Biology subjects

Little, G.

Publications and source records attributed to Little, G..

4 recordsLinked to original sources

bioRxiv2026

Life cycle complexity shapes parasite sharing amongst migratory and resident hosts

Migratory animals are potentially important parasite dispersers. However, understanding the impact of host migration on parasite distributions is challenging because variation in parasite life histories can mediate dispersal potential. Furthermore, studies of parasite dispersal via host migration often compare parasites in different species of migrant and resident hosts, despite differences in host phylogeny, ecology, and exposure history, which can complicate ascertaining the impact of migration. The Tasmanian population of silvereye (Zosterops lateralis lateralis) exhibits partial migration. Some members of the population overwinter on the Australian mainland, where they co-occur with residents of another silvereye subspecies (Z. l. cornwalli). Utilising targeted PCR, metabarcoding and high-throughput sequencing, we characterise a range of parasite genera from blood and faecal samples in Tasmanian resident, migrant and mainland resident birds. Greater parasite richness was documented in migrant individuals, possibly reflecting exposure to varied parasite faunas at stopovers or during overwintering. The increased richness was primarily driven by parasites with simple life cycles. Reduced sharing of parasites with complex life cycles amongst migratory and resident host populations may be explained by ecological constraints in establishing transmission, such as vector or secondary host availability. Our study exemplifies the utility of molecular methods for characterising multi-parasite systems and makes use of a single host species to provide insights on patterns of parasite distributions that result from migratory movements. Knowing how parasite life histories constrain or promote dispersal via regular host migration will be essential for predicting future patterns of pathogen dispersal under climate change and shifting migratory regimes.

ecology↗

bioRxiv2023

Automated Surface-Based Segmentation of Deep Gray Matter Regions Based on Diffusion Tensor Images Reveals Unique Age Trajectories Over the Healthy Lifespan

Many studies have demonstrated unique trajectories of deep gray matter (GM) volumes over development and aging, suggesting but not measuring microstructural alterations over the lifespan. Only a few studies have measured diffusion tensor imaging (DTI) parameters in deep GM or reported these values across a wide age range in a large cohort. To enable efficient DTI studies of deep GM in large cohorts without the need of T1-weighted images, an automated segmentation technique is proposed here that works solely on parametric maps calculated from DTI. The algorithm segments the globus pallidus, striatum, thalamus, hippocampus and amygdala per hemisphere by deforming 3D models of these structures to their boundaries visible on the contrast provided by diffusion tensor maps and images alone. This new DTI-only method is compared against standard T1-weighted image segmentation for (i) 1.25 mm isotropic diffusion data from the Human Connectome Project (HCP) test-retest cohort (n=44) and (ii) 1.5 mm isotropic test-retest diffusion data from a local normative study (n=24). Dice coefficients of voxel overlap between methods in the HCP test-retest cohort were high (>0.7) for 7 of 10 structures, but were low for the left globus pallidus (0.54) and left/right amygdala (0.67, 0.69). The proposed DTI-only segmentation qualitatively appeared more accurate and yielded smaller volumes than T1w for 8/10 structures in both cohorts, with the exception of the globus pallidus which showed larger volumes in the HCP test-retest data but lower volumes in the local normative study data. The DTI-only segmentation method was then applied to two local single site development/aging lifespan cohorts (cohort 1: n=365 5-90 years, cohort 2: n= 164 5-74 years) to assess age changes in volume, fractional anisotropy (FA) and mean diffusivity (MD). In both cohorts, MD trajectories were quadratic for all five structures, decreasing slightly and then increasing after [~]30-35 years. In cohort #1, FA trajectories remained flat from 5 to [~]25 years and then started to decrease for the globus pallidus and hippocampus and over 5 to 90 years, FA decreased linearly for amygdala, increased linearly for striatum, and remained constant for the thalamus. In the second cohort, using an alternate acquisition protocol, the FA trajectories of all 5 structures across all ages were similar, except for the globus pallidus and thalamus which both increased in value from 5 [~] 20 years and likely reflect differences in acquisition details. Notably, the development and aging trajectories for DTI were distinct from those of the deep GM volumes. The proposed automated deep GM segmentation method on DTI-only will facilitate the analysis of deep GM DTI (currently ignored in nearly all studies despite the data there within the field-of-view) and will be advantageous particularly for studies that do not have a T1-weighted scan, as in many clinical populations.

neuroscience↗

bioRxiv2023

Mapping caudolenticular gray matter bridges in the human brain striatum through diffusion magnetic resonance imaging and tractography

In primates, the putamen and the caudate nucleus are connected by [~]1mm-thick caudolenticular gray matter bridges (CLGBs) interspersed between the white matter bundles of the internal capsule. Little is understood about the functional or microstructural properties of the CLGBs. In studies proposing high resolution diffusion magnetic resolution imaging (dMRI) techniques, CLGBs have been qualitatively identified as an example of superior imaging quality, however, the microstructural properties of these structures have yet to be examined. In this study, it is demonstrated for the first time that dMRI is sensitive to an organized anisotropic signal oriented in the direction parallel to the CLGBs, suggesting that dMRI could be a useful imaging method for probing the microstructure of the CLGBs. To demonstrate the anisotropic diffusion signal is coherently organized along the extent of the CLGBs and to enable a subsequent CLGB microstructural measurement, a novel tractography algorithm is proposed that utilizes the shape of the human striatum (putamen + caudate nucleus) to reconstruct the CLGBs in 3D. The method is applied to two publicly available and one locally acquired diffusion imaging datasets varying in resolution and imaging quality, thereafter demonstrating that the reconstructed CLGBs directly overlap expected gray matter regions in the human brain. In addition, the method is shown to accurately reconstruct CLGBs repeatedly across multiple test-retest cohorts. The novel tractography CLGB reconstructions are then used to extract a quantitative measurement of microstructure from a local model of the diffusion signal along the CLGBs themselves. This is the first work to comprehensively study the CLGBs in-vivo using dMRI and presents techniques suitable for future human neuroscience studies targeting these structures.

neuroscience↗

bioRxiv2018

Single-axon-resolution intravital imaging reveals a rapid onset form of Wallerian degeneration in the adult neocortex

Despite the widespread occurrence of axon degeneration in the injured and diseased nervous system, the mechanisms of the degenerative process remain incompletely understood. In particular, the factors that regulate how individual axons degenerate within their native environment in the mammalian brain are unknown. Longitudinal imaging of >120 individually injured cortical axons revealed a threshold length below which injured axons undergo a rapid-onset form of Wallerian degeneration (ROWD). ROWD consistently starts 10 times earlier and is executed 4 times slower than classic Wallerian degeneration (WD). ROWD is dependent on synaptic density, unlike WD, but is independent of axon complexity. Finally, we provide both pharmacological and genetic evidence that a Nicotinamide Adenine Dinucleotide (NAD+)-dependent pathway controls cortical axon ROWD independent of transcription in the damaged neurons. Thus, our data redefine the therapeutic window for intervention to maintain neurological function in injured cortical neurons, and support the use of in vivo optical imaging to gain unique insights into the mechanisms of axon degeneration in the brain.

neuroscience↗