Ants of Ranchos Tinamu

Ants of Ranchos Tinamu, Costa Rica

Report by John T. Longino and Michael G. Branstetter, The University of Utah. Student participants: Irene Calderon, Josue Corrales, Krissy Dominguez, Scott Heacox, Josh Kouri, Irene Mata, Mac Pierce, Marianela Solís.

This is a list of the ants of Ranchos Tinamu and vicinity, Costa Rica, based on Project ADMAC sampling. Ranchos Tinamu is on the Pacific slope in the Río Savegre drainage.

Project ADMAC carried out ant sampling at Ranchos Tinamu from 3-14 July 2015. MiniWinkler transects were carried out at three sites. Site 6 was Cerro Plano, with mature wet forest at 1000m elevation. The forest was on an isolated hilltop and had a lower cloud forest aspect. Site 7 was at 500m near the Río Savegre. The area was a mosaic of second growth vegetation and small fragments of mature lowland rainforest. Site 8 was at 700m and was more highly fragmented and disturbed rainforest.

Specimen records have been uploaded to the AntWeb database and are periodically updated. Names in the species list are linked to individual specimen records on AntWeb, from which a link can be followed to the general species page. These specimens function as site-specific vouchers, whose identities may change. The species names in the list are static text on this page. Following the specimen link to AntWeb will allow one to see if the name has changed. The list of Pseudomyrmex species was provided by Phil Ward and is not linked to AntWeb.

There are at least 329 species.

Notable discoveries include:

Anochetus micans: This species was moderately abundant at site 6, the cloud forest site, less abundant at site 8, and absent from site 7, the lowest site. The species was first described by Forel (1908) as A. emarginatus subsp. testaceus var. micans [a quadrinomial and thus unavailable; first made available by Brown (1978), as a binomial], with types from "Altos del Cangrejal de Aserri, cote Pacifique de Costa-Rica, 1000 metres." Brown identified as micans scattered material from Belize, Honduras, and the Bahamas. Longino, in many years of collecting in Costa Rica, never encountered it in Costa Rica, but did see material from Guatemala and Honduras. It was thus gratifying to finally find a population of micans in Costa Rica, on the same slope and same elevation as the type locality.

Camponotus JTL032: Longino first noticed the distinctive minor workers of this species in 1981, at 700m on Cerro Rincón, Osa Pensinsula. The minors have a transverse ridge on the first gastral segment, a rare condition in New World Camponotus. Mike Kaspari found some minor workers at Wilson Botanical Garden in the southern Talamanca range of Costa Rica, and more recently Longino found minor workers at El Copé, a 700m cloud forest site in Panama. Thus it was a delight to find this species relatively abundant at site 6, with occasional occurrences at sites 7 and 8. More exciting yet, major workers and queens were discovered for the first time, revealing that the species is a member of the subgenus Hypercolobopsis. This subgenus is known from scattered species in South America, their distinctive feature being major workers with strikingly and distinctively phragmotic heads, in which the flat, circular, truncate face is oblique and encompasses all of the clypeus and much of the upper surface of the head, extending to the upper vertex. The base of the antennal scape lies in a narrow groove in the face, then abruptly bends to lie over the rounded posterior portion of the vertex.

Although minor workers were found in beating samples (beating low vegetation to capture the low arboreal fauna), this species was also found frequently in Winkler samples, and the examples of major workers and queens were from Winkler samples. The many other species of Camponotus at the site were mostly collected in beating samples, and rarely or never found in Winkler samples. This suggests that C. JTL032 nests in the litter or soil. Perhaps the extreme phragmosis is an adaptation that allows this group of Camponotus, a genus that normally nests arboreally, to nest in the hypercompetitive leaf litter zone.

Camponotus JTL069: This is a bizarre singleton from a beating sample, and to Longino it is unlike any Camponotus he has seen anywhere, ever. It looks a bit like a Camponotus trying to be Cylindromyrmex.

Camponotus JTL070: This is an interesting species, probably new, that is a black shiny version of C. constructor (which also occurred at the site). These two species are unusual in having the mesosoma highly constricted in the middle, like an hour-glass, and the integument is very smooth and polished.

Carebara longii: This species was previously known only from north Texas, where it is rare. The species was relatively abundant at site 6. Morphologically the specimens share the diagnostic characters of C. longii and they look just like the AntWeb images of the type. It will be interesting to carry out sequencing work to see if the Texas and Costa Rica populations at least form a clade, versus being convergent.

Megalomyrmex incisus: This is the first record of the species for Costa Rica. The species occurs from southern Mexico to Peru and central Brazil, but previously Costa Rica was an odd gap in the distribution.

Neivamyrmex diana_nr: Two workers of this tiny Neivamyrmex species were collected in a Winkler sample. It keys to N. diana but does not match images of N. diana types on AntWeb. What it does match, very closely, is images of a specimen collected by Phil Ward in Bolivia!

Pheidole: As usual, this hyperdiverse genus yielded a high number of species, at least 60, 13 of which are probably new. A notable collection was an excellent series of P. nasutoides, a species described by Holldobler and Wilson in 1992. They collected a nest series at La Selva Biological Station, observing that the major workers had a distinctive coloration, yellow with contrasting black heads, that made them look like nasute termite soldiers in the field (hence the name). The species has not been subsequently collected, except for a few minor workers collected in La Selva fogging samples and tentatively identified as nasutoides. The new series was collected in a beating sample by Irene Calderón, one of the ADMAC students.

Strumigenys: This is a diverse genus of mostly litter predators, with high local diversity. There were 29 species, 2 of which are new. One of these, S. JTL032, is particularly interesting because it is one of the few New World species with only 4 antennal segments. The other two Pyramica-form Strumigenys with 4-segmented antennae are S. minuscula from Brazil and S. simulans from Cuba. Strumigenys umboceps was another interesting find, previously known from a single specimen from cloud forest in Ecuador.