Diet and functional feeding groups of Chironomidae (Diptera) in Alpine freshwater habitats

Abstract

A gut content analysis (GCA) was performed to quantify the relative use of food resources by larvae of chironomids (Diptera: Chironomidae) inhabiting different Alpine freshwater habitats fed by meltwater (kryal), groundwater (krenal) and mixed waters (glacio-rhithral, proglacial pond) in the Italian Alps (Trentino). GCA was performed on the 13 most frequent and abundant taxa in these habitats: Diamesa bertrami, Diamesa latitarsis, Diamesa steinboecki, Diamesa zernyi, Pseudokiefferiella parva, Eukiefferiella minor, Metriocnemus eurynotus gr., Parametriocnemus stylatus, Thienemanniella clavicornis, Tvetenia calvescens, Macropelopia sp., Zavrelimyia sp., Micropsectra atrofasciata gr. Guts were removed, mounted in Canada Balsam, and examined under a microscope (1000x). The gut of each individual was assumed to be 100% full, and proportions of the different food items were estimated using a 10x10 grid designed with the NIS-BR software. Food items were divided into 10 categories: Mineral Material, Animal Tissue, Algae (except diatoms), Diatoms, Plant tissue, Amorphous detritus, Lichens, Bryophytes, Fungi, and Pollen. The gut content of different taxa contained significantly different (p < 0.05) food categories based on a non-parametric statistical test. Differences in the diet were observed between species living in the same habitat type and classified into the same trophic category (detritivores, grazers, or predators) and individuals belonging to the same species living in different habitat types. A certain trophic flexibility and omnivory was found, which may facilitate the adaptation of chironomids to changes in available resources due to glacier retreat.