In situ measurements of hydrodynamic forces imposed on Chondrus crispus Stackhouse

Among the hydrodynamic forces experienced by intertidal organisms, drag and the impingement force are thought to have the greatest effect on macroalgae. These forces are modified by biotic factors such as algal morphology, reconfiguration, and the presence of a canopy. However, much of what is known about the hydrodynamics of macroalgae has been garnered from low-velocity laboratory flume studies. Few field studies have measured drag and none have directly measured the effects of the canopy on force. To examine in situ hydrodynamic forces imposed on the turf forming macroalga Chondrus crispus, compact digital force sensors were developed that measure and record the 3-dimensional force imposed on a macroalga without disturbing the surrounding canopy. Sensors were positioned within natural Chondrus beds and the effects of the canopy, algal morphology, and sea state on in situ hydrodynamic force were examined. Additionally, the predictions of a new model for drag on flexible macroalgae were tested by simultaneously measuring force and water velocity. Digital force recordings indicated that Chondrus only experience drag; lift and impingement force were negligible in all combinations of factors. Canopies significantly reduced drag by 15-65%. Morphology and size also influenced drag, such that lower forces were imposed on small planar algae than large arborescent individuals. Further, planar algae experienced low drag in all combinations of sea and canopy state, indicating that these individuals may not be as susceptible to wave disturbance as arborescent individuals. Overall, these data indicate that the ability for Chondrus to grow large, arborescent individuals is dependent on the drag reducing properties of the canopy, while more hydrodynamically harsh habitats may be accessible to planar morphologies. Additionally, these data suggest that drag models for canopy forming macroalgae must incorporate the effects of the canopy to predict drag accurately in situ.     

Ecological studies of economic red algae. II. Culture studies of Chondrus crispus Stackhouse and Gigartina stellata (Stackhouse) batters

The carpospores of Chondrus crispus Stackhouse and Gigartina stellata (Stackhouse) Batters were grown under a variety of light intensities, temperatures, and salinities. Chondrus exhibited a rapid increase in growth concurrent with increasing intensities up to 440 ft-c and tended to level off above this intensity. Gigartina exhibited a less rapid, but more consistent, increase in cell production coincident with increasing light intensity through 770 ft-c. The growth of both species was accelerated with increasing temperatures to 19 °C. Spores of C. crispus germinated and grew relatively rapidly over a broad range of salinities (15–45‰ at 19°C). Gigartina exhibited a more restricted tolerance to reduced salinity (20 ‰ at 19°C). The local distribution and abundance of both species are correlated with their responses in culture as well as with previous observations on their photosynthesis and respiration.     

Growth regulators from the seaweed Chondrus crispus L. (Lyn.)

The level of auxin-like compounds extracted from the seaweed Chondrus crispus L. (Lyn.) is reported. Their presence before and after alkaline hydrolysis is studied to confirm that the bound auxin-like substances are present in algae in greater concentration than the free form.     

Demographic models to simulate the stable ratio between ecologically similar gametophytes and tetrasporophytes in populations of the Gigartinaceae (Rhodophyta)

In populations of the Gigartinaceae (Rhodophyta), gametophytes often predominate numerically over tetrasporophytes. Several hypotheses have been proposed to explain this dominance, based on the usually implicit assumption that the stable ratio between gametophytes and tetrasporophytes (G:T ratio) should be 1 if both reproductive phases are ecologically similar. We developed demographic models to test this assumption, for which we considered that both phases are ecologically similar. Defining ecologic similarity for most demographic rates is relatively straightforward, except for rates of spore output. The first set of models considered the same spore output per thallus of both phases as representing ecologic similarity. Model iterations led to stable G:T ratios of 1 for triennial and for perennial thalli, regardless of the initial G:T ratio, but not for annual thalli with initial G:T ratios different from 1. However, equal spore output may not represent ecologic similarity, due to size differences between carpospores and tetraspores. The second set of models considered the lowest possible spore output for each phase, according to the life history of this family: only one carposporangium, with one carpospore, is produced from every two gametophytes and only one tetrasporangium, with four tetraspores, is produced by every tetrasporophyte. Model iterations led to stable G:T ratios of 2.8 for most cases, a ratio of 1 being obtained only every 2 years for annual thalli with an initial G:T ratio of 1. Increasing absolute spore output, without altering the relative output between phases and incorporating density-independent mortality through a matrix model, given the same mortality rate for both phases, did not modify results. We suggest that the combination of both modeling and field research may uncover more rapidly than otherwise the most relevant ecologic differences between phases, if any, that underlie the G:T ratio observed for a given population.     

The effects of phenological mismatches on demography

Climate change is altering the phenology of species across the world, but what are the consequences of these phenological changes for the demography and population dynamics of species? Time-sensitive relationships, such as migration, breeding and predation, may be disrupted or altered, which may in turn alter the rates of reproduction and survival, leading some populations to decline and others to increase in abundance. However, finding evidence for disrupted relationships, or lack thereof, and their demographic effects, is difficult because the necessary detailed observational data are rare. Moreover, we do not know how sensitive species will generally be to phenological mismatches when they occur. Existing long-term studies provide preliminary data for analysing the phenology and demography of species in several locations. In many instances, though, observational protocols may need to be optimized to characterize timing-based multi-trophic interactions. As a basis for future research, we outline some of the key questions and approaches to improving our understanding of the relationships among phenology, demography and climate in a multi-trophic context. There are many challenges associated with this line of research, not the least of which is the need for detailed, long-term data on many organisms in a single system. However, we identify key questions that can be addressed with data that already exist and propose approaches that could guide future research.     

Composes halogenes d'une algue rouge,Falkenbergia rufolanosa tetrasporophyte d' Asparagopsis armata

Water extraction of fresh Falkenbergia rufolanosa followed by water-ether partition, yielded halomethanes, polyhalo ethyl and methyl acetates and especially polyhalo acetones. It is the first example of polyhalo compounds extracted from a tetrasporophyte in the Bonnemaisoniaceae.     

The Shanidar cave Proto-Neolithic human population: Aspects of demography and paleopathology

This paper presents bio-anthropological data concerning the Shanidar cave, Proto-Neolithic, Homo sapiens population at the dawn of sedentary life in SW Asia. It was proposed that changes in human organizational systems and perceived environmental contexts, as reflected by ecofacts and tool assemblages, indicating the intensification of harvesting of resources during this Proto-Neolithic cultural component, could have altered existing interrelationships between pathogens, vectors, and human hosts. The individuals comprising the skeletal collection represent both sex subcategories and most age subgroups. Further, no evidence of bio-distance has been documented between them judging from morphometrics and mensurational analyses. Paleopathological investigations of the skeletal record revealed the presence of infectious diseases, lesions of the joints, lesions of the jaws and teeth, benign tumors, hemopoietic and metabolic disorders, as well as severe traumatic conditions. Bone isotopic testing for investigations of dietary patterns indicated a diet heavily based on C3 plants, while the animal protein component was calculated to an intake of less than 10%. The paleopathological profile in conjunction with the archeometric studies, and the rest of the archaeological record present significant reflections of the lives of these Proto-Neolithic people in SW Asia, during this transitional time period.     

The roles of demography and genetics in the early stages of colonization

Colonization success increases with the size of the founding group. Both demographic and genetic factors underlie this relationship, yet because genetic diversity normally increases with numbers of individuals, their relative importance remains unclear. Furthermore, their influence may depend on the environment and may change as colonization progresses from establishment through population growth and then dispersal. We tested the roles of genetics, demography and environment in the founding of Tribolium castaneum populations. Using three genetic backgrounds (inbred to outbred), we released individuals of four founding sizes (2–32) into two environments (natal and novel), and measured establishment success, initial population growth and dispersal. Establishment increased with founding size, whereas population growth was shaped by founding size, genetic background and environment. Population growth was depressed by inbreeding at small founding sizes, but growth rates were similar across genetic backgrounds at large founding size, an interaction indicating that the magnitude of the genetic effects depends upon founding population size. Dispersal rates increased with genetic diversity. These results suggest that numbers of individuals may drive initial establishment, but that subsequent population growth and spread, even in the first generation of colonization, can be driven by genetic processes, including both reduced growth owing to inbreeding depression, and increased dispersal with increased genetic diversity.     

Before senescence: the evolutionary demography of ontogenesis

The age-specific mortality curve for many species, including humans, is U-shaped: mortality declines with age in the developing cohort (ontogenescence) before increasing with age (senescence). The field of evolutionary demography has long focused on understanding the evolution of senescence while largely failing to address the evolution of ontogenescence. The current review is the first to gather the few available hypotheses addressing the evolution of ontogenescence, examine the basis and assumptions of each and ask what the phylogenetic extent of ontogenescence may be. Ontogenescence is among the most widespread of life-history traits, occurring in every population for which I have found sufficiently detailed data, in major groups throughout the eukaryotes, across many causes of death and many life-history types. Hypotheses seeking to explain ontogenescence include those based on kin selection, the acquisition of robustness, heterogeneous frailties and life-history optimization. I propose a further hypothesis, arguing that mortality drops with age because most transitions that could trigger the risks caused by genetic and developmental malfunctions are concentrated in early life. Of these hypotheses, only those that frame ontogenescence as an evolutionary by-product rather than an adaptation can explain the tremendous diversity of organisms and environments in which it occurs.     

Carrageenan patterns in the Gigartinaceae

Carrageenans of known reproductive phases of gigartinacean species are shown to differ: gelling κ (τ)-type carrageenan occurs in all instances in gametophytes, and viscous non-gelling λ-carrageenan or its variant ξ- or π-carrageenan in tetrasporophytes. Multiple analyses demonstrate that the carrageenan type is a species characteristic, with little difference between individual samples. No difference exists between the carrageenans of male and female plants of each species. Carrageenan chemistry combined with morphological, reproductive and life history feature is useful for defining the taxonomic limits of this family and these genera.     

The demography and population genomics of evolutionary transitions to self-fertilization in plants

The evolution of self-fertilization from outcrossing has occurred on numerous occasions in flowering plants. This shift in mating system profoundly influences the morphology, ecology, genetics and evolution of selfing lineages. As a result, there has been sustained interest in understanding the mechanisms driving the evolution of selfing and its environmental context. Recently, patterns of molecular variation have been used to make inferences about the selective mechanisms associated with mating system transitions. However, these inferences can be complicated by the action of linked selection following the transition. Here, using multilocus simulations and comparative molecular data from related selfers and outcrossers, we demonstrate that there is little evidence for strong bottlenecks associated with initial transitions to selfing, and our simulation results cast doubt on whether it is possible to infer the role of bottlenecks associated with reproductive assurance in the evolution of selfing. They indicate that the effects of background selection on the loss of diversity and efficacy of selection occur rapidly following the shift to high selfing. Future comparative studies that integrate explicit ecological and genomic details are necessary for quantifying the independent and joint effects of selection and demography on transitions to selfing and the loss of genetic diversity.     

The demography of a haemoglobin polymorphism in the Atlantic cod, Gadus morhua L.

Genetic stability was investigated at a polymorphic haemoglobin gene-locus in 13 124 Atlantic cod, Gadus morhua L. A total of 30 year-classes, sampled over 18 years, were variously sampled in 33 named localities. Regional populations showed distinctive allele frequencies, and each major cod fishery showed some degree of genetic imbalance, which was expressed as excessive numbers of homozygotes. This imbalance occurred seasonally in a proportion of the population samples in each of the major cod fisheries. The findings are attributable to migrations of distinctive genetic populations.     

Root demography in kiwifruit (Actinidia deliciosa)

A rhizotron was used to study fine-root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty-one per cent of the roots survived ≤28d, 69% died at an age ≤56d and only 8% survived >252d. For each year, the cumulative length of roots grown was equivalent to about 2·75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover yet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.