The 'island rule' in birds: medium body size and its ecological explanation

Do birds show a different pattern of insular evolution from mammals? Mammals follow the ''island rule'', with large-bodied species getting smaller on islands and small-bodied species getting bigger. By contrast, the traditional view on birds is that they follow no general island rule for body size, but that there is an insular trend for large bills. Insular shifts in feeding ecology are, therefore, widely assumed to be the primary cause of divergence in island birds. We use a comparative approach to test these ideas. Contrary to the traditional view, we find no evidence for increased bill size in insular populations. Instead, changes in both bill size and body size obey the ''island rule''. The differences between our results and the traditional view arise because previous analyses were based largely on passerines. We also investigate some ecological factors that are thought to influence island evolution. As predicted by the traditional view, shifts in bill size are associated with feeding ecology. By contrast, shifts in body size are associated with the potential for intraspecific competition and thermal ecology. All these results remain qualitatively unchanged when we use different methods to score the ecological factors and restrict our analyses to taxa showing pronounced morphological divergence. Because of strong covariation between ecological factors, however, we cannot estimate the relative importance of each ecological factor. Overall, our results show that the island rule is valid for both body size and bill length in birds and that, in addition to feeding ecology, insular shifts in the level of intraspecific competition and the abiotic environment also have a role.     

Bmp signaling is required for development of primary lens fiber cells

We have investigated the role of Bmp signaling in development of the mouse lens using three experimental strategies. First, we have shown that the Bmp ligand inhibitor noggin can suppress the differentiation of primary lens fiber cells in explant culture. Second, we have expressed a dominant-negative form of the type 1 Bmp family receptor Alk6 (Bmpr1b -- Mouse Genome Informatics) in the lens in transgenic mice and shown that an inhibition of primary fiber cell differentiation can be detected at E13.5. Interestingly, the observed inhibition of primary fiber cell development was asymmetrical and appeared only on the nasal side of the lens in the ventral half. Expression of the inhibitory form of Alk6 was driven either by the alpha A-cystallin promoter or the ectoderm enhancer from the Pax6 gene in two different transgenes. These expression units drive transgene expression in distinct patterns that overlap in the equatorial cells of the lens vesicle at E12.5. Despite the distinctions between the transgenes, they caused primary fiber cell differentiation defects that were essentially identical, which implied that the equatorial lens vesicle cells were responding to Bmp signals in permitting primary fiber cells to develop. Importantly, E12.5 equatorial lens vesicle cells showed cell-surface immunoreactivity for bone-morphogenetic protein receptor type 2 and nuclear immunoreactivity for the active, phosphorylated form of the Bmp responsive Smads. This indicated that these cells had the machinery for Bmp signaling and were responding to Bmp signals. We conclude that Bmp signaling is required for primary lens fiber cell differentiation and, given the asymmetry of the differentiation inhibition, that distinct differentiation stimuli may be active in different quadrants of the eye.     

Cdk5 is essential for synaptic vesicle endocytosis

Synaptic vesicle endocytosis (SVE) is triggered by calcineurin-mediated dephosphorylation of the dephosphin proteins. SVE is maintained by the subsequent rephosphorylation of the dephosphins by unidentified protein kinases. Here, we show that cyclin-dependent kinase 5 (Cdk5) phosphorylates dynamin I on Ser 774 and Ser 778 in vitro, which are identical to its endogenous phosphorylation sites in vivo. Cdk5 antagonists and expression of dominant-negative Cdk5 block phosphorylation of dynamin I, but not of amphiphysin or AP180, in nerve terminals and inhibit SVE. Thus Cdk5 has an essential role in SVE and is the first dephosphin kinase identified in nerve terminals.     

The cAMP signaling pathway has opposing effects on Rac and Rho in B16F10 cells: implications for dendrite formation in melanocytic cells

A hallmark of melanocytic cells is their ability to form dendrites in response to growth factors and to ultraviolet irradiation. It is known that the cyclic adenosine monophosphate (cAMP) second messenger pathway stimulates melanocyte dendrite formation because agents that increase cAMP such as forskolin and dibutyrl cAMP induce dendrite formation in normal human and murine melanocytes and melanoma cell lines. The Rho family of guanosine triphosphate (GTP)-binding proteins regulates cytoskeletal reorganization in all cells tested and Rac and Rho have both been shown to regulate melanocyte dendrite formation. In this report, we analyzed the effect of cAMP on the activation of Rac and Rho and show that elevation of cAMP stimulates Rac and inhibits Rho in B16F10 cells. The Rho GTP-binding proteins have also been shown to either cross-activate or inhibit each other and in this report we show that Rac activates Rho in B16F10 cells. Microinjection of C3 botulinum exoenzyme toxin, an agent that specifically inactivates Rho or microinjection of constitutively active mutant Rac protein-induced dendricity in human melanocytes and in B16F10 and B16F1 murine melanoma cell lines. We conclude that cAMP-mediated dendrite formation in melanocytic cells is mediated through upregulation of Rac activity and downregulation of Rho activity.     

Two distinct domains within CIITA mediate self-association: involvement of the GTP-binding and leucine-rich repeat domains

CIITA is the master regulator of class II major histocompatibility complex gene expression. We present evidence that CIITA can self-associate via two domains: the C terminus (amino acids 700 to 1130) and the GTP-binding domain (amino acids 336 to 702). Heterotypic and homotypic interactions are observed between these two regions. Deletions within the GTP-binding domain that reduce GTP-binding and transactivation function also reduce self-association. In addition, two leucine residues in the C-terminal leucine-rich repeat region are critical for self-association as well as function. This study reveals for the first time a complex pattern of CIITA self-association. These interactions are discussed with regard to the apoptosis signaling proteins, Apaf-1 and Nod1, which share domain arrangements similar to those of CIITA.     

Individuals with higher metabolic rates have lower levels of reactive oxygen species in vivo

There is increasing interest in the effect of energy metabolism on oxidative stress, but much ambiguity over the relationship between the rate of oxygen consumption and the generation of reactive oxygen species (ROS). Production of ROS (such as hydrogen peroxide, H₂O₂) in the mitochondria is primarily inferred indirectly from measurements in vitro, which may not reflect actual ROS production in living animals. Here, we measured in vivo H₂O₂ content using the recently developed MitoB probe that becomes concentrated in the mitochondria of living organisms, where it is converted by H₂O₂ into an alternative form termed MitoP; the ratio of MitoP/MitoB indicates the level of mitochondrial H₂O₂ in vivo. Using the brown trout Salmo trutta, we tested whether this measurement of in vivo H₂O₂ content over a 24 h-period was related to interindividual variation in standard metabolic rate (SMR). We showed that the H₂O₂ content varied up to 26-fold among fish of the same age and under identical environmental conditions and nutritional states. Interindividual variation in H₂O₂ content was unrelated to mitochondrial density but was significantly associated with SMR: fish with a higher mass-independent SMR had a lower level of H₂O₂. The mechanism underlying this observed relationship between SMR and in vivo H₂O₂ content requires further investigation, but may implicate mitochondrial uncoupling which can simultaneously increase SMR but reduce ROS production. To our knowledge, this is the first study in living organisms to show that individuals with higher oxygen consumption rates can actually have lower levels of H₂O₂.     

The related effector proteins SopD and SopD2 from Salmonella enterica serovar Typhimurium contribute to virulence during systemic infection of mice

Salmonella resides within host cells in a vacuole that it modifies through the action of virulence proteins called effectors. Here we examined the role of two related effectors, SopD and SopD2, in Salmonella pathogenesis. Salmonella enterica serovar Typhimurium (S. Typhimurium) mutants lacking either sopD or sopD2 were attenuated for replication in the spleens of infected mice when competed against wild-type bacteria in mixed infection experiments. A double mutant lacking both effector genes did not display an additive attenuation of virulence in these experiments. The double mutant also competed equally with both of the single mutants. Deletion of either effector impaired bacterial replication in mouse macrophages but not human epithelial cells. Deletion of sopD2 impaired Salmonella's ability to form tubular membrane filaments [Salmonella-induced filaments (Sifs)] in infected cells; the number of Sifs decreased, whereas the number of pseudo-Sifs (thought to be a precursor of Sifs) was increased. Transfection of HeLa cells with the effector SifA induced the formation of Sif-like tubules and these were observed in greater size and number after co-transfection of SifA with SopD2. In infected cells, SifA and SopD2 were localized both to Sifs and to pseudo-Sifs. In contrast, deletion of sopD had no effect on Sif formation. Our results indicate that both SopD and SopD2 contribute to virulence in mice and suggest a functional relationship between these two proteins during systemic infection of the host.     

Declining egg viability explains higher hatching failure in a suburban population of the threatened Florida scrub‐jay Aphelocoma coerulescens

Hatching failure occurs in approximately 10% of all avian eggs, but varies both within and among species. This reduction in viable offspring can have significant fitness consequences for breeding parents; therefore, it is important to understand which factors influence variation in hatching failure among populations. Previous research suggests that hatching failure is higher in a suburban than in a wildland population in the Florida scrub‐jay. From 2003 to 2007, we performed two experiments to examine whether increased hatching failure in the suburbs resulted from 1) increased length of off‐bouts during incubation (predation risk hypothesis, 2003–2004) or 2) increased exposure to ambient temperature during laying (egg viability hypothesis, 2005–2007). Hatching failure was higher for females that took fewer off‐bouts, but the length of those off‐bouts did not influence hatching failure. Thus, nest predation risk does not appear to explain higher hatching failure in the suburbs. Alternatively, hatching failure increased with increasing exposure of eggs to ambient conditions during the laying period. First‐laid eggs in the suburbs had the greatest pre‐incubation exposure to ambient temperature and the greatest rate of hatching failure, consistent with the egg viability hypothesis. Urbanization influences hatching failure through a series of complex interactions. Access to predictable food sources advances mean laying date in suburban scrub‐jays, leading to larger clutch sizes. Because scrub‐jays begin incubation with the ultimate egg, first‐laid eggs in the suburbs may be exposed to ambient temperatures for longer periods, thus reducing their viability.     

Soluble adenylyl cyclase (sAC) is indispensable for sperm function and fertilization

We previously demonstrated that male mice deficient in the soluble adenylyl cyclase (sAC) are sterile and produce spermatozoa with deficits in progressive motility and are unable to fertilize zona-intact eggs. Here, analyses of sAC(-/-) spermatozoa provide additional insights into the functions linked to cAMP signaling. Adenylyl cyclase activity and cAMP content are greatly diminished in crude preparations of sAC(-/-) spermatozoa and are undetectable after sperm purification. HCO(3)(-) is unable to rapidly accelerate the flagellar beat or facilitate evoked Ca(2+) entry into sAC(-/-) spermatozoa. Moreover, the delayed HCO(3)(-)-dependent increases in protein tyrosine phosphorylation and hyperactivated motility, which occur late in capacitation of wild-type spermatozoa, do not develop in sAC(-/-) spermatozoa. However, sAC(-/-) sperm fertilize zona-free oocytes, indicating that gamete fusion does not require sAC. Although ATP levels are significantly reduced in sAC(-/-) sperm, cAMP-AM ester increases flagellar beat frequency, progressive motility, and alters the pattern of tyrosine phosphorylated proteins. These results indicate that sAC and cAMP coordinate cellular energy balance in wild-type sperm and that the ATP generating machinery is not operating normally in sAC(-/-) spermatozoa. These findings demonstrate that sAC plays a critical role in cAMP signaling in spermatozoa and that defective cAMP production prevents engagement of multiple components of capacitation resulting in male infertility.