Syscia augustae ( Wheeler, 1902 )

Longino, John T. & Branstetter, Michael G., 2021, Integrating UCE Phylogenomics With Traditional Taxonomy Reveals a Trove of New World Syscia Species (Formicidae: Dorylinae), Insect Systematics and Diversity 5 (2), No. 2, pp. 1-51 : 16-20

Syscia augustae ( Wheeler, 1902)

Figure 11 (map, worker), S4 (worker), S5 (brachypterous queen), S6 (male)

Cerapachys (Parasyscia) augustae Wheeler, W. M., 1902: 182 , fig. 1, 2. Syntype worker, apterous queen: USA, Texas, Austin , 11 May 1902 (Rucker) [USNM, not examined]. Wheeler, W. M., 1903: 206 (description of immature larva). Wheeler, G. C., 1950: 106 (review of larvae of Cerapachyinae ; no new material, W. M. Wheeler’s 1903 observations repeated).

Syscia augustae: Borowiec, 2016: 224 .

Smith (1942) described the putative male of S. augustae , but Borowiec (2016) reidentified Smith’s male as Acanthostichus .

Geographic Range. United States (Texas, Arkansas), Mexico (Nuevo Leon).

Diagnosis. Occipital carina strongly developed, visible in face view; subpetiolar process subtriangular with small convexity on posterior margin; AIII in dorsal view trapezoidal, with nearly flat sides; AIV in dorsal view with sides flat to weakly convex, subparallel, anterior margin somewhat truncate; dorsal profile of AIII and AIV flat; standing pilosity of medium length and thickness; puncta on AIII small, widely spaced; puncta on AIV small, widely spaced, fading at midlength; color red brown. Based on the COI barcode of the sequenced specimen (GenBank accession MT267543 ), the smallest pairwise interspecific distance was 9.16%.

Three species are within size and geographic range of S. augustae : S. disjuncta , S. madrensis , and S. setosa .

S. disjuncta ( Fig. 11 ): allopatric; AIV in dorsal view with sides more convex; dorsal profile of AIII and AIV more convex; standing pilosity longer; smaller on average (mean HW 0.56 vs. 0.62).

S. madrensis ( Fig. 11 ): allopatric; subpetiolar process less triangular, more quadrate; sides of AIII in dorsal view less convex; standing pilosity less evident; smaller on average (mean HW 0.56 vs. 0.62); AIII narrower on average (mean AIII-I 96 vs. 107).

S. setosa ( Fig. 11 ): allopatric; AIII in dorsal view with more convex sides; puncta on AIII large, widely spaced; standing pilosity long, coarse.

Measurements, Worker. HW 0.62 (0.62–0.63), HL 0.79 (0.75–0.83), SL 0.45 (0.44–0.45), MSL 1.02 (0.99–1.05), AIIIW 0.54 (0.53– 0.55), AIIIL 0.50 (0.49–0.53), AIVW 0.70 (0.67–0.71), AIVL 0.88 (0.86–0.89), SI 72 (70–73), AIII-I 107 (105–108), AIV-I 79 (76–82) (n = 4).

Measurements, Queen. HW 0.67, HL 0.84, SL 0.46, MSL 1.23, AIIIW 0.66, AIIIL 0.61, AIVW 0.81, AIVL 1.09, SI 69, AIII-I 109, AIV-I 75 (n = 1).

Biology. The first American species of Syscia to be described was named for Miss Augusta Rucker, who found the type series on the outskirts of Austin, Texas. Wheeler had not found this species previously, in spite of 3 yr of careful collecting in the vicinity of Austin. Wheeler (1903) discovered a second colony the next year. He kept them alive for a while, recording his observations as follows:

‘The colony of C. augustae , on which the following observations were made, was discovered May 6th, 1903, near high water mark in the bottom of Shoal Creek at Austin, Texas. It was inhabiting a simple, straight gallery about 5 cm. long by 7 mm. in diameter, under the very center of a large block of limestone. At one end the gallery dipped down into the soil to a depth of 4 cm. The ants, 29 in number, were all congregated in the surface gallery with their long bodies wrapped about a large packet of eggs. Only workers were found, though careful search was made for the peculiar wingless female described in my former paper. The whole colony, with the possible exception of a few ants that may have been out foraging, was captured and placed in a small Petri dish, the bottom of which had been provided with a thin layer of damp soil partly covered with a glass microscope slide. The ants soon took up their abode under the slide after collecting their scattered eggs. Nymphs of two common Texan termites ( Amitermes tubiformans and Eutermes cinereus ) were cut into a few pieces and given them as food. Even when these were placed only a few millimeters from the ants, the latter showed no signs of noticing them till they were actually touched with the antennae. And even then the ants often hesitated before attacking the still struggling heads and thoraces. Eventually the termites were dispatched by the ants curling about them and using both mandibles and sting. The latter produced sudden paralysis. Then the ants eagerly lapped up the juices excuding from the cut ends of the termite fragments, while remaining very quiet as if absorbed in the delight of feeding. The mandibles seemed to be too feeble to cut or puncture even so thin a chitinous investment as that of the termites’.

Wheeler (1902) described the queen of S. augustae . The specimen had fully developed compound eyes, ocelli, and an enlarged mesosoma with all the typical sclerites of winged queens, but he wrote ‘There is nothing to show that the thorax has ever borne wings’. We examined a similar queen in a series collected in Arkansas. One side of the mesosoma bears minute wing remnants, suggesting brachyptery. The wings are mere linear stubs and could not function in flight.

The first male of the species was discovered by Alex Wild in the University of Texas Insect Collection. It was from a Malaise trap, from the Brackenridge Field Lab in Austin, Texas. It is assumed to be conspecific, since it is from the type locality and there are unlikely to be multiple species of Syscia in the vicinity.

MacGown et al. (2017) report the species from USA, Arkansas.

Comments. This species is at the far northern range limit of the genus in the Americas. Within its geographic range it is not known to be sympatric with any other Syscia species. However, the southernmost record of the species, from Nuevo Leon, Mexico, is less than 300 km north of the Rancho Cielo site in Tamaulipas, where four species occur.

Material from southern New Mexico and Arizona has been identified as S. augustae (e.g., Mackay 2002, AntWeb), but here we describe these populations as a distinct species, S. madrensis . UCE sequence data are available for two specimens of S. madrensis from Arizona and one specimen of S. augustae from Texas. The three specimens form a clade, but the genetic distance between the Texas specimen and the two Arizona specimens is relatively large. We examined five collections of S. madrensis : four from Arizona and one from Baja California. We examined three widely-dispersed collections of S. augustae : from Arkansas, Texas, and the Mexican state of Nuevo Leon. The two groups of specimens were morphologically distinct, with differences greater than many examples of sympatric species elsewhere in the range of Syscia . Variation within the groups was low, with the Arkansas, Texas, and Nuevo Leon specimens being very similar to each other, regardless of the large geographic distances among them, and the Arizona and Baja California specimens of S. madrensis being very similar to each other.

The S. augustae clade shows a sister taxon relationship with a single specimen from Costa Rica (S. JTL064). The Costa Rican specimen is morphologically completely different from the S. augustae clade. COI data show S. augustae , S. madrensis , and JTL064 in a single cluster, but as three separate groups with deep divergences.

Figures

Fig. 11. Distribution map, face view, lateral view of petiole-AIV, and dorsal view of AIII-AIV of Syscia madrensis (holotype worker), S. JTL066 (worker, CASENT0610648), S. benevidesae (holotype worker), S. chiapaneca (holotype worker), S. parietalis (holotype worker), S. setosa (holotype worker), S. JTL073 (worker, MCZ-ENT00511569), S. JTL075 (worker, CASENT0601445), S. disjuncta (holotype worker), and S. augustae (worker, CASENT0644275). Species are in order of mean HW, which is shown in the lower left of the distribution map. Scale bars 0.2 mm. On distribution maps, red dots are sites with UCE sequence data. Red boxes are type locality.