Kamaljit S. Bawa

Breeding systems of tree species of a lowland tropical community

Little information is available on the breeding systems of tropical forest trees. Yet a knowledge of reproductive methods is essential for an understanding of the patterns of gene flow and genetic differentiation within and between populations. Such information, in turn, is fundamental to an understanding of speciation and the genetic relationships between species. This paper reports the results of a study on the breeding systems of tree species of a lowland tropical community. The main objective was to determine the relative proportions of self-compatible and selfincompatible species in the community. Controlled pollinations were performed to test for self-compatibility. Supplementary data in the form of observations on floral biology were collected to determine the frequency of dioecious, monoecious, and dichogamous species.

Late-acting self-incompatibility in angiosperms

In most self-incompatible (SI) plants, pollen tube growth in self-pollinated flowers is inhibited on the stigma or in the style. SI systems that operate in the ovary have been assumed to be extremely rare. Evidence from many plant species is presented to show that the SI barriers in the ovary, described here as late-acting SI systems, are quite common. The late-acting SI systems are divided into four categories: (1) ovarian inhibition of incompatible pollen tubes before the ovule is reached; (2) prefertilization inhibition in the ovule; (3) post-zygotic rejection of the embryo, and (4) ovular inhibition for which the cytological details have not been established.Whether or not post-zygotic incompatibility systems can be distinguished from inbreeding depression depends upon the assumptions underlying the genetic models of self-incompatibility. However, four approaches are outlined that could distinguish between active uniform rejections that are presumably evolved responses to inbreeding depression and the passive, variable failures that are commonly understood to be expressions of typical inbreeding depression.Possible advantages of late-acting SI include an extended period of time over which pollen genotypes may be evaluated by the maternal parent and greater flexibility in the choice of male parents.Due to a paucity of data regarding the genetics and physiology of lateacting SI systems, little can be said at this time about the possible diversity of such systems of their evolutionary relationships with classical gametophytic and sporophytic SI.An hypothesis for the operation of post-zygotic SI is described whereby maternal resources to developing embryos are terminated if the embryo (and/or endosperm) fall below a threshold level of heterosis. This hypothesis is a modification of one first proposed by Westoby and Rice in 1982 to explain variable maternal resource allocation to developing embryos.ResuméPour la majorité des plantes autostériles, la croissance du tube pollinique, lorsque l’autopollinisation a lieu, est inhibée sur le stigmate ou dans le style. Il avait été supposé jusqu’ici que les mécanismes l’autostérilisation opérant dans l’ovaire étaient extrêmement rares. Des exemples provenant de plusieurs espèces végétales sont présentés ici pour montrer que les phénomènes d’autostérilisation au niveau de l’ovaire (désignés dans ce qui suit par l’expression “systèmes d’autostérilisation à action tardive”) sont en fait très communs. Les systèmes d’autostérilisation à action tardive son divisés en quatre catégories: (1) Inhibition ovarienne des tubes polliniques incompatibles avant que l’ovule ne soit atteint; (2) Inhibition dans l’ovule avant la fertilisation; (3) Rejet de l’embryon postzygotique; (4) Inhibition ovulaire (les détails cytologiques n’en ont pas encore été entièrement décrits).Suivant les hypothèses sur lesquelles sont basés les différents modèles génétiques décrivant l’autostérilité, il est ou n’est pas possible de faire la distinction entre les systèmes d’incompatibilité post-zygotiques et la dégénérescence consanguine. Quatre différentes approches de la question sont proposées ici pour tenter de distinguer les rejets uniformes actifsqui sont présumés être des conséquences évolutionnaires de la dégénérescence consanguine—des défaillances variables passives, habituellement considérées comme l’expression caractéristique de la dégénérescence consanguine.Deux avantages possibles des systèmes d’autostérilisation à action tardive pourraient être l’extension de la période durant laquelle les génotypes du pollen peuvent être évalués par le parent femelle, et une plus grande flexibilité dans le choix des parents mâles.Vu la rareté des données génétiques et physiologiques en ce qui concerne les systèmes d’autostérilisation à action tardive, il est difficile d’estimer le degré de diversité de ces systèmes, ou leur corrélation évolutionnaire avec les systèmes classiques gamétophytiques et sporophytiques d’autostérilisation.Une hypothèse décrivant le fonctionnement de l’autostérilisation postzygotique est exposée: les ressources maternelles cessent d’être fournies à l’embryon si le niveau d’hétérose de ce dernier (et/ou de l’endosperme) tombe en-dessous d’un seuil. Cette hypothèse est une modification de celle qui fut proposée en premier par Westoby et Rice en 1982 pour expliquer la variation dans l’attribution des ressources maternelles à l’embryon.

Dioecism in tropical forest trees.

The existence of dioecism among angiosperms is universally acknowledged, yet is poorly understood both from the ecological and evolutionary points of view. The reason for this hiatus might be that some have believed the relative proportion of dioecious taxa to be low (Yamplosky and Yamplosky, 1922; Lewis, 1942), while others have felt that since the number of seed-bearing individuals is halved in a dioecious population its evolution is an unlikely and perhaps inconsequential event (HeslopHarrison, 1972). However, recent studies have reported a large proportion of dioecious tree species in tropical forests (Ashton, 1969; Bawa, 1974; see also Tomlinson, 1974); this indicates that the incidence and importance of dioecism may have been underestimated in the past. These new data are significant in at least one other respect. Dioecious (and monoecious) flowers in temperate plants are presumed to have evolved in response to selective pressures favoring wind-pollination (Grant, 1951; Stebbins, 1951), yet windpollination is probably either absent or uncommon in tropical forests (Whitehead, 1969; see also Daubenmire, 1972). Here we present an overview of the adaptive and evolutionary significance of dioecism in general and its expression in certain tropical forests in particular. We first present data on the frequency of dioecious species in a lowland tropical semi-deciduous forest in Costa Rica, then proceed to an examination of available information on

Widespread climate change in the Himalayas and associated changes in local ecosystems.

Background Climate change in the Himalayas, a biodiversity hotspot, home of many sacred landscapes, and the source of eight largest rivers of Asia, is likely to impact the well-being of ∼20% of humanity. However, despite the extraordinary environmental, cultural, and socio-economic importance of the Himalayas, and despite their rapidly increasing ecological degradation, not much is known about actual changes in the two most critical climatic variables: temperature and rainfall. Nor do we know how changes in these parameters might impact the ecosystems including vegetation phenology. Methodology/Principal Findings By analyzing temperature and rainfall data, and NDVI (Normalized Difference Vegetation Index) values from remotely sensed imagery, we report significant changes in temperature, rainfall, and vegetation phenology across the Himalayas between 1982 and 2006. The average annual mean temperature during the 25 year period has increased by 1.5°C with an average increase of 0.06°C yr−1. The average annual precipitation has increased by 163 mm or 6.52 mmyr−1. Since changes in temperature and precipitation are immediately manifested as changes in phenology of local ecosystems, we examined phenological changes in all major ecoregions. The average start of the growing season (SOS) seems to have advanced by 4.7 days or 0.19 days yr−1 and the length of growing season (LOS) appears to have advanced by 4.7 days or 0.19 days yr−1, but there has been no change in the end of the growing season (EOS). There is considerable spatial and seasonal variation in changes in climate and phenological parameters. Conclusions/Significance This is the first time that large scale climatic and phenological changes at the landscape level have been documented for the Himalayas. The rate of warming in the Himalayas is greater than the global average, confirming that the Himalayas are among the regions most vulnerable to climate change.

The economic value and sustainable harvest of plants and animals from the tropical forest: Assumptions, hypotheses, and methods

Recent studies of non-timber products from tropical rain forests have emphasized the economic value of these products and the sustainability of present harvests. Many of these studies rely upon a set of untested assumptions about the effects of harvesting upon the forest and the economic value of non-timber forest products in both the marketplace and in the daily life of rural people. These assumptions were formulated as a series of hypotheses during the workshop held in the Regional Community Forestry Training Center, Kesetsart University, Bangkok, in May 1992. The six hypotheses developed by workshop participants will be used to guide future research. As the hypotheses are tested, the data will be used to create a more realistic assessment of the sustainability and economic value of extraction of non-timber products from tropical forests.

SEX RATIOS IN TROPICAL FOREST TREES

Sex ratios of dioecious plants often depart significantly from unity (Correns, 1922; Dzhapardize, 1967; Godley, 1964; Pauley and Mennel, 1957; Rathore, 1969). Explanations for these deviations have usually been sought in the genetics of sexdetermination (for a review see Westergaard, 1958; Lloyd, 1974). However, biased sex ratios may also have an ecological basis, and thereby have important implications for the reproductive ecology of the subject plants. Yet, relatively few studies have considered the ecological aspects of deviant sex ratios (Harris, 1968; Lloyd, 1973; Lloyd and Webb, 1977; Putwain and Harper, 1972). Here we present data on the sex ratios of 23 species of tropical forest trees and attempt to explain these ratios with respect to certain ecological factors. Our study may be considered noteworthy because most previous studies of sex ratios in dioecious species have been conducted on plants of temperate regions. Since dioecism is more common in tropical than in temperate ecosystems (Bawa and Opler, 1975; see also Ashton, 1969; Tomlinson, 1973), studies of sex ratios in tropical trees should contribute significantly toward an understanding of deviant sex ratios in flowering plants.

Population structure delineated with microsatellite markers in fragmented populations of a tropical tree, Carapa guianensis (Meliaceae)

Deforestation and selective logging in the tropics may have serious consequences on genetic processes in tropical tree populations, affecting long‐term survival of a given species as well as tropical forest communities. Because understanding the effects of human‐induced changes on genetic processes is of utmost importance in formulating sound conservation and management plans for tropical forest communities, we developed microsatellite or simple sequence repeat (SSR) markers for the tropical tree Carapa guianensis (Meliaceae) and assessed the polymorphism of SSRs in adult and sapling populations in a large contiguous forest and in selectively logged and fragmented forests. The number of alleles in polymorphic loci ranged between 4 and 28. No inbreeding was detected in saplings or adult cohorts, but the allelic richness was lower in the sapling cohort of the isolated fragment. Genetic distances, Nei’s D and (δµ)2, and RST values among saplings were greater than among adult cohorts, suggesting restriction of gene flow due to deforestation and habitat fragmentation. These SSR loci may be used to address many related questions regarding the population and conservation genetics of tropical trees.

Isolation and characterization of microsatellites in trembling aspen (Populus tremuloides)

Abstract We have identified, isolated, and characterized microsatellite/simple sequence repeat (SSR) loci in trembling aspen (Populus tremuloides) by screening partial genomic libraries. We have also examined the compatibility and use of the P. tremuloides SSR primers to resolve microsatellites in other Populus species. Fourteen microsatellites were identified from 1600 clones screened. The TC/AG microsatellites were the most abundant. A total of 29 alleles were detected in 36 P. tremuloides individuals at the four SSR loci (two each of di- and tri-nucleotide repeats) characterized. The number of alleles at the SSR loci ranged from 5 to 11, with an average of 7.25 alleles per locus, and the observed heterozygosity ranged from 0.19 to 0.82, with a mean of 0.46 per locus. Although the highest polymorphism was observed for a dinucleotide SSR locus, the trinucleotide SSR loci showed substantial polymorphism. There were 34 unique multilocus genotypes among the 36 P. tremuloides individuals examined, and 89% of the individuals had unique multilocus genotypes. Two pairs of SSR primers were successful in PCR, amplifying genomic DNA and resolving microsatellites of comparable size from Populus deltoides, P. nigra, P.×canadensis, and P. maximowiczii. The microsatellite DNA markers developed could be used for clonal fingerprinting, certification of controlled crosses, genome mapping, marker-assisted early selection, genetic diversity assessments, and conservation and sustainable management of poplar genetic resources.

The effect of ecological factors on the mating system of a South American shrub species (Helicteres brevispira)

Mating systems are influenced by several ecological factors, including plant density, number of flowers per plant, and pollinator movements. In this study, we investigated the simultaneous effects of these three factors on the mating system of a self-compatible Brazilian shrub species: Helicteres brevispira St. Hil. Outcrossing rate is directly correlated with plant density. Changes in the number of flowers per plant affect outcrossing rate through their effect on the density of flowers. Variation in foraging behaviour of hummingbird pollinators is a consequence of the interaction between plant density and number of flowers per plant. Territorialist pollinators are common in high density areas but visit few flowers on each plant, thereby promoting outcrossing. In areas of low plant density, trapliners and rare territorialists visit several flowers per plant, thus increasing selfing. Our results indicate that outcrossing rate is a dynamic parameter, with the extent of variation depending on a number of ecological factors. In successional species such as those in the genus Helicteres, demographic changes may be accompanied by alterations in mating system parameters, with concomitant effects on the genetic structure of populations.

Local perceptions of climate change validated by scientific evidence in the Himalayas

The Himalayas are assumed to be undergoing rapid climate change, with serious environmental, social and economic consequences for more than two billion people. However, data on the extent of climate change or its impact on the region are meagre. Based on local knowledge, we report perceived changes in climate and consequences of such changes for biodiversity and agriculture. Our analyses are based on 250 household interviews administered in 18 villages, and focused group discussions conducted in 10 additional villages in Darjeeling Hills, West Bengal, India and Ilam district of Nepal. There is a widespread feeling that weather is getting warmer, the water sources are drying up, the onset of summer and monsoon has advanced during last 10 years and there is less snow on mountains than before. Local perceptions of the impact of climate change on biodiversity included early budburst and flowering, new agricultural pests and weeds and appearance of mosquitoes. People at high altitudes appear more sensitive to climate change than those at low altitudes. Most local perceptions conform to scientific data. Local knowledge can be rapidly and efficiently gathered using systematic tools. Such knowledge can allow scientists to test specific hypotheses, and policy makers to design mitigation and adaptation strategies for climate change, especially in an extraordinarily important part of our world that is experiencing considerable change.