonies becoming more aggressive, threat-responsive and phototactic within as little as two weeks. We found no effect of threat disturbance on morphological phenotypes, potentially because constraints such as resource limitation outweighed the benefit for colonies of producing larger individuals. The results suggest that plasticity in behavioural phenotypes can enable insect societies to respond to threats even when constraints prevent alteration of morphological phenotypes

The role of juvenile hormone in regulating reproductive physiology and dominance in Dinoponera quadriceps ants

Unequal reproductive output among members of the same sex (reproductive skew) is a common phenomenon in a wide range of communally breeding animals. In such species, reproductive dominance is often acquired during antagonistic interactions between group members that establish a reproductive hierarchy in which only a few individuals reproduce. Rank-specific syndromes of behavioural and physiological traits characterize such hierarchies, but how antagonistic behavioural interactions translate into stable rank-specific syndromes remains poorly understood. The pleiotropic nature of hormones makes them prime candidates for generating such syndromes as they physiologically integrate environmental (social) information, and often affect reproduction and behaviour simultaneously. Juvenile hormone (JH) is one of several hormones that occupy such a central regulatory role in insects and has been suggested to regulate reproductive hierarchies in a wide range of social insects including ants. Here we use experimental manipulation to investigate the effect of JH levels on reproductive physiology and social dominance in high-ranked workers of the eusocial ant Dinoponera quadriceps, a species that has secondarily reverted to queenless, simple societies. We show that JH regulated reproductive physiology, with ants in which JH levels were experimentally elevated having more regressed ovaries. In contrast, we found no evidence of JH levels affecting dominance in social interactions. This could indicate that JH and ovary development are decoupled from dominance in this species, however only high-ranked workers were investigated. The results therefore confirm that the regulatory role of JH in reproductive physiology in this ant species is in keeping with its highly eusocial ancestors rather than its secondary reversion to simple societies, but more investigation is needed to disentangle the relationships between hormones, behaviour and hierarchies

Problems of multi-species organisms: endosymbionts to holobionts

The organism is one of the fundamental concepts of biology and has been at the center of many discussions about biological individuality, yet what exactly it is can be confusing. The definition that we find generally useful is that an organism is a unit in which all the subunits have evolved to be highly cooperative, with very little conflict. We focus on how often organisms evolve from two or more formerly independent organisms. Two canonical transitions of this type—replicators clustered in cells and endosymbiotic organelles within host cells—demonstrate the reality of this kind of evolutionary transition and suggest conditions that can favor it. These conditions include co-transmission of the partners across generations and rules that strongly regulate and limit conflict, such as a fair meiosis. Recently, much attention has been given to associations of animals with microbes involved in their nutrition. These range from tight endosymbiotic associations like those between aphids and Buchnera bacteria, to the complex communities in animal intestines. Here, starting with a reflection about identity through time (which we call “Theseus’s fish”), we consider the distinctions between these kinds of animal–bacteria interactions and describe the criteria by which a few can be considered jointly organismal but most cannot

Sustainable sewerage servicing options for peri-urban areas with failing septic systems

The provision of water and wastewater services to peri-urban areas faces very different challenges to providing services to cities. Sustainable solutions for such areas are increasingly being sought, in order to solve the environmental and health risks posed by failing septic systems. These solutions should have the capability to reduce potable water demand, provide fit for purpose reuse options, and minimise impacts on the local and global environment. A methodology for the selection of sustainable sewerage servicing systems and technologies is presented in this paper. This paper describes the outcomes of applying this methodology to a case study in rural community near Melbourne, Australia, and describes the economic and environmental implications of various sewerage servicing options. Applying this methodology has found that it is possible to deliver environmental improvements at a lower community cost, by choosing servicing configurations not historically used by urban water utilities. The selected solution is currently being implemented, with the aim being to generate further transferable learnings for the water industry

Raiders from the sky: slavemaker founding queens select for aggressive host colonies

Reciprocal selection pressures in host-parasite systems drive coevolutionary arms races that lead to advanced adaptations in both opponents. In the interactions between social parasites and their hosts, aggression is one of the major behavioural traits under selection. In a field manipulation, we aimed to disentangle the impact of slavemaking ants and nest density on aggression of Temnothorax longispinosus ants. An early slavemaker mating flight provided us with the unique opportunity to study the influence of host aggression and demography on founding decisions and success. We discovered that parasite queens avoided colony foundation in parasitized areas and were able to capture more brood from less aggressive host colonies. Host colony aggression remained consistent over the two months experiment, but did not respond to our manipulation. However, as a fifth of all host colonies were successfully invaded by parasite queens, slavemaker nest foundation acts as a strong selection event selecting for high aggression in host colonies.Organismic and Evolutionary Biolog

Social environment affects the transcriptomic response to bacteria in ant queens

Abstract Social insects have evolved enormous capacities to collectively build nests and defend their colonies against both predators and pathogens. The latter is achieved by a combination of individual immune responses and sophisticated collective behavioral and organizational disease defenses, that is, social immunity. We investigated how the presence or absence of these social defense lines affects individual‐level immunity in ant queens after bacterial infection. To this end, we injected queens of the ant Linepithema humile with a mix of gram+ and gram− bacteria or a control solution, reared them either with workers or alone and analyzed their gene expression patterns at 2, 4, 8, and 12 hr post‐injection, using RNA‐seq. This allowed us to test for the effect of bacterial infection, social context, as well as the interaction between the two over the course of infection and raising of an immune response. We found that social isolation per se affected queen gene expression for metabolism genes, but not for immune genes. When infected, queens reared with and without workers up‐regulated similar numbers of innate immune genes revealing activation of Toll and Imd signaling pathways and melanization. Interestingly, however, they mostly regulated different genes along the pathways and showed a different pattern of overall gene up‐regulation or down‐regulation. Hence, we can conclude that the absence of workers does not compromise the onset of an individual immune response by the queens, but that the social environment impacts the route of the individual innate immune responses