Heredity 85 (2000) 338±345 Received 6 January 2000, accepted 26 June 2000 Mating system parameters of Dryobalanops aromatica Gaertn. f. (Dipterocarpaceae) in three different forest types and a seed orchard S. L. LEE* Forest Research Institute Malaysia (FRIM), Kepong, 52109 Kuala Lumpur, Malaysia The mating system of Dryobalanops aromatica in three dierent forest types and a seed orchard was quanti®ed by allozyme analysis of progeny arrays using a mixed-mating model. The primary forest (Bukit Sai) had the highest multilocus outcrossing rate (tm 0.923 0.035), followed by logged forest (Lesong; tm 0.766 0.056) and arti®cial forest (FRIM; tm 0.661 0.066) with seed orchard showing the lowest (Tampin; tm 0.551 0.095). Deviations from the mixed mating model were evident from dierences in pollen and ovule allele frequencies, and heterogeneity of pollen pools in all three dierent forest types and the seed orchard. A high rate of outcrossing in primary forest (tm 0.92) may indicate that the species is self-incompatible, but a lower value in the seed orchard (tm 0.55) might suggest further that the self-incompatibility system is weak. The outcrossing rate was greater in the primary forest (tm 0.92) than in logged forest (tm 0.77). It is argued that this might be a consequence of the lower density of ¯owering trees and alteration of pollinator foraging behaviour in logged forest. Higher values of correlated mating (rp) and biparental mating (tm ) ts)in primary forest (0.08 and 0.39, respectively) in comparison with logged forest (0.03 and 0.11, respectively) demonstrate that logging activities might reduce the seeds produced through consan- guineous mating. Compared with primary forest, it is argued that lower rates of outcrossing in arti®cial forest (tm 0.67) and seed orchard (tm 0.55) might be attributed to lack of ¯owering synchrony and insucient number of pollinators. The high level of correlated mating (rp 0.43) and biparental mating (tm ) ts 0.12) in the seed orchard may further suggest that the seed orchard was established using related seed sources. Keywords: allozyme, Dipterocarpaceae, Dryobalanops aromatica, Kapur, mating system, tropical rain forest. Introduction behaviour and relative number of pollinators (Brown et al., 1989; Adams, 1992; Mitton, 1992). The mating system is an important determinant of the The destruction of tropical forest by logging activities genetic structure and evolutionary inherent of natural may have many diverse eects on the forest biodiversity. populations because it establishes the pattern of how These include the changes of competitors among plant uniting gametes form the next generation (Allard, 1975). species, alteration in pollen and seeds dispersal patterns It is dynamic and can vary in space and time. Hetero- via animal vectors, and contraction in eective popula- geneity of outcrossing rates has been observed among tion sizes of plants and animals (Nason et al., 1997). As populations (Liengsiri et al., 1998), among individuals most tropical trees are animal pollinated (Bawa et al., within a population and between fruiting seasons 1985; Bawa, 1990), changes in plant density and the (Murawski et al., 1994a). It can be a result of ecological destruction of pollinator habitats may have critical factors, such as size and density of populations, density eects on the fertilization success of individual trees of ¯owering trees, ¯ower phenology, pollinator foraging within a fragmented landscape (Aizen & Feinsinger, 1995). Dryobalanops aromatica, locally known as Kapur, is *Correspondence. E-mail: [email protected] an emergent canopy tree occurring in Sumatra, Riau 338 Ó 2000 The Genetical Society of Great Britain. MATING SYSTEM OF DRYOBALANOPS AROMATICA 339 Archipelaga, Borneo and Peninsular Malaysia (Syming- in an arti®cial forest and a seed orchard, established ton, 1943). It occurs abundantly in the lowlands but also outside the native range of the species. No information occurs in the hills (up to 365 m altitude). In Peninsular on D. aromatica mating system parameters from arti®- Malaysia, it is limited to the eastern coast of Trengganu, cial forest and seed orchards is currently available. It is Pahang and Johor, as long belts just inside the beach postulated that in arti®cial forest and seed orchards, area. In Johor, it spreads westwards into the hills eective breeding population sizes are reduced due to (Wyatt-Smith, 1964). In gregarious stands, it may make lack of ¯owering synchrony. up to 90% of the total volume of timber (Foxworthy, 1927). The tree is easily distinguished by its purple Materials and methods brown, scaly bark, its aromatic cut and small, aromatic, ovate leaves. It ¯owers simultaneously and has small The three dierent forest types and a seed orchard were white hermaphrodite ¯owers. In Peninsular Malaysia, located in Peninsular Malaysia. Bukit Sai (Compart- the reported ¯oral visitors are honey bees, Apis dorsata ment 8b) was the primary forest, Lesong (compartment and A. indica var. cerrana (Appanah, 1981; Ashton, 129) the logged forest, Forest Research Institute 1988). The fruits have an ovate nut, large wing (about Malaysia (FRIM; ®eld 25, 9/11 and 10v) the arti®cial 5 cm long) and are dispersed by gravity; thus most of forest, and Tampin the seed orchard. Bukit Sai and the fruits fall under the crown of the mother tree. It is Lesong belong to the lowland dipterocarp forest types one of the fastest growing timber species in Peninsular with D. aromatica being the predominant species. Selec- Malaysia. The timber is a medium hardwood and is tive logging operations in Lesong carried out between moderately durable in tropical conditions. It is suitable 1996 and 1997 intensively reduced the density of mature for heavy construction, posts, beams, joints and railway D. aromatica and other dipterocarp trees. The arti®cial sleepers. forest of FRIM was established in 1927; its 200 ha Estimations of outcrossing rates in plant populations comprises D. aromatica and various dipterocarp and have been reported for several tropical species and most nondipterocarp timber tree species, and is surrounded of the species are predominantly outcrossing (summar- by primary and secondary forests. The D. aromatica ized by Nason & Hamrick, 1997). Recent studies have seed orchard of Tampin (2 ha) was established in 1928 focused on how the outcrossing rates can be in¯uenced by the Forest Department and is surrounded by rubber by forest activities. Murawski et al. (1994b) found that plantations. The seed source of the arti®cial forest and the reduction in population density of Shorea megisto- seed orchard is unknown. phylla following a selective logging event had enhanced Estimations of the densities of D. aromatica mature sel®ng substantially. Similarly, Murawski & Hamrick trees (more than 30 cm d.b.h.) were made from ®ve (1992a) reported that the outcrossing rates of Cavanil- plots, each 0.25 ha in area, in each of the three forest lesia platanifolia were positively correlated with density types and the seed orchard. Fifteen individuals per of ¯owering trees. However, Hall et al. (1996) demon- hectare were found in Bukit Sai, seven in Lesong, 16 in strated outcrossing rates to be independent of tree FRIM and 20 in Tampin. During August 1998, the mass density in Pithecellobium elegans. The low density of fruiting season of D. aromatica in Peninsular Malaysia, ¯owering adults just resulted in poor seed crops or estimates based on the ®ve plots showed that approxi- failure to set fruit for many individuals. Doligez & Joly mately 60% of the adult trees in Bukit Sai and Lesong, (1997) reported that in Carapa procera, outcrossing rates 40% in FRIM and 30% in Tampin were fruiting. Ten in logged plots were signi®cantly lower than in undis- mother trees were selected each from Bukit Sai, Lesong turbed plots, even though tree density in logged plots and Tampin and 15 from FRIM. Mother trees were was not signi®cantly dierent from undisturbed plots. In selected randomly with intervening distances of contrast, Kitamura et al. (1994) found no signi®cant 100±1000 m. Seeds were collected using the `shaking- dierence for outcrossing rates of D. aromatica from catch' method, in which a weight attached to a nylon Brunei in secondary (tm 0.79) and primary forest ®shing string was shot over a branch using a catapult, stands (tm 0.86), even though ¯owering tree density and used to haul up a thicker, stronger nylon line. The in secondary forest was signi®cantly lower than primary ends of the line were then pulled vigorously to detach forest. Comparing outcrossing in arti®cial and natural the seeds; the seeds were easily caught as they gyrated forests is fundamental to a better understanding of toward the ground (Lee et al. 2000a). mating systems in arti®cial populations and provides Embryos of 35±40 seeds of each mother tree were useful information for seed orchard design and man- homogenized in 200 lL extraction buer, consisting of agement. Besides looking at natural populations 50 mM borate buer (pH 8.0), 1% PVP-40, 2% BSA, (primary forest and logged forest), this study also 10 mM ascorbic acid, 6 mM DTT, 20 mM Na2S2O5, investigated the mating characteristics of D. aromatica 0.1% b-mercaptoethanol, 0.05 M DIECA, 0.5 M Ó The Genetical Society of Great Britain, Heredity, 85, 338±345. 340 S. L. LEE sucrose, 1% tween-80, 1% 20 M PEG, 0.5% 2-phen- maternal genotypes; and (vi) the pollen pool is assumed oxyethanol, 1% tergitol, 0.2% MgCl2, 0.2% CaCl2 and to be homogeneous over all the maternal trees (Ritland 5mM EDTA. Electrophoresis was performed using & Jain, 1981; Brown et al., 1989). In order to test for horizontal starch gel. Genetic interpretations of the violations of the last assumption of the mixed mating banding patterns were based on two criteria: (i) if the model, chi-squared tests were performed to determine maternal genotype for a given locus was heterozygous, homogeneity of the pollen pool reaching each female.