Genetic Diversity Within and Among Sinai Populations of Three Ballota Species ( Lamiaceae )

Ballota undulata, Ballota kaiseri, and Ballota saxatilis are very rare (and endemic—B. kaiseri), threatened species growing in St. Catherine Protectorate, southern Sinai, Egypt. They are subjected to a number of threats that have caused populations to decline in both number and size. For the long-term survival of these species, an appropriate conservation strategy for the maintenance of their genetic variation should be developed. This study measures genetic diversity within and among populations of these Ballota species and determines the conservation implications of the results. The genetic analyses demonstrated that the three Ballota species maintain relatively high levels of genetic diversity (He5 0.195–0.317) and that most of the their genetic diversity was found within populations (GST 5 0.045–0.099). Indirect estimates of historical gene flow for B. undulata and B. saxatilis were relatively high (Nm(W) 5 5.25 and 3.37, respectively) but suggest that there is somewhat less gene movement among B. kaiseri populations (Nm(W) 5 2.29). The levels of genetic diversity maintained within populations of the three Ballota species indicate that an appropriate sampling design for ex situ safeguarding should capture the majority of the genetic diversity found within these taxa. A long-term objective of most conservation efforts is to maintain the evolutionary viability of taxa, maximizing their chances for persistence in the face of changing environmental conditions. Genetic considerations may also have short-term importance for the development of strategies for the successful management of rare plants. Thus, plant conservation biologists face a series of decisions when developing plans for the preservation of a species ex situ or for its preservation or reestablishment in the wild. It is important to determine to what extent local populations are genetically differentiated, whether such differences have adaptive value, and whether mixing gene pools from different populations will affect successful establishment and longterm survival. The level and distribution of genetic diversity within any plant species is influenced by interactions among at least three factors. The first factor encompasses abiotic conditions including climate, habitat conditions, and soil factors. Biotic interactions such as competition, symbiosis, parasitism, and predation form the second factor. The third and last factor includes species characteristics such as population size, mating system, gene flow, and dispersal. All the three factors influence the genetic composition of populations in both a directed (e.g., selection) or a stochastic fashion (Frankel et al. 1995). Although a rare species may occur within reserves, its populations may not be viable or may represent only a small proportion of the total genetic variation within the species (Cropper 1993). Genetic analyses can help conservation managers to choose protected areas by providing genetic information on rare plant populations. Genetic studies can identify priority populations to conserve, alter the boundaries of reserves, and change reserve design (Hopper and Coates 1990). A major conclusion that has emerged from the past three decades of plant population genetic research is that species differ greatly in their levels and distribution of genetic variation (Hamrick and Godt 1989). An understanding of the variation in genetic composition and population genetic structure is basic to planning the conservation of plant biodiversity. One immediate implication is that optimal sampling strategies to conserve genetic diversity will differ among species. Descriptions of the level and distribution of genetic variation maintained within a species permit comparisons of the Journal of Heredity 2006:97(1):45–54 doi:10.1093/jhered/esj008 Advance Access publication January 11, 2006 a The American Genetic Association. 2006. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org. 45 D ow naded rom http/academ ic.p.com /jhered/articlract/97/1/45/2187643 by gest on 03 April 2019 species of conservation interest with other species having similar life history characteristics and similar geographic ranges. Comparisons with congeneric species sharing a common evolutionary past and having similar mating systems and seed-dispersal mechanisms are perhaps the most informative (e.g., Godt et al. 1995; Karron 1987) but are not always feasible. Studies of geographically restricted species are of interest to evolutionary biologists because rapid evolutionary change often takes place in isolated populations (Stebbins 1979; Wright 1931). Information on the ecology and the genetics of these taxa is also important to those responsible for the management of rare species, a problem that is gaining increasing attention (e.g., Frankel and Soulé 1981; Ledig 1986; Soulé 1980). Drury (1974) noted that although many researchers predicted low levels of genetic polymorphism in plant species with limited ranges and small numbers of individuals, few had measured genetic variation in such taxa. During the past three decades, many researchers used allozyme analyses to investigate the genetic composition and structure of plant populations (e.g., Brown 1979; Gottlieb 1981; Hamrick and Godt 1989) and there have been several studies involving rare, endemic species with small geographic ranges (e.g., Godt and Hamrick 1998; Karron 1987; Moran and Hopper 1983). Ballota undulata, Ballota kaiseri, and Ballota saxatilis are rare (and endemic—B. kaiseri) species growing in southern Sinai, Egypt, that are subjected to threats that have caused declines in population number and size. The loss of genetic variation through stochastic factors and the deleterious effects of inbreeding in small populations are potential threats that may compromise attempts to maintain the long-term viability of populations of these rare species. Our goal in this study is to measure genetic variation within and among Ballota populations and to determine implications for the conservation of these species. Materials and Methods