Reproductive isolation between wild and domesticated chaya (Cnidoscolus aconitifolius) in sympatry.

Reproductive isolation is a necessary condition for plant domestication in their domestication centre where crops co-occur with their wild progenitors. However, the identification of reproductive barriers and their relative contribution to reproductive isolation have been overlooked in plants under domestication. We assessed pre- and post-pollination reproductive barriers and their relative contribution to reproductive isolation between wild and domesticated chaya (Cnidoscolus aconitifolius) in its domestication centre. We found that wild and domesticated chaya both exhibit a high degree of reproductive isolation. However, the reproductive isolation barriers exhibited some asymmetry: while pre-pollination barriers (differential pollen production and pollinator specificity) were only detected in wild plants, post-pollination barriers (pollen-pistil incompatibility and/or failure to set fruit) were observed in both wild and domesticated plants. We conclude that complete reproductive isolation has evolved in sympatry in co-occurring domesticated and wild chaya.

Pollination system of the Pilosocereus leucocephalus columnar cactus (tribe Cereeae) in eastern Mexico.

It has been suggested that there is a geographic dichotomy in the pollination systems of chiropterophilous columnar cacti: in intra-tropical areas they are pollinated almost exclusively by bats, whereas in extratropical areas they are pollinated by bats, birds and bees. However, currently the studies are clumped both taxonomically (mainly Pachycereeae species) and geographically (mainly in the Tehuacan Valley and the Sonoran Desert). This clumping limits the possibility of generalising the pattern to other regions or cactus tribes. Only four of the 36 chiropterophilous cacti in Pilosocereus have been studied. Despite the tropical distribution of two Pilosocereus species, bees account for 40-100% of their fruit set. We examined how specialised is the pollination system of P. leucocephalus in eastern Mexico. As we studied tropical populations, we expected a bat-specialised pollination system. However, previous studies of Pilosocereus suggest that a generalised pollination system is also possible. We found that this cactus is mainly bat-pollinated (bats account for 33-65% of fruit set); although to a lesser degree, diurnal visitors also caused some fruit set (7-15%). Diurnal visitors were more effective in populations containing honeybee hives. P. leucocephalus is partially self-compatible (14-18% of fructification) but unable to set fruit without visitors. Despite the variation in pollination system, P. leucocephalus shows more affinity with other columnar cacti from tropical regions than with those from extratropical regions. Although we report here that a new species of tropical Pilosocereus is relatively bat-specialised, this Cereeae genus is more flexible in its pollination system than the Pachycereeae genera.