Phylogenetic conservatism of environmental niches in mammals

Phylogenetic niche conservatism is the pattern where close relatives occupy similar niches, whereas distant relatives are more dissimilar. We suggest that niche conservatism will vary across clades in relation to their characteristics. Specifically, we investigate how conservatism of environmental niches varies among mammals according to their latitude, range size, body size and specialization. We use the Brownian rate parameter, σ(2), to measure the rate of evolution in key variables related to the ecological niche and define the more conserved group as the one with the slower rate of evolution. We find that tropical, small-ranged and specialized mammals have more conserved thermal niches than temperate, large-ranged or generalized mammals. Partitioning niche conservatism into its spatial and phylogenetic components, we find that spatial effects on niche variables are generally greater than phylogenetic effects. This suggests that recent evolution and dispersal have more influence on species' niches than more distant evolutionary events. These results have implications for our understanding of the role of niche conservatism in species richness patterns and for gauging the potential for species to adapt to global change.     

Phylogenetic studies of cardiac myosins from amphibia to mammals

Comparison between pig atrial and ventricular myosins was performed on the light chains (using SDS-PAGE) and on the heavy chains (using Ca2+-ATPase measurements and NTCBA peptide mapping). Light chain composition of pig cardiac myosins was compared to three other species ones (frog, chicken and human). Up to birds, atrial and ventricular myosin light chain composition was identical whereas in mammals atrial and ventricular myosin light chain composition was different; likewise the heavy chains. Six cardiac myosin isoenzymes have been thus characterized. No correlation can be established between cardiac myosin light chain pattern and species evolution.     

Phylogenetic and regional variations in brain gangliosides of tetrapods.

1. Ganglioside patterns were analyzed from four neural tissues (medulla, midbrain, forebrain and retina) in a representative from each of the four tetrapod classes. 2. Regional variations in ganglioside patterns were noted within some species, but differences were greater across phylogenetic lines. 3. These results suggest that evolutionary history plays a greater role than neural differentiation in the expression of brain ganglioside patterns.     

CCN5 Expression in mammals. II. Adult rodent tissues

CCN5 is a secreted heparin- and estrogen-regulated matricellular protein that inhibits vertebrate smooth muscle cell proliferation and motility. CCN5 is expressed throughout murine embryonic development in most organs and tissues. However, after embryonic development is complete, we hypothesized that CCN5 distribution would be largely restricted to small set of tissues, including smooth muscle cells of the arteries, uterus, airway, and digestive tract. Because CCN5 inhibits proliferation of smooth muscle cells in vitro, it might function to prevent excessive growth in vivo. In contrast, another member of the CCN family, CCN2, promotes smooth muscle cell proliferation in vitro, and thus it was expected that its expression levels would be low in uninjured normal adult tissues. Frozen sections from adult tissues and organs were analyzed immunohistochemically using anti-CCN5 and anti-CCN2 antibodies. Both proteins were detected in arteries, the uterus, bronchioles, and the digestive tract as expected, and also in many other tissues including the pancreas, spleen, liver, skeletal muscle, ovary, testis, thymus, brain, olfactory epithelium, and kidney. CCN5 and CCN2 protein was found in smooth muscle, endothelial cells, epithelial cells, skeletal muscle, cells of the nervous system, and numerous other cell types. In many cells, both CCN5 and CCN2 was present in the nucleus. Rather than having opposite patterns of localization, CCN5 and CCN2 often had similar sites of expression. The wide distribution of both CCN5 and CCN2 suggests that both proteins have additional biological functions beyond those previously identified in specific cellular and pathological models.     

Cerebrosides and sulfocerebrosides in the brain of insectivorous mammals

Brain cerebrosides (C) and sulfocerebrosides (S) of Insectivora, which represent the most ancient and primitive order of placentary mammals, were first studied. The content of C and S is higher in hedgehogs (Erinaceus europaeus, E. auritus) and mole (Talpa europaea) brains as compared to shrew (Sorex araneus) brain. Hydroxy fatty acids predominate over normal fatty acids in C of all studied insectivora brains. The fatty acid content of C and S of the Insectivora brains is similar in being rich in palmitic, stearic and behenic normal acids and hydroxybehenic and hydroxylignocerinic acids. Hydroxy fatty acids of C and S are more saturated and they have a longer chain (sum C24-26 acids) than the normal acids. C and S of insectivora and primate brains are compared. The data may be of importance for the understanding of the biochemical evolution of the nervous system of mammals.     

Phylogenetic assessment of molecular and morphological data for eutherian mammals

The interordinal relationships of eutherian (placental) mammals were evaluated by a phylogenetic analysis of four published data sets (three sequences and one morphological). The nature and degree of support and conflict for particular groups were assessed by separate bootstrap and homogeneity tests, which were followed by combined analyses of the sequence and morphological data. Between orders, strong support (i.e., > or = 95% bootstrap scores) was found for a paraphyletic Artiodactyla (relative to Cetacea) and a monophyletic Cetartiodactyla (Artiodactyla and Cetacea) and Paenungulata (Hyracoidea, Proboscidea, and Sirenia). In turn, some reasonable to strong evidence (> or = 85%) was obtained for Hyracoidea with Sirenia, Dermoptera with Scandentia, Glires (Lagomorpha with Rodentia), and Afrotheria (Amblysomus, Macroscelidea, Paenungulata, and Tubulidentata). Otherwise, no other interordinal clades were supported at these reasonable to strong levels. This overall lack of resolution for eutherian interordinal clusters agrees with other studies that suggest further progress will continue to be slow and difficult. Further resolution will require the integration of more recently published data, the continued sampling of taxa and characters, and the use of more powerful methods of data analysis.     

Stem cell niches in mammals

Stem cells safeguard tissue homeostasis and guarantee tissue repair throughout life. The decision between self-renewal and differentiation is influenced by a specialized microenvironment called stem cell niche. Physical and molecular interactions with niche cells and orientation of the cleavage plane during stem cell mitosis control the balance between symmetric and asymmetric division of stem cells. Here we highlight recent progress made on the anatomical and molecular characterization of mammalian stem cell niches, focusing particularly on bone marrow, tooth and hair follicle. The knowledge of the regulation of stem cells within their niches in health and disease will be instrumental to develop novel therapies that target stem cell niches to achieve tissue repair and re-establish tissue homeostasis.     

Small mammals of a woodland-savannah ecosystem in Zimbabwe. II. Community structure

Community characteristics of small mammals in five woodland-savannah habitats (riverine grassland, miombo, mopane, talus, thicket) were studied at Sengwa Wildlife Research Area in Zimbabwe between July 1992 and July 1993. The study was initiated following a drought year and extended over a year of average rainfall. Fourteen species of small mammals were recorded during mark-and-recapture trapping, with the number of species known to occur in a single community ranging from three to nine. Species complements and biomass (g/ha) were lowest during the first portion of the study and peaked during the 1993 cool dry season. Species diversity (H') was lowest in the hot dry season and highest in the cool dry season. Temporal variation in biomass and species diversity was least in talus and greatest in riverine grassland. Communities in talus and thicket were most similar and those in riverine grassland and thicket least similar. In general, these results suggest that woodland-savannah communities are highly variable and appear to be resource-limited.     

Establishment of the germ cell lineage in mammals

The germ cell lineage in mice becomes lineage-restricted about 7.2 days postcoitum. Its progenitors have migrated from the proximal region of the epiblast. Cells from the distal region of the epiblast will also give rise to germ cells, if they are transplanted to the proximal region at the appropriate time. Cells in this region are subject to a predisposing signal from the adjacent extra-embryonic ectoderm. It appears that this and other signals determine the emergence of germ cells: unlike in some other organisms, this event is not predetermined.