Community ecology of helminth parasitism in an insular passerine avifauna.

Three hundred and thirty specimens of 7 species of passerine birds from South Bass Island, Ottawa County, Ohio, were examined for helminth parasites. The total number of helminth specimens collected was 4,333. Forty-one helminth taxa were identified. Ten species of helminths were identified as having foci of infection on the island. An index of association for these 10 species is presented. The low association revealed between helminth species utilizing common species of intermediate hosts indicated that a single intermediate host specimen is likely to harbor infective stages of only one species of parasitic helminth. An index of similarity is presented to express the species importance relationships of the helminth faunas of the 7 species of birds: red-winged blackbirds (Agelaius phoeniceus), blue jays (Cyanocitta cristata), brown-headed cowbirds (Molothrus ater), common grackles (Quiscalus quiscula), house sparrows (Passer domesticus), starlings (Sturnus vulgaris), and robins (Turdus migratorius). The results reveal that competition between these avian species for invertebrate food resources helps to maximize the transmission of those helminth populations which utilize these same invertebrates as intermediate hosts. The aggregation of birds into mixed feeding flocks insures a heavy loading of the feeding grounds with agents infective for the invertebrate populations.     

The prevention of dehydration injury in celery seeds by polyethylene glycol, abscisic acid, dark and high temperature

Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.