111.1 The Motion-Sensing Hairs of Arthropods:
Using Physics to Understand Sensory Ecology
and Adaptive Evolution
J. A. C. Humphrey\ F. G. Barth 2 and K. Voss 3
1 Department of Mechanical and Aerospace Engineering, University of Virginia,
Charlottesville, Virginia 22904, USA
2 Biocenter, Zoology Institute, Vienna University, Althanstr. 14, 1090 Vienna,
Austria
3 Department of Mathematics, College of Arts and Sciences, Bucknell University,
Lewisburg, Pennsylvania 17837, USA
Abstract.
In an effort to understand the "design" principles of arthropod filiform hairs, it is
desirable to explain the effects that ecology and, therefore, natural selective
pressures may have had on the adaptive evolution of these medium motion sensors
in terrestrial and aquatic habitats, respectively. This is a complex interdisciplinary
problem involving various facets of biology, mechanics, and mathematics. Using a
simplified, physically approximate theoretical analysis, the present work places on
a more general foundation the understanding of the observed variations of the
maximum angular deflection and maximum angular velocity, and their respective
resonance frequencies, of filiform hairs as a function of the physical parameters
that affect these four quantities. Calculated results obtained using the approximate
analysis are compared with corresponding results from a more exact physical
analysis and with previous measurements and calculations to show that all
qualitative aspects of hair behavior are correctly captured by the simplified theory.
The theory is then used to explain the dependence of hair motion on the physical
parameters that affect it, and to explore the sensitivity of hair motion to small
changes in these parameters.
Key words Trichobothria, viscosity, inertia, sensory ecology, modeling
1 Introduction
1.1 Purpose and Background of This Study
Among the many types of mechanoreceptive cuticular hairs of arthropods, the
filiform hairs of insects and the analogous trichobothria of the arachnids are the
most spectacular ones regarding the sensitivity of their response to the slightest
movement of air (Shimozawa and Kanou 1984; Barth et al. 1993). In a series of
Using Physics to Understand Sensory Ecology
and Adaptive Evolution
J. A. C. Humphrey\ F. G. Barth 2 and K. Voss 3
1 Department of Mechanical and Aerospace Engineering, University of Virginia,
Charlottesville, Virginia 22904, USA
2 Biocenter, Zoology Institute, Vienna University, Althanstr. 14, 1090 Vienna,
Austria
3 Department of Mathematics, College of Arts and Sciences, Bucknell University,
Lewisburg, Pennsylvania 17837, USA
Abstract.
In an effort to understand the "design" principles of arthropod filiform hairs, it is
desirable to explain the effects that ecology and, therefore, natural selective
pressures may have had on the adaptive evolution of these medium motion sensors
in terrestrial and aquatic habitats, respectively. This is a complex interdisciplinary
problem involving various facets of biology, mechanics, and mathematics. Using a
simplified, physically approximate theoretical analysis, the present work places on
a more general foundation the understanding of the observed variations of the
maximum angular deflection and maximum angular velocity, and their respective
resonance frequencies, of filiform hairs as a function of the physical parameters
that affect these four quantities. Calculated results obtained using the approximate
analysis are compared with corresponding results from a more exact physical
analysis and with previous measurements and calculations to show that all
qualitative aspects of hair behavior are correctly captured by the simplified theory.
The theory is then used to explain the dependence of hair motion on the physical
parameters that affect it, and to explore the sensitivity of hair motion to small
changes in these parameters.
Key words Trichobothria, viscosity, inertia, sensory ecology, modeling
1 Introduction
1.1 Purpose and Background of This Study
Among the many types of mechanoreceptive cuticular hairs of arthropods, the
filiform hairs of insects and the analogous trichobothria of the arachnids are the
most spectacular ones regarding the sensitivity of their response to the slightest
movement of air (Shimozawa and Kanou 1984; Barth et al. 1993). In a series of