On springtails (Hexapoda: Collembola): a morphofunctional study of the jumping apparatus

Abstract

Background Springtails (Hexapoda: Collembola) are tiny organisms that lead a hidden life, mostly occuring deep in the soil and on leaf litter. They have a variety of interesting body morphology patterns, the most famous of which is the catapult-like structure that enables them to jump and flee from predators. This highly specialized jumping apparatus consists of a mobile furca, which when at rest fits into a trigger, "the retinaculum" on the ventral side of the abdomen. Despite the many studies that have attempted to investigate the jumping apparatus, the actual mechanisms involved in the jump, for example the way in which the furca is released by the retinaculum, how and where the mechanisms of spring and hydrostatic pressure originate, are still not properly understood. The morphology of the jumping apparatus of Orchesella cincta was investigated in detail using confocal laser scanning microscopy and MicroCT techniques for 3D reconstruction. Results The morphology of O. cincta with both flexed and extended furca is analysed and described. The abdominal musculature involved in the jumping mechanism and relevant structures of the exoskeleton of retinaculum and furca are described in detail. With the data obtained in this study, hypotheses can be made about (1) where and how the spring and hydrostatic pressure mechanisms originate; (2) which muscles act on the extension and flexion of the furca; (3) which muscles act on the retinaculum and (4) how the retinaculum is released from the furca. Conclusions The comparative morphological study proved informative, and shows how springtail jumping involves mechanisms unique to this taxon. Hydrostatic pressure regulation possibly varies between animals with distinct segmentation, and those with fused segmentation. Interesting cuticular characters were revealed, such as basal plates and sclerites related to the construction of the spring mechanism. The present study establishes itself as a model option for future morphofunctional studies on springtail’s jumping. Analysis of videos and images using a high speed camera will be useful for understanding how the jump develops through take-off, aerial and landing phases.

On latches in biological systems: a comparative morphological and functional study of the retinaculum and the dens lock in Collembola

“…The spring mechanism in springtails includes a latching system in which the retinaculum is capable of actively holding the components of the spring (including the basal plates and sclerites) when it itself is latched on the dens lock, a region of the furca [ 32 ]. Both structures originate on the ventral surface of the abdomen, the retinaculum on the third and the furca on the fourth segment [ 5 , 16 , 17 , 29 , 32 , 41 ].…”

“…The spring mechanism in springtails includes a latching system in which the retinaculum is capable of actively holding the components of the spring (including the basal plates and sclerites) when it itself is latched on the dens lock, a region of the furca [ 32 ]. Both structures originate on the ventral surface of the abdomen, the retinaculum on the third and the furca on the fourth segment [ 5 , 16 , 17 , 29 , 32 , 41 ]. The retinaculum has been described as an abdominal structure with an unpaired proximal part known as the corpus tenaculi and a paired distal part known as the ramus, in which several teeth are present [ 5 , 20 , 29 , 32 ].…”

“…Both structures originate on the ventral surface of the abdomen, the retinaculum on the third and the furca on the fourth segment [ 5 , 16 , 17 , 29 , 32 , 41 ]. The retinaculum has been described as an abdominal structure with an unpaired proximal part known as the corpus tenaculi and a paired distal part known as the ramus, in which several teeth are present [ 5 , 20 , 29 , 32 ]. Although developments have been made into understanding the functioning of the retinaculum in Entomobryomorpha springtails [ 29 , 32 ], little is known about its architecture and functioning in representatives of other groups.…”

“…The retinaculum has been described as an abdominal structure with an unpaired proximal part known as the corpus tenaculi and a paired distal part known as the ramus, in which several teeth are present [ 5 , 20 , 29 , 32 ]. Although developments have been made into understanding the functioning of the retinaculum in Entomobryomorpha springtails [ 29 , 32 ], little is known about its architecture and functioning in representatives of other groups. According to Manton [ 29 ], the contraction of intersegmental longitudinal muscles could cause the segments to overlap, creating a hemolymphatic pump which could then act to (1) distend the retinaculum, and (2) confer force at the moment of the jump.…”

“…Eisenbeis & Ulmer [ 17 ] performed ectomy experiments (cutting off parts of the furca, legs, thorax and abdomen) to test the role of hemolymphatic pressure in jumping efficiency, concluding that the animal could still jump, but with some loss of efficiency. Oliveira [ 32 ], after carrying out a detailed comparative morphological study of the jumping apparatus of Orchesella cincta (Linnaeus, 1758) [ 26 ] in states of extended or flexed furca, rejected the hypothesis that hemolymphatic pressure acts on the functioning of the retinaculum since no evidence in support of it was found. He concluded that the distention of the retinaculum is made possible by muscle force alone.…”