Genetic Erosion in the Santa Cruz Sandhills

Genetic erosion is the loss of unique genetic material, including alleles (gene forms), genes, and genotypes. In the Sandhills, genetic erosion can result from many factors including:

Introduction of Non-Sandhills Genetic Material

The introduction of plants and animals from non-Sandhills populations can dilute the locally adapted genetic complexes-genetic resources that adapt Sandhills populations to their unique environment. Introduction of non-sandhills genes can swamp the native genes, reducing the success of the native Sandhills populations and disrupting the evolutionary processes through which they might become distinct species.

Sandhills poppies with yellow flowers
Sandhills poppy colorful foliage
California poppy from grassland
For example, Sandhills poppies (Eschscholzia californica) have small, yellow flowers and colorful pigments in the leaves (top), whereas more widespread populations of our State flower typically have green foliage and orange flowers (middle). Research has shown that the traits of the Sandhills poppy have a genetic basis, and do not simply result from growth in the unique environmental conditions. These traits may be important adaptations for life in the Sandhills. For example, Sandhills insects may preferentially visit yellow flowers, so orange flowers might not be pollinated.

Occasionally poppies with intermediate flower and foliage characteristics are observed in the Sandhills (bottom), suggesting that the genetic material of more widespread poppies is being introduced into the Sandhills, perhaps from nearby developments where they are commonly planted. This introduction of non-Sandhills poppy genes could disrupt the locally adapted gene complexes and alter the course of evolution of Sandhills poppies as a unique species.

Small but orange hybrid poppy flower in the Sandhills
California poppies with green foliage in grasslands
Colorful foliage of hybrid poppy in Sandhills
Movement of Genetic Material Among Naturally Isolated Sandhills Sites

Sandhills habitat occurs as biological islands within a sea of mixed evergreen and redwood forests. Populations on separate habitat patches may have been isolated for millions of years, even though they are within a kilometer. Geographically isolated populations can go down separate evolutionary trajectories, and ultimately differentiate into separate species.

Several plant populations exhibit morphological differences among Sandhills sites. Three plant species have multii-color flowers in certain Sandhills habitat patches, yet yellow flower morphs at other sites. This shift toward all yellow flowers could result from pollinators preferentially visiting yellow flowers. If they have a genetic basis, these morphological differences may represent speciation in progress!

Artificial movement of genetic material among Sandhills sites could erode the genetic diversity between Sandhills populations. To avoid this, restoration and reclamation projects must use only site-specific genetic material (e.g. seeds, cuttings.)

typical yellow and white inflorescence morph of Malacothrix floccifera
Typicaly yellow and white flower morph of Meconella linearis
multi-color flower morph of Linanthus parviflorus
all yellow inflorescence morph of Malacothrix floccifera found in just a few Sandhills sites
Population of Linanthus parviflorus with all yellow flowers
Yellow flower morph of Meconella linearis found in just one Sandhills site
Three plant species that typically have yellow and white flowers, but have all yellow flowers at certain, isolated Sandhills sites.
Left: Woolly dandelion (Malacothrix floccifera).
Center: common linanthus (Linanthus parviflorus).
Right: poppy (Meconella linearis)
Extirpations Due to Habitat Loss, Fragmentation, and Degradation

The greatest cause of genetic erosion in the Sandhills is the local extinction (extirpation) of populations due to the loss, fragmentation, and degradation of habitat. Populations in geographically isolated Sandhills sites can become genetically differentiated, as a result of genetic drift as well as natural selection. Extirpations or dramatic reductions in populations cause genetic bottlenecks, which decrease genetic diversity, thus further threatening the persistence of rare and endangered species.

Habitat loss and fragmentation in the Sandhills
Sandhills Alliance for Natural Diversity (S.A.N.D.)
PO Box 2363 Boulder Creek, CA 95006 ● e-mail:
Web design, text, and images by Jodi M. McGraw © 2005. All rights reserved. Not for use without permission.