Evaluating contemporary pollen dispersal in two common grassland species Ranunculus bulbosus L. (Ranunculaceae) and Trifolium montanum L. (Fabaceae) using an experimental approach.

Pollen flow is a key biological process that connects plant populations, preventing genetic impoverishment and inbreeding. Pollen-mediated long-distance dispersal (LDD) events are especially important for plant species in increasingly fragmented landscapes. Patterns of pollen dispersal were directly estimated and dispersal kernels modelled in an experimental population of Ranunculus bulbosus and Trifolium montanum to determine the potential for LDD. Eight and 11 microsatellite markers were used for R. bulbosus and T. montanum, respectively, to run a likelihood-based paternity analysis on randomly chosen offspring (Ntotal = 180 per species) from five maternal plants. High rates of selfing were found in R. bulbosus (average 45.7%), while no selfing was observed in T. montanum. The majority (60%) of mating events occurred at very short distances: the median of the observed dispersal distances was 0.8 m in both species, and the average distances were 15.9 and 10.3 m in R. bulbosus and T. montanum, respectively. Modelling the pollen dispersal kernel with four different distribution functions (exponential-power, geometric, 2Dt and Weibull) indicated that the best fit for both species was given by a Weibull function. Yet, the tail of the T. montanum pollen dispersal kernel was thinner than in R. bulbosus, suggesting that the probability for LDD is higher in the latter species. Even though the majority of pollen dispersal occurred across short distances, the detection of several mating events up to 362 m (R. bulbosus) and 324 m (T. montanum) suggests that pollen flow may be sufficient to ensure population connectivity in these herb species across fragmented grasslands in Swiss agricultural landscapes.

Does long-distance pollen dispersal preclude inbreeding in tropical trees? Fragmentation genetics of Dysoxylum malabaricum in an agro-forest landscape.

Tropical trees often display long-distance pollen dispersal, even in highly fragmented landscapes. Understanding how patterns of spatial isolation influence pollen dispersal and interact with background patterns of fine-scale spatial genetic structure (FSGS) is critical for evaluating the genetic consequences of habitat fragmentation. In the endangered tropical timber tree Dysoxylum malabaricum (Meliaceae), we apply eleven microsatellite markers with paternity and parentage analysis to directly estimate historic gene flow and contemporary pollen dispersal across a large area (216 km(2)) in a highly fragmented agro-forest landscape. A comparison of genetic diversity and genetic structure in adult and juvenile life stages indicates an increase in differentiation and FSGS over time. Paternity analysis and parentage analysis demonstrate high genetic connectivity across the landscape by pollen dispersal. A comparison between mother trees in forest patches with low and high densities of adult trees shows that the frequency of short-distance mating increases, as does average kinship among mates in low-density stands. This indicates that there are potentially negative genetic consequences of low population density associated with forest fragmentation. Single isolated trees, in contrast, frequently receive heterogeneous pollen from distances exceeding 5 km. We discuss the processes leading to the observed patterns of pollen dispersal and the implications of this for conservation management of D. malabaricum and tropical trees more generally.

Forest fragmentation genetics in a formerly widespread island endemic tree: Vateriopsis seychellarum (Dipterocarpaceae).

Habitat fragmentation and changed land use have seriously reduced population size in many tropical forest tree species. Formerly widespread species with limited gene flow may be particularly vulnerable to the negative genetic effects of forest fragmentation and small population size. Vateriopsis seychellarum (Dipterocarpaceae) is a formerly widespread canopy tree of the Seychelles, but is now reduced to 132 adult individuals distributed in eleven sites. Using ten microsatellite loci, a genetic inventory of all adult trees and a sample of 317 progeny, we demonstrate that despite its restricted range, overall genetic diversity was relatively high (H(E) : 0.56). The juvenile cohort, however, had significantly lower allelic richness (adults R(S) : 3.91; juveniles R(S) : 2.83) and observed heterozygosity than adult trees (adults H(O) : 0.62; juveniles H(O) : 0.48). Rare alleles were fewer and kinship between individuals was stronger in juveniles. Significant fine-scale spatial genetic structure was observed in remnant adults, and parentage analysis indicated that more than 90% of sampled progeny disperse <25 m and pollen dispersed <50 m. The molecular data confirmed that two populations were derived entirely from self-fertilized offspring from a single surviving mother tree. These populations produce viable offspring. Despite this extreme genetic bottleneck, self-compatibility may provide V. seychellarum with some resistance to the genetic consequences of habitat fragmentation, at least in the short term. We discuss our findings in the context of other rare and threatened dipterocarp species which are vulnerable to miss-management of genetic resources and population fragmentation.

Back from the brink: potential for genetic rescue in a critically endangered tree.

Rare plant species are vulnerable to genetic erosion and inbreeding associated with small population size and isolation due to increasing habitat fragmentation. The degree to which these problems undermine population viability remains debated. We explore genetic and reproductive processes in the critically endangered long-lived tropical tree Medusagyne oppositifolia, an endemic to the Seychelles with a naturally patchy distribution. This species is failing to recruit in three of its four populations. We evaluate whether recruitment failure is linked to genetic problems associated with fragmentation, and if genetic rescue can mitigate such problems. Medusagyne oppositifolia comprises 90 extant trees in four populations, with only the largest (78 trees) having successful recruitment. Using 10 microsatellite loci, we demonstrated that genetic diversity is high (H(E) : 0.48-0.63; H(O) : 0.56-0.78) in three populations, with only the smallest population having relatively low diversity (H(E) : 0.26 and H(O) : 0.30). All populations have unique alleles, high genetic differentiation, and significant within population structure. Pollen and seed dispersal distances were mostly less than 100 m. Individuals in small populations were more related than individuals in the large population, thus inbreeding might explain recruitment failure in small populations. Indeed, inter-population pollination crosses from the large donor population to a small recipient population resulted in higher reproductive success relative to within-population crosses. Our study highlights the importance of maintaining gene flow between populations even in species that have naturally patchy distributions. We demonstrate the potential for genetic and ecological rescue to support conservation of plant species with limited gene flow.

Identifying the early genetic consequences of habitat degradation in a highly threatened tropical conifer, Araucaria nemorosa Laubenfels.

The early genetic effects of habitat degradation were investigated in the critically endangered conifer Araucaria nemorosa. This species occurs in New Caledonia, a global biodiversity hotspot where the world's greatest concentration of endemic conifer species coincides with an extremely high level of habitat destruction due to fire and mining. Using seven microsatellite loci, estimates were made of genetic marker variation, inbreeding coefficients and population differentiation of adult and seedling cohorts of A. nemorosa. These were contrasted with equivalent estimates, made over similar spatial scales and with the same marker loci, in the locally common and more widespread sister species Araucaria columnaris. There were no significant differences in population genetic parameters between adult populations of the two species, despite their different abundances. However, in A. nemorosa, the juvenile cohort showed a loss of rare alleles and elevated levels of inbreeding when compared to the adult cohort. These genetic differences between the cohorts were not observed in the locally common A. columnaris. This suggests that recent environmental degradation is influencing the genetic structure of A. nemorosa populations. Although this is not detectable among predisturbance adult populations, an early warning of these impacts is evident in more recently established seedling cohorts. The conservation implications of these results are discussed.

The effects of the peptide-coupling agent, EEDQ, on 5-HT2A receptor binding and function in rat frontal cortex.

This ex vivo study in rat frontal cortex determined the influence of 5-HT receptor agonists and antagonists on EEDQ-induced depletion of 5-HT2A binding sites and reduction in their functional coupling to phospholipid hydrolysis. Twenty-four hours after EEDQ (6 mg/kg) administration a marked reduction (66%) of cortical 5-HT2A binding sites with no change in binding affinity was observed. The 5HT2A antagonists ritanserin (1 mg/kg), ketanserin (1 and 5 mg/kg), metergoline (3 mg/kg) or the 5HT2A agonist, DOI (3 and 10 mg/kg) also significantly reduced (by 15-44%) these binding sites 24 h after injection. Thirty minute pretreatment with ritanserin, ketanserin, metergoline or DOI (at the doses above) afforded 49-65% protection against the loss of 5-HT2A binding sites induced by EEDQ (6 mg/kg). DOI (10 mg/kg) pretreatment (-24 h) decreased by 26% the accumulation of [3H]inositol phosphates (IPs) evoked by 5-HT (100 microM), but did not affect that produced by DOI (100 microM). Ketanserin (5 mg/kg, -24 h) decreased 5-HT- and DOI-induced IP formation by 65% and 53%, respectively. The EEDQ (6 mg/kg, -24 h)-evoked reductions (-50%) of 5-HT- and DOI-induced IP formation were not altered by DOI (10 mg/kg) or ketanserin (5 mg/kg) given 30 min before EEDQ. G-protein-stimulated IP accumulation was unaffected by EEDQ (6 mg/kg). Overall, EEDQ reduces 5-HT2A binding sites and function in rat frontal cortex, whereas its effects on binding were attenuated by various 5-HT receptor antagonists and agonists, its effects on function was unaltered by these drugs.

D1 receptor binding in rat striatum: modification by various D1 and D2 antagonists, but not by sibutramine hydrochloride, antidepressants or treatments which enhance central dopaminergic function.

[3H]SCH 23390 is a selective high affinity ligand for D1 receptors in vitro. Using this ligand persistent blockade of D1 receptors by SCH 23390 and cis-flupenthixol was shown to significantly increase the number of D1 receptor binding sites in rat striatum. In contrast, repeated administration of the D2-selective antagonist, clebopride, resulted in a small, but significant, reduction in number. No differences in binding affinity were observed and a single dose of these compounds was without effect. The D2-selective antagonist, haloperidol, the non-selective D1/D2 receptor antagonist, chlorpromazine, the dopamine reuptake inhibitors, bupropion, GBR 12909 and nomifensine, and the dopamine releasing agent, d-amphetamine, had no effect on D1 receptors. The antidepressant treatments, desipramine, zimeldine, amitriptyline, tranylcypromine, mianserin and ECS and the monoamine reuptake inhibitor, sibutramine, similarly did not alter striatal D1 sites. Thus, of the treatments investigated only chronic receptor blockade by high affinity antagonists altered D1 receptor binding in rat striatum.