Life Cycle Transitions Research Articles

Life cycle association of the coccolithophore Syracosphaera gaarderae comb. nov. (ex Alveosphaera bimurata): Taxonomy, ecology and evolutionary implications

Abstract The coccolithophores are an important group of marine phytoplankton bearing external calcite plates called coccoliths, and displaying complex sexual life cycles, composed of two main cell phases (haploid and diploid) that in most species can produce distinct coccolith types. Typically, diploid cells produce heterococcoliths, whereas haploid cells produce holococcoliths. An important source of evidence for the ability of coccolithophores to undergo life cycle transitions comes from observations of combination coccospheres. These combination cells bearing both hetero- and holococcoliths are interpreted as cells undertaking sexual transitions and enable linking morphologically distinct life phases, thus expanding our knowledge of coccolithophore life cycle diversity, but more widely on coccolithophore ecology and evolution. Here we report on a newly discovered life cycle in the genus Syracosphaera, linking the heterococcolithophore previously named Alveosphaera bimurata Okada & McIntyre, erroneously placed within the Calciosoleniaceae, and the holococcolithophore Poricalyptra gaarderae Borsetti & Cati, resulting in a new combination, Syracosphaera gaarderae (Borsetti & Cati) comb. nov. This life cycle association is supported by several combination coccospheres collected in the Northern Red Sea and is the first involving both the genus Poricalyptra and a Syracosphaera belonging to the lamina type subgroup. Biennial survey indicates that cells of both life cycle phases are only found during summer stratification periods and display clear depth zonation with S. gaarderae appearing in the lower photic zone and P. gaarderae in the upper photic zone. This marked vertical separation between life phases was further confirmed across other oceanic basins through bibliographic revision, confirming the prevailing view that coccolithophore life phases occupy different ecological niches.

The genome of the jellyfish Clytia hemisphaerica and the evolution of the cnidarian life-cycle

Jellyfish (medusae) are a distinctive life-cycle stage of medusozoan cnidarians. They are major marine predators, with integrated neurosensory, muscular and organ systems. The genetic foundations of this complex form are largely unknown. We report the draft genome of the hydrozoan jellyfish Clytia hemisphaerica and use multiple transcriptomes to determine gene use across life-cycle stages. Medusa, planula larva and polyp are each characterized by distinct transcriptome signatures reflecting abrupt life-cycle transitions and all deploy a mixture of phylogenetically old and new genes. Medusa-specific transcription factors, including many with bilaterian orthologues, associate with diverse neurosensory structures. Compared to Clytia, the polyp-only hydrozoan Hydra has lost many of the medusa-expressed transcription factors, despite similar overall rates of gene content evolution and sequence evolution. Absence of expression and gene loss among Clytia orthologues of genes patterning the anthozoan aboral pole, secondary axis and endomesoderm support simplification of planulae and polyps in Hydrozoa, including loss of bilateral symmetry. Consequently, although the polyp and planula are generally considered the ancestral cnidarian forms, in Clytia the medusa maximally deploys the ancestral cnidarian–bilaterian transcription factor gene complement.

Space and the navigation of intimacy in intergenerational Tongan-European Australian relationships during partnering and early parenthood

Drawing on a larger study of a diverse group of eight Tongan-European Australian intercultural couples' experiences of partnering and becoming parents, this article explores participants' accounts of relationships with parents and parents-in-law over the course of these key family life cycle transitions. In particular, the article seeks to understand the role of geographical space in couples' experiences of navigating intimacy in intercultural, intergenerational relationships, understood as sites for cosmopolitanization, and what this reveals about intercultural partnering and parenting in the context of wider social and economic changes impacting family life. The analysis shows that participants placed importance on both intimate relationships with their parents and parents-in-law, and on autonomy as a couple, but that balancing these objectives was challenging. The article also illustrates how the occupation and sharing of space can enhance or disrupt intimacy between adult children in intercultural relationships and their parents/-in-law. Alternatively, space can be used to remedy uncomfortable cosmopolitanized encounters and reinscribe preferred degrees of physical proximity and distance. These findings highlight the importance of attending to the ‘doing’ and undoing of intimacy, including non-verbal gestures and responses. The article contributes to our understanding of emotional experiences of cosmopolitanization, and of intimacy in intercultural, intergenerational relationships.

Further confirmation of second- and third-generation Eimeria necatrix merozoite DEGs using suppression subtractive hybridization.

In our previous study, we obtained a large number of differentially expressed genes (DEGs) between second-generation merozoites (MZ-2) and third-generation merozoites (MZ-3) of Eimeria necatrix using RNA sequencing (RNA-seq). Here, we report two subtractive cDNA libraries for MZ2 (forward library) and MZ3 (reverse library) that were constructed using suppression subtractive hybridization (SSH). PCR amplification revealed that the MZ2 and MZ3 libraries contained approximately 96.7% and 95% recombinant clones, respectively, and the length of the inserted fragments ranged from 0.5 to 1.5kb. A total of 106 and 111 unique sequences were obtained from the MZ2 and MZ3 libraries, respectively, and were assembled into 13 specific consensus sequences (contigs or genes) (5 from MZ2 and 8 from MZ3). The qRT-PCR results revealed that 11 out of 13 genes were differentially expressed between MZ-2 and MZ-3. Of 13 genes, 11 genes were found in both SSH and our RNA-seq data and displayed a similar expression trend between SSH and RNA-seq data, and the remaining 2 genes have not been reported in both E. necatrix genome and our RNA-seq data. Among the 11 genes, the expression trends of 8 genes were highly consistent between SSH and our RNA-seq data. These DEGs may provide specialized functions related to the life-cycle transitions of Eimeria species.

Co-cultures of Oophila amblystomatis between Ambystoma maculatum and Ambystoma gracile hosts show host-symbiont fidelity

A unique symbiosis occurs between embryos of the spotted salamander (Ambystoma maculatum) and a green alga (Oophila amblystomatis). Unlike most vertebrate host-symbiont relationships, which are ectosymbiotic, A. maculatum exhibits both an ecto- and an endo-symbiosis, where some of the green algal cells living inside egg capsules enter embryonic tissues as well as individual salamander cells. Past research has consistently categorized this symbiosis as a mutualism, making this the first example of a “beneficial” microbe entering vertebrate cells. Another closely related species of salamander, Ambystoma gracile, also harbors beneficial Oophila algae in its egg capsules. However, our sampling within the A. gracile range consistently shows this to be a strict ectosymbiotic interaction—with no sign of tissue or presumably cellular entry. In this study we swapped cultured algae derived from intracapsular fluid of different salamander hosts to test the fidelity of tissue entry in these symbioses. Both A. maculatum and A. gracile embryos were raised in cultures with their own algae or algae cultured from the other host. Under these in vitro culture conditions A. maculatum algae will enter embryonic A. maculatum tissues. Additionally, although at a much lower frequency, A. gracile derived algae will also enter A. maculatum host tissues. However, neither Oophila strain enters A. gracile hosts in these co-culture conditions. These data reveal a potential host-symbiont fidelity that allows the unique endosymbiosis to occur in A. maculatum, but not in A. gracile. However, preliminary trials in our study found that persistent endogenous A. maculatum algae, as opposed to the cultured algae used in subsequent trials, enters host tissues at a higher frequency. An analysis of previously published Oophila transcriptomes revealed dramatic differences in gene expression between cultured and intracapsular Oophila. These include a suite of genes in protein and cell wall synthesis, photosynthesis, central carbon metabolism suggesting the intracapsular algae are assimilating ammonia for nitrogen metabolism and may be undergoing a life-cycle transition. Further refinements of these co-culture conditions could help determine physiological differences between cultured and endogenous algae, as well as rate-limiting cues provided for the alga by the salamander.

Towards causal forecasting of international migration

International migration is dicult to predict because of uncertainties. The identification of sources of uncertainty and the measurement and modelling of uncertainties are necessary, but they are not sucient. Uncertainties should be reduced by accounting for the heterogeneity of migrants, the reasons why some people leave their country while most stay, and the causal mechanisms that lead to those choices. International migration takes place within a context of globalisation, technological change, growing interest in migration governance, and the emergence of a migration industry. Young people are more likely than older people to respond to these contextual factors, as they are better informed, have greater self-ecacy, and are more likely to have a social network abroad than previous generations. My aim in this paper is to present ideas for the causal forecasting of migration. Wolfgang Lutz’s demographic theory of socioeconomic change is a good point of departure. The cohort-replacement mechanism, which is central to Lutz’s theory, is extended to account for cohort heterogeneity, life-cycle transitions, and learning. I close the paper by concluding that the time has come to explore the causal mechanisms underlying migration, and to make optimal use of that knowledge to improve migration forecasts.

Molecular cloning of heat shock protein 60 (Hsp60) and 10 (Hsp10) genes from the cosmopolitan and harmful dinoflagellate Scrippsiella trochoidea and their differential transcriptions responding to temperature stress and alteration of life cycle

Heat shock protein 60 (Hsp60) and Hsp10 are two chaperones important to both stress responses and cellular metabolisms in most organisms. In this study, the cosmopolitan Scrippsiella trochoidea was used as a model of HAB-forming dinoflagellates to explore the possible functional roles of Hsp60 and Hsp10 in the adaptation of dinoflagellates to temperature stress and life cycle transition. The full-length cDNAs of a Hsp60 and a Hsp10 gene from S. trochoidea (StHsp60 and StHsp10) were obtained via rapid amplification of cDNA ends (RACE) and their deduced amino acid sequences both included family-characteristic conservative structures and motifs, indicating a conserved function for both among different taxa. Real-time qPCR revealed that StHsp60 and StHsp10 exhibited highly similar mRNA accumulation patterns in response to temperature stresses. Their mRNA amounts, compared to that at 20 °C (control), were rapidly up-regulated upon exposure to both lower (15 °C, 10 °C, 5 °C) and higher (25 °C, 30 °C) temperatures and showed a clear time-dependent manner, suggesting a possible involvement of StHsp60 and StHsp10 in the urgent adaptation of S. trochoidea to drastic temperature stress. Furthermore, significantly elevated mRNA levels of both genes were detected in resting cysts (newly formed and that maintained in dormancy for different durations) relative to that in vegetative cells, suggesting that higher levels of StHsp60 and StHsp10 are demanded by S. trochoidea resting cysts. The results of this work, as the first investigation to characterize Hsp60 and Hsp10 genes from dinoflagellates, enrich the knowledge about Hsps and lay an important foundation for further probing their functions in dinoflagellate resting cysts.

CRISPR knockouts reveal an endogenous role for ancient neuropeptides in regulating developmental timing in a sea anemone.

Neuropeptides are evolutionarily ancient peptide hormones of the nervous and neuroendocrine systems, and are thought to have regulated metamorphosis in early animal ancestors. In particular, the deeply conserved Wamide family of neuropeptides-shared across Bilateria (e.g. insects and worms) and its sister group Cnidaria (e.g. jellyfishes and corals)-has been implicated in mediating life-cycle transitions, yet their endogenous roles remain poorly understood. By using CRISPR-Cas9-mediated reverse genetics, we show that cnidarian Wamide-referred to as GLWamide-regulates the timing of life cycle transition in the sea anemone cnidarian Nematostella vectensis. We find that mutant planula larvae lacking GLWamides transform into morphologically normal polyps at a rate slower than that of the wildtype control larvae. Treatment of GLWamide null mutant larvae with synthetic GLWamide peptides is sufficient to restore a normal rate of metamorphosis. These results demonstrate that GLWamide plays a dispensable, modulatory role in accelerating metamorphosis in a sea anemone.

Colony formation in <i>Phaeocystis antarctica</i>: connecting molecular mechanisms with iron biogeochemistry

Abstract. Phaeocystis antarctica is an important phytoplankter of the Ross Sea where it dominates the early season bloom after sea ice retreat and is a major contributor to carbon export. The factors that influence Phaeocystis colony formation and the resultant Ross Sea bloom initiation have been of great scientific interest, yet there is little known about the underlying mechanisms responsible for these phenomena. Here, we present laboratory and field studies on Phaeocystis antarctica grown under multiple iron conditions using a coupled proteomic and transcriptomic approach. P. antarctica had a lower iron limitation threshold than a Ross Sea diatom Chaetoceros sp., and at increased iron nutrition (> 120 pM Fe') a shift from flagellate cells to a majority of colonial cells in P. antarctica was observed, implying a role for iron as a trigger for colony formation. Proteome analysis revealed an extensive and coordinated shift in proteome structure linked to iron availability and life cycle transitions with 327 and 436 proteins measured as significantly different between low and high iron in strains 1871 and 1374, respectively. The enzymes flavodoxin and plastocyanin that can functionally replace iron metalloenzymes were observed at low iron treatments consistent with cellular iron-sparing strategies, with plastocyanin having a larger dynamic range. The numerous isoforms of the putative iron-starvation-induced protein (ISIP) group (ISIP2A and ISIP3) had abundance patterns coinciding with that of either low or high iron (and coincident flagellate or the colonial cell types in strain 1871), implying that there may be specific iron acquisition systems for each life cycle type. The proteome analysis also revealed numerous structural proteins associated with each cell type: within flagellate cells actin and tubulin from flagella and haptonema structures as well as a suite of calcium-binding proteins with EF domains were observed. In the colony-dominated samples a variety of structural proteins were observed that are also often found in multicellular organisms including spondins, lectins, fibrillins, and glycoproteins with von Willebrand domains. A large number of proteins of unknown function were identified that became abundant at either high or low iron availability. These results were compared to the first metaproteomic analysis of a Ross Sea Phaeocystis bloom to connect the mechanistic information to the in situ ecology and biogeochemistry. Proteins associated with both flagellate and colonial cells were observed in the bloom sample consistent with the need for both cell types within a growing bloom. Bacterial iron storage and B12 biosynthesis proteins were also observed consistent with chemical synergies within the colony microbiome to cope with the biogeochemical conditions. Together these responses reveal a complex, highly coordinated effort by P. antarctica to regulate its phenotype at the molecular level in response to iron and provide a window into the biology, ecology, and biogeochemistry of this group.

Epigenetic Variation and Regulation in Malaria Parasites.

Eukaryotic pathogens must survive in different hosts, respond to changing environments, and exploit specialized niches to propagate. Plasmodium parasites cause human malaria during bloodstream infections, where they must persist long enough to be transmitted. Parasites have evolved diverse strategies of variant gene expression that control critical biological processes of blood-stage infections, including antigenic variation, erythrocyte invasion, innate immune evasion, and nutrient acquisition, as well as life-cycle transitions. Epigenetic mechanisms within the parasite are being elucidated, with discovery of epigenomic marks associated with gene silencing and activation, and the identification of epigenetic regulators and chromatin proteins that are required for the switching and maintenance of gene expression. Here, we review the key epigenetic processes that facilitate transition through the parasite life cycle and epigenetic regulatory mechanisms utilized by Plasmodium parasites to survive changing environments and consider epigenetic switching in the context of the outcome of human infections.

Transcriptional repression by ApiAP2 factors is central to chronic toxoplasmosis

Tachyzoite to bradyzoite development in Toxoplasma is marked by major changes in gene expression resulting in a parasite that expresses a new repertoire of surface antigens hidden inside a modified parasitophorous vacuole called the tissue cyst. The factors that control this important life cycle transition are not well understood. Here we describe an important transcriptional repressor mechanism controlling bradyzoite differentiation that operates in the tachyzoite stage. The ApiAP2 factor, AP2IV-4, is a nuclear factor dynamically expressed in late S phase through mitosis/cytokinesis of the tachyzoite cell cycle. Remarkably, deletion of the AP2IV-4 locus resulted in the expression of a subset of bradyzoite-specific proteins in replicating tachyzoites that included tissue cyst wall components BPK1, MCP4, CST1 and the surface antigen SRS9. In the murine animal model, the mis-timing of bradyzoite antigens in tachyzoites lacking AP2IV-4 caused a potent inflammatory monocyte immune response that effectively eliminated this parasite and prevented tissue cyst formation in mouse brain tissue. Altogether, these results indicate that suppression of bradyzoite antigens by AP2IV-4 during acute infection is required for Toxoplasma to successfully establish a chronic infection in the immune-competent host.

The role of cold cues at different life stages on germination and flowering phenology

The timing of major phenological transitions is critical to lifetime fitness, and life history theory predicts differences for annual and perennial plants. To correctly time these transitions, many plants rely on environmental cues such as exposure to extended periods of cold, which may occur at different stages throughout their lifetime. We studied the role of cold at different life stages, by jointly exposing seed (stratification) and rosettes (vernalization) to cold. We used 23 populations of Mimulus guttatus, which vary from annuals to perennials, and investigated how cold at one or both stages affected germination, flowering, growth, and biomass. We found that stratification and vernalization interact to affect life cycle transitions, and that cold at either stage could synchronize flowering phenology. For perennials, either stratification or vernalization is necessary for maximum flowering. We also found that germination timing covaried with later traits. Moreover, plants from environments with dissimilar climates displayed different phenological responses to stratification or vernalization. In general, cold is more important for seed germination in annuals and plants from environments with warm temperatures and variable precipitation. In contrast, cold is more important for flowering in perennials: it accelerates flowering in plants from lower precipitation environments, and it increases flowering proportion in plants from cooler, more stable precipitation environments. We discuss our findings in the context of the variable environments plants experience within a population and the variation encountered across the biogeographic native range of the species.

Plasmodium falciparum Liver Stage Infection and Transition to Stable Blood Stage Infection in Liver-Humanized and Blood-Humanized FRGN KO Mice Enables Testing of Blood Stage Inhibitory Antibodies (Reticulocyte-Binding Protein Homolog 5) In Vivo.

The invention of liver-humanized mouse models has made it possible to directly study the preerythrocytic stages of Plasmodium falciparum. In contrast, the current models to directly study blood stage infection in vivo are extremely limited. Humanization of the mouse blood stream is achievable by frequent injections of human red blood cells (hRBCs) and is currently the only system with which to study human malaria blood stage infections in a small animal model. Infections have been primarily achieved by direct injection of P. falciparum-infected RBCs but as such, this modality of infection does not model the natural route of infection by mosquito bite and lacks the transition of parasites from liver stage infection to blood stage infection. Including these life cycle transition points in a small animal model is of relevance for testing therapeutic interventions. To this end, we used FRGN KO mice that were engrafted with human hepatocytes and performed a blood exchange under immune modulation to engraft the animals with more than 50% hRBCs. These mice were infected by mosquito bite with sporozoite stages of a luciferase-expressing P. falciparum parasite, resulting in noninvasively measurable liver stage burden by in vivo bioluminescent imaging (IVIS) at days 5–7 postinfection. Transition to blood stage infection was observed by IVIS from day 8 onward and then blood stage parasitemia increased with a kinetic similar to that observed in controlled human malaria infection. To assess the utility of this model, we tested whether a monoclonal antibody targeting the erythrocyte invasion ligand reticulocyte-binding protein homolog 5 (with known growth inhibitory activity in vitro) was capable of blocking blood stage infection in vivo when parasites emerge from the liver and found it highly effective. Together, these results show that a combined liver-humanized and blood-humanized FRGN mouse model infected with luciferase-expressing P. falciparum will be a useful tool to study P. falciparum preerythrocytic and erythrocytic stages and enables the testing of interventions that target either one or both stages of parasite infection.

Psychosocial Issues of the Adolescent PI Patient & The Development of the PI Teen Outreach Program

Background: The effects of disruptions in the lives of the adolescent Primary Immunodeficiency (PI) patient require psychosocial staff involved in their care to find unique approaches to treatment. The demands of living with PI in adolescence complicates this already turbulent life cycle transition. Absence from school due to infections and treatment can lead to social isolation and in turn issues of self-esteem, creating challenges for teenagers with chronic diseases. The importance of maintaining social support with peers and developing a new network of social supports with teens with similar diagnoses is highlighted in the literature as an important factor in helping teens successfully cope with the demands of chronic illness.Methods: To best meet the complex needs of this population, the PI Teen Outreach Program was created in 2010. The goal was to connect teens with PI to one another in an environment that engages them in “normal” activities while providing an opportunity to discuss diagnosis, coping...

Spirit Birds at Neolithic Çatalhöyük

ABSTRACTAs they soar into the air and dive below the water's surface, birds inspire awe for their superhuman capacity to pass among earth, air, and water. People often see birds as spirits, or as messengers to and from the spirit world. Whereas at earlier sites in the region birds made a significant contribution to human diet, at Neolithic Çatalhöyük in Central Anatolia their nutritional significance is small. Body part distributions suggest that for the most part feathers were more important than meat. Bird remains, mainly the feathery parts of wings, appear in a number of special deposits at Çatalhöyük. Together with artistic representations, these deposits suggest that cranes and vultures played key roles in life cycle transitions and were invoked mimetically through dance. Additionally, waterbirds, particularly in association with newborn human infants, may have mediated between human and spirit worlds. Although there is little indication that Çatalhöyük residents made much use of brightly coloured feathers, bird wing deposits do attest to the importance of colour symbolism at the site. Thus bird remains offer material evidence of aspects of Neolithic cosmology and ontology, as well as social structure.

Short-term cortisol exposure alters cardiac hypertrophic and non-hypertrophic signalling in a time-dependent manner in rainbow trout.

ABSTRACTCardiac disease is a growing concern in farmed animals, and stress has been implicated as a factor for myocardial dysfunction and mortality in commercial fish rearing. We recently showed that the stress hormone cortisol induces pathological cardiac remodelling in rainbow trout. Wild and farmed salmonids are exposed to fluctuations and sometimes prolonged episodes of increased cortisol levels. Thus, studying the timeframe of cortisol-induced cardiac remodelling is necessary to understand its role in the pathogenesis of cardiovascular disease in salmonids. We here establish that 3 weeks of cortisol exposure is sufficient to increase relative ventricular mass (RVM) by 20% in rainbow trout. Moreover, increased RVMs are associated with altered expression of hypertrophic and non-hypertrophic remodelling markers. Further, we characterised the time course of cortisol-induced cardiac remodelling by feeding rainbow trout cortisol-containing feed for 2, 7 and 21 days. We show that the effect of cortisol on expression of hypertrophic and non-hypertrophic remodelling markers is time-dependent and in some cases acute. Our data indicate that short-term stressors and life cycle transitions associated with elevated cortisol levels can potentially influence hypertrophic and non-hypertrophic remodelling of the trout heart.

Crohn’s Disease and the Young Couple: An Interpretative Phenomenological Analysis

This study explores how an individual’s diagnosis of Crohn’s disease is perceived to affect the couple relationship and young adult life-cycle transitions. Design. Qualitative interview study. Interpretive Phenomenological Analysis (IPA) was employed to analyze qualitative couple and individual interviews from five young adult couples in which one partner has a diagnosis of Crohn’s disease. Data was collected through both structuring and interview sessions. Analysis involved transcription and reading of the interviews; exploratory initial coding; development of emergent themes; and a final analysis utilizing abstraction, subsumption, and polarization. The systemic effects of Crohn’s disease are seen at diagnosis and throughout the course of the illness. The numerous stressors posed by Crohn’s disease can lead to couples withdrawing from one another. In order to overcome this distance, couples seek to find strength in one another as their life trajectory is taken day by day. Family therapists, healthcare providers, and researchers can better understand how the numerous physical symptoms of Crohn’s disease cause psychological and social implications for the diagnosed individual and partner. A systemic, biopsychosocial understanding of Crohn’s disease will encourage couple level clinical assessment and increase systemic interventions, promoting greater resilience among young adult couples.

Processes affecting altitudinal distribution of invasive Ageratina adenophora in western Himalaya: The role of local adaptation and the importance of different life-cycle stages.

The spread of invasive plants along elevational gradients is considered a threat to fragile mountain ecosystems, but it can also provide the opportunity to better understand some of the basic processes driving the success of invasive species. Ageratina adenophora (Asteraceae) is an invasive plant of global importance and has a broad distribution along elevational gradients in the Western Himalayas. Our study aimed at understanding the role of evolutionary processes (e.g. local adaptation and clinal differentiation) and different life history stages in shaping the distribution pattern of the invasive plant along an elevational gradient in the Western Himalaya. We carried out extensive distributional surveys, established a reciprocal transplant experiment with common gardens at three elevational levels, and measured a suite of traits related to germination, growth, reproduction and phenology. Our results showed a lack of local adaptation, and we did not find any evidence for clinal differentiation in any measured trait except a rather weak signal for plant height. We found that seed germination was the crucial life-cycle transition in determining the lower range limit while winter mortality of plants shaped the upper range limit in our study area, thus explaining the hump shaped distribution pattern. Differences in trait values between gardens for most traits indicated a high degree of phenotypic plasticity. Possible causes such as apomixis, seed dispersal among sites, and pre-adaptation might have confounded evolutionary processes to act upon. Our results suggest that the success and spread of Ageratina adenophora are dependent on different life history stages at different elevations that are controlled by abiotic conditions.

Comparative demography of two common scleractinian corals: Orbicella annularis and Porites astreoides.

BackgroundStudies directed at understanding the demography and population dynamics of corals are relatively scarce. This limits our understanding of both the dynamics of coral populations and our capacity to develop management and conservation initiatives directed at conserving such ecosystems.MethodsFrom 2012 to 2014, we collected data on the growth, survival, and recruitment rates of two common Caribbean coral species, the stress-tolerant Orbicella annularis and the weedy Porites astreoides. A set of size-based population matrix model was developed for two localities in Northeastern Puerto Rico and used to estimate population growth rates (λ) and determine the life cycle transition(s) that contribute the most to spatiotemporal differences in λs. The model was parameterized by following the fate of 100 colonies of each species at the two sites for two years.ResultsOur data indicate that spatial variability in vital rates of both species was higher than temporal variability. During the first year, populations of O. annularis exhibited λs below equilibrium at Carlos Rosario (0.817) and Palomino (0.694), followed by a considerable decline at both sites during the second year (0.700 and 0.667). Populations of P. astreoides showed higher λs than O. annularis during the first census period at Carlos Rosario (0.898) and Palomino (0.894) with a decline at one of the sites (0.681 and 0.893) during the second census period. Colony fate in both species exhibited a significant interaction with respect to location but not to time (G2 = 20.96; df = 3 for O. annularis and G2 = 9.55; df = 3 for P. astreoides).DiscussionThe similar variability of λs as well as the similar survival rates for both species during the two-year census period (2012–2014) show similar variability on demographic patterns in space and time. Our results suggest that location rather than time is important for the resiliency in coral colonies. Also, P. astreoides will show higher resistance to disturbance in the future than O. annularis.

Low-Income Dynamics in Canadian Society: Debates on Low-Income Measures and New Empirical Evidence

In the existing research on poverty/low income, there are emerging initiatives to use multiple thresholds of low income instead of a single threshold and to analyze persistent low income over several years instead of low income in a single year. Although most recent studies have identified low-income incidences for multiple years (at least one year, at least four years, or at least six years) associated with multiple low-income thresholds, they unintentionally bury short-run low-income spells (for one to three years) in longer low-income spells (for four to six years). In this article, we review the debates on measures of low income and attempt to differentiate the short-run low-income spells clearly from their chronic counterparts. We further identify the characteristics of Canadians who are trapped under these two types of low-income spells. Using our approach and the 1999–2007 Canadian Survey of Labour and Income Dynamics (SLID) data, we have found that approximately 73% of low-income Canadians are in short-run low income, while about 27% are in chronic low income. Short-run low income is generally associated with life cycle transitions, while chronic low income is generally associated with certain high-risk groups. These findings are fairly robust across various thresholds of low income.