Disentangling controls on animal abundance: Prey availability, thermal habitat, and microhabitat structure.

The question of what controls animal abundance has always been fundamental to ecology, but given rapid environmental change, understanding the drivers and mechanisms governing abundance is more important than ever. Here, we determine how multidimensional environments and niches interact to determine population abundance along a tropical habitat gradient. Focusing on the endemic lizard Anolis bicaorum on the island of Utila (Honduras), we evaluate direct and indirect effects of three interacting niche axes on abundance: thermal habitat quality, structural habitat quality, and prey availability. We measured A. bicaorum abundance across a series of thirteen plots and used N-mixture models and path analysis to disentangle direct and indirect effects of these factors. Results showed that thermal habitat quality and prey biomass both had positive direct effects on anole abundance. However, thermal habitat quality also influenced prey biomass, leading to a strong indirect effect on abundance. Thermal habitat quality was primarily a function of canopy density, measured as leaf area index (LAI). Despite having little direct effect on abundance, LAI had a strong overall effect mediated by thermal quality and prey biomass. Our results demonstrate the role of multidimensional environments and niche interactions in determining animal abundance and highlight the need to consider interactions between thermal niches and trophic interactions to understand variation in abundance, rather than focusing solely on changes in the physical environment.

Cysteine thioesters as myelin proteolipid protein analogues to examine the role of butyrylcholinesterase in myelin decompaction.

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disorder involving demyelination, axonal transection, and neuronal loss in the brain. Recent studies have indicated that active MS lesions express elevated levels of butyrylcholinesterase (BuChE). BuChE can hydrolyze a wide variety of esters, including fatty acid esters of protein. Proteolipid protein (PLP), an important transmembrane protein component of myelin, has six cysteine residues acylated, via thioester linkages, with fatty acids, usually palmitic, that contribute to the stability of myelin. Experimental chemical deacylation of PLP has been shown to lead to decompaction of myelin. Because of elevated levels of BuChE in active MS lesions and its propensity to catalyze the hydrolysis of acylated protein, we hypothesized that this enzyme may contribute to deacylation of PLP in MS, leading to decompaction of myelin and contributing to demyelination. To test this hypothesis, a series of increasing chain length (C2-C16) acyl thioester derivatives of N-acetyl-l-cysteine methyl ester were synthesized and examined for hydrolysis by human cholinesterases. All N-acetyl-l-cysteine fatty acyl thioester derivatives were hydrolyzed by BuChE but not by the related enzyme acetylcholinesterase. In addition, it was observed that the affinity of BuChE for the compound increased the longer the fatty acid chain, with the highest affinity for cysteine bound to palmitic acid. This suggests that the elevated levels of BuChE observed in active MS lesions could be related to the decompaction of myelin characteristic of the disorder.