Social learning in nest-building birds: a role for familiarity

It is becoming apparent that birds learn from their own experiences of nest building. What is not clear is whether birds can learn from watching conspecifics build. As social learning allows an animal to gain information without engaging in costly trial-and-error learning, first-time builders should exploit the successful habits of experienced builders. We presented first-time nest-building male zebra finches with either a familiar or an unfamiliar conspecific male building with material of a colour the observer did not like. When given the opportunity to build, males that had watched a familiar male build switched their material preference to that used by the familiar male. Males that observed unfamiliar birds did not. Thus, first-time nest builders use social information and copy the nest material choices when demonstrators are familiar but not when they are strangers. The relationships between individuals therefore influence how nest-building expertise is socially transmitted in zebra finches.     

Revised evidence for facultative sex ratio adjustment in birds: a correction

We provide a revision to the calculation of effect sizes and heterogeneity statistics in our original article, 'Facultative primary sex ratio variation: a lack of evidence in birds' (Ewen et al. 2004). Our revision shows that significant heterogeneity in sex ratio study effect sizes does indeed exist and that for a series of key traits the average effect sizes (while still weak) are in fact significantly different from zero.     

Pair-bonding in birds and the active role of females: a critical review of the empirical evidence

Over the recent years the role of females in maintaining or breaking the pair-bond in socially monogamous birds has received growing attention. Here, we review the overall evidence for a direct and predominant role of female behaviour in initiating or preventing divorce and its relevance for the understanding of both interspecific and intraspecific variation in divorce rate in monogamous bird species. The evidence is so far limited to a few species. We discuss the relevance of some alternative explanations and confounding factors. We conclude that the possible predominance of females in both initiating divorce or limiting its occurrence deserves further consideration. Future studies should favour experimental approaches, such as mate-removal experiments.     

Studies of mechanisms of niridazole-elicited embryotoxicity: evidence against a major role for covalent binding

Studies reported here were designed to examine the hypothesis that covalent binding of reactive intermediates to macromolecules of the conceptus represents a major mechanism for the embryotoxicity of niridazole (NDZ). The roles of embryonic thiol content and oxygenation on: 1) malformation incidence; 2) reductive metabolism; and 3) covalent binding to embryonic macromolecules of metabolites resulting from reductive biotransformation of NDZ were studied. Results were compared with those from studies with the nondysmorphogenic analog of NDZ, 4'-methylniridazole (MNDZ). Day 10 rat embryos were pretreated for 5 hours in vitro with either L-buthionine-S, R-sulfoximine (BSO) or N-acetylcysteine (NAC) to modulate their glutathione (GSH) content. BSO reduced GSH levels, but NAC was ineffective. Following pretreatment, embryos were cultured for an additional 15 hours in the presence of [14C]NDZ or [14C]MNDZ with an initial oxygen concentration of 5%. At the end of the culture period (day 11, AM), those embryos with active heartbeat and vitelline circulation were examined for asymmetric malformations. Drug metabolites were subjected to multiple extractions from the culture medium and subjected to quantitative high-performance liquid chromatography (HPLC) analysis. Homogenates of the embryos were extracted with trichloroacetic acid (TCA) to estimate the covalent binding of radiolabeled parent compound/metabolites. Autoradiographic analyses were performed on other embryos. BSO pretreatment, which reduces embryonic GSH tissue levels, dramatically increased both the conversion of NDZ to 1-thiocarbamoyl-2-imidazolidinone (TCI) (generated via reductive metabolism of NDZ) and covalently bound label but failed to increase embryotoxicity. NAC, by contrast, did not significantly affect embryonic GSH levels, TCI generation, or covalent binding. Because both rates of metabolism of NDZ to TCI and covalent binding could vary independently of malformation incidence, we concluded that they do not represent critical mechanistic factors for the embryotoxicity of NDZ and related nitroheterocycles.     

New evidence for a multi-functional role of herbivore-induced plant volatiles in defense against herbivores

A diverse, often species-specific, array of herbivore-induced plant volatiles (HIPVs) are commonly emitted from plants after herbivore attack. Although research in the last 3 decades indicates a multi-functional role of these HIPVs, the evolutionary rationale underpinning HIPV emissions remains an open question. Many studies have documented that HIPVs can attract natural enemies, and some studies indicate that neighboring plants may eavesdrop their undamaged neighbors and induce or prime their own defenses prior to herbivore attack. Both of these ecological roles for HIPVs are risky strategies for the emitting plant. In a recent paper, we reported that most branches within a blueberry bush share limited vascular connectivity, which restricts the systemic movement of internal signals. Blueberry branches circumvent this limitation by responding to HIPVs emitted from neighboring branches of the same plant: exposure to HIPVs increases levels of defensive signaling hormones, changes their defensive status, and makes undamaged branches more resistant to herbivores. Similar findings have been reported recently for sagebrush, poplar and lima beans, where intra-plant communication played a role in activating or priming defenses against herbivores. Thus, there is increasing evidence that intra-plant communication occurs in a wide range of taxonomically unrelated plant species. While the degree to which this phenomenon increases a plant’s fitness remains to be determined in most cases, we here argue that withinplant signaling provides more adaptive benefit for HIPV emissions than does between-plant signaling or attraction of predators. That is, the emission of HIPVs might have evolved primarily to protect undamaged parts of the plant against potential enemies, and neighboring plants and predators of herbivores later co-opted such HIPV signals for their own benefit.Key words: intra-plant signaling, plantplant communication, eavesdropping, systemic wound signals, plant defense, tri-trophic interactionsPlants often emit a unique blend of volatiles in response to herbivore attack. The emission of these herbivore-induced plant volatiles (HIPVs) is an active response to herbivore feeding, producing a blend of volatiles that is distinct from those emitted following mechanical injury alone.¹ Their emission can be variable; while some compounds follow a diurnal pattern with increasing amounts during the time of high photosynthesis,^2,3 others are emitted primarily at night.⁴ In some cases, the HIPV blend produced also differs depending on the species of herbivore feeding on the plant.⁵ This specificity is thought to be due to chemicals in the herbivore’s regurgitant, such as the fatty-acid amino-acid conjugate volicitin, that activate the emission of volatiles in plants.^6,7 Furthermore, HIPVs are emitted not only from the site of damage, but also at times from systemically undamaged parts of the plant.⁸ This and other systemic responses are, however, restricted within a plant such that only parts of the plant that share vascular connections with the damaged tissue receive wound signals and have the potential to respond.^9,10The ecological role of HIPVs has been a subject of fascination and the evolutionary advantage gained for plants by emitting HIPVs remains an unresolved topic of discussion. While some HIPV compounds, and some of their precursors, have sufficient volatility that their release is essentially inevitable after synthesis,¹¹ most tend to be tightly regulated. Assuming that HIPV emissions evolved as a result of trophic interactions among plants, herbivores, and natural enemies, there are four general ecological roles that HIPVs may play: (1) a direct negative effect on the herbivore, (2) a signal to alert natural enemies of the herbivore, (3) a warning signal to nearby undamaged plants, and (4) a systemic warning signal within the damaged plant (Fig. 1). The first two potential roles involve the manipulation of animal behavior, while the last two may alter plant “behavior”.Open in a separate windowFigure 1Herbivore-induced plant volatiles (HIPVs) play multiple roles in interactions among plants, herbivores, and natural enemies (possible interactions are depicted by arrows). Some of them benefit the HIPV-emitting plant (Emitter); these positive interactions include repellent effects on herbivores, attraction of natural enemies of herbivores, activation or priming of defenses in unwounded parts within the emitting plant (within-plant signaling), and growth inhibitory effects on neighboring plants (Receiver) through allelopathy. On the other hand, HIPVs may negatively affect the emitting plant by attracting herbivores or natural enemies (e.g., certain parasitoids) that result in increased damage. Finally, neighboring plants may “eavesdrop” from the emitting plant by responding to HIPVs (between-plant signaling). This latter interaction may be negative to the emitter if it is outcompeted by neighbors who receive wound signals, but beneficial to the receiving plant. Drawing by Robert Holdcraft.Scents can have a demonstrable effect on animal behavior. With respect to plant-herbivore interactions, scents can provide information about the status of a plant to herbivores and their natural enemies. For example, HIPVs may repel adults moths searching for oviposition sites,³ which has been interpreted from the perspective of either a plant minimizing damage or, perhaps more realistically, an adult moth searching for an undamaged, high quality resource for her offspring. Conversely, HIPV-emitting plants may increase their chance of being injured if herbivores are attracted to these volatiles.¹² The more commonly accepted role of HIPVs in manipulating animal behavior is to attract natural enemies of the herbivores. This tri-trophic “cry for help”¹³ has a potential evolutionary benefit for both the plant emitting the volatiles and the natural enemies responding to this emission.^14–16 Although this idea makes sense in an evolutionary perspective, only a few studies have documented the occurrence of this phenomenon in natural systems.¹⁷ Indeed, the effectiveness of a cry for help depends on the presence of a helper and, equally importantly, the ability of the helper to increase plant fitness. In the case of predator attraction, the herbivore may be removed from the plant and consumed, thereby reducing damage for the emitting plant.¹⁸ However, insect herbivores infected by parasitoids, which also use HIPV cues to locate hosts,¹⁹ may also consume less plant material²⁰ but may also in some cases consume more plant material than unparasitized insect herbivores.²¹ Since there is currently no evidence that plants can modify HIPV blends to attract selectively predators versus parasitoids, an answered cry for help may not reliably decrease the total amount of damage to an emitting plant. Thus, the fact that natural enemies respond to HIPVs does not imply that these volatiles evolved for this purpose or that there is an adaptive advantage for a plant to use HIPVs to attract natural enemies. Rather, natural enemies of insect herbivores may have learned to co-opt the HIPV signal emitted by plants and, by doing so, increased their fitness irrespective of the ultimate fitness outcome to the plant.Though more controversial, scents can also have an effect on plant behavior.²² Early work suggested that HIPVs from wounded willows,²³ poplars²⁴ and sugar maples²⁴ could trigger defense responses from other neighboring conspecifics. More recent studies have shown that this signaling can occur between different species of plants.²⁵ While these results are intriguing, they appear to have little adaptive function from the perspective of an emitting plant, which could be facilitating the fitness of potential resource competitors. Further, unless the individual within the same plant species shared some degree of kinship,²⁶ an emitting plant would also be at a disadvantage by providing an HIPV wound signal to a conspecific that, in theory, occupies the same competitive niche space. On the other hand, unwounded conspecific should benefit from being able to ‘eavesdrop’ by detecting HIPVs from wounded plants as they share the same herbivore complex and thus are vulnerable to attack. Moreover, from a heterospecific receiver’s perspective, the benefits of eavesdropping can be confounded by the potential of mounting defenses against a signal generated by incompatible herbivores feeding on a different plant species.²⁷ So, eavesdropping may be adaptive for a receiving plant if it realizes increased fitness relative to a conspecific that did not receive the signal. The emitting plant derives no apparent adaptive benefit of using HIPVs to warn neighboring plants. However, the emitting plant may benefit if their HIPVs have inhibitory allelopathic activity on neighboring plants.²⁸Our recent work¹ highlighted another scenario by which an HIPV-emitting plant would derive a direct benefit from the emissions: when HIPVs act as systemic wound signals within damaged plants. We showed that branches of blueberry shrubs lack effective vascular connections and thus cannot transmit wound signals among branches via the vasculature. To compensate, HIPVs can be transmitted among branches and, in so doing, overcome the vascular constraints of the branching life history strategy. Exposure to HIPVs increased levels of defensive signaling hormones in undamaged branches, changed their defensive chemical status, and made them more resistant to herbivores.¹ This idea that HIPVs may function in intra-plant communication to activate or prime defenses in other parts of the emitting plant against future attack was first suggested separately by Farmer²⁹ and Orians.⁹ The hypothesis was first tested with mechanically clipped wild sagebrush,³⁰ and it was further tested with insect herbivores of wild lima bean³¹ and hybrid poplar.³² Under this scenario, the emitting plant derives a direct benefit from the HIPVs, providing an unambiguous fitness advantage.So, what is the most beneficial factor to a plant for emitting volatiles in response to herbivore feeding? In terms of maximizing the potential benefit and minimizing the potential risk to the emitting plant, the function of HIPVs in mediating systemic wound signaling clearly provides the greatest potential adaptive advantage. Thus, we propose that the primary adaptive benefit for the evolution of HIPVs is to signal and protect unwounded parts of the attacked plant with high risk of infestation against herbivores. Later, these volatiles provided cues that led to adaptive fitness advantages for neighboring plants and natural enemies of herbivores, which may or may not benefit the HIPV-emitting plant. Indeed, ecologically adaptive advantages have emerged and contribute to a diverse, multi-functional chemical ecology mediated by HIPVs.     

TCR vaccines against a murine T cell lymphoma: a primary role for antibodies of the IgG2c class in tumor protection

Tumor-associated proteins can act as effective immunotherapeutic targets. Immunization with tumor TCR protein conjugated to the immunogenic protein keyhole limpet hemocyanin (KLH) protects mice from tumor challenge with the murine T cell lymphoma C6VL. The immune mechanisms responsible for this tumor protection are of interest for designing more effective vaccine strategies. Previous studies using depletion experiments had suggested a CD8-mediated component of protection induced by TCR-KLH vaccines. In this study we used CD8alpha knockout, micro MT, and FcgammaR knockout mice to investigate the relative roles of CD8+ T cells and Ab in protective immunity induced by TCR-KLH immunization. We found that CD8+ T cells are not required for tumor protection, although they may contribute to protection. Vaccine-induced Abs are sufficient to mediate protection against this murine T cell lymphoma through an FcR-dependent mechanism. This was confirmed with Ab transfers, which protect challenged mice. Additionally, recombinase-activating gene 1(-/-) splenocytes can mediate Ab-dependent cellular cytotoxicity against this tumor in the presence of bound anti-TCR Abs. IFN-gamma knockout mice demonstrated a requirement for IFN-gamma, probably via generation of IgG2c Abs, in vaccine-induced tumor protection. IFN-gamma knockout mice were not protected by immunization and had a severe impairment in IgG2c Ab production in response to immunization. Although mock-depleted anti-TCR Abs could transfer tumor protection, IgG2c-deficient anti-TCR Abs were unable to transfer tumor protection to wild-type mice. These results suggest that TCR-KLH vaccine-induced tumor protection in the C6VL system is primarily attributable to the induction of IgG2c Abs and humoral immunity.     

Inclusive fitness of 'kissing cousins': new evidence of a role for kin selection in the evolution of extra-pair mating in birds

Social monogamy is nearly ubiquitous across avian taxa,but evidence from a proliferation of studies utilizing molecular paternity analysis suggests that sexual monogamy is the rare exception rather than the rule (Griffith et al. 2002). Efforts to explain the prevalence of extra-pair paternity (EPP) have largely focused on the potential fitness benefits for offspring genetic quality, as females are less likely to benefit directly from seeking extra-pair mates. In particular, there has been considerable interest in the degree to which EPP may represent an adaptive female strategy to avoid inbreeding (or outbreeding)depression when paired with a highly related (or unrelated)social mate (Kempenaers 2007). Others have argued that, because relatives share many genes identical by descent,females might increase their own inclusive fitness by providing additional breeding opportunities to genetically related males (Waser et al. 1986; Kokko & Ots 2006). Thus, in the absence of significant inbreeding depression, pursuing EPP with relatives should be favoured by kin selection, although there exist few unambiguous empirical examples of such preferences in the literature. In this issue of Molecular Ecology, Wang &Lu (2011) present an analysis of mating patterns with respect to genetic relatedness of social and extra-pair partners in the ground tit (Parus humilis), a facultative cooperative breeder in which socially monogamous pairs occasionally form cooperative groups with unpaired helper males (Fig. 1). Consistent with the predictions of the kin-selection hypothesis, females in both bi-parental and cooperative groups preferentially engaged in extra-pair matings with relatives, irrespective of relatedness to their social mates, and while suffering no apparent costs of inbreeding depression in their progeny. These finding shave several exciting implications for our understanding of avian mating system diversity and the evolution of cooperative breeding.     

Mhc diversity in two passerine birds: no evidence for a minimal essential Mhc

Humans express an array of Mhc genes, while the chicken has an Mhc that is relatively small and compact with fewer expressed genes. Here we ask whether the "minimal essential Mhc" of the chicken is representative for birds. We investigated the RFLP genotypes in 55 great reed warblers Acrocephalus arundinaceus and 10 willow warblers Phylloscopus trochilus to obtain an overview of the number of class II B genes. There were 13-17 bands per individual in the great reed warblers and 25-30 in the willow warblers, and every individual had a unique RFLP genotype. The high number of RFLP bands indicates that both species have a large number of class II B genes although some may be pseudogenes. Seven different class II B sequences were detected in a great reed warbler cDNA library. There was considerable sequence divergence between the cDNA sequences in exon 2 (peptide-binding region, PBR), whereas they were very similar in exon 3. The cDNA sequences were easily alignable to a classical chicken class II B sequence, and balancing selection was acting in the PBR. One of the cDNA sequences had two deletions and is likely nonfunctional. Finally, the polymorphic class I and class II B RFLP fragments seemed to be linked in the five studied great reed warbler families. These and previous results suggest that birds of the order Passeriformes in general have more Mhc class I and II B genes than birds of the order Galliformes. This difference could be caused by their phylogenetic past, and/or by variance in the selection pressure for maintaining a high number of Mhc genes.     

Expression of a beta 1-related integrin by oligodendroglia in primary culture: evidence for a functional role in myelination

We have investigated the expression of integrins by rat oligodendroglia grown in primary culture and the functional role of these proteins in myelinogenesis. Immunochemical analysis, using antibodies to a number of alpha and beta integrin subunits, revealed that oligodendrocytes express only one detectable integrin receptor complex (alpha OL beta OL). This complex is immunoprecipitated by a polyclonal anti-human beta 1 integrin subunit antibody. In contrast, astrocytes, the other major glial cell type in brain, express multiple integrins including alpha 1 beta 1, alpha 3 beta 1, and alpha 5 beta 1 complexes that are immunologically and electrophoretically indistinguishable from integrins expressed by rat fibroblasts. The beta subunit of the oligodendrocyte integrin (beta OL) and rat fibroblast beta 1 have different electrophoretic mobilities in SDS-PAGE. However, the two beta subunits appear to be highly related based on immunological cross- reactivity and one-dimensional peptide mapping. After removal of N- linked carbohydrate chains, beta OL and beta 1 comigrated in SDS-PAGE and peptide maps of the two deglycosylated subunits were identical, suggesting differential glycosylation of beta 1 and beta OL accounts entirely for their size differences. The oligodendrocyte alpha subunit, alpha OL, was not immunoprecipitated by antibodies against well characterized alpha chains which are known to associate with beta 1 (alpha 3, alpha 4, and alpha 5). However, an antibody to alpha 8, a more recently identified integrin subunit, did precipitate two integrin subunits with electrophoretic mobilities in SDS-PAGE identical to alpha OL and beta OL. Functional studies indicated that disruption of oligodendrocyte adhesion to a glial-derived matrix by an RGD-containing synthetic peptide resulted in a substantial decrease in the level of mRNAs for several myelin components including myelin basic protein (MBP), proteolipid protein (PLP), and cyclic nucleotide phosphodiesterase (CNP). These results suggest that integrin-mediated adhesion of oligodendrocytes may trigger signal(s) that induce the expression of myelin genes and thus influence oligodendrocyte differentiation.     

Exercise hyperpnea in chronic heart failure: relationships to lung stiffness and expiratory flow limitation.

The changes in breathing pattern and lung mechanics in response to incremental exercise were compared in 14 subjects with chronic heart failure and 15 normal subjects. In chronic heart failure subjects, exercise hyperpnea was achieved by increasing breathing frequency more than tidal volume. The rate of increase in breathing frequency with carbon dioxide output was inversely correlated (r = -0.61, P < 0.05) with dynamic lung compliance measured at rest, but not with static lung compliance either at rest or at maximum exercise. Although decrease in expiratory flow reserve near functional residual capacity in chronic heart failure occurred earlier with exercise than in the normal subjects (P < 0.01), it was not correlated with changes in breathing pattern or occurrence of tachypnea. Tachypnea was achieved in chronic heart failure subjects with an increase in duty cycle because of a greater than normal decrease in expiratory time with exercise. We conclude that in chronic heart failure preexisting increase in lung stiffness plays a significant role in causing tachypnea during exercise. The results of the present study do not support the hypothesis that dynamic compression of the airways downstream from the flow-limiting segment occurring during exercise contributes to hyperpnea.     

Remarkable new evidence for island radiation in birds

If island biogeography has a sweet spot, it's where islands generate their own species diversity rather than merely taking on mainland immigrants. In birds and other highly dispersive taxa, however, this 'zone of radiation', may be vanishingly small. Darwin's finches and Hawaiian Honeycreepers are among only a handful of examples of island radiation in birds (Price 2008), suggesting that winged powers of dispersal make sufficient isolation from mainland colonists unlikely, while also hindering speciation within and among isolated islands. Nevertheless, two studies in this issue of Molecular Ecology join a string of other recent analyses suggesting that island radiation in birds remains under-appreciated (see also Moyle et al. 2009; Kisel & Barraclough 2010; Rosindell & Phillimore 2011). Melo et al. (2011) use a phylogenetic analysis of white-eyes on islands in the Gulf of Guinea to identify two previously overlooked island radiations, and reveal replicated adaptive divergence on islands where species occur in pairs. Sly et al. (2011), meanwhile, consider possible explanations for speciation and geographic differentiation within a large island, and find the same type of oceanic barriers that are critical to bird speciation across archipelagos may also contribute to divergence that appears to have occurred within a single island.     

Little evidence for sympatric speciation in island birds

It has been suggested that the presence of sister species in small circumscribed areas, such as isolated lakes or islands, might imply that these species originated sympatrically. To investigate this possibility in birds, we searched for endemic, congeneric species on isolated islands in the ocean. Among 46 islands and small archipelagos chosen because they contain at least one species of endemic land bird, we identified seven pairs of endemic congeners (excluding flightless rails). Of these seven, only four pairs are potentially sister species and thus possible candidates for sympatric speciation. However, three of these four pairs have always been considered the results of double invasion from a mainland source (in two of these cases, molecular-phylogenetic work has either confirmed a double invasion or is ambiguous). The one remaining pair may have speciated allopatrically on a small archipelago. Additional phylogenetic studies are required to understand these cases, and our results should also be considered in light of the large number of island-bird extinctions in historic time. We conclude that, at present, there is little evidence for sympatric speciation in island birds.     

Yeast actin-binding proteins: evidence for a role in morphogenesis

Three yeast actin-binding proteins were identified using yeast actin filaments as an affinity matrix. One protein appears to be a yeast myosin heavy chain; it is dissociated from actin filaments by ATP, it is similar in size (200 kD) to other myosins, and antibodies directed against Dictyostelium myosin heavy chain bind to it. Immunofluorescence experiments show that a second actin-binding protein (67 kD) colocalizes in vivo with both cytoplasmic actin cables and cortical actin patches, the only identifiable actin structures in yeast. The cortical actin patches are concentrated at growing surfaces of the yeast cell where they might play a role in membrane and cell wall insertion, and the third actin-binding protein (85 kD) is only detected in association with these structures. This 85-kD protein is therefore a candidate for a determinant of growth sites. The in vivo role of this protein was tested by overproduction; this overproduction causes a reorganization of the actin cytoskeleton which in turn dramatically affects the budding pattern and spatial growth organization of the yeast cell.     

In vivo evidence against a role for adenosine in the exercise pressor reflex in humans.

The pressor response to exercise is of great importance in both physiology and pathophysiology. Whether endogenous adenosine is a trigger for this reflex remains controversial. Muscle interstitial adenosine concentration can be determined by microdialysis. However, there are indications that local muscle cell damage by the microdialysis probe confounds these measurements in exercising muscle. Therefore, we used the nucleoside uptake inhibitor dipyridamole as pharmacological tool to bypass this confounding. We used microdialysis probes to measure endogenous adenosine in forearm skeletal muscle of healthy volunteers during two cycles of 15 min of intermittent isometric handgripping. During the second contraction, dipyridamole (12 microg.min(-1).dl forearm(-1)) was administered into the brachial artery. Dipyridamole potentiated the exercise-induced increase in dialysate adenosine from 0.30 +/- 0.08 to 0.48 +/- 0.10 micromol/l (n = 9, P < 0.05), but it did not potentiate the exercise-induced increase in blood pressure. A time-control study without dipyridamole revealed no difference in exercise-induced increase in adenosine between both contractions (n = 8). To exclude the possibility that the dipyridamole-induced increase in dialysate adenosine originates from extravasation of increased circulating adenosine, we simultaneously measured adenosine with microdialysis probes in forearm muscle and antecubital vein. In a separate group of nine volunteers, simultaneous intrabrachial infusion of 100 microg.min(-1).dl(-1) dipyridamole and 5 microg.min(-1).dl(-1) adenosine increased dialysate adenosine from the intravenous but not the interstitial probe, indicating preserved endothelial barrier function for adenosine. We conclude that dipyridamole significantly inhibits uptake of interstitial adenosine without affecting the pressor response to exercise, suggesting that interstitial adenosine is not involved in the pressor response to rhythmic isometric exercise.     

Tarsal development in birds: evidence for homology with the theropod condition

Theropod dinosaurs and birds share a specialized ankle joint in which the proximal tarsal series. the astragalus and calcaneum is braced against the tibia by an ascending process. This feature has been used since T. H. Huxley's time (1870) to support the proposal that birds evolved from dinosaurs. However, according to Martin, Stewart & Whetstone (1980), the avian tarsus is not homologous with that of theropods. They argue that while the ascending process in theropods is continuous with the astragalus in Archaeopteryx and all later birds, it is an independent ossification associated primarily with the calcaneum. A preliminary study of tarsal ontogeny in birds (McGowan, 1984), undertaken to resolve this problem, revealed two developmental pathways, one exemplified in ratites and the other in carinates. The ratite condition corresponded to that of theropods, the bony ascending process being part of the astragalus, while in carinates the corresponding process was part of the calcaneum. The present study, based on more extensive material, reveals that, although the carinate process becomes associated with the calcaneum during later development, there is evidence that it originates as a cartilaginous process from the astragalus and is therefore homologous with the ratite condition. As the avian tarsus is homologous with that of theropods, and of Archaeopteryx , it may be used to support a close phylogenetic relationship among them.