Forelius pruinosus

Guerrero, R. J. & Fernández, F., 2008, A new species of the ant genus Forelius (Formicidae: Dolichoderinae) from the dry forest of Colombia., Zootaxa 1958, pp. 51-60 : 57-59

Forelius pruinosus (Roger 1863)

(Fig. 6)

Material examined: Colombia. (3w), Magdalena; Santa Marta; Vda. Mosquito. 11°10'23.6"N 74°10'45"W 96 m; Manual collection; 03.Jan.2008; D. Olivero & M. Escarraga, coll. Deposited in Insect Collection of University of Magdalena (CEUM), Santa Marta, Colombia.

Geographic distribution: Bahamas, Colombia (Magdalena), Costa Rica (Guanacaste), Cuba, Guatemala, Mexico, Panama, The West Indies, USA [Arizona, California, Florida, Georgia, Missouri, North Dakota (Wheeler & Wheeler 1963), Texas].

Cuezzo (2000) provided a taxonomic key for all species of Forelius known. Due to the new synonymy between F. analis and F. pruinosus (Ward 2005) and the description of F. damiani , we provide a new key for the species with circular propodeal spiracle, with the exception of F. keiferi . The descriptions of F. keiferi and F. pruinosus given in Cuezzo (2000) overlap in many characters and the status of F. keiferi as a species distinct from F. pruinosus is not certain.

Key to species of Forelius Emery with spiracles rounded [based on workers; modified from Cuezzo (2000)]

1. Small workers (TL 1.6 - 1.7 mm). Scapes barely reaching vertex margin (SI <90). Mesosomal outline always continuous in lateral view. (Argentina, Brazil, Paraguay)..................... pusillus (Santschi) (Fig. 4)

- Worker size variable (TL 1.4 - 2.5 mm). Scapes reaching or surpassing vertex margin by at least 1/6 of their length (SI> 90). Mesosomal outline variable.....................................................................................2

2. Pronotum bearing only two erect setae. Dorsal face of propodeum lacking erect setae. (Colombia, Costa Rica, USA)...................................................................................................... damiani sp. nov. (Fig. 1 & 2)

- Pronotum bearing more than two erect setae. Dorsal face of propodeum bearing erect setae. Note: Some evidence of intergradation between F. pruinosus and F. mccooki (Ward 2005) suggests that F. pruinosus may contain a number of cryptic species, and may also hybridize with the very similar F. mccooki ........3

3. Mandibles with four teeth and three to four denticles. Pronotum usually with six erect setae. Dorsal face of mesosoma bearing more than 10 erect setae. (Jamaica, Mexico, USA) ...... mccooki (McCook) (Fig. 5)

- Mandibles with five teeth and one or two denticles. Pronotum usually with four erect setae. Dorsal face of mesosoma bearing 2 to 6 erect setae. (Bahamas, Colombia, Costa Rica, Cuba, Guatemala, Jamaica, Mexico, Nicaragua, Panama, USA)........................................................................... pruinosus (Roger) (Fig. 6)

Discussion

Forelius damiani and F. pruinosus are the first species of the genus Forelius known from Colombia. Both species have been collected in the lowland dry forest of the Sierra Nevada de Santa Marta while F. damiani has also been collected in Zambrano (Bolivar), northern Colombia. The Zambrano specimens do not differ from those of the type locality. The workers of F. damiani from Costa Rica differ somewhat in size (TL 1.50 - 1.68 mm in Costa Rica vs. TL 1.40 - 1.58 mm in Colombia) and the length of the scapes (exceeding the vertexal margin by 0.04 mm in Costa Rica, not exceeding the vertexal margin in Colombia). While the TL of the workers showed differences between the populations of Costa Rica and Colombia, the length of mesosoma is less variable and the measurements for the two countries broadly overlap (MsL 0.46 - 0.56 mm in Costa Rica vs. MsL 0.44 - 0.58 mm in Colombia). Specimens from Costa Rica are darker brown than those from Colombia.

Forelius damiani is relatively similar to F. pruinosus (Roger) , but F. damiani has only two erect pronotal hairs while F. pruinosus can have two to four erect pronotal hairs; the promesonotum of F. damiani is lower compared with F. pruinosus ; the dorsal face of the propodeum is longer than the declivitous face in F. damiani , moreover it lacks propodeal hairs; and F. damiani is smaller than F. pruinosus in some measurements such as TL, HL, HW and SL (see measurements above and Cuezzo (2000) for comparison). Forelius damiani is similar to F. pusillus , however several characters show differences: the mandibles of F. damiani have four teeth while those of F. pusillus have five; the propodeum of F. pusillus has four conspicuous setae but F. damiani has none; the workers in F. pusillus are a little larger (TL 1.6 - 1.8 mm in F. pusillus vs. 1.40 - 1.68 mm in F. damiani ). Characters that distinguish Forelius damiani from most other Forelius species are the circular propodeal spiracle and the absence of erect hairs on the dorsal face of the propodeum.

The occurrence of round spiracles on the new species F. damiani reinforces a pattern in which the few species found north of the Amazon basin all have round spiracles, while south of the Amazon many species have elongate, slit-like spiracles and only one species has round spiracles. Several hypotheses can explain this pattern, based on whether round spiracles are plesiomorphic, apomorphic, or homoplasious in the genus. If round spiracles are plesiomorphic, the genus could have originated north or south of the Amazon basin and then dispersed across the Amazon (perhaps during a period of drier climate). Subsequently, elongate spiracles evolved in the south (as one adaptation to arid conditions, reducing water loss through the spiracle) and perhaps allowed a greater diversification there. In the south, forms with elongate spiracles may have displaced previously more abundant and diverse forms with round spiracles. Alternatively, round spiracles could be apomorphic. An initial radiation of forms with elongate spiracles may have occurred in southern South America. Subsequently, a form with round spiracles evolved which was better suited to humid conditions and better able to cross the Amazon Basin. Once on the other side it diversified into the present species found north of the Amazon. Finally, round spiracles could be homoplasious, evolving independently north and south of the Amazon. Further phylogenetic work on the genus is needed to differentiate among these hypotheses.