How temperature influences the viscosity of hornworm hemolymph

Abstract

Hemolymph is responsible for the transport of nutrients and metabolic waste within the insect circulatory system. Circulation of hemolymph is governed by viscosity, a physical property, which is well known to be influenced by temperature. However, the effect of temperature on hemolymph viscosity is unknown. We used larvae to measure hemolymph viscosity across a range of physiologically relevant temperatures. Measurements were taken from 0 to 45°C using a cone and plate viscometer in a sealed environmental chamber. Hemolymph viscosity decreased with increasing temperature, showing a 6.4-fold change (11.08 to 1.74 cP) across the temperature range. Viscosity values exhibited two behaviors, changing rapidly from 0 to 15°C and slowly from 17.5 to 45°C. To test the effects of large particulates (e.g. cells) on viscosity, we also tested hemolymph plasma alone. Plasma viscosity also decreased as temperature increased, but did not exhibit two slope regimes, suggesting that particulates strongly influence low-temperature shifts in viscosity values. These results suggest that as environmental temperatures decrease, insects experience dramatic changes in hemolymph viscosity, leading to altered circulatory flows or increased energetic input to maintain similar flows. Such physical effects represent a previously unrecognized factor in the thermal biology of insects.

Physiological responses to gravity in an insect

“…However, we can assess whether it is likely that these pressure gradients could result from viscous loss associated with hemolymph flow using Hagen-Poiseuille theory. The pressure drop due to viscosity in a pipe is Δp = 8πμvL A , where μ is dynamic viscosity (taken as 2.3 cP [15]), v is average flow speed, L is the length of a theoretical pipe between thorax and abdomen (taken as 1.5 cm), and A is cross-sectional area of that pipe. To estimate the area, we consider a cylindrical grasshopper with a 5-mm radius, which would have a cross-sectional area of 79 mm 2 .…”

“…To test the role of gravity in causing hemolymph pressure changes with alterations in body orientation, we compared our measured pressures to calculated expected values based on the change in fluid height above the sensor after orientation changes, using P = ρgh, where P is pressure, ρ is hemolymph density (using the value reported for Manduca sexta larvae, 1.02 ± 0.03 g•mL −1 [15]), g is gravitational acceleration (9.81 m•s −2 ), and h is height (SI Appendix, Fig. S5).…”

Sperm transfer through hyper-elongated beetle penises – morphology and theoretical approaches

“…For a more accurate estimation, the physical properties of the sperm and the inner surface of the flagellum from variable species ideally need to be characterized. In a few recent studies, the viscosity of small volumes of liquids from small insects was successfully measured (for feet secretions 47 and hemolymph 48 ). Although the semen is a mixture of liquids and movable spermatozoa, the methods used in those studies could also be applied to measure the properties of the semen.…”

Fluid mechanics and rheology of the jumping spider body fluid

“…Anti-coagulants were not used as they could affect the physical properties. 26 The hemolymph was kept cool to slow down any biochemical reactions. Before experiments, it was warmed up to room temperature by hand.…”

“…Additionally, a decrease in temperature could cause reduced deformability of the hemolymph cells. 26 All of these Fig. 2 Femur-patella cross-sectional X-ray scan images.…”