More than just slippery: the impact of biofilm on the attachment of non-sessile freshwater mayfly larvae

Abstract

While terrestrial insects can usually attach directly to a substrate, for aquatic insects the situation is more complicated owing to the presence of a biofilm on the primary substrates. This important fact has been neither the subject of investigation nor commonly taken into account in the interpretation of functional aspects of attachment in mobile freshwater animals. In this study, we investigate the impact of a biofilm on the attachment of living mayfly larvae. We performed in vivo attachment experiments in a flow channel using different substrates with defined surface roughness. Additionally, we measured friction forces directly generated by dissected tarsal claws on the same substrates. On substrates with smooth or slightly rough surfaces, which have little or no surface irregularities large enough for the claws to grasp, the presence of a biofilm significantly increases the friction force of claws. Consequently, larvae can endure higher flow velocities on these smooth substrates. The opposite effect takes place on rough substrates, where the friction force of claws decreases in the presence of a biofilm. Consequently, a biofilm is a critical ecological structure for these larvae, and other aquatic organisms, not only as a food source but also as a factor influencing attachment ability.

Attachment to challenging substrates – fouling, roughness and limits of adhesion in the northern clingfish (Gobiesox maeandricus)

“…In our experiments, these fouled surfaces include both biofilm and periphyton. The resistance of these materials to deformation, characterized by Young's modulus of elasticity (E), has been measured as 100-500 kPa for algae, 50-2000 kPa for bacteria, <600 kPa for soft parts of a biofilm developed in drinking water (>0.5 μm height), and approximately 200 kPa for a freshwater biofilm (Abe et al, 2011;Ditsche et al, 2014;Francius et al, 2008). This range is encompassed by various preparations of agar and is indicative of the low stress needed to stretch or compress the soft biofilm (Nayar et al, 2012).…”

“…The deposition of EPS smooths rough surfaces by filling in the 'valleys', but the growth of macroalgae and the settlement of invertebrates increase surface roughness (Ditsche et al, 2014). Compared with the surface irregularities of the primary substrates, the surface irregularities caused by macroalgae can be considerably larger (Fig.…”

“…Epidermal papillae made of tiny hairlike rods, which are subdivided at the tips into tiny filaments, cover the margin of the disc and we expect they play a role in adhering to rough surfaces (Arita, 1962;Green and Barber, 1988). However, intertidal surfaces are not simply rough, they are fouled by microbes, algae and invertebrates, which change the original substrate by forming a surface with different frictional and adhesive properties (Denny and Gaines, 2007;Ditsche et al, 2014).…”

“…In addition, different species of macro-organisms can settle on substrates, adding to the heterogeneity of fouled surfaces (Donlan, 2002). Fouling influences surface properties such as roughness, material stiffness, wettability Attachment to challenging substrates -fouling, roughness and limits of adhesion in the northern clingfish (Gobiesox maeandricus) and surface chemistry, which can then affect adhesive strength and friction (Ditsche-Kuru et al, 2010;Ditsche et al, 2014;Scherge and Gorb, 2001). A biofilm can lead to an increase in attachment force in the face of biofouling or a decrease, depending on many different factors (Ditsche et al, 2014;Hadfield, 2011).…”

Functional morphology of suction discs and attachment performance of the Mediterranean medicinal leech (Hirudo verbanaCarena)

“…influences of metabolic rates and stress levels) perspectives. Furthermore, depth effects and the presence of biofilms on the test substrates may alter the attachment ability [37,41,42,48]. The relevance of the leech attachment system functioning as possible role model for novel biomimetic applications could then be evaluated.…”