Effects of spatio-temporal variation in food supply on red squirrel Sciurus vulgaris body size and body mass and its consequences for some fitness components

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat‐related differences in body size and variability of seed‐crops, suggesting differential selection for smaller squirrels in spruce‐larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed‐crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.     

Regional mapping of a liver alpha-subunit gene of phosphorylase kinase (PHKA) to the distal region of human chromosome Xp.

X-linked liver glycogenosis (XLG) is a glycogen storage disorder resulting from deficient activity of phosphorylase kinase (PHK). PHK consists of four different subunits: alpha, beta, gamma, and delta. Several genes encoding PHK subunits have been cloned and localized, but only the muscle alpha-subunit (PHKA) gene has been assigned to the X chromosome, in the region Xq12----q13. However, we have previously excluded the muscle PHKA gene as a candidate gene for the XLG mutation, as linkage analysis indicated that the mutation responsible for XLG is located in Xp22 and not in Xq12----q13. We report here the chromosomal localization by in situ hybridization of a liver PHKA gene to the distal region of chromosome Xp. Strong hybridization signals were observed on the distal part of the short arm of a chromosome identified as the X chromosome by cohybridization with an X chromosome-specific centromeric probe. The localization of this gene in the same chromosomal region as the disease gene responsible for XLG suggests that the liver PHKA gene is a highly likely candidate gene for the XLG mutation.     

Maternal Influences on Feeding and General Activity in Domestic Chicks

The aim of this study was to determine if and how the presence of a hen influences the behaviour of chicks and, more precisely, their food preferences. We observed two types of young, brooded and non‐brooded chicks in the presence of three different food types. Results revealed that brooded chicks performed more locomotion and more sustained feeding activities than non‐brooded chicks. Moreover, brooded chicks had different preferences from non‐brooded chicks and very clearly followed their mother's preferences. We concluded that social facilitation and local enhancement could play a significant role in determining the importance of feeding activities and preferences of brooded chicks.     

Activity budget and foraging behaviour of red squirrels (Sciurus vulgaris) in coniferous and deciduous habitats

Activity pattern, activity budget and foraging behaviour are compared between radiotagged squirrels in a coniferous and a deciduous habitat. Differences between habitats are explained in terms of differences in food availability, food choice and feeding rate.     

LRRK2 mutations impair depolarization-induced mitophagy through inhibition of mitochondrial accumulation of RAB10

ABSTRACT

Parkinson disease (PD) is a disabling, incurable disorder with increasing prevalence in the western world. In rare cases PD is caused by mutations in the genes for PINK1 (PTEN induced kinase 1) or PRKN (parkin RBR E3 ubiquitin protein ligase), which impair the selective autophagic elimination of damaged mitochondria (mitophagy). Mutations in the gene encoding LRRK2 (leucine rich repeat kinase 2) are the most common monogenic cause of PD. Here, we report that the LRRK2 kinase substrate RAB10 accumulates on depolarized mitochondria in a PINK1- and PRKN-dependent manner. RAB10 binds the autophagy receptor OPTN (optineurin), promotes OPTN accumulation on depolarized mitochondria and facilitates mitophagy. In PD patients with the two most common LRRK2 mutations (G2019S and R1441C), RAB10 phosphorylation at threonine 73 is enhanced, while RAB10 interaction with OPTN, accumulation of RAB10 and OPTN on depolarized mitochondria, depolarization-induced mitophagy and mitochondrial function are all impaired. These defects in LRRK2 mutant patient cells are rescued by LRRK2 knockdown and LRRK2 kinase inhibition. A phosphomimetic RAB10 mutant showed less OPTN interaction and less translocation to depolarized mitochondria than wild-type RAB10, and failed to rescue mitophagy in LRRK2 mutant cells. These data connect LRRK2 with PINK1- and PRKN-mediated mitophagy via its substrate RAB10, and indicate that the pathogenic effects of mutations in LRRK2, PINK1 and PRKN may converge on a common pathway.

Abbreviations : ACTB: actin beta; ATP5F1B: ATP synthase F1 subunit beta; CALCOCO2: calcium binding and coiled-coil domain 2; CCCP: carbonyl cyanide m-chlorophenylhydrazone; Co-IP: co-immunoprecipitation; EBSS: Earle’s balanced salt solution; GFP: green fluorescent protein; HSPD1: heat shock protein family D (Hsp60) member 1; LAMP1: lysosomal associated membrane protein 1; LRRK2: leucine rich repeat kinase 2; IF: immunofluorescence; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MFN2: mitofusin 2; OMM: outer mitochondrial membrane; OPTN: optineurin; PD: Parkinson disease; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT1: ras homolog family member T1; ROS: reactive oxygen species; TBK1: TANK binding kinase 1; WB: western blot.     

Estimating offspring production using capture-mark-recapture and genetic methods in red squirrels

Reproductive rate is a key demographic parameter of life history and population ecology. In traditional population-ecology studies of small mammals, this and other vital rates are inferred from capture-mark-recapture (CMR) data. However, CMR assumes that immigrants at first capture can be distinguished from unmarked locally born offspring, an assumption not always met. We verified CMR estimates of locally born red squirrel (Sciurus vulgaris) offspring as a measure of reproductive rate, with candidate offspring (CO)–candidate parent (mothers, CPs) assignment by CERVUS, using ten DNA microsatellite loci. Seventy-two of 122 candidate offspring (59%) were assigned to 52 of 125 CPs in six populations. Estimates of mean litter size were 1.5 young (range 1–3). The 50 CO (41%) not assigned to a reproducing female in the study site were considered immigrants. Parentage assignment also provided evidence of dispersal between two of our sites. Overall, CMR and CERVUS agreed in 77% of cases. Considering only the 55 juveniles determined as locally born by CMR, 50 (91%) were also assigned as local offspring with CERVUS. The main discrepancy between the two methods was that 22 subadult squirrels classified immigrants by CMR, were assigned by CERVUS to females which had reproduced in our sites. It is concluded that although in our study system agreement between CMR and CERVUS in determining local offspring was high, using genetic parentage assignment helped to correctly classify some subadults, considered immigrants by CMR, as locally born. Hence, in large-scale demographic studies, combining CMR with parentage assignment will allow more precise estimates of reproduction and dispersal.     

Leptin Levels,Leptin Receptor Gene Polymorphisms,and Energy Metabolism in Women

Objective: Resting metabolic rate (RMR) is mainly determined by fat‐free mass and additionally by age, sex, hormones, and possibly genetic differences. We evaluated whether leptin levels and polymorphisms in the leptin receptor (LEPR) gene were associated with energy expenditure phenotypes. Methods: RMR, body composition, and leptin levels were measured in 125 overweight and obese women. Three LEPR polymorphisms, Lys109Arg, Gln223Arg, and Lys656Asn, were typed on genomic DNA of another group of 192 women in whom RMR was measured. Fat, protein, and carbohydrate oxidation were calculated for 103 of these subjects. In 38 subjects, glucose‐induced thermogenesis was measured over 3 hours. Results: In the first study group, a negative correlation between RMR and leptin levels was found after controlling for fat and fat‐free mass. In multiple regression analysis, leptin contributed significantly to RMR, independent of body composition. In the second study group, RMR was not associated with LEPR polymorphisms. Differences in substrate oxidation rates were found among genotypes at the Lys656Asn site. In fasting conditions, Lys656Lys showed a trend to oxidize more carbohydrates and less fat than Asn656 carriers, a trend which became significant after the glucose load when carbohydrate oxidation rate in Lys656Lys was 15% higher than in Asn656 carriers (p = 0.04), and fat oxidation rate was 44% lower (p = 0.02). Discussion: These results suggest that DNA sequence variations in the LEPR gene could affect substrate oxidation. We hypothesize that this might be caused by differences in glucose levels, leading to differences in glucose oxidation rates.     

Complex relationships between physiological stress and endoparasite infections in natural populations

Short-term elevation of glucocorticoids (GCs) is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors (stressors). However, when exposure to stressors occurs repeatedly or over a prolonged period of time, animals may experience chronic elevation of GCs, which reduces the immune response efficiency and can lead to higher intensity of parasitic infection. Here, we used invasive gray squirrels Sciurus carolinensis introduced in Northern Italy and their 2 most prevalent gastrointestinal parasites, the nematode Strongyloides robustus and coccidia of the genus Eimeria, as a model to investigate relationships among macroparasite infection and concentrations of fecal glucocorticoid metabolites (FGMs), an integrated measure of circulating GCs. Our results revealed an association of FGMs with infection by St. robustus, but not with coccidia. Individuals with higher FGMs appear to be responsible for the greatest St. robustus egg shedding within gray squirrel populations, thus possibly acting as superspreaders. However, FGMs were negatively associated with adult St. robustus, suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs, but is only affected by it through immune-mediated effects on its fecundity. Finally, the relationship between St. robustus (both eggs and adult parasites) and FGMs was not linear, suggesting that only high levels of physiological stress influence parasite infection. Our findings highlight that the direction and magnitude of the stress–infection relationship may depend not only on the specific host–parasite system, but also on the different life stages of the same parasite.