Variation in tolerance to heterospecific pollen from a non‐native congener depends on co‐existence history of maternal and paternal source populations

Premise Plants in sympatric populations with congeners may have evolved tolerance to the negative effects of heterospecific pollen (HP) through selection on female or male reproductive traits. If so, then the degree of HP tolerance may vary depending on the co‐existence history of the maternal and paternal plant source populations. Empirical evidence from species with a known history of contact is limited. Methods This study focused on sympatric and allopatric populations of the native Oxalis corniculata and its recently arrived congener O. dillenii in Japan. Specifically, we conducted heterospecific and conspecific crosses with O. corniculata and two sequential pollination treatments using conspecific (CP) followed by heterospecific (HP) pollen, with CP donors from sympatric or allopatric populations. Results Heterospecific crosses revealed lower seed production in O. corniculata than conspecific crosses, with sympatric populations showing a significantly greater reduction. Sequential pollination experiments reduced conspecific seed production, particularly when both the recipients and CP donor originated from sympatric populations. Conclusions Our results suggest that individuals from sympatric populations may mitigate the negative effects of HP caused by hybrid seed formation. Furthermore, the variation in tolerance to the inhibition of conspecific fertilization by HP could be attributed to the recipient and CP donor origins. But the unexpectedly high susceptibility of sympatric populations to HP highlights the complex ecological and evolutionary factors that influence HP tolerance.