Nutrient fluxes from water to land: seabirds affect plant nutrient status on Gulf of California islands

Energy and nutrient fluxes across habitat boundaries can exert profound direct and indirect effects on the dynamics of recipient systems. Transport from land to water is common and well studied; here, we document a less recognized process, substantial flows from water to land. On hyperarid, naturally nutrient poor islands in the Gulf of California, nutrient input via seabird guano directly increases N and P concentrations up to 6-fold in soils; these nutrients enrich plants. Nutrients in a long-lived cactus, a short-lived shrub, and annuals were 1.6- to 2.4-fold greater on bird versus nonbird islands. Because plant quality affects consumer growth and reproduction, we suggest that nutrient enrichment via guano ramifies to affect the entire food web on these islands. Received: 6 April 1998 / Accepted: 6 October 1998     

Paternal Care by Genetic Fathers and Stepfathers II: Reports by Xhosa High School Students

In this article we present a biosocial model of human male parental care that allows relationship (mating) effort to influence male parental allocations. The model recognizes four classes of relationships between men and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investment collected from 340 Xhosa high school students in Cape Town, South Africa. Six measures of paternal investment are examined: the amount of money men spent on students for school, clothing, and miscellaneous expenditures, respectively, and how often men spent time with children, helped them with their homework, or spoke English with them. The tests provide support for the roles of both parental and relationship effort in influencing parental care: men invest significantly more in their genetic offspring and in the children of their current mates. We also examine several proximate influences on parental care, specifically the age and sex of the child, and the percentage of the child's life the father figure coresided with him or her.     

cGMP and cAMP cause pulmonary vasoconstriction in the presence of hemolysate.

We recently reported that addition of a small amount of hemolysate to the salt solution that perfused isolated rat lungs hypersensitized the vasculature to subsequent additions of ANG II or exposure to hypoxia, and addition of NO gas (. NO) to the perfusate that contained hemolysate caused a strong vasoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually associated with vasodilation) exert similar effects in hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound vasoconstriction in the isolated rat lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimilar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated that lungs perfused with hemolysate exhibit increased phosphorylation of several proteins. These data indicate that, in the presence of hemolysate, pulmonary vasculature responds to nominally vasodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstriction rather than vasodilation. The importance of our finding is the paradoxical nature of the response to (analogs of) cyclic nucleotides because, to our knowledge, cyclic nucleotide-induced vasoconstriction has not been previously reported.     

Polarized distribution of endogenous Rac1 and RhoA at the cell surface.

Rac1 and RhoA regulate membrane ruffling and stress fiber formation. Both molecules appear to exert their control from the plasma membrane. In fibroblasts stimulated with platelet-derived growth factor or lysophosphatidic acid, the reorganization of the cytoskeleton begins at specific sites on the cell surface. We now report that endogenous Rac1 and RhoA also have a polarized distribution at the cell surface. Cell fractionation and immunogold labeling show that in quiescent fibroblasts both of these molecules are concentrated in caveolae, which are plasma membrane domains that are associated with actin-rich regions of the cell. Treatment of these cells with platelet-derived growth factor stimulated the recruitment of additional Rac1 and RhoA to caveolae fractions, while lysophosphatidic acid only caused the recruitment of RhoA. We could reconstitute the recruitment of RhoA using either whole cell lysates or purified caveolae. Surprisingly, pretreatment of the lysates with exoenzyme C3 shifted both resident and recruited RhoA from caveolae to noncaveolae membranes. The shift in location was not caused by inactivation of the RhoA effector domain. Moreover, chimeric proteins containing the C-terminal consensus site for Rac1 and RhoA prenylation were constitutively targeted to caveolae fractions. These results suggest that the polarized distribution of Rho family proteins at the cell surface involves an initial targeting of the protein to caveolae and a mechanism for retaining it at this site.     

Reproductive biology of Lactoris fernandeziana (Lactoridaceae)

Lactoris fernandeziana, monotypic in its family, is endemic to the cloud forests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative primitive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation programs. The species is gynomonoecious. The overall proportion of flowers is ∼1 female:1 hermaphrodite. The inconspicuous semipendulous green flowers, usually in mixed-gender inflorescences, do not produce rewards. Hermaphrodite flowers are herkogamous and protogynous. Pollen grains are shed from the extrorse anthers in permanent dry tetrads. There is a mean of 12879 tetrads per hermaphrodite flower. Both flower types bear an average of ∼18 ovules. The P/O (pollen/ovule) ratios imply facultative or obligate xenogamy, but hand pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open-pollinated flowers bore tetrads, and 64% of such styles had pollen tubes. Flowers enclosed in large mesh (1 mm) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous, a syndrome perhaps reflected by the P/O ratio. Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal. The small size of the island, the ± 1000 extant Lactoris plants, coupled with anemophily, self-compatibility, and pendant flower position, have yielded a geitonogamous system with high seed set and low genetic diversity. If inbreeding depression is expressed, it is in seed germination and seedling vigor, for Lactoris is very difficult to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.     

Morphology and crystal structure of a recombinant silk-like molecule,SLP4

Morphology and crystal structure of a recombinant silk-like molecule, SLP4, were studied. Wide angle x-ray scattering (WAXS) and electron diffraction revealed that SLP4 lyophilized powder and thin films were isomorphic with the silk I crystal structure. Transmission electron microscopy of SLP4 thin films demonstrated a morphology of flat, variable width, crystallites that may aggregate in an epitaxial manner. Theoretical diffraction patterns from silk I crystal structure models were critically compared with SLP4 WAXS data. The analysis concluded that while the crankshaft model is capable of describing details of the SLP4 structural data well, the out-of-register model does not explain the experimental results. In particular, the predicted intensities of the crystallographic reflections for the out-of-register model are inconsistent with the SLP4 WAXS data. © 1998 John Wiley & Sons, Inc. Biopoly 45: 307–321, 1998     

Does carbon partitioning in ectomycorrhizal pine seedlings under elevated CO2 vary with fungal species?

Enhanced soil respiration in response to elevated atmospheric CO₂ has been demonstrated, and ectomycorrhizal (ECM) fungi are of particular interest since they partition host-derived photoassimilates belowground. Although a strong response of ECM fungi to elevated CO₂ has been shown, little is still known about the functional diversity among species. We studied carbon (C) partitioning in mycorrhizal Scots pine seedlings in response to short-term CO₂ enrichment, using seven ECM species with different ecological strategies. Mycorrhizal associations were synthesised and seedlings grown in large Petri dishes containing peat:vermiculite and nutrient solution for 10–15 weeks, after which half of the microcosms were exposed to elevated CO₂ treatment (710 ppm) for 15 days and the other half were kept in ambient CO₂ treatment. Partitioning of C was quantified by pulse labelling the seedlings with ¹⁴CO₂ and examining the distribution of labelled assimilates in shoot, root and extraradical mycelial compartments by destructive harvest and liquid scintillation counting. Fungal biomass was determined with PLFA analysis. The respiratory loss of ¹⁴CO₂ was on average greater in the elevated CO₂ treatment for most species compared to the ambient CO₂ treatment. More label was retrieved in the shoots in the ambient CO₂ treatment compared to elevated CO₂ (significant for P. involutus and P. fallax). Greater amounts of label were found in the extraradical mycelial compartment in all species (except P. involutus) in elevated CO₂ compared to ambient CO₂ (significant for L. bicolor, P. byssinum, P. fallax and R. roseolus). Fungal biomass production increased significantly with elevated CO₂ for two species (H. velutipes and A. muscaria); three species (P. fallax, P. involutus and R. roseolus) showed a similar but non-significant trend, whereas L. bicolor and P. byssinum produced less biomass in elevated CO₂ compared to ambient CO₂. When ¹⁴C in the mycelial compartment and respiration was expressed per unit fungal PLFA the difference between CO₂ treatments disappeared. We demonstrated that different ECM fungal isolates respond differently in C partitioning in response to CO₂ enrichment. These results suggest that under certain growth conditions, when nutrients are not limiting, ECM fungi respond rapidly to increasing C-availability through changed biomass production and respiration.