Oriental and Australian Leptogenys species groups

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Leptogenys crassicornis group

Xu, 2000

Squared head; smooth, mandibles with dentate masticatory margin, antennae short.

Leptogenys chalybaea group

Arimoto and Yamane, 2018

Key to Leptogenys chalybaea species group workers

Diagnosis The Leptogenys chalybaea species group is defined by the following character states: eyes situated in posterior half of head in full-face view, apex of median lobe of clypeus truncate, and a subrectangular petiolar node higher than long in profile.

Distribution Laos, Vietnam, Myanmar, Thailand, Cambodia, Malaysia (Borneo).

Description

Worker Head in full-face view longer than wide (CI: 75–87). Mandible without distinct teeth; masticatory margin three-fifths as long as basal margin. Eye in full-face view situated posterior to mid-length of head; outer margin protruding above or close to lateral outline of head. Anterior edge of torulus in full-face view posterior to transverse line extending across mandible bases. Lateral margin of clypeus with a shallow notch on each side; median lobe of clypeus abruptly extends anterad, one-fifth to one-fourth of head length; apex of median lobe truncate with weak concavity, with two or three peg-like setae. Hypostomal tooth absent. Metanotal groove distinctly impressed. Metapleuro-propodeal suture present. Petiolar node high and subrectangular (LPI: 121–151) and highest dorsoposteriorly in profile; anterior margin inclined anterad, basally straight and parallel to posterior margin, but then forms a convexity with anterodorsal margin. Subpetiolar process consisting of wide rectangular anterior lobe and thick posterior extension.

Queen General morphology similar to worker; without ocelli; differs from worker by smaller body size except for voluminous gaster, petiolar node in profile shorter and higher, simpler-shaped subpetiolar process, and shorter gastral segment I.

Male Known for Leptogenys atra and Leptogenys cyanicatena . See description of each species.

Discussion The Leptogenys chalybaea group is most similar to the Leptogenys diminuta group, which Xu (2000) defined for Chinese species, having a worker caste with a wide mandibular masticatory margin, high and subrectangular petiolar node, and anterior margin of the node anteriorly inclined. The Leptogenys chalybaea and Leptogenys diminuta groups are restricted to the Oriental and Australian regions. The Leptogenys chalybaea group is sympatric with the Leptogenys diminuta group in Southeast Asia, but differs from the Leptogenys diminuta group in terms of the following characters (the Leptogenys diminuta group is in parentheses): median lobe of clypeus extends abruptly anterad (extends gradually); apex of clypeal median lobe truncate, (apex broadly rounded); lateral margin of clypeus medially with shallow notch (smoothly curved); eyes in full-face view situated posterior to mid-length of head (situated near mid-length of head); and subpetiolar process consisting of well-developed rectangular anterior lobe and thick posterior extension (consisting of a small narrow anterior lobe). We believe that the difference in eye position is an important diagnostic character distinguishing the species groups. The Leptogenys chalybaea species group is distinguished from the Leptogenys diminuta group and from other Oriental congeners in that its eyes are situated in the posterior half of the head in full-face view.

Biology Our observations indicate that colonies of this species group contain many ergatoid queens. Because the gaster of one queen is expanded more than those of other queens in the colony, it is thought that only one queen reproduces, whereas the other queens do not reproduce but remain in the colon. We believe the virgin queens can either reproduce or function as helpers, making them a multi-purpose caste like that observed within Leptogenys diminuta or the subfamily Amblyoponinae (Molet et al., 2009). We could not observe their function as helpers directly in this study. Leptogenys diminuta has a similar colony composition in terms of ergatogynes (Itô and Ohkawara, 2000). There is probably an evolutionary relationship between the presence of many virgin ergatoid queens and multi-purpose queens. Further studies of the development of ovaries and spermatheca in each caste are needed to obtain a complete picture of the evolution of multi-purpose queens in Leptogenys. Chain-making behavior for the collective transport of food was confirmed in Leptogenys atra and Leptogenys cyanicatena (Peeters and De Greef, 2015). Among congeners, this behavior occurs only in this species group.

Leptogenys chinensis group

Xu, 2000

Elongate head smooth, mandibles with edentate masticatory margin, antennae elongate.

Leptogenys diminuta group

Xu, 2000

defined for Chinese species, having a worker caste with a wide mandibular masticatory margin, high and subrectangular petiolar node, and anterior margin of the node anteriorly inclined.

Elongate head longitudinally striate, mandibles with edentate masticatory margin, antennae evenly elongate.

Leptogenys modiglianii group

Arimoto, 2017

Leptogenys modiglianii species group

Key to Leptogenys modiglianii species group workers

Leptogenys zhuangzii group

Xu, 2000

Elongate head densely punctate, mandibles usually with edentate masticatory margin, antennae elongate.

Additional Resources

References