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Subject: search.filters.subject.310913 Invertebrate biology

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    Morphology, life history and colour variability in the endemic New Zealand isopod, Isocladus armatus : a thesis in partial fulfilment for the requirements for the degree of Master of Science, Zoology at Massey University, Auckland, New Zealand
    (Massey University, 2022) Pester, Samantha
    Research into colour polymorphism has been central to understanding the evolutionary mechanisms that maintain variation within populations. This is because colour polymorphism is quantifiable and often associated with differential selective pressures. Work on colour polymorphic organisms requires detailed knowledge of both the natural history of the focal organism and of the specific mechanisms that generate colour variation. Isocladus armatus is a Sphaeromatid isopod crustacean endemic to New Zealand. This marine isopod is found in semi-sheltered shores across the country and is well known for its astonishing diversity of colour morphs. Although previous research into this species has been limited, I. armatus appears to have a considerably higher degree of colour polymorphism than most other isopod species. In this study, I document the developmental life history, sexual dimorphism and reproductive behaviour of this species and I explore the potential genetic factors influencing the expression and maintenance of colour polymorphism. The research described here required the development of methods for breeding and maintaining isopods under laboratory conditions, making this the first comprehensive investigation of reproductive biology in I. armatus. Because there have been no prior published studies on the I. armatus lifecycle or how and when females are sexually receptive, uncovering the reproductive biology of this species was a challenge. However, through trial and error and detailed observation of male and female morphology and development, this research describes the first successful multi-generation reproduction of this species in captivity. In addition, through these generations, I demonstrate a clear genetic basis to colour variability in this species. The work in this thesis will inform future studies on this species, isopod biology in general and provides necessary insight into the wider question of how colour variation is maintained in natural populations.
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    Optimization of the rearing environment for the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), a promising agent for organic waste bioconversion : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Liu, Zhongyi
    Bioconversion is an environmentally, socially and economically sound measure for organic waste management. The black soldier fly (BSF), Hermetia illucens L. (Diptera Stratiomyidae), is one of the promising species for organic waste bioconversion. Larvae of BSF (BSFL) can feed on multiple types of organic waste, and the harvested larvae could be processed into valuable products such as animal feed, chitin, and organic fertilizer. To maximize the efficiency of a bioconversion system using BSFL, it is necessary to optimize the rearing environment of the insects, which requires knowledge of the impact of environmental factors on BSF at different life stages. This thesis reports my investigations on (1) the effect of diet on selected BSF larval (BSFL) life history and physiological traits and bioconversion efficiency, (2) the effect of substrate type and moisture content on BSF pupation, and (3) the effect of artificial light type, light regime, and adult density on BSF reproduction. First of all, I tested three types of organic waste (brewer’s waste, pig manure, and semidigested grass) against a standard diet (broll; a mixture of wheat bran and wheat flour). Among the organic wastes tested, brewer’s waste led to the fastest larval growth and highest larval weight gain. However, protein conversion efficiency of BSFL fed on brewer’s waste was lower than the larvae fed on the standard diet, which may be due to the high protein content in brewer’s waste. A meta-analysis revealed that dietary lignocellulosic content has an adverse impact on BSFL weight gain. Second, I investigated the effects of two pupation substrates (vermiculite and wood chips) and nine moisture levels on BSF pupation rate and depth. Using moist pupation substrate could reduce prepupal water loss, improve prepupal survival rate, and move forward the onset of pupation. BSF prepupae were found to stay at shallower depth levels when moisture content exceeded 20% and 70% for vermiculite and wood chips, respectively, which may be due to reduced oxygen availability. Third, I assessed four types of artificial light for their suitability of supporting mating of BSF from two different colonies. The artificial light that matches the spectral sensitivity of photoreceptors of BSF adults led to the highest mating success. Interestingly, artificial light resembling summer sunlight failed to support BSF mating, which may be due to its flickering. Colony effect was also significant on BSF mating success. Moreover, I found an interaction between the light regime and adult density on mean individual female reproductive output and adult survival rate. To optimize the reproductive output of a BSF colony, 8 h of photoperiod would be sufficient for a low adult density (e.g., lower than 800 individuals∙m−3), whereas longer photoperiods may be needed for higher adult densities. Finally, I present the implications that can be drawn from my findings, and my recommendations for future research and the relevant industry.
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    Life history strategies of the spider mite, Tetranychus ludeni Zacher, in response to environmental conditions : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Manawatu, New Zealand
    (Massey University, 2022) Ristyadi, Dwi
    Tetranychus ludeni Zacher (Acari: Tetranychidae) is an invasive pest of many horticultural crops and now occurs in all continents except Antarctic. Its invasive nature and pest status have stimulated the need for understanding the plasticity of its life history strategies under different environmental conditions. So far, little is known about effects of environmental factors on the life history traits in T. ludeni. In this thesis, I investigated its life history strategies in response to temperature, food deprivation, and predator threat. I show that life history traits of T. ludeni were highly flexible and adaptive to dynamic thermal environment. Higher temperature accelerated development but reduced adult body size and longevity. Increasing temperature elevated the intrinsic rate of increase (rm) but shortened generation time (T) and the time to double the population size (Dt). The net population growth rate (R0) was higher at 20 and 25ºC compared to lower and higher temperatures. Thermotolerance in T. ludeni was stage-dependent with eggs being the most vulnerable and adults the most tolerant. No eggs hatched after exposed to 45°C for ≥ 15 hours, 48°C for ≥ 12 hours, or 51°C for three hours; no adults survived 51°C or 54°C for ≥12 hours or 57°C for ≥ six hours, and heat tolerance of other life stages fell in between. Intermittent fasting (IF) had sex-specific and mating status-specific effects on the lifespan of T. ludeni. It extended the lifespan of females regardless of mating status but shortened that of mated males and had no effect on virgin males. IF reduced fecundity and egg size and extended offspring developmental time. My study indicates that predator-induced fears significantly lowered the fitness of T. ludeni. Cues from predators and injured prey shortened the longevity by 23–25% and oviposition period by 35–40% and reduced the fecundity by 31–37% in T. ludeni females. These cues significantly reduced intrinsic rate of increase (rm) and net population growth rate (R0), and extended time to double the population size (Dt). Findings from this study contribute to our understanding of the effects of environmental stressors on life history traits in T. ludeni, providing knowledge for pest risk analysis and development of pest management programs.
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    Life history strategies of Tetranychus ludeni Zacher (Acari: Tetranychidae) with special reference to biological invasion : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Zhou, Peng
    With the increase of worldwide trade and travel in recent decades, increasingly more arthropod species have become established outside their natural range of distribution, causing substantial ecological and economic impacts in novel habitats. Successful invaders may bear certain life history traits that can overcome various barriers such as mate and food shortage and inbreeding depression. Here, I investigated the life history strategies of a haplodiploid pest, Tetranychus ludeni Zacher (Acari: Tetranychidae), with special reference to its invasion success. It is native to Europe but now cosmopolitan. Virgin females laid larger eggs than mated females, giving rise to larger adults, and sons from virgin females produced more daughters at a higher rate than sons from mated females in their lifetime. Virgin females produced maximum number of sons in their early life to ensure subsequent mother-son mating but later saved resources to prolong longevity for potential future mating. Females maximised their resource allocation to egg production immediately after mating regardless of whether mating delay occurred to secure production of maximum number of both daughters and sons as early as possible. Mated females with mating delay increased proportion of daughters in offspring produced to compensate the loss of production of daughters during their virgin life. Neither mother-son mating nor sibling mating affected female reproductive output and longevity in any of the 11 successive inbred generations and neither sex showed inbreeding avoidance behaviour, suggesting that inbreeding has no negative impact on its invasion success at any points or generations. Mated females did not trade off their survival and lifetime reproductive output with dispersal. Long-distance dispersers invested more in dispersal in their early life while resident mites and short-distance dispersers invested more in reproduction during their early life, which may allow long-distance dispersers to explore the novel environment more effectively without compromising lifetime reproductive fitness. Older females with more mature eggs were more likely to disperse and move longer distances than younger ones with fewer eggs. Females increased dispersal probability and distance with the increase of population density. The synchronization of dispersal and reproduction and the positive density-dependent dispersal strategy may facilitate habitat colonization and invasion speed of T. ludeni. Findings from this study improve our understanding of the invasion mechanisms of T. ludeni and other haplodiploid species, providing knowledge for development of programmes for prediction and management of biological invasions.
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    Evolution and stable isotopes in Placostylus species of the southwest Pacific : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology, Massey University, New Zealand
    (Massey University, 2021) Quenu, Mathieu
    Human activities during the Holocene have induced a sixth biodiversity crisis and initiated rapid changes in the climate. The anthropogenic pressures put on ecosystems can result in direct or indirect environmental degradation, fragmentation and defaunation. Understanding local patterns of wildlife population structure, species interactions and initial biodiversity are all crucial to making well-informed decisions that leads to population sustainability and conservation of global biodiversity. This thesis is focused on the genus of giant land snail Placostylus and seeks to improve our overall knowledge of the genus and its potential to store information about the local environment (such as temperature and humidity) during shell formation. Placostylus is a genus endemic to the southwest Pacific and the many species present a valuable opportunity to integrate studies of ecology and environment at a scale relevant to current anthropogenic climate change. The characteristics of Placostylus shells can be used to investigate extant and extinct morphological variation within the genus, and their chemical composition can be used to track the environmental conditions in which the snails lived. In parallel to shell analysis the generation of genetic data can be used to infer phylogenetic relationships between distant taxa, and at a fine-scale patterns of population structure allow us to infer gene flow and differentiation. Understanding the extent to which shell shape and size is controlled by genetic differences and how much phenotypic plasticity leads to differences is essential if we are to correctly interpret the significant of phenotypic variation. For example, arid conditions can lead to Placostylus snails maturing when much smaller in size. Potentially, intraspecific shell shape and size variation and shell chemistry can all inform us about the local environmental conditions that existed as snail shells were formed. Three main axes are developed throughout the thesis. First the diversity of Placostylus and extended species of the super-family Orthalicoidea are introduced using a phylogenetic investigation. Evolutionary relationships are inferred from DNA sequences of mitochondrial and nuclear genetic datasets. Second, morphological variation is examined in detail where two Placostylus snail species are sympatric (the Isle of Pines, New Caledonia). The variation in shell shape of taxa living and growing in the same environment must represent genetic differences rather than phenotypic plasticity. However, genetic data from the Placostylus species present on the Isle of Pines was needed when a third snail morphotype was discovered. On the Isle of Pines giant land snails of the species P. fibratus are harvested for food, where iii they are sympatric with the vulnerable species P. porphyrostomus. Understanding local population structure of both species and their interaction will inform management decisions for both species. Third, the stable isotopic composition of extant Placostylus shells is analysed from Placostylus shells from New Zealand and New Caledonia. This works has the aim to establish a climate proxy system which through the analysis of fossil shells could inform us about past environmental conditions. A protocol to sample high-resolution isotopic signatures from Placostylus shells is developed and the stable isotopic composition of shells are examined in light of the environmental variables of the snail collection locations.
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    Fluctuations in population size of Theileria orientalis Ikeda within the tick vector Haemaphysalis longicornis Neumann : an investigation into the life cycle of T. orientalis Ikeda : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Zoology, Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Zhao, Yilin
    Theileria orientalis Ikeda is a protozoan parasite of cattle that causes disease through the destruction of the host's erythrocytes. In 2012, the parasite caused an epidemic of bovine theileriosis in New Zealand at great economic cost to the farming community. As a result, a large number of scientific studies have been undertaken to understand the epidemiology of the T. orientalis Ikeda parasite in the hopes of mitigating the damage done by the parasite. An essential part of the epidemiology of any pathogen is the understanding of its life cycle and this holds true with T. orientalis Ikeda which, like other Theileria parasites, exhibits a complex life cycle involving multiple hosts. In this thesis, fluctuations of T. orientalis Ikeda populations within nymph tick hosts were investigated over the course of six months. By doing so, this investigation highlights a part of the T. orientalis Ikeda lifecycle that is poorly covered in the scientific literature. The population of T. orientalis Ikeda within the tick was determined through qPCR analysis. Analysis of the qPCR results found that populations of T. orientalis Ikeda fluctuated greatly within the ticks over the course of six months. Ticks infected with Theileria were procured through the development of a novel mass tick- rearing protocol: the artificial infestation of a cattle-beast with naïve ticks through the fixation of tick-containing ear-bags. A pilot study of the protocol showed that the fixation of ear-bags onto cattle using Kamar® adhesive did not negatively impact the welfare of the cattle involved. The subsequent field trial of the protocol resulted in the successful engorgement and infection of five thousand naïve tick larva. These results demonstrated a viable method to obtain T. orientalis Ikeda infected ticks that would be suitable for further research. Also described in detail in this thesis are attempts at adapting the protocol of Krober and Guerin (2007) to create a silicone membrane for the artificial feeding of tick larvae on Theileria-infected blood without the involvement of live hosts. Despite multiple attempts, the experiments yielded no successful attachments of ticks onto the synthetic membranes. Failure here was attributed largely to the adapted protocol creating silicone membranes that were too thick for the larval ticks to successfully penetrate with their mouthparts. However, the in vitro feeding of ticks presents itself as a great potential contributor to future tick research. It is hoped that the knowledge gained from the repeated trials of the in vitro feeding apparatus in this experiment may help in the development of successful protocols in the future.