Reproductive performance of a spider mite Tetranychus ludeni Zacher (Acari: Tetranychidae) in response to social environments : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Palmerston North, New Zealand
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Date
2023
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Massey University
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Abstract
Animals are sensitive to changes in social environments and may plastically adjust their life history traits in response to multiple socio-environmental factors. Population size and density are two key socio-environmental factors affecting female reproductive output and offspring sex ratio. However, previous studies have mostly focused on only one factor at a time, ignoring the other and their interactions. Moreover, the reproductive plasticity of females in response to social environments has been investigated under constant population size and density, but whether they could adjust their reproductive strategies in response to the fluctuations or shifts of population size and density during the breeding period is largely unknown. Using a haplodiploid spider mite, Tetranychus ludeni Zacher, I carried out a series of experiments to examine how ovipositing females alter their reproductive investment under different population sizes and densities. Results demonstrate that both population size and density and their interaction significantly affected reproduction and sex allocation. I reveal that when the population was small, females tended to reduce local mate competition among sons by producing more daughters. When the population was large and dense, females were more likely to reduce local resource competition by producing more daughters early in life that would disperse from the natal patch to found new colonies. My findings show that the extremely high female-biased offspring sex ratios in large populations could not be explained by local mate competition models alone, and local resource competition and local resource enhancement might also be involved in sex allocation of T. ludeni. However social environments had weaker effects on T. ludeni sex allocation compared to the life history traits, and social environments influencing offspring sex ratio was implemented or mediated through other life history traits. T. ludeni females adjusted their reproductive strategies in response to the shifts of population density and size during their breeding period. Females constrained fecundity in response to the fluctuating environments. Females traded off egg number for size in response to dynamics of population size and increasing egg size significantly raised the proportion of daughters. They fertilized more larger eggs laid in a small population but fertilized more smaller eggs laid in a large population by lowering the egg size dependent fertilization threshold. This study provides evidence that spider mites can manipulate their reproductive output and adjust offspring sex ratio in response to various static and dynamic social environments.
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The articles in the Appendix published in Systematic & Applied Acarology are © Systematic & Applied Acarology Society and were removed. The other articles in the Appendix are reproduced under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license.
Listed in 2023 Dean's List of Exceptional Theses
Keywords
Tetranychus, Reproduction, Sex ratio, Dean's List of Exceptional Theses