A DNA and morphology based phylogenetic framework of the ant genus Lasius with hypotheses for the evolution of social parasitism and fungiculture

Thoracic crop formation is spatiotemporally coordinated with flight muscle histolysis during claustral colony foundation in Lasius japonicus queens

In a majority of ants, a newly mated queen independently founds a colony and claustrally raises her first brood without foraging outside the nest. During claustral independent colony foundation (ICF) in several ants, the esophagus of the founding queen expands and develops into a "thoracic crop," which is then filled with a liquid substrate for larval feeding. It has been suggested that these substrates are converted from the founding queen's body reserves (e.g., histolyzed flight muscles) or redistributed from a gastral crop. Here, we describe thoracic crop development in Lasius japonicus queens during claustral ICF. The foundresses claustrally feed their larvae from weeks 2-5 after ICF onset, and the first worker emerges at week 6. The development proceeds as follows: in week 0, the foundress' dorsal esophageal wall is pleated and thickened. Then, from weeks 2-5, the esophagus expands toward a dorsal space previously occupied by flight muscles, following flight muscle histolysis. Gastral crop expansion follows esophageal expansion. Thus, thoracic crop formation may be spatiotemporally coordinated with flight muscle histolysis in Lasius japonicus queens, and similar developmental regulations might be common in other claustral ICF ants.

Integrative taxonomy reveals cryptic diversity in North American Lasius ants, and an overlooked introduced species

Biological invasions are a grave threat to ecosystems. The black garden ant (Lasius niger) is a pest species in Europe. Current literature states that L. niger occupies a disjunct native distribution in the Holarctic, however, based on recent work, we re-evaluate this distribution. The native range of L. niger is reconsidered based on phylogenetic relationships (nine mitochondrial and nuclear markers, 5670 bp), DNA-barcoding (98 Holarctic specimens), morphometry (88 Holarctic specimens, 19 different measurements) and subjective assessment of phenotype. The potential spread of this species is estimated using ecological niche modeling. Lasius niger is more closely related to other Palearctic species than to the Nearctic ants known under this name. The latter are described as a distinct species, L. ponderosae sp. nov. However, DNA-barcoding discovered established populations of L. niger in metropolitan areas in Canada (Vancouver and Halifax). We describe a morphometrical method to delineate L. ponderosae sp. nov. and L. niger. MtDNA diversity and divergence is high within L. ponderosae sp. nov., but low within L. niger. More than 1,000,000 km² are suitable as a habitat for L. niger in North America. This case emphasizes the critical role of integrative taxonomy to detect cryptic species and identify potential biological invasions in their nascent stages.

The evolution of social parasitism in Formica ants revealed by a global phylogeny

Studying the behavioral and life history transitions from a cooperative, eusocial life history to exploitative social parasitism allows for deciphering the conditions under which changes in behavior and social organization lead to diversification. The Holarctic ant genus Formica is ideally suited for studying the evolution of social parasitism because half of its 172 species are confirmed or suspected social parasites, which includes all three major classes of social parasitism known in ants. However, the life history transitions associated with the evolution of social parasitism in this genus are largely unexplored. To test competing hypotheses regarding the origins and evolution of social parasitism, we reconstructed a global phylogeny of Formica ants. The genus originated in the Old World ∼30 Ma ago and dispersed multiple times to the New World and back. Within Formica, obligate dependent colony-founding behavior arose once from a facultatively polygynous common ancestor practicing independent and facultative dependent colony foundation. Temporary social parasitism likely preceded or arose concurrently with obligate dependent colony founding, and dulotic social parasitism evolved once within the obligate dependent colony-founding clade. Permanent social parasitism evolved twice from temporary social parasitic ancestors that rarely practiced colony budding, demonstrating that obligate social parasitism can originate from a facultative parasitic background in socially polymorphic organisms. In contrast to permanently socially parasitic ants in other genera, the high parasite diversity in Formica likely originated via allopatric speciation, highlighting the diversity of convergent evolutionary trajectories resulting in nearly identical parasitic life history syndromes.

Complete mitochondrial genome of the jet ant Lasius spathepus Wheeler, W.M., 1910 (Formicidae; Hymenoptera)

The genus Lasius is a conspicuous and popular genus of ants found in the Holarctic regions. We have completed the mitochondrial genome of Lasius spathepus as the first mitochondrial genome of Lasius. The mitochondrial genome is 18,951 bp long, which is the sixth longest ant mitochondrial genome known to science. It contains 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a control region in a gene order shared with other species of subfamily Formicinae. The control region is 2,147 bp long, longest of all ants. Phylogenetic analysis shows L. spathepus groups with Nylanderia flavipes of the same tribe Lasiini.

Cryptic Diversity in the Aphid-Parasitizing Wasp Protaphidius nawaii (Hymenoptera: Braconidae): Discovery of Two Attendant-Ant-Specific mtDNA Lineages

The parasitoid wasp Protaphidius nawaii parasitizes the aphid Stomaphis japonica, which is obligatorily attended by several species of ants of genus Lasius. Subgenus Lasius or Dendrolasius ants use different defense strategies to protect the aphids that they attend (Lasius, shelter building; Dendrolasius, aggressive attack). We performed molecular phylogenetic analysis based on partial mitochondrial DNA sequences of P. nawaii and found that the parasitoid wasp consists of two highly differentiated genetic lineages. Although these two lineages distributed sympatrically, one tends to parasitize aphids attended by ants of subgenus Lasius, and the other parasitizes aphids attended by ants of subgenus Dendrolasius. The two lineages of P. nawaii appear to exhibit different oviposition behaviors adapted to the different aphid-protection strategies of the two ant subgenera.

Evolutionary diversification of Japanese Stomaphis aphids (Aphididae, Lachninae) in relation to their host plant use and ant association

Phytophagous insects are among the most diverse of the earth's organisms, and their diversification patterns and the driving forces behind these have attracted considerable research interest. Host shifting to closely related plant species is thought to play an important role in phytophagous insect diversification, but the extent to which other interactions such as mutualistic associations affect diversification is not yet known. In this study, we reconstructed the molecular phylogeny of Japanese Stomaphis aphids and determined whether host shifting or mutualistic association with different ant species could explain diversification in this aphid genus. We analyzed 12 species of Stomaphis and grouped them into ten well-supported DNA lineages. Species in each lineage used a single or a few host plant species, but were mutualistically associated with many ant species of the genus Lasius. This result suggests that Stomaphis evolutionarily diversified primarily through host plant shifts. Interestingly, the reconstructed phylogeny suggests that Stomaphis host shifts occasionally occurred between very distantly related host plant taxa (spanning up to five plant orders). The dependence of Stomaphis on long-lasting Lasius ant colonies situated in temperate deciduous forests where Lasius is the dominant ant genus may have led the aphids to shift to distantly related but spatially adjacent host tree species.

A new species of the ant genus Lasius Fabricius, 1804 from Crete (Hymenoptera, Formicidae)

Lasiustapinomoidessp. n. from Crete, Greece, is described and illustrated. It belongs to L.turcicus complex and is well characterized by very small body, extremely shallow metanotal groove and presence of suberect to erect setae on the apical part of scape. New records of Cretan members of the genus Lasius Fabricius, 1804 are provided, their checklist is updated, and the key to their determination is presented.

The evolution of queen pheromones in the ant genus Lasius

Queen pheromones are among the most important chemical messages regulating insect societies yet they remain largely undiscovered, hindering research into interesting proximate and ultimate questions. Identifying queen pheromones in multiple species would give new insight into the selective pressures and evolutionary constraints acting on these ubiquitous signals. Here, we present experimental and comparative evidence that 3-methylalkanes, hydrocarbons present on the queen's cuticle, are a queen pheromone throughout the ant genus Lasius. Interspecific variation in the chemical profile is consistent with 3-methylalkanes evolving more slowly than other types of hydrocarbons, perhaps due to differential selection or evolutionary constraints. We argue that the sensory ecology of the worker response imposes strong stabilizing selection on queen pheromones relative to other hydrocarbons. 3-Methylalkanes are also strongly physiologically and genetically coupled with fecundity in at least one Lasius species, which may translate into evolutionary constraints. Our results highlight how honest signalling could minimize evolutionary conflict over reproduction, promoting the evolution and maintenance of eusociality.

Low genetic diversity in Polish populations of sibling ant species: Lasius niger (L.) and Lasius platythorax Seifert (Hymenoptera, Formicidae)

We present preliminary data on mitochondrial DNA diversity within and among populations of the ants Lasius niger and Lasius platythorax in Poland. Phylogenetic analysis based on the mitochondrial DNA markers: cytochrome c oxidase subunit I (cox1) and 16S ribosomal RNA (16S rRNA) confirms the species status of L. niger and L. platythorax. Intraspecific variability is low in both species, which might be a result of severe bottlenecks and rapid postglacial expansion into Central Europe.

Evolution of cuticular hydrocarbon diversity in ants

The cuticular hydrocarbons (CHCs) of ants provide important cues for nest-mate and caste recognition. There is enormous diversity in the composition of these CHCs, but the manner in which this diversity has evolved is poorly understood. We gathered data on CHC profiles for 56 ant species, relating this information to their phylogeny. We deduced the mode of evolution of CHC profiles by reconstructing character evolution and then relating the number of changes in CHC components along each branch of the phylogeny to the length of the branch. There was a strong correlation between branch length and number of component changes, with fewer changes occurring on short branches. Our analysis thereby indicated a gradual mode of evolution. Different ant species tend to use specific CHC structural types that are exclusive of other structural types, indicating that species differences may be generated in part by switching particular biosynthetic pathways on or off in different lineages. We found limited, and contradictory, evidence for abiotic factors (temperature and rainfall) driving change in CHC profiles.

Phylogeny, divergence-time estimation, biogeography and social parasite-host relationships of the Holarctic ant genus Myrmica (Hymenoptera: Formicidae)

We reconstructed a molecular phylogeny of the ant genus Myrmica, tested reciprocal monophyly of the Nearctic and Palearctic representatives, and inferred social parasite-host relationships for five workerless inquilines and four temporary parasites. We sequenced six gene fragments of 106 specimens (17 not identified to species), analysed the data with Bayesian phylogenetic inference and maximum likelihood, and estimated divergence times using penalized likelihood. Our well resolved phylogeny supported most morphologically defined species groups. The Nearctic and Palearctic species were not reciprocally monophyletic, which suggested repeated species interchange across the Beringian land bridge. Parasitism evolved several times in Myrmica. Three inquilines and one temporary parasite were closest relatives of their host, two inquiline species and one temporary parasite clustered basally to their host(s), and two temporary parasites more distantly. Myrmica probably diversified following drastic climatic cooling at the Eocene-Oligocene boundary ca. 34 Ma, the oldest species groups being rugosa and ritae in central and southeastern Asia. The oldest inquiline, Myrmica karavajevi, was estimated at 17 Ma, the youngest species M. hirsuta at 0.8 Ma, whereas the microgyne of M.rubra is an intraspecific inquiline.