  We present the first three-dimensional hybrid simulations of the evolution of
ion-scale current sheets, with an investigation of the role of temperature
anisotropy and associated kinetic instabilities on the growth of the tearing
instability and particle heating. We confirm the ability of the ion cyclotron
and firehose instabilities to enhance or suppress reconnection, respectively.
The simulations demonstrate the emergence of persistent three-dimensional
structures, including patchy reconnection sites and the fast growth of a
narrow-band drift-kink instability, which suppresses reconnection for thin
current sheets with weak guide fields. Potential observational signatures of
the three-dimensional evolution of solar wind current sheets are also
discussed. We conclude that kinetic instabilities, arising from non-Maxwellian
ion populations, are significant to the evolution of three-dimensional current
sheets, and two-dimensional studies of heating rates by reconnection may
therefore over-estimate the ability of thin, ion-scale current sheets to heat
the solar wind by reconnection.
