Phil E. Cowan

MASTING BY EIGHTEEN NEW ZEALAND PLANT SPECIES: THE ROLE OF TEMPERATURE AS A SYNCHRONIZING CUE

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed-consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem-level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra- and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four families across >150 000 km2. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Nina phase of ...

Genetic analysis of the mating system of the common brushtail possum (Trichosurus vulpecula) in New Zealand farmland

We examined male reproductive success in a common brushtail possum population in New Zealand farmland. Paternity was assigned to 66 of 91 pouch young (maternity known), using a likelihood approach applied to genotypes at six microsatellite loci having an overall average exclusion probability of around 99%. The distribution of number of offspring per male was L‐shaped with a standardized variance of 1.52. At least 46% of the 76 sampled reproductively mature males, bred, siring between one and four offspring each. Although breeding males were on average older and larger than nonbreeding males, the small differences did not result in a significant overall difference between the two groups in a multivariate permutation test analagous to a t‐test. Paternity analysis of 22 sibling pairs (resulting from experimental removal of pouch young early in the breeding season, inducing a second oestrous) suggested that sequential mating of females with the same male was uncommon (≈ 16–27%). Whilst there was a tendency for female possums to mate with nearby males, consistent with previous observations of territorial mating behaviour in Australian populations, some interhabitat matings were also inferred. The study population displayed only a low degree of polygyny, which may in part reflect population and habitat characteristics of the study site. A comprehensive understanding of the mating system of Trichosurus vulpecula awaits genetic paternity analysis in additional populations from both Australia and New Zealand, using quantitative approaches undertaken in this study.

Advances in New Zealand mammalogy 1990–2000: Brushtail possum

Brushtail possum numbers appear to be increasing in many urban areas in Australia (Pietsch 1994; Statham & Statham 1997), and in Tasmania following conversion of woodland to pasture (Coulson & Herron 1981). In the arid regions of Australia, however, possum populations are being reduced by fox and cat predation and by changes in the fire regime (Foulkes 2000). In some areas, such as Uluru National Park in central Australia, possum reintroduction programmes are underway (J. A. Kerle unpubl. data).

Factors influencing annual variation in breeding by common brushtail possums (Trichosurus vulpecula) in New Zealand

We assembled data on annual variation in breeding rates of brushtail possums from four long-term studies in the lower North Island of New Zealand, three of which spanned more than 20 years. In each study, more than 80% of adult females bred in most years. The major exception was in 1996, when breeding failed synchronously at sites separated by up to 122 km. The overall breeding rate in 1996 at these sites was 28% (n = 201). Other instances of low breeding rate (<70%) occurred asynchronously at particular sites. We analysed variation in breeding rates to determine the contributions to annual variation of individual condition (body weight), population density, food resources and other environmental predictors. The probability of breeding declined rapidly as body condition fell below average. An index of fruitfall of hinau (Elaeocarpus dentatus), a highly nutritious food used by possums, and population density in the previous year were the most important predictors of possum condition and breeding rate. High density in the previous year coupled with low hinau fruitfall in the current year predicted below-average body condition and reduced breeding rate. Although the magnitude of these effects were only significant in ‘extreme’ years, they are consistant with delayed density-dependent effects on fecundity in brushtail possums.

Immunogenicity and contraceptive potential of three infertility-relevant zona pellucida 2 epitopes in the marsupial brushtail possum (Trichosurus vulpecula).

In a previous study, three infertility-relevant epitopes of possum ZP2 (Pep12 (amino acids 111-125), Pep31 (amino acids 301-315), and Pep44 (amino acids 431-445)) were identified using sera from possums (Trichosurus vulpecula) immunized with recombinant possum zona pellucida 2 (ZP2) constructs, and a synthetic peptide library of possum ZP2 protein. In this study, the three peptides were conjugated to keyhole limpet hemocyanin and 300 mug of each conjugated peptide were administered subcutaneously to female possums (n = 20 per peptide) in complete Freunds adjuvant. Immunogen doses were repeated 3 and 6 weeks later using incomplete Freunds adjuvant. Control animals were immunized with either phosphate-buffered saline only (n = 10) or 300 mug keyhole limpet hemocyanin (n = 10), administered with the same adjuvants. Serum antibodies from animals immunized against these three epitopes bound to the corresponding possum ZP2 peptides, recombinant possum ZP2 protein constructs, and native zona. Possum fertility was assessed following superovulation and artificial insemination. Peptides Pep12 and Pep31 had no significant effects on fertility parameters (P > 0.05). However, animals immunized with Pep44 had lower egg fertilization rates (immunized 19.5% versus control 60.5%, P < 0.05) and produced significantly fewer embryos than control animals (immunized 0.5 embryos versus control 2.4 embryos, P < 0.05). The number of Pep44-immunized females that produced embryos was reduced by 64%. Identification and characterization of possum infertility-relevant epitopes on possum ZP2 protein will assist development of safe, humane, and possum-specific immunocontraceptive vaccines for controlling the introduced possums in New Zealand.

Bacterial ghosts as a delivery system for zona pellucida-2 fertility control vaccines for brushtail possums (Trichosurus vulpecula)

The introduced brushtail possum is a serious pest in New Zealand and there is much interest in the development of an immunocontraceptive vaccine for population control. Immunisation of female possums against recombinant possum zona pellucida protein-2 (ZP2) is known to reduce embryo production by 72-75% but successful development of fertility control will depend on a delivery system that is effective for field use. Bacterial ghost vaccine technology is a promising system to formulate a non-living vaccine for bait or aerosol delivery. The N-terminal (amino acid residues 41-316, ZP2N) and C-terminal (amino acid residues 308-636, ZP2C) regions of possum ZP2 were fused to maltose-binding protein and expressed in the periplasmic space of Escherichia coli NM522 bacterial ghosts. Female possums (n=20 per treatment group) were immunised with 20mg of either plain ghosts, ZP2N ghosts, or ZP2C ghosts in phosphate-buffered saline applied to the nostrils and eyes (nasal/conjunctival mucosa) at weeks 0, 2 and 4. Effects of immunisation on fertility were assessed following superovulation and artificial insemination. Both constructs evoked humoral (antibody) and cell-mediated immune responses in possums and significantly fewer eggs were fertilised in females immunised against ZP2C ghosts. Results in this study indicate that bacterial ghosts containing possum ZP antigens can reduce possum fertility when delivered by mucosal immunisation and offer a promising delivery system for fertility control of wild possum populations.

Management of animal and plant pests in New Zealand – patterns of control and monitoring by regional agencies

Context. Significant resources are spent annually in New Zealand controlling pests to mitigate impacts on native biodiversity and agricultural production, but there are few reliable estimates of the benefits. Concerns have been expressed aboutinconsistentmonitoringmethodologies,differingfrequenciesandintensitiesofcontrolacrossorganisations,andpoor definition of desired outcomes. Aims.Toconductandreportonasurveyofanimalandplantpestcontrolandmonitoringbyregionalagencies,toidentify issues with current practice and to provide advice on improvements. Methods.Wesurveyed15regionalagenciesinNewZealandaboutthepestcontrolandassociatedmonitoringundertaken during2005–08.Werecordedthepeststargeted,thecontrolworkdoneanditsoperationaldetails,anyresultand/oroutcome monitoring conducted, and estimated costs. Key results. About 21% of the NZ

High microsatellite diversity and differential structuring among populations of the introduced common brushtail possum, Trichosurus vulpecula, in New Zealand.

20million expenditure on pest control was for monitoring. Excluding compliance (62%),monitoringchangesinpestpopulationsaccountedfor31%ofthetotalmonitoringexpenditure,whereasonly7%was spent measuringresponseintheresourcethatwassupposedlybeingprotected.Themostcommonmonitoringdesign(71%) comprised a single treatment area with no non-treatment area, in which only results were monitored. Only three programs (4%) had both treatment and non-treatment areas and both results and outcome monitoring. Conclusions.Suchlimitedoutcomemonitoringconstrainsseverelytheabilityofregionalandlocalauthoritiestoprovide robust justification for their pest management activities and expenditures. Implications.Improvedoutcomemonitoringrequiresbetterdesignofandadditionalresourcesformonitoringprograms, improved institutional/political support for long-term programs, and better definition of long-term outcomes and objectives for pest management.

Possums (Trichosurus vulpecula) on Hawke's Bay farmland: Spatial distribution and population structure before and after a control operation

An understanding of genetic variation and structure of pest populations has the potential to improve the efficiency of measures to control them. Genetic analysis was undertaken at five microsatellite loci in four native Australian and 14 introduced New Zealand populations of the common brushtail possum Trichosurus vulpecula in order to document these parameters. Genetic variation in New Zealand populations, and phylogenetic relationships among Australian and New Zealand populations, were largely predicted by the recorded introduction history. Populations on the two main islands of New Zealand had only slightly lower genetic diversity than did Australian populations, except that allelic richness on the South Is. was significantly lower. Diversity was higher in North Is. than in South Is. populations (although not significantly so) and mainland New Zealand populations as a group were significantly more diverse than offshore islands that represented secondary population size bottlenecks. In phylogenetic analyses South Is. and offshore island populations grouped with Tasmania, while North Is. populations grouped either with mainland Australia or were intermediate between the two Australian sources. This scheme was supported by admixture coefficients showing that North and South Is./offshore island populations were largely mainland Australian and Tasmanian in origin, respectively. Population structure differed markedly between the North and South Islands: populations were typically more genetically differentiated on the former than the latter, which also showed significant isolation-by-distance. Substantial linkage disequilibrium in most sampled New Zealand but no Australian population between microsatellite loci Tv16 and Tv27 suggests they may be physically linked.

Effects of possum browsing on northern rata, Orongorongo Valley, Wellington, New Zealand

Over 6.5 years, 723 possums were live‐trapped and marked in swamp, willow, and farmland habitats on approx. 350 ha of two adjoining sheep farms in Hawkes Bay, New Zealand. About equal numbers of males and females were trapped in each habitat, but males were recaptured more often than females. Eighty‐five percent of the possums were trapped along the margins of swamp and willow habitats that comprised only 6% of the study area. The swamp habitat contained at least 8.8 possums ha‐1, the willow habitat 16.7 possums ha‐1, and the farmland habitat 0.13 possums ha‐1. Possums generally moved less than 200 m between successive recaptures, and there were few trap‐revealed movements between habitats. Possums on part of one farm comprising 23 ha of swamp and willows were then poisoned with cyanide in bait stations. Two hundred and fifty‐eight possums—including 142 previously marked animals—were found dead, an estimated 90% of the population. Fifty‐nine percent of the marked possums were poisoned within 100 m of the...