Skip to Main Content
Recent evolution and divergence among populations of a rare Mexican endemic, Chihuahua spruce, following holocene climatic warmingAuthor(s): F. Thomas Ledig; Virginia Jacob-Cervantes; Paul D. Hodgskiss
Source: Evolution 51(6): 1815-1827
Publication Series: Miscellaneous Publication
PDF: Download Publication (933 KB)
DescriptionFragmentation and reduction in population size are expected to reduce genetic diversity. However, examples from natural populations of forest trees are scarce. The range of Chihuahua spruce retreated northward and fragmented coincident with the warming climate that marked the early Holocene. The isolated populations vary from 15 to 2441 trees, which provided an opportunity to test whether census number is a good predictor of genetic diversity. Mean expected heterozygosity, He, based on 24 loci in 16 enzyme systems, was 0.093 for 10 sampled populations, which is within the range reported for conifers. However, estimates varied more than two-fold among populations and He was closely related to the logarithm of the number of mature trees in the population (rHe,N = 0.93). Diversity among populations, FST, was 24.8% of the total diversity, which is higher than that observed in almost all conifer species studied. Nei's genetic distance, D, was not related to geographic distance between populations, and was 0.033, which is higher than estimates for most wide-ranging species. Most populations had excess homozygosity and the fixation index, FIS, was higher than that reported for all but one species of conifer. NM, the number of migrants per generation, was 0.43 to 0.76, depending on estimation procedure, and is the smallest observed in conifers. The data suggest that populations of Chihuahua spruce have differentiated by drift and that they are effectively isolated. The results illustrate how a combination of paleontological observation and molecular markers can be used to illuminate recent evolutionary events. Multilocus estimates of outcrossing for two small populations were zero (complete selfing) and 0.153, respectively, which are in striking contrast to the near complete outcrossing observed in most conifers. The high fixation index and a high proportion of empty seeds (45%) suggest that inbreeding may be a serious problem for conservation of Chihuahua spruce.
- You may send email to email@example.com to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationLedig, F. Thomas; Jacob-Cervantes, Virginia; Hodgskiss, Paul D. 1997. Recent evolution and divergence among populations of a rare Mexican endemic, Chihuahua spruce, following holocene climatic warming. Evolution 51(6): 1815-1827
KeywordsGene flow, genetic diversity, genetic drift, inbreeding, isozymes, Picea, population decline
- The mating system and genic diversity in Martínez spruce, an extremely rare endemic of México’s Sierra Madre Oriental: an example of facultative selfing and survival in interglacial refugia
- Genetic diversity, genetic structure, and mating system of brewer spruce (Pinaceae), a relict of the acto-tertiary forest
- Field survey of growth and colonization of nonnative trees on mainland Alaska.
XML: View XML