Agricultural food subsidies, migratory connectivity and large-scale disturbance in arctic coastal systems: a case study.

An allochthonous input can modify trophic relationships, by providing an external resource that is normally limiting within a system. The subsidy may not only elicit a growth response of the primary producers via a bottom-up effect, but it also may lead to runaway herbivore growth in the absence of increased predation. If the consumer is migratory and predation is similarly dampened in the alternative system, the increased numbers may produce a top-down cascade of direct and indirect effects on an ecosystem that may be a great distance from the source of the subsidy. In an extreme case, it can lead to a catastrophic shift in ecosystem functioning as a result of biotic exploitation that produces an alternative stable state. The loss of resilience is particularly sensitive to herbivore density which can result in two different outcomes to the vegetation on which the consumer feeds. Over-compensatory growth of above-ground biomass gives way to sward destruction and near irreversible changes in soil properties as density of a herbivore increases. A striking temporal asymmetry exists between a reduction in the consumer population and recovery of damaged vegetation and degraded soils.

The biologic effects of C225, a chimeric monoclonal antibody to the EGFR, on human prostate carcinoma.

For prostate cancer, a correlation exists between overexpression of the epidermal growth factor receptor (EGFR) and poor clinical prognosis. In addition, late-stage metastatic disease is characterized by a change from a paracrine to an autocrine mode of expression for TGF-alpha, the ligand for the EGFR. These observations suggest that activation of the EGFR may be important for the growth of prostatic carcinoma in situ, and blockade of the receptor-ligand interaction may offer a means of therapeutic intervention for this disease. We describe the biologic effects of a chimeric anti-EGFR monoclonal antibody, C225, on several human prostate tumor cell lines in culture and the tumor inhibitory properties of the antibody for the treatment of human prostate carcinoma xenografts in nude mice. In vitro analysis of the EGFR from androgen-responsive and independent prostatic carcinoma cell lines revealed that C225 blocked EGF-induced receptor activation and induced internalization of the receptor. In vivo, a treatment regimen of C225 alone or antibody plus doxorubicin significantly inhibited tumor progression of well-established DU145 and PC-3 xenografts in nude mice. These results suggest that C225 may have utility for the treatment of human prostate carcinoma in a clinical setting.

Effective Population Size and Lifetime Reproductive Success.

The mean and variance of lifetime reproductive success, ELRS and VLRS , influence the ratio of effective to census population size, Ne /Nc . Because the complete data needed to calculate ELRS and VLRS are seldom available, we provide alternatives for estimating Ne /Nc from incomplete data. These estimates should be useful to conservation biologists trying to compute the effective size of a censused population. An analytical approach makes assumptions regarding the process influencing offspring survival. We provide a method for examining the validity of those assumptions and show that particular violations can result in either over- or underestimates. When the assumptions are violated or when more data are available, we suggest estimating Ne /Nc using computer simulations of models based on individuals. We examine how such simulations can be used to estimate Ne /Nc using an individual-based model for Lesser Snow Geese (Anser caerulescens). We demonstrate that such estimates can be biased unless the simulations are based on complete cohorts and samples of known age. We show that because the estimate of Ne /Nc depends on the stage of the reproductive cycle used as a point of reference in the model, the census population size Nc must be based on the same stage to provide unbiased estimates of Ne . Tamaño poblacional efectivo y el éxito reproductivo vitalicio.

Resumen: La media y la varianza del éxito reproductivo vitalicio (ELRS y VLRS ) influencía el cociente entre tamaño poblacional efectivo y el tamaño censal Ne /Nc . Dado que los datos completos necesarios para calcular ELRS y VLRS están raramente disponibles, nosotros proveemos alternativas para estimar Ne /Nc a partir de datos incompletos. Estas estimaciones deberían ser útiles para los biólogos de la conservación que tratan de computar el tamaño efectivo de una población censada. Una aproximación analítica utiliza supuestos acerca del proceso que influencía la supervivencia de la progenie. Nosotros proveemos de un método para examinar la validez de esos supuestos y mostramos violaciones particulares que resultan en sobreestimaciones o subestimaciones. Cuando los supuestos son violados o cuando más datos estan disponibles, nosostros sugerimos estimar Ne /Nc utilizando simulaciones de modelos basados en individuos. Examinamos como tales simulaciones pueden ser usadas para estimar Ne /Nc utilizando un modelo basado en individuos para el ganso (Anser caerulescens). Demostramos que tales estimaciones pueden estar sesgadas a menos que las simulaciones esten basadas en cohortes completas y muestras de edades conocidas. Mostramos que dado que la estimación de Ne /Nc depende del estado del ciclo reproductivo usado como punto de referencia en el modelo, el tamaño poblacional censal (Nc ) debe estar basado en el mismo estado a efecto de proveer estimaciones de Ne no sesgadas.

Variance of lifetime reproductive success: estimation based on demographic data.

Variance of lifetime reproductive success is not a well-defined parameter; it is a function of the way a life cycle is defined. Therefore, comparisons of such variance across studies and taxa will only be valid if the life cycles employed are complete (i.e., an entire generation), precisely defined (e.g., egg to egg or adult to adult), and identical. Given a well-defined life cycle, we present methods for obtaining estimates of the variance of lifetime reproductive success among individuals using demographic data. The estimates are based on the assumptions of no selection and negligible covariance between life span and reproductive effort. The techniques can be used to investigate the effects of alternate life histories on the distribution of reproductive success in a population, as well as to obtain estimates of effective population size. They may also provide a null model for investigations of selection. Some theoretical and empirical results are presented. A method for obtaining confidence intervals for the estimates is described.

Fitness consequences of egg-size variation in the lesser snow goose.

We investigated the relationship between eggsize variation and (a) egg hatching success, (b) chick survival to fledging and recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of egg size for successful and unsuccessful eggs, our aim was to assess the relative fitness of eggs of different sizes and to determine the type of selection operating on egg size in this species. As both egg size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-size variation is very marked in this population, varying by up to 52% for eggs hatching successfully. However, there was no relationship between egg size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling across years. Egg size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons. First-laid eggs surviving to onset of incubation, and eggs hatching successfully, were on average larger than unsuccessful eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific egg survival. Variance of egg size differed significantly between successful and unsuccessful eggs in only 3 of 24, and 0 of 21, individual year comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between egg-size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on egg size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that egg-size variation is maintained by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that egg-size variation represents the pleiotropic expression of alleles affecting more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct effects on egg size we suggest that their contribution to heritable egg size is small.

Environmental change and the cost of philopatry: an example in the lesser snow goose.

The consequences of philopatric and dispersal behaviours under changing environmental conditions were examined using data from the colony of Lesser Snow Geese (Anser caerulescens caerulescens) breeding at La Pérouse Bay, Manitoba, Canada. In response to increased population size and decreased food abundance over time, increasing numbers of family groups have been dispersing from the traditional feeding areas. Goslings from dispersed broods were significantly heavier (7.3%), and had longer culmens (3.1%), head lengths (2.6%) and marginally longer tarsi (1.9%) on average than goslings that remained within La Pérouse Bay itself. These differences were consistent in each of 5 years. There was no evidence that the larger size of dispersed goslings was due to either a tendency for larger adults to disperse to alternative sites, or increased mortality of smaller goslings among dispersed broods. The most likely cause for the larger size of goslings from dispersed broods was the significantly greater per capita availability of the preferred salt-marsh forage species at non-traditional brood-rearing areas. The larger goslings in non-traditional feeding areas showed significantly higher firstyear survival, suggesting that the use of deteriorating traditional feeding areas may currently be maladaptive in this population.

Studies of sibling Drosophila species from Laguna Verde, Veracruz, Mexico: I. Species frequencies, viability, desiccation resistance, and vagility.

The sibling species Drosophila melanogaster and D. simulans were collected at Laguna Verde, Veracruz, Mexico. D. melanogaster was found in significantly greater frequency than was D. simulans. Ten isofemale lines of each species were tested for egg to adult viability, desiccation resistance, and vagility. D. melanogaster surpassed D. simulans in all three characteristics. The findings are discussed with reference to the climatic conditions at Laguna Verde and the expected effect of such an environment on the relative frequencies of these species. The dichotomous results in regard to desiccation resistance and vagility that were observed between recently collected D. melanogaster and the Oregon-R laboratory stock of that species are also discussed.

Nuclear power plants and natural populations of Mexican Drosophila.

With the worldwide proliferation of nuclear power plants has come the need to study the biological effects of the operation of the reactors on surrounding populations. We have begun a long-term study of the sibling species Drosophila melanogaster and D. simulans in the area of Laguna Verde in the state of Veracruz in Mexico. Laguna Verde, on the Gulf of Mexico about 75 km north of the city of Veracruz, is the location of the country's first nuclear power plant. This plant has not yet gone "on-line." The species have been collected from two sites, one of which is south of the reactor and is in the path of the prevailing north to south wind flow. The other collecting site is west of the plant. The species are being studied for the following: species frequency, desiccation resistance, vagility, proportion of larvae pupating, pupation height, and egg to adult survival after irradiation. To date we have noted both spatial and seasonal differences in a number of these characteristics. The information being gathered will serve as base-line data for monitoring the future operation of the nuclear power plant.

Desiccation resistance in two species of Drosophila.

Three populations of Drosophila pseudoobscura, each one represented by 12 isofemale lines, and one laboratory strain of D. melanogaster were tested for desiccation resistance at two time periods. Except in the case of one population of D. pseudoobscura, the ability to withstand drying was significantly greater in females than in the corresponding males. The males of the three populations of D. pseudoobscura differed significantly among themselves in their resistance to desiccation, as did the females. The females of D. melanogaster exhibited a consistently higher survival rate than those of D. pseudoobscura, but not the males. These results are discussed with reference to the third chromosome inversion polymorphism of D. pseudoobscura and the cosmopolitan distribution of D. melanogaster.

Chromosomal and behavioral studies of Mexican Drosophila. III. Inversion polymorphism of D. pseudoobscura.

Four new gene arrangements of chromosome 3 of Drosophila pseudoobscura are reported, as well as an updated phylogenetic sequence of the inversion polymorphism in this species. Evidence that the Tree Line gene arrangement of chromosome 3 was the original form in D. pseudoobscura, and that Central Mexico is the center of distribution of this species is discussed.

LIFE HISTORY STUDIES OF THE LESSER SNOW GOOSE (ANSER CAERULESCENS CAERULESCENS). VI. PLUMAGE POLYMORPHISM, ASSORTATIVE MATING AND FITNESS.

The investigated the hypothesis that positive assortative mating for plumage coloration observed in populations of the dichromatic Lesser Snow Goose (Anser caerulescens caerulescens) evolved and persists due to selective advantages accruing to individuals choosing mates phenotypically similar to themselves. We examined potential differences between pure (white × white, blue × blue) and mixed (white × blue, blue × white) pairs for an array of fitness components related to both fecundity and viability. While no differences were detected for most components, mixed pairs consistently enjoyed enhanced nesting success relative to their pure counterparts. In addition, pre-reproductive viability and female offspring recruitment were significantly greater for mixed pairs for some of the cohorts examined. Not only have we failed to find enhanced reproductive success associated with positive assortment, we have provided evidence that there is some advantage associated with negative assortment. In light of our findings, we suggest: 1) that positive assortment results from the use of familial color as one element in species recognition; 2) that the enhanced fitness of mixed pairs, particularly with respect to nesting success, results from complementation of parental behavior; and 3) that while negative assortment will not likely become the rule in this population, the selective advantage of mixed pairs is a potential determinant of pair type frequencies in the La Pérouse Bay population.

Photobehavioral differentiation in natural populations of Drosophila: changes of photoresponse over time in Drosophila pseudoobscura and Drosophila persimilis.

The photobehavior of a sympatric assemblage of Drosophila pseudoobscura and D. persimilis from California was examined over a 13-month period. During that time, certain aspects of the behavior remained constant (e.g., the mean resting photoresponse), while other aspects changed (e.g., the level of genotypic variation of the resting photoresponse of D. persimilis). The data support the contention of Rockwell et al. [Rockwell, R. F., Cooke, F., and Harmsen, R. (1975). Behav. Genet. 5:189-202] that genotypic variation and phenotypic plasticity are central features of photobehavior in natural populations of these species. The evolutionary importance of such genotypic variation and phenotypic plasticity is discussed.

Functional relationships between genotypes and environments in behavior. Effects of different kinds of early social experience on interstrain fighting in male mice.

Comparisons are made of the interstrain fighting behavior of adult male mice from two inbred strains (ST-albino; CBA-black-agouti), raised in one of three postweaning social situations: 1) isolated from other males, 2) reared with males of the same strains, or 3) reared with males of the opposite strain. Using the fighting behavior of isolated males as a baseline, it is found that each type of early social experience affects the fighting behavior of the males from each of the two inbred strains differently, indicating that the functional relationships between genotype and environment studied in these experiments are nonadditive. The importance of these results in describing the norm of reaction of a behavioral phenotype and in extrapolating data from one experiment to another is discussed.

Assortative mating in lesser snow geese (Anser caerulescens).

Assortative mating occurs in the dimorphic lesser snow geese in the wild. Mixed matings between the blue and white phases are much less frequent than would be expected by chance. Evidence from marked birds in field conditions indicated that mate choice was correlated with familial color. Birds from white families usually chose white mates, birds from blue families usually chose blue mates, and birds from mixed families chose mates of either color. Similar results were obtained under captive conditions when offspring from foster families with particular parental and offspring color combinations were allowed to choose mates. Both parental color and sibling color appeared to influence mate choice. The bird's own color did not appear to be important in mate choice in either field or experimental conditions, and in those cases where male and female parents differed in color neither parental color was more influential than the other in determining offspring mate choice. The results provide the first evidence, to our knowledge, that mate selection based on familial appearance operates intraspecifically in the wild.

Photobehavioral differentiation in natural populations of Drosophila pseudoobscura and Drosophila persimilis.

The photoresponses of natural populations of D. pseudoobscura and D. persimilis, occurring sympatrically, are measured in two environmental conditions ("at rest" and "disturbed"). Comparisons of the responses, intraspecifically and interspecifically, lead to the following conclusions. These must be considered within the confines of the operational nature of the measurement of laboratory photoresponses. (1) Within each species population, significant nonenvironmental differentiation has been allowed or produced by selection in the "at rest" photoresponse. No significant nonenvironmental differentiation is found in the photoresponse measured in a disturbed condition. (2) Within each species population, a higher mean "disturbed" photoresponse has been favored. The intensities or patterns of selection acting on these two photoresponses have differed such that more intrapopulation differentiation has been allowed or produced in the "at rest" photoresponse. (3) A higher mean photoresponse has been favored in D. persimilis for both conditions. The intensities or patterns of selection acting between these two species populations on the "at rest" photoresponse have differed such that more intrapopulation differentiation has been allowed or produced in D. persimilis. (4) Comparisons of this study with one on intraspecific and interspecific differentiation in wing length lead to the conclusion that the selective differences inferred above have acted at a level more specifically attuned to photobehavior.