Hybridizations and fruit geography of Solanum jamesii

Premise: Plant domestication can be detected when transport, use and
manipulation of propagules impact reproductive functionality, especially
in species with self-incompatible breeding systems. Methods: Evidence for
human-caused founder effect in the Four Corners potato (Solanum jamesii
Torr.) was examined by conducting 526 controlled matings between
archaeological and non-archaeological populations from field-collected
tubers grown in a greenhouse.  Specimens from 24 major herbaria,
along with collection records from >160 populations were examined
to determine which produced fruits. Results: Archaeological populations
did not produce any fruits when self-crossed or out-crossed between
individuals from the same source.  A weak ability to self- or
out-cross within populations was observed in non-archaeological
populations.  Out-crossing between archaeological and
non-archaeological populations, however, produced fully formed,
seed-containing fruits, especially with a non-archaeological pollen
source.  Fruit formation was observed in 51 of 162 occurrences,
with minimal evidence of constraint by monsoonal drought, lack of
pollinators, or spatial separation of suitable partners.  Some
archaeological populations (especially those along ancient trade routes)
had records of fruit production (Chaco Canyon) while others (those in
northern Arizona, western Colorado, and southern Utah) did not. 
Conclusions: The present study suggests that archaeological populations
could have different origins at different times – some descending directly
from large genepools to the south and others derived from gardens already
established around occupations.  The latter experienced a chain
of founder events, which presumably would further reduce genetic diversity
and mating capability.  Consequently, some archaeological
populations lack the genetic ability to sexually reproduce, likely as the
result of human-caused founder effect.