Do rare pines need different conservation strategies? Evidence from three Mexican species Francisco Molina-Freaner, Patricia Delgado, Daniel Piñero, Nidia Perez-Nasser, and Elena Alvarez-Buylla Abstract: Mexico is a major center of diversity for the genus Pinus as it has the greatest number of species in the world. Many species are now restricted to Mexico, and some are represented by very small populations and are in dan- ger of extinction. In this study we examined allozyme variation in three rare species of Mexican pines: Pinus pinceana Gord., Pinus lagunae M.F. Passini, and Pinus muricata D. Don, with the objective of providing conservation guide- lines. The three species had relatively high levels of genetic variation with mean expected heterozygosities of 0.373, 0.386, and 0.346 for P. pinceana, P. lagunae, and P. muricata, respectively. We found marked differentiation among populations and significant inbreeding within populations of the three species. These values are larger than the range reported for most conifers and suggest that conservation strategies of these rare pines require focusing on the viability of several populations. Given that our knowledge about the demographic status of the three species is scarce, we pro- pose a mixed strategy of conservation. For P. lagunae, we propose an in situ strategy, whereas for P. pinceana and P. muricata we propose an ex situ strategy of conservation until permanent protection can be provided for several of their populations. Key words: genetic structure, conservation, rare pines, Pinus pinceana, Pinus lagunae, Pinus muricata. Résumé : Avec le plus grand nombre d’espèces au monde, le Mexique constitue un centre majeur de diversité pour le genre Pinus. Plusieurs espèces sont aujourd’hui restreintes au Mexique, certaines d’entre elles n’étant représentées que par de très petites populations en danger d’extinction. Dans cette étude, afin de jeter les bases pour leur conservation, les auteurs examinent la variation allozymique chez trois espèces de pins rares, du Mexique : Pinus pinceana Gord., Pinus lagunae M.F. Passini et Pinus muricata D. Don. Les trois espèces montrent des degrés relativement élevés de va- riation génétique avec des hétérozygocités moyennes attendues de 0,373, 0,386 et 0,346 pour les P. pinceana, P. la- gunae et P. muricata, respectivement. On observe une différenciation marquée entre les populations et une autofécondation significative dans les populations des trois espèces. Ces valeurs sont plus élevées que celles qui ont été rapportées pour la plupart des conifères et suggèrent que les stratégies de conservation de ces pins rares nécessitent qu’on s’attarde à la viabilité de plusieurs populations. Compte tenu que les connaissances de l’état démographique de ces trois espèces sont limitées, on propose une stratégie mixte de conservation. Pour le P. lagunae, les auteurs suggè- rent une stratégie in situ, alors que pour le P. pinceana et le P. muricata ils proposent une stratégie de conservation ex situ, en attendant qu’on puisse assurer la protection de plusieurs de leurs populations. Mots clés : structure génétique, conservation, pins rares, Pinus pinceana, Pinus lagunae, Pinus muricata. [Traduit par la Rédaction] Molina-Freaner et al. 138 Introduction The extinction of species is a process that depends on de- mographic and genetic factors. Although demographic fac- tors are sometimes of more immediate importance in determining population viability (Lande 1988), long-term conservation strategies depend upon knowledge of the ge- netic structure of the species (Schemske et al. 1994). For in- stance, some knowledge about the genetic structure is im- portant for optimal sampling in ex situ conservation and the identification of critical populations for in situ conservation. Although in situ strategies are generally preferred for long- term conservation, recent case histories of forest genetic re- sources from North America have revealed that relying on just in situ programs can be risky and that, in some cases, ex situ programs are the best alternative (Ledig et al. 1998). Surveys of enzyme polymorphisms in plant populations have revealed that forest tree species usually have higher ge- netic diversity than other groups of plants (Hamrick et al. 1979). In conifers, most of this diversity is distributed within populations with a small proportion of variation occurring among populations (El-Kassaby 1991; Ledig 1998). In pines and other coniferous species, usually less than 10% of the genetic variation is distributed among populations (El- Kassaby 1991; Ledig 1998). Large population sizes, a pre- dominantly outcrossing mating system, and the potential for Can. J. Bot. 79: 131–138 (2001) © 2001 NRC Canada 131 DOI: 10.1139/cjb-79-2-131 Received June 20, 2000. Published on the NRC Research Press website on February 8, 2001. F. Molina-Freaner. 1 Instituto de Ecologia, Universidad Nacional Autonoma de México, Apartado Postal 1354, Hermosillo, Sonora, Mexico C.P. 83000. P. Delgado, D. Piñero, N. Perez-Nasser, and E. Alvarez- Buylla. Instituto de Ecologia Universidad Nacional Autonoma de México, Apartado Postal 70-275, Mexico D.F. C.P. 04510. 1 Corresponding author (e-mail: freaner@servidor.unam.mx).