Free-living Juveniles Research Articles

Evaluation of Pasteuria penetrans alone in combination with oxamyl, plant resistance and solarization for control of Meloidogyne spp. on vegetables grown in greenhouses in Crete

In a plastic polytunnel in Crete, spores of Pasteuria penetrans (Pp) contained in powdered tomato roots were incorporated in 61 of soil at planting sites at a concentration of 25 000 spores g −1 of soil. The soil had been artificially infested with a natural population that was a mixture of Meloidogyne javanica and M. incognita. In one experiment the root galling and egg production on a nematode-susceptible tomato variety was significantly less in plots treated with Pp and oxamyl than in untreated controls. Pp and oxamyl had an additive effect in combined applications. Yields, however, did not differ significantly between treatments. There were reductions of nematode populations and root galling on a subsequent cucumber crop, which became severely damaged. This had to be curtailed because of premature senescence and death in the nematode-only control plots. The presence of Pp in 65–75% of mature females and on free-living juveniles in soil indicated that Pp had persisted in the soil and had increased over the two crops. The efficacy of the parasite was enhanced by oxamyl applications. In one experiment, nematodes failed to develop in a resistant tomato cv. and there was no beneficial effect from application of Pp and oxamyl. In a subsequent cucumber crop planted in the same plots, nematode population remained small in all treatments but 16–18% of mature females in Pp-treated plots were infected with the bacterium and 25–40% of J2 in the soil had spores attached to them. In another experiment when a solarization treatment was included, root galling, egg production and J2 in soil were significantly less after growing cucumber for 10 weeks in Pp, oxamyl and solarization treatments, In this case the efficacy of Pp was enhanced after oxamyl application and probably in solarized soil; when all factors were combined the treatments were additive.

Ophiuroid Skeleton Ontogeny Reveals Homologies Among Skeletal Plates of Adults: A Study of Amphiura filiformis, Amphiura stimpsonii and Ophiophragmus filograneus (Echinodermata).

The characteristic oral papillae of the Family Amphiuridae are shown to have conservative patterns of ontogenesis, even among congeners with differing modes of reproduction such as Amphiura stimpsonii, a brooder, and A. filiformis which has free-living juveniles. Homologous oral papillae can be identified by tracing the distinctive ontogenetic transformations of individual skeletal elements. This method shows that the oral papillae of adults are not serially homologous, and that homologies cannot necessarily be inferred from the relative positions of papillae in any particular ontogenetic stage. For example, the most proximal oral papilla develops like a tooth on the dental plate and later moves to the proximal oral plate; a distal papilla grows as a spine on the adoral shield and moves to the distal oral plate. Based on the development of the oral papillae of Amphiura, Amphioplus, and Ophiophragmus species, it appears that post-larval ontogenesis of the amphiurids can be more reliable than larval morphology as an indicator of phylogenetic affinity. However, there are striking differences in postlarval skeletal ontogenesis among congeners, such as in formation of the adoral shield spines and primary plates of the disc, which may be related to modes of reproduction and post-larval biology. It can take over a year for adult oral armature to develop in free-living amphiurid juveniles, and the process occurs before hatching in brooded young. Specializations in the oral armature of postlarvae are probably critical to their survival.

Undissociated bases as the stimulus for the development of early parasitic stages of nematodes

Petronijevic T. and Rogers W. P. 1987. Undissociated bases as the stimulus for the development of early parasitic stages of nematodes. International Journal for Parasitology 17 :911–915. The effects of NH 4Cl and NH 2CH 3 on infective stages of Haemonchus contortus, Nematospiroides dubius and Ascaris suum have been compared with the action of H 2CO 3. Detailed experiments were carried out with H. contortus. NH 4Cl at pH 8 under air was less toxic to infective stages than it was to free-living juveniles of Panagrellus redivivus. The induction of exsheathment or hatching by bases was slow (20–30 h) though the time of development of 4th stage H. contortus was not proportionally increased. Activity at pH 6 was less than that at pH 8. In contrast to the action of H 2CO 3 as the stimulus, NH 4Cl was not Ca 2+-dependent. Prolonged exposure to anoxia at pH 8 was toxic, but in the presence of NH 4Cl or H 2CO 3 toxicity was decreased. The inhibition of exsheathment due to Dnp at pH 7 was greater when NH 4Cl was the stimulus. The process whereby host signals induce development of parasitic stages is discussed.

Physiological Ecology and Salt Loading of California Gulls at an Alkaline, Hypersaline Lake

Behavioral and physiological research were combined to determine how California gulls (Larus californicus) are able to survive and breed at Mono Lake, California, a lake that is two and one-half times more concentrated (2,400 mOsm kg⁻¹) than seawater and contains high concentrations of sulfates and carbonates as well as sodium and chloride. Adults avoided salt loading by (1) taking in very little lake water along with brine shrimp (and brine flies) they obtained from the lake and (2) visiting freshwater sources along the shore. Their stomach contents averaged 466 mOsm kg⁻¹, slightly more dilute than the salt concentration of brine shrimp (~500 mOsm kg⁻¹). Stomach contents of chicks and fledglings averaged 636 and 651 mOsm kg⁻¹, respectively. Hematocrits, serum osmolality, serum sodium and potassium, and body-water content of adults, chicks, and fledglings were similar to those of other birds and indicated neither salt loading nor dehydration. Salt glands of adults and chicks were not hypertrophied. Experiments with captive juveniles showed that (1) gulls dislike the taste of even 10% Mono Lake water and (2) flightless juveniles can survive at least 3 days on brine shrimp in 125% Mono Lake water. Free-living juveniles can evidently survive much longer without access to fresh water. It is likely that gulls that are adapted to hypersaline lakes do not require fresh water so long as they are feeding on prey with dilute body fluids and high body-water content. However, during the transition to independence when chicks must learn to feed for themselves-a period of several days-salt loading and dehydration may pose a problem.