Common latitudinal gradients in functional richness and functional evenness across marine and terrestrial systems.

Functional diversity is an important aspect of biodiversity, but its relationship to species diversity in time and space is poorly understood. Here we compare spatial patterns of functional and taxonomic diversity across marine and terrestrial systems to identify commonalities in their respective ecological and evolutionary drivers. We placed species-level ecological traits into comparable multi-dimensional frameworks for two model systems, marine bivalves and terrestrial birds, and used global species-occurrence data to examine the distribution of functional diversity with latitude and longitude. In both systems, tropical faunas show high total functional richness (FR) but low functional evenness (FE) (i.e. the tropics contain a highly skewed distribution of species among functional groups). Functional groups that persist toward the poles become more uniform in species richness, such that FR declines and FE rises with latitude in both systems. Temperate assemblages are more functionally even than tropical assemblages subsampled to temperate levels of species richness, suggesting that high species richness in the tropics reflects a high degree of ecological specialization within a few functional groups and/or factors that favour high recent speciation or reduced extinction rates in those groups.

Early diversification of sperm size in the evolutionary history of the old world leaf warblers (Phylloscopidae).

Sperm morphological traits are highly variable among species and are commonly thought to evolve by post-copulatory sexual selection. However, little is known about the evolutionary dynamics of sperm morphology, and whether rates of evolutionary change are variable over time and among taxonomic groups. Here, we examine sperm morphology from 21 species of Old World leaf warblers (Phylloscopidae), a group of generally dull, sexually monochromatic birds, which are known to have high levels of extra-pair paternity. We found that sperm length differs markedly across species, spanning about 40% of the range observed across a larger selection of passerine birds. Furthermore, we found strong support for an 'early-burst' model of trait evolution, implying that the majority of divergence in sperm length has occurred early in the evolutionary history of this clade with subsequent evolutionary stasis. This large early divergence matches the early divergence reported in ecological traits (i.e. body size and feeding behaviour). Our findings demonstrate that rates of evolution in sperm morphology can change over time in passerine taxa, and that evolutionary stasis in sperm traits can occur even in species exhibiting characteristics consistent with moderate-to-high levels of sperm competition. It remains a major challenge to identify the selection mechanisms and possible constraints responsible for these variable rates of sperm evolution.

Revisiting Fisher: range size drives the correlation between variability and abundance of British bird eggs.

We evaluate the correlation between intraspecific variation in egg size and population size in breeding British birds. Using information on abundance, range occupancy, migration status and phylogenetic relationships among species, we show that a wider geographical distribution rather than larger population size per se best predicts egg size variability. A similar result applies to wing length variability. Results from a phylogenetic path analysis suggest that geographical variation is the most parsimonious causal explanation for high intraspecific variation in common species.

Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi.

An isolated population of dark-eyed juncos, Junco hyemalis, became established on the campus of the University of California at San Diego (UCSD), probably in the early 1980s. It now numbers about 70 breeding pairs. Populations across the entire natural range of the subspecies J. h. thurberi are weakly differentiated from each other at five microsatellite loci (FST = 0.01). The UCSD population is significantly different from these populations, the closest of which is 70 km away. It has 88% of the genetic heterozygosity and 63% of the allelic richness of populations in the montane range of the subspecies, consistent with a harmonic mean effective population size of 32 (but with 95% confidence limits from four to > 70) over the eight generations since founding. Results suggest a moderate bottleneck in the early establishment phase but with more than seven effective founders. Individuals in the UCSD population have shorter wings and tails than those in the nearby mountains and a common garden experiment indicates that the morphological differences are genetically based. The moderate effective population size is not sufficient for the observed morphological differences to have evolved as a consequence of genetic drift, indicating a major role for selection subsequent to the founding of the UCSD population.

Maternal effects, paternal effects and sexual selection.

Maternal and paternal effects can lead to complicated evolutionary dynamics, including evolution in the opposite direction to selection. Recent studies demonstrate that parental effects on sexually selected traits, as well as preferences for those traits, might be large. Although these findings are likely to have consequences for both the evolutionary dynamics and equilibria of sexual selection, theory is lacking. Because parents are expected to maximize their own fitness, rather than that of a specific offspring, the magnitude (and even direction) of parental effects are context dependent. By extension, this dynamic nature of parental effects might help to explain the maintenance of variation in many sexually selected traits.

Speciation in a ring.

The evolutionary divergence of a single species into two has never been directly observed in nature, primarily because speciation can take a long time to occur. A ring species, in which a chain of intergrading populations encircles a barrier and the terminal forms coexist without interbreeding, provides a situation in which variation in space can be used to infer variation in time. Here we reconstruct the pathway to speciation between two reproductively isolated forms of greenish warbler (Phylloscopus trochiloides). These two taxa do not interbreed in central Siberia but are connected by a long chain of intergrading populations encircling the Tibetan Plateau to the south. Molecular data and climatic history imply that the reproductively isolated taxa came into contact following expansions northward around the western and eastern sides of the plateau. Parallel selection pressures for increased song complexity during the northward expansions have been accompanied by divergence in song structure. Playback experiments show that the two Siberian forms do not recognize each other's songs. Our results show how gradual divergence in a trait involved in mate choice leads to the formation of new species.

Ring species as bridges between microevolution and speciation.

A demonstration of how small changes can lead to species-level differences is provided by ring species, in which two reproductively isolated forms are connected by a chain of intermediate populations. We review proposed cases of ring species and the insights they provide into speciation. Ring species have been viewed both as illustrations of the history of divergence of two species from their common ancestor and as demonstrations that speciation can occur in spite of gene flow between the diverging forms. Theoretical models predict that speciation with gene flow can occur when there is divergent ecological selection, and geographical differentiation increases the likelihood of speciation. Thus ring species are ideal systems for research into the role of both ecological and geographical differentiation in speciation, but few examples have been studied in detail. The Greenish warbler is a ring species in which two northward expansions around the Tibetan plateau have been accompanied by parallel evolution in morphology, ecology, and song length and complexity. However, songs have diverged in structure, resulting in a lack of recognition where the reproductively isolated forms come into contact in Siberia. Our analysis suggests that these differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.

Evaluation of selection on cliff swallows.

Estimates of the intensity of selection based on measurements of the living and the dead require knowledge of the fraction of the original population dying. We apply recently developed methods (Blanckenhorn et al. 1999) to estimate the intensity of selection in a population of cliff swallows. In this population the fraction of individuals dying was unknown, but certainly high. The inferred selection is very strong and impossible to achieve if the original population is assumed to have followed a normal distribution. We consider several alternative explanations for this result including measurement biases, undetected immigration, and sampling biases. Of these, sampling biases are perhaps the most likely. We conclude that the intensity of selection on the swallows was probably strong, but its absolute magnitude is unknown.

Little evidence for sympatric speciation in island birds.

It has been suggested that the presence of sister species in small circumscribed areas, such as isolated lakes or islands, might imply that these species originated sympatrically. To investigate this possibility in birds, we searched for endemic, congeneric species on isolated islands in the ocean. Among 46 islands and small archipelagos chosen because they contain at least one species of endemic land bird, we identified seven pairs of endemic congeners (excluding flightless rails). Of these seven, only four pairs are potentially sister species and thus possible candidates for sympatric speciation. However, three of these four pairs have always been considered the results of double invasion from a mainland source (in two of these cases, molecular-phylogenetic work has either confirmed a double invasion or is ambiguous). The one remaining pair may have speciated allopatrically on a small archipelago. Additional phylogenetic studies are required to understand these cases, and our results should also be considered in light of the large number of island-bird extinctions in historic time. We conclude that, at present, there is little evidence for sympatric speciation in island birds.

The need and user requirements for integrating images with radiology reports.

Radiology reports are likely to be more useful if they contain appropriate graphic material. Diagnostic conclusions and recommendations become more convincing and useful when the clinician personally can review the image on which these are based. Modern desk-top publishing techniques make it possible to incorporate radiographic images, appropriately selected and annotated, as part of the radiology report. It is believed that such illustrated reports would be preferred by referring physicians, notwithstanding a significant loss of image detail. A survey of these referring physicians was carried out to determine whether this hypothesis was correct.

Bone chemistry and prehistoric diet: strontium studies of laboratory rats.

Strontium analysis of prehistoric human bone for the reconstruction of past diets is a relatively new technique in anthropology. In order to evaluate certain assumptions of the method, diets with low and high levels of strontium were fed to male, virgin female, and pregnant female laboratory rats. Analysis of the femurs of these rats by inductively coupled plasma/atomic emission spectrometry indicates that dietary intake is directly reflected in levels of strontium in bone ash. When dietary strontium levels were low, the observed ratio for bone:diet in the laboratory rats averaged 0.26, a value similar to that observed by other investigators. Among the groups fed high levels of strontium, pregnant females accumulated the most and virgin females accumulated the least strontium in bone. Males were intermediate. Gender differences in bone strontium among prehistoric human populations are considered in these terms.

Ecological Character Displacement in Darwin's Finches.

Character displacement resulting from interspecific competition has been extremely difficult to demonstrate. The problem was addressed with a study of Darwin's ground finches (Geospiza). Beak sizes of populations of G. fortis and G. fuliginosa in sympatry and allopatry were compared by a procedure that controls for any possible effects on morphology of variation among locations in food supply. The results provide strong evidence for character displacement. Measurement of natural selection in a population of G. fortis on an island (Daphne) lacking a resident population of G. fuliginosa shows how exploitation of G. fuliginosa foods affects the differential survival of G. fortis phenotypes.

Recurrent patterns of natural selection in a population of Darwin's finches.

The adaptive significance of morphological traits can be assessed by measuring and identifying the forces of selection acting on them. Boag and Grant documented directional selection in a small population of Darwin's medium ground finches, Geospiza fortis, on I. Daphne Major, Galápagos, in 1977. Large beak and body size were favoured at a time of diminishing food supply and high adult mortality. We show here that in two subsequent periods of moderate to high adult mortality (1980 and 1982), the population was subject to the same selection. We have used a recently developed technique to ascertain the targets of direct selection. Beak depth and body weight were commonly under direct selection to increase but, surprisingly, beak width was directly selected to decrease, over all three periods of mortality. The results have implications for our understanding of evolutionary change in morphological traits of Darwin's finches.

Effect of ethylenediaminetetraacetic acid-Tris(hydroxymethyl)aminomethane on release of the acid-soluble nucleotide pool and on breakdown of ribosomal ribonucleic acid in Escherichia coli.

Brief treatment of Escherichia coli with 2 x 10(-4)m ethylenediaminetetraacetic acid (EDTA)-0.12 m tris(hydroxymethyl)aminomethane (Tris), pH 8.0, or 0.12 m Tris alone resulted in the release of the acid-soluble nucleotide pool at 3 or 23 C. Exposure to EDTA-Tris for up to 90 min at 3 C did not result in the release of increasing amounts of 260-mmu-absorbing material. At 23 and 37 C, EDTA-Tris resulted in a steady increase in acid-soluble 260-mmu-absorbing material. Previous growth environment did not alter the release. There appeared to be degradation of 23S ribonucleic acid (RNA) after 10 min of exposure at 23 C. In addition, there was degradation of nucleotides to nucleosides and bases. This occured either within the cells with altered permeability or in the periplasmic space. This occurred in the presence of EDTA and Tris but was not seen with EDTA-phosphate. The mechanism of this degradation is unclear, since it occurs in ribonuclease I-deficient strains. Exposure to Tris buffer for long periods of time at 23 C resulted in release of the nucleotide pool and in degradation of RNA and nucleotides. These studies point out that the EDTA-Tris effect on E. coli must be divided into two parts, an early (4 to 5 min) change in permeability and a later phase of actual RNA breakdown and nucleotide degradation. Studies utilizing EDTA and Tris as agents altering permeability must thus be viewed with caution. Although the cells are viable, they have lost their acid-soluble nucleotide pool and have undergone degradation of some ribosomal RNA.