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Chironomids show a wide distribution and can occupy several habitats due to their high adaptive capacity in different freshwater environments. The genus Polypedilum is found along a wide elevational and environmental gradient in the neotropics, and its genetic variability could help to elucidate factors determining its distribution and tolerance to the environmental changes of different species or populations. This study examines the genetic variability of Polypedilum in an important biogeographic area that acts as a geographical barrier of biodiversity at the border of the Choco and Tumbes biomes. We identified five Polypedilum morphotypes using classic taxonomic methods. We examined 68 Polypedilum individuals from eight sampling sites in El Oro Province, Ecuador, analyzing the putative molecular species using the cytochrome c oxidase subunit 1 (CO1) mitochondrial gene fragment. Then, we calculated molecular diversity indices, Haplotype diversity (Hd), and θs and θπ estimators. Seven Polypedilum OTUs were determined from which a high molecular diversity was registered. A CCA was conducted to understand the population composition in relation to environmental characteristics. Results indicated that dissolved oxygen and temperature are the main environmental factors affecting Polypedilum distribution across elevational gradients and between basins.

Population growth and increasing production demands threaten the highly diverse Andean freshwater ecosystems. Biological indicators constitute a valuable tool for evaluating the ecological quality of freshwater ecosystems under different pressures. Diatom and macroinvertebrate assemblages are the most used bioindicators to assess water pollution, whereby these biotic groups occupy the first and second trophic levels and respond to habitat pollution. Several studies have explored the response of these communities to water pollution in other regions, but no studies have examined their performance in Andean rivers. In this context, this research aimed to evaluate the responses and relationships of both groups of bioindicators in the Upper Guayllabamba basin. We collected macroinvertebrate and diatom samples from nine sites in this basin during the dry and wet seasons, calculated trophic indices for both groups, and related them to environmental characteristics. The results indicated that both bioindicators were sensitive to changes in land use and nutrients. Epilithic diatoms were more sensitive to changes in water chemistry and macroinvertebrates to changes in fluvial habitat and land use. The index based on macroinvertebrates better-detected changes in quality classes between sites and seasons. Therefore, both indices gave complementary information, and their joint use seems suitable in Andean streams.