Geographic distribution of Atta robusta Borgmeier (Hymenoptera: Formicidae)

Distribuição geográfica de Atta robusta Borgmeier (Hymenoptera: Formicidae)

SCIENTIFIC NOTE

Geographic distribution of Atta robusta Borgmeier (Hymenoptera: Formicidae)

Distribuição geográfica de Atta robusta Borgmeier (Hymenoptera: Formicidae)

Marcos C. Teixeira^I; José H. Schoereder^II; Antônio J. Mayhé-Nunes^III

^IDepto. Biologia Animal

^IIDepto. Biologia Geral. Universidade Federal de Viçosa, 36570-000,Viçosa - MG

^IIIDepto. Biologia Animal, Universidade Federal Rural do Rio de Janeiro, 23890-000, Seropédica, RJ

ABSTRACT

The available information regarding the geographic distribution of Atta robusta Borgmeier is confused and raised the necessity of revision of both its distribution and its endemic status. This paper ascertained the occurrence of A. robusta in restingas of Espírito Santo and Rio de Janeiro states, Brazil, through fieldwork, museum visits and bibliographical revision. No reference mentioned its occurrence out of restinga vegetation, as well as in states located south of Rio de Janeiro. We confirmed that A. robusta is endemic of restinga vegetation and it is restricted to the strip of the denominated Moist Oriental Tertiary Brazilian Coast. Such a distribution is possibly due to geographical and ecological barriers that obstruct its dispersion to other environments.

Key words: Leaf-cutting ant, endemic occurence, coastal ecosystem

RESUMO

Dúvidas geradas pelas informações disponíveis na literatura levaram à necessidade de uma revisão na distribuição geográfica de Atta robusta Borgmeier e seu status de endemicidade. Por meio de coletas em campo, exame de coleções entomológicas e revisão bibliográfica, verificou-se que A. robusta ocorre em todos os ambientes de restingas dos estados do Espírito Santo e Rio de Janeiro. Nenhuma referência foi encontrada sobre sua ocorrência fora dos ambientes de restingas, bem como para os estados localizados ao sul do Rio de Janeiro. Sugere-se que A. robusta é endêmica das restingas e está restrita à faixa do litoral brasileiro denominado de Terciário Oriental Úmido, devido às barreiras geográficas e ecológicas que impedem sua dispersão.

Palavras-chave: Saúva, endemismo, restinga

Biological studies of leaf-cutting ants of the genus Atta have been motivated more by the economic importance than by their ecological role. Species that do not usually invade agroecosystems, therefore, have been virtually ignored in the research, as happened with Atta robusta, described by Borgmeier (1939) from São Bento, a locality near Baía da Guanabara in the Duque de Caxias City, Rio de Janeiro, Brazil. Although Mariconi (1970) suggested that A. robusta is endemic to the region around the city of Rio de Janeiro, Gonçalves (1960) had already registered its occurrence in the coast of Rio de Janeiro State, from São João da Barra to the Marambaia restinga, even though this information has been largely ignored in subsequent researches. Fowler (1995) and Fowler et al. (1996) reinforced their occurrence only in the region around the city of Rio de Janeiro, alerting that this species may be in extinction due to the advance of human-made disturbances in restinga vegetation, which favor its substitution by A. sexdens rubropilosa Forel. The available literature information, therefore, is contradictory regarding A. robusta geographic distribution, being insufficient to define its endemism and conservation status. This paper provides additional information on this subject based on fieldwork, museum visits and a wider bibliographic revision.

The revision was carried out through field sampling in restingas and revision of entomological collections. Fieldwork was carried out from October 1996 to July 1998. Twenty-four sites in the Brazilian coast were surveyed in eight localities with restinga vegetation. The sites were distributed from the North of Espírito Santo State (Conceição da Barra) to the North of Rio de Janeiro State (São João da Barra) (Table 1), and three sites were surveyed in each locality. The sites were thoroughly searched for the presence of Atta nests, and the leaf-cutting ants found were sampled to further identification based on Mariconi (1970) and Fowler et al. (1993). After taxonomic confirmation the specimens were deposited in the following collections: Museu de Entomologia of the Universidade Federal de Viçosa (Viçosa, Minas Gerais), Centro de Pesquisas do Cacau (CEPLAC, Itabuna, Bahia), Museu de Zoologia of the Universidade de São Paulo (São Paulo, SP) and Museu Nacional (Rio de Janeiro, RJ).

The above museums, and the entomological collection of the Reserva Florestal de Linhares, were visited to check for the presence of A. robusta specimens. The collection of the Reserva Florestal de Linhares has specimens sampled in forest ecosystems contiguous to restinga vegetation, and was expected to lack specimens of A. robusta if this species is really endemic to restinga. Specimens were submitted to a new taxonomic confirmation and data regarding collection sites were registered.

A. robusta was found in all sampling sites, being registered a total of 86 nests. No other Atta species were found in the restinga vegetation. All specimens deposited in the museums were originated from the Rio de Janeiro State restingas, and were confirmed as A. robusta. No A. robusta specimens were found in the collection of the Reserva Florestal de Linhares. Such results demonstrated that (i) A. robusta is not endemic from the region around the city of Rio de Janeiro, also occurring in restinga environments of Rio de Janeiro and Espírito Santo states (Fig. 1); (ii) it does not occur in forest ecosystems near restinga vegetation; and (iii) its occurrence has sharply defined northern and southern boundaries, which may be caused by climatic and geomorphologic characteristics of the Brazilian coast.

The Brazilian coast strip from the south of Rio de Janeiro State to the middle of Bahia State (Recôncavo Bahiano) presents moist climate and wide plains with restinga vegetation, named Moist Oriental Tertiary Brazilian Coast (Schobbenhaus 1984). The southern boundary of such strip is the mountain ridge named Serra do Mar, which is a barrier impeding or impairing the link between restinga ecosystems occurring further south, and probably impeding dispersion of alate females of A. robusta.

The hypothesis that A. robusta is restricted to the Moist Oriental Tertiary Brazilian Coast is reinforced by results obtained by other authors who studied ant fauna in regions located in the South of Serra do Mar and North of Espírito Santo. Mariconi (1965) studied the Oriental region of São Paulo State, where littoral and restinga vegetation are included, not revealing the presence of A. robusta. Bonnet & Lopes (1993) carried out an ant survey in dune and restinga vegetation further Southern in Santa Catarina state, and neither have found A. robusta. Lopes leaf-cutting ant survey (1998), in restinga vegetation in Paraná State, evidenced the absence of A. robusta.

The absence of other Atta species in restinga vegetation in Rio de Janeiro and Espírito Santo states is also noteworthy. According to Mariconi (1965) the superficial water table may account for the absence of leaf-cutting ants in São Paulo coast, because the water may impede nest development. Further studies must be carried out to explain the evolutionary strategies that differentiate A. robusta from the other species of the genus regarding restinga occupation.

There is no evident physical barrier impeding A. robusta dispersion beyond the northern limits studied in the present paper. Nevertheless, J. H. C. Delabie (pers. comm.), who exhaustively studied ant fauna in the south of Bahia state, did not register the occurrence of A. robusta in the state, including in restinga vegetation.

Geographic barriers explain why A. robusta apparently occurs in a restricted strip of Brazilian coast, but do not explain why it is restricted to restinga vegetation. The absence of records of this species outside restinga vegetation suggests that A. robusta may have acquired very specific ecological needs, impeding its dispersion to the Atlantic Forest, which is now an ecological barrier to the species dispersion. The absence of A. robusta in the Reserva Florestal de Linhares is evidence for the above hypothesis, because the reserve is an Atlantic Forest contiguous to restinga vegetation in the distribution range of A. robusta.

Concluding, A. robusta may have evolved in the restinga vegetation of a specific strip of the Brazilian coast, and it is impeded to disperse to other areas due to physical barriers, and to historical and ecological factors. Such questions must receive more attention with the study of historical factors involved in restinga formation and of Atta phylogeny, which remains little studied. Nevertheless, as the species has a distribution wider than it was though, its conservation status needs to be revised, because its populations seem to be self-maintained in the protected areas of the Brazilian coast.

Acknowledgments

This paper is part of the M.Sc. thesis of the first author. Jacques H. C. Delabie and C. Roberto F. Brandão kindly confirmed the specimen's identifications. Ana Paula Agizzio, João Luiz da Cunha Teixeira, Elaine Bernini and Carlos Alberto Doná helped at the fieldwork. Og DeSouza and Marcelo N. Schlindwein gave important suggestions to a draft version. The authors are supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq grants.

Literature Cited

Received 30/11/02

Accepted 15/07/03

• Bonnet, A. & B.C. Lopes. 1993. Formigas de dunas e restingas da Praia da Joaquina, Ilha de Santa Catarina, SC (Insecta: Hymenoptera). Biotemas 6: 107-114.
• Borgmeier, T. 1939. Nova contribuição para o conhecimento das formigas neotropicais. Rev. Entomol. 10: 403-428.
• Fowler, H.G. 1995. The population status of the endangered Brazilian endemic leaf-cutting ant Atta robusta (Hymenoptera: Formicidae). Biol. Cons. 74: 147-150.
• Fowler, H.G., J.H.C. Delabie & M.N. Schlindwein. 1996. The endemic Brazilian leaf-cutting ants, Atta silvai and Atta robusta (Hymenoptera: Formicidae): Population status. Rev. Bras. Entomol. 40: 111-112.
• Fowler, H.G., T.M.C. Della Lucia & D.D.O. Moreira. 1993. Posição taxonômica das formigas cortadeiras. p. 4-25. In T.M.C. Della Lucia (ed.), As formigas cortadeiras. Viçosa, Editora Folha de Viçosa, 262p.
• Gonçalves, C.R. 1960. Distribuição, biologia e ecologia das saúvas. Div. Agron. 1: 2-10.
• Lopes, B.C. 1998. Formigas cortadeiras (Formicidae: Attini) de praias e restingas da Ilha de Santa Catarina, SC. Anais do II Simpósio Brasileiro de Restingas e Lagoas Costeiras, 49p.
• Mariconi F.A.M. 1965 Aspectos ecológicos e bionômicos das saúvas da região oriental do estado de São Paulo. An. Esc. Sup. Agric. ''L. Queiroz'' 22: 213-232.
• Mariconi, F.A.M. 1970. As Saúvas. São Paulo. Agronômica Ceres, 167p.
• Schobbenhaus, C. 1984. Geologia do Brasil. Brasília, Departamento Nacional da Produção Mineral, 501p.

Publication Dates

• Publication in this collection
  09 Mar 2004
• Date of issue
  Dec 2003

History

• Accepted
  15 July 2003
• Received
  30 Nov 2002