ELSEVIER Biological Conservation 70 (1994) 19-24 © 1994 Elsevier Science Limited Printed in Great Britain. All rights reserved 0006-3207/94/$07.00 EVOLUTION OF HIGH GENETIC VARIABILITY IN THE RARE HAWAIIAN FERN Adenophorusperiens AND IMPLICATIONS FOR CONSERVATION MANAGEMENT Tom A. Ranker University Museum and Department of EPO Biology, University of Colorado, Campus Box 350, Boulder, Colorado 80309, USA (Received 19 January 1993; revised version received 9 November 1993; accepted 1 December 1993) Abstract Adenophorus periens is a rain forest-dwelling epiphytic fern and is known only from one population on the island of Hawaii (Kahaualea) and from a few scattered individ- uals on the islands of Kauai and Molokai. A genetic survey was conducted of the Kahaualea population employing protein electrophoresis. The individuals sam- pied expressed extremely high levels of allozymic vari- ability compared to two more widespread congeneric species (A. tamariscinus and A. tripinnatifidus). All in- dividuals examined were produced via sexual recombina- tion. Given the extremely young volcanic substrate upon which the Kahaualea forest has developed, the historical factors leading to the high genetic variability of A. periens are somewhat obscure. The outcrossed mating system of this species may play a key role in the main- tenance of genetic diversity in combination with its perennial life cycle. Because the lack of neighboring populations precludes the influx of new genetic variability via gene flow, the population must rely solely on the appearance and incorporation of new mutations as sources of new variability. The data suggest that this genetically diverse popula- tion is not likely to suffer genetically from minor reduc- tions in population size over the short term. The most obvious potential threats to A. periens are those affecting the demography of the population and include habitat de- struction by lava flows, death of host trees through stand- level dieback, chance loss of individuals by a variety of mechanisms, and the adverse effects of gaseous emissions from volcanic activity and geothermal development. The State of Hawaii shouM undertake an artificial propaga- tion and transplantation program to establish populations in less threatened, suitable habitats. Keywords: Hawaii, Adenophorus, genetics, evolution. INTRODUCTION Low levels of genetic variability have been documented for a variety of geographically restricted plant species (e.g. Ledig & Conkle, 1983; Lesica et al., 1988; Hickey et al., 1991). Although these data are consistent with the theoretically expected relationship between genetic diversity and population size (Wright, 1931), several 19 exceptions to this relationship have been described (discussions and references in Karron, 1987, 1991 and Hamrick & Godt, 1990). Since the extent of genetic variability is critical for the long-term survival and con- tinued evolution of a population or species (Lande & Barrowclough, 1987), genetic analyses of threatened and endangered species are useful to aid conservation decisions. Such studies may provide crucial data for the assessment of present and future population viability and for unraveling the historical factors accounting for existing levels and patterns of genetic diversity. Ranker (1992a) surveyed allozymic variability in two widespread species of the endemic Hawaiian fern genus Adenophorus Gaud. (Grammitidaceae). Populations of A. tamariscinus (Kaulf.) Hook. &Grev. were found to have higher levels of genetic variability than has been reported for a variety of mainland homosporous ferns (Soltis & Soltis, 1990; Ranker, 1992b). Populations of A. tripinnatifidus Gaud. exhibited slightly lower levels of genetic diversity, intermediate between historically outcrossing and inbreeding continental populations. Although these two species both occur on all of the main Hawaiian Islands (i.e. Kauai, Oahu, Molokai, Lanai, Maui, and Hawaii; Bishop, 1974), A. tripin- natifidus is usually ecologically restricted to extremely wet forests whereas A. tamariscinus occupies a greater variety of montane habitats (Bishop, 1974; personal observations). The greater ecological amplitude of the latter species may be directly linked to its ability to maintain higher levels of genetic variability. The slight difference in levels of variability between these two species along with the possible relationship between genetic diversity and ecological amplitude suggests that the extent of geographical distribution alone (i.e. in terms of the number of islands on which a species is found) may not be a good predictor of populational genetic variability in species of Adenophorus. In light of the information gathered on these two widespread species of Adenophorus (Ranker, 1992a), the present study was undertaken to explore the popu- lation genetics of one of the rarest Hawaiian ferns, A. periens L. E. Bishop. Although this epiphyte has been collected historically on all the Hawaiian Islands that support rain forests (Bishop, 1974), it is presently known from only a few locations in middle-elevation