The Relationship Between Body Size, Pupal Thoracic Horn Development and Dissolved Oxygen in Chironomini (Diptera: Chironomidae)

The area of the base of the thoracic horn (ring organ, RO) and abdomen length (ABD) of pupae were measured in different species of Chironomini (Diptera, Chironomidae). Ring organ/abdomen length ratio (ROA) and distances from the regression line (RROA) with ring organ as predictor and abdomen length as criterion were calculated to have less body size-dependent measures. RO was significantly correlated with ABD, Chironomus plumosus, C. riparius and Glyptotendipes pallens had the highest ROA, Microtendipes britteni, Paralauterborniella nigrohalteralis and Pseudochironomus prasinatus had the lowest ROA, some species (C. riparius, Cladopelma virescens and Einfeldia pagana) had a RO larger, whereas other species (M. britteni, P. prasinatus and Stenochironomus gibbus) had a RO value smaller than the one predicted by regression with ABD. ROA was significantly correlated with 25th percentile of dissolved oxygen (PCTL) experienced by the larvae, the species with the highest distance from the regression line of RO against PCTL were Pseudochironomus prasinatus with a RO lower than predicted and Lobochironomus dissidens with a RO higher than predicted. Hemoglobin concentration measured in 6 species was not correlated with ABD and RO, an high hemoglobin content was measured both in small species with a small RO (Polypedilum nubeculosum) and in large species with a large RO (Glyptotendipes pallens). The ring organ is proposed as a morphological trait useful to indicate oxygen concentration in the environment, even if other factors (e. g. hemoglobin in the larvae) surely affect the species ability to respond to oxygen shortage.JRC.H.5-Rural, water and ecosystem resource