Cochrane, C. | Search bioRxiv

bioRxiv2024

Urban effects on timing and variability of diel activity differ across passerine species and seasons

1. Life on Earth is adapted to rhythmic cycles in environmental conditions throughout the day and year via diel patterns of behavioural activity. 2. Urban conditions can disrupt such behavioural rhythms of activity. However, most studies so far have investigated urban effects on patterns of activity of single species in a single season. Additionally, we know little about the level of between and within-individual variation in urban and non-urban populations, and whether they differ. 3. Here, we use automated radio telemetry to record patterns of daily activity in six passerine species (blackbird, robin, great tit, blue tit, dunnock and chaffinch) across two urban and two forest populations during the pre-breeding and post-breeding season. We investigate urban effects on five activity-related traits: time of activity onset, time of activity end, duration of diurnal activity, level of diurnal activity and level of nocturnal activity. We employ statistical tools that allow us to estimate urban effects on mean phenotypic values, but also quantify urban versus forest differences in between-individual and within-individual phenotypic variation. 4. We found the strongest urban effects on time of activity onset in blackbirds and robins during the pre-breeding season: urban populations of blackbird and robin started their daily activity earlier than their forest counterparts. We did not find this effect in the other species. Urban populations of all species showed higher levels of nocturnal activity than forest populations, but this effect was not offset by lower diurnal activity, suggesting that urban birds may incur higher daily energetic demands. 5. Lastly, our analysis revealed large and consistent differences in variation in the investigated timing traits. Urban birds were more variable between individuals, implying lower population synchronization, and more variable within individuals, implying less consistent behaviour than their forest counterparts. Conversely, activity levels were more variable in forest birds. 6. We conclude that, for birds, urban life is associated with less rest, less consistency, and lower synchronicity, but that effect sizes depend on species and time of the year. Our results warn against generalising the effects of urbanisation on daily rhythms of birds, and call for future studies to understand the mechanisms behind species and seasonal differences.

animal behavior and cognition↗

bioRxiv2018

The ortholog of chloroquine resistance transporter (TgCRT) plays a key role in maintaining the integrity of the endolysosomal system in Toxoplasma gondii to facilitate host invasion

Toxoplasma gondii is an apicomplexan parasite with the ability to use foodborne, zoonotic, and congenital routes of transmission that causes severe disease in immunocompromised patients. The parasites harbor a lysosome-like digestive vacuole, termed the \"Vacuolar Compartment/Plant-Like Vacuole\" (VAC/PLV), which plays an important role in maintaining the lytic cycle and virulence of T. gondii. The VAC supplies proteolytic enzymes that are required to mature the parasites invasion effectors and that digest autophagosomes and endocytosed host proteins. Previous work identified a T. gondii ortholog of the Plasmodium falciparum chloroquine resistance transporter (PfCRT) that localized to the VAC. Here, we show that TgCRT is a membrane transporter that is functionally similar to PfCRT. We also genetically ablate TgCRT and reveal that TgCRT protein plays a key role in maintaining the integrity of the parasites endolysosomal system by controlling morphology of the VAC. When TgCRT is absent, the VAC dramatically increases in size by ~15-fold and co-localizes with its adjacent endosome-like compartment. Presumably to reduce aberrant swelling, transcription and translation of endolysosomal proteases are decreased in {Delta}TgCRT parasites. Expression of one endolysosomal subtilisin protease is quite significantly reduced, which impedes trimming of micronemal proteins, and significantly decreases parasite invasion. Chemical and genetic inhibition of proteolysis within the VAC reverses these effects, reducing VAC size and partially restoring the endolysosomal system, micronemal protein trimming, and invasion. Taken together, these findings reveal for the first time a physiological role of TgCRT in controlling VAC volume and the integrity of the endolysosomal system in T. gondii.\n\nAuthor SummaryToxoplasma gondii is an obligate intracellular protozoan parasite that belongs to the phylum Apicomplexa and that infects virtually all warm-blooded organisms. Approximately one-third of the human population is infected with Toxoplasma. The parasites invade host cells via processed invasion effectors in order to disseminate infection. A lysosome-like digestive vacuole (VAC) is involved in refining these invasion effectors to reach their final forms. A T. gondii ortholog of the malarial chloroquine resistance transporter protein (TgCRT) was found to be localized to the VAC membrane. Although the mutated version of the malarial chloroquine resistance transporter (PfCRT) has been shown to confer resistance to chloroquine treatment, its physiologic function remains poorly understood. Comparison between the related PfCRT and TgCRT proteins facilitates definition of the physiologic role of CRT proteins. In this study, we report that TgCRT plays a key role in regulating the integrity and proteolytic activity of the VAC and adjacent organelles, the secretion of invasion effectors, and parasite invasion and virulence. To relieve osmotic stress caused by VAC swelling when TgCRT is deleted, parasites repress proteolytic activities within this organelle to decrease solute accumulation, which then has secondary effects on parasite invasion. Our findings highlight a common function for PfCRT and TgCRT proteins in regulating apicomplexan parasite vacuolar size and function.

microbiology↗