Gypsophila bermejoi G. López: A possible case of speciation repressed by bioclimatic factors

Abstract

Gypsophila bermejoi G. López is an allopolyploid species derived from the parental G. struthium L. subsp. struthium and G. tomentosa L. All these plants are gypsophytes endemic to the Iberian Peninsula of particular ecological, evolutionary and biochemical interest. In this study, we present evidence of a possible repression on the process of G. bermejoi speciation by climatic factors. We modelled the ecological niches of the three taxa considered here using a maximum entropy approach and employing a series of bioclimatic variables. Subsequently, we projected these models onto the geographical space of the Iberian Peninsula in the present age and at two past ages: the Last Glacial Maximum and the mid-Holocene period. Furthermore, we compared these niches using the statistical method devised by Warren to calculate their degree of overlap. We also evaluated the evolution of the bioclimatic habitat suitability at those sites were the soil favors the growth of these species. Both the maximum entropy model and the degree of overlap indicated that the ecological behavior of the hybrid differs notably from that of the parental species. During the Last Glacial Maximum, the two parental species appear to take refuge in the western coastal strip of the Peninsula, a region in which there are virtually no sites where G. bermejoi could potentially be found. However, in the mid-Holocene period the suitability of G. bermejoi to sites with favorable soils shifts from almost null to a strong adaptation, a clear change in this tendency. These results suggest that the ecological niches of hybrid allopolyploids can be considerably different to those of their parental species, which may have evolutionary and ecologically relevant consequences. The data obtained indicate that certain bioclimatic variables may possibly repress the processes by which new species are formed. The difference in the ecological niche of G. bermejoi with respect to its parental species prevented it from prospering during the Last Glacial Maximum. However, the climatic change in the mid-Holocene period released this block and as such, it permitted the new species to establish itself. Accordingly, we favor a recent origin of the current populations of G. bermejoi.

Fig 1

Appearance of G. struthium subsp. struthium (A), G. tomentosa(B) and G. bermejoi (C). Map of the Iberian Peninsula showing the presence of Ononis tridentata L. (D), a plant that is indicative of gypsum and gypsiferous loam soils.

Fig 2

Habitat suitability predicted for G. tomentosa (A), G. struthium subsp. struthium (B) and G. bermejoi (C) during the Last Glacial Maximum. These are the potential areas according to the bioclimatic variables for the three taxa. All these plants are strict gypsophytes and the real values of suitability are 0 in the locations without suitable soils. (D) shows the differences in bioclimatic suitability for the three species. To produce these box plots, only those values from locations with favorable soils (see map Fig 1D) have been taken into account. Notice that both, maps and box plots, show a suitability of almost 0 for G. bermejoi during this period.

Fig 3

Habitat suitability predicted for G. tomentosa (A), G. struthium subsp. struthium (B) and G. bermejoi (C) during the Mid Holocene. In this case, (D) shows the variation of the habitat suitability for the three taxa with the climatic change from Last Glacial Maximum to Mid Holocene. For G. struthium subsp. struthium and G. tomentosa, the medians have decreased. However, there are some outliers indicating locations with a relative high bioclimatic suitability. For G. bermejoi, those values have increased dramatically.

Fig 4

Habitat suitability predicted for G. struthium subsp. struthium (A), G. tomentosa (B) and G. bermejoi (C) using current climatic data. For G. bermejoi (D) shows the emergence of several sites with atypically high values, a behavior consistent with its highly endemic character.