Sympatric and allopatric niche shift of endemic Gypsophila (Caryophyllaceae) taxa in the Iberian Peninsula

Several species of the Gypsophila genus are endemic to the Iberian Peninsula, including gypsophytes of particular ecological, evolutionary and biochemical interest, and taxa that have undergone both sympatric and allopatric genetic differentiation. The niche shift among these taxa has been assessed using ecological niche modelling and ordination techniques, adopting a niche overlap approach to compare the similarity and equivalency of the ecological niches. We used the Maximum Entropy method to study the potential distribution of these taxa in different eras: the Last Glacial Maximum (LGM), the Mid Holocene and the current conditions. We present evidence of niche shift during the speciation of G. bermejoi, with a strong niche overlap between the parental taxa (G. struthium subsp. struthium and G. tomentosa), yet both overlap much more weakly with the hybrid species. This phenomenon may be explained by genetic and epigenetic interactions, and it has been described in other species. We also studied the sister subspecies G. struthium subsp. struthium and G. struthium subsp. hispanica, with mostly allopatric distributions and with the Iberian System mountain range acting as a geographical barrier. The Iberian System and other mountain ranges may have favored differences in the climatic conditions on either side of the mountain range, which is consistent with an incipient process of bioclimatic ecological speciation. These results seem to indicate that niche shift can occur over very different timespans. In the case of G. bermejoi, speciation may have produced significant niche shifting in one or two generations due to its alloploid nature. By contrast, G. struthium subsp. struthium and G. struthium subsp. hispanica seem to have undergone a more gradual process of allopatric genetic differentiation driven by bioclimatic factors. Both these processes are relatively recent and they will have been strongly influenced by the climate change at the end of LGM.