不受欢迎的生物多样性：香港的外来植物物种

香港早在19世纪中叶开始就有外来植物入侵的记录,迄今为止,已发现多达238种已归化的外来或怀疑为外来的植物,其中又以薇甘菊（Mikania micrantha)、五爪金龙（Ipomoea cairica)、假臭草（Eupatorium catarium)、大黍（Panicum maximum)等最常见,外来植物最常见于受人为干扰的生境,例如荒废农田及路旁等,而较少在天然林地生境及贫瘠的灌草丛中发现,外来植物的对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少了生境及贫瘠的灌草丛中发现,外来植物对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少少了生境及动植物的多样性,外来动物对香港原生植物影响最大的是于20世纪70年代入侵的松树线虫（Bur-saphelenchus xylophilus)。外来的脊椎动物也有可能对香港的植物被演替产生影响,目前香港的外来植物当中,有些在大陆较少分布或没有记录,作为华南最大的港口,香港对外来物种的引入扮演着重要的角色,因此制定控制外来种在香港及华南地区的引入及传播的政策及措施非常重要。     

Tracking island colonization history and phenotypic shifts in Indian Ocean bulbuls (Hypsipetes: Pycnonotidae)

Molecular phylogenies of island organisms provide useful systems for testing hypotheses of convergent or parallel evolution, since selectively neutral molecular characters are likely to be independent of phenotype, and the existence of similar environments on multiple isolated islands provides numerous opportunities for populations to evolve independently under the same constraints. Here we construct a phylogenetic hypothesis for Hypsipetes bulbuls of the western Indian Ocean, and use this to test hypotheses of colonization pattern and phenotypic change among islands of the region. Mitochondrial sequence data were collected from all extant taxa of the region, combined with sequence data from relevant lineages in Asia. Data are consistent with a single Hypsipetes colonization of the western Indian Ocean from Asia within the last 2.6 Myr. The expansion of Hypsipetes appears to have occurred rapidly, with descendants found across the breadth of its western Indian Ocean range. The data suggest that a more recent expansion of Hypsipetes madagascariensis from Madagascar led to the colonization of Aldabra and a secondary colonization of the Comoros. Groupings of western Indian Ocean Hypsipetes according to phenotypic similarities do not correspond to mtDNA lineages, suggesting that these similarities have evolved by convergence or parallelism. The direction of phenotypic change cannot be inferred with confidence, since the primary expansion occurred rapidly relative to the rate of mtDNA substitution, and the colonization sequence remains uncertain. However, evidence from biogeography and comparison of independent colonization events are consistent with the persistence of a small grey continental bulbul in India and Madagascar, and multiple independent origins of large size and green plumage in insular island populations of the Comoros, Mascarenes and Seychelles. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 271–287.     

Character Displacement in Evolutionary Time

Patterns of distribution of morphology in the fossil recordshould be examined more rigorously to evaluate the relativeeffectiveness of alternative evolutionary models and to integratethe dimension of true evolutionary time more directly with evolutionarytheory. Grant (1972) has discussed three main problems in the detectionof character displacement: we must assume that sympatry followedallopatry, that the state in allopatry represents the static,pre-contact state, and that there are no other reasons accountingfor differences within a species in allopatric and sympatriczones. These problems can be largely avoided with suitable paleoiitologicaldata. In an example involving the coincident 10 million-year historiesof two congeneric species of Devonian trilobites, the one knowninstance of sympatry reveals marked divergent shifts in onespecies and a "mixed" reaction of convergent, divergent, andneutral shifts in the other species. The characters undergoingthese shifts are largely those which (i) serve as specific differentia,and (ii) show the most change within one of the species overits entire history. This suggests that character displacementmay be simply a magnified microcosm of a general pattern ofinteraction between two species even when allopatric, providedthat allopatry is sustained through competitive exclusion.     

Do pollen feeding,pupal‐mating and larval gregariousness have a single origin in Heliconius butterflies? Inferences from multilocus DNA sequence data

Phylogenetic information is useful in understanding the evolutionary history of adaptive traits. Here, we present a well-resolved phylogenetic hypothesis for Heliconius butterflies and related genera. We use this tree to investigate the evolution of three traits, pollen feeding, pupal-mating behaviour and larval gregariousness. Phylogenetic relationships among 60 Heliconiina species (86% of the subtribe) were inferred from partial DNA sequences of the mitochondrial genes cytochrome oxidase I , cytochrome oxidase II and 16S rRNA, and fragments of the nuclear genes elongation factor-1α , apterous , decapentaplegic and wingless (3834 bp in total). The results corroborate previous hypotheses based on sequence data in showing that Heliconius is paraphyletic, with Laparus doris and Neruda falling within the genus, demonstrating a single origin for pollen feeding but with a loss of the trait in Neruda . However, different genes are not congruent in their placement of Neruda ; therefore, monophyly of the pollen feeding species cannot be ruled out. There is also a highly supported monophyletic 'pupal-mating clade' suggesting that pupal mating behaviour evolved only once in the Heliconiina. Additionally, we observed at least three independent origins for larval gregariousness from a solitary ancestor, showing that gregarious larval behaviour arose after warning coloration.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 221–239.     

Nucleotide polymorphism in the acidic chitinase locus (ChiA) region of the wild plant Arabidopsis thaliana

To investigate DNA variation in natural plant populations, a 1.8-kb region of the acidic chitinase locus (ChiA)was analyzed for 17 ecotypes of Arabidopsis thaliana sampled worldwide and 3 Arabis species in Japan. As in the Adh region, dimorphism was detected throughout the investigated ChiA region, suggesting the possibility that dimorphic DNA variation exists in the entire nuclear genome of A. thaliana. The ChiA region was divided into two blocks by an intragenic recombination between two parental sequence types, which diverged 7.4 MYA under the assumption that nucleotide mutation rate per site per year is mu = 10(- 9). Nucleotide diversity in the entire ChiA region was 0.0104. Tajima's test was significantly negative for both nucleotide and indel variations, which was manifested as an excess of unique polymorphisms. However, the level and pattern of polymorphism in the ChiA region were inconsistent with simple theoretical explanations. The HKA test detected no difference in the levels of intra- and interspecific variations between the ChiA and Adh regions. In the ChiA coding region, no difference in the patterns of synonymous and replacement variation was found in intra- and interspecific comparisons by the MK test. Although it was difficult to determine the exact genetic mechanism acting on the ChA locus, these results suggested that the ChA locus region was under the same genetic mechanism before and after the establishment of A. thaliana as a species.      

Colonization, population expansion, and lineage turnover: phylogeography of Mesoamerican characiform fish

We present a phylogeographical analysis of four genera of Mesoamerican primary freshwater fish ( Brycon , Bryconamericus , Eretmobrycon , and Cyphocharax ). Three hundred and thirty-nine individuals were genotyped into one of 31 operational taxonomic units (OTUs) based on the nucleotide sequence of their mitochondrial ATPase 6 & 8 genes (842–839 bp). Contrary to inference based on the species-level taxonomy of these genera, molecular data identified only a single case of sympatry between closely related OTUs, despite extensive parapatry. Polytomies dominate the mtDNA-based phylogenies and demonstrate multiple, noncontemporaneous waves of rapid expansion across Mesoamerica from South American sources. Analyses based on genetic distances observed among congeneric species of Mesoamerican primary freshwater fishes in comparison to divergence between transisthmian marine fishes permit the strong inference that the Pliocene rise of the Panama land bridge provided the first opportunity for the colonization of Mesoamerica by Characiform fishes. We develop a priority-effect model, based on the assumption that genetically closely related OTUs share similar ecological niches, to reconcile the general lack of contemporary sympatry between closely related OTUs with the substantial historical connectivity among Mesoamerican drainages demonstrated by the rapid expansion of Brycon , Bryconamericus , and Cyphocharax . Finally, in most cases, we infer that the westerly limits of freshwater fish distributions in Mesoamerica are more consistent with being defined by ecological factors rather than by dispersal limitation.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 235–255.