The use of geometric morphometries to improve conservation outcomes of a ‘sugar glider’ Petaurus cryptic complex in Australia and New Guinea

<p dir="ltr">Understanding the geographic distribution and morphological variation of species is crucial for biodiversity conservation, particularly in regions with complex biogeographic histories such as Australia. Despite some recent research, the distribution and morphological characteristics of many Australian terrestrial species remain ambiguous, often due to unresolved taxonomy. This thesis focuses on the Petaurus genus, specifically Petaurus breviceps, Petaurus notatus and Petaurus papuanus to address gaps in their range boundaries by identifying morphological variation of the skull. The study employed geometric morphometries and linear measurements to analyze skull size and shape, providing new insights into species distribution and evolutionary responses to geographic and ecological pressures.</p><p dir="ltr">The first chapter of this thesis examines the distribution of <i>Petaurus breviceps</i> and <i>Petaurus notatus</i> across three key regions: the eastern, middle, and western areas of the Great Dividing Range (GDR), as well as north and south of the Brisbane Valley Barrier (BVB). These biogeographical barriers have long been hypothesized to influence species distribution. Significant differences in skull size and shape were found between P. breviceps populations located in the mid-GDR and southern eastern regions. However, no significant shape differences were observed between mid- and west-GDR populations. Additionally, skull size and shape differed significantly between north and south eastern specimens, though northern populations showed no significant intra-regional shape differences. These findings suggest that <i>P. breviceps</i> is primarily restricted to the eastern coastal zone south of the BVB, with hybridization likely occurring in the northern regions. This study refines the distribution of <i>P. breviceps</i>, emphasizing the role of geographic barriers in shaping species ranges and informing conservation strategies.</p><p dir="ltr">The second chapter focused on unresolved taxonomic classifications within the <i>Petaurus</i> genus, particularly for populations in Cape York and New Guinea. Historically, <i>Petaurus breviceps</i> from northeastern Queensland has been considered a distinct taxon. Recent revisions recognized three subspecies at the species level: <i>P. notatus</i>, <i>P. </i><i>ariel</i>, and <i>P. papuanus</i> (the latter distributed across New Guinea). Using geometric morphometries, we compared known Australian species with specimens from Cape York and New Guinea. Our analysis revealed no significant shape differences between Cape York specimens and <i>P. notatus</i>, supporting their identification as <i>P. </i><i>notatus</i> (formerly <i>P. longicaudatus</i>). Conversely, significant shape variation was found between Cape York and New Guinea populations, indicating no close association with <i>P. papuanus</i>. Further, island specimens from New Guinea exhibited significant morphological divergence from the mainland specimens. This variation likely reflects evolutionary responses to isolation and novel environmental pressures. Mainland New Guinea populations, however, showed no significant morphological differences, suggesting overlapping distributions and possible hybridization. These results contribute to the growing body of evidence for the complex evolutionary history of the <i>Petaurus</i> genus and highlight the need for continued taxonomic and biogeographic research.</p><p dir="ltr">The third chapter of this thesis investigated the introduction of <i>Petaurus notatus</i> to Tasmania in the 1830s, an event that provides a unique opportunity to study phenotypic plasticity and its ecological implications. Translocated as pets, <i>P. notatus</i> established a wild population that has since been associated with predation on endemic and migratory birds. Using geometric morphometric techniques, we assessed whether the Tasmanian population exhibited morphological changes in response to the novel environment. Our findings reveal significant skull shape variation between Tasmanian and Victorian<i> P. notatus</i> specimens. Notably, Tasmanian specimens exhibited increased skull size, with a pronounced elongation of the rostrum and dorsal shift in the frontal bones. These changes were accompanied by an increase in the posterior angle of the coronoid process on the mandible. Interestingly, these morphological changes occurred without a corresponding increase in overall body size. The observed phenotypic changes in Tasmanian populations may be indicative of a dietary shift towards camivory. Similar morphological adaptations have been documented in other species undergoing dietary transitions. This case study underscores the importance of monitoring introduced species and their potential impact on native ecosystems.</p><p dir="ltr">These findings also contribute to the growing body of evidence for the complex evolutionary history of the four species within the <i>Petaurus</i> genus and highlight the need for continued taxonomic and biogeographic research. It provides a comprehensive reassessment of the geographic distribution and morphological variation for ‘sugar gliders’. By integrating geometric morphometric analyses with biogeographical data, the research highlights the importance of geographic barriers in shaping species distributions and emphasizes the evolutionary responses of isolated populations. The findings have implications for conservation management, particularly in refining species distributions and identifying populations at risk of hybridization. Future research should focus on the genetic underpinnings of the observed morphological variation and explore the potential ecological consequences of dietary shifts in introduced populations. This thesis contributes to the broader understanding of species distribution, evolution, and conservation in the unique and diverse ecosystems of Australia and New Guinea.</p>