Strategic Selfing as Reproductive Assurance in Response to Pollinator Instability: The Mixed Mating System of a Dry-Season Flowering Pioneer Shrub, Wigandia urens

In the context of global pollinator decline, understanding reproductive strategies under unpredictable environments is crucial. Wigandia urens (Boraginaceae) is a dominant shrub in central Mexico that blooms during the dry season when pollinator activity is significantly diminished. We employed a controlled pollination experiment with eight treatments and 15 replicates to quantify the contributions of autonomous self-pollination, biotic pollination, and abiotic factors. Floral visitation rates were also monitored throughout the flowering phenology. W. urens exhibited a mixed mating system predominantly oriented toward self-pollination. The species showed exceptionally high auto-fertility (AF = 0.699) and significant reproductive assurance (RA = 0.372). While biotic pollinators contributed to 46.5% of total seed set, visitation rates progressively declined (0.016 to 0.009 visits/flower/min) as the dry season peaked. No significant self-pollination limitation was detected (PLs = -0.020). Despite marginal seed set in exclusion treatments, field observations suggest that gravity-mediated selfing or secondary pollen presentation, rather than functional anemophily, are the likely abiotic drivers. Our findings demonstrate that W. urens prioritizes reproductive certainty through autonomous selfing to buffer against pollinator scarcity in the dry season, while maintaining biotic pathways for potential genetic exchange. This dual strategy provides a vital evolutionary advantage in disturbed habitats. These results offer key insights into plant adaptive evolution under the contemporary crisis of pollinator diversity loss.