Z. 2009. Effect of habitat fragmentation on the genetic diversity of Stipa krylovii Reshov. in an agro-pastoral ecotone in northern China. Can. J. Plant Sci. 89: 875Á882. Native grassland in China have been fragmented due to the introduction of agriculture, which has the potential to reduce genetic diversity. In order to understand the potential effects of fragmentation, we conducted a study to examine the genetic diversity between two populations of Stipa krylovii in a typical steppe ecoregion, in northern China. One population was fragmented by farmland (PF) while the second was continuous steppe (PS). The populations were 30 km apart. Genetic diversity was assessed by sampling plants in four geographically similar subpopulations in each population and analyzed for their DNA using the inter-simple sequence repeats (ISSR) markers. Of 50 primers tested, 7 produced 122 amplified bands from 120 individuals, of which 92% (112) were polymorphic. According to the UPGMA dendogram, the four PF subpopulations were grouped separately from the four PS subpopulations. However, AMOVA analysis indicated that habitat fragmentation over the past 50 yr had not changed genetic diversity and variation among S. krylovii populations in an agro-pastoral ecotone in northern China. Therefore, the genetic diversity of this species can be maintained if agriculture disturbance is not increased.Key words: Genetic variation, gene flow, ISSR, fragmented population, non-fragmented population Zheng, S., Wang, K., Zhao, M., Mi, J., Sui, X., Feng, Y. et Cao, Z., 2009. Incidence du fractionnement de l'habitat sur la diversite´ge´ne´tique de Stipa krylovii Reshov. dans un e´cotone agropastoral du nord de la Chine. Can. J. Plant Sci. 89: 875Á882. En Chine, l'ave`nement de l'agriculture a fractionne´les prairies naturelles, ce qui pourrait susciter une diminution de la diversite´ge´ne´tique. Pour comprendre les conse´quences e´ventuelles d'un tel fractionnement, les auteurs ont entrepris une e´tude sur la diversite´ge´ne´tique de deux populations de Stipa krylovii dans une e´core´gion typique a`la steppe du nord de la Chine. Une population (PF) avait e´te´fragmente´e par des terres agricoles alors que la seconde (PS) formait une steppe continue, les deux e´tant distantes de 30 kilome`tres. On a e´value´la diversite´ge´ne´tique en e´chantillonnant les plants de quatre populations secondaires ge´ographiquement semblables au sein de chaque population et en analysant leur ADN graˆce a`des marqueurs ISSR (amplification intermicrosatellite). Sur les 50 amorces teste´es, 7 ont donne´122 bandes chez 120 individus dont 92 % (112) e´taient polymorphes. Selon le dendogramme UPGMA, les quatre sous-populations PF forment un groupe distinct des quatre sous-populations PS. Ne´anmoins, l'analyse de la variance mole´culaire (AMOVA) indique que le fractionnement de l'habitat survenu au cours des 50 dernie`res anne´es n'a modifie´ni la diversite´ni les variations ge´ne´tiques observe´es chez S. krylovii dans l'e´cotone agropastoral du nord de la Chine. Par conse´que...

BackgroundIt is clear that exercise helps the symptoms of osteoarthritis. However, the relationship between physical activity (PA) and progression of knee osteoarthritis (OA) remains controversial. Moreover, no guideline on the amount of PA to prevent OA progression in general older population has been recommended, and it is still uncertain whether PA should be promoted among subgroups with knee OA such as female gender, obesity, radiographic osteoarthritis (ROA) and knee injury history. Osteophyte (OP) has long been viewed as a defining structural feature of knee OA. Recently, MRI-detected OPs have been shown to be more sensitive to change than radiographs.ObjectivesThe aims of this study were to describe the longitudinal association between objectively-measured PA and knee MRI-detected (OPs), and to test the interactions between PA and gender, obesity, ROA or knee injury history on the increases in MRI-detected OPs.Methods408 community-dwelling adults aged 51–81 were randomly selected from local community and measured at baseline and 2.6 years later. T1-weighted fat suppressed MRI was used to evaluate knee OPs at baseline and after 2.6 years. PA was assessed at baseline by pedometers (steps per day) and categorized as 3 groups: low PA (≤7499 steps per day), moderate PA (7500 to 9999 steps per day) and high PA (≥10000 steps per day). Radiographs were obtained and scored for individual features of radiographic osteoarthritis (ROA). Knee injury history was recorded by questionnaire and body mass index (BMI) was calculated. Logistic regression and log binomial regression were used in longitudinal analyses.ResultsIn total study sample, doing moderate PA was associated with reduced risk of an increase in MRI-detected OPs, comparing to low PA (RR=0.73, p=0.03). There were significant interactions between PA and gender, obesity, ROA or knee injury history (all p<0.05) for an increase in MRI-detected OPs. In stratified analyses, moderate PA was protective against an increase in MRI-detected OPs in females (OR=0.23, p<0.01), obese participants (OR=0.23, p<0.01), participants with ROA (OR=0.45, p=0.02) and participants with knee injury history (OR=0.05, p=0.02). These significant associations still existed after further adjustments for age, sex, BMI, ROA and/or knee injury history (where appropriate). High PA was not associated with an increase in MRI-detected OPs in total sample or the stratified analyses but there were relatively few in this category.ConclusionsModerate PA is protective for change in MRI-detected OPs in older adults, especially in those with female gender, ROA, obesity and knee injury history. This implies older people with above risks of knee OA may need to aim for a range from 7500 to 9999 steps per day.References Dore DA, Winzenberg TM, Ding C, Otahal P, Pelletier JP, Martel-Pelletier J, et al. The association between objectively measured physical activity and knee structural change using MRI. Ann Rheum Dis 2013; 72: 1170–1175. AcknowledgementsThe authors thank the participants who made this study pos...