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We argue that the genetic diversity of a dominant plant is important to the associated dependent community because dependent species such as herbivores are restricted to a subset of genotypes in the host-plant population. For plants that function as habitat, we predicted that greater genetic diversity in the plant population would be associated with greater diversity in the dependent arthropod community. Using naturally hybridizing cottonwoods (Populus spp.) in western North America as a model system, we tested the general hypothesis that arthropod alpha (within cross-type richness) and beta (among cross-type composition) diversities are correlated with cottonwood cross types from local to regional scales. In common garden experiments and field surveys, leaf-modifying arthropod richness was significantly greater on either the F1(1.54 times) or backcross (1.46 times) hybrid cross types than on the pure broadleaf cross type (P. deltoides Marshall or P. fremontii Watson). Composition was significantly different among three cross types of cottonwoods at all scales. Within a river system, cottonwood hybrid zones had 1.49 times greater richness than the broadleaf zone, and community composition was significantly different between each parental zone and the hybrid zone, demonstrating a hierarchical concentration of diversity. Overall, the habitats with the highest cottonwood cross-type diversity also had the highest arthropod diversity. These data show that the genetics of habitat is an important conservation concept and should be a component of conservation theory.

The oxygen carrier hemocyanin occurs in the blood of Scutigera coleoptrata, a uniramous arthropod, as well as the crustaceans and chelicerates. The native polymer appears to be composed of substructures having the same size and electron-dense image as those of other arthropod hemocyanins but assembled into a unique multiple and arranged in a unique configuration. The simplest explanation of these findings is that the arthropod hemocyanins have a common origin, exemplifying a derived (as opposed to primitive) character shared by each of the three living groups.

There has been no work on the immunological response of birds to helminth infections since the late 1960s, an area of investigation that has been too long ignored. Similarly, studies of arthropod-mediated responses in birds are lacking except for a few scattered investigations. Recently, a serum antibody response has been seen against one arthropod, the northern fowl mite. The appearance of antibodies recognizing an 8-10 kilodalton mite antigen seems to correlate with a reduction in the mite population on infested chickens. Most of the studies on parasite immunity in avian species have centered on the economically important Eimeria species, protozoan parasites that infect the intestine of chickens and turkeys. These investigations encompass wide areas of interest including the effect of immunity on parasite invasion, development of T-cell proliferation assays and T-cell clones, inhibition of parasite penetration and development by hybridoma antibody treatment, production of genetically engineered Eimeria antigens used in bird immunization studies, and studies using inbred or congenic lines of birds to determine what effect the major histocompatibility complex has on parasite immunity. From these efforts it has been learned that not only is the immunity species-specific, but also depending on where in the intestine the parasite invades, penetration is either not affected or inhibited by as much as 50%. The T-cell proliferation assays suggest that this specificity may be due to a species-specific T-cell response. Immunization studies using a genetically engineered antigen have indicated that at least partial protection against one species of Eimeria is possible. Studies done with the inbred congenic lines of birds have shown that the genetic makeup of the bird is important in how it responds to either a natural infection or to immunization with a genetically engineered antigen. Clearly, these results show not only the complexity of the bird response to parasite infection, but also the amount of work still undone.