Crematogaster Lund, 1831

Hosoishi, Shingo & Ogata, Kazuo, 2017, Phylogenetic analysis and systematic position of two new species of the ant genus Crematogaster (Hymenoptera, Formicidae) from Southeast Asia, European Journal of Taxonomy 370, pp. 1-17 : 5-6

Genus Crematogaster Lund, 1831

Phylogenetic position and divergence time estimation

The five nuclear gene sequences consisted of 2301 bp and contained 652 variable characters (VC) and 420 parsimony informative characters (PIC) ( Table 2 ). The MP and ML analyses resulted in similar topologies for the position of C. khmerensis sp. nov., but the BI analysis differed in topology from the MP and ML analyses. As our results from the BI analysis had similar results to the tree inferred by Blaimer (2012c), we use the BI tree to illustrate all our results ( Fig. 1 ).

In MP analysis, the concatenated five-gene dataset yielded 1800 equally parsimonious trees (length = 1407, consistency index = 0.48, retention index = 0.77), of which the strict consensus tree is well resolved. The MP analysis recovered that C. khmerensis sp. nov. was nested within node A with high bootstrap support (100%) ( Fig. 2 ). Further splitting of the node resulted in a trichotomy having branches with C. khmerensis sp. nov., C. borneensis -group and node C.

The ML analysis recovered that C. khmerensis sp. nov. was nested within node A with high bootstrap support (100%) ( Fig. 2 ). Similarly the node displayed a trichotomy among C. khmerensis sp. nov., C. borneensis -group and node C.

The BI recovered that C. khmerensis sp. nov. was nested within node A ( Fig. 2 ). Despite the relatively low level of support (0.88 posterior probability), C. khmerensis sp. nov. at node B was a sister to node C ( Fig. 2 ).

Estimations of divergence time showed that the common ancestor of C. khmerensis sp. nov. and clade C began to diverge approximately 15 million years ago ( Fig. 3 ).

Diagnosis of the Crematogaster khmerensis -group

the Crematogaster khmerensis -group is easily distinguished from other Asian species of Crematogaster by the vertically directed propodeal spines and large propodeal spiracles.

Species included in the Crematogaster khmerensis -group:

C. khmerensis Hosoishi & Ogata sp. nov.

C. pfeifferi Hosoishi & Ogata sp. nov.

Key to species based on the worker caste

1. Propodeal spiracles large and touching metapleural gland bulla. Petiole scoop shaped, broader anteriorly. Subpetiolar process undeveloped ( Cambodia) ..…………………. C. khmerensis sp. nov.

– Propodeal spiracles large and apart from metapleural gland bulla. Petiole elliptical with convex sides. Subpetiolar process developed acutely (Borneo) ..………………………. C. pfeifferi sp. nov.

Figures

Fig. 1. Bayesian majority rule consensus tree reconstructed for 90 taxa using five genes (ArgK, CAD, LWRh, Top1, Wg) in a MrBayes analysis. Above node numbers indicate posterior probability. Data were partitioned by PartitionFinder v.1.1.1 and analyzed using a best fit model for each gene and codon position, with 10 million generations and a burn-in of 25 %. Area enclosed by dashed lines is enlarged on Fig. 2.

Fig. 2. Bayesian majority rule consensus tree reconstructed for 90 taxa using five genes (ArgK, CAD, LWRh, Top1, Wg) in a MrBayes analysis. Most of the outgroups are not shown. Above node numbers indicate posterior probability, bootstrap value for MP, and bootstrap value for ML. Data were partitioned by PartitionFinder v.1.1.1 and analyzed using a best fit model for each gene and codon position, with 10 million generations and a burn-in of 25 %.

Fig. 3. Posterior estimates of divergence time of 24 taxa on the phylogenetic tree. Blue bars depict the 95% highest posterior density (HPD). Estimations were performed with MCMCTree using the independent rate model.