The amount of genetic diversity and its distribution among populations has been associated to species’ attributes such as mating system, dispersal ability and geographic range size. Another attribute that could contribute to explain intraspecific phylogeographic patterns is niche breadth, but this relationship barely has been tested. Here, we studied a Mexican oak (Quercus glaucoides) with a comparatively narrow climatic niche breadth. Genetic diversity and structure were assessed, as well as historical demography dynamics and connectivity. Then, we tested for a general correlation of genetic diversity and structure with niche breadth, using our data and previous results from other co-distributed Mexican oaks with variable niche breadths.

Methods

Descriptors of genetic diversity and structure were obtained from 21 Q. glaucoides populations using chloroplast DNA (cpDNA) and nuclear microsatellites (nSSRs). Historical demography dynamics were inferred with approximate Bayesian computation (ABC) and past potential distribution models. To test for an association between niche breadth and phylogeographic patterns, we used genetic diversity and differentiation values of Q. glaucoides plus those previously published for other ten species. Niche breadth was estimated for all species and linear regressions were performed.

Results

Genetic diversity calculated from nSSRs (H_O= 0.539; H_E= 0.714) was among the lowest, and cpDNA differentiation (N_ST= 0.88) was the highest so far obtained for comparable Mexican oaks. Moderate changes in demographic size and distribution shifts throughout the last glacial cycle were inferred, explaining some of the observed genetic patterns. A positive correlation of H_O and a negative correlation of N_ST with niche breadth were detected across species. 

Main conclusions

Distinct phylogeographic patterns in Q. glaucoides could be explained because a narrower niche may cause lower historical effective population sizes and more fragmented distributions in comparison to species with a wider niche breadth, even with similar range sizes.

Microsatellites data was obtained through the following procedures:

PCR reactions were performed using the Platinum Multiplex PCR Master Mix (Thermo Fisher Scientific) in a final volume of 6 uL. Four groups of primers were used for the PCR reaction according to the colour of the fluorescent tag and fragment size. The temperatures of reactions were as follows: denaturation at 95 °C for 5 min; 40 cycles of 95 °C for 30 s, alignment between 45 and 61 °C (according to the primer group) for 45 s and extension at 72 °C for 1 min; followed by a final step at 72 °C for 10 min. PCR products were analysed in an ABI-PRISM 3300 Avant sequencer. Fragment sizes were determined using the program GeneMarker 2.6.4 (SoftGenetics) using Gene-scan-600 Liz as a size standard.