Nearshore marine benthic algal communities along the western Antarctic Peninsula harbour extremely high densities of amphipods that probably play important roles in nutrient and energy flow. This study extends our evaluation of the importance of amphipods in the nearshore Antarctic Peninsular benthic communities and focuses on sponge associations. We found a mean density of 542 amphipods per litre (L) sponge for twelve species of ecologically dominant sponges. The highest mean density (1295 amphipods per L sponge) occurred with Dendrilla membranosa Pallas. The amphipod community associated with the 12 sponges was diverse (38 species), with mean species richness values ranging from two to eight species. Mean Shannon diversity indices (H’) ranged from 0.52 to 1.49. Amphipods did not appear to have obligate host relationships. Qualitative gut content analyses indicated that 12 of the 38 amphipod species were found with sponge spicules in their guts. However, only one of the amphipods, Echiniphimedia hodgsoni Walker, had considerable amounts of spicules in the gut. Organic lipophilic and hydrophilic extracts of the twelve sponges were presented in alginate food disks to a sympatric omnivorous amphipod in feeding bioassays and extracts of only two sponges deterred feeding.

The brooded embryos and/or juveniles of the sea stars Neosmilaster georgianus (Studer, 1885) and Lysasterias perrieri (Studer, 1885) and the isopod Glyptonotus antarcticus (Eights, 1853) were examined for their acceptability using the sympatric sea star Odontaster validus (Koehler, 1906) as a predator. Organic extracts were prepared from embryos of both sea stars and juveniles of Lyasterias perrieri and Glyptonotus antarcticus and tested in alginate food pellets to confirm whether lack of acceptability was chemically based. We found both intact whole embryos and juveniles of the sea star Neosmilaster georgianus were not acceptable to Odontaster validus. A methanol extract of the embryos was palatable. This could be the result of either the sequestration of deterrent chemicals within embryos or the presence of noxious compounds that were not extractable in methanol. Embryos and juveniles of the sea star Lysasterias perrieri were not acceptable to sea stars. Food pellets containing methanol extracts of unacceptable embryos were deterrent against sea stars, suggesting a chemical defence. Juvenile brooded isopods (Glyptonotus antarcticus) were also found to be unacceptable in sea star feeding bioassays. Significant rejection of alginate pellets containing a lipophilic dichloromethane methanol extract of juveniles indicated that this lack of acceptability was chemically based. Our study provides further support for chemical defences in the offspring of brooding lecithotrophic Antarctic marine invertebrates.

The soybean plant introduction (PI)227687 is highly resistant to 16 different insect pests of soybean in Australia, Brazil, Taiwan and the United States. In most of the pest Lepidoptera, resistance is expressed as greatly increased mortality in the later larval instars. The soybean looper, Pseudoplusia includens (Walker) is most severely affected in the final larval instar. Antibiotic effects include reduced weight gain, growth rate and increased mortality. These effects are enhanced by mechanically wounding foliage 24 hr prior to larval consumption. Antibiosis appears to be due to the combined effects of a feeding deterrent and a growth inhibitor. Resistance is location-specific on (PI)227687 plants and occurs abruptly on the third fully-expanded leaf from the plant apex. Larval growth on leaves of the susceptible variety ‘Davis’ is similar to or greater than that of the upper, susceptible leaves of (PI)227687. Resistance appears to be chemically based, since larvae fed artificial diets containing leaf extracts exhibit antibiotic symptoms similar to those fed fresh (PI)227687 leaves.