Rapid Loss of Genetic Variation in Large Captive Populations of Drosophila Flies: Implications for the Genetic Management of Captive Populations

Levels of variation in eight large captive populations of D. melanogaster (census sizes ∼ 5000) that had been in captivity for periods from 6 months to 23 years (8 to 365 generations) were estimated from allozyme heterozygosities, lethal frequencies, and inversion heterozygosities and phenotypic variances, additive genetic variances ( V _A), and heritabilities ( h ²) for sternopleural bristle numbers. Correlations between all measures of variation except lethal frequencies were high and significant. All measures of genetic variation declined with time in captivity, with those for average heterozygosities, V _A, and h ² being significant. The effective population size ( N _e) was estimated to be 185–253 in these populations, only 0.037–0.051 of census size (N). Levels of allozyme heterozygosities declined rapidly in two large captive populations founded from another wild stock, being reduced by 86% and 62% within 2.5 years in spite of being maintained at sizes of approximately 1000 and 3500. Estimates of N _e/ N for these populations were only 0.016 and 0.004. Two estimates of N _e/ N for captive populations of D. pseudoobscura from data in the literature were also low at 0.036 and 0.012. Consequently, the rate of loss of genetic variation in captive populations and endangered species may be more rapid than hitherto recognized. Merely maintaining captive populations at large census sizes may not be sufficient to maintain essential genetic variation.     

Genetic Variation for Morphological and Allozyme Variation in Relation to Population Size in Clarkia dudleyana, an Endemic Annual

Abstract: The maintenance of genetic variation within populations is expected to allow species to respond to evolutionary challenges such as selection and environmental stress. Larger populations are generally expected to maintain larger amounts of genetic variation. Although several studies have found a positive relationship between population size and levels of genetic variation for molecular markers such as allozymes, few comparisons have been made between molecular measures of variation and genetic variation that is likely to be ecologically important. Most ecologically important traits require quantitative genetic analyses. I examined the relationship between levels of genetic variation and population size for both allozymes and morphological traits in a California endemic annual plant, Clarkia dudleyana . Levels of genetic variation for allozymes did not show a significant positive relationship with population size. The level of genetic variance for all of the 18 morphological traits exhibited no significant relationship with population size. Further, allozyme heterozygosities were not related to levels of quantitative genetic variation. These results indicate that levels of allozyme variability do not predict levels of genetic variation for morphological traits in C. dudleyana , suggesting that molecular measures of variation, in general, differ from quantitative genetic measures. These results imply that conservation genetic studies should generally focus on aspects other than measuring levels of genetic variation found within populations.     

Comparisons of Genetic Diversity in the Endangered Adenophora lobophylla and Its Widespread Congener, A. potaninii

Abstract: Starch-gel electrophoresis was used to examine the levels and distribution of genetic diversity in two Adenophora species: the narrow endangered Adenophora lobophylla and its widespread congener, A. potaninii . Based on allozyme variation at 18 putative loci, we measured high levels of genetic variability both in the endangered and the widespread species, with 83.3% of the loci being polymorphic. The mean expected heterozygosity within populations (   H _ep  ) and within species (   H _es  ) were 0.234 and 0.244 for A. potaninii and were as high as 0.210 and 0.211 for A. lobophylla . There was higher differentiation among populations in A. potaninii (   F _ST = 0.155) than in A. lobophylla (   F _ST = 0.071). The high levels of genetic diversity in the present allozyme survey are consistent with the morphological variation observed in these species and may be attributed to high outcrossing rates in the Adenophora species. In addition, A. lobophylla was identified as a distinct species on the basis of Nei's genetic distances and thus should be given a high priority for protection. It is noteworthy that the endangered A. lobophylla maintains much higher genetic diversity than most endemic or narrowly distributed plant species in spite of its restricted distribution. We hypothesize that A. lobophylla has become endangered for ecological and stochastic reasons, including habitat destruction or environmental changes, mud slides, and human disturbance such as grazing and mowing. Consequently, habitat protection is of particular importance for conserving this endangered species.     

A Reassessment of Homozygosity and the Case for Inbreeding Depression in the Cheetah, Acinonyx jubatus: Implications for Conservation

Preservation of genetic diversity within declining populations of endangered species is a major concern in the discipline of conservation biology. The endangered cheetah, Acinonyx jubatus , exhibits relatively little genetic variability (polymorphism = 0.02–0.04, heterozygosity = 0.0004–0.014). Since the discovery of the cheetah's relative homozygosity, this species has been frequently cited as an example of one whose survival may be compromised by the loss of genetic diversity. The cheetah's genetic uniformity is generally believed to be the result of an historical population bottle-neck followed by a high level of inbreeding. Evidence offered in support of this hypothesis includes the cheetah's present low level of genetic variability and symptoms of inbreeding depression in captive populations. Using available data on fluctuating asymmetry and genetic variation in other carnivores, I question the assumption that the present level of genetic diversity in the cheetah is indicative of a loss of former variability. Carnivores exhibit significantly lower levels of genetic variation than other mammals, and several carnivores for which data are available exhibit lower levels of heterozygosity and polymorphism than the cheetah does. Measures of fluctuating asymmetry do not support the hypothesis that the cheetah is suffering an increased level of bomozygosity due to genetic stress. Many of the phenotypic effects attributed to inbreeding depression, such as infertility, reduced litter sizes, and increased susceptibility to disease, are limited to captive individuals and may be explained as physiological or behavioral artifacts of captivity. In sum, the genetic constitution of the cheetah does not appear to compromise the survival of the species. Conservation efforts may be more effectively aimed at a real, immediate threat to the cheetah's future: the loss of its natural habitat.     

Translocations and the Preservation of Allelic Diversity

Translocation is a tool commonly used for the conservation of threatened and endangered fish species. Despite extensive use, the biological implications of translocation remain poorly understood. Of particular interest is the effect of translocation on genetic variability. Maintenance of genetic variability in these "refuge" populations is assumed to be important for both short- and long-term success. We examined allozyme variability at 16 loci for western mosquitofish ( Gambusia affinis ) populations with known histories of introduction. Refuge populations had significantly lower levels of heterozygosity. Refuge populations also had considerably lower levels of allelic diversity than parental populations. All losses were of relatively rare alleles (frequency less than 0.1 in parental population). These losses were probably due to an undocumented bottleneck early in the introduction history. These results were surprising because the initial transplant involved 900 fish and because mosquitofish have numerous reproductive traits that should minimize the effects of bottlenecks on genetic diversity. A literature review revealed that genetic variability is often reduced in refuge populations and that such reductions typically involve the loss of alleles. We suggest that translocated populations be examined periodically for losses of genetic variability.     

Genetic Variation and the Immune Response in Natural Populations of Pocket Gophers

It is thought that genetic variation can affect the persistence of a population through its influence on disease susceptibility. We assessed genome-wide genetic variation, variation at a locus involved in the immune system, and acceptance or rejection of skin grafts in three natural populations of the pocket gopher ( Thomomys bottae ). Multilocus DNA fingerprints confirmed previous allozyme data, revealing high levels of variation among Hastings Reserve pocket gophers and almost complete within-population identity for individuals from the two Patricks Point populations (Patricks J and Patricks F), although Patricks J animals were dissimilar to animals from Patricks F despite their proximity. Individuals from the high-variation population consistently rejected within-population reciprocal skin grafts, whereas Patricks J and Patricks F individuals accepted within-population grafts. Patricks J and Patricks F individuals were found to be immunocompetent, however, as revealed by the ability of all individuals to reject between-population grafts, including those that previously accepted within-population grafts. A DNA heteroduplex analysis was then used to directly characterize variability at DQα, a locus of the immune system's major histocompatability complex. Both populations low in genetic variation were fixed for unique DQα alleles, whereas observed heterozygosity in the Hastings population was 0.43, ascribable to at least three unique alleles. These data are in accord with previous cheetah skin-graft results and confirm that skin grafts can be used to assess genetic similarity. We suggest that although many animal populations can persist with extremely low levels of genetic variation in the wild, such populations may be at a greater risk of extinction from particular pathogens because of their genetic uniformity.     

Genetic Structure of Fragmented Populations of the Endangered Daisy Rutidosis leptorrhynchoides

Abstract: The endangered grassland daisy Rutidosis leptorrhynchoides has been subject to severe habitat destruction and fragmentation over the past century. Using allozyme markers, we examined the genetic diversity and structure of 16 fragmented populations. The species had high genetic variation compared to other plant species, and both polymorphism and allelic richness showed strong positive relationships with log reproductive population size, reflecting a loss of rare alleles (frequency of q < 0.1) in smaller populations. Fixation coefficients were positively related to size, due either to a lack of rare homozygotes in small populations or to Wahlund effects (owing to spatial genetic structure) in large ones. Neither gene diversity nor heterozygosity was related to population size, and other population parameters such as density, spatial contagion, and isolation had no apparent effect on genetic variation. Genetic divergence among populations was low , despite a large north-to-south break in the species' current distribution. To preserve maximum genetic variation, conservation strategies should aim to maintain the five populations larger than 5000 reproductive plants, all of which occur in the north of the range, as well as the largest southern population of 626 plants at Truganina. Only one of these is currently under formal protection. High heterozygosity in smaller populations suggests that they are unlikely to be suffering from inbreeding depression and so are also valuable for conservation. Erosion of allelic richness at self-incompatibility loci, however, may limit the reproductive capacity of populations numbering less than 20 flowering plants.     

Conservation Genetics of Potentially Endangered Mutualisms: Reduced Levels of Genetic Variation in Specialist versus Generalist Bees

Abstract:  Oligolectic bees collect pollen from one or a few closely related species of plants, whereas polylectic bees visit a variety of flowers for pollen. Because of their more restricted range of host plants, it maybe expected that specialists exist in smaller, more isolated populations, with lower effective population sizes than generalists. Consequently, we hypothesized that oligolectic bees have reduced levels of genetic variation relative to related polylectic species. To test this hypothesis, we used five phylogenetically independent pairs of species in which one member was oligolectic and the other was polylectic. We assayed genetic variation in our species pairs at an average of 32 allozyme loci. Within each species pair, the oligolectic member had fewer polymorphic loci, lower average allelic richness, and lower average expected heterozygosity than its polylectic relative. Averaged over all species pairs, this corresponds to a 21% reduction in allelic richness, a 72% reduction in the proportion of polymorphic loci, and an 83% reduction in expected heterozygosity in specialists compared with generalists. Our data support the hypothesis of reduced effective population size in oligolectic bees and suggest that they may be more prone to extinction as a result. We suggest that in instances in which bee specialists are involved in mutually codependent relationships with their floral hosts, these mutualisms may be endangered for genetic and ecological reasons.     

Long-term demographic and genetic effects of releasing captive-born individuals into the wild

Because of continued habitat destruction and species extirpations, the need to use captive breeding for conservation purposes has been increasing steadily. However, the long-term demographic and genetic effects associated with releasing captive-born individuals with varied life histories into the wild remain largely unknown. To address this question, we developed forward-time, agent-based models for 4 species with long-running captive-breeding and release programs: coho salmon (Oncorhynchus kisutch), golden lion tamarin (Leontopithecus rosalia), western toad (Anaxyrus boreas), and Whooping Crane (Grus americana). We measured the effects of supplementation by comparing population size and neutral genetic diversity in supplemented populations to the same characteristics in unaltered populations 100 years after supplementation ended. Releasing even slightly less fit captive-born individuals to supplement wild populations typically resulted in reductions in population sizes and genetic diversity over the long term when the fitness reductions were heritable (i.e., due to genetic adaptation to captivity) and populations continued to be regulated by density-dependent mechanisms over time. Negative effects for species with longer life spans and lower rates of population replacement were smaller than for species with shorter life spans and higher rates of population replacement. Programs that released captive-born individuals over fewer years or that avoided breeding individuals with captive ancestry had smaller reductions in population size and genetic diversity over the long term. Relying on selection in the wild to remove individuals with reduced fitness mitigated some negative demographic effects, but at a substantial cost to neutral genetic diversity. Our results suggest that conservation-focused captive-breeding programs should take measures to prevent even small amounts of genetic adaptation to captivity, quantitatively determine the minimum number of captive-born individuals to release each year, and fully account for the interactions among genetic adaptation to captivity, population regulation, and life-history variation.     

Conservation Genetics of the Endangered Isle Royale Gray Wolf

Abstract. The small group of wolves on Isle Royale has been studied for over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to as few as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population, a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale wolves have an mDNA genotype that is very rare on the mainland, being found in only one of 144 mainland wolves ThFF suggests that the remaining Isle Royale wolves areprobably derived from a single female founder     

Measurement of Genetic Variation in Endangered Populations: Bandicoots (Marsupialia: Peramelidae) as an Example

Abstract. Attempts to monitor the genetic variation of endangered populations by the use of blood protein electrophoresis often suffer from three drawbacks: a small sample of loci, lack of control populations with "normal" variation, and, sometimes, difficulty in confirming inheritance of electromorphs.
An endangered isolate (Hamilton, Victoria) of the eastern barred bandicoot, Perameles gunnii, was compared with a widespread, dense, conspecific population in Tasmania. A previous study of the effective size of the siolate suggested that the loss of variation should be detectable by protein electrophoresis if average heterozygosity () was approximately 0.057 in widespread, dense populations and 20 to 50 individuals from each population were analysed for 25 or more loci. However, no genetic variation was detected within or between samples.
Similar studies proposed as a baseline for monitioring genetic variation could be equally powerless to detect changes in variation, even with quite high values. The analysis of variation in DNA is expected to avoid many of the problems associated with blood protein studies.
This study highlights the importance of a control population. Analysis of the Hamilton population alone might have led us to concludce that the recent population crash has been responsible for the low variation; however, this conclusion is not warranted, because = 0 in the much larger Tasmania population.     

Application of Reproduction Technologies to the Conservation of Genetic Resources

Abstract: Maintaining the levels of genetic variability in captive populations of endangered species is an important objective of conservation biology. Because of the generally low sizes of captive populations, genetic drift is the main cause of loss of diversity. Several simple management rules, such as equalization of contributions from parents to the next generation, are recommended for minimizing genetic drift, but it cannot be removed completely because of the unavoidable random segregation of heterozygotes. Recent advances in reproductive technology, particularly developed for mammals, are now making a reality of the possibility of using more than one cell from a single meiosis in reproduction. With this technology it is possible to reduce or even completely cancel the genetic drift caused by segregation of heterozygotes. We evaluated the theoretical benefits of the use of such technologies to conservation biology. The effective population size can be increased enormously and, consequently, the amount of drift can be greatly reduced if manipulations in reproduction are made.     

Fitness in the Endangered Gila Topminnow

The Gila topminnow (Poeciliopsis o. occidentalis) is a small, live-bearing, endangered fish extant in a maximum of nine locales in four separate watersheds in the United States. To determine if these populations differed in their fitness, we obtained samples from the four watersheds and examined them for four fitness correlates: survival, growth rate, fecundity, and bilateral asymmetry. Earlier research found that one population, Sharp Spring, had higher allozyme heterozygosity than the other three and had higher survival, growth rate, and fecundity and lower bilateral asymmetry than a sample from one of the other populations with no polymorphic allozyme loci, Monkey Spring. We also verified that Sharp Spring fish were polymorphic for the same allozyme loci whereas the Monkey Spring population was not. We did not, however, find positive associations of allozyme heterozygosity with the four fitness correlates for the four samples. Because the earlier study had much lower survival, it is likely that the differences resulted from differential response of the two populations to a stressful laboratory environment. Whether this unknown stress occurs in natural environments or its effect is predictive of other stresses remains unresolved. As a result, we concur with suggestions in the draft recovery plan that topminnows from nearby sources be used for reintroductions and that the Sharp Spring stock not be used outside the upper Santa Cruz River drainage.     

Genetic Variation and Outcrossing Rate in Relation to Population Size in Gentiana pneumonanthe L

The amount of genetic variation in the rare perennial herb Gentiana pneumonanthe L. was determined to explore its relation to population size. Differences in isozyme variation between maternal plants and their offspring were used to investigate the relationship between population size and outcrossing rate. In 25 populations in The Netherlands, differing in size from 1 to more than 50,000 flowering individuals, 16 allozyme loci were analyzed on leaves of maternal plants and offspring grown in a greenhouse. Population size was significantly positively correlated with the proportion of polymorphic loci, but only marginally with heterozygosity and the mean effective number of alleles. Most of the studied populations were characterized by a complete absence of rare alleles, and F -statistics suggest relatively high levels of genetic differentiation among populations and thus a low level of gene flow. Leaf samples (maternal) were mostly in Hardy-Weinberg equilibrium, while several offspring samples showed an excess of homozygotes, which suggests selection favoring heterozygotes. Because most small populations consist only of adult survivors from formerly larger populations, this may partly explain the absence of a clear relationship between genetic variation of the maternal plants and population size. A significant positive correlation was found between the level of cross-fertilization and population size. From these results, we conclude that, to some degree, small populations have a reduced level of genetic variation, while their present isolation in nature reserves has resulted in a very limited interpopulational gene flow level. At present a higher level of inbreeding in small populations contributes to a further loss of genetic variation and may also result in reduced offspring fitness.     

Experimental Tests of Captive Breeding for Endangered Species

Abstract: Several captive breeding regimes were compared for their ability to maintain fitness ( larval viability) and genetic variation in small populations of the housefly ( Musca domestica L.). Populations were either maintained at constant sizes of 40, 200, or 2000 individuals or initiated with two pairs of flies and allowed to grow to 40 individuals ( low-founder-number populations). Low-founder-number populations without migration exhibited low larval viability (22%) after 24 generations, compared to larger populations maintained at either 200 (49%) or 2000 (69%) individuals, and suffered high extinction, with only 44% of the lines surviving 24 generations. Low-founder-number populations subjected to two additional founder ( bottleneck) episodes, reducing them to two pairs of flies, suffered little additional loss in fitness or extinction compared to the single-founder treatments. Migration as low as one individual per generation (2.5% migration) significantly offset both reduced fitness and rate of extinction. Conversely, fitness was not significantly increased for low-founder-number populations when founders were selected from the top performing 20% of pairs under full-sib mating. Populations maintained at 40 individuals were not sustainable, exhibiting low larval viability (35%) and a high extinction rate (40%) over 24 generations, similar to the extinction rates for populations initiated with only four founders. Although none of the populations maintained at 200 individuals went extinct, their fitness was reduced by 20% compared to a large control population maintained at 2000 individuals. Electrophoretic variation was significantly correlated with fitness across treatments, but the correlation of fitness to narrow-sense heritability of two morphometric traits was not significant.     

Choosing between darkness and light: The ecological genetics of photic behaviour in the planktonic larva of Spirorbis borealis

The light-dark preference of individual Spirorbis borealis larvae was measured by the relative amount of time spent in the lighted half of a container. Specimens taken from a tidal pool were 20% more photonegative than those obtained outside the pool, probably because of natural selection against being washed out of the pool at high tide. The between-population behavioural difference was maintained in the laboratory, and is genetic in origin. Applying biometrical genetic analysis to larvae grouped into half-sib families, the within-population variation was used to estimate an upper limit to the heritability of 0.36. It is concluded that the differences among populations greatly exceed heritable variation within populations. A numerical selection model based on the estimated maximum heritability suggests, however, that the populations could diverge by 20% in less than a year, in response to local differences in the selection regime.     

Heterozygosity‐Fitness Correlations and Inbreeding Depression in Two Critically Endangered Mammals

The relation among inbreeding, heterozygosity, and fitness has been studied primarily among outbred populations, and little is known about these phenomena in endangered populations. Most researchers conclude that the relation between coefficient of inbreeding estimated from pedigrees and fitness traits (inbreeding‐fitness correlations) better reflects inbreeding depression than the relation between marker heterozygosity and fitness traits (heterozygosity‐fitness correlations). However, it has been suggested recently that heterozygosity‐fitness correlations should only be expected when inbreeding generates extensive identity disequilibrium (correlations in heterozygosity and homozygosity across loci throughout the genome). We tested this hypothesis in Mohor gazelle (Gazella dama mhorr) and Iberian lynx (Lynx pardinus). For Mohor gazelle, we calculated the inbreeding coefficient and measured heterozygosity at 17 microsatellite loci. For Iberian lynx, we measured heterozygosity at 36 microsatellite loci. In both species we estimated semen quality, a phenotypic trait directly related to fitness that is controlled by many loci and is affected by inbreeding depression. Both species showed evidence of extensive identity disequilibrium, and in both species heterozygosity was associated with semen quality. In the Iberian lynx the low proportion of normal sperm associated with low levels of heterozygosity was so extreme that it is likely to limit the fertility of males. In Mohor gazelle, although heterozygosity was associated with semen quality, inbreeding coefficient was not. This result suggests that when coefficient of inbreeding is calculated on the basis of a genealogy that begins after a long history of inbreeding, the coefficient of inbreeding fails to capture previous demographic information because it is a poor estimator of accumulated individual inbreeding. We conclude that among highly endangered species with extensive identity disequilibrium, examination of heterozygosity‐fitness correlations may be an effective way to detect inbreeding depression, whereas inbreeding‐fitness correlations may be poor indicators of inbreeding depression if the pedigree does not accurately reflect the history of inbreeding. Correlaciones Heterocigosidad‐ Adaptabilidad y Depresión Endogámica en Dos Especies de Mamíferos Críticamente en Peligro     

Translating effects of inbreeding depression on component vital rates to overall population growth in endangered bighorn sheep

Evidence of inbreeding depression is commonly detected from the fitness traits of animals, yet its effects on population growth rates of endangered species are rarely assessed. We examined whether inbreeding depression was affecting Sierra Nevada bighorn sheep (Ovis canadensis sierrae), a subspecies listed as endangered under the U.S. Endangered Species Act. Our objectives were to characterize genetic variation in this subspecies; test whether inbreeding depression affects bighorn sheep vital rates (adult survival and female fecundity); evaluate whether inbreeding depression may limit subspecies recovery; and examine the potential for genetic management to increase population growth rates. Genetic variation in 4 populations of Sierra Nevada bighorn sheep was among the lowest reported for any wild bighorn sheep population, and our results suggest that inbreeding depression has reduced adult female fecundity. Despite this population sizes and growth rates predicted from matrix-based projection models demonstrated that inbreeding depression would not substantially inhibit the recovery of Sierra Nevada bighorn sheep populations in the next approximately 8 bighorn sheep generations (48 years). Furthermore, simulations of genetic rescue within the subspecies did not suggest that such activities would appreciably increase population sizes or growth rates during the period we modeled (10 bighorn sheep generations, 60 years). Only simulations that augmented the Mono Basin population with genetic variation from other subspecies, which is not currently a management option, predicted significant increases in population size. Although we recommend that recovery activities should minimize future losses of genetic variation, genetic effects within these endangered populations-either negative (inbreeding depression) or positive (within subspecies genetic rescue)-appear unlikely to dramatically compromise or stimulate short-term conservation efforts. The distinction between detecting the effects of inbreeding depression on a component vital rate (e.g., fecundity) and the effects of inbreeding depression on population growth underscores the importance of quantifying inbreeding costs relative to population dynamics to effectively manage endangered populations.     

Developing a Sampling Strategy for Baptisia arachnifera Based on Allozyme Diversity

We analyzed the amount and distribution of genetic variation in Baptisia arachnifera Duncan to develop a sampling strategy for ex situ research. Baptisia arachnifera is an endangered plant species endemic to the coastal plain of Georgia (U.S.) where all populations are within 16 km of each other. A reduction in numbers of individuals has been observed during the last 50 years. Baptisia arachnifera was polymorphic at 24% of the 37 loci examined with an average of 1.32 alleles per locus. The genetic diversity index was relatively low ( H_e = 0.097) as expected for endemic species. Populations were in Hardy-Weinberg equilibrium, suggesting that the species is outcrossing. Consistent with this conclusion is the observation that the majority (approximately 90%) of the genetic variation present in the species is found within individual populations. Indirect evidence of gene flow between populations was detected (   Nm = 2.35). The close proximity of the populations and the recent reduction in population sizes suggest that the populations surveyed may be fragments of a once more continuous gene pool. Based on the observed distribution of genetic diversity among populations (G_ST = 0.096), sampling two populations would capture 99% of the allozyme diversity surveyed. Allozyme data were used to determine which 2 of the 10 populations surveyed should be sampled to maximize the ex situ conservation of genetic diversity. Although the paper-producing companies that own most of the land where Baptisia arachnifera occurs are modifying their harvesting techniques, the species could become extinct without more effective management and preservation efforts.     

Effect of Forest Fragmentation on Genetic Diversity and Mating System in a Tropical Tree, Pithecellobium elegans

Genetic diversity, population differentiation, and temporal variation in outcrossing rates were examined for Pithecellobium elegans , a Neotropical rain forest canopy tree. Several forest fragments and a large reserve (1500 ha) were compared for several population genetic parameters. For eight populations sampled on the Atlantic coastal plain of Costa Rica, allozyme heterozygosity (0.13), polymorphism (35%), and effective number of alleles (1.24) were similar to values reported for other tropical tree species that occur at similar densities of less than one individual per hectare. These measures of genetic variation were lowest in populations of the smallest size, farthest from the reserve, and more isolated from other populations. Differentiation among samples collected in small forest fragments and the reserve population accounted for 10% of the total genetic variation observed. There was a positive relationship between the level of differentiation of populations from the reserve population and their distance from the reserve. Though predominantly an annually flowering species, the number of trees in flower at any one time varied from 80% of observed trees to only 6%. Outcrossing rates did not differ for two episodes in which the proportions of flowering trees were 33% and 80%. But periods of low density of flowering adults resulted in poor seed crops or failure to set fruit for many individuals. Population size at many sites will be effectively decreased because of the variation in flowering. Fragmentation of what was once a large, continuous forested area is resulting in genetic erosion of small, isolated populations of Pithecellobium elegans .