Free-living freshwater nematodes from Brazil: checklist of genera and regional patterns of diversity

Summary Brazil has one of the largest varieties of aquatic ecosystems and rich freshwater biodiversity, but these components have constantly been damaged by the expansion of unsustainable activities. Free-living nematodes are an abundant and ubiquitous component of continental benthic communities, occurring in all freshwater habitats, including extreme environments. Despite this, hardly any studies have examined the generic composition of nematodes in different latitudes and the geographic overlap of assemblages. We provide data on nematode genera from six regions in Brazil, over a north-south gradient spanning about 4000 km, encompassing rivers, coastal lakes, and reservoirs with different levels of human impact. Interpolation/extrapolation curves were generated and the zeta diversity was used to assess the overlap of nematode assemblages. Freshwater nematode assemblages comprised 54 families and 132 genera. Mononchidae, Monhysteridae, Chromadoridae, Tobrilidae and Dorylaimidae were the most diverse families. Differences in diversity and high turnover of genera were found among regions, probably related to stochastic processes. Mononchus was the only widely distributed genus. Our results revealed a high biodiversity of free-living freshwater nematodes among the regions. The limited spatial coverage of the data reveals an enormous knowledge gap in a country with 12% of the world’s freshwater resources. The lack of spatial patterns, e.g., latitudinal variation, suggests that freshwater nematode assemblages are primarily structured by the intrinsic properties of habitats. This reinforces the uniqueness of freshwater ecosystems and suggests that the nematode assemblages may be sensitive to environmental disturbances, since the limited distributions of taxa may lead to lower resilience.

Freshwater nematodes as bioindicators in field studies - the NemaSPEAR[%]-index.

This chapter, after a general introduction to quality assessments of freshwater habitats, reviews the use of freshwater nematodes as in situ bioindicators, including in monitoring the ecological quality of freshwater habitats. By drawing on studies of nematode communities in unpolluted and polluted habitats as examples, it highlights both the different methods used to assess the quality of freshwater ecosystems and their applications. A focus of the chapter is the development of a new index that uses freshwater nematodes to assess chemically induced changes in the ecological status of freshwater habitats, the NemaSPEAR[%]-index (Nematode SPEcies At Risk).

Freshwater nematodes in metacommunity studies.

This chapter discusses the application of the metacommunity concept to data on freshwater nematodes. First, the theoretical concepts, terminology, and methods used in metacommunity analyses are introduced. Second, metacommunity studies of freshwater nematodes are summarized and the results are compared with those obtained from studies of other organismal groups. Finally, research gaps in metacommunity ecology in general and freshwater nematodes in particular are highlighted.

Introduction to freshwater nematodes in ecology: current knowledge and research.

This chapter provides information on nematode morphology and reproduction; role of nematodes in freshwater ecosystems; and distribution and dispersal of free-living nematodes and their role in food webs.

Sampling and processing of freshwater nematodes with emphasis on molecular methods.

This chapter provides an introduction to current methods of nematode sampling and processing, with the latter including molecular methods as well. It highlights that nematode sampling and processing for different habitats will require different sampling methods; nematode identification can be achieved with morphological or molecular approaches; the analysis of specific gene fragments can be used to delimitate nematode species; and molecular species identification can give further information about phylogenetic background and cryptic species.

Production of freshwater nematodes.

This chapter focuses on the methods used to determine freshwater nematode production. It begins by briefly describing the methods used in sampling and measuring nematodes, followed by a summary of the common allometric models developed to estimate secondary production. It then presents a case study in which the results of those models are compared. Finally, it evaluates the drivers of nematode production in different lakes and streams and compares nematode secondary production with that achieved by macrobenthos, other meiobenthic taxa and microbes.

Ecology of freshwater nematodes

This book, with its 12 chapters, not only encourages all ecologists to consider free-living nematodes as a model organism in their investigations, but also shows how important it is to study the fundamentals of ecology, for example, the distribution and diversity of a group of organisms as well as the interactions of those organisms with others. Detailed studies of this type will ultimately provide a better understanding of food webs, their role in the respective habitat, and the changes therein caused by human activities. In this context, research during the past 20 years has determined that, in addition to aquatic environments, nematodes are good indicators of sediment and soil quality. This book takes into account much of the recent research on the ecology of freshwater nematodes. It contains many new chapters as well as revisions and updates of the chapters of the 2006 book. The objective was to write a comprehensive yet readable guide for interested biologists, from students to career scientists.

Morphological differences between free-living soil and freshwater nematodes in relation to their environments

Summary There is no single feature to distinguish free-living soil nematodes from freshwater nematodes, also because all free-living nematodes are essentially aquatic. This notwithstanding, by examining the frequencies of some characters of 1141 European species, differences of qualitative/quantitative characters between soil and freshwater nematodes were found. In particular, aquatic and semi-aquatic species are, on average, longer and slimmer than soil species, have a longer tail, greater body weight, smooth cuticle and larger amphids. A new body parameter, length of the pharynx in relation to the length of the whole digestive tract (e), was also taken into consideration.

The early catfish catches the worm: predation of Corydoras aeneus (Siluriformes, Callichthyidae) on freshwater nematodes

In this study, we measured the daily consumption of four different nematode species by a small freshwater catfish species, Corydoras aeneus (Gill, 1858). Consumption of nematodes by fishes was significant with a single C. aeneus individual being able to consume in 24 h between 40 581 and 75 849 adult nematodes depending on the nematode species offered. This represented the ingestion of up to 238 mg wet weight when considering the largest nematode species: Panagrellus redivivus. Our results strengthen the growing evidence of a significant trophic channel existing between meiobenthic invertebrates like nematodes and small bottom-feeding fishes like C. aeneus. We also discuss the relevance of using P. redivivus as live food for rearing C. aeneus which is a popular ornamental fish.