New insights into a life in current: do the gill lamellae of Epeorus assimilis and Iron alpicola larvae (Ephemeroptera: Heptageniidae) function as a sucker or as friction pads?

Abstract

Epeorus assimilis and Iron alpicola larvae inhabit swift running waters where they scrape algae from the stones. Previous authors suggested that the gill lamellae are modified to a sucker as an adaptation to withstand currents. Video observations show that the gill lamellae stay tilted in strong currents. Larvae can attach to the surface without any problem even if single gill lamellae are missing and therefore no negative pressure can be developed. Consequently, gill lamellae cannot have a sucker function. SEM analysis reveals areas with spike-shaped microtrichia on the abdominal sternites and setose pads ventrally on the gill lamellae. These setose pads look very similar to those described in some terrestrial insects. Setae of I. alpicola have a similar size, but a higher density than those of E. assimilis, what might cause a greater adhesive strength and could be an adaptation to the swifter currents in which the latter species lives.

Keywords:

• Ephemeroptera
• underwater attachment
• attachment devices
• sucker
• attachment pads
• flow velocity

Acknowledgements

We would like to thank Wilhelm Barthlott for support and helpful discussions. Bernd Mockenhaupt was a great help during the field work and provided technical assistance with the experimental flume. Zdravko Colic helped preparing animals for the SEM. Furthermore, we thank Stanislav Gorb for inspiring discussions. Our special thanks go to the Senckenberg Research Institute and Natural History Museum for making available exemplars of I. alpicola larvae. We also thank Janice Peters for kindly providing examples of Drunella doddsi. This work was financially supported by the Federal Ministry of Transport, Building and Urban Affairs.