  We present a spectroscopic analysis of VLT/X-Shooter observations of six
O-type stars in the low-metallicity (Z ~ 1/7 Z\odot) galaxies IC 1613, WLM and
NGC 3109. The stellar and wind parameters of these sources allow us, for the
first time, to probe the mass-loss versus metallicity dependence of stellar
winds below that of the Small Magellanic Cloud (at Z ~ 1/5Z\odot) by means of a
modified wind momentum versus luminosity diagram. The wind strengths that we
obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not
agree with theoretical predictions. The objects in IC 1613 tend towards a
higher than expected mass-loss rate, but remain consistent with predictions
within their error bars. We discuss potential systematic uncertainties in the
mass-loss determinations to explain our results. However, if further
scrutinization of these findings point towards an intrinsic cause for this
unexpected sub-SMC mass-loss behavior, implications would include a higher than
anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity
environments, but a reduced number of long-duration gamma-ray bursts produced
through a single-star evolutionary channel.
