Evolutionary change in the germination niche between related species within Neoporteria clade (Cactaceae) is idiosyncratic to habitat type

Resumo

An appropriate germination response to environmental conditions is the first requirement for the establishment of a plant in a determined geographic area; therefore changes in the germination niche may be critical in configuring the current pattern of species distributions. Furthermore, the spread of many Neotropical groups to higher latitudes are constrained by the combination of cold and humid conditions. This raises the question whether evolutionary trends in germination niche are essential for the mechanism that allows the colonization of edge habitats characterized by humid and cold conditions. Here, we evaluated the variation of seed germination probabilities of two species of cacti (Neoporteria clade), closely related but endemic to habitats with different temperature and water availability conditions. The germination niche and differences in germination performance of Eriosyce subgibbosa and E. villosa were evaluated, using common garden experiments and varying temperature and soil water potential (?) conditions. Seeds of E. subgibbosa showed overall higher germination probabilities compared to E. villosa. Interestingly, most of the detected differences on seed germination performance are related with a higher ability of E. subgibbosa seeds to germinate under conditions with more water availability and under colder conditions compared to E. villosa seed germination. This study highlights one of the critical features that could be involved in the mechanism that leads to the expansion of the Neoporteria clade to more mesic habitats. Particularly the adaptation of the germination niche of E. subgibbosa may allow an expansion from an arid habitat that characterized basal species of the group (plesiomorphic state) to more humid and cold habitats.