Population assignment in autopolyploids.

Understanding the patterns of contemporary gene dispersal within and among populations is of critical importance to population genetics and in managing populations for conservation. In contrast to diploids, there are few studies of gene dispersal in autopolyploids, in part due to complex polysomic inheritance and genotype ambiguity. Here we develop a novel approach for population assignment for codominant markers for autotetraploids and autohexaploids. This method accounts for polysomic inheritance, unreduced gametes and unknown allele dosage. It can also utilise information regarding the origin and genotype of one parent for population assignment of maternal or paternal parents. Using simulations, we demonstrate that our approach achieves high levels of accuracy for assignment even when population divergence is low (FST~0.06) and with only 12 microsatellite loci. We also show that substantially higher accuracy is achieved when known maternal information is utilised, regardless of whether allele dosage is known. Although this novel method exhibited near identical levels of accuracy to Structure when population divergence was high, it performed substantially better for most parameters at moderate (FST=0.06) to low levels of divergence (FST=0.03). These methods fill an important gap in the toolset for autopolyploids and pave the way for investigating contemporary gene dispersal in a widespread group of organisms.

Source population characteristics affect heterosis following genetic rescue of fragmented plant populations.

Understanding the relative importance of heterosis and outbreeding depression over multiple generations is a key question in evolutionary biology and is essential for identifying appropriate genetic sources for population and ecosystem restoration. Here we use 2455 experimental crosses between 12 population pairs of the rare perennial plant Rutidosis leptorrhynchoides (Asteraceae) to investigate the multi-generational (F(1), F(2), F(3)) fitness outcomes of inter-population hybridization. We detected no evidence of outbreeding depression, with inter-population hybrids and backcrosses showing either similar fitness or significant heterosis for fitness components across the three generations. Variation in heterosis among population pairs was best explained by characteristics of the foreign source or home population, and was greatest when the source population was large, with high genetic diversity and low inbreeding, and the home population was small and inbred. Our results indicate that the primary consideration for maximizing progeny fitness following population augmentation or restoration is the use of seed from large, genetically diverse populations.

Study to investigate the potential of probiotics in children attending school.

BACKGROUND/OBJECTIVES: To determine if consumption of yogurt containing a high dose of probiotic (1×10(10) colony-forming unit per 100 ml), Bifidobacterium animalis subsp. lactis (B. lactis), decreases absences in children 2-4 years attending daycare/school centers. SUBJECTS/METHODS: We conducted a double-blinded, randomized, placebo-controlled, allocation concealment clinical trial in the Washington, DC area. Our active intervention was a strawberry yogurt-based drink supplemented with B. lactis BB-12. The placebo was indistinguishable from the active drink, differing only in absence of the probiotic BB-12. RESULTS: A total of 172 children between the ages of 2 and 4 from the Washington, DC area were enrolled. The primary outcome, missed days of school because of illness per 100 days, was similar in both the active (2.54 days absent/100 school days) and control groups (2.42 days absent/100 school days) (P=0.873). CONCLUSIONS: The probiotic-containing yogurt-based beverage studied did not decrease absences because of illnesses in daycare/school for healthy children ages 2-4 years.

Patterns of hybridization and asymmetrical gene flow in hybrid zones of the rare Eucalyptus aggregata and common E. rubida.

The patterns of hybridization and asymmetrical gene flow among species are important for understanding the processes that maintain distinct species. We examined the potential for asymmetrical gene flow in sympatric populations of Eucalyptus aggregata and Eucalyptus rubida, both long-lived trees of southern Australia. A total of 421 adults from three hybrid zones were genotyped with six microsatellite markers. We used genealogical assignments, admixture analysis and analyses of spatial genetic structure and spatial distribution of individuals, to assess patterns of interspecific gene flow within populations. A high number of admixed individuals were detected (13.9-40% of individuals), with hybrid populations consisting of F(1) and F(2) hybrids and backcrosses in both parental directions. Across the three sites, admixture proportions were skewed towards the E. aggregata genetic cluster (x=0.56-0.65), indicating that backcrossing towards E. aggregata is more frequent. Estimates of long-term migration rates also indicate asymmetric gene flow, with higher migration rates from E. aggregata to hybrids compared with E. rubida. Taken together, these results indicate a greater genetic input from E. aggregata into the hybrid populations. This asymmetry probably reflects differences in style lengths (E. rubida: ~7 mm, E. aggregata: ~4 mm), which can prevent pollen tubes of smaller-flowered species from fertilizing larger-flowered species. However, analyses of fine-scale genetic structure suggest that localized seed dispersal (<40 m) and greater clustering between hybrid and E. aggregata individuals may also contribute to directional gene flow. Our study highlights that floral traits and the spatial distributions of individuals can be useful predictors of the directionality of interspecific gene flow in plant populations.

Population size, self-incompatibility and genetic rescue in diploid and tetraploid races of Rutidosis leptorrhynchoides (Asteraceae).

Self-incompatibility systems function to prevent inbreeding, and work effectively in large, genetically diverse populations. However, a decrease in population size can reduce genetic diversity at the self-incompatibility locus, which leads to a reduction in mate availability and has important demographic implications for small populations. Currently, little is known about the response of self-incompatible polyploid species to a reduction in population size. In Rutidosis leptorrhynchoides there was a significant decrease in the within-population probability of fertilization with a decline in population size for diploid populations and a marginally significant relationship for tetraploid populations, suggesting that in small populations of both chromosome races fertilization success is reduced due to a decrease in self-incompatibility allele (S-allele) diversity. There was no significant difference between the slopes of the fertility-population size relationship for diploid and tetraploid populations which indicates a similar rate of decline in fertilization success with population size for both chromosome races. Fertilization success increased when crosses were undertaken between populations and this was significantly related to population size for diploid and tetraploid populations, indicating that small populations gain the greatest benefit to fertilization success from crossing between populations. For tetraploid populations the benefits of crossing between populations tended to decline more rapidly with increasing population size. These results suggest that for small populations that have reduced fertilization success, genetic rescue by introducing new genetic material from other populations is an important means of ameliorating mate limitation issues associated with reduced S-allele diversity in both diploid and tetraploid races.

Low neighbourhood size and high interpopulation differentiation in the endangered shrub Grevillea iaspicula McGill (Proteaceae).

Mating system parameters and genetic diversity were examined for five populations of the endangered shrub Grevillea iaspicula (Proteaceae). Controlled pollinations show that G. iaspicula has an effective self-incompatibility system and little potential for agamospermy. This is reflected in uniformly high multilocus outcrossing rates (tm=0.96-1.00). However, average paternal diversity within open-pollinated sibships is low (rp=0.31-0.54), suggesting that mating within populations is quite restricted. Despite the small size of most populations (four of the five populations studied have fewer than 20 reproductive individuals) the species still possesses moderate to high allelic richness (A=1.6-2.5). Interpopulation genetic differentiation is high (D=0.04-0.32), suggesting that gene flow is limited, even among populations separated by only a few kilometres.

Genetic diversity and phylogenetic relatedness among six endemic Pterostylis species (Orchidaceae; series Grandiflorae) of Western Australia, as revealed by allozyme polymorphisms.

Starch gel electrophoresis was employed to survey the allozyme polymorphism and phylogenetic relationships among 35 populations covering six closely related Western Australian endemic Pterostylis species (series Grandiflorae); viz P. rogersii, P. aspera, P. angusta, P. hamiltonii, P. scabra and P. aff. alata. The aim of this study was to determine intraspecific and interspecific genetic diversity and species relationships based on allozyme analysis. The frequencies of 56 alleles at 12 enzyme systems coded by 15 loci were determined along with a mean intraspecific genetic identity value. Allozyme markers clearly discriminated populations belonging to different species. Nei's genetic distance/identity co-efficient was used to measure the level of genetic differentiation among populations and species. Based on these values, a dendrogram was constructed which revealed that all the populations clustered into groups corresponding to the respective species. Gene diversity analysis among all the species revealed total genetic diversity H(t) of 0.23 with co-efficient of gene differentiation 10% (G(st)=0.10). Mean genetic variability (H(e)=0.136, P=40%) was also higher than for other outbreeding plant species. Mean genetic identity coefficient of populations of all species was 0.859 which increased to 0.877 upon exclusion of P. aff. alata, indicating a high degree of similarity among all species except P. aff. alata which segregated distinctively from the rest. Overall, the investigation provided independent support for the morphological segregation of these taxa.

Low outcrossing rates and shift in pollinators in New Zealand pohutukawa (Metrosideros excelsa; Myrtaceae).

New Zealand pohutukawa (Metrosideros excelsa), a member of the Myrtaceae, is a large, mass-flowering tree endemic to northern New Zealand coastlines. Mainland populations have been reduced to fragmented stands, and the original suite of bird pollinators has been largely replaced by introduced species. The native pollinator fauna on several offshore islands is largely intact and includes three species of the New Zealand honeyeaters (Meliphagidae) and native, solitary bees. We estimated multilocus outcrossing rates for three mainland and two island populations and found that they were among the lowest in the Myrtaceae (t(m) = 0.22-0.53). The shift in pollinators had no measurable effect on the mating system. Mass-flowering facilitates geitonogamous selfing, and inbreeding depression in seedling height was detectable at 6 mo of growth. F(s) [Wright's (1965) Fixation Index] was consistently higher than F(m) in all populations, indicating that selection may eliminate selfed offspring from populations prior to achieving reproductive maturity. Results suggest that increased selfing in mainland populations due to pollinator changes is not responsible for current patterns of poor regeneration of this species.

Genetic diversity in tetraploid populations of the endangered daisy Rutidosis leptorrhynchoides and implications for its conservation.

Polyploidy is an important variable in assessing the genetics of endangered plant species. Species consisting of populations with different chromosome numbers pose questions as to the mode of inheritance, relative variability status, population divergence and gene flow. The self-incompatible species Rutidosis leptorrhynchoides (Asteraceae) in south-eastern Australia is a good example. The remnant populations in the northern sector of the species range are diploid, whereas southern ones are either diploid or tetraploid. Allozyme analysis of the tetraploid populations showed tetrasomic inheritance confirming an autopolyploid genetic system, a modest increase in their allelic richness over diploid populations in the same region and a lack of genetic divergence. Conservation and replenishment strategies should take account of these genetic features of mixed ploidy.