Zoology - Theses
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ItemPredicting ectotherm life cycles under a variable climate: physiological diversity of matchstick grasshopper eggs and their ecological and evolutionary implications( 2019)Understanding the processes underlying the phenology and distribution of species is a key problem in ecology. These relationships are important for predicting the responses to species to environmental change. Phenology and distribution are closely linked to climate and weather through the thermal dependence of life cycles. However, for many biodiverse taxa, like insects, we have a poor understanding of the mechanistic links between adaptive traits and how life cycles are adapted to seasonal and variable temperature patterns. Insect life cycles are synchronised with suitable climatic conditions at critical life stages, such as the egg stage. Variation in thermal sensitivity of development and dormancy are two mechanisms by which insects can generate adaptive life cycle phenotypes. Eggs, therefore, present a unique opportunity to link adaptive variation in traits with corresponding variation in life cycles and thermal environments to examine how life cycles are adapted to variable climates. To understand the adaptation of insect life cycles to variable climates, we require a mechanistic understanding of the interactions between adaptive developmental traits of eggs and variation in the thermal environment on adaptations. Our ability to test thermal adaptation in ectotherms is also limited by our ability to efficiently characterise thermal responses. In this thesis, I described how thermocyclers are an efficient means of characterising the thermal response of small ectotherms with enough precision and sample size. I then used the widely distributed, endemic and flightless Australian matchstick grasshopper genera Warramaba (Orthoptera: Morabidae) as a model system to examine the significance of variation in thermal responses at the egg stage for life cycles under a variable climate. I used a mechanistic modelling framework to tease apart developmental and environmental sources of variation in life cycles at the egg stage and simulate their consequences for phenology and distribution in the field. Matchstick grasshoppers showed remarkable diversity in developmental responses to temperature at the egg stage, primarily in the expression of dormancy. I found that diverse Warramaba life cycles are shaped by the interactions between such developmental variation and local environmental temperatures. I demonstrated that we can achieve a mechanistic understanding of life cycle adaptation by considering the evolution of temperature-dependent traits and the evolution of life history within the context of seasonal temperature cycles. Mechanistic models are powerful tools to investigate the sources of life cycle variation and their consequences for insect distribution and phenology. Such frameworks are directly transferrable to other socio-economically important or threatened species to understand how insects are adapted to local climatic conditions and predict responses to a changing climate.
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ItemA predictive framework to assess response of invasive invertebrates to climate change: pest mite species of Australian grains( 2012)Climate change is set to place enormous pressure on both biodiversity and agricultural production. Important vectors of agricultural damage, such as pest invertebrates, are likely to respond to climate change in different ways. Differing pest invertebrate responses in grain crops will translate to shifts in outbreak frequency and persistence of pests, changes to pest species assemblages, and alter biocontrol by natural enemies. Successful management will thus require predictions of how climate change will affect individual species in terms of distributions and abundance. Climate change predictions for species are often based on models that characterize distributions though species-environment relationships. However, there are important factors relating to the ecology and evolutionary biology of species that are not incorporated and will mediate climate change response. This thesis aims to establish a transferrable framework, employing multiple, complimentary lines of enquiry, to build on distribution models and understand how climate change may affect different crop pests. I focus on two important mite species groups, the blue oat mites (Penthaleus spp.) and the redlegged earth mite (Halotydeus destructor). These mite species are invasive, and so understanding how they have adapted since being introduced into Australia will help predict response to climate change in the future. The first part of this thesis applies environmental niche models to distribution data of the three cryptic Penthaleus species, to make preliminary assessments of response to climate change. These models found that the distributions of each species are governed by different climate variables, and that species assemblages are likely to shift under climate change. The remainder of the thesis builds on such models by applying a more integrated approach to assess climate change response of H. destructor. This species provides an ideal candidate to develop this framework as the biology and ecology is well understood, and its introduction and spread in Australia has been well documented.