Ecological Controls on the Evolutionary Recovery of Post-Paleozoic Crinoids

Why does pollen morphology vary? Evolutionary dynamics and morphospace occupation in the largest angiosperm order (Asterales)

Morphological diversity (disparity) is a key component of biodiversity and increasingly a focus of botanical research. Despite the wide range of morphologies represented by pollen grains, to date there are few studies focused on the controls on pollen disparity and morphospace occupation, and fewer still considering these parameters in a phylogenetic framework. Here, we analyse morphospace occupation, disparity and rates of morphological evolution in Asterales pollen, in a phylogenetic context. We use a dataset comprising 113 taxa from across the Asterales phylogeny, with pollen morphology described using 28 discrete characters. The Asterales pollen morphospace is phylogenetically structured around groups of related taxa, consistent with punctuated bursts of morphological evolution at key points in the Asterales phylogeny. There is no substantial difference in disparity among these groups of taxa, despite large differences in species richness and biogeographic range. There is also mixed evidence for whole-genome duplication as a driver of Asterales pollen morphological evolution. Our results highlight the importance of evolutionary history for structuring pollen morphospace. Our study is consistent with others that have shown a decoupling of biodiversity parameters, and reinforces the need to focus on disparity as a key botanical metric in its own right.

Shared patterns in body size declines among crinoids during the Palaeozoic extinction events

Crinoids were among the most abundant marine benthic animals throughout the Palaeozoic, but their body size evolution has received little attention. Here, we compiled a comprehensive database on crinoid calyx biovolumes throughout the Palaeozoic. A model comparison approach revealed contrasting and complex patterns in body size dynamics between the two major crinoid clades (Camerata and Pentacrinoidea). Interestingly, two major drops in mean body size at around two mass extinction events (during the late Ordovician and the late Devonian respectively) are observed, which is reminiscent of current patterns of shrinking body size of a wide range of organisms as a result of climate change. The context of some trends (marked declines during extinctions) suggests the cardinal role of abiotic factors (dramatic climate change associated with extinctions) on crinoid body size evolution; however, other patterns (two intervals with either relative stability or steady size increase in periods between mass extinctions) are more consistent with biotic drivers.

Selectivity and the effect of mass extinctions on disparity and functional ecology

Selectivity of mass extinctions is thought to play a major role in coupling or decoupling of taxonomic, morphological, and ecological diversity, yet these measures have never been jointly evaluated within a single clade over multiple mass extinctions. We investigate extinction selectivity and changes in taxonomic diversity, morphological disparity, and functional ecology over the ~160-million-year evolutionary history of diplobathrid crinoids (Echinodermata), which spans two mass extinctions. Whereas previous studies documented extinction selectivity for crinoids during background extinction, we find no evidence for selectivity during mass extinctions. Despite no evidence for extinction selectivity, disparity remains strongly correlated with richness over extinction events, contradicting expected patterns of disparity given nonselective extinction. Results indicate that (i) disparity and richness can remain coupled across extinctions even when selective extinction does not occur, (ii) simultaneous decreases in taxonomic diversity and disparity are insufficient evidence for extinction selectivity, and (iii) selectivity differs between background and mass extinction regimes.

Species richness and disparity of parareptiles across the end-Permian mass extinction

The amniote clade Parareptilia is notable in that members of the clade exhibited a wide array of morphologies, were successful in a variety of ecological niches and survived the end-Permian mass extinction. In order to better understand how mass extinction events can affect clades that survive them, we investigate both the species richness and morphological diversity (disparity) of parareptiles over the course of their history. Furthermore, we examine our observations in the context of other metazoan clades, in order to identify post-extinction survivorship patterns that are present in the clade. The results of our study indicate that there was an early increase in parareptilian disparity, which then fluctuated over the course of the Permian, before it eventually declined sharply towards the end of the Permian and into the Triassic, corresponding with the end-Permian mass extinction event. Interestingly, this is a different trend to what is observed regarding parareptile richness, that shows an almost continuous increase until its overall peak at the end of the Late Permian. Moreover, richness did not experience the same sharp drop at the end of the Permian, reaching a plateau until the Anisian, before dropping sharply and remaining low, with the clade going extinct at the end of the Triassic. This observed pattern is likely to be due to the fact that, despite the extinction of several morphologically distinct parareptile clades, the procolophonoids, one of the largest parareptilian clades, were diversifying across the Permian-Triassic boundary. With the clade's low levels of disparity and eventually declining species richness, this pattern most resembles a 'dead clade walking' pattern.

Early bursts of disparity and the reorganization of character integration

'Early bursts' of morphological disparity (i.e. diversity of anatomical types) are common in the fossil record. We typically model such bursts as elevated early rates of independent character change. Developmental theory predicts that modules of linked characters can change together, which would mimic the effects of elevated independent rates on disparity. However, correlated change introducing suboptimal states should encourage breakup (parcellation) of character suites allowing new (or primitive) states to evolve until new suites arise (relinkage). Thus, correlated change-breakup-relinkage presents mechanisms for early bursts followed by constrained evolution. Here, I analyse disparity in 257 published character matrices of fossil taxa. For each clade, I use inverse-modelling to infer most probably rates of independent change given both time-homogeneous and separate 'early versus late' rates. These rates are used to estimate expected disparity given both independent change models. The correlated change-breakup-relinkage model also predicts elevated frequencies of compatible character state-pairs appearing out of order in the fossil record (e.g. 01 appearing after 00 and 11; = low stratigraphic compatibility), as one solution to suboptimal states induced by correlated change is a return to states held before that change. As predicted by the correlated change-breakup-relinkage model, early disparity in the majority of clades both exceeds the expectations of either independent change model and excess early disparity correlates with low stratigraphic compatibility among character-pairs. Although it is possible that other mechanisms for linking characters contribute to these patterns, these results corroborate the idea that reorganization of developmental linkages is often associated with the origin of groups that biologists recognize as new higher taxa and that such reorganization offers a source of new disparity throughout the Phanerozoic.

Morphospace saturation in the stem-gnathostomes pteraspidiformes heterostracans: an early radiation of a 'bottom' heavy clade

Ostracoderms (fossil armoured jawless fishes) shed light on early vertebrate evolution by revealing the step-wise acquisition of jawed vertebrate characters, and were important constituents of Middle Palaeozoic vertebrate faunas. A wide variety of head shield shapes are observed within and between the ostracoderm groups, but the timing of these diversifications and the consistency between different measures of their morphospace are unclear. Here, we present the first disparity (explored morphospace) versus diversity (number of taxa) analysis of Pteraspidiformes heterostracans using continuous and discrete characters. Patterns of taxic diversity and morphological disparity are in accordance: they both show a rise to a peak in the Lochkovian followed by a gradual decline in the Middle-Late Devonian. Patterns are largely consistent for disparity measures using sum of ranges or total variance, and when using continuous or discrete characters. Pteraspidiformes heterostracans can be classified as a "bottom-heavy clade", i.e., a group where a high initial disparity decreasing over time is detected. In fact, the group explored morphospace early in its evolutionary history, with much of the subsequent variation in dermal armour occurring as variation in the proportions of already evolved anatomical features. This Early Devonian radiation is also in agreement with the paleobiogeographic distribution of the group, with a maximum of dispersal and explored morphospace during the Lochkovian and Pragian time bins.

Phenotypic Innovation and Adaptive Constraints in the Evolutionary Radiation of Palaeozoic Crinoids

To better understand the patterns and processes shaping large-scale phenotypic diversification, I integrate palaeobiological and phylogenetic perspectives to investigate a ~200-million-year radiation using a global sample of Palaeozoic crinoid echinoderms. Results indicate the early history of crinoid diversification is characterized by early burst dynamics with decelerating morphologic rates. However, in contrast with expectation for a single “early burst” model, morphospace continued to expand following a slowdown in rates. In addition, I find evidence for an isolated peak in morphologic rates occurring late in the clade’s history. This episode of elevated rates is not associated with increased disparity, morphologic novelty, or the radiation of a single subclade. Instead, this episode of elevated rates involved multiple subclade radiations driven by environmental change toward a pre-existing adaptive optimum. The decoupling of morphologic disparity with rates of change suggests phenotypic rates are primarily shaped by ecologic factors rather than the origination of morphologic novelty alone. These results suggest phenotypic diversification is far more complex than models commonly assumed in comparative biology. Furthermore, palaeontological disparity patterns are not a reliable proxy for rates after an initial diversifying phase. These issues highlight the need for continued synthesis between fossil and phylogenetic approaches to macroevolution.

Beyond the Big Five: Extinctions as Experiments in the History of Life

The past century has witnessed a number of significant breakthroughs in the study of extinction in the fossil record, from the discovery of a bolide impact as the probable cause of the end-Cretaceous (K/T) mass extinction to the designation of the “Big 5” mass extinction events. Here, I summarize the major themes that have emerged from the past thirty years of extinction research and highlight a number of promising directions for future research. These directions explore a central theme—the evolutionary consequences of extinction— and focus on three broad research areas: the effects of selectivity, the importance of recovery intervals, and the influence of spatial patterns. Examples of topics explored include the role that trait variation plays in survivorship, the comparative effects of extinctions of varying magnitudes on evolutionary patterns, the re-establishment of macroevolutionary patterns in the aftermath of extinction, and the extent to which spatial autocorrelation affects extinction patterns. These topics can be approached by viewing extinctions as repeated natural experiments in the history of life and developing hypotheses to explicitly test across multiple events. Exploring the effects of extinction also requires an interdisciplinary approach, applying evolutionary, ecological, geochronological, geochemical, tectonic, and paleoclimatic tools to both extinction and recovery intervals.

MORPHOLOGICAL DIVERSIFICATION AND ADAPTIVE RADIATION: A COMPARISON OF TWO DIVERSE LIZARD CLADES

We compared the morphological diversity (i.e., the amount of morphological space occupied) of two similar clades, the lizard genera Anolis and Sceloporus. These species-rich monophyletic clades are similar in body size, age of origin, and many aspects of their natural history. We examined a number of morphological traits whose variation is likely to represent adaptation to different aspects of the environment, including body size, limb proportions, head dimensions, and tail length. Examination of the position of species in multidimensional space, based on a principal components analysis, indicates that the morphological diversity of Anolis, which we refer to as disparity, is significantly greater than that of Sceloporus. One potential explanation for this pattern is that morphological diversification in Anolis was facilitated by the evolution of subdigital toe-pads, which allow anoles to use the environment in ways not available to Sceloporus. The geographic location of diversification (tropical and subtropical for Anolis, arid for Sceloporus) may also have been important.

What limits the morphological disparity of clades?

The morphological disparity of species within major clades shows a variety of trajectory patterns through evolutionary time. However, there is a significant tendency for groups to reach their maximum disparity relatively early in their histories, even while their species richness or diversity is comparatively low. This pattern of early high-disparity suggests that there are internal constraints (e.g. developmental pleiotropy) or external restrictions (e.g. ecological competition) upon the variety of morphologies that can subsequently evolve. It has also been demonstrated that the rate of evolution of new character states decreases in most clades through time (character saturation), as does the rate of origination of novel bodyplans and higher taxa. Here, we tested whether there was a simple relationship between the level or rate of character state exhaustion and the shape of a clade's disparity profile: specifically, its centre of gravity (CG). In a sample of 93 extinct major clades, most showed some degree of exhaustion, but all continued to evolve new states up until their extinction. Projection of states/steps curves suggested that clades realized an average of 60% of their inferred maximum numbers of states. Despite a weak but significant correlation between overall levels of homoplasy and the CG of clade disparity profiles, there were no significant relationships between any of our indices of exhaustion curve shape and the clade disparity CG. Clades showing early high-disparity were no more likely to have early character saturation than those with maximum disparity late in their evolution.

Trait-based diversification shifts reflect differential extinction among fossil taxa

Evolution provides many cases of apparent shifts in diversification associated with particular anatomical traits. Three general models connect these patterns to anatomical evolution: (i) elevated net extinction of taxa bearing particular traits, (ii) elevated net speciation of taxa bearing particular traits, and (iii) elevated evolvability expanding the range of anatomies available to some species. Trait-based diversification shifts predict elevated hierarchical stratigraphic compatibility (i.e., primitive→derived→highly derived sequences) among pairs of anatomical characters. The three specific models further predict (i) early loss of diversity for taxa retaining primitive conditions (elevated net extinction), (ii) increased diversification among later members of a clade (elevated net speciation), and (iii) increased disparity among later members in a clade (elevated evolvability). Analyses of 319 anatomical and stratigraphic datasets for fossil species and genera show that hierarchical stratigraphic compatibility exceeds the expectations of trait-independent diversification in the vast majority of cases, which was expected if trait-dependent diversification shifts are common. Excess hierarchical stratigraphic compatibility correlates with early loss of diversity for groups retaining primitive conditions rather than delayed bursts of diversity or disparity across entire clades. Cambrian clades (predominantly trilobites) alone fit null expectations well. However, it is not clear whether evolution was unusual among Cambrian taxa or only early trilobites. At least among post-Cambrian taxa, these results implicate models, such as competition and extinction selectivity/resistance, as major drivers of trait-based diversification shifts at the species and genus levels while contradicting the predictions of elevated net speciation and elevated evolvability models.

On the relationship between the macroevolutionary trajectories of morphological integration and morphological disparity

How does the organization of phenotypes relate to their propensity to vary? How do evolutionary changes in this organization affect large-scale phenotypic evolution? Over the last decade, studies of morphological integration and modularity have renewed our understanding of the organizational and variational properties of complex phenotypes. Much effort has been made to unravel the connections among the genetic, developmental, and functional contexts leading to differential integration among morphological traits and individuation of variational modules. Yet, their macroevolutionary consequences on the dynamics of morphological disparity-the large-scale variety of organismal designs-are still largely unknown. Here, I investigate the relationship between morphological integration and morphological disparity throughout the entire evolutionary history of crinoids (echinoderms). Quantitative analyses of interspecific patterns of variation and covariation among characters describing the stem, cup, arm, and tegmen of the crinoid body do not show any significant concordance between the temporal trajectories of disparity and overall integration. Nevertheless, the results reveal marked differences in the patterns of integration for Palaeozoic and post-Palaeozoic crinoids. Post-Palaeozoic crinoids have a higher degree of integration and occupy a different region of the space of integration patterns, corresponding to more heterogeneously structured matrices of correlation among traits. Particularly, increased covariation is observed between subsets of characters from the dorsal cup and from the arms. These analyses show that morphological disparity is not dependent on the overall degree of evolutionary integration but rather on the way integration is distributed among traits. Hence, temporal changes in disparity dynamics are likely constrained by reorganizations of the modularity of the crinoid morphology and not by changes in the variability of individual traits. The differences in integration patterns explain the more stereotyped morphologies of post-Palaeozoic crinoids and, from a broader macroevolutionary perspective, call for a greater attention to the distributional heterogeneities of constraints in morphospace.

The evolutionary diversification of seed size: using the past to understand the present

The Devonian origin of seed plants and subsequent morphological diversification of seeds during the late Paleozoic represents an adaptive radiation into unoccupied ecological niche space. A plant's seed size is correlated with its life-history strategy, growth form, and seed dispersal syndrome. The fossil record indicates that the oldest seed plants had relatively small seeds, but the Mississippian seed size envelope increased significantly with the diversification of larger seeded lineages. Fossil seeds equivalent to the largest extant gymnosperm seeds appeared by the Pennsylvanian, concurrent with morphological diversification of growth forms and dispersal syndromes as well as the clade's radiation into new environments. Wang's Analysis of Skewness indicates that the evolutionary trend of increasing seed size resulted from primarily passive processes in Pennsylvanian seed plants. The distributions of modern angiosperms indicate a more diverse system of active and some passive processes, unbounded by Paleozoic limits; multiple angiosperm lineages independently evolved though the upper and lower bounds. Quantitative measures of preservation suggest that, although our knowledge of Paleozoic seeds is far from complete, the evolutionary trend in seed size is unlikely to be an artifact of taphonomy.

The role of the LAT-PLC-gamma1 interaction in T regulatory cell function

The interaction between the linker for activation of T cells (LAT) with PLC-gamma1 is important for TCR-mediated Ca(2+) signaling and MAPK activation. Knock-in mice harboring a mutation at the PLC-gamma1 binding site (Y136) of LAT develop a severe lymphoproliferative syndrome. These mice have defective thymic development and selection and lack natural regulatory T cells, implicating a breakdown of both central and peripheral tolerance. To bypass this developmental defect, we developed a conditional knock-in line in which only LATY136F is expressed in mature T cells after deletion of the wild type LAT allele. Analysis of LATY136F T cells indicated that the interaction between LAT and PLC-gamma1 plays an important role in TCR-mediated signaling, proliferation, and IL-2 production. Furthermore, the deletion of LAT induced development of the lymphoproliferative syndrome in these mice. Although Foxp3(+) natural Treg cells were present in these mice after deletion, they were unable to suppress the proliferation of conventional T cells. Our data indicate that the binding of LAT to PLC-gamma1 is essential for the suppressive function of CD4(+)CD25(+) regulatory T cells.

Selective press extinctions, but not random pulse extinctions, cause delayed ecological recovery in communities of digital organisms

A key issue concerning recovery from mass extinctions is how extinction and diversification mechanisms affect the recovery process. We evolved communities of digital organisms, subjecting them to instantaneous "pulse" extinctions, choosing survivors at random, or to prolonged "pulse" extinctions involving a period of low resource availability. Functional activity at low trophic levels recovered faster than at higher levels, with the most extensive delays seen at the top level. Postpress communities generally did not fully recover functional activity in the allotted time, which equaled that of their original diversification. We measured recovery of phenotypic diversity, observing considerable variation in outcomes. Communities subjected to pulse extinctions recovered functional activity and phenotypic diversity substantially faster than when subjected to press extinctions. Follow-up experiments tested whether organisms with shorter generation times and low functional activity contributed to delayed recovery after press extinctions. The results indicate that adaptation during the press episode degraded the organisms' ability to re-evolve preextinction functionality. There are interesting parallels with patterns from the paleontological record. We suggest that some delayed recoveries from mass extinction may reflect the need to both re-evolve biological functions and reconstruct ecological interactions lost during the extinction. Adaptation to conditions during an extended disturbance may hinder subsequent recovery.

IP3 receptor-mediated Ca2+ release in naive CD4 T cells dictates their cytokine program

IP(3) (inositol 1,4,5-trisphosphate) receptors (IP(3)Rs) regulate the release of Ca(2+) from intracellular stores in response to IP(3). Little is known about regulation of the expression of IP(3)Rs and their role during the activation of CD4 T cells. In this study we show that mouse naive CD4 T cells express IP(3)R1, IP(3)R2, and IP(3)R3, but that gene expression of IP(3)R3 primarily is down-regulated upon activation due to loss of the Ets-1 transcription factor. Down-regulation of IP(3)R expression in activated CD4 T cells is associated with the failure of TCR ligation to trigger Ca(2+) release in these cells. We also show that down-regulation of specific IP(3)Rs in activated CD4 T cells correlates with the requirement of IP(3)R-mediated Ca(2+) release only for the induction of, but not for the maintenance of, IL-2 and IFN-gamma expression. Interestingly, while inhibition of IP(3)R function early during activation blocks IL-2 and IFN-gamma production, it promotes the production of IL-17 by CD4 T cells. Thus, IP(3)Rs play a key role in the activation and differentiation of CD4 T cells. The immunosuppressive effect of pharmacological blockers of these receptors may be complicated by promoting the development of inflammatory CD4 T cells.

Density-dependent diversification in North American wood warblers

Evidence from both molecular phylogenies and the fossil record suggests that rates of species diversification often decline through time during evolutionary radiations. One proposed explanation for this pattern is ecological opportunity, whereby an initial abundance of resources and lack of potential competitors facilitate rapid diversification. This model predicts density-dependent declines in diversification rates, but has not been formally tested in any species-level radiation. Here we develop a new conceptual framework that distinguishes density dependence from alternative processes that also produce temporally declining diversification, and we demonstrate this approach using a new phylogeny of North American Dendroica wood warblers. We show that explosive lineage accumulation early in the history of this avian radiation is best explained by a density-dependent diversification process. Our results suggest that the tempo of wood warbler diversification was mediated by ecological interactions among species and that lineage and ecological diversification in this group are coupled, as predicted under the ecological opportunity model.

Evolutionary patterns in early tetrapods. II. Differing constraints on available character space among clades

Radiations of large clades often accompany rapid morphological diversification. Evolutionary biologists debate the impact of external restrictions imposed by ecology, and intrinsic constraints imposed by development and genetics, on the rate at which morphological innovations are gained. These issues are particularly interesting for groups such as tetrapods, which evolved novel body plans relative to their piscine ancestors and which also invaded new ecosystems following terrestrialization. Prior studies have addressed these issues by looking at either ranges of morphological variation or rates of character change. Here, we address a related but distinct issue: the numbers of characters that freely vary within a clade. We modify techniques similar to those used by ecologists to infer species richnesses to estimate the number of potentially varying characters given the distributions of changes implied by a model phylogeny. Our results suggest both increasing constraints/restrictions and episodes of 'character release' (i.e. increasing the number of potentially varying characters). In particular, we show that stem lissamphibians had a restricted character space relative to that of stem amniotes, and that stem amniotes both had restrictions on some parts of character space but also invaded new character space that had been unavailable to stem tetrapods.

Cdc2/Cyclin B1 Interacts with and Modulates Inositol 1,4,5-Trisphosphate Receptor (Type 1) Functions

The resistance of inositol 1,4,5-trisphosphate receptor (IP3R)-deficient cells to multiple forms of apoptosis demonstrates the importance of IP3-gated calcium (Ca2+) release to cellular apoptosis. However, the specific upstream biochemical events leading to IP3-gated Ca2+ release during apoptosis induction are not known. We have shown previously that the cyclin-dependent kinase 1/cyclin B (cdk1/CyB or cdc2/CyB) complex phosphorylates IP3R1 in vitro and in vivo at Ser421 and Thr799. In this study, we show that: 1) the cdc2/CyB complex directly interacts with IP3R1 through Arg391, Arg441, and Arg871; 2) IP3R1 phosphorylation at Thr799 by the cdc2/CyB complex increases IP3 binding; and 3) cdc2/CyB phosphorylation increases IP3-gated Ca2+ release. Taken together, these results demonstrate that cdc2/CyB phosphorylation positively regulates IP3-gated Ca2+ signaling. In addition, identification of a CyB docking site(s) on IP3R1 demonstrates, for the first time, a direct interaction between a cell cycle component and an intracellular calcium release channel. Blocking this phosphorylation event with a specific peptide inhibitor(s) may constitute a new therapy for the treatment of several human immune disorders.

Naive CD4+ T Cells from Lupus-Prone Fas-Intact MRL Mice Display TCR-Mediated Hyperproliferation Due to Intrinsic Threshold Defects in Activation

Autoreactive T cell activation is a consistent feature of murine lupus; however, the mechanism of such activation remains unclear. We hypothesized that naive CD4+ T cells in lupus have a lower threshold of activation through their TCR-CD3 complex that renders them more susceptible to stimulation with self-Ags. To test this hypothesis, we compared proliferation, IL-2 production, and single cell calcium signaling of naive CD4+ T cells isolated from Fas-intact MRL/+(Fas-lpr) mice with H-2k-matched B10.BR and CBA/CaJ controls, following anti-CD3 stimulation in the presence or absence of anti-CD28. We also assessed the responsiveness of naive CD4+ T cells isolated from Fas-intact MRL and control mice bearing a rearranged TCR specific for amino acids 88-104 of pigeon cytochrome c to cognate and low affinity peptide Ags presented by bone marrow-matured dendritic cells. TCR transgenic and wild-type CD4+ T cells from MRL mice displayed a lower threshold of activation than control cells, a response that was class II MHC dependent. The rise in intracellular calcium in MRL vs controls was enhanced and prolonged following anti-CD3 triggering, suggestive of proximal defects in TCR-engendered signaling as the mechanism for the observed hyperactivity. These findings were observed as early as 1-2 mo postweaning and, based on analysis of F1 T cells, appeared to be dominantly expressed. This genetically altered threshold for activation of MRL T cells, a consequence of a proximal defect in CD3-mediated signal transduction, may contribute to the abrogation of T cell tolerance to self-Ags in lupus.

Mechanism of bradykinin-induced Ca2+ mobilization in murine proximal tubule epithelial cells

Despite the recognized physiological role of bradykinin (BK) in the kidney in maintaining glomerular and tubule function and its role in pathological states such as endotoxemia, diabetes, and other diseases, relatively little is known about the mechanisms by which BK can impact kidney function. Furthermore, the signaling of BK receptors in the murine nephron has not been fully characterized. The present studies were undertaken to examine BK-stimulated Ca(2+) signaling using Fura-2 in the murine proximal tubule epithelial cell line TKPTS. BK produced a concentration-dependent rise in intracellular Ca(2+) ([Ca(2+)])(i) (pEC(50) = 8.39 +/- 0.04). Selective antagonists showed the rise in [Ca(2+)](i) was mediated through B2 receptors. The rise in [Ca(2+)](i) was rapid and reversible and was maximally stimulated at 1 microM (697 +/- 70 nM above basal level of 115 +/- 6 nM). Studies with thapsigargin and EGTA showed Ca(2+) mobilization was dependent on two events: release and influx. Both U73122 (1-[6-[[17-beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione) [a phospholipase C (PLC) inhibitor] and genistein (a tyrosine kinase inhibitor) partially inhibited BK-stimulated rise in [Ca(2+)](i). When combined, both agents produced a further decrease, suggesting multiple pathways for PLC activation may be involved. The ability of Ni(2+) to inhibit influx indicated the activation of a Ca(2+) release-activated channel (CRAC). Ca(2+) mobilization did not seem to be affected by cyclic nucleotides or protein kinase C. In summary, the TKPTS murine proximal tubule cell line expresses functional B2 receptors linked to Ca(2+) mobilization that is dependent on phospholipase C and activation of CRAC.

Measuring changes in articulate brachiopod morphology before and after the Permian mass extinction event: do developmental constraints limit morphological innovation?

The pattern of decreasing disparity has been observed in both the metazoans and metaphytes throughout the Phanerozoic. The pattern is manifest as a decreasing trend in the origination of higher taxa. Currently, two competing evolutionary hypotheses have been proposed to explain this phenomenon: the empty ecospace hypothesis and the developmental constraint hypothesis. To empirically distinguish between these hypotheses, the change in disparity before and after the end-Permian mass extinction event was measured in the articulated brachiopods. The assumption is that ecospace-limiting constraints are removed after mass extinctions revealing the effect of developmental constraints. For each taxon within the group, both continuous and discrete character sets were analyzed. Four different measures of disparity were used to analyze each character suite. Additionally, a separate analysis was performed on a subset of the articulated brachiopods, the rhynchonellids and terebratulids. In most cases investigated, disparity rebounded to comparable levels, with the rhynchonellids and terebratulids showing the largest increase in disparity after the end-Permian extinction, a clear example of an increase in disparity without a significant increase in taxonomic diversity. The results indicate that developmental constraints may not be responsible for the decreasing disparity in this group. The more likely scenario is that increasingly structured ecological guilds have made it much more difficult for large increases in disparity to occur.

Increased endothelin-induced Ca2+ signaling, tyrosine phosphorylation, and coronary artery disease in diabetic dyslipidemic Swine are prevented by atorvastatin

Endothelin-1 (ET-1) signaling mechanisms have been implicated in the pathogenesis of excess coronary artery disease in diabetic dyslipidemia. We hypothesized that in diabetic dyslipidemia ET-1-induced coronary smooth muscle calcium (Ca2+m) and tyrosine phosphorylation would be increased, and the lipid lowering agent, atorvastatin, would inhibit these increases. Male Yucatan miniature swine groups were treated for 20 weeks: normal low-fat fed control, high-fat/cholesterol fed (hyperlipidemic), hyperlipidemic made diabetic with alloxan (diabetic dyslipidemic), and diabetic dyslipidemic treated with atorvastatin (atorvastatin-treated). Blood glucose values were 5-fold greater in diabetic dyslipidemic and atorvastatin-treated versus control and hyperlipidemic. Total and low-density lipoprotein (LDL) plasma cholesterol in hyperlipidemic, diabetic dyslipidemic, and atorvastatin-treated were approximately 5-fold greater than control. Intravascular ultrasound detectable coronary disease and hypertriglyceridemia were only observed in diabetic dyslipidemic and were abolished by atorvastatin. In freshly isolated cells, the Ca2+m response to ET-1 in diabetic dyslipidemic was greater than in control, hyperlipidemic, and atorvastatin-treated groups. Selective ET-1 receptor antagonists showed in the control group that the ETB subtype inhibits ETA regulation of Ca2+m. There was almost a complete switch of receptor subtype regulation of Ca2+m from largely ETA in control to an increased inhibitory interaction between ETA and ETB in hyperlipidemic and diabetic dyslipidemic groups, such that neither ETA nor ETB antagonist alone could block the ET-1-induced Ca2+m response. The inhibitory interaction was attenuated in the atorvastatin-treated group. In single cells, basal and ET-1-induced tyrosine phosphorylation in diabetic dyslipidemic were more than 3- and 6-fold greater, respectively, than in control, hyperlipidemic, and atorvastatin-treated. Attenuation by atorvastatin of coronary disease and ET-1-induced Ca2+m and tyrosine phosphorylation signaling with no change in cholesterol provides strong evidence for direct actions of atorvastatin and/or triglycerides on the vascular wall.

Lessons from the past: biotic recoveries from mass extinctions

Although mass extinctions probably account for the disappearance of less than 5% of all extinct species, the evolutionary opportunities they have created have had a disproportionate effect on the history of life. Theoretical considerations and simulations have suggested that the empty niches created by a mass extinction should refill rapidly after extinction ameliorates. Under logistic models, this biotic rebound should be exponential, slowing as the environmental carrying capacity is approached. Empirical studies reveal a more complex dynamic, including positive feedback and an exponential growth phase during recoveries. Far from a model of refilling ecospace, mass extinctions appear to cause a collapse of ecospace, which must be rebuilt during recovery. Other generalities include the absence of a clear correlation between the magnitude of extinction and the pace of recovery or the resulting ecological and evolutionary disruption the presence of a survival interval, with few originations, immediately after an extinction and preceding the recovery phase, and the presence of many lineages that persist through an extinction event only to disappear during the subsequent recovery. Several recoveries include numerous missing lineages, groups that are found before the extinction, then latter in the recovery, but are missing during the initial survival-recovery phase. The limited biogeographic studies of recoveries suggest considerable variability between regions.

Negative control of store-operated Ca2+ influx by B cell receptor cross-linking

An increase in the intracellular Ca(2+) concentration by B cell receptor (BCR) cross-linking plays important roles in the regulation of B cell functions. [Ca(2+)](i) is regulated by Ca(2+) release from the Ca(2+) store as well as store-operated Ca(2+) influx (SOC). Protein tyrosine kinases downstream of BCR cross-linking were shown to regulate the mechanism for Ca(2+) release. However, it remains elusive whether BCR cross-linking regulates SOC or not. In this study, we examined the effect of BCR cross-linking on thapsigargin-induced SOC in the DT40 B cells. We found that the SOC-mediated increase in intracellular Ca(2+) concentration was inhibited by BCR cross-linking. Using a membrane-potential-sensitive dye, we found that BCR cross-linking induced depolarization, which is expected to decrease the driving force of Ca(2+) influx and SOC channel conductance. When membrane potential was held constant by the transmembrane K(+) concentration gradient in the presence of valinomycin, the BCR-mediated inhibition of SOC was still observed. Thus, the BCR-mediated inhibition of SOC involves both depolarization-dependent and depolarization-independent mechanisms of SOC inhibition. The depolarization-independent inhibition of the SOC was abolished in Lyn-deficient, but not in Bruton's tyrosine kinase-, Syk- or SHIP (Src homology 2 domain containing phosphatidylinositol 5'-phosphatase)-deficient cells, indicating that Lyn is involved in the inhibition. These results show novel pathways of BCR-mediated SOC regulations.