Juvenile Desoria gracilliseta (Collembola, Isotomidae) with four anal spines

Abstract

Desoria gracilliseta colonizes a fruticose lichen, Cladonia sp., in a snowy habitat in Hokkaido, Japan. Juveniles appear in October, continue to develop under snow, and mature in May. Recent surveys from mid-September to mid-October revealed the presence of a Tetracanthura-like collembolan, in addition to D. gracilliseta juveniles. Body lengths of the Tetracanthura-like collembolan remained consistent throughout the duration of the surveys averaging 0.49 mm, whereas D. gracilliseta juveniles grew steadily from 0.54 mm to 0.8 mm. Both forms were almost indistinguishable except that the Tetracanthura-like collembolan had four anal spines on abdominal segment VI and short spines on the head and thorax segment II. Large individuals distinctive of D. gracilliseta collected in March were also included for comparisons in morphology and DNA sequences. Antennal segment IV and the furca developed with increasing body length. DNA barcode analysis, using mitochondrial cytochrome c oxidase subunit 1 and 16S ribosomal RNA genes confirmed the genetic identities of the Tetracanthura-like collembolan, and juveniles and subadults of D. gracilliseta to be D. gracilliseta. The significance of morphological changes in D. gracilliseta was discussed in terms of survival strategy against predation.