  The Born cross sections of the $e^{+}e^{-}\to\Sigma^{+}\bar{\Sigma}^{-}$ and
$e^{+}e^{-}\to\Sigma^{-}\bar{\Sigma}^{+}$ processes are determined with high
precision for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII
detector. Nonzero cross sections near threshold are observed. The resulting
ratio of effective form factors for the $\Sigma^{+}$ and $\Sigma^{-}$ is
consistent with 3, agreeing with the ratio of the incoherent sum of the squared
charges of the $\Sigma^{+}$ and $\Sigma^{-}$ valence quarks, but disagreeing
with various theoretical predictions. In addition, ratios of the $\Sigma^{+}$
electric and magnetic form factors, $|G_{E}/G_{M}|$, are obtained at three
center-of-mass energies through an analysis of the angular distributions. These
measurements, which are studied for the first time in the off-resonance region,
provide precision experimental input for understanding baryonic structure. The
observed novel features of the $\Sigma^{\pm}$ form factors require a new
theoretical description for the hyperons.
