Hazel M. Chapman

Molecular diversity and derivations of populations of Silene acaulis and Saxifraga oppositifolia from the high Arctic and more southerly latitudes

A survey of allozyme diversity within and between populations of Silene acaulis from Spitsbergen, Norway, Iceland and Scotland, showed that populations from the high Arctic (Spitsbergen, > 76°N) contained high levels of diversity and were genetically similar to populations from more southern locations. Indirect measures of gene flow (Nm), calculated from Wrighs F indicated that there had been extensive gene flow between Spitsbergen and some Norwegian populations. A restriction site analysis of chloroplast DNA (cpDNA) in S. acaulis revealed that all populations contained a single identical cpDNA haplotype, except one population from Norway which also contained a second haplotype. In contrast, five different cpDNA haplotypes were distinguished in a more limited survey of cpDNA variation in Saxifraga oppositifolia, with all five haplotypes present in one of two Spitsbergen populations surveyed. The contrasting cpDNA results for the two species suggest that whereas high‐Arctic populations of Silene acaulis have most likely been derived from immigrants which arrived from the south after the last glacial period, high‐Arctic populations of Saxifraga oppositifolia may be derived, in part, from ancient northern stocks which survived the last glaciation in high‐Arctic refugia.

Variation inHieracium subgen.Pilosella (Asteraceae): What do we know about its sources?

The present paper reviews mechanisms producing complicated patterns of variation withinHieracium subgen.Pilosella. The taxonomic complexity of this subgenus is due to highly variable basic species and intermediate (hybridogenous) species. The most important sources of variation are polyploidy, hybridization and (mostly) facultative apomixis of the aposporous type. The combination of hybridization, apomixis and clonal growth leads to the maintenance of various hybrids having originated from backcrossing and hybridization among more than two species, which is possible because of the fertile pollen of apomictic hybrids. Ever since Mendel’s experiments, some of F1 hybrids have been found to be highly variable, probably reflecting the high heterozygosity of some of the basic species. Variable progeny can also result from unreduced gametes, or the rare parthenogenetic development of reduced gametes. While these processes were detected in experiments, their role within field populations remains unknown. However, multiple origins of intermediate species, and introgression within basic species are highly likely to result in high levels of variation. While few population level studies have been undertaken in Europe, several such studies have been carried out on adventive populations in New Zealand, and these show a different pattern. Aneuploid plants, rare in Europe, are common in New Zealand, and there is frequently more than one ploidy level within a population.

Potential impact of climatic warming on Arctic vegetation

Summary Plants from high latitudes possess a number of positive adaptations to short growing seasons and low temperatures which are so precisely adapted to microhabitat in terms of morphology, metabolism, and phenology that any significant change in climate is likely to alter the relative efficiency of species in capturing resources and consequently in surviving from one season to the next. It is probable that changes in potential productivity will not take place equally in all species and therefore the competitive relationships in arctic communities are likely to alter as a consequence of climatic warming. Examination of areas where climatic warming has been evident for over 70 years, as in Spitsbergen, is already providing evidence that a rise in winter temperatures is causing changes in ecotype frequencies within species. The impact of temperature on species distribution has therefore to be considered, not just in terms of migration, but through an understanding of population processes and how they will be affected by temperature-induced physiological changes. In view of the polymorphic nature of most plant species, this aspect of response to change is fundamental to understanding how vegetation will alter as a result of climatic warming. This paper reviews some particular characteristics of Arctic plants that may become maladaptive should there be a significant increase in arctic temperatures and suggests some probable consequences for their future ecology.

Interspecific hybridization among Hieracium species in New Zealand: evidence from flow cytometry

Hieracium pilosella (Asteraceae) was accidentally introduced to New Zealand about 100 years ago. Since then it has become an aggressive weed, and an unexpected degree of genetic and genome size variation has been detected; features that might result from interspecies hybridization. We investigated the possibility that H. pilosella has hybridized with related taxa. Of the four other subgenus Pilosella species introduced to New Zealand, H. praealtum is the most abundant and, on morphological and distributional evidence, most likely to be the other parent. Flow cytometry was used to estimate relative genome size for 156 Hieracium plants collected from the wild. Plants assigned to either parental or hybrid morphotypes were found to comprise tetraploid and pentaploid individuals using genome size measurements, and this was confirmed with direct mitotic chromosome counts for a subset of plants. The haploid DNA content of H. praealtum was approximately 22% larger than that of H. pilosella. Putative hybrids that were tetraploid had mean genome sizes equivalent to two H. pilosella and two H. praealtum haploid chromosome sets, implying they were hybrids arising from the fertilization of two reduced gametes. Similar results were obtained from tetraploid hybrids produced by controlled pollination. However, the majority of field hybrids were pentaploid with a genome size equivalent to four H. pilosella and one H. praealtum haploid chromosome sets. We infer that these are not first-generation hybrids but represent successful backcrossing with H. pilosella and/or hybrid–hybrid crossing, and that sexual tetraploid hybrids have been the parents. We note that populations putatively of H. pilosella often comprise apomictic pentaploid hybrids. Significantly, our data indicate the emergence of sexual hybrids that provide further opportunity for gene flow among taxa in this complex.

A review of genetic analyses of hybridisation in New Zealand

Abstract Hybridisation between related taxa has a range of possible biological consequences, ranging from the production of sterile offspring, through introgression of alleles into populations, to the formation of new species. Examples of plant and animal species hybridising with related taxa abound in the New Zealand region. We review New Zealand examples of hybridisation that have been verified with chromosomal, protein or DNA data. Contemporary hybridisation has been studied at hybrid zones where distinct populations meet and mate in a defined and stable zone of contact. The role of human habitat modification is highlighted with examples of recent range changes that have led to hybridisation and subsequent conservation problems. Hybridisation can result in the swamping of endangered species, although it can also act as a bridge for the transfer of adaptations among lineages. Historical hybridisation in New Zealand has been examined with phylogenetics and there are many examples of organelle introgression or capture. The origin of new species of New Zealand stick insects, ferns and daisies via hybridisation has been demonstrated with cytogenetic and DNA sequence evidence. Thus the importance of hybridisation in the evolution of New Zealands flora and fauna is highlighted.

Anoxia Tolerance in High Arctic Vegetation

A uniquely high level of anoxia tolerance has been observed in Spitsbergen populations of some common high arctic vascular plant species. The most surprising aspect of anoxia tolerance in these species is their ability to maintain turgid, green leaves throughout the period of anoxia and into the postanoxic recovery phase. Prolonged anoxia tolerance has never been reported previously for green leaves, which normally lose turgor and wither rapidly when deprived of oxygen. Tests on more southern populations from Norway, Iceland, and Scotland of species found to be tolerant of anoxia in Spitsbergen failed to detect an equivalent ability to survive oxygen deprivation. This distinctive feature of high arctic populations as compared to more southern populations of the same species suggests a different evolutionary history for arctic populations as compared with those from lower latitudes. Possession of a such an unusual physiological feature whole-plant anoxia tolerance, not found in more southerly populations, is an additional argument for suggesting that some arctic populations of vascular plants may have survived part of the Pleistocene epoch at high latitudes in ice-free polar deserts. Such populations will have been exposed to many climatic alterations in the past and this history of a long-term presence in the High Arctic is discussed in relation to current threats to arctic vegetation from climatic warming.

An assessment of changes in the montane forests of Taraba State, Nigeria, over the past 30 years

During October–December 2002 a team from the University of Canterbury, New Zealand, the Nigerian Conservation Foundation and the Nigerian National Parks visited the montane forests of Taraba State, eastern Nigeria. Their aim was to identify changes in the forests that had occurred since they were last described in detail during the 1970s. Then the forests were rich in Afromontane endemics, were home to at least 24 threatened plant species, and harboured abundant wildlife. In 2002 all but one of the forest fragments visited were intact, although some of the smaller fragments had further reduced in size. The most obvious differences between 2002 and the 1970s were the dramatic reduction in wildlife, and the depletion of montane grassland and associated species. For these forests and their associated fauna to survive, more local, national and global support is urgently required for management to prevent species loss.

A CASE OF REVERSAL: THE EVOLUTION AND MAINTENANCE OF SEXUALS FROM PARTHENOGENETIC CLONES IN HIERACIUM PILOSELLA

We provide evidence for the origin of sexual individuals from parthenogenetic progenitors in natural populations. We demonstrate that this reversal has occurred independently in three geographically separated populations of the Asteraceous polyploid, Hieracium pilosella. We used chromosome counts and flow cytometry to determine ploidy and crossing experiments and flow cytometry to confirm sexuality. Inter–simple sequence repeat and allozyme markers demonstrated that the sexuals at each site were more closely related to their parthenogenetic neighbors than to sexuals at other sites. The same markers were used to estimate levels of ramet diversity, which were equally high among the parthenogens and sexuals. The observation that sexuals were always tetraploid is possibly explained by their having arisen through a rare sexual event, the fusion of two reduced (2x) gametes from pentaploid, facultatively apomictic parents. Such a reversal from almost total clonality to obligate sexual reproduction is unusual, and further work will determine whether the sexuals are in evolutionary equilibrium, are increasing at the expense of asexuals, or are simply surviving because of a lack of negative selection pressure.

Chloroplast DNA diversity of Hieracium Pilosella (Asteraceae) introduced to New Zealand: reticulation, hybridization, and invasion

The European hawkweed Hieracium pilosella is a successful invader and a troublesome weed in New Zealand. The systematics of the genus Hieracium is extremely complex and contentious, probably due to recent speciation, hybridization, polyploidy, and diverse reproductive strategies. In the first chloroplast DNA survey of the group, we sequenced 285 plants (including H. pilosella and 12 other species of subgenus Pilosella) from New Zealand and Europe for 900 bp of trnL-trnF. Eleven haplotypes were identified with much sharing among species. Three haplotypes (A, D, G) were found in seven, three, and four species, respectively, but two species (H. lactucella and H. auricula) had single, private haplotypes. Our cpDNA data for subgenus Pilosella are consistent with the groups having incomplete lineage sorting and/or recent reticulate evolution. Six haplotypes were identified in H. pilosella, four of these unique to this taxon in our sample. In New Zealand, haplotype A was common and occurred in plants of different ploidy (i.e., 4×, 5×, 6×), whereas haplotypes C, B, and M were restricted to 4×, 5×, and 6× plants, respectively. The distribution of haplotype variation suggests that some or all of the H. pilosella seeds accidentally introduced into New Zealand probably came from east Europe rather than the United Kingdom and that a minimum of four lineages were introduced. Within New Zealand, hybridization of H. pilosella with a related taxon (probably H. praealtum) has occurred at least three times, involving both obligate sexual tetraploids and facultative apomictic pentaploids of H. pilosella.

A population estimate of the Endangered chimpanzee Pan troglodytes vellerosus in a Nigerian montane forest: implications for conservation

Pan troglodytes vellerosus , the Nigerian-Cameroon chimpanzee, is the most recently recognized chimpanzee subspecies and is categorized as Endangered on the IUCN Red List. Current estimates, based on a range of sources, suggest the total number of individuals to be between 5,000–8,000. This study used a transect survey to estimate the population of P. t. vellerosus within the Nigerian submontane forest of Ngel Nyaki Forest Reserve, in Taraba State. The forest is an isolated fragment of c . 7.5 km 2 . Total nest building population size (n = 12.5) and population density (1.67 weaned chimpanzees km -2 ) were estimated from the number of nests observed along line transects. The maximum nest-group size (n = 11) suggests that this population comprises a single community. The low estimated population numbers within Ngel Nyaki forest, compounded by the forests isolated location, highlight the urgent need for conservation action.