title: Clustering using finite mixture models

authors: Hunt, Lynette Anne

abstract: This thesis introduces a class of multivariate mixture models that includes latent class models and mixtures of multivariate normal distributions as special cases. Like latent class models, these models make free use of local independence to reduce the number of parameters in the model and to lead to descriptions of clusters that are easily understood. Provision is made for the introduction of within cluster associations between the variables. 

Discrete, multivariate normal and location model distributions are the ‘atoms’ with which the models are built, but where more is known about the nature of the distributions in sub-populations other types of distributions could be used in place of these. 

We use the EM algorithm to find the maximum likelihood estimates of the model parameters, however the emphasis is less on parameter estimation than on the use of the estimated component distributions to cluster the data. We implement the approach of multivariate mixture models with a Fortran 77 program. The program is used to fit models to several data sets, including a large medical data set. Analysis of the resulting clusters shows that sensible clusters have been achieved. 

The thesis shows how our ability to analyse data using multivariate mixture models can be extended to include the facility to handle situations where data are missing at random in the sense of Rubin (1976). The program written for this thesis incorporates this facility. The scope of the methods proposed is illustrated by clustering several data sets.

text: Clustering using finite mixture models This thesis introduces a class of multivariate mixture models that includes latent class models and mixtures of multivariate normal distributions as special cases. Like latent class models, these models make free use of local independence to reduce the number of parameters in the model and to lead to descriptions of clusters that are easily understood. Provision is made for the introduction of within cluster associations between the variables. 

Discrete, multivariate normal and location model distributions are the ‘atoms’ with which the models are built, but where more is known about the nature of the distributions in sub-populations other types of distributions could be used in place of these. 

We use the EM algorithm to find the maximum likelihood estimates of the model parameters, however the emphasis is less on parameter estimation than on the use of the estimated component distributions to cluster the data. We implement the approach of multivariate mixture models with a Fortran 77 program. The program is used to fit models to several data sets, including a large medical data set. Analysis of the resulting clusters shows that sensible clusters have been achieved. 

The thesis shows how our ability to analyse data using multivariate mixture models can be extended to include the facility to handle situations where data are missing at random in the sense of Rubin (1976). The program written for this thesis incorporates this facility. The scope of the methods proposed is illustrated by clustering several data sets.

year: 1996

title: Genomic insights into the evolution of the parasitoid Microctonus aethiopoides

authors: Hussain, Meeran

abstract: Parasitoids are used as biocontrol agents in classical biological control programmes for controlling invasive pest populations. In Aotearoa New Zealand, there are two strains of Microctonus aethiopoides that have been used against two serious pest weevils of the Sitona group. However, there is limited understanding of M. aethiopoides adaptability, particularly in the area of reproductive mode and host associations. My thesis explores these gaps, using population and comparative genomic approaches to investigate the adaptability of M. aethiopoides.
Chapter 2 is a review that synthesises global research on parasitoid adaptation and identifies knowledge gaps across four key traits i.e., reproductive mode, olfaction, thermal tolerance, and microbiomes. Using the three Microctonus species in New Zealand as a focal example, this chapters explains why these traits matter for biocontrol and how genomic technologies reveal their underlying molecular mechanisms. 
Chapter 3 explores the adaptation of Irish asexual M. aethiopoides in New Zealand by analysing whole-genome resequencing data from 43 individuals representing historic (Ireland) and contemporary populations. The study reveals two distinct genetic clusters, most likely reflecting the genetic ancestry of introduced populations rather than post-introduction geographic isolation. All populations exhibit very low diversity and limited population expansion since release, consistent with their asexual nature and suggesting limited adaptation. Asexual M. aethiopoides show some heterozygosity across populations, supporting automictic thelytoky, likely via central fusion, as the primary reproductive mechanism. However, linkage disequilibrium patterns resemble those of sexual organisms, raising the possibility of facultative sex. This chapter sheds light on the adaptation, spread, and reproductive strategies of asexual M. aethiopoides in New Zealand.
Chapter 4 further examines parasitoid adaptation, with a focus on host-associated divergence. Using eight newly assembled genomes from M. aethiopoides strains collected from three different hosts (Hypera postica, Sitona discoideus, S. obsoletus) and geographically distinct regions, this study investigates how host use and geography shape genomic structure. Comparative genomics reveals a clear host-associated phylogenetic split, with the H. postica lineage distinct from Sitona-associated lineages. Heterozygosity patterns support this separation, showing highest diversity in the H. postica group. However, gene families are mostly conserved across strains, with transposable element-related genes showing rapid evolution, suggesting their active role in genome restructuring. Chemosensory genes are also largely conserved, with only modest variation in odourant receptors that may reflect host-associated differences, although fragmentation and annotation bias cannot be ruled out. Overall, host association appears to be a key driver of divergence in M. aethiopoides, largely shaped by genome-level variation rather than major shifts in host-specific gene families.
Finally, Chapter 5 assembles and characterises the first complete mitochondrial genome of M. aethiopoides, generated using a hybrid Oxford Nanopore-Illumina assembly. This study uncovers a long circular (33,173 bp) mitogenome with a unique gene arrangement, contributing a valuable genetic resource for future studies of mitochondrial evolution in parasitoids.
Overall, my thesis demonstrates how genomic technologies can be used to provide a more comprehensive understanding of the evolutionary factors shaping a species’ genome and population structure. It provides a valuable genomic resource and sets a foundation of resources for continuing to build understanding of adaptation in the context of asexuality and host association in M. aethiopoides.

text: Genomic insights into the evolution of the parasitoid Microctonus aethiopoides Parasitoids are used as biocontrol agents in classical biological control programmes for controlling invasive pest populations. In Aotearoa New Zealand, there are two strains of Microctonus aethiopoides that have been used against two serious pest weevils of the Sitona group. However, there is limited understanding of M. aethiopoides adaptability, particularly in the area of reproductive mode and host associations. My thesis explores these gaps, using population and comparative genomic approaches to investigate the adaptability of M. aethiopoides.
Chapter 2 is a review that synthesises global research on parasitoid adaptation and identifies knowledge gaps across four key traits i.e., reproductive mode, olfaction, thermal tolerance, and microbiomes. Using the three Microctonus species in New Zealand as a focal example, this chapters explains why these traits matter for biocontrol and how genomic technologies reveal their underlying molecular mechanisms. 
Chapter 3 explores the adaptation of Irish asexual M. aethiopoides in New Zealand by analysing whole-genome resequencing data from 43 individuals representing historic (Ireland) and contemporary populations. The study reveals two distinct genetic clusters, most likely reflecting the genetic ancestry of introduced populations rather than post-introduction geographic isolation. All populations exhibit very low diversity and limited population expansion since release, consistent with their asexual nature and suggesting limited adaptation. Asexual M. aethiopoides show some heterozygosity across populations, supporting automictic thelytoky, likely via central fusion, as the primary reproductive mechanism. However, linkage disequilibrium patterns resemble those of sexual organisms, raising the possibility of facultative sex. This chapter sheds light on the adaptation, spread, and reproductive strategies of asexual M. aethiopoides in New Zealand.
Chapter 4 further examines parasitoid adaptation, with a focus on host-associated divergence. Using eight newly assembled genomes from M. aethiopoides strains collected from three different hosts (Hypera postica, Sitona discoideus, S. obsoletus) and geographically distinct regions, this study investigates how host use and geography shape genomic structure. Comparative genomics reveals a clear host-associated phylogenetic split, with the H. postica lineage distinct from Sitona-associated lineages. Heterozygosity patterns support this separation, showing highest diversity in the H. postica group. However, gene families are mostly conserved across strains, with transposable element-related genes showing rapid evolution, suggesting their active role in genome restructuring. Chemosensory genes are also largely conserved, with only modest variation in odourant receptors that may reflect host-associated differences, although fragmentation and annotation bias cannot be ruled out. Overall, host association appears to be a key driver of divergence in M. aethiopoides, largely shaped by genome-level variation rather than major shifts in host-specific gene families.
Finally, Chapter 5 assembles and characterises the first complete mitochondrial genome of M. aethiopoides, generated using a hybrid Oxford Nanopore-Illumina assembly. This study uncovers a long circular (33,173 bp) mitogenome with a unique gene arrangement, contributing a valuable genetic resource for future studies of mitochondrial evolution in parasitoids.
Overall, my thesis demonstrates how genomic technologies can be used to provide a more comprehensive understanding of the evolutionary factors shaping a species’ genome and population structure. It provides a valuable genomic resource and sets a foundation of resources for continuing to build understanding of adaptation in the context of asexuality and host association in M. aethiopoides.

year: 2026

title: He Pikinga Waiora: Supporting Maori health organisations to respond to pre-diabetes

authors: Beaton, Angela

subjects: Science & Technology

abstract: Background
Type 2 Diabetes (T2D) is a common long-term condition affecting the health and wellbeing of New Zealanders; one in every four New Zealanders is pre-diabetic. Māori, the Indigenous people of New Zealand, are at an increased risk of developing pre-diabetes and T2D and there are significant inequities between Māori and non-Māori for T2D complications. The purpose of this study was to explore the questions of how the strengths of Māori heath organisations may be leveraged, and how the barriers and constraints experienced by Māori health organisations may be negotiated, for the benefit of Māori; and from a systems perspective, to identify strategic opportunities that may be considered and applied by Māori health organisations, funders and policy makers to respond more effectively to pre-diabetes and reduce health inequities between Māori and non-Māori.

Methods
Utilising case study methodology, a range of data sources were triangulated including nine semi-structured interviews, documents, and a diabetes system map to identify possible strategic opportunities for key stakeholders to respond more effectively to pre-diabetes.

Results
Key themes and possible actions to improve health outcomes for Māori with pre-diabetes include: (1) Recognising Māori health organisations as conduits for the community voice and influential partners in the community to effect change; (2) Strengthened partnerships with Māori health organisations for community benefit and to support measurable, evidence-based change and service delivery, particularly when Māori knowledge systems are viewed alongside a Western scientific approach; and (3) Intersectoral integration of health and social services to support provision of whānau-centred care and influence the social determinants of health and local environment.
Conclusions
Māori health organisations are important actors in systems seeking to improve outcomes and eliminate health inequities. Support from funders and policy makers will be required to build on the strengths of these organisations and to overcome system challenges. To realise improved health outcomes for Māori, the value placed on whānau and community perspectives not only needs to be acknowledged in the implementation of health interventions, health and social policies and funding arrangements, but performance measures, service design and delivery must evolve to accommodate these perspectives in practice.

text: He Pikinga Waiora: Supporting Maori health organisations to respond to pre-diabetes Background
Type 2 Diabetes (T2D) is a common long-term condition affecting the health and wellbeing of New Zealanders; one in every four New Zealanders is pre-diabetic. Māori, the Indigenous people of New Zealand, are at an increased risk of developing pre-diabetes and T2D and there are significant inequities between Māori and non-Māori for T2D complications. The purpose of this study was to explore the questions of how the strengths of Māori heath organisations may be leveraged, and how the barriers and constraints experienced by Māori health organisations may be negotiated, for the benefit of Māori; and from a systems perspective, to identify strategic opportunities that may be considered and applied by Māori health organisations, funders and policy makers to respond more effectively to pre-diabetes and reduce health inequities between Māori and non-Māori.

Methods
Utilising case study methodology, a range of data sources were triangulated including nine semi-structured interviews, documents, and a diabetes system map to identify possible strategic opportunities for key stakeholders to respond more effectively to pre-diabetes.

Results
Key themes and possible actions to improve health outcomes for Māori with pre-diabetes include: (1) Recognising Māori health organisations as conduits for the community voice and influential partners in the community to effect change; (2) Strengthened partnerships with Māori health organisations for community benefit and to support measurable, evidence-based change and service delivery, particularly when Māori knowledge systems are viewed alongside a Western scientific approach; and (3) Intersectoral integration of health and social services to support provision of whānau-centred care and influence the social determinants of health and local environment.
Conclusions
Māori health organisations are important actors in systems seeking to improve outcomes and eliminate health inequities. Support from funders and policy makers will be required to build on the strengths of these organisations and to overcome system challenges. To realise improved health outcomes for Māori, the value placed on whānau and community perspectives not only needs to be acknowledged in the implementation of health interventions, health and social policies and funding arrangements, but performance measures, service design and delivery must evolve to accommodate these perspectives in practice.

year: 2019