Adaptations of Crustaceans to Land: A Summary and Analysis of New Findings

Crustaceans have adapted to land through various morphological,physiological, biochemical, and behavioral modifications, ofwhich some are shared by all land-dwelling crustaceans and othersare unique to animals within a particular habitat. Among thethree groups of crustaceans having truly terrestrial members,the amphipods have achieved their success on land primarilyby behavioral means, while the isopods and the decapods havedeveloped many morphological, physiological, and biochemicaladaptations as well. In all three groups, behavioral modifications ensure that lossof water is minimal, that the animals are exposed to favorablerather than extreme environmental conditions, and that the fineline between evaporative cooling and excessive dehydration ismaintained. In most crustaceans the excretion of nitrogenous wastes requiresthat copious supplies of water be available for washing awaythe soluble end-products. Yet terrestrial isopods are able toexcrete ammonia as a gas, without being subject to toxic side-effects.In decapods, either ammonia or insoluble uric acid may be excreted,with ammonia the more likely product when water is available,uric acid when water is scarce. In adult land crabs water balance is maintained through theconcerted action of gills, pericardial sacs, and gut. Theseorgans may take up, store, and redistribute salts and waterin response to control exerted by the central nervous systemthrough its secretory products. In larvae of land crabs theseorgans are not known to function in this way. Rather, the larvaeare adapted to cope with osmotic problems of their planktonicexistence. Gaseous exchange in adult land crabs is carried on not onlyby the gills but also by the highly vascularized lining of thebranchial chambers, and the hemocyanin ot these crabs is adaptedto function in the environment peculiar to each species. Terrestrialcrabs seem unable to withstand low temperatures, but their highrate of cytochrome c oxidase activity may help them to survivewhen temperatures are high. Modifications in behavior must have occurred quite early inthe transition of crustaceans from sea to land. Then, as now,appropriate behavioral responses to light, temperatuie, humidity,tidal cycles, and so on. were crucial if a terrestrial animalwas to survive. Social interactions, both for courtship andfor aggression, required the sending and receiving of appropriatevisual and acoustic signals and were promoted by the ritualizationof potentially injurious patterns of behavior.     

Intranasal Immunization of Mice Against Naegleria fowleri1

ABSTRACT. The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 × 10³ amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 10³ amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge.     

Theileria gilberti n. sp. (Apicomplexa: Theileriidae) in the Gilbert's Potoroo (Potorous gilbertii)

ABSTRACT. The morphology and genetic characterisation of a new species of piroplasm identified in the blood of the Gilbert's potoroo ( Potorous gilbertii ) from the Two Peoples Bay Nature Reserve near Albany, Western Australia, is described from blood and tissue samples from 16 Gilbert's potoroos. Microscopy of blood showed these parasites are highly pleomorphic with a mean length of 1.8 μm and mean width of 0.85 μm. Phylogenetic analysis of 18S rRNA sequence data identified the piroplasm as a new species of Theileria that is closely related to other Australian marsupial piroplasm species. Based on biological and molecular data, it is proposed that the parasite from Gilbert's potoroo be given the name Theileria gilberti n. sp.     

The origin of eutherian mammals

Palaeontologically recognizable eutherians originated no later than the Early Cretaceous in warm, probably moderately seasonal climates. Immediate ancestors were small, sharing many anatomical, physiological and reproductive features with small modern marsupials. Development of characteristically eutherian features involved interactions of body size, rates of metabolism, energetic costs of reproduction, anatomical/physiological processes of development and effects of each upon rates of population growth. In contrast to eutherians, marsupials have a narrow range of basal metabolic rates (lacking high rates), and show no direct links between rate of energy expenditure and gestation period, postnatal growth rate, fecundity or reproductive potential. Biological implications of this contrast are most pronounced at small body sizes. When resources are abundant, the relatively higher growth rates and earlier maturation of small eutherians (particularly those with high rates of metabolism) can lead to rapid population growth; among most marsupials, however, both pre- and postnatal constraints apparently preclude attainment of such high rates of reproduction. Also, only eutherians among the amniotes combine intimacy of placentation with prolonged active intra-uterine morphogenesis. Once established, that combination permitted (and even favoured) increases in diversity of adaptation in such disparate aspects as elevated metabolic rate, increased pre- and postnatal growth rates, increased encephalization, greater longevity, increased gregariousness, greater karyotypic flexibility, and augmented variability in adult morphology. However, all such boosts in diversity were probably secondary and dependent upon prior innovation of trophoblastic/uterine wall immunological protection of foetal tissues during prolonged intra-uterine development. Increased metabolic rates followed thereafter, with synergisms that may have speeded evolution among early eutherians. Eutherian-style trophoblast probably originated in the Mesozoic. Dependent adaptations, variably expressed, evolved later in sundry descendant lineages. Reproductive differences between marsupials and eutherians are not biologically trivial; to the contrary, breakthroughs among eutherians assured their dominance: (1) in high intensity food habits; (2) at small body masses; and (3) in very cold climates.     

Inter‐regional comparison of land‐use effects on stream metabolism

1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first‐order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions. 2. Stream metabolism was measured in nine streams in each of eight regions (n = 72) across the United States and Puerto Rico. In each region, three streams were selected from a range of three land uses: agriculturally influenced, urban‐influenced, and reference streams. Stream metabolism was estimated from diel changes in dissolved oxygen concentrations in each stream reach with correction for reaeration and groundwater input. 3. Gross primary production (GPP) was highest in regions with little riparian vegetation (sagebrush steppe in Wyoming, desert shrub in Arizona/New Mexico) and lowest in forested regions (North Carolina, Oregon). In contrast, ecosystem respiration (ER) varied both within and among regions. Reference streams had significantly lower rates of GPP than urban or agriculturally influenced streams. 4. GPP was positively correlated with photosynthetically active radiation and autotrophic biomass. Multiple regression models compared using Akaike’s information criterion (AIC) indicated GPP increased with water column ammonium and the fraction of the catchment in urban and reference land‐use categories. Multiple regression models also identified velocity, temperature, nitrate, ammonium, dissolved organic carbon, GPP, coarse benthic organic matter, fine benthic organic matter and the fraction of all land‐use categories in the catchment as regulators of ER. 5. Structural equation modelling indicated significant distal as well as proximal control pathways including a direct effect of land‐use on GPP as well as SRP, DIN, and PAR effects on GPP; GPP effects on autotrophic biomass, organic matter, and ER; and organic matter effects on ER. 6. Overall, consideration of the data separated by land‐use categories showed reduced inter‐regional variability in rates of metabolism, indicating that the influence of agricultural and urban land use can obscure regional differences in stream metabolism.