Food Transfer Among Adult Lion Tamarins: Mutualism,Reciprocity or One-Sided Relationships?

Tamarins (Callitrichidae) are cooperative breeders. Groups typically contain only two or three breeding individuals and subordinate group members are reproductively suppressed. Nonreproductive individuals, which are usually the offspring of the group's breeding members, delay dispersal while providing care to infant siblings. Callitrichid breeder-infant and helper-infant relationships have been well studied but empirical studies regarding the dynamics of breeder-helper relationships are sparse. I examined food-transfer interactions among parents and natal adults in 7 groups of captive lion tamarins, Leontopithecus spp., to test whether relationships are maintained by mutualism or reciprocity or are to the benefit of one side of a dyad. Individuals that had recently received food from a group member most frequently released food to the previous donor as their next act of transfer. Conversely, food transfer was not dependent on symmetrical relationships within groups over a time frame of several weeks. These results suggest that mutualism plays a role in the maintenance of food-transfer relationships but reciprocity does not. However, there is evidence for a reciprocal relationship between grooming and food transfer in one group. Subadults and adults living in their natal groups transferred proportionally more food to mothers than to oppositely-sexed subadult and adult siblings. Thus, individuals most likely to receive aggression preferentially released food to individuals most likely to inflict injury upon them. Although these results support the coercion hypothesis, they may suggest alternatively that food transfer by helpers to breeding adults is driven by inclusive fitness considerations.     

Development of microsatellite markers in the green algae Enteromorpha intestinalis (Chlorophyta)

The fouling green algae Enteromorpha intestinalis is a cosmopolitan benthic species, which causes green tides in many coastal areas and is used as an indicator species for eutrophication in the Baltic Sea area. The life cycle of E. intestinalis alternates between two morphologically identical reproductive stages, a haploid gametophyte phase and a diploid sporophyte phase. However, it also reproduces through asexual propagation. The reproductive cycles of E. intestinalis in the Baltic Sea and elsewhere are largely unknown. Here we report five polymorphic microsatellite markers developed from enriched genomic libraries. The number of alleles per locus ranged from 7 to 25.     

Assembly of Tom6 and Tom7 into the TOM core complex of Neurospora crassa

Translocation of preproteins across the mitochondrial outer membrane is mediated by the translocase of the outer mitochondrial membrane (TOM) complex. We report the molecular identification of Tom6 and Tom7, two small subunits of the TOM core complex in the fungus Neurospora crassa. Cross-linking experiments showed that both proteins were found to be in direct contact with the major component of the pore, Tom40. In addition, Tom6 was observed to interact with Tom22 in a manner that depends on the presence of preproteins in transit. Precursors of both proteins are able to insert into the outer membrane in vitro and are assembled into authentic TOM complexes. The insertion pathway of these proteins shares a common binding site with the general import pathway as the assembly of both Tom6 and Tom7 was competed by a matrix-destined precursor protein. This assembly was dependent on the integrity of receptor components of the TOM machinery and is highly specific as in vitro-synthesized yeast Tom6 was not assembled into N. crassa TOM complex. The targeting and assembly information within the Tom6 sequence was found to be located in the transmembrane segment and a flanking segment toward the N-terminal, cytosolic side. A hybrid protein composed of the C-terminal domain of yeast Tom6 and the cytosolic domain of N. crassa Tom6 was targeted to the mitochondria but was not taken up into TOM complexes. Thus, both segments are required for assembly into the TOM complex. A model for the topogenesis of the small Tom subunits is discussed.     

Tob38, a novel essential component in the biogenesis of beta-barrel proteins of mitochondria

Insertion of beta-barrel proteins into the outer membrane of mitochondria is mediated by the TOB complex. Known constituents of this complex are Tob55 and Mas37. We identified a novel component, Tob38. It is essential for viability of yeast and the function of the TOB complex. Tob38 is exposed on the surface of the mitochondrial outer membrane. It interacts with Mas37 and Tob55 and is associated with Tob55 even in the absence of Mas37. The Tob38-Tob55 core complex binds precursors of beta-barrel proteins and facilitates their insertion into the outer membrane. Depletion of Tob38 results in strongly reduced levels of Tob55 and Mas37 and the residual proteins no longer form a complex. Tob38-depleted mitochondria are deficient in the import of beta-barrel precursor proteins, but not of other outer membrane proteins or proteins of other mitochondrial subcompartments. We conclude that Tob38 has a crucial function in the biogenesis of beta-barrel proteins of mitochondria.     

Signal-anchor domains of proteins of the outer membrane of mitochondria: structural and functional characteristics

We have studied the topogenesis of a class of mitochondrial outer membrane proteins that expose a hydrophilic domain to the cytosol and are anchored to the membrane by a single transmembrane domain in the N-terminal region. To determine the role of these latter sequences in the targeting and insertion of such proteins we took two approaches. First, a functional complementation assay was used to define the structural elements that together with the anchor domain make up the topogenic signal. Moderate hydrophobicity of the transmembrane domain was found to be the most important requirement. Variants with a scrambled sequence of the membrane-spanning segment were only partially functional suggesting that specificity in the amino acid sequence is also of considerable importance. A net positive charge at both flanking regions of the transmembrane domain contributes to the efficiency of targeting and membrane integration but is not an essential structural feature of this signal. Second, chimeras of Tom20, Tom70, and OM45 were generated that contained the cytosolic domain of Tom20 or Tom70 and the anchor domain of one of the other members of the class. These hybrid proteins were able to rescue the growth of cells lacking Tom20 or Tom70. Thus, anchor domains of outer membrane proteins are functionally interchangeable. They play only a minor role in the specific function of these proteins, but have a decisive role in topogenic signaling.     

Finding the right organelle. Targeting signals in mitochondrial outer-membrane proteins

The mitochondrial outer membrane contains a diverse set of proteins that includes enzymes, components of the preprotein translocation machinery, pore-forming proteins, regulators of programmed cell death, and those that control the morphology of the organelle. All these proteins, like the vast majority of mitochondrial proteins, are encoded in the nucleus, so they are synthesized in the cytosol and contain signals that are essential for their subsequent import into mitochondria. This review summarizes our current knowledge of the signals that target mitochondrial outer-membrane proteins to their correct intracellular location. In addition, the mechanisms by which these signals are decoded by the mitochondria are discussed.     

The mitochondrial TOM complex is required for tBid/Bax-induced cytochrome c release

Cytochrome c release from mitochondria is a key event in apoptosis signaling that is regulated by Bcl-2 family proteins. Cleavage of the BH3-only protein Bid by multiple proteases leads to the formation of truncated Bid (tBid), which, in turn, promotes the oligomerization/insertion of Bax into the mitochondrial outer membrane and the resultant release of proteins residing in the intermembrane space. Bax, a monomeric protein in the cytosol, is targeted by a yet unknown mechanism to the mitochondria. Several hypotheses have been put forward to explain this targeting specificity. Using mitochondria isolated from different mutants of the yeast Saccharomyces cerevisiae and recombinant proteins, we have now investigated components of the mitochondrial outer membrane that might be required for tBid/Bax-induced cytochrome c release. Here, we show that the protein translocase of the outer mitochondrial membrane is required for Bax insertion and cytochrome c release.     

Mim1, a protein required for the assembly of the TOM complex of mitochondria

The translocase of the outer mitochondrial membrane (TOM complex) is the general entry site for newly synthesized proteins into mitochondria. This complex is essential for the formation and maintenance of mitochondria. Here, we report on the role of the integral outer membrane protein, Mim1 (mitochondrial import), in the biogenesis of mitochondria. Depletion of Mim1 abrogates assembly of the TOM complex and results in accumulation of Tom40, the principal constituent of the TOM complex, as a low-molecular-mass species. Like all mitochondrial beta-barrel proteins, the precursor of Tom40 is inserted into the outer membrane by the TOB complex. Mim1 is likely to be required for a step after this TOB-complex-mediated insertion. Mim1 is a constituent of neither the TOM complex nor the TOB complex; rather, it seems to be a subunit of another, as yet unidentified, complex. We conclude that Mim1 has a vital and specific function in the assembly of the TOM complex.     

Can marine protected areas enhance both economic and biological situations?

This paper investigates impacts of the creation of Marine Protected Areas (MPAs), in both economic and biological perspectives. The economic indicator is defined as the sum of discounted benefits derived from exploitation of the resource in the fishery sector, assumed to be optimally managed. The biological indicator is taken as the stock density of the resource. The basic fishery model (C.W. Clark, Mathematical Bioeconomics: The Optimal Management of Renewable Resources, second ed., John Wiley and Sons, New York, 1990) will serve as a convenient benchmark in comparing results with those that are derived from a model of two patchy populations (cf. R. Hannesson, Marine reserves: what would they accomplish, Mar. Resour. Econ. 13 (1998) 159). In the latter, a crucial characteristic is the migration coefficient with describes biological linkages between protected and unprotected areas. A set of situations where both economic and biological criteria are enhanced, after introducing a MPA, is presented. These results are obtained with the help of numerical simulations.