title: Assessing New Zealand's spider (Araneae) fauna, using DNA barcoding

authors: Binks, Nigel

subjects: Biodiversity

abstract: The ability to accurately monitor biological diversity is the foundation to most ecological research. However, the morphological identification of spiders, as with many arthropod taxa, is often complicated by phenotypic plasticity and sexual dimorphism. New Zealand’s spider fauna is highly endemic (97% of known species), consisting of an estimated 2,000 species. Given such high diversity, it is critical to seek cost-effective measures of assessing species diversity and distributions, and for the identification of cryptic unidentified taxa. 

The aim of my research was to determine whether the described spider fauna can be effectively delineated from unidentified taxa using DNA barcoding. Overall, I establish a molecular inventory for 100 described species and 71 additional unidentified species of spiders found in New Zealand. Using barcoding I determined there to be 59 native described species and classify 66 of the unidentified species as native, leaving 45 species which were recognised as having international distributions by taxonomic descriptions and/or from comparative DNA sequences from the Barcode of Life Datasystem (www.boldsystems.org). The repository of species presented here represent native species pertaining to 26 families and cosmopolitan species from 17 families of which species from the Araneidae, Linyphiidae and Theridiidae families are the most diversly represented in this study. This foundational inventory was used to assess the presence of spider species around the marginal habitats of 5 Waikato study lakes (Puketi, Rotoiti, Kohahuake, Waiwhakareke and Koraha), in relation to community assemblage variation across lakes, habitat (shoreline vs. pasture) and sampling method. 

The combined morphological and molecular approach to identification used here has demonstrated community composition assessments of spiders are viable. Furthermore, the study of these community assemblages revealed a greater diversity of habitat specialists among shoreline samples from lakes Kohahuake, Koraha and Waiwhakareke where greater vegetative heterogeneity along the shoreline provides a greater range of niches for spiders to occupy. This compiled species inventory indicates that New Zealand’s diverse Araneae fauna has been infiltrated by species with international distributions. Further, not all species are easily recognisable due to dissimilarities in their morphological appearance, or because they remain to be genetically identified, and therefore the extent of non-native species infiltration into New Zealand ecosystems is unclear. This lack of knowledge highlights an important area for future biosurveillance work. Lake ecosystems were selected for this study because a variety of spider species prey upon adult aquatic invertebrates as they emerge from the aquatic realm and into the terrestrial. 

Methods which provide complementary data for ranking lake ecosystems is a priority for biodiversity management in the Waikato region due to habitat fragmentation primarily associated with deforestation and subsequent conversion to pastoral habitat. Land use practices affect the distribution and dispersal of many native species and connected expanses of pasture provide opportunities for exotic species to infiltrate established food-webs associated with ecosystems of significant natural character. In conclusion, this molecular inventory provides a key foundation for a COI barcode library for New Zealand’s most commonly-encountered spiders and validates the ability of this identification method to discern between male, female and juvenile specimen from described and unrecognised species with native or international distributions.

text: Assessing New Zealand's spider (Araneae) fauna, using DNA barcoding The ability to accurately monitor biological diversity is the foundation to most ecological research. However, the morphological identification of spiders, as with many arthropod taxa, is often complicated by phenotypic plasticity and sexual dimorphism. New Zealand’s spider fauna is highly endemic (97% of known species), consisting of an estimated 2,000 species. Given such high diversity, it is critical to seek cost-effective measures of assessing species diversity and distributions, and for the identification of cryptic unidentified taxa. 

The aim of my research was to determine whether the described spider fauna can be effectively delineated from unidentified taxa using DNA barcoding. Overall, I establish a molecular inventory for 100 described species and 71 additional unidentified species of spiders found in New Zealand. Using barcoding I determined there to be 59 native described species and classify 66 of the unidentified species as native, leaving 45 species which were recognised as having international distributions by taxonomic descriptions and/or from comparative DNA sequences from the Barcode of Life Datasystem (www.boldsystems.org). The repository of species presented here represent native species pertaining to 26 families and cosmopolitan species from 17 families of which species from the Araneidae, Linyphiidae and Theridiidae families are the most diversly represented in this study. This foundational inventory was used to assess the presence of spider species around the marginal habitats of 5 Waikato study lakes (Puketi, Rotoiti, Kohahuake, Waiwhakareke and Koraha), in relation to community assemblage variation across lakes, habitat (shoreline vs. pasture) and sampling method. 

The combined morphological and molecular approach to identification used here has demonstrated community composition assessments of spiders are viable. Furthermore, the study of these community assemblages revealed a greater diversity of habitat specialists among shoreline samples from lakes Kohahuake, Koraha and Waiwhakareke where greater vegetative heterogeneity along the shoreline provides a greater range of niches for spiders to occupy. This compiled species inventory indicates that New Zealand’s diverse Araneae fauna has been infiltrated by species with international distributions. Further, not all species are easily recognisable due to dissimilarities in their morphological appearance, or because they remain to be genetically identified, and therefore the extent of non-native species infiltration into New Zealand ecosystems is unclear. This lack of knowledge highlights an important area for future biosurveillance work. Lake ecosystems were selected for this study because a variety of spider species prey upon adult aquatic invertebrates as they emerge from the aquatic realm and into the terrestrial. 

Methods which provide complementary data for ranking lake ecosystems is a priority for biodiversity management in the Waikato region due to habitat fragmentation primarily associated with deforestation and subsequent conversion to pastoral habitat. Land use practices affect the distribution and dispersal of many native species and connected expanses of pasture provide opportunities for exotic species to infiltrate established food-webs associated with ecosystems of significant natural character. In conclusion, this molecular inventory provides a key foundation for a COI barcode library for New Zealand’s most commonly-encountered spiders and validates the ability of this identification method to discern between male, female and juvenile specimen from described and unrecognised species with native or international distributions.

year: 2018

title: Mechanical behaviour of Titanium, Ti-6Al-4V (wt %) alloy and Ti-47Al-2Cr (at %) alloy produced using powder compact forging

authors: Nadakuduru, Vijay Navaratna

subjects: mechanical behaviour

abstract: Powder compact forging was used to produce bulk consolidated titanium and Ti-6Al-4V (wt %) and Ti-47Al-2Cr (at%) alloy disks from hydrogenated and dehydrogenated (HDH) and gas atomised powders (GA) powders (in the case of titanium and Ti-6Al-4V) and a mechanically milled powder (in the case of Ti-47Al-2Cr alloy). The bulk titanium and Ti-6Al-4V (wt %) alloy have been produced by forging of the powder compacts. The Ti-47Al-2Cr (at %) alloy was produced using canned powder compact forging of a Ti/Al/Cr composite powder. The purpose of the present study is to investigate the deformation and fracture behaviour of the bulk consolidated as-forged materials, by conducting tensile testing at room temperature (RT) and examination of the fractured specimens which had near-α, α + β and γ phase structures, respectively. It was found that as-forged bulk titanium disk produced using HDH powder showed a yield point with a yield strength of ~700 MPa and with a considerable amount of ductility. While the as-forged Ti-6Al-4V (wt %) alloy produced using HDH powder, fractured prematurely without any yielding. On the other hand yielding was observed in the as-forged Ti-6Al-4V (wt %) alloy produced using GA powder, showing a yield strength of ~970 MPa and a considerable amount of plastic strain to fracture. The bulk consolidated Ti-47Al-2Cr (at %) alloy also fractured prematurely with fracture strength of ~125 MPa. The mechanical behaviour of the as-forged bulk materials was found to be dependent on several factors such as initial powders used, green density of the powder compact, forging parameters used during forging. It was expected that the entrapped gas in green compacts, absorbed oxygen, porosity and inter-particle bonding play an important role on the quality of the as-forged material, which in turn affected the mechanical behaviour of the bulk material.

text: Mechanical behaviour of Titanium, Ti-6Al-4V (wt %) alloy and Ti-47Al-2Cr (at %) alloy produced using powder compact forging Powder compact forging was used to produce bulk consolidated titanium and Ti-6Al-4V (wt %) and Ti-47Al-2Cr (at%) alloy disks from hydrogenated and dehydrogenated (HDH) and gas atomised powders (GA) powders (in the case of titanium and Ti-6Al-4V) and a mechanically milled powder (in the case of Ti-47Al-2Cr alloy). The bulk titanium and Ti-6Al-4V (wt %) alloy have been produced by forging of the powder compacts. The Ti-47Al-2Cr (at %) alloy was produced using canned powder compact forging of a Ti/Al/Cr composite powder. The purpose of the present study is to investigate the deformation and fracture behaviour of the bulk consolidated as-forged materials, by conducting tensile testing at room temperature (RT) and examination of the fractured specimens which had near-α, α + β and γ phase structures, respectively. It was found that as-forged bulk titanium disk produced using HDH powder showed a yield point with a yield strength of ~700 MPa and with a considerable amount of ductility. While the as-forged Ti-6Al-4V (wt %) alloy produced using HDH powder, fractured prematurely without any yielding. On the other hand yielding was observed in the as-forged Ti-6Al-4V (wt %) alloy produced using GA powder, showing a yield strength of ~970 MPa and a considerable amount of plastic strain to fracture. The bulk consolidated Ti-47Al-2Cr (at %) alloy also fractured prematurely with fracture strength of ~125 MPa. The mechanical behaviour of the as-forged bulk materials was found to be dependent on several factors such as initial powders used, green density of the powder compact, forging parameters used during forging. It was expected that the entrapped gas in green compacts, absorbed oxygen, porosity and inter-particle bonding play an important role on the quality of the as-forged material, which in turn affected the mechanical behaviour of the bulk material.

year: 2011

title: Marine inequality, borderization, and the radical potential of kinship

authors: McCormack, Fiona

subjects: Aquaculture

abstract: This article utilizes scholarship on borders to interpret the persistence of inequality in Indigenous seascapes, irrespective of moves to redress colonial wrongs or the growing anthropocenic recognition of human-nature interconnectedness. I examine border politics in the context of Māori claims for marine title and rights and the post-settlement development of aquaculture. Drawing on Harsha Walia’s concept of “border imperialism” and Achille Mbembe’s thesis on “borderization,” the article highlights the endurance of colonial forms alongside their neoliberal transformation into the enclosures and entrapments arising in the context of accelerated marine industrialization. By holding in tension the interconnection between marine environments and kinship, on one hand, and scholarship on borders, on the other, the article suggests that Indigenous Māori kinship, expanding through multiple layers of difference, constitutes a site of resistance that has the potential to refute the logic of borderization.

text: Marine inequality, borderization, and the radical potential of kinship This article utilizes scholarship on borders to interpret the persistence of inequality in Indigenous seascapes, irrespective of moves to redress colonial wrongs or the growing anthropocenic recognition of human-nature interconnectedness. I examine border politics in the context of Māori claims for marine title and rights and the post-settlement development of aquaculture. Drawing on Harsha Walia’s concept of “border imperialism” and Achille Mbembe’s thesis on “borderization,” the article highlights the endurance of colonial forms alongside their neoliberal transformation into the enclosures and entrapments arising in the context of accelerated marine industrialization. By holding in tension the interconnection between marine environments and kinship, on one hand, and scholarship on borders, on the other, the article suggests that Indigenous Māori kinship, expanding through multiple layers of difference, constitutes a site of resistance that has the potential to refute the logic of borderization.

year: 2025