No abstract

The extreme morphological simplicity of lingulide brachiopod shells makes them particularly useful for investigating the species-level taxonomic resolution of the fossil record as well as the relationships between taxonomy, morphological complexity, and evolutionary rates. Lingulides have undergone little change in shell morphology and have had low taxonomic diversity since the Paleozoic. Is this pattern an evolutionary phenomenon or an artifact of the shell's simplicity? Multivariate methods were used to establish morphogroups among seven populations of four extant species of Glottidia. Six characters (three shell dimensions and three internal septa) were measured for 162 specimens from field and museum collections. All populations follow similar allometric trajectories: internal septa display positive allometry and shell dimensions display negative allometry. The allometric pattern may reflect D'Arcy Thompson's Principle of Similitude. Principal component analysis does not reveal any distinct clusters in Glottidia morphospace but suggests that some differences independent from ontogeny exist among the populations. Size-free canonical variate analysis indicates the presence of five size-invariant groups that are statistically distinct. Bootstrap-corrected error rates indicate that four specimens are enough to classify a sample correctly at α = 0.05 and eight specimens at α = 0.01. The groups are consistent with neontological classification with the exception of two populations of G. pyramidata identified by discriminant analysis as two distinct groups. The size-free morphogroups reflect geographic separation rather than ontogenetic or substrate differences among the populations.Despite the morphological simplicity of the shell, size-free multivariate analysis of Glottidia delineates groups that offer taxonomic resolution comparable with the neontological classification. The method offers a promising tool for identifying natural morphogroups on the basis of few morphological characters. Moreover, the agreement between neontological taxonomy and the morphogroups suggests that the size-free approach can be applicable for evaluating the reality of the low diversity and turnover rates observed in the fossil record of lingulide brachiopods (= Family Lingulidae). Assuming that the neontological species of Glottidia are biologically meaningful, this study shows that morphological simplicity of lingulides does not necessarily result in taxonomic underresolution. Our analysis, as well as several previous case studies, suggests that taxonomic diversity and turnover rates do not have to be dependent on the morphological complexity of preservable parts. In many cases, when rigorous quantitative methods are employed, the differences in the rates of morphological evolution may be a real evolutionary phenomenon and not artifacts of morphological complexity.

No abstract

Bacteria use a wide range of immune systems to counter phage infection. A subset of these genes share homology with components of eukaryotic immune systems, suggesting that eukaryotes horizontally acquired certain innate immune genes from bacteria. Here we show that proteins containing a NACHT module, the central feature of the animal nucleotide-binding domain and leucine-rich repeat containing gene family (NLRs), are found in bacteria and defend against phages. NACHT proteins are widespread in bacteria, provide immunity against both DNA and RNA phages, and display the characteristic C-terminal sensor, central NACHT, and N-terminal effector modules. Some bacterial NACHT proteins have domain architectures similar to human NLRs that are critical components of inflammasomes. Human disease-associated NLR mutations that cause stimulus-independent activation of the inflammasome also activate bacterial NACHT proteins, supporting a shared signaling mechanism. This work establishes that NACHT module-containing proteins are ancient mediators of innate immunity across the tree of life.

No abstract

Hydrography and exchange processes in a tropical estuary, the Gulf of Nicoya, Costa Rica, are described from data collected in 1979 and 1980 . The measurements and analyses were made in both the dry season and wet season and include temperature, salinity, and density at twenty locations in the gulf and currents (over a semi-diurnal tidal cycle) at five locations . These new results enlarge on the early study by Peterson (1958) . Circulation in the lower gulf shows a marked east-west asymmetry due to the predominant runoff along its eastern shore from Rio Barranca and Tarcoles . The freshened surface water from the upper gulf combines with the runoff from these rivers and flows southward along the eastern side of the lower gulf . This flow is compensated by a northward flow of more saline water on the western side at all depths and on the eastern side along the bottom . The boundary between the southward and northward surface flow is marked by a strong salinity front in the rainy season . There is a rapid increase in tidal energy density toward the shoaling northern reaches of the lower gulf, between San Lucas Island and Puntarenas Peninsula . Enhanced mixing must accompany this increase, and direct measurements in the constriction between San Lucas and Puntaneras show that tidal mixing is dominant in transporting salt into the upper gulf against the freshwater runoff .

No abstract

No abstract