Distributional patterns of freshwater ascomycetes communities along an Andes to Amazon elevational gradient in Peru

Abstract

Freshwater ascomycetes are the predominant fungal colonizers of ligno-cellulosic substrates submerged in freshwater habitats. Although considered important decomposers and a food resource in freshwater food webs, little is known about the influence of environmental factors on their geographical distribution patterns, species richness and community structure. We undertook a study of the distribution of freshwater lignolytic ascomycetes in the Madre de Dios River basin in Peru along an elevational gradient from the headwater regions dominated by the Inambari and Araza Rivers to the lowlands of the Madre de Dios River. The gradient extended from 218 to 3870 m; collections were made at low ( 1000 m) elevations. Three separate collecting trips were conducted during the dry seasons over 3 years. Samples of submerged woody debris were returned to the University of Illinois where they were incubated in moist chambers and examined for the presence of sexual and asexual reproductive structures, which were used for identification. GPS location, altitude, water temperature and pH were measured at the time of collection. A total of 2187 vouchered fungal collections representing 268 fungal taxa were collected. One hundred and fifty-nine taxa were collected at low elevations, 201 at middle elevations and 56 at high elevations. Only 33 of 268 taxa occurred at all three elevational ranges. Canonical analyses of principal coordinates and Sorensons Similarity Index of species based on presence/absence data revealed different structuring of freshwater fungal communities at low, middle, and high elevations, indicating a change in species composition along the Andes to Amazon elevation gradient. Mantel’s tests demonstrated that beta diversity is strongly impacted by both elevation and pH as rapid taxonomic turnover was associated with both these factors. Of 140 species found in their sexual reproductive state, only ten occurred at all three elevational ranges. The most commonly occurring species was Annulatascus velatisporus, a species with a worldwide distribution. Of 128 taxa found in their asexual reproductive state, 23 occurred at all three elevational ranges. The most commonly collected species was Candelabrum broccchiatum, also a species with a worldwide distribution. Most of the taxa reported from Peru have been reported previously from Asian and/or Australian freshwater tropical habitats. One hundred and three species are new records for South America and 137 species are new records for Peru. About 80 species found in Peru have a pan-tropical distribution. Whether these distribution patterns exist due to vicariance or geodispersal remains to be determined. This study indicates that the composition of fungal communities in mountainous areas is influenced by elevation and has implications for the effects of global warming.