Distribución, estructura genética y conservación de la especie microendémica Guaiacum unijugum (Zygophyllaceae) en la región de los Cabos de Baja California, México.

Abstract

Guaiacum unijugum is a rare shrub endemic to a 70 km stretch of coastline extending east from San José del Cabo in Baja California and is the least well-known of the 4 species of Guaiacum in Mexico. To increase our knowledge of this species and assess its conservation status we surveyed the extent of occurrence using both herbarium material and field work, assessed levels of genetic diversity, determined its phylogenetic relationships, and completed an evaluation of risk of extinction (MER). Herbarium material identified 5 known localities of occurrence with field work verifying the continued persistence of 4 of these with an additional site discovered. Genetic analysis across the small range using 17 microsatellite loci showed very low levels of genetic diversity with a mean expected heterozygosity (H E) of 0.162 over all polymorphic loci. Most loci were found to be monomorphic and genetic divergence was small, maintained by the presence of rare private alleles in widely-separated populations. Phylogenetic analysis indicated a sister group relationship to G. coulteri along the Pacific coast suggesting vicariance for the origin and occurrence of G. unijugum. The unique evolutionary history coupled with current small population sizes warrants increased conservation via listing as a critically endangered species.

Molecular genetic analysis of two native desert palm genera,WashingtoniaandBrahea, from the Baja California Peninsula and Guadalupe Island

“…As expected, levels of haplotype diversity were low in Washingtonia for both the chloroplast and nuclear sequence data, whereas nuclear diversity in peninsular Brahea was somewhat higher (Figures and ). The levels of diversity that we found were broadly comparable to other relict plant species of the region (e.g., Guaiacum unijugum , McCauley et al., ; Quercus brandegeei, Cavender‐Bares et al., ) as well as to Washingtonia populations in the USA (McClenaghan & Beauchamp, ). Moreover, sequence diversity at the nuclear loci was not evenly distributed along the peninsula and also showed differences between Washingtonia and Brahea (Figure ).…”

“…The continental rifting of the Peninsula away from mainland Mexico and the volcanic upwelling of Guadalupe Island are the most ancient (>5 million years ago, MYA) and resulted in ecological speciation, island endemism and disjunctions in mainland‐peninsular and peninsular‐island sister species distributions (Aleixandre, Hernandez Montoya, & Mila, ; Grismer, ; León De La Luz, Rebman, & Oberbauer, ; Riddle et al., ; Rosas‐Escobar, Gernandt, Pinero, & Garcillan, ). More recently (1–3 MYA) and more locally, complex physical interactions between the land and the sea, such as the inundation of the Isthmus of La Paz and the formation of the temporal mid‐peninsular seaway, resulted in a north‐south genetic discontinuity within the peninsula and the generation of regions of high local endemism (Dolby et al., ; León‐De la Luz & Breceda, ; McCauley, Cortés‐Palomec, & Oyama, ; Riddle et al., ). This complex interplay was followed by progressive aridification of the Baja Peninsula and adjacent areas after the Last Glacial Maximum (LGM) (Hafner & Riddle, ; Lindell et al., ; Riddle et al., ).…”

Phylogeny and biogeography of the American live oaks (QuercussubsectionVirentes): a genomic and population genetics approach

“…The Baja California shrub Guaiacum unijugum shows similar ecological and reproductive patterns to Q. brandegeei occurring only along occasional waterways and showing very limited seedling recruitment (McCauley et al . ). Other distribution shifts consistent with climatic drying include the northward expansion of columnar cacti along the Baja California peninsula (Nason et al .…”

Distribution pattern in the rupiculous genus Orthophytum (Bromelioideae/Bromeliaceae) reveals high microendemicity in different types of rocky outcrops

“…The concept of microendemism includes species with highly restricted and geographically proximate distributions (Townsend et al 2011), as was also adopted by McCauley et al (2010) for Guaiacum unijugum Brandegee (Zygophyllaceae), which occurs in less than 5% of the Baja California in Mexico. Giulietti et al (2005) also determined that approximately 96% of all Brazilian species of the Eriocaulaceae family are microendemic.…”