Paradoxical absence of M lines and downregulation of creatine kinase in mouse extraocular muscle.

The M lines are structural landmarks in striated muscles, necessary for sarcomeric stability and as anchoring sites for the M isoform of creatine kinase (CK-M). These structures, especially prominent in fast skeletal muscles, are missing in rodent extraocular muscle, a particularly fast and active muscle group. In this study, we tested the hypotheses that 1). myomesin and M protein (cytoskeletal components of the M lines) and CK-M are downregulated in mouse extraocular muscle compared with the leg muscles, gastrocnemius and soleus; and 2). the expression of other cytosolic and mitochondrial CK isoforms is correspondingly increased. As expected, mouse extraocular muscles expressed lower levels of myomesin, M protein, and CK-M mRNA than the leg muscles. Immunocytochemically, myomesin and M protein were not detected in the banding pattern typically seen in other skeletal muscles. Surprisingly, message abundance for the other known CK isoforms was also lower in the extraocular muscles. Moreover, total CK activity was significantly decreased compared with that in the leg muscles. Based on these data, we reject our second hypothesis and propose that other energy-buffering systems may be more important in the extraocular muscles. The downregulation of major structural and metabolic elements and relative overexpression of two adenylate kinase isoforms suggest that the extraocular muscle group copes with its functional requirements by using strategies not seen in typical skeletal muscles.     

Sex differences in the social behavior of wild spider monkeys (Ateles geoffroyi yucatanensis)

Competition for resources and the need for cooperation are reported to affect patterns of social interactions and thus the quality of social relationships in primates. Relationships may be described as high quality when both individuals behave in a way that benefits their partner. We investigated the distribution of a wide range of social behaviors across sex partner combinations of adult spider monkeys with specific reference to contested resources. Data were collected from two communities of wild spider monkeys (Ateles geoffroyi yucatanensis) in the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico. Affiliative behavior was exchanged most frequently between males, and as male-male aggression was rare, male-male social relationships were characterized as high quality. Female-female social relationships were best described as low quality as females showed no preference to be in proximity with other females and female-female affiliative behavior was rare. Relationships between the sexes generally were characterized by high rates of female-directed male aggression, although additional investigation into the effects of kinship and female reproductive state on male-female relationships is required before further conclusions can be drawn. Dyadic and coalitionary female-female aggression was significantly higher than expected in a feeding context, confirming that female spider monkeys primarily compete for access to food. Male-male aggression did not increase significantly when in the presence of females, but males embraced at higher rates when in mixed-sex subgroups. As embraces serve to reduce the likelihood of aggression during tense situations, high rates of male-male embraces in mixed-sex subgroups may mitigate male conflicts over access to females.     

Lipid body formation plays a central role in cell fate determination during developmental differentiation of Myxococcus xanthus

Cell differentiation is widespread during the development of multicellular organisms, but rarely observed in prokaryotes. One example of prokaryotic differentiation is the Gram-negative bacterium Myxococcus xanthus . In response to starvation, this gliding bacterium initiates a complex developmental programme that results in the formation of spore-filled fruiting bodies. How the cells metabolically support the necessary complex cellular differentiation from rod-shaped vegetative cells into spherical spores is unknown. Here, we present evidence that intracellular lipid bodies provide the necessary metabolic fuel for the development of spores. Formed at the onset of starvation, these lipid bodies gradually disappear until they are completely used up by the time the cells have become mature spores. Moreover, it appears that lipid body formation in M. xanthus is an important initial step indicating cell fate during differentiation. Upon starvation, two subpopulations of cells occur: cells that form lipid bodies invariably develop into spores, while cells that do not form lipid bodies end up becoming peripheral rods, which are cells that lack signs of morphological differentiation and stay in a vegetative-like state. These data indicate that lipid bodies not only fuel cellular differentiation but that their formation represents the first known morphological sign indicating cell fate during differentiation.     

Extreme endurance flights by landbirds crossing the Pacific Ocean: ecological corridor rather than barrier?

Mountain ranges, deserts, ice fields and oceans generally act as barriers to the movement of land-dependent animals, often profoundly shaping migration routes. We used satellite telemetry to track the southward flights of bar-tailed godwits (Limosa lapponica baueri), shorebirds whose breeding and non-breeding areas are separated by the vast central Pacific Ocean. Seven females with surgically implanted transmitters flew non-stop 8,117-11,680 km (10153+/-1043 s.d.) directly across the Pacific Ocean; two males with external transmitters flew non-stop along the same corridor for 7,008-7,390 km. Flight duration ranged from 6.0 to 9.4 days (7.8+/-1.3 s.d.) for birds with implants and 5.0 to 6.6 days for birds with externally attached transmitters. These extraordinary non-stop flights establish new extremes for avian flight performance, have profound implications for understanding the physiological capabilities of vertebrates and how birds navigate, and challenge current physiological paradigms on topics such as sleep, dehydration and phenotypic flexibility. Predicted changes in climatic systems may affect survival rates if weather conditions at their departure hub or along the migration corridor should change. We propose that this transoceanic route may function as an ecological corridor rather than a barrier, providing a wind-assisted passage relatively free of pathogens and predators.     

Genetic Subdivision of Chemosynthetic Endosymbionts of Solemya velum along the Southern New England Coast

Population-level genetic diversity in the obligate symbiosis between the bivalve Solemya velum and its thioautotrophic bacterial endosymbiont was examined. Distinct populations along the New England coast shared a single mitochondrial genotype but were fixed for unique symbiont genotypes, indicating high levels of symbiont genetic structuring and potential symbiont-host decoupling.Studies of endosymbioses between marine invertebrates and sulfur-oxidizing chemosynthetic bacteria have yielded tremendous insight into the biology of bacterium-eukaryote interactions. Though best described for deep-sea vents and cold seeps, these mutualisms, in which symbiont thioautotrophy supports the nutrition of both partners, are also ubiquitous in coastal sediments (17). Our understanding of these interactions stems largely from studies of symbioses involving protobranch bivalves in the family Solemyidae (16). Though solemyids and other species that form chemosynthetic symbioses occur globally, little is known about how symbionts and hosts are structured genetically across distinct populations. Characterizing these patterns is critical for understanding how symbiosis drives the coevolution of interacting species, as well as how environmental heterogeneity and dispersal affect local adaptation. This study examines the geographic structure of genetic variation in the symbiosis between chemosynthetic bacteria and the Atlantic protobranch Solemya velum.Solemya velum is ideal for studying the evolution of highly coadapted bacterium-eukaryote mutualisms. This small bivalve (∼1.5 to 3 cm) burrows in sulfide-rich coastal sediments, where it obtains most of its nutrition from thioautotrophic bacteria living within specialized gill cells (1, 10). Though observed from Florida to Canada (20), the distribution of S. velum is highly patchy, with seemingly suitable habitat often devoid of individuals (12). Consequently, molecular characterizations of this symbiosis have focused primarily on stable and locally abundant populations near Woods Hole, MA. Direct sequencing of the symbiont 16S rRNA gene from these individuals has revealed a single, unique phylotype clustering within the Gammaproteobacteria (5, 6, 9). DNA from this symbiont has been extracted from S. velum ovarian tissue, raising the hypothesis that symbionts are transmitted vertically from mother to offspring (11) and are therefore tightly coupled to the host''s life cycle and evolutionary history.If symbiont acquisition is strictly vertical in Solemya populations, the genealogies of the symbiont and the cotransmitted host mitochondrion should diverge in parallel (cospeciation) (8, 15, 18). However, lateral acquisition involving either symbiont uptake from the environment or horizontal transfer between co-occurring hosts has not been ruled out for Solemya populations and could decouple symbiont and host genealogies (18). Indeed, 16S phylogenies show that symbionts of diverse Solemya species are polyphyletic, a pattern inconsistent with the putative monophyly of the hosts (based on nonmolecular characters) and suggestive of multiple evolutionary origins (2, 9, 16). However, tests for symbiont-host codiversification below the species level in S. velum are lacking; sequence data from multiple populations will help resolve questions of cospeciation and symbiont transmission in this group.Here, distinct Solemya velum populations were genotyped to examine how symbiont diversity covaries with host diversity and geography. Individual bivalves (n = 12 to 22 per site) were collected from mudflats at four sites along the southern New England coast (Fig. ​(Fig.1A).1A). DNA was extracted from the symbiont-containing gills and used for PCR amplification of fragments of the mitochondrial cytochrome c oxidase subunit I gene (COI) and the symbiont 16S gene and hypervariable internal transcribed spacer (16S-ITS) (Table ​(Table1;1; also see the supplemental material). Unambiguous contigs of 340 nucleotides (nt) for the COI locus and 716 nt for the 16S-ITS locus, including 241 nt of the 16S and 475 nt (∼95%) of the ITS, were generated via bidirectional direct sequencing of amplicons using BigDye chemistry. Symbiont identity was confirmed by blasting the 16S-ITS (Woods Hole [WH] phylotype) against an assembly of the S. velum symbiont genome from the same population (C. Cavanaugh, unpublished data). Blastn returned a single full-length hit with 100% identity across the locus. Genotype networks were then inferred via statistical parsimony in the program TCS (3).Open in a separate windowFIG. 1.(A) Locations of Solemya velum collection sites (stars) along the Atlantic Coast were Naushon Island, Woods Hole, MA (WH; 41.514°N, −70.712°W); Lake Tashmoo, Martha''s Vineyard, MA (MV; 41.465°N, −70.623°W); Judith Pond, RI (RI; 41.380°N, −71.502°W); and Shark River Island, NJ (NJ; 40.186°N, −74.030°W). (B) Parsimony networks of host COI and symbiont 16S-ITS genotypes. Open circle, single-nucleotide substitution in either the host COI (top; 340 nt) or symbiont 16S (241 nt); filled circle, single-nucleotide substitution in the ITS portion (475 nt) of the 16S-ITS sequence fragment (716 nt total); diagonal bar, single-nucleotide indel in the symbiont ITS; gen1 and gen2, genotypes 1 and 2. Values in parentheses show the number of S. velum individuals from which sequences were obtained at each site.

TABLE 1.

Symbiont and host primers used in PCR^a and direct sequencing

Quantifying nonspecific TEM beta-lactamase (blaTEM) genes in a wastewater stream

To control the antibiotic resistance epidemic, it is necessary to understand the distribution of genetic material encoding antibiotic resistance in the environment and how anthropogenic inputs, such as wastewater, affect this distribution. Approximately two-thirds of antibiotics administered to humans are beta-lactams, for which the predominant bacterial resistance mechanism is hydrolysis by beta-lactamases. Of the beta-lactamases, the TEM family is of overriding significance with regard to diversity, prevalence, and distribution. This paper describes the design of DNA probes universal for all known TEM beta-lactamase genes and the application of a quantitative PCR assay (also known as Taqman) to quantify these genes in environmental samples. The primer set was used to study whether sewage, both treated and untreated, contributes to the spread of these genes in receiving waters. It was found that while modern sewage treatment technologies reduce the concentrations of these antibiotic resistance genes, the ratio of bla(TEM) genes to 16S rRNA genes increases with treatment, suggesting that bacteria harboring bla(TEM) are more likely to survive the treatment process. Thus, beta-lactamase genes are being introduced into the environment in significantly higher concentrations than occur naturally, creating reservoirs of increased resistance potential.