Queen pheromones in Temnothorax ants: control or honest signal?

Background The division of reproductive labor among group members in insect societies is regulated by "queen pheromones". However, it remains controversial whether these are manipulative, i.e., actively suppress worker reproduction, or honestly signal the fertility status of the queen to which workers react in their own interest by refraining from laying eggs. Manipulative queen control is thought to lead to an evolutionary arms race between queens and workers, resulting in complex queen bouquets that diverge strongly among different populations and species. In contrast, honest signals would evolve more slowly and might therefore differ less strongly within and among species. Results We aimed at determining the tempo of the evolution of queen signals in two ways. First, we investigated whether queens of Temnothorax ants are capable of controlling egg laying by workers of their own, closely, and distantly related species. Second, we compared the species- and caste-specific patterns of cuticular hydrocarbons, which are assumed to convey information on reproductive status. In mixed-species colonies, queens were not able to fully suppress egg-laying and male production by workers of unrelated species, while workers did not reproduce under the influence of a queen from their own species. Furthermore, the chemical profiles differed more strongly among queens of different species than among the respective workers. Conclusions Our results suggest that cuticular hydrocarbons associated with fecundity are not fully conserved in evolution and evolve slightly faster than worker-specific components in the blend of cuticular hydrocarbons. While this higher rate of evolution might reflect an arms race between queens and workers, the observation that workers still respond to the presence of a queen from another species support the honest signal hypothesis. Future studies need to examine alternative explanations for a higher rate of evolution of queen-specific substances, such as an involvement of such compounds in mating

Not dear neighbours: Antennation and jerking, but not aggression, correlate with genetic relatedness and spatial distance in the ant Lasius niger

1. Neighbour–stranger response differences (NSRDs) are when individuals are either more aggressive (“Nasty Neighbour”) or less aggressive (“Dear Enemy” or “Dear Neighbour”) to direct neighbours than to other competitors perceived as “strangers” by the residents. Such effects are often reported in ants which, being fixed-location central-place foragers, may compete directly with their neighbours for resources or raid each other for brood. Overlayed onto this are potential spatial distance and relatedness effects on aggression, which are often not differentiated from NSRDs. 2. The literature on NSRDs and distance effects in ants does not reveal a systematic pattern across all ants due to their diversity of life histories, requiring each species to be evaluated individually. Lasius niger is a common Eurasian ant species, which can form very dense populations of colonies and shows pronounced nestmate recognition, so may be expected to show NSRDs. 3. Here, we take advantage of a semi-regular colony array to examine the effect of spatial distance and relatedness on aggression and probe for NSRDs. 4. Overt aggression does not vary with relatedness or spatial distance, and there is no evidence that direct neighbours represent a special case in terms of aggression. However, antennation and jerking decrease between less related and more spatially distant pairs, but are almost completely absent from allospecific interactions. 5. We tentatively propose that antennation and jerking together represent a ‘negotiation’ phase, which may either precede or reduce the need for overt aggression. While a Nasty Neighbour effect might occur, a Dear Neighbour effect is unlikely in this species, and overall NSRDs do not play a large role in the ecology of this species. More broadly, this work highlights the importance of considering non-overtly aggressive responses when studying NSRDs

Absence of genetic isolation across highly fragmented landscape in the ant Temnothorax nigriceps

Background Human activities, including changes in agricultural landscapes, often impact biodiversity through habitat fragmentation. This potentially reduces genetic exchange between previously connected populations. Using a combination of nuclear and mitochondrial markers, we investigated (i) genetic diversity and population structure at multiple spatial scales and (ii) colony genetic structure and queen mating frequency in the ant species Temnothorax nigriceps in a highly anthropized environment. Results Although the results highlighted genetic structure on a European spatial scale, they did not reveal an impact of fragmentation on a regional scale, and we did not observe any genetic population structure on a regional scale. Across all populations, regardless of their geographical location, colony structure suggested monogyny (a single queen per colony) and monandry (single mating). However, nestmates were more related than expected, indicating that large-scale dispersal does not fully prevent genetic isolation. Conclusions Despite living in fragmented patches of habitat, populations of Temnothorax nigriceps are apparently genetically not isolated at a regional scale. However, large-scale dispersal alone does not prevent genetic isolation. The ecological requirements of T. nigriceps may explain their resilience to habitat fragmentation by allowing them to survive in very small patches of suitable habitat. The deeper investigation of the diversity of functional habitats for this species should allow to appreciate better the mechanisms permitting this species to overcome the negative impacts of fragmentation

Clonal reproduction and genetic caste differences in a queen-polymorphic ant, Vollenhovia emeryi

Most social Hymenoptera are characterized by simple haploid sex determination and environment-based caste differentiation. This appears to be strikingly different in the queen-polymorphic ant Vollenhovia emeryi. Almost all long- and short-winged queens from a population in Central Japan were homozygous at three microsatellite loci, whereas workers were mostly heterozygous, suggesting either a complex system of genetic caste determination or, more likely, the production of female sexuals from unfertilized eggs by thelytokous parthenogenesis and of workers from fertilized eggs. Furthermore, male genotypes were not compatible with those of the queens and had exclusively the paternal allele found in the sterile, heterozygous workers, probably because males are produced from fertilized eggs after the exclusion of maternal nuclear DNA as recently reported for Wasmannia auropunctata. The genus Vollenhovia might provide an interesting model system to trace the evolution of unusual caste and sex determination systems

Cryptic diversity in the Mediterranean Temnothorax lichtensteini species complex (Hymenoptera:Formicidae)

In this paper we provide insight into the cryptic diversity and biogeographic patterns of a widely distributed Mediterranean ant species, Temnothorax lichtensteini (Bondroit, 1918), based on evidences from multiple data sources. An exploratory analysis of morphometric data, combined with sequencing of a 658bp fragment of the mitochondrial gene for the cytochrome c oxidase subunit I (CO I), indicates the existence of three distinct lineages. Divergence of two recognized genetic lineages, Western and Easten Mediterranean clusters, is not reliably supported by confirmatory analysis of morphological data. We hypothesize that this reflects incomplete speciation in separate glacial refugia and therefore discuss only biogeographic aspects of these two parapatric populations. However, the third, Peloponnese lineage is divergent in both morphology and CO I sequences and its separation from the other two lineages is convincingly confirmed. For this lineage we assume a completed speciation and describe the taxon formally as Temnothorax laconicus sp.n., the sister species of T. lichtensteini