Distance-dependence seed set of Vasconcellea chilensis

Plant reproductive failure is a critical concern for conserving rare and
endangered species that typically have low-density and sparse populations.
One important factor contributing to reproductive failure is the spatial
arrangement of plants within a population, which can lead to isolation and
negatively affect seed output, particularly in obligate outcrosses.
Additionally, this effect can be compounded by plant size. Here, we
investigate how plants' spatial distribution and size influence the
reproductive success of Vasconcellea chilensis, a threatened
papaya species from northern Chile. Using flower exclusion
experiments, we first examined whether V. chilensis can produce seeds via
apomixis. We then used Spatial Point Pattern Analysis (SPPA) in three
populations to examine the spatial arrangement of plants in three
populations, and, finally, we assessed whether plant size and mate
distance influence the reproductive success of this plant species. V.
chilensis is a dioecious shrub unable to produce fruits through apomixis.
The SPPA revealed significant clustering of female and male plants at
different spatial scales, indicating a non-random distribution. Moreover,
a significant attraction between the sexes suggested a preference for
proximity. In two populations, closer proximity to male plants was linked
to higher seed production. Our study revealed that the absence of
apomixis in V. chilensis makes it prone to experiencing distance-dependent
reproductive failure. In particular, the seed set was compromised in
female plants isolated from male neighbors. This link between isolation
and seed production was especially significant in the driest site, and we
discussed how environmental factors can exacerbate this effect.