Summary• Polymorphic simple sequence repeat (SSR) markers were used to investigate the impact of habitat fragmentation on the population structure and gene flow of Changiostyrax dolichocarpa , a critically endangered tree in central China.• Intrapopulation genetic diversity, population structure and gene flow in the five extant populations of this species were analysed by eight SSR markers.• Intrapopulation genetic diversity results suggest that C . dolichocarpa remnants maintained a relatively high degree of genetic diversity despite severe fragmentation. Low genetic differentiation among populations was found based on Wright's F ST and AMOVA analysis. Both the F ST -based estimate and private allele method revealed high historical gene flow among the remnant populations. Recent immigrants, detected by assignment tests, tend to decrease from the grandparent generation to the current generation.• The potentially highly restricted current gene flow among fragments may render the fragmented populations of C . dolichocarpa at a higher risk of local extinction several generations after fragmentation. Both in situ and ex situ conservation management for the remnant populations of C . dolichocarpa are therefore urgently needed to rescue remaining genetic diversity.

Background:Brachial plexus block (BPB) for upper extremity surgery provides superior analgesia, but this advantage is limited by the pharmacological duration of local anesthetics. Dexmedetomidine (DEX) as a local anesthetics adjuvant for BPB has been utilized to prolong the duration of the nerve block in some randomized controlled trials (RCTs) but is far from unanimous in the efficacy and safety of the perineural route. Hence, an updated meta-analysis was conducted to assess the efficacy and safety of DEX as local anesthetic adjuvants on BPB.Methods:A search in electronic databases was conducted to collect the RCTs that investigated the impact of adding DEX to local anesthetics for BPB. Sensory block duration, motor block duration, onset time of sensory and motor block, time to first analgesic request, the common adverse effects were analyzed.Results:Eighteen trails (1014 patients) were included with 515 patients receiving perineural DEX. The addition of DEX prolonged the duration of sensory block (WMD 257 minutes, 95%CI 191.79–322.24, P < 0.001), motor block (WMD 242 minutes, 95%CI 174.94–309.34, P < 0.001), and analgesia (WMD 26 6 minutes, 95%CI 190.75–342.81, P < 0.001). Perineural DEX also increased the risk of bradycardia (OR=8.25, 95%CI 3.95–17.24, P < 0.001), hypotension (OR = 5.62, 95%CI 1.52–20.79, P < 0.01), and somnolence (OR = 19.67, 95%CI 3.94–98.09, P < 0.001). There was a lack of evidence that perineural DEX increased the risk of other adverse events.Conclusions:DEX is a potential anesthetic adjuvant that can facilitate better anesthesia and analgesia when administered in BPB. However, it also increased the risk of bradycardia, hypotension, and somnolence. Further research should focus on the efficacy and safety of the preneural administration of DEX.