Cardiocondyla itsukii

A pan-Pacific species with a large distribution.

Identification
Seifert et al. (2017) - There is no doubt that species separation in the C. nuda group is difficult. It requires careful consideration of character definitions and the use high-resolution optical and measurement systems. The diagnose presented here uses numerous morphological characters to achieve an acceptable identification error rate.

Meeting the following definition:


 * Discriminant 176.328×PPH - 49.049×CW + 51.521×SP - 59.844×PPW + 6.61 < 0
 * Discriminant 214.193×PLG - 88.759×SP + 57.676×SL - 106.17×PEH - 10.465 > 0
 * Discriminant 319.279×PLG - 49.672×PPW + 133.938×FRS - 177.726×EYE + 91.370×CW - 63.848×SL - 12.955 > 0

where:


 * CW: Maximum cephalic width; the maximum is found usually across and including the eyes, exceptionally posterior of the eyes.


 * EYE: Eye-size - the arithmetic mean of the large (EL) and small diameter (EW).


 * FRS: Distance of the frontal carinae immediately caudal of the posterior intersection points between frontal carinae and the lamellae dorsal of the torulus. If these dorsal lamellae do not laterally surpass the frontal carinae, the deepest point of scape corner pits may be taken as reference line. These pits take up the inner corner of scape base when the scape is fully switched caudad and produce a dark triangular shadow in the lateral frontal lobes immediately posterior of the dorsal lamellae of scape joint capsule (Fig. 1).


 * PEH: Maximum petiole height. The straight section of ventral petiolar profile at node level is the reference line perpendicular to which the maximum height of petiole node is measured at node level.


 * PLG: Mean length of pubescence hairs on dorsum of first gaster tergite as arithmetic mean of at least 7 measurements measured at magnifications of 320x.


 * PPH: Maximum postpetiole height; the lateral suture of dorsal and ventral sclerites is the reference line perpendicular to which the maximum height of postpetiole is measured.


 * PPW: Maximum width of postpetiole.


 * SL: Maximum straight line length of scape excluding the articular condyle given as the arithmetic mean of both scapes.


 * SP: Maximum length of propodeal spines; measured in dorsofrontal view along the long axis of the spine, from spine tip to a line that orthogonal to the long axis and touches the bottom of the interspinal meniscus (Fig. 3). Left and right SP are averaged. This mode of measuring is less ambiguous than other methods but yields higher spine length values in species with reduced spines. This is the case in the dentiform spines found in the C. nuda group where it is difficult to correctly define the long axis. In such cases, the deviation of the assumed spine axes from longitudinal mesosomal axis should not exceed 30°.

Distribution
Seifert et al. (2017) - C. itsukii shows a huge range extending over 17000 km from the Island Reunion in the Indian Ocean, over East India, Indochina, Japan and diverse Pacific Islands east to Hawaii. The most marginal, isolated populations on Island Reunion and Hawaii most probably have been founded by anthropogenous introduction. Despite showing tramp species properties C. itsukii is rare in the Indo-Malayan Archipelago where Cardiocondyla kagutsuchi and Cardiocondyla strigifrons dominate.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Hawaii, Indonesia, Kiribati, Philippines. Malagasy Region: Réunion. Oriental Region: Bhutan, India, Nepal, Sri Lanka, Thailand. Palaearctic Region: China, Japan.

Biology
Seifert et al. (2017) - On Hawaii it is one of the very few ants occurring in high densities in primary rain forests with Metrosideros sp. trees and Cibotium ferns and is found also at higher elevations on Mauna Kea volcano (Krushelnycky et. al. 2005, Wetterer et. al. 1998). Biological traits of C. itsukii were studied by Frohschammer & Heinze (2009), Heinze et. al. (2013) and Okita et. al. (2015). Winged males are not known in C. itsukii but only wingless ergatoid males with more than one male usually being present in a colony. The males are in reproductive competition and use the strong shear-shaped mandibles to attack freshly eclosed rivals by crushing their heads or cutting-off appendages but males do not fight when in adult stage. As in Cardiocondyla mauritanica, the strictly intranidal mating and polygyny is considered as a preadaptation for a successful tramp species strategy. The total number of sexual offspring of queens is positively associated with their life-span. More fecund queens live longer than less fecund queens and early onset of sexual production does not negatively affect the queen’s life-span. The number of eggs present in colonies increased with queen’s age until shortly before death, indicating negligible reproductive senescence. Several queens produced only males late in their lives, suggesting the occurrence of sperm depletion.

Nomenclature

 *  itsukii. Cardiocondyla itsukii Seifert, Okita & Heinze, 2017: 339, figs. 10-12 (w.q.m.) JAPAN.

Worker
Head less elongated than in all other members of the C. nuda group, CL/CW 1.169. Postocular distance moderately large, PoOc/CL 0.444. Eyes relatively small, EYE 0.228. Frontal carinae immediately caudal of the FRS level parallel or very slightly converging. Foveolae on vertex without interspaces, deeply impressed, with 15–22 μm diameter, and with an inner corona (a flat tubercle) of 7–9 μm diameter having the base of a decumbent pubescence hair in its center. This type of sculpture can also be described as a strongly sculptured microreticulum. Longitudinal sculpture on vertex reduced; only frontal laminae, clypeus, and a narrow area on anteromedian vertex finely longitudinally carinulate; a weak semicircular rugosity is found around the antennal fossae. Lateral mesosoma on whole surface regularly and strongly microreticulate; longitudinal sculpture except for 4–6 weak and short carinulae on metapleuron entirely absent; dorsal promesonotum with more irregular reticulum the meshes of which have twice the diameter than on lateral mesosoma. Whole surface of petiole and postpetiole more shining, with a very fine microreticulum. The strength of sculpture on mesosoma and waist in particular shows considerable variation within the huge distributional range, without showing regional trends. Cuticular surface of first gaster tergite smooth and shining, a very delicate microreticulum with wide meshes becomes visible at higher microscopic resolution. Pubescence hair length on gaster tergites is the largest within the C. nuda group, PLG/CS 7.12%. Metanotal groove distinct but rather flat, MGr/CS 2.16%. Propodeal spines reduced to short dents. Petiolar profile in many specimens with a steeper frontal face compared to C. strigifrons and C. kagutsuchi. Petiole node slightly longer than wide. Postpetiole narrower than in C. mauritanica; in dorsal view with clearly angulate sides and straight anterior margin that is clearly shorter than posterior margin; postpetiolar sternite flat, without any protrusions. Color most variable over the huge distributional range: most frequent are morphs with a medium brown mesosoma and waist, a dark brown head and a dark to blackish brown gaster but much lighter or darker color morphs are not rare.

Type Material
The holotype plus 8 paratypes (4 workers, 2 gynes and 2 males) are on three pins labelled "JAP: 34.72297 N, 137.83881 E / Shizuoka Pref. Iwata-shi, 12 m / street margin in rural land/ leg. I. Okita 2010.09.05-81". The pin with the holotype carries a red type label "Holotype (top specimen) / & Paratypes / Cardiocondyla itsukii / Seifert & Okita" and the two pins with paratypes have labels "Paratypes / Cardiocondyla itsukii / Seifert & Okita". These are deposited at. Five additional paratype workers are deposited at. Furthermore, 120 workers, 86 gynes, and 1 ergatoid male are stored in ethanol at MNEHS.

Etymology
The species is dedicated to Itsuki Okita, the son of the junior author.

References based on Global Ant Biodiversity Informatics

 * Seifert B., I. Okita,and J. Heinze. 2017. A taxonomic revision of the Cardiocondyla nuda group (Hymenoptera: Formicidae). Zootaxa 4290: 324-356.
 * Yamane S., Y. Harada and H. Furukawa. 2019. Establishment of two tramp species of the ant genus Pheidole (Hymenoptera: Formicidae: Myrmicinae) in mainland Kagoshima, Japan. Nature of Kagoshima 46: 239–241.