Gryllus

Abstract: Adult Gryllus assimilis given an analog of juvenile hormone exhibited reduced flight muscles and enlarged ovaries similar to those found in naturally occurring flightless individuals of species that are polymorphic for dispersal capability. Control and hormone-treated (flightless) G. assimilis did not differ in the amount of food consumed or assimilated on any of three diets that differed in nutrient quantity. Thus, enhanced ovarian growth of flightless individuals resulted from increased allocation of internal nutrients to reproduction (i.e., a trade-off) rather than from increased acquisition of nutrients. Compared with flight-capable controls, flightless G. assimilis also had reduced whole-organism respiration, reduced respiration of flight muscles, and reduced lipid and triglyceride (flight fuel) reserves. These differences are remarkably similar to those between naturally occurring flightless and flight-capable morphs of other Gryllus species. Results collectively suggest that the increased allocation of nutrients to ovarian growth in flightless G. assimilis and other Gryllus species results from reduced energetic costs of flight muscle maintenance and/or the biosynthesis or acquisition of lipids. Reduction in these energetic costs appears to be an important driving force in the evolution of flightlessness in insects. Respiratory metabolism associated with flight capability utilizes an increasing proportion of the energy budget of crickets as the quantity of nutrients in the diet is decreased. This leads to a magnification of greater ovarian growth of flightless versus flight-capable individuals on nutrient-poor diets.

Abstract: Gryllus field and wood crickets of the United States, mostly west of the Mississippi River, are reviewed and revised. We validate the following 18 Gryllus cricket names: G. armatus, G. assimilis, G. brevicaudus, G. cayensis, G. cohni, G. firmus, G. fultoni, G. integer, G. lineaticeps, G. multipulsator, G. ovisopis, G. pennsylvanicus, G. personatus, G. rubens, G. texensis, G. veletis, G. vernalis, and G. vocalis. We synonymize G. alogus under G. vocalis. We designate a lectotype for G. armatus. We describe the following 17 new Gryllus species: G. chisosensis, G. leei, G. lightfooti, G. longicercus, G. makhosica, G. montis, G. navajo, G. planeta, G. regularis, G. saxatilis, G. sotol, G. staccato, G. thinos, G. transpecos, G. veintinueve, G. veletisoides, and G. vulcanus. We present biology, distribution, and genetic analysis of all taxa and discuss their nearest relatives.

Abstract: Deep-sea scavenging amphipod distributions, abundance, and behavior were studied with five-vehicle baited traps. The species composition and numerical abundances were comparable in the areas sampled. All size classes of the four predominant species (Paralicella caperesca, P. tenuipes, Orchomene gerulicorbis, and Eurythenes gryllus) were trapped including sexually mature individuals, but no females were ovigerous. The central North Pacific E. gryllus is morphologically distinct from Atlantic E. gryllus and may represent a different species. Pelagic and demersal amphipod guilds exist, as determined by body size and vertical and horizontal distributional patterns. The demersal guild is composed of P. caperesca, P. tenuipes, and O. gerulicorbis, all of which are <2 cm in total body length and occur within 1 m of the sediment. E. gryllus, the only representative of the pelagic guild, ranges between 1.7 and 14 cm in total body length and has its greatest abundance several to tens of meters above the sediment. Members of the demersal guild probably can detect and exploit both large and small food falls or autochthonous organic particles because of their proximity to the sediment. They reside within the area of the benthic boundary layer where currents are slowest, and the diffusion of odor is slower than higher in the water column, thus reducing the area from which they can be attracted to a food item. The vertical distribution of E. gryllus correlates well with several physical features of the benthic boundary layer. Their vertical abundance increases an order of magnitude near the top of the Ekman layer, correlating with the increase in current velocities. It continues to increase up to 20 m, corresponding with the probable vertical extent of more than two-thirds of an odor trace. Their abundance decreases significantly above 20 m. The above correlations imply that the vertical distribution of E. gryllus is an adaptation that provides a wide chemosensory overview of the sediment, and that they may be adapted to use the swifter background currents above the Ekman layer in their search for food. Finally, their vertical distribution implies that they feed primarily on relatively large food particles. Individuals found above 50 m are likely to be unaware of food falls and probably feed by predation. Species in the demersal guild are very patchy and probably occur in groups even when not feeding; film data indicate that E. gryllus occurs singly when not at bait. Near an odeor source all species tend to choose bait with other amphipods on it, neglecting similar bait nearby. When given a choice of traps, individual E. gryllus prefer to enter traps containing individuals of similar age and sex. At least at close range, locating a food item is probably based more on information received from other amphipods rather than food odor. It is unknown how this communication might occur.