| Summary: | The group <i>Pinus </i>subsection <i>Cembroides </i>belongs to section <i>Parrya </i>which, together with section <i>Strobus, </i>forms subgenus <i>Strobus, </i>the haploxylon or “soft pines”. There are 14 taxa recognized for Mexico. Eight <i>(Pinus catarinae, P. cembroides, P. culminicola, P. johannis, P. nelsonii, P. pinceana, P. remota </i>and <i>P. cembroides </i>var. <i>bicolor) </i>occur in the Northeast. Two of these species, P. <i>nelsonii </i>and <i>P. pinceana </i>are highly localized and are clearly defined taxonomically on the basis of cone morphology, whereas the other species are often very difficult to delimit. The aim of this thesis is to use a variety of DNA based techniques to study whether the current taxonomy of the group is correct and to analyse the genetic structure of the species and populations. PCR-RFLP and sequence analysis give some evidence for the separation of <i>P.</i> <i>nelsonii </i>and <i>P. pinceana </i>from the other species of pinyon pines, placing them in a different subsection. This distinction was initially based on morphological characters and is now corroborated by chloroplast DNA analysis. There is insufficient variation in the chloroplast genome to elucidate the relationships among the remaining species, suggesting that they have evolved only recently or that they are not distinct taxa. Random amplified polymorphic DNA markers (RAPD) have been used to investigate the relationship in the 6 remaining taxa. RAPD analysis suggests that <i>P.</i> <i>catarinae is </i>synonymous with <i>P. remota, </i>and that <i>P. johannis </i>should now be treated as <i>P cembroides </i>var. <i>bicolor. </i>Within taxa genetic variation is high and differentiation among populations is low. This suggests that even though species have restricted and isolated distributions gene flow among populations has been sufficient to prevent a dramatic loss of genetic variation.
|
|---|
