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.

Haemodynamic mechanism of dissipation of muscular energy in hovering hawkmoths (Sphingidae)

“…To validate the MRS data, we measured plasma viscosity of M. sexta larvae at room temperature ( T = 23 o C). The MRS-obtained viscosity η = 1.66 ± 0.37 mPa ⋅ s matched that of [32 ], η = 1.6 -1.9 mPa ⋅ s. In our dataset [16 ,31 ], M. rustica was the largest species; its viscosity was less than that of mid-sized hawkmoths.…”

Haemodynamic mechanism of dissipation of muscular energy in hovering hawkmoths (Sphingidae)

“…To validate the MRS data, we measured plasma viscosity of M. sexta larvae at room temperature ( T = 23 o C). The MRS-obtained viscosity η = 1.66 ± 0.37 mPa ⋅ s matched that of [32 ], η = 1.6 -1.9 mPa ⋅ s. In our dataset [16 ,31 ], M. rustica was the largest species; its viscosity was less than that of mid-sized hawkmoths.…”

The sex of organ geometry

“…We suggest that trachea maintain (or, when required, change) the 3D configuration of organs to enable or constrain paracrine and/or contact-based exchange of peptide 'hormones', metabolites and/or mechanical cues in or between them. If secreted, signals could be confined spatially by the fact that adult haemolymph is very viscous and, in some areas of the body cavity, must pass through very narrow spaces between organs [53][54][55] , potentially rendering insect circulation less 'open' than once thought, at least in adults. Proximity-enabled, spatially confined communication could help explain paradoxes which have emerged from the study of 'systemic' signals.…”

Haemolymph viscosity in hawkmoths and its implications for hovering flight

“…Haemolymph characteristics associated with metamorphosis reflect responses to different selection pressures. The hawkmoth M. sexta , for instance, experiences a marked reduction in haemocyte numbers from larva to adult [6,7], beginning in the final-instar larva [71]. Larvae experience intense selection pressure from wounding by parasitoids and predators and from ingested pathogens, and the immune response is mediated by haemocytes [72].…”

Haemodynamic mechanism of dissipation of muscular energy in hovering hawkmoths (Sphingidae)

“…To validate the MRS data, we measured plasma viscosity of M. sexta larvae at room temperature ( T = 23 o C). The MRS-obtained viscosity η = 1.66 ± 0.37 mPa ⋅ s matched that of [32 ], η = 1.6 -1.9 mPa ⋅ s. In our dataset [16 ,31 ], M. rustica was the largest species; its viscosity was less than that of mid-sized hawkmoths.…”

The sex of organ geometry

“…We suggest that trachea maintain (or, when required, change) the 3D configuration of organs to enable or constrain paracrine and/or contact-based exchange of peptide 'hormones', metabolites and/or mechanical cues in or between them. If secreted, signals could be confined spatially by the fact that adult haemolymph is very viscous and, in some areas of the body cavity, must pass through very narrow spaces between organs [53][54][55] , potentially rendering insect circulation less 'open' than once thought, at least in adults. Proximity-enabled, spatially confined communication could help explain paradoxes which have emerged from the study of 'systemic' signals.…”

Haemolymph viscosity in hawkmoths and its implications for hovering flight

“…Haemolymph characteristics associated with metamorphosis reflect responses to different selection pressures. The hawkmoth M. sexta , for instance, experiences a marked reduction in haemocyte numbers from larva to adult [6,7], beginning in the final-instar larva [71]. Larvae experience intense selection pressure from wounding by parasitoids and predators and from ingested pathogens, and the immune response is mediated by haemocytes [72].…”

Haemodynamic mechanism of dissipation of muscular energy in hovering hawkmoths (Sphingidae)

“…To validate the MRS data, we measured plasma viscosity of M. sexta larvae at room temperature ( T = 23 o C). The MRS-obtained viscosity η = 1.66 ± 0.37 mPa ⋅ s matched that of [32 ], η = 1.6 -1.9 mPa ⋅ s. In our dataset [16 ,31 ], M. rustica was the largest species; its viscosity was less than that of mid-sized hawkmoths.…”

The sex of organ geometry

“…We suggest that trachea maintain (or, when required, change) the 3D configuration of organs to enable or constrain paracrine and/or contact-based exchange of peptide 'hormones', metabolites and/or mechanical cues in or between them. If secreted, signals could be confined spatially by the fact that adult haemolymph is very viscous and, in some areas of the body cavity, must pass through very narrow spaces between organs [53][54][55] , potentially rendering insect circulation less 'open' than once thought, at least in adults. Proximity-enabled, spatially confined communication could help explain paradoxes which have emerged from the study of 'systemic' signals.…”

Haemolymph viscosity in hawkmoths and its implications for hovering flight

“…Haemolymph characteristics associated with metamorphosis reflect responses to different selection pressures. The hawkmoth M. sexta , for instance, experiences a marked reduction in haemocyte numbers from larva to adult [6,7], beginning in the final-instar larva [71]. Larvae experience intense selection pressure from wounding by parasitoids and predators and from ingested pathogens, and the immune response is mediated by haemocytes [72].…”