PubMed Health⌕ Search

Biomedical subjects

R E Ricklefs

Publications and source records attributed to R E Ricklefs.

At least 19 recordsLinked to original sources
PubMed2005

Climatic unpredictability and parasitism of caterpillars: implications of global warming.

Insect outbreaks are expected to increase in frequency and intensity with projected changes in global climate through direct effects of climate change on insect populations and through disruption of community interactions. Although there is much concern about mean changes in global climate, the impact of climatic variability itself on species interactions has been little explored. Here, we compare caterpillar-parasitoid interactions across a broad gradient of climatic variability and find that the combined data in 15 geographically dispersed databases show a decrease in levels of parasitism as climatic variability increases. The dominant contribution to this pattern by relatively specialized parasitoid wasps suggests that climatic variability impairs the ability of parasitoids to track host populations. Given the important role of parasitoids in regulating insect herbivore populations in natural and managed systems, we predict an increase in the frequency and intensity of herbivore outbreaks through a disruption of enemy-herbivore dynamics as climates become more variable.

Animals↗
PubMed2004

Temporal stability of insular avian malarial parasite communities.

Avian malaria is caused by a diverse community of genetically differentiated parasites of the genera Plasmodium and Haemoproteus. Rapid seasonal and annual antigenic allele turnover resulting from selection by host immune systems, as observed in some parasite populations infecting humans, may extend analogously to dynamic species compositions within communities of avian malarial parasites. To address this issue, we examined the stability of avian malarial parasite lineages across multiple time-scales within two insular host communities. Parasite communities in Puerto Rico and St Lucia included 20 and 14 genetically distinct parasite lineages, respectively. Lineage composition of the parasite community in Puerto Rico did not vary seasonally or over a 1 year interval. However, over intervals approaching a decade, the avian communities of both islands experienced an apparent loss or gain of one malarial parasite lineage, indicating the potential for relatively frequent lineage turnover. Patterns of temporal variation of parasite lineages in this study suggest periodic colonization and extinction events driven by a combination of host-specific immune responses, competition between lineages and drift. However, the occasional and ecologically dynamic lineage turnover exhibited by insular avian parasite communities is not as rapid as antigenic allele turnover within populations of human malaria.

Animals↗
PubMed2003

Age-related patterns of fertility in captive populations of birds and mammals.

We have analyzed birth records from the International Species Inventory System database of zoo animals to describe patterns of fertility as a function of age in birds and mammals. Unlike age at death, fertility in captive populations is partly controlled by animal keepers depending on availability of space and potential mates and on the aims of captive propagation programs. Thus, fertility records must be considered carefully to avoid potential age-specific biases. The zoo data suggest that fertility declines from a peak at young adult ages in most species. The rate of decline in reproductive function is correlated with the rate of somatic aging, indicated by the increase in mortality rate with age, and with the age at peak fertility. Over the sample as a whole, these patterns do not differ systematically between the sexes, nor do they differ between birds and mammals. While it is clear that the demographic consequences of aging of the reproductive system follow a different course than the aging of somatic tissue, the rates of each are correlated either through functional connections or through parallel evolutionary responses to common selective factors.

Aging↗
PubMed2003

Detecting avian malaria: an improved polymerase chain reaction diagnostic.

We describe a polymerase chain reaction (PCR) assay that detects avian malarial infection across divergent host species and parasite lineages representing both Plasmodium spp. and Haemoproteus spp. The assay is based on nucleotide primers designed to amplify a 286-bp fragment of ribosomal RNA (rRNA) coding sequence within the 6-kb mitochondrial DNA malaria genome. The rRNA malarial assay outperformed other published PCR diagnostic methods for detecting avian infections. Our data demonstrate that the assay is sensitive to as few as 10(-5) infected erythrocytes in peripheral blood. Results of avian population surveys conducted with the rRNA assay suggest that prevalences of malarial infection are higher than previously documented, and that studies based on microscopic examination of blood smears may substantially underestimate the extent of parasitism by these apicomplexans. Nonetheless, because these and other published primers miss small numbers of infections detected by other methods, including inspection of smears, no assay now available for avian malaria is universally reliable.

Animals↗
PubMed2002

Host plants influence parasitism of forest caterpillars.

Patterns of association between herbivores and host plants have been thought to reflect the quality of plants as food resources as influenced by plant nutrient composition, defences, and phenology. Host-plant-specific enemies, that is, the third trophic level, might also influence the distribution of herbivores across plant species. However, studies of the evolution of herbivore host range have generally not examined the third trophic level, leaving unclear the importance of this factor in the evolution of plant-insect herbivore interactions. Analysis of parasitoid rearings by the Canadian Forest Insect Survey shows that parasitism of particular Lepidoptera species is strongly host-plant-dependent, that the pattern of host-plant dependence varies among species of caterpillars, and that some parasitoid species are themselves specialized with respect to tree species. Host-plant-dependent parasitism suggests the possibility of top-down influence on host plant use. Differences in parasitism among particular caterpillar-host plant combinations could select for specialization of host plant ranges within caterpillar communities. Such specialization would ultimately promote the species diversification of Lepidoptera in temperate forests with respect to escape from enemies.

Animals↗
PubMed2002

Physiological, growth, and immune responses of Japanese quail chicks to the multiple stressors of immunological challenge and lead shot.

Exposure to the combination of a contaminant and an immunological challenge during development may greatly increase the impact of either or both of these stressors on an individual. This study investigated the interacting effects of a nonpathogenic immunological challenge and lead shot exposure early in the development of a precocial species. Seventy-one quail (Coturnix coturnix japonica) chicks orally received either one #9 lead shot (0.05 g), four lead shots (0.2 g), or no lead at the age of 8 days. A third of each of these groups of chicks were intraperitoneally injected with either 0.075 ml of 10% chukar (Alectoris graeca) red blood cells (CRBCs), Newcastle disease virus (NDV), or a placebo oil vaccine at 13 and 35 days of age. There was no difference in the survival between any of the lead or antigen treatment groups. Lead concentrations in blood were greater for the lead-dosed groups on day 49 but not on day 128. Growth curves were approximated by Weibull functions; growth parameters did not differ between lead-treated and antigen-treated birds. CRBC antigen increases fluctuating asymmetry (FA) for primary feather five, while NDV reduced FA. Lead did not affect antibody production or cell-mediated immune response. White blood cell numbers increased 7 days after antigen injection on days 27 and 49 of age. Granulocyte numbers were significantly higher for the lead-treated quail than the control quail, and both antigen-treated groups had lower granulocyte numbers than control quail. The treatment groups of combining NDV and lead shot had an average plasma protein 14% lower than other groups. Lead shot in the highest of these doses lowered asymptotic weights, increased hematocrits, lowered plasma protein, and increased granulocyte numbers of quail.

Adaptation, Physiological↗
PubMed2001

Nonequilibrium diversity dynamics of the Lesser Antillean avifauna.

MacArthur and Wilson's model of island diversity predicts an increase in the number of species until colonization and extinction are balanced at a long-term steady state. We appraise this model on an evolutionary time scale by molecular phylogenetic analysis of the colonization of the Lesser Antilles by small land birds. The pattern of accumulation of species with time, estimated by genetic divergence between island and source lineages, rejects a homogeneous model of colonization and extinction. Rather, our results suggest an abrupt, roughly 10-fold increase in colonization rate or a 90% mass extinction event 0.55 to 0.75 million years ago.

Animals↗
PubMed2001

The molecular basis of an avian plumage polymorphism in the wild: a melanocortin-1-receptor point mutation is perfectly associated with the melanic plumage morph of the bananaquit, Coereba flaveola.

BACKGROUND: Evolution depends on natural selection acting on phenotypic variation, but the genes responsible for phenotypic variation in natural populations of vertebrates are rarely known. The molecular genetic basis for plumage color variation has not been described in any wild bird. Bananaquits (Coereba flaveola) are small passerine birds that occur as two main plumage variants, a widespread yellow morph with dark back and yellow breast and a virtually all black melanic morph. A candidate gene for this color difference is the melanocortin-1 receptor (MC1R), a key regulator of melanin synthesis in feather melanocytes. RESULTS: We sequenced the MC1R gene from four Caribbean populations of the bananaquit; two populations of the yellow morph and two populations containing both the yellow morph and the melanic morph. A point mutation resulting in the replacement of glutamate with lysine was present in at least one allele of the MC1R gene in all melanic birds and was absent in all yellow morph birds. This substitution probably causes the color variation, as the same substitution is responsible for melanism in domestic chickens and mice. The evolutionary relationships among the MC1R haplotypes show that the melanic alleles on Grenada and St. Vincent had a single origin. The low prevalence of nonsynonymous substitutions among yellow haplotypes suggests that they have been under stabilizing selection, whereas strong selective constraint on melanic haplotypes is absent. CONCLUSIONS: We conclude that a mutation in the MC1R is responsible for the plumage polymorphism in a wild bird population and that the melanic MC1R alleles in Grenada and St. Vincent bananaquit populations have a single evolutionary origin from a yellow allele.

Animals↗
PubMed2001

Comparison of aging-related mortality among birds and mammals.

We use the Weibull model to characterize initial (extrinsic) mortality rates (m(0)) and rate of increase in mortality with age (omega) for natural and captive populations of birds and mammals. Weibull parameters can be estimated for small samples of ages at death by constructing survival curves and fitting the Weibull model by nonlinear least-squares regression. Both m(0) and omega decrease in captivity, on average, and omega bears a strong relationship to m(0), as it does in nature, irrespective of body mass or differences between birds and mammals. Rate of aging is most closely related to brain size in birds and to rate of postnatal growth in mammals. It is not related to duration of embryonic development, body size independently of brain size, or genome size. We suggest that causes of extrinsic mortality in nature may be replaced in captivity by intrinsically controlled causes of mortality related to processes that regulate the rate of aging.

Aging↗
PubMed2000

Large-scale processes and the Asian bias in species diversity of temperate plants.

An important issue in the study of biodiversity is the extent to which global patterns of species richness reflect large-scale processes and historical contingencies. Ecological interactions in local assemblages may constrain the number of species that can coexist, but differences in diversity in similar habitats within different regions (diversity anomalies) suggest that this limit is not firm. Variation in rate of species production could influence regional and perhaps local diversity independently of the ecological capacity of an area to support coexisting species, thereby creating diversity anomalies. Temperate Zone genera of plants that are disjunct between similar environments in eastern Asia and eastern North America (EAS-ENA) have twice as many species in Asia as in North America. Because lineages of these genera in Asia and North America are mostly sister pairs, they share a common history of adaptation and ecological relationship before disjunction. Thus, the diversity anomaly in EAS-ENA genera is not an artefact of taxon or habitat sampling but reflects differences in the net diversification (speciation-extinction) of the lineages in each of the continents. Here we propose that the most probable cause of the EAS-ENA anomaly in diversity is the extreme physiographical heterogeneity of temperate eastern Asia, especially compared with eastern North America, which in conjunction with climate and sea-level change has provided abundant opportunities for evolutionary radiation through allopatric speciation.

Asia↗
PubMed2000

Systematic affinities of Rhizophoraceae and Anisophylleaceae, and intergeneric relationships within Rhizophoraceae, based on chloroplast DNA, nuclear ribosomal DNA, and morphology.

A cladistic analysis of sequences from the chloroplast gene rbcL was used to determine the systematic affinities of Rhizophoraceae and Anisophylleaceae. This analysis rejects close relationships of Rhizophoraceae with Celastraceae or Elaeocarpaceae, suggested previously, and identifies Erythroxylaceae as sister group within the Malpighiales, supported by several morphological and anatomical characters. Our molecular results also indicate that Anisophylleaceae are nested within Cucurbitales. Although this placement is novel, this affinity is also well supported by shared morphological characters. Tribal and generic relationships within Rhizophoraceae are evaluated with a combination of six molecular data sets (rbcL, atpB-rbcL intergenic spacer, trnL-trnF intergenic spacer, ITS1, ITS2, and 5.8S) and a morphological data set. These relationships are compared with results from previous morphological cladistic analyses. Against the background of the molecular results, we briefly discuss the evolution of morphological characters traditionally used for tribal subdivision as well as characters presumably significant for adaptation to mangrove habitats, namely, aerial stilt roots and vivipary.

Journal Article↗
PubMed1999

Growth, developmental stability and immune response in juvenile Japanese quails (Coturnix coturnix japonica).

Stresses are environmental factors which restrict growth or cause a potentially adverse change in an organism. The exposure of developing organisms to environmental stresses may have several physiological consequences including a decrease in immunocompetence. However, mounting an immune response against a foreign antigen may in itself constitute a cost for developing organisms. This cost has potentially long-term consequences for adult function and fitness. This study examines the growth and developmental stability of Japanese quail++ chicks challenged by three non-pathogenic antigens: sheep red blood cells, which assess T-cell-dependent immune responses, and Mycoplasma synoviae and Newcastle disease virus, which assess T-cell-independent responses. Increases in both body mass and wing length were significantly reduced in antigen-challenged birds compared to control birds. Fluctuating asymmetry (FA) in the masses of primary feathers increased from the innermost (1) to the outermost (10) position on the wing. In addition, antigen challenge by M. synoviae and sheep red blood cells was associated with an increase in FA. The cell-mediated response measured by reaction to phytohaemagglutinin was significantly depressed in M. synoviae-challenged birds. White blood cell counts, except for monocytes, were elevated in response to all three antigen treatments. Total plasma protein and haematocrit also differed between treatments but exhibited no clear relationship to antigen challenge. Immune responses clearly impose a stress on developing chicks. Additional research will be required to determine the long-term consequences of developmental stress and assess the selective forces that influence the strength of the immune responses of chicks.

Acclimatization↗
PubMed1992

Embryonic development period and the prevalence of avian blood parasites.

Variation in prevalence of avian hematozoa is related to taxonomic affiliation at the level of the family or subfamily but not of the genus within families. Prevalence is comparatively insensitive to the influences of habitat and season; however, temperate species have higher incidences of infection than tropical species belonging to the same families. Among taxa of nonraptorial altricial landbirds, hematozoan prevalence is inversely related to the length of the incubation period but shows little relationship to body size and rate of postnatal development. This finding suggests a possible link between the duration of embryonic development and the ability to resist or control infection, possibly due to maturational processes in the avian immune system.

Animals↗
PubMed1989

Contributions of bird studies to biology.

Birds are widely distributed, highly diversified, and exhibit behavior and social organizations equal in complexity to mammals, yet they are generally more conspicuous and approachable in natural environments. These attributes make birds excellent subjects in many areas of biological research. The topics in which studies on birds have figured prominently include the mechanisms of species formation, the regulation of the distribution and abundance of animals, the effects of the environment on behavior and physiology, the biological and evolutionary significance of variations in social organizations, the encoding of information in animal communication, the sensory basis for migration and navigation, the effects of hormones on nerve cells and behavior, the ontogeny of brain and behavior, and the structure and function of the vertebrate brain. The outstanding record of avian research suggests that birds will continue to provide important models for developing and testing new ideas in various fields of biology.

Adaptation, Physiological↗
PubMed1987

Comparative analysis of avian embryonic growth.

The relationships between weight (W) and age (t) of embryos of 27 species of birds are described by parabolic equations of the form W = a*(t-i)b*, where a*,b*, and i are constants and i accounts for a time lag before the onset of parabolic growth. A simple transformation gives values of a and b for the equation dW/dt = aWb. Some mathematical properties of the parabolic equation, relating growth rate (dW/dt) to weight and age, extrapolating different curves to their intersection (point of divergence), and relating the length of the incubation period to constants of the parabolic equation and to hatching weight, are described. Fitted constants for most species formed a cluster in the vicinity of a = 0.4-0.5 and b = 0.65-0.75, within which one could not differentiate precocial and altricial species, nor among precocial families. Pelagic seabirds consistently had reduced values of b and were the only group with i greater than 0 (5-19 days). The relation between fitted constants and incubation periods is discussed. The rate at which embryo growth rate decreases with respect to size (b) is directly related to the rate of accumulation of dry matter in the tissues, suggesting that both express an underlying program of development. This study emphasizes the relationship between growth rate and development of the embryo, illustrates the degree of evolutionary flexibility and diversification within and among taxonomic groups, and reveals the sensitivity of the very young embryo to environmental conditions.

Animals↗