Metabolic consequences of shell choice in Pagurus bernhardus: do hermit crabs prefer cryptic or portable shells?

Hermit crabs are unique among crustaceans in that they choose their shell and can, therefore, be used to investigate apparent preferences for the presence of epizoic fauna. These may be beneficial due to increased protection from predators via enhanced crypsis but may also make the shell more difficult to carry. The effects of encrusting fauna on the physical properties of empty gastropod shells, the shell preferences of hermit crabs and the physiological costs of shell carrying were examined in the present laboratory study. Heavily encrusted shells weighed more than shells of the same internal volume that were free of epizoic fauna, hermit crabs showed a clear preference for un-encrusted shells and those that occupied encrusted shells had elevated haemolymph lactate in comparison to those supplied with un-encrusted shells. Under laboratory conditions, any benefit from increased crypsis is, therefore, outbalanced by the increased costs of carrying encrusted shells.     

Distribution normality of pH and H<Superscript>+</Superscript> activity in soil

Soil pH, a log-transformed form of hydrogen ion (H⁺) activity, is often used for various statistics. However whether soil pH meets the requirement of distribution normality for statistical analyses is unknown. We studied the statistical suitability of both soil pH and H⁺ activity by examining their distribution normalities. Results show that the variability of H⁺ activity is higher and its distribution is skewer, which is significantly different from the normal and soil pH, regardless of soil conditions and analytical methods. Here we demonstrate that soil pH is more appropriate than the H⁺ activity for performing statistical analysis in terms of distribution normality.     

Optimal investment policies with exhaustible resources: An information-based model

An information-based model of the “optimal control” type is developed using concepts from information theory to explore the dynamics of fossil resource exhaustion and the phenomenon of substitution by other forms of capital and technological knowledge. All exhaustible resources stocks and forms of capital (and knowledge) are taken to be equivalent to forms of information in the physical sense. It is shown that, with optimal policies, the planning period, or cycle, has several distinct phases, with different optimal investment patterns. The model has two important qualitative implications: (1) economic growth rates are inherently discontinuous and (2) the model predicts an evolutionary structural change, viz., the creation of a new sector in response to the progressive exhaustion (or obsolescence) of previously essential resources or capital stocks. A multiperiod extension is suggested, leading to a tentative explanation for the Kondratieff long-wave phenomenon.     

Uncommon diversity in developmental mode and larval form in the genus <Emphasis Type="Italic">Macrophiothrix</Emphasis> (Echinodermata: Ophiuroidea)

Development mode in the ophiuroid genus Macrophiothrix includes an unusual diversity of planktonic larval forms and feeding types. The modes of development for seven congeners that coexist in coral reef habitats at Lizard Island, Australia were compared using larvae generated from crosses over several reproductive seasons from 1999 to 2003. Three species (Macrophiothrix koehleri Clark, Macrophiothrix longipeda Lamarck, Macrophiothrix lorioli Clark) develop from small eggs (<170 μm) into typical obligately feeding planktonic (planktotrophic) pluteus larvae with four larval arm pairs. The remaining four species develop from larger eggs (≥230 μm) into either facultatively-feeding or non-feeding (lecithotrophic) larval forms. The facultative planktotroph (Macrophiothrix rhabdota Clark) retains the ability to digest and benefit from food but does not require particulate food to complete metamorphosis. Among the lecithotrophic species, Macrophiothrix caenosa Hoggett retains the pluteus morphology with four pairs of larval arms, but is incapable of feeding, depending instead on maternal provisions for larval development. The remaining two lecithotrophs have simplified larval morphologies with only a single pair of full length (Macrophiothrix nereidina Lamarck) or highly reduced (Macrophiothrix belli Doderlein) larval arms and no functional mouth or gut. This genus includes the first example of facultative planktotrophy in ophiuroids, the first example in echinoderms of a complete pluteus morphology retained by a lecithotrophic larva, and three degrees of morphological simplification among lecithotrophic larval forms. Egg volume varies 20-fold among species and is related to variation in feeding mode, larval form, and development time, as predicted for the transition from planktotrophic to lecithotrophic development.     

Tail size and female choice in the guppy (Poecilia reticulata)

Summary Under laboratory conditions, female guppies demonstrate a clear preference for males with larger tails, and this preference translates into enhanced reproductive fitness for these males. Females also prefer males with higher display rates, a behavior which appears to be linked to tail size, but which can be experimentally disassociated. This appears to be a case of female-choice sexual selection.     

Decomposition and microbial dynamics for standing,naturally positioned leaves of the salt-marsh grass Spartina alterniflora

Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23 N; 81°17 W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed > 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).