E1 = Seed dispersal by myrmecochory of the Mediterranean region

I. Li Vigni - Banca di Germoplasma del Mediterraneo ONLUS

Via P. Floridia, 2 - 90129 Palermo - Internet http:// www.bancadigermoplasma.it

Myrmecochory, specifically, is the transport of seeds by ants, with the ants eating the only edible part of the seed: elaiosome. These ants do not kill the seeds, which still can germinate far from the place where they originated. Nowadays we know of more than 4,000 species of myrmecochorous Angiospermae belonging to more than 70 families, who’s diasporas are dispersed by ants (1, 2).

This study examines plants and ants found in the Mediterranean region (Sicily), observed in their natural habitat in three different locations: the Ficuzza woods, the Madonie mountains and the coastline of Addaura. In each plant community, we investigated the relative effectiveness of myrmecochory, by experimentally offering elaiosome-bearing seeds of Viola odorata, Portulaca oleracea, Chelidonium majus and Borago officinalis and seeds of the same species deprived of their elaiosome. The ant species known to disperse seeds and fruits all belong to one of four subfamilies of the Formicidae: the Ponerinae, the Myrmicinae, the Dolichoderinae and the Formicinae (3). Species such Acantholepis nigra, Camponotus barbaricus, Camponotus ligniperda, Camponotus policornis ssp. siculus, Formica lugubris, Formica sanguinea, Lasius alienatus, Lasius niger, Lasius flavus and Plagiolepis pygmaea (Formicinae) are found throughout the Mediterranean region (4). Elaiosomes are found both in seed (e.g. in Ricinus communis, Viola odorata, Portulaca oleracea, Corydalis cava, Poligala vulgaris, Luzula campestris and Chelidonium majus) and in fruit (e.g. Borago officinalis and Lamium album) and appear in plants in no way systematically, so that in these cases we can talk about converging evolution (5, 6).

Myrmecochory is an almost worldwide phenomenon. Seed dispersal by ants is important to many species of plants, especially in eastern North America and Australia. Dispersion of seeds by ants happens in temperate and tropical areas but seems prevalent in dry areas such as Australia, the Sahel zone and South Africa; it is also often carried on by harvester ants, even though normally they kill the seeds. There is a general increase in ant-dispersed plant species from the poles to the equator that parallels the increasing diversity of ants across the same gradient. However, there may be a peak of abundance at the warm-temperate and Mediterranean midlatitudes (7).

1) S. N. Handel, A. J. Beattie (1990). La dispersione dei semi da parte delle formiche. Le Scienze 266, 60-67.

2) I. Li Vigni, B. Paternostro, V. Giusquiano (1999). Le strategie evolutive della dispersione mirmecocòra in Primula acaulis (L.) Hill (= P. vulgaris Huds.). 94° Congresso Soc. Bot. Italiana 122.

3) B. Holldobler, E. O. Wilson (1990). The ants. Harvard University Press, Cambridge, Massachusetts, USA 732 Pp.

4) C. Baroni Urbani (1971). Catalogo delle specie di Formicidae d’Italia. Memorie della Società Entomologica Italiana 50, 267-275.

5) A. J. Beattie (1985). The evolutionary ecology of ant-plant mutualisms. Cambridge University Press, Cambridge, UK 182 Pp.

6) I. Li Vigni, M. R. Melati (1999). Examples of seed dispersal by entomochory. Acta Bot. Gallica 146 (2). 145-156.

7) J. M. Herbers (1989). Community structure in north temperate ants: temporal and spatial variation. Oecologia 81, 201-211.