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(2022)ThesisSexual conflict could play an important role in shaping spatial variation in sex ratio in facultatively parthenogenetic species. This is because if females of such species avoid mating, they can establish all-female populations via parthenogenetic reproduction. By contrast, if females cannot avoid mating (i.e., males), they reproduce offspring of both sexes and establish mixed-sex populations in the wild. In Australia, natural populations of Megacrania batesii exhibit extreme spatial variation in sex ratio, with all-female and mixed-sex populations occurring over a small scale. However, it is unclear how facultatively parthenogenetic females avoid mating and establish all-female populations. Sex-specific patterns of dispersal could play a role because, depending on whether females are mated or unmated, they could establish mixed-sex and all-female populations if they successfully disperse to new areas. However, if males invade all-female populations, they could convert these populations into mixed-sex populations via mating. In chapter one, I therefore investigated dispersal rate of females and males from a mixed-sex population and single females from an all-female population. I found that females from the all-female population were less dispersive than females and males from the mixed-sex population. I also found that dispersal was limited to movement within habitat patches. Additionally, in chapter two, I examined whether costs associated with mate guarding (which is widespread and long-lasting in M. batesii) imposes energetic costs on females (i.e., reduction in foraging rate) because guarded females carry males. If females’ foraging rates were impacted by guarding males, mate guarding could be a manifestation of sexual conflict in M. batesii. However, I found little evidence that laboratory-reared females from mixed-sex populations fed more while unpaired than while paired with males. Overall, these studies contribute insights into how sex-specific dispersal and costs of mating and guarding might contribute to sexual conflict and variation in sex ratio in natural populations of the facultative parthenogenetic species, M. batesii.
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(2022)ThesisAnthropogenic debris has been documented in all habitats of the ocean that have been explored by humankind. In order to reduce the flow of debris to the ocean we must understand its sources, pathways, and distribution. The distribution of debris is determined by how it enters the marine environment and where it accumulates. Urban debris often enters the marine ecosystem via stormwater networks or is deposited during recreational activities such as fishing and boating. Here we show that debris abundance is higher under piers than adjacent soft sediment benthic habitats and appears to be related to the type of activity occurring at piers, specifically recreational fishing. Subtidal benthic habitats recorded high amounts of fishing related debris items, particularly under piers in the outer harbour. Land use and intensity of activity drive debris type and abundance entering stormwater drains. The onset of the COVID-19 pandemic allowed us to investigate changes in debris type and abundance entering drains during government-mandated lockdown periods, when human activity was vastly reduced in urban areas. We found that single-use plastics and cigarette butts were prevalent debris items in areas of high human activity, such as city centres, transport hubs, and shopping centres, and that lockdown measures impacted debris abundance in these zones. Debris abundance in industrial zones was less impacted by lockdown measures, and microplastics were abundant in these zones both before and during COVID-19 lockdowns. Our results demonstrate that marine debris reduction and remediation efforts must be targeted to the type and intensity of activity at the source of debris. For example, source reduction strategies are needed in industrial zones to manage microplastics escape into stormwater drains. Problematic debris types, such as cigarettes and single-use plastics, necessitate targeted management strategies in areas with high foot traffic, and recreational fishing debris can be targeted at piers in urbanised estuaries. Successful efforts to manage marine debris must incorporate broadscale policy changes and individual action. We anticipate these studies will inform public and private sector management interventions, and educational or awareness campaigns at a societal level.