Evolutionary physiology of New Zealand stick insects: A thermal biology approach

Temperature affects biology at all levels of organization, dictating what organisms can and cannot do. Ectotherms, especially those with limited dispersal capacity, are obligated to modify their physiology to cope with short- or long-term temperature changes through phenotypic plasticity or adaptation. Although many single-species studies document how ectotherms tune their phenotypes in response to temperature, our understanding of how different thermal adaptations evolve is limited to a few model organisms. New Zealand stick insects are a monophyletic group that originated from New Caledonian tropical ancestors and currently occur in habitats ranging from subtropical to temperate and alpine. This work aims to understand if the physiology of different lineages of New Zealand stick insects evolved to facilitate the colonization of novel thermal environments. This thesis uses the phylogenetic comparative method as an analytical tool to integrate aspects of morphology, life history, and biochemistry. First, I described the morphology, morphometry, and the ultrastructure of the digestive tract of New Zealand stick insects. Although the digestive tract of New Zealand stick insects does not differ among species, using scanning electron microscopy, I could identify a new pattern of proventricular dentition within Phasmatodea. Secondly, the temperature-size rule (TSR) – the size reduction of ectotherms reared on warm temperatures compared to cold-reared counterparts – has puzzled ecologists for over a century. Here, I identified for the first time, in a common garden experiment, the evolutionary origin of the TSR in a lineage of insects. Although thermal plasticity for size at maturity is usually attributed to differences in the thermal sensitivities of growth and development rates, the thermal response of these two rates did not vary in the species that follow the TSR. Further research on the genus Acanthoxyla is encouraged to elucidate what has driven the evolution of the TSRR. Finally, I compared the thermal responses of trypsin kinetics from eleven species of New Zealand phasmids to test whether species from cold habitats overcome thermodynamic constraints by evolving cold-active enzymes. I found that the kinetic properties of trypsin are not predicted by latitude. However, significant phylogenetic signal for trypsin Vmax and KM suggest that phylogenetic constraints might be limiting the evolution of thermal adaptation in the function of this enzyme across New Zealand stick insects. Overall, my results provide evidence for divergent evolution in deep nodes of the phylogeny at the levels of enzymes and whole organism and highlight the genus Acanthoxyla as an interesting group to study the adaptive evolution of thermal plasticity in size at maturity.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Biological Sciences

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2023

Author dc:creator

• Cubillos Pefaur, Claudio Andrés

Advisors dc:contributor.advisor

• Buckley, Thomas
• Augustine, Kate
• Sinclair, Brent

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/64058

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/64058