Basic PackThis is the core game and is a playable version of the game, with a few slaves, assistants and minor slaves. It also contains all the standard events and all the game executables, including a Mac OSX version in this release.If you have not played the game before then download this version and try it out.
The transition to a parasitic lifestyle entails comprehensive changes to the selective regime. In parasites, genes encoding for traits that facilitate host detection, exploitation and transmission should be under selection. Slavemaking ants are social parasites that exploit the altruistic behaviour of their hosts by stealing heterospecific host brood during raids, which afterwards serve as slaves in slavemaker nests. Here we search for evidence of selection in the transcriptomes of three slavemaker species and three closely related hosts. We expected selection on genes underlying recognition and raiding or defense behaviour. Analyses of selective forces in species with a slavemaker or host lifestyle allowed investigation into whether or not repeated instances of slavemaker evolution share the same genetic basis.
To investigate the genetic basis of host-slavemaker co-evolution, we created orthologous clusters from transcriptome sequences of six Temnothorax ant species - three slavemakers and three hosts - to identify genes with signatures of selection. We further tested for functional enrichment in selected genes from slavemakers and hosts respectively and investigated which pathways the according genes belong to.
Our phylogenetic analysis, based on more than 5000 ortholog sequences, revealed sister species status for two slavemakers as well as two hosts, contradicting a previous phylogeny based on mtDNA. We identified 309 genes with signs of positive selection on branches leading to slavemakers and 161 leading to hosts. Among these were genes potentially involved in cuticular hydrocarbon synthesis, thus species recognition, and circadian clock functionality possibly explaining the different activity patterns of slavemakers and hosts. There was little overlap of genes with signatures of positive selection among species, which are involved in numerous different functions and different pathways.
We identified different genes, functions and pathways under positive selection in each species. These results point to species-specific adaptations rather than convergent trajectories during the evolution of the slavemaker and host lifestyles suggesting that the evolution of parasitism, even in closely related species, may be achieved in diverse ways.
Here we explore the evolution of the slavemaker lifestyle in North American Temnothorax ants, a taxon in which slavery evolved several times independently . We specifically focus on three slavemaker species T. americanus, T. duloticus and T. pilagens, and their three closely related host species, T. longispinosus, T. curvispinosus and T. ambiguus [39, 40]. The dulotic lifestyle of these three slavemakers is characterized by recurrent and destructive slave raids during summer . During these raids, slavemaker worker raiding parties search for and attack host colonies to steal worker brood. Upon their emergence as adult workers in slavemaker nests, the social behaviours of these enslaved host workers will be exploited by the slavemakers, whose workers lost the ability to care for themselves . While host nests on average contain around 50 workers , the number of workers in slavemaker nests is much lower with on average approximately five workers [39, 40, 43]. Moreover, slavemaker workers are only active during the raiding season and do not take over normal worker chores such as brood care and foraging [44, 45]. Each slavemaker species exhibits distinct morphological characteristics (e.g. size and colour), and raiding behaviours [41, 44]. T. americanus - the most derived parasite in the group in terms of morphology and behaviour - mainly uses a propaganda pheromone to induce panic among hosts, preventing organized evacuation or nest defence [41, 46, 47]. The strategy of T. pilagens is quite variable, and may also depend on the aggressiveness of the host colony [40, 48]. In some instances host workers are killed by stinging, while in other cases the raid is seemingly peaceful without any casualties, facilitating the incorporation of even adult host workers into the slavemaker colony . T. duloticus is a fierce slavemaker that mostly stings all opponents to death before taking the brood, resulting in the local eradication of host colonies [41, 43, 44, 49]. Each of the three slavemakers can exploit several host species, but has a clearly preferred host. The derived T. americanus uses all three Temnothorax species, but focusses when possible on T. longispinosus . T. duloticus occasionally attacks T. longispinosus but prefers T. curvispinosus  and T. pilagens prefers T. ambiguus over T. longispinosus [40, 48].
Co-evolution between the obligate social parasites and their hosts not only leads to adaptations in slavemakers, but also to counter-adaptations in behavioural, chemical and life history traits in host species and populations [11, 47, 51,52,53,54]. Host aggression , as well as host defence strategies  are linked to geographic variation in parasite pressure. It is known that adaptations to similar ecological conditions may lead to the evolution of similar (convergent) phenotypes in non-related species. The degree to which parallelism extents to the molecular level has recently experienced an upsurge of interest [56,57,58,59,60]. Evidence is ambiguous, with some studies pointing to parallelism, and others to species-specific trajectories [59, 61 and authors therein]. Moreover, it becomes clear that the level of organisation plays a major role in detecting convergent evolution, as the degree of parallelism is predicted to increase from the nucleotide level to features of whole organisms . The North American Temnothorax system, with six closely related slavemaker and host species is ideal to study the genetic basis of repeated evolution of phenotypic traits involved in host-parasite co-evolution.
The main objective of this study was to investigate the selective forces shaping the host and slavemaker lifestyles, and the organisational level of convergence. The main questions we tried to answer were: Which genes are under positive selection in slavemakers or hosts? Is molecular parallelism involved in the convergent evolution of slavemaker lifestyles? Do we find convergence on the gene, functional or pathway level?
RAxML obtained Maximum Likelihood phylogenetic relationship of the six slavemaker and host species with Acromyrmex echinatior as outgroup, and based on 5199 ortholog gene-clusters (ML bootstrap percentages depicted at nodes). Slavemaker species names are given in red, host species names in black. Arrows connect slavemaker-host species pairs
The slavemaker lifestyle evolved several times independently in ants, with a hotspot of slavery evolution in the genus Temnothorax . As slavemakers and their hosts are engaged in a constant co-evolutionary arms-race, the evolution of ant slavery is tightly linked to the evolution of behaviour, physiology and morphology in their hosts [78,79,80]. The focus of our study was the genomic basis of the (co-) evolution of the slavemaker and host lifestyle. We were thus interested in identifying genes with signatures of positive selection in slavemakers and hosts respectively. Furthermore, we asked whether or not, and at which organisational level, the three slavemaker/host species show signs of genetic convergence; or whether each species follows its own specific evolutionary trajectory.
We identified twice as many genes under positive selection on branches leading to slavemakers as compared to host branches. This finding is in line with our expectation that the derived slavemaker mode of life should have led to the selection of more genes in comparison to the ancestral host lifestyle. However, based on the number of species-specific selected genes it becomes evident that 70% of the positively selected genes in slavemakers can be assigned to T. americanus only. All other slavemaker and host species have comparable and lower numbers of positively selected genes. T. americanus is the most distantly related species in this taxon and its behaviour and morphology are most derived from the other species. T. americanus workers have large square heads, which make them easily distinguishable from their hosts. They do not engage in normal worker behaviour, such as brood care or foraging, and are so dependent upon enslaved hosts that T. americanus will starve to death if not fed. During raids, they manipulate host behaviour via the release of glandular secretions [11, 41, 46], but never use their stinger, which is a typical behaviour for other Temnothorax hosts during aggressive interactions [7, 41, 48]. Foraging and brood care are standard behavioural repertoires in the hosts, and in the lack of slaves, will still be performed by T. duloticus [41, 44] and T. pilagens (pers. observation) slavemakers to some extent. In addition to many lifestyle differences, the longer evolutionary history with the possibility for co- and counter adaptations to T. longispinosus and its host ancestor, might explain the large number of positively selected genes in T. americanus in contrast to the other species.
Within the 309 positively selected genes on the branches to slavemakers, we were able to identify several candidate genes with a possible link to their slavemaker lifestyle. Amongst these, three different DNAJ-like protein subfamily members, which are heat shock protein homologs, and function as co-chaperons. They are involved in stress response in humans , and could thus play a role during stressful slave raids into fiercely defending host colonies. 2b1af7f3a8