We meet, we wiggle

[Thomas Daniel <danielt@u.washington.edu>]

Our speaker this week is Erica Goldman who will entertain us Wed and Fri
in 114 Kincaid Hall.


Please come, bring a friend, and enjoy







Material properties shape dynamical responses of hydrozoan jellyfish

        Radially symmetrical and composed of acellular mesoglea, two
cell
layers, and a primitive nervous system, jellyfish are an elegantly
simple
launching point to investigate how material properties of the
musculoskeletal system shape the dynamics of locomotion.  Mesoglea,
composed of mucopolysaccharides, collagen, and water, has a
characteristic
nonlinear response to an applied strain.  This study asks how such
nonlinearities determine the dynamical response of a jellyfish's simple
geometry subject to periodic forcing.  I compare the strain-dependent
stiffness of mesoglea between three species of jellyfish, Mitrocoma
cellularia, Polyorchis penicillatus, and Aequorea victoria, each with a
distinctive overall shape. Because of the nonlinear and time-dependent
behavior of mesoglea, I measure the complex modulus by recording its
stress in response to sinusoidal strains at a variety of frequencies and

mean lengths. Surprisingly, data from two summers show that there are no

mechanical differences between the mesoglea of Polyorchis, Mitrocoma,
and
Aequorea.  Thus, interspecific variation in overall swimming dynamic
must
emerge at a level higher than the material properties of the mesoglea,
implicating the importance of geometry and material allocation in
swimming.

        Using a simple power law to fit the resultant relationships
between complex modulus and mean length, I describe the strength of
nonlinearity in mesoglea by the size of the exponent.  Armed with these
estimates, I use a simple dynamical model to show that a nonlinear
stiffness term can manifest as significant changes in the shape,
position,
amplitude, and transient duration of the spectral responses of the
musculoskeletal system to periodic forcing.