Acropyga palaga

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Acropyga palaga
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Plagiolepidini
Genus: Acropyga
Species: A. palaga
Binomial name
Acropyga palaga
LaPolla, 2004

According to label data it has been collected at coffee roots. Males were collected in both April and August, apparently from nests.

Identification

LaPolla (2004) - Worker: 9-10 segmented antennae (but see description); metanotal area distinct; mandibles with 3 distinct teeth; otherwise as in Acropyga goeldii. Queen: unknown. Male: 12 segmented antennae; parameres rectangular, about the same width throughout length; penis valves sharply curved ventrally from tip of penis to ventral extension. Compare with A. goeldii and other members of the goeldii complex.

Based on samples I have examined, workers of A. palaga are virtually indistinguishable from Acropyga goeldii. One possible way to distinguish workers is by the shape of the clypeus. In A. goeldii the posterior clypeal margin rises slightly toward the torulae and is wider, whereas in A. palaga the posterior clypeal margin is strictly transverse toward the torulae and is narrower. However, the extent to which both species vary is not possible to assess at this time due to the low number of specimens available for study. Another worker character that appears to be stable for A. palaga is that of the distinct metanotal area (with two sulci present), but A. goeldii may sometimes possess a distinct metanotal area. A. palaga appears to possess fewer hairs on the mesosoma than A. goeldii, but given the variation observed in A. goeldii the utility of this character remains unclear.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Costa Rica (type locality).

This species has only been collected from two localities in Costa Rica.

Check distribution from AntMaps.

Distribution based on specimens

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The above specimen data are provided by AntWeb. Please see Acropyga palaga for further details

Biology

Little is known about Acropyga palaga. Until further studies reveal more about this species we can infer that its natural history and biology should be similar to other Acropyga. LaPolla published a worldwide revision of the Acropyga in 2004 and the following synopsis is based on this excellent treatment of the genus.

In overall appearance Acropyga are small, robust, yellowish ants possessing a thin, easily collapsible cuticle. The species generally appear rather similar to each other morphologically. In some species workers and queens display an unusual range of phenotypic variation. Antennal segment number, for example, can vary within and between species. Even a single specimen may posses antennae with a different number of antennal segments and workers in numerous species possess one more antennal segment than conspecific males.

The small eyes, reduced antennae segmentation, lightly pigmented cuticle, and hairs covering the cuticle of Acropyga species are suggestive of a completely subterranean existence. Species also display photophobic behavior (Weber, 1944; LaPolla et al., 2002). Acropyga can survive in a wide range of habitats, from deserts to rainforests, though they do not seem able to survive in regions where temperatures below freezing persist for several months at a time. Some species, such as Acropyga pallida and Acropyga silvestrii for example, are found within a very wide range of habitats. Undoubtedly, the Acropyga lifestyle of existing below the surface buffers them against extremes of the outside environment.

Acropyga nests are found in leaf litter, under stones, in rotten wood (lying on or near the soil surface) and in the soil. Observations of nests of various species show the nests are large, consisting of at least several thousand individuals. The nest structure is diffuse with apparently no central nesting location (LaPolla et al., 2002). Tunnels and indistinct chambers stretch out over large areas through the nesting medium. Polygyny has been suggested for several species. The origins of polygyny remains uncertain, but two routes are suggested based on field observations. Biinzli (1935) found both the occurrence of pleometrosis (founding of a colony by multiple queens) and the acquisition of young queens by established colonies in Acropyga exsanguis.

All Acropyga are thought to be hypogaeic (living entirely underground), surviving primarily by "tending" mealybugs (Hemiptera: Pseudococcidae) on underground roots for their exudate (sometimes referred to as "honeydew") (Weber, 1944; Williams, 1998). This mutually beneficial relationship is called trophobiosis (Holldobler and Wilson, 1990).

Acropyga species are all believed to be obligate coccidophiles (dependent on their tended mealybugs for survival). The strength of this trophophitic relationship is clarified by a number of observations. Queens of eleven species have been observed emerging from their nests prior to their mating flight with a mealybug held in their mandibles (Biinzli, 1935; Wheeler, 1935b; Brown, 1945; Eberhard, 1978; Prins, 1982; Buschinger et al., 1987; Williams, 1998; Johnson et al., 2001). The mealybug that each queen carries presumably serves as a "seed individual" from which a new generation of mealybugs will be started in the newly founded ant colony (Weber, 1944; Williams, 1998). This behavior is called trophophoresy (LaPolla et al. 2002) with queens exhibiting this behavior said to be trophophoretic. The mealybugs utilized by Acropyga belong to the subfamily Rhizoecinae, and it is likely that the mealybugs are not able to survive independently of the ants (Williams, 1998). LaPolla et al. (2002) observed that Acropyga epedana keeps mealybugs with their brood. When a nest in captivity was starved, workers refused a variety of food items presented to them, suggestiving that the ants are completely dependent on the mealybugs as a food source. Fossil evidence suggests that the trophobiotic behavior ofAcropyga ants is an ancient one. Johnson et al. (2001) reported that Acropyga queens were discovered in Dominican amber, either holding a mealybug or with a mealybug nearby in the amber matrix. The amber was dated to the Miocene and is at least 15-20 million years old.

Castes

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • palaga. Acropyga palaga LaPolla, 2004a: 54, figs. 21, 39, 45 (w.m.) COSTA RICA.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Despite similarities in workers, examination of males suggests at least two species are present (see A. goeldii discussion for more detail). A. palaga males possess rectangular parameres in which width does not change much across their length. This in contrast to A. goeldii males in which the parameres typically decrease in width toward the apex. Once dissected the penis valves are distinct from A. goeldii, with a curved ventral aspect from the penis valve tip through the ventral extension. The dorsal margins of A. palaga penis valves are nearly straight, whereas A. goeldii possesses a humped dorsal margin. Additionally, the penis valves also exhibit a straight margin toward the apodeme from the ventral portion of the ventral extension. Finally, A. palaga possesses a ventral extension that narrows significantly toward the base, unlike A. goeldii.

I did notice some variation in paramere width between the two populations of A. palaga examined. Specimens from Alajuela, Costa Rica had wider parameres than those from Estrella Valley, Costa Rica. The penis valves from the Alajuela specimens were not quite as curved at the penis valve caudal ends as the Estrella specimens. Despite those differences both populations had males with a more or less parallel dorsal margins and narrow, curved ventral extensions. The agreement of those characters with each population has led me to consider them the same species. But as more specimens become available for study, variation can be more accurately addressed and changes may be necessary in the taxonomy.

Description

Worker

(n=8): TL: 1.97-2.5; HW: 0.52-0.608; HL: 0.504-0.6; SL: 0.344-0.472; ML: 0.573-0.706; GL: 0.869-1.18; CI: 99.62-104.65; SI: 66.15-77.76.

Head: yellow; head about as broad as long; posterior margin slightly concave; covered in a layer of short appressed hairs, with several erect hairs usually along posterior margin; 9-10 segmented, incrassate antennae (males have 12 segments, so it is likely this species can have workers with up to 11 segments); scape fails to reach posterior margin by less than half length of pedicel; clypeus convex and narrow, covered with abundant erect hairs; mandible with 3 distinct teeth; gap exists between anterior clypeal margin and inner mandibular margin. Mesosoma: yellow; in lateral view pronotum with a short anterior shelf before rising sharply toward mesonotum; posterior pronotum with many erect hairs; mesonotum covered in a thick layer of appressed hairs, with scattered erect hairs; mesonotum higher than propodeum; metanotal area distinct; propodeum rounded with a thick layer of appressed hairs; declivity steep. Gaster: petiole thick and erect; petiole does not reach level of propodeum; gaster yellow; covered in a layer of appressed hairs, with scattered erect hairs throughout.

Queen

Queens are not known for this species.

Male

(n=8): TL: 2.23-2.46; HW: 0.425-0.473; HL: 0.424-0.494; SL: 0.398-0.426; ML: 0.794-0.854; GL: 0.91-1.24; CI: 86.03-101.5; SI: 89.03-103.29.

Head: brownish-yellow to brown, darkest at apex around 3 prominent ocelli; head longer than broad, becoming broader toward apex; covered in a layer of short appressed hairs; 12 segmented, slightly incrassate antennae, apical segment about as long as proceeding 2 segments; scape surpasses posterior margin by about length of pedicel; clypeus narrow, convex medially, covered in thick layer of erect hairs; mandible with 3 distinct teeth; a gap exists between anterior clypeal margin and inner mandibular margin. Mesosoma: brownish-yellow; pronotum short and collar-like; mesonotum anteriorly rounded, dorsally flat, covered in layer of short appressed hairs, with widely scattered erect hairs; propodeum low, with indistinct declivity. Gaster: petiole thick and erect; gaster brownish-yellow, covered in layer of appressed hairs, with scattered erect hair throughout. Genitalia: in lateral view, parameres long, rectangular, with scattered erect to suberect hairs; cuspi long, cylindrical; digiti with long, stalk-like posterior portion, apices anvil-shaped; digiti meet cuspi dorsally, where both have structures have a series of short, peg-like teeth.

Type Material

Holotype worker, COSTA RICA: Estrella Valley (W.M. Mann) (USNM); 3 paratype workers, 6 paratype males, same locality as holotype (USNM) (MCZC). The holotype is labeled JSL TYPE # 105.

Etymology

The specific epithet palaga is Latin for an ingot of gold, in reference to the yellowish color of the workers.

References