Factors Controlling Morphotaxa Distributions of Diptera Chironomidae in Freshwaters

Response of Chironomids (Diptera, Chironomidae) to Environmental Factors at Different Spatial Scales

Factors responsible for species distribution of benthic macroinvertebrates, including responses at different spatial scales, have been previously investigated. The aim of the present research was to review the most relevant factors explaining chironomid species distribution focusing on factors operating at different spatial scales, such as latitude, longitude, altitude, substrate, salinity, water temperature, current velocity, conductivity, acidity, dissolved oxygen, nutrient content etc. acting at regional levels and at a large or small water basin level. Data including chironomid species abundances from different lentic and lotic waters in Italy and other surrounding countries were analyzed using partial canonical correspondence analysis (pCCA) and multiple discriminant analysis (DISCR). Spatial analyses, including univariate Moran's I correlograms, multivariate Mantel correlograms and Moran's eigenvector maps (MEMs), were thereafter carried out. The results showed that habitat type, including different types of lotic waters (i.e., kryal, crenal, rhithral, potamal) and different lake types (i.e., littoral, sublittoral, profundal zones), is the most significant factor separating chironomid assemblages, while spatial factors act only as indirect influencers.

Response of Chironomids to Key Environmental Factors: Perspective for Biomonitoring

Chironomids are the species-richest family among macroinvertebrates and are often used as indicators of ecological conditions in inland waters. High taxonomic expertise is needed for identification and new species are still being described even in the well-known West Palearctic region. Our Microsoft Access relational database comprises data on Chironomid species collected in rivers and lakes in Italy and some other European countries over a period of about 50 years, often associated with physical-chemical data, but in some cases, only data on Chironomids are available with no associated environmental data. The aim of the present paper was to propose the calculation of ecological traits of Chironomid species as a tool to derive information on water quality, when only data on Chironomid species composition are present, while environmental data are lacking. Traits summarizing the species' response to environmental variables were evaluated, with emphasis on natural and man-influenced factors: current velocity, water temperature, conductivity, dissolved oxygen, and nutrients. Traits calculations were carried out in the R environment using a subset of our data, including both environmental data and Chironomid abundances. The relations between sites, Chironomid, species and traits were evaluated using correspondence analysis and other multivariate methods. The response of species showed an interaction among different factors, with the possibility of ordering species along a single environmental gradient, extending from cold running waters to warm standing waters, with few exceptions.

Genetic Variability of Polypedilum (Diptera: Chironomidae) from Southwest Ecuador

Simple Summary

Polypedilum is a genus of aquatic non-biting midges in the family Chironomidae. This genus is widely distributed in neotropical rivers from lowlands to Andean highlands. Nevertheless, making species identification based on morphology is quite complex, even more so in the Neotropics, since systematic studies of this group are scarce. DNA barcoding can help to overcome this problem using a short DNA sequence as a barcode for species delimitation. A fragment of the mitochondrial gene cytochrome c oxidase I (CO1) has been successfully employed as a barcode in the genus Polypedilum. In this study, our aim was to understand the effect of environmental characteristics on Polypedilum diversity and distribution. We examined the CO1 sequence of 68 Polypedilum specimens from rivers with different environmental conditions located in an important biogeographic area of Ecuador. We identified five morphotypes and seven putative species which revealed high genetic variability among them. Polypedilum distribution seems to be affected mainly by two environmental factors, dissolved oxygen, and temperature. Our study is the first evidence of richness within the genus in Ecuador, highlighting the importance of developing taxonomic studies along with ecological assessments to further describe and identify new species.

Abstract

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.