The relationship between nucleolar organizer size and growth in Chironomus riparius larvae (Diptera:Chironomidae)

• Published in: Freshwater science Vol. 32; no. 3; pp. 922 - 932
• Main Authors: Martin, Joshua P., Wytrykush, Carla M., Ciborowski, Jan J. H.
• Format: Journal Article
• Language: English
• Published: North American Benthological Society 01.09.2013; The University of Chicago Press
• Subjects: biomarker; Chironomidae; Chironomus riparius; chromosome; Freshwater; growth; nucleolar organizer region; polytene; puff; Chironomidae; puff; nucleolar organizer region; polytene; chromosome; growth; biomarker
• ISSN: 2161-9549; 2161-9565
• DOI: 10.1899/12-168.1

Chironomid larvae possess giant polytene chromosomes. When genes on these chromosomes undergo transcription, they are visible as puffs. The nucleolar organizer region (NOR), visible as an especially large puff, shrinks when a larva is at particular developmental stages or is subjected to chemical stress. However, whether reduced NOR size is indicative of reduced growth is unknown. Therefore, we conducted 2 experiments to examine the relationship between NOR size and chironomid growth under controlled laboratory conditions. In the 1st experiment, we quantified the effect of ration quality on larval growth and NOR size. In the 2nd, we determined whether NOR size varied as a function of recent growth, independently of larval size. The combined results demonstrated that NOR size varied as a function of prepupal development and was positively correlated with a chironomid's most recent growth rate, independently of its biomass. The finding that NOR size is related to growth validates its use as a biomarker of sublethal stress. NOR size also has potential value as a measure of instantaneous growth state of field-collected larvae and, thus, may provide a surrogate measure useful for estimating secondary production in natural populations.