**4. The expedition to Galápagos in the search of yeasts**

Beetles species are relatively more abundant, occurring in all the vegetation zones. Some of them are found around flowers of cacti, *Ipomoea* sp., *Datura* sp., and a number of other plant

Additionally there is a number of introduced species of insects such as cockroaches*, Drosophi‐ la* sp, ants and flies, among the most conspicuous. The changes in the insect biota composition in the islands occurred with the introduction of foreign species by aboriginal peoples and later by colonization activities of Europeans [11]. These insects also play a fairly important role in

The Galápagos Islands represent a strategic geographic zone in the planet to carry out studies on biodiversity, speciation, adaptation, ecology and dispersion of species belonging to different kingdoms. In an attempt to explain the current biogeography of the islands, a number

It is well known that the islands geological origin is oceanic, while the origin of its biota is continental [15]. The studies on the Galapagos Islands' biogeography and evolution were predominantly (if not exclusively) focused on macro organisms: there is a marked shortfall in the knowledge of microbial populations, communities and biodiversity in the Galapagos

Standard biogeographic tracks link the archipelago of Galápagos with Central America, western North and South America, the Caribbean, Asia and Australasia [14]. The Galápagos Islands community characteristics share the common features of the biota occurring in oceanic

The archipelago of Galápagos is composed by oceanic islands where the terrestrial colonists such as plants, animals, and part of the microorganisms, should have crossed an oceanic barrier to reach the land. It means that the origin of the biota in this group of islands is entirely explained by the dispersal with no vicariant component, since the islands were never con‐ nected to the mainland by any land bridge or island chain [14]. Furthermore, since the Galápagos Islands are separated from the centers of origin of species in the mainland, there

The colonization of the varied environments within the islands by yeast species must be primarily explained by the occurrence of colonizing terrestrial species of plants and animals that arrived to the islands as a sweepstake along the natural history of the archipelago. The sea water and marine fauna must have been other sources of colonizing yeasts species. Finally, the yeasts flora inhabiting the gut of insects associated to plants as well as birds and terrestrial

Undoubtedly the strong association of plants and microorganisms must be regarded as a dispersion factor for microorganisms, including yeasts in the Galápagos. In 1976 [18] deter‐

vertebrates must have completed the cast of yeast diversity in the Islands.

of studies have been done since the Darwin's times in the 19th Century [12-14].

species. It has been reported a number of about 200 beetles species [10].

dispersion and introduction of yeast species into the islands.

islands such as: disharmony, endemism and relictualism [16].

are abundant "empty" ecological niche spaces [17].

**3. On the Galápagos biogeography**

198 Biodiversity - The Dynamic Balance of the Planet

Islands.

In the past, the studies of microorganisms in the Galápagos Islands were focused on topics such as the bacterial dynamics around the islands [19] some studies referring to entomogenous fungi found in the Galápagos Islands [20]; and probably some other works devoted to punctual groups of moulds, etc.

To the best of our knowledge there is not any yeast collection from the Galápagos Islands or any other study involving yeasts in the past. Based upon this, we can say that this is likely the first study focused on the biodiversity of yeasts carried out in this zone of the planet.

The yeast biodiversity in four populated islands is the first approach that we've done in order to try shortening the lack of previous knowledge of the yeasts biodiversity in this archipelago. Nevertheless it is to say that inhabited islands' environments present certain degrees of disturb and where human mediated introduction of certain yeast species is a real issue. The islands herein reported as the localities for our collections were explored for logistical reasons, since those islands that are mostly pristine, represent a major logistic challenge that could be faced in future expeditions.

There's interesting islands to be explored in future works, such as Española, Pinta, Genovesa, Marchena, etc. Additionally there are rock shelters that could be explored in the search of substrates for yeasts isolation. In these environments no fresh water is available, moreover, most of these islets or rocks are inaccessible since their precipitous cliffs, rising directly out of the water present hazards to landing that almost no one has attempted to collect any living organism from those inaccessible and still pristine environments [3].

In this expedition we were able to focus our attention in collecting yeasts from several substrates, so we can draw a general overview of the yeasts biodiversity in the islands. Nevertheless, there is still much work to be done in future expedition in order to refine the current data of the yeasts biodiversity in the archipelago, since it is one of the still unexplored regions in the planet [21].
