DIVERGENT AMBULATORY AND GROOMING BEHAVIOR IN SERIALLY BOTTLENECKED LINES OF THE HOUSEFLY

The extent of genome-wide restructuring predicted in bottleneck models of speciation is addressed in assays of non-reproductive behavior in lines of the housefly. After five serial founder-flush cycles of one of three sizes (1, 4, or 16 pairs), each bottleneck line showed significant differentiation from the outbred control in ambulatory levels and grooming sequences in videotaped records of precopulatory activity. Only one line (4-pair) showed overall lethargy which was associated to inbreeding depression in egg-to-adult viability, thus exemplifying a case of probable extinction due to bottlenecks. The two most hyperactive lines (1- and 16-pair) showed very similar directions of differentiation from the control in locomotor activity and grooming behavior, as well as in mating behavior evaluated from a separate study. This high congruence suggested that directional selection toward the phenotypic optima of the ancestor operated on the bottleneck populations and that a 10-fold difference in theoretical inbreeding coefficients did not affect the magnitude of response. The remaining two bottleneck lines showed some independence from these general trajectories, their divergence along minor axes of ancestral intercorrelation structure possibly being more important to the formation of new species. Significant perturbations of the thresholds for execution of grooming and locomotor movements suggested increased evolutionary potential for ritualization (i.e., sexual selection for adoption of non-reproductive behavior into courtship repertoire) due to bottlenecks.     

REPRODUCTIVE ATTRITION IN THE RARE CHAPARRAL SHRUB FREMONTODENDRON DECUMBENS LLOYD (STERCULIACEAE)

We examined reproductive attrition in Fremontodendron decumbens to characterize sexual reproduction in this rare California shrub. Reproductive individuals produced an average of 2,900 flower buds in a season, with no significant difference in bud production between two seasons. Because of intense insect predation, <;2% of initiated flower buds became mature fruits. A threefold decrease in predation of flower buds between seasons resulted in an increase in seed output the second season, indicating that seed production was partially predator-limited. Most seeds (97.8%) were dormant due to an impermeable seed coat. Breaking of the coat, mechanically or by heat, allowed high levels of germination. Chamise charate and ash added to the potting medium resulted in the highest level of germination and emergence. Rodents were more important than birds as seed predators, destroying 90% of seeds under parent shrub canopies within 8–10 months. Seeds already integrated into the seed bank were comparatively safe from predation, relative to newly added seeds. If predation was prevented, seeds were long-lived under field conditions (>;80% survived after 5.75 years). Most seedlings produced in unburned chaparral by planting heat-treated seeds in openings between shrubs were destroyed by predators (rodents and insects). All seedlings that escaped predation died during the summer drought. We concluded that sexual reproduction was limited by (in order of importance): 1) lack of fire, 2) predehiscence predation by insects, and 3) postdehiscence predation by rodents. Size distributions from two populations revealed that, despite the apparent absence of sexual reproduction in unbumed chaparral, two unbumed sites contained a large proportion of individuals in small size classes. Excavation of several small individuals demonstrated they were sprouts from the roots of nearby larger shrubs. Because asexual reproduction by rootsprouting circumvents the high attrition of sexual reproductive effort on unbumed sites, rootsprouting may be a significant reproductive strategy of some ‘sprouter’ species in chaparral.     

Recovery of the simian immunodeficiency virus (SIV) and depression of colony formation in in vitro infected progenitor cell-enriched rhesus bone marrow (BM)

Rhesus progenitor-enriched BM was exposed overnight to SIV and cultured in a limiting dilution assay where the potential for progenitor interaction with lymphocytes or macrophages was low. Virus was consistently isolated late in culture, detection being aided by coculture with CEM₁₇₄ lymphoblasts. Although infected cells had reduced clonogenic activity, colonies were indistinguishable from those derived from uninfected BM with respect to proliferative potential, morphology, and longevity in culture. Primate immunodeficiency viruses, therefore, may infect immature BM populations, directly affecting hematopoietic activity.     

A receptor for protein import into potato mitochondria

Five potential surface receptors for protein import into plant mitochondria were identified by gentle trypsin treatment of intact mitochondria from potato tubers and subsequent preparation of outer mitochondrial membranes. One of them, a 23 kDa protein, was purified to homogeneity and analysed by direct protein sequencing. Copy DNA clones encoding the corresponding polypeptide were isolated with labelled oligonucleotides derived from the amino acid data. The 23 kDa protein shares significant sequence similarity with protein import receptors from fungal mitochondria and contains one of their typical tetratricopeptide motifs. Its integration into the outer membrane is independent of protease accessible surface receptors and not accompanied by proteolytic processing. Monospecific antibodies against the 23 kDa protein significantly reduce import capacity of isolated mitochondria indicating that this component is indeed involved in the recognition or import of precursor proteins. As in fungi, immunological inhibition of protein import with IgGs against a single receptor is incomplete suggesting the existence of other receptors in the outer mitochondrial membrane of plant mitochondria.     

Development of a new method for obtaining osteoclasts from endosteal surfaces

Summary Techniques for the isolation of ahhighly pure population of viable osteoclasts are limited. For this reason, we developed an isolation procedure that results in a high yield of osteoclast-like cells, up to 92% pure, from 3-wk-old chicken tibias. The unique feature of the method is the migration of cells from marrow-free endosteal surfaces to vitronectin-coated plates. The cells retain the osteoclast phenotype and remain viable in culture for a minimum of 1 wk. The cells were characterized and compared to two populations of authentic avian osteoclasts, which were isolated on the basis of association with fibronectin-coated plates. The cells contained substantial amounts of tartrate-resistant acid phosphatase. Alkaline phosphatase levels were negligible, suggesting little contamination by osteoblasts. Response to parathyroid hormone, dibutyryl cyclic adenosine monophosphate, calcitonin, acetazolamide, 17β-estradiol, and prostaglandin E₂ was evident, as detected by measuring acid production. The vitronectin-associating cells contained numerous mitochondria, had the ability to resorb bone in anin vitro bone slice assay, and specifically bound biotinylated vitronectin. At 5 d of culture, the cells demonstrated marginal multinuclearity, having two to three nuclei. A large number (∼1×10⁶ cells/tibia) of viable cells that exhibit characteristics of authentic osteoclasts can be obtained by the method described. Potentially, this method could be applied to other species.     

Sperm motility in the presence of boundaries

The fluid dynamics of sperm motility near both rigid and elastic walls is studied using the immersed boundary method. Simulations of both single and interacting organisms are presented. In particular, we find that nearby organisms originally undulating with a 90° phase shift may adjust their relative swimming velocities and phase-lock. Comparisons with previous analytical results are also discussed. The tendency of a near-wall to attract organisms is demonstrated.     

Repair mechanisms of UV-induced DNA damage in soybean chloroplasts

In order to better understand the biochemical mechanisms of DNA metabolism in chloroplasts, repair of UV induced plastome damage in vivo was determined by exposure of soybean suspension cells to UV light and subsequent quantitation of the damage remaining in nuclear and chloroplast encoded genes with time by quantitative polymerase chain reaction (QPCR). The kinetics of damage rapir in the nuclear rbcS gene suggest that photoreactivation and dark mechanisms are active, while for the plastome encoded psbA gene only a light-dependent repair process was detected which is considerably slower than would be expected for photolyase-mediated photoreactivation.     

Phenotypic features of breast cancer cells overexpressing ornithine-decarboxylase

Polyamines (PA) have been shown to be critical mediators of estradiol-induced breast cancer cell proliferation. This finding suggests that constitutive activation of the PA pathway may promote tumor progression, possibly leading to hormone independence. To test this hypothesis, we transfected hormone-responsive MCF-7 breast cancer cells with a complementary DNA coding for ornithine-decarboxylase (ODC), the first rate-limiting enzyme in PA biosynthesis. Marked ODC over-expression observed in stably transfected clones was associated with a selective increase in cellular putrescine content, while spermidine and spermine levels were not altered. ODC-overexpressing MCF-7 cells were resistant to the antiproliferative effects of low but not high concentrations of the enzyme inhibitor, α-difluoromethylornithine. In agreement with our hypothesis, sensitivity to the growth-promoting action of estradiol was reduced by approximately one third (P < 0.001) in ODC-overexpressing MCF-7 cells compared with vector-only transfected clones. Basal growth under anchorage-dependent conditions was only marginally increased by ODC overexpression (P = 0.048), while clonogenicity in soft agar was actually reduced. These data suggest that activation of PA biosynthesis may contribute in part to the acquisition of estrogen independence by breast cancer cells. Since only putrescine content was increased as a result of ODC overexpression, these data may underestimate the overall influence of the PA pathway on breast cancer phenotype. © 1995 Wiley-Liss, Inc.     

AN ANALYSIS OF SELECTIONAL RESPONSE IN RELATION TO A POPULATION BOTTLENECK

Selection for increased morphometric shape (ratio of wing length to thorax width) was compared between control (nonbottlenecked) populations and bottlenecked populations founded with two male–female pairs of flies. Contrary to neutral expectation, selectional response was not reduced in bottlenecked populations, and the mean realized heritabilities and additive genetic variances were higher for the bottlenecked lines than for the nonbottlenecked lines. Additive genetic variances based on these realized heritabilities were consistent with independent estimates of genetic variances based on parent–offspring covariances. Joint scaling tests applied to the crosses between selected lines and their controls revealed significant nonadditive components of genetic variance in the ancestor, which were not detected in the crosses involving bottlenecked lines. The nonbottlenecked lines responded principally by changes in one trait or the other (wing length or thorax width) but not in both, and regardless of which trait responded, larger trait size was dominant and epistatic to smaller size. Stabilizing selection for morphometric shape in the ancestor likely molded the genetic architecture to include nonadditive genetic effects.