Myrmicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Nesomyrmex echinatinodis complex: tropical Mexico to southern and western Brazil. Costa Rica: widespread in lowland and mid-elevations sites.
Identification
Species complex: antennae 11-segmented; metasternal lobes rounded; propodeal spiracles directed posteriorly, not highly visible in dorsal view (contrast pleuriticus). Nesomyrmex echinatinodis s.s.: face largely smooth and shining, reticulate rugose sculpture confined to cheeks; fourth abdominal tergite smooth and shining.
See discussion below of two related species, dalmasi and JTL-008.
Natural History
The Nesomyrmex echinatinodis species complex occurs as three separate species in Costa Rica. The three species differ in morphology, habitat preference, and colony structure.
Nesomyrmex echinatinodis s.s. has the face shiny, with reticulate-rugose sculpture restricted to the cheeks. The fourth abdominal tergite is smooth and shining. This species is found in mature wet forest areas. It develops large, polydomous colonies with many thousands of workers. In branch falls or fresh treefalls they may be conspicuous, forming columns of workers. I have collected it at Corcovado National Park, Carara Biological Reserve, Alto Palma just southwest of San Jose, Manuel Antonio National Park, Pitilla Station in the Guanacaste Conservation Areea, La Selva Biological Station, and Hitoy Cerere Biological Reserve. At La Selva it is a relatively common element of the arboreal fauna. It occurred in 7 of 52 canopy trees fogged by Project ALAS. In the floodplain of the Rio Cerere I observed a colony nesting in Acacia ruddiae. These are medium size trees that have swollen stipular thorns much like the ant acacias, but lacking food bodies or any specialized ant inhabitant. The colony occupied many of the thorns on a tree in which I was collecting. I collected the entire contents of a pair of dead thorns, and they contained 37 adult workers, 4 adult males, 1 queen with tattered wing stubs, and brood. The brood was concentrated in one of the thorns. The queen with tattered wing stubs suggests polygyny, with adoption of daughter queens. At Alto Palma I found a colony in one internode of a Cecropia obtusifolia sapling along the roadside. It contained 134 adult workers, 1 adult male, 1 dealate queen, and abundant brood of all sizes. At Corcovado I observed workers tending membracid nymphs on Acalypha diversifolia.
Nesomyrmex dalmasi has more extensive sculpture on the face, with faint longitudinal etchings extending up the sides. The fourth abdominal tergite is either smooth and shining or very faintly shagreened anteriorly. I have collected it in Corcovado National Park, Carara Biological Reserve, La Pita at 200m elevation on the road to Monteverde, and at La Selva Biological Station. Thus it is broadly sympatric with echinatinodis in Costa Rica. Collections have all been from scrubby vegetation, roadsides, regenerating pastures, and other early successional habitats, usually as isolated workers. They are not at all conspicuous and occur in very small colonies. In Carara I found a nest in a 6mm diameter dead stick. At La Pita I found a small nest in a dead knot in a guava tree (Psidium). At La Selva I collected a nest in a node of a Cordia alliodora tree. The tree was in a small demonstration forestry plot in open second growth vegetation.
Nesomyrmex JTL-008 has yet more extensive sculpturing, with the face entirely punctatorugose and the fourth abdominal tergite strongly shagreened anteriorly. I have only one collection of this species, from Palo Verde Biological Station in seasonally dry northwestern Costa Rica. A sprawling vine was common along the river bank. The stems had soft pith and were often inhabited by ants. A small Nesomyrmex nest occurred in one of the live stems.
I have several collections of queens, some associated with workers and others not. So far I have not been able to find any distinguishing characters among the queens that would allow me to identify them to species.
Comments
Kempf (1959) recognized echinatinodis as a "residue of classification," synonymizing the various infraspecific forms. He understood that his actions were provisional, pending a better understanding of character variation in the complex. The following is a review of the published names that have been associated with N. echinatinodis (original combinations):
Leptothorax echinatinodis Forel 1886:48-49. Holotype worker: Brazil, Rio de Janeiro.Leptothorax pungentinodis Emery 1896:2. Holotype queen: Panama, Colon.
Leptothorax aculeatinodis Emery 1896:60. Syntype worker: Costa Rica, Jimenez (Alfaro); Brazil, Mato Grosso.
Leptothorax echinatinodis dalmasi Forel 1899:55-56. Syntype worker, queen: Colombia, Sierra Nevada de Santa Marta, San Antonio (Forel).
Leptothorax echinatinodis schmidti Menozzi 1927:275-276. Syntype worker, queen, male: Costa Rica, San Jose (Schmidt).
Leptothorax echinatinodis cordincola Wheeler 1942:205-206. Syntype worker: Panama Canal Zone: Red Tank; Panama: Las Sabanas, Tumba Muerta Rd.
Kempf never saw any of the types of this complex, and neither have I. Nevertheless, I have attempted to use the published descriptions to associate names with the species in Costa Rica.
Forel's description of echinatinodis states that the front and vertex of the head are sublucid, the rest of the face subopaque, and the fourth abdominal tergite smooth and shiny. Emery's description of aculeatinodis states that the face is smooth and shiny, with shallow sparse puncta, the cheeks are reticulate-rugose, and the fourth abdominal tergite is smooth and shiny, with faint anterior striation. Emery's key separates echinatinodis and aculeatinodis on the differences in face sculpture. Forel (1899) subsequently tried to differentiate echinatinodis and aculeatinodis by color, indicating that the face sculpture differences that Emery used to differentiate the species did not really exist and were caused by the inexactness of Forel's original description of echinatinodis. He amended the description, stating that the type of echinatinodis had a smooth and shiny face with only the cheeks sculptured. He then described the race dalmasi, stating that the face was feebly but distinctly striolate/reticulate throughout, all the way to the occiput, yet still rather shiny, and the abdomen was smooth and shiny. Menozzi described subspecies schmidti as a more robust version of echinatinodis, the face sublucid, strongly sculptured anteriorly, with weak rugae posteriorly, and the anterior portion of the fourth abdominal tergite finely striate. Wheeler described subspecies cordincola with "head very shining, but finely, superficially and not very evenly striate... Gaster smooth and shining, its base very finely and obscurely striate."
Currently we have a large-scale picture of one lineage that could be called echinatinodis, but we also have a fine-scale picture for Costa Rica that shows more detail and the presence of differentiated sympatric species. For naming, a lumper could call all the Costa Rican forms one species, and call them echinatinodis. A splitter sees three species in Costa Rica and assumes that such diversity will be manifest throughout the Neotropics. If this diversity is like other groups, it may take the form of one widespread species that is common in human disturbed habitats, and many locally differentiated species that are found in undisturbed habitats.
Due to Forel's emendation of his description of echinatinodis, I am using the name echinatinodis to refer to the shiny-faced species in Costa Rica. The type locality of echinatinodis is very far from Costa Rica, and if further character analysis and specimen examination suggests there are multiple species and that echinatinodis should be broken up, Emery's aculeatinodis would certainly apply to the Costa Rican species.
I use the name dalmasi to refer to the Costa Rican species with moderately sculptured face. I hypothesize that there is one widespread species that inhabits highly disturbed habitats. On this species the face is sublucid but with faint sculpture extending to the vertex margin. Forel's dalmasi fits here, as does Wheeler's cordincola.
From the description Menozzi's schmidti is possibly also dalmasi, but the reported size is too large. Examination of types will be necessary to resolve the status of schmidti. Emery's pungentinodis is based on a queen, and there is currently no way to differentiate queens in the echinatinodis complex. Unfortunately it is an old name, the second oldest in the complex, and thus will probably emerge as a senior synonym of one or more of the later names when it can be reliably identified.
Finally, I use a temporary code name (JTL-008) for the species with strongly sculptured face collected at Palo Verde. The strong sculpturing on the face does not match any of the described taxa.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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