Place, space and memory cells

SummarySelf-localization and navigation are critical functions for the survival of mobile animals. By processing sensory information such as landmarks and environmental features, as well as keeping track of the path they have taken, animals are able to remain oriented as they explore the world, learning what resources are where and planning how to reach them. This ancient capacity for self-orientation has, through evolution, become intimately entwined with the ability to remember the events of daily life — an ability known as episodic memory. Spatial and episodic memory involve the interaction of many cognitive faculties and brain circuits, and so are fascinating subjects for study that reveal much about how the brain works

A framework for three-dimensional navigation research

We have argued that the neurocognitive representation of large-scale, navigable three-dimensional space is anisotropic, having different properties in vertical versus horizontal dimensions. Three broad categories organize the experimental and theoretical issues raised by the commentators: (1) frames of reference, (2) comparative cognition, and (3) the role of experience. These categories contain the core of a research program to show how three-dimensional space is represented and used by humans and other animal

Navigating in a three-dimensional world

The study of spatial cognition has provided considerable insight into how animals (including humans) navigate on the horizontal plane. However, the real world is three-dimensional, having a complex topography including both horizontal and vertical features, which presents additional challenges for representation and navigation. The present article reviews the emerging behavioral and neurobiological literature on spatial cognition in non-horizontal environments. We suggest that three-dimensional spaces are represented in a quasi-planar fashion, with space in the plane of locomotion being computed separately and represented differently from space in the orthogonal axis-a representational structure we have termed "bicoded.” We argue that the mammalian spatial representation in surface-travelling animals comprises a mosaic of these locally planar fragments, rather than a fully integrated volumetric map. More generally, this may be true even for species that can move freely in all three dimensions, such as birds and fish. We outline the evidence supporting this view, together with the adaptive advantages of such a schem

Detection of "Rickettsia sp strain Uilenbergi" and "Rickettsia sp strain Davousti" in Amblyomma tholloni ticks from elephants in Africa

Background: To date, 6 tick-borne rickettsiae pathogenic for humans are known to occur in Africa and 4 of them were first identified in ticks before being recognized as human pathogens. Results: We examined 33 and 5 Amblyomma tholloni ticks from African elephants in the Central African Republic and Gabon, respectively, by PCR amplification and sequencing of a part of gltA and ompA genes of the genus Rickettsia. The partial sequences of gltA and ompA genes detected in tick in Gabon had 99.1% similarity with those of R. heilongjiangensis and 97.1% with those of Rickettsia sp. HL-93 strain, respectively. The partial gltA and ompA gene sequences detected in tick in the Central African Republic were 98.9% and 95.1% similar to those of Rickettsia sp. DnS14 strain and R. massiliae, respectively. Phylogenetic analysis showed Rickettsia sp. detected in Gabon clusters with R. japonica and R. heilongjiangensis in a phylogenetic tree based on the partial gltA and ompA genes. The genotype of the Rickettsia sp. detected in the Central African Republic is close to those of R. massiliae group in the phylogenetic tree based on partial gltA gene sequences, and distantly related to other rickettsiae in the tree based on partial ompA gene. Conclusion: The degrees of similarity of partial gltA and ompA genes with recognized species indicate the rickettsiae detected in this study may be new species although we could only study the partial sequences of 2 genes regarding the amount of DNA that was available. We propose the Rickettsia sp. detected in Gabon be provisionally named "Rickettsia sp. stain Davousti" and Rickettsia sp. detected in the Central African Republic be named "Rickettsia sp. strain Uilenbergi"

Fine-scale genetic structure and cryptic associations reveal evidence of kin-based sociality in the African forest elephant

Spatial patterns of relatedness within animal populations are important in the evolution of mating and social systems, and have the potential to reveal information on species that are difficult to observe in the wild. This study examines the fine-scale genetic structure and connectivity of groups within African forest elephants,Loxodonta cyclotis, which are often difficult to observe due to forest habitat. We tested the hypothesis that genetic similarity will decline with increasing geographic distance, as we expect kin to be in closer proximity, using spatial autocorrelation analyses and Tau Krtests. Associations between individuals were investigated through a non-invasive genetic capture-recapture approach using network models, and were predicted to be more extensive than the small groups found in observational studies, similar to fission-fusion sociality found in African savanna (Loxodonta africana) and Asian (Elephas maximus) species. Dung samples were collected in Lopé National Park, Gabon in 2008 and 2010 and genotyped at 10 microsatellite loci, genetically sexed, and sequenced at the mitochondrial DNA control region. We conducted analyses on samples collected at three different temporal scales: a day, within six-day sampling sessions, and within each year. Spatial autocorrelation and Tau Krtests revealed genetic structure, but results were weak and inconsistent between sampling sessions. Positive spatial autocorrelation was found in distance classes of 0–5 km, and was strongest for the single day session. Despite weak genetic structure, individuals within groups were significantly more related to each other than to individuals between groups. Social networks revealed some components to have large, extensive groups of up to 22 individuals, and most groups were composed of individuals of the same matriline. Although fine-scale population genetic structure was weak, forest elephants are typically found in groups consisting of kin and based on matrilines, with some individuals having more associates than observed from group sizes alone

Un modèle de croissance pour l’azobé, Lophira alata, au Gabon

Azobé, Lophira alata, is a major timber species in Central Africa classified as vulnerable into the IUCN red list. To date, despite numerous measures of increment, no growth model has been published for this species. This study aims to distinguish the effects between tree size and local competition on tree growth. A growth model was fitted for azobé, using data from four sites in Gabon. The growth model was designed to be useful for forest management that means it relied on variables that could be computed using forest inventory data. A lognormal growth model with a negative response to stand density and basal area has been selected. The relation between growth and size was unimodal with a maximum at 60 cm of diameter at breast height. A significant residual social status effect on growth has been found (with a slower growth for suppressed trees) while no residual site effect was found

Fire management in a changing landscape: a case study from Lopé National Park, Gabon

A key management goal in Lopé National Park, Gabon, is to protect regionally-rare savannah ecosystems within the continuous rainforest block. In order to evaluate the impact of existing protection efforts, data on burning season environmental conditions, burning effort and current woody values for savannahs were examined between 1995 and 2008. Results showed (a) spatial heterogeneity in woody values to be correlated with grassy vegetation type (b) a negative relationship between woody vegetation and fire return frequency over the study, suggesting that decreased fire return frequency may favour savannah thickening and (c) that inconsistent burn effort by Park staff, and burns designed for reduced heat, may limit the efficiency of fire to prevent savannah thickening or forest expansion. Optimal humidity and fuel moisture conditions for burning are identified and recommendations made for improving the existing fire plan to achieve the management goal. Modifications will require significant investment of resources and training and require urgent experimental work to disentangle the direct impacts of fire from other processes of vegetation change. Lopé's fire policy should ultimately be a dynamic response to change in the local landscape driven by direct fire impacts or by global climate change

Impact of woody encroachment on soil organic carbon storage in the Lopé National Park, Gabon

This study quantifies changes in soil organic carbon (SOC) stock as a result of woody encroachment on savannas. Changes in SOC stocks occur below 30cm depth, indicating the subsoil as the principal compartment contributing to SOC sequestration, and suggesting the need to consider the entire profile (0–100cm) to thoroughly assess the effect of woody encroachment on SOC stocks