Ants are common flower visitors, but their effects on plant reproductive fitness have not often been assessed. Flower-visiting ants were studied to determine whether they are antagonists or ...mutualists and whether they could influence floral or breeding system evolution in gynodioecious wild strawberry (Fragaria virginiana). Ant and flying pollinator (bees/flies) access to plants was manipulated, and visitation, fruit, and seed set were assessed. Ants visited flowers of hermaphrodites more often than those of females when bees and flies were excluded, but visited the sex morphs equally when they were present. Insect class did not influence fruit or seed set of hermaphrodites. In contrast, ants had both positive and negative effects on seed set in females. Females visited only by ants had 90% of the seed set of those visited only by bees/flies, and their seed set increased with ant visitation. The spatial pattern of seed set, however, suggests that ants may also damage pistils. Lastly, in contrast to bees and flies, ants failed to increase visitation with floral display size, suggesting that ant presence at flowers could reduce selection on this attractive trait. Findings suggest that when in high abundance, flower-visiting ants could affect breeding system and floral evolution in this gynodioecious plant.
Question: What is the effect of level of host inbreeding on fungal root colonization? Hypothesis: Selfed plants are poorer hosts than outcrossed ones and should be less intensively colonized. ...Organism: Hermaphroditic individuals of the self-compatible wild strawberry Fragaria virginiana (Rosaceae). Methods: Selfed and outcrossed progeny were grown at three resource levels. Plants were scored for vegetative size, leaf disease, and root fungi in semi-natural conditions. Results: Hyphal colonization was greater in outcrossed than in selfed plants, but the effect was marginal for vesicular colonization. Neither resource level nor maternal genotype influenced the effect of plant inbreeding on colonization. But fungi associated with plants in high resources produced more vesicles. Inbreeding depression in plant vegetative size was positively correlated with cross differential root colonization.
Antagonists can play a role in sexual system evolution if tolerance or resistance is sex-dependent. Our understanding of this role will be enhanced by consideration of the effects of antagonists on ...other plant-animal interactions. This study determined whether the sex morphs of a gynodioecious Fragaria virginiana differ in their susceptibility and response to damage by spittlebugs and whether damage altered pollinator attraction traits or interactions with other antagonists. Tolerance, but not resistance, to spittlebugs differed between the sexes. Generally, spittlebugs were more damaging to hermaphrodites than females, a finding in accord with the hypothesis that the pollen-bearing morph is less tolerant of source-damage than the pollen-sterile morph when damage is incurred during flowering. In both sex morphs, spittlebugs reduced inflorescence height, increased petal size, but did not affect the number of open flowers per day, suggesting that the net effect of damage may be to increase pollinator attraction. Spittlebug infestation modified interactions with other antagonists in a sex-dependent manner: spittlebugs reduced attack by bud-clipping weevils in hermaphrodites but increased infection by leaf fungi in females. The complex interactions between plant sex, antagonists, and pollinator attraction documented here emphasize the importance of considering sex-differential multi-species interactions in plant sexual evolution.
Effective mating in plant populations need not occur during periods of peak pollinator activity and flowering. Seasonal and diurnal patterns of pollinator activity, pollen and ovule availability, and ...seed production in an experimental population of Raphanus sativus were measured to infer the times of reproductively effective mating. On a seasonal scale, most "effective matings", those resulting in mature seeds, occurred very early in the season, well before the peak of flowering and pollinator activity. At a finer scale, diurnal schedules of flower opening, stigma saturation with pollen, and pollen removal indicated that most effective matings occurred before noon, even though pollinator activity increased later in the day. These patterns may be most common in populations that are not pollen limited, but other ecological factors (e.g. seed predation, resource depletion) could weaken the correspondence between pollination and effective mating.
The c-kit proto-oncogene product is a member of the family of growth factor receptors with intrinsic tyrosine kinase activity. In the mouse c-kit maps to the W locus, which is known to be of central ...importance in hematopoiesis. Monoclonal antibody (MoAb) YB5.B8, which was raised against peripheral blood blast cells from a patient with acute myeloid leukemia (AML), was recently shown to bind to the extracellular domain of the c-kit product. This antibody does not bind detectably to normal peripheral blood cells and identifies a sub-group of AML patients with poor prognosis. We have used MoAb YB5.B8 to study the expression of c-kit by normal human bone marrow cells by immunofluorescence and flow cytometry, and to isolate multipotential and erythroid colony-forming cells, In a series of 11 normal adult bone marrow specimens, MoAb YB5.B8 bound to 4.0% ± 1.8% of the cells in the low-density fraction. Dual-labeling experiments were performed with YB5.B8, and CD33, CD34, and CD10 MoAbs.Three populations of cells binding YB5.B8 could be identified based on their pattern of coexpression of the other markers; ie, YB5.B8+/CD34+/CD33-, YB5.B8+/CD34+/CD33+ and YB5.B8+ /CD34- /CD33+. These populations had distinctive two-dimensional light scatter characteristics and are likely to correspond to precursor colony-forming cells, colony-forming cells, and maturing mast cells, respectively. No cells binding both YB5.B8 and an MoAb to the early lymphoid marker CD10 were found, implying that most early lymphoid cells do not express c-kit. MoAbs to the c-kit protein should prove valuable in multimarker studies of human hematopoietic stem and progenitor cells. Definition of a reference range of c-kit expression in normal human bone marrow will provide a sound basis for further studies of this marker in diagnosis and prognosis in AML.
Competition among pollen grains to fertilize ovules is expected to lead to increased vigor of the resulting progeny. Tests of this "pollen-competition hypothesis," however, have been equivocal, and ...this may, in part, result from the levels of pollen competition (pollen load sizes) and/or progeny growth environment chosen. Our study of Fragaria virginiana controlled for these variables by identifying seeds produced under low and high pollen loads from an empirically derived pollen load-seed set response curve. We assessed fitness of seeds at germination under uniform conditions but fitness of progeny at juvenile and adult life stages under two different resource levels in the greenhouse. We hypothesized that the effect of pollen load size on progeny vigor would be stronger when progeny were grown under low resources than when grown under high resources. We found that the effect of pollen load size was negligible at germination but was significant in later life when assessed under two resource levels. The direction of the pollen load effect, however, depended on the progeny growth environment. Under low resources, progeny from high pollen loads grew faster, attained greater biomass, and had a higher probability of flowering than progeny from low pollen loads, while the reverse was true under high resource availability. These results indicate that the effects of pollen competition on juvenile and adult characters depend on progeny growth environment.
Morgan and Ashman describe how selection shapes traits expressed in females and hermaphrodites of a gynodioecious species where sex is under simple nuclear gene control. Combining information on ...average fitness, morph frequencies, selection gradients, and genetic variation provide a complete view of petal size evolution. An additional consequence of low additive genetic covariation is that between-population differences in female character change are dominated by differences in female sex morph selection responses. These results emphasize the importance of accounting for sex ration and relative female fertility of the sex morphs in addition to selection through female and male fertilities for the response to selection.
Pollination is known to be sensitive to environmental change but we lack direct estimates of how quantity and quality of pollen transferred between plant species shifts along disturbance gradients. ...This limits our understanding of how species compositional change impacts pollen receipt per species and structure of pollen transfer networks.
We constructed pollen transfer networks along a plant invasion gradient in the Hawaiian dry tropical forest ecosystem. Flowers and stigmas were collected from both native and introduced plants, pollen was identified and enumerated and floral traits were measured. We also characterized pollen loads carried by individuals of the dominant invasive pollinator, Apis mellifera.
Species flowering in native-dominated sites were more tightly connected by pollen transfer than those in heavily invaded sites. Compositional turnover in the pollen loads of A. mellifera was correlated (70%) with turnover in the composition of pollen transfer networks. Floral traits predicted species roles within pollen transfer networks, but many of these differed qualitatively depending on whether plants were native or introduced.
Our work indicates that pollen transfer networks change with invasion. Floral morphology and foraging behaviour of the introduced super-generalist pollinator are implicated as key in determining the roles introduced species play within native pollen transfer networks.
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