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PubMed2002

Correlational selection and the evolution of genomic architecture.

We review and discuss the importance of correlational selection (selection for optimal character combinations) in natural populations. If two or more traits subject to multivariate selection are heritable, correlational selection builds favourable genetic correlations through the formation of linkage disequilibrium at underlying loci governing the traits. However, linkage disequilibria built up by correlational selection are expected to decay rapidly (ie, within a few generations), unless correlational selection is strong and chronic. We argue that frequency-dependent biotic interactions that have 'Red Queen dynamics' (eg, host-parasite interactions, predator-prey relationships or intraspecific arms races) often fuel chronic correlational selection, which is strong enough to maintain adaptive genetic correlations of the kind we describe. We illustrate these processes and phenomena using empirical examples from various plant and animal systems, including our own recent work on the evolutionary dynamics of a heritable throat colour polymorphism in the side-blotched lizard Uta stansburiana. In particular, male and female colour morphs of side-blotched lizards cycle on five- and two-generation (year) timescales under the force of strong frequency-dependent selection. Each morph refines the other morph in a Red Queen dynamic. Strong correlational selection gradients among life history, immunological and morphological traits shape the genetic correlations of the side-blotched lizard polymorphism. We discuss the broader evolutionary consequences of the buildup of co-adapted trait complexes within species, such as the implications for speciation processes.

Animals↗
PubMed2003

Isolation and characterization of the Arabidopsis organ fusion gene HOTHEAD.

The outer epidermal plant cell wall and cuticle play an important role in regulating both abiotic and biotic interactions between the plant and its environment. In addition to acting as a protective barrier that limits water loss, the effects of detrimental irradiation and invasion by pathogens, the epidermis also offers an interface that is inert to interactions between organs and ensures proper separation and expansion of organs at the growing points of the plant. Here, we describe the molecular cloning and characterization of HOTHEAD (HTH), a gene required to limit cellular interactions between contacting epidermal cells during floral development. HTH is a member of a small gene family in Arabidopsis and encodes an enzyme related to a group of FAD-containing oxidoreductases that have been described in several other species. Characterization of 11 independently derived mutant alleles suggests that key amino acids are shared between these related groups of enzymes and identify a cluster of other functionally important residues that are highly conserved only within the Arabidopsis gene family. Our findings add this new type of enzyme to a growing list of enzymes that have been shown to be involved in regulating post-genital organ fusion. Expression analysis of the HTH gene shows that it is expressed in all tissues tested, including roots, and is not epidermis-specific. Furthermore, the sequence data unequivocally show that none of the alleles isolated are epigenetic alleles as suggested by genetic behavior previously observed at this locus.

Arabidopsis↗
PubMed2002

Extremely productive microbial communities in shallow saline pools respond immediately to changing meteorological conditions.

Diel changes in bacterial and cyanobacterial numbers, as well as heterotrophic bacterial production, were examined in two shallow alkaline pools, harbouring dense populations of cyanobacteria (up to 1100 x 109 cells l-1) and bacteria (up to 500 x 109 cells l-1). Together with the recorded bacterial production rates (925 micro gC l-1x h-1), these values are the highest reported for natural aquatic ecosystems. The investigations were performed during a fair-weather situation, and during a rapid change after a long-term fair-weather situation to thunderstorms and heavy rainfall. During fair weather, bacterial growth was significantly correlated to the diurnal light and temperature cycle. Prokaryotic abundances were fairly constant, and loss by grazing and viral lysis must have been of significant importance. During the invasion of rainy weather, the prokaryotic community showed a strong and immediate response. A significant enhancement of bacterial growth followed after rainfall, suggesting that the high salt concentrations had inhibited bacterial activity. Changes in bacterial and cyanobacterial numbers were consistent with this pattern. From comparison with the available literature, we conclude that diel changes of bacterioplankton are regulated by a complex combination of environmental factors specific for each investigated ecosystem. In the soda pools investigated, external abiotic factors were dominant on a diel scale. In larger ecosystems, such factors are much more buffered and internal biotic interactions may prevail.

Ecosystem↗
PubMed2002

Multiple archaeal groups mediate methane oxidation in anoxic cold seep sediments.

No microorganism capable of anaerobic growth on methane as the sole carbon source has yet been cultivated. Consequently, information about these microbes has been inferred from geochemical and microbiological observations of field samples. Stable isotope analysis of lipid biomarkers and rRNA gene surveys have implicated specific microbes in the anaerobic oxidation of methane (AOM). Here we use combined fluorescent in situ hybridization and secondary ion mass spectrometry analyses, to identify anaerobic methanotrophs in marine methane-seep sediments. The results provide direct evidence for the involvement of at least two distinct archaeal groups (ANME-1 and ANME-2) in AOM at methane seeps. Although both archaeal groups often occurred in direct physical association with bacteria, they also were observed as monospecific aggregations and as single cells. The ANME-1 archaeal group more frequently existed in monospecific aggregations or as single filaments, apparently without a bacterial partner. Bacteria associated with both archaeal groups included, but were not limited to, close relatives of Desulfosarcina species. Isotopic analyses suggest that monospecific archaeal cells and cell aggregates were active in anaerobic methanotrophy, as were multispecies consortia. In total, the data indicate that the microbial species and biotic interactions mediating anaerobic methanotrophy are diverse and complex. The data also clearly show that highly structured ANME-2/Desulfosarcina consortia are not the sole entities responsible for AOM at marine methane seeps. Other microbial groups, including ANME-1 archaea, are capable of anaerobic methane consumption either as single cells, in monospecific aggregates, or in multispecies consortia.

Archaea↗
PubMed2002

Survival without recovery after mass extinctions.

Because many survivors of mass extinctions do not participate in postrecovery diversifications, and therefore fall into a pattern that can be termed "Dead Clade Walking" (DCW), the effects of mass extinctions extend beyond the losses observed during the event itself. Analyses at two taxonomic levels provide a first-order test of the prevalence of DCWs by using simple and very conservative operational criteria. For four of the Big Five mass extinctions of the Phanerozoic, the marine genera that survived the extinction suffered approximately 10-20% attrition in the immediately following geologic stage that was significantly greater than the losses sustained in preextinction stages. The stages immediately following the three Paleozoic mass extinctions also account for 17% of all order-level losses in marine invertebrates over that interval, which is, again, significantly greater than that seen for the other stratigraphic stages (no orders are lost immediately after the end-Triassic or end-Cretaceous mass extinctions). DCWs are not evenly distributed among four regional molluscan time-series following the end-Cretaceous extinction, demonstrating the importance of spatial patterns in recovery dynamics. Although biotic interactions have been invoked to explain the differential postextinction success of clades, such hypotheses must be tested against alternatives that include stochastic processes in low-diversity lineages-which is evidently not a general explanation for the ordinal DCW patterns, because postextinction fates are not related to the size of extinction bottlenecks in Paleozoic orders-and ongoing physical environmental changes.

Animals↗
PubMed1994

Climate change and temperature-dependent sex determination in reptiles.

Despite increasing concern over the possible impact of global temperature change, there is little empirical evidence of direct temperature effects on biotic interactions in natural systems. Clear assessment of the ecological and evolutionary impact of changing climatic temperature requires a natural system in which populations exhibit a direct unambiguous fitness response to thermal fluctuation. I monitored nests of a population of painted turtles (Chrysemys picta) with temperature-dependent sex determination to investigate the causal relationship between local climatic variation in temperature and offspring sex ratio. Consistent with theoretical predictions, annual offspring sex ratio was highly correlated with mean July air temperature, validating concerns about the effect of climate change on population demography. This correlation implies that even modest increases in mean temperature (< 2 degrees C) may drastically skew the sex ratio. Statistical evaluation of the variance in climate change indicates that an increase in mean temperature of 4 degrees C would effectively eliminate production of male offspring. Quantitative genetic analyses and behavioral data suggest that populations with temperature-dependent sex determination may be unable to evolve rapidly enough to counteract the negative fitness consequences of rapid global temperature change. Populations of species with temperature-dependent sex determination may serve as ideal indicators of the biological impact of global temperature change.

Animals↗
PubMed2005

Biofilm formation by bacterial associations under various salinities and copper ion stress.

The study addresses the effect of abiotic (medium salinity and copper ions) and biotic (interactions between populations) factors on the formation of structured communities by binary associations consisting of halotolerant bacteria (Alcaligenes sp. 1-1 or Acinetobacter sp. 1-19) and a wild-type B. subtilis 2335 strain or a transgenic strain. The results showed that 250 mg l(-1) of copper ions inhibit formation of biofilms by monocultures of the tested strains. Binary associations of the strains were more resistant to high concentrations (250 mg l(-1)) of copper ions. At the lowest NaCl concentration (0.05% and 2.5%) and in the presence of copper ions, bacilli seemed to help halotolerant bacteria survive. Under increased salinity and in the presence of copper ions, structured communities developed due to halotolerant bacteria. Coexistence under stressful conditions was beneficial for the both groups of bacteria.

Acinetobacter↗
PubMed2004

Temporal variation can facilitate niche evolution in harsh sink environments.

We examine the impact of temporal variation on adaptive evolution in "sink" environments, where a species encounters conditions outside its niche. Sink populations persist because of recurrent immigration from sources. Prior studies have highlighted the importance of demographic constraints on adaptive evolution in sinks and revealed that adaptation is less likely in harsher sinks. We examine two complementary models of population and evolutionary dynamics in sinks: a continuous-state quantitative-genetics model and an individual-based model. In the former, genetic variance is fixed; in the latter, genetic variance varies because of mutation, drift, and sampling. In both models, a population in a constant harsh sink environment can exist in alternative states: local maladaptation (phenotype comparable to immigrants from the source) or adaptation (phenotype near the local optimum). Temporal variation permits transitions between these states. We show that moderate amounts of temporal variation can facilitate adaptive evolution in sinks, permitting niche evolution, particularly for slow or autocorrelated variation. Such patterns of temporal variation may particularly pertain to sinks caused by biotic interactions (e.g., predation). Our results are relevant to the evolutionary dynamics of species' ranges, the fate of exotic invasive species, and the evolutionary emergence of infectious diseases into novel hosts.

Adaptation, Biological↗
PubMed2005

A quantitative model for assessing community dynamics of pleistocene mammals.

Previous studies have suggested that species responded individualistically to the climate change of the last glaciation, expanding and contracting their ranges independently. Consequently, many researchers have concluded that community composition is plastic over time. Here I quantitatively assess changes in community composition over broad timescales and assess the effect of range shifts on community composition. Data on Pleistocene mammal assemblages from the FAUNMAP database were divided into four time periods (preglacial, full glacial, postglacial, and modern). Simulation analyses were designed to determine whether the degree of change in community composition is consistent with independent range shifts, given the distribution of range shifts observed. Results indicate that many of the communities examined in the United States were more similar through time than expected if individual range shifts were completely independent. However, in each time transition examined, there were areas of nonanalogue communities. I conducted sensitivity analyses to explore how the results were affected by the assumptions of the null model. Conclusions about changes in mammalian distributions and community composition are robust with respect to the assumptions of the model. Thus, whether because of biotic interactions or because of common environmental requirements, community structure through time is more complex than previously thought.

Animals↗
PubMed2006

Coadaptation: a unifying principle in evolutionary thermal biology.

Over the last 50 yr, thermal biology has shifted from a largely physiological science to a more integrated science of behavior, physiology, ecology, and evolution. Today, the mechanisms that underlie responses to environmental temperature are being scrutinized at levels ranging from genes to organisms. From these investigations, a theory of thermal adaptation has emerged that describes the evolution of thermoregulation, thermal sensitivity, and thermal acclimation. We review and integrate current models to form a conceptual model of coadaptation. We argue that major advances will require a quantitative theory of coadaptation that predicts which strategies should evolve in specific thermal environments. Simply combining current models, however, is insufficient to understand the responses of organisms to thermal heterogeneity; a theory of coadaptation must also consider the biotic interactions that influence the net benefits of behavioral and physiological strategies. Such a theory will be challenging to develop because each organism's perception of and response to thermal heterogeneity depends on its size, mobility, and life span. Despite the challenges facing thermal biologists, we have never been more pressed to explain the diversity of strategies that organisms use to cope with thermal heterogeneity and to predict the consequences of thermal change for the diversity of communities.

Acclimatization↗
PubMed2006

Phytogeographical analysis of seed plant genera in China.

BACKGROUND AND AIMS: A central goal of biogeography and ecology is to uncover and understand distributional patterns of organisms. China has long been a focus of attention because of its rich biota, especially with respect to plants. Using 290 floras from across China, this paper quantitatively characterizes the composition of floristic elements at multiple scales (i.e. national, provincial and local), and explores the extent to which climatic and geographical factors associated with each flora can jointly and independently explain the variation in floristic elements in local floras. METHODS: A study was made of 261 local floras, 28 province-level floras and one national-level flora across China. Genera of seed plants in each flora were assigned to 14 floristic elements according to their worldwide geographical distributions. The composition of floristic elements was related to climatic and geographical factors. KEY RESULTS AND CONCLUSIONS: Variations in percentages of cosmopolitan, tropical and temperate genera among local floras tend to be greater at higher latitudes than at lower latitudes. Latitude is strongly correlated with the proportions of 13 of the 14 floristic elements. Correlations of the proportions of floristic elements with longitude are much weaker than those with latitude. Climate represented by the first principal component of a principal component analysis was strongly correlated with the proportions of floristic elements in local floras (|r| = 0.75 +/- 0.18). Geographical coordinates independently explained about four times as much variation in floristic elements as did climate. Further research is necessary to examine the roles of water-energy dynamics, geology, soils, biotic interactions, and historical factors such as land connections between continents in the past and at present in creating observed floristic patterns.

China↗
PubMed2007

Corolla herbivory, pollination success and fruit predation in complex flowers: an experimental study with Linaria lilacina (Scrophulariaceae).

BACKGROUND AND AIMS: Herbivory on floral structures has been postulated to influence the evolution of floral traits in some plant species, and may also be an important factor influencing the occurrence and outcome of subsequent biotic interactions related to floral display. In particular, corolla herbivory may affect structures differentially involved in flower selection by pollinators and fruit predators (specifically, those ovopositing in ovaries prior to fruit development); hence floral herbivores may influence the relationships between these mutualistic and antagonistic agents. METHODS: The effects of corolla herbivory in Linaria lilacina (Scrophulariaceae), a plant species with complex flowers, were considered in relation to plant interactions with pollinators and fruit predators. Tests were made as to whether experimentally created differences in flower structure (resembling those occurring naturally) may translate into differences in reproductive output in terms of fruit or seed production. KEY RESULTS: Flowers with modified corollas, particularly those with lower lips removed, were less likely to be selected by pollinators than control flowers, and were less likely to be successfully visited and pollinated. As a consequence, fruit production was also less likely in these modified flowers. However, none of the experimental treatments affected the likelihood of visitation by fruit predators. CONCLUSIONS: Since floral herbivory may affect pollinator visitation rates and reduce seed production, differences among plants in the proportion of flowers affected by herbivory and in the intensity of the damage inflicted on affected flowers may result in different opportunities for reproduction for plants in different seasons.

Animals↗
PubMed2026

Environmental Gradients as a Dominant Force in the Macroevolution of a Host-Associated Marine Bacterium.

Natural selection is imposed by both abiotic environmental filtering and biotic interactions, yet their relative roles in shaping the deep phylogeny of widespread, generalist host-associated bacteria remain unclear. Here, we integrate large-scale phylogenomics, environmental sequencing, functional genomics, and global metagenomic analysis to demonstrate that tidal zonation overrides host association as the dominant macroevolutionary force structuring the marine bacterial genus Ruegeria. Analysis of 533 genomes and 74 global coastal metagenomes reveals that the intertidal-subtidal boundary structures the deepest phylogenetic splits, driving the repeated evolution of distinct ecotypes through independent zonation transitions across global coastlines. These ecotypes possess divergent genomic toolkits: intertidal strains are enriched for genes coding for stress resistance and anaerobic metabolism, whereas subtidal strains specialize in high-affinity nutrient scavenging. Our findings establish that predictable physicochemical gradients act as filters that generate foundational diversity from which specialized host symbionts subsequently emerge, reframing how environmental gradients shape microbial evolution at the eco-evolutionary interface.

Journal Article↗
PubMedDate not supplied

Patterns of genetic structure among populations of an oligophagous pollinating yucca moth (Tegeticula yuccasella).

Plant-insect associations have served as models for investigations of coevolution and the influence of biotic interactions on diversification. The pollination association between yuccas and yucca moths is a classic example of an obligate mutualism often suggested to have been affected by coevolution. Recent work has shown high host specificity in pollinating yucca moths, and here we use Tegeticula yuccasella, the species with the widest diet breadth, to ask how host specificity and isolation by distance contribute to specialization. Isolation by distance at a regional scale was observed in nucleotide variation within the mitochondrial gene cytochrome oxidase I (COI) (r =.294; P =.003). Host-related genetic structure (F(ct) = 0.08) was found to be slightly lower than the level of structure observed between eastern and western moth populations (F(ct) = 0.096). However, 56% of the COI haplotypes sampled from moths on Yucca filamentosa mapped to a host-specific clade in the haplotype network. Taken together, these results suggest that differentiation among T. yuccasella populations on alternative hosts is slight, but gene flow is influenced by both host association and geographic distance.

Animals↗
PubMed2006

Transcriptomics and functional genomics of plant defence induction by phloem-feeding insects.

The relationship between phloem-feeding insects (PFIs) and plants offers an intriguing example of a highly specialized biotic interaction. These insects have evolved to survive on a nutritionally imbalanced diet of phloem sap, and to minimize wound responses in their host plants. As a consequence, plant perception of and responses to PFIs differ from plant interactions with other insect-feeding guilds. Transcriptome-wide analyses of gene expression are currently being applied to characterize plant responses to PFIs in crop plants with race-specific innate resistance, as well as in compatible interactions with susceptible hosts. Recent studies indicate that PFIs induce transcriptional reprogramming in their host plants, and that plant responses to PFIs appear to be quantitatively and qualitatively different from responses to other insects or pathogens. Transcript profiling studies also suggest that PFIs induce cell wall modifications, reduce photosynthetic activity, manipulate source-sink relations, and modify secondary metabolism in their hosts, and many of these responses appear to occur within the phloem tissue. Plant responses to these insects appear to be regulated in part by the salicylate, jasmonate, and ethylene signalling pathways. As additional transcript profiling data become available, forward and reverse genetic approaches will be necessary to determine which changes in gene expression influence resistance or susceptibility to PFIs.

Animals↗
PubMed2005

Genomic blueprint of Hahella chejuensis, a marine microbe producing an algicidal agent.

Harmful algal blooms, caused by rapid growth and accumulation of certain microalgae in the ocean, pose considerable impacts on marine environments, aquatic industries and even public health. Here, we present the 7.2-megabase genome of the marine bacterium Hahella chejuensis including genes responsible for the biosynthesis of a pigment which has the lytic activity against a red-tide dinoflagellate. H.chejuensis is the first sequenced species in the Oceanospiralles clade, and sequence analysis revealed its distant relationship to the Pseudomonas group. The genome was well equipped with genes for basic metabolic capabilities and contained a large number of genes involved in regulation or transport as well as with characteristics as a marine heterotroph. Sequence analysis also revealed a multitude of genes of functional equivalence or of possible foreign origin. Functions encoded in the genomic islands include biosynthesis of exopolysacchrides, toxins, polyketides or non-ribosomal peptides, iron utilization, motility, type III protein secretion and pigmentation. Molecular structure of the algicidal pigment, which was determined through LC-ESI-MS/MS and NMR analyses, indicated that it is prodigiosin. In conclusion, our work provides new insights into mitigating algal blooms in addition to genetic make-up, physiology, biotic interactions and biological roles in the community of a marine bacterium.

Adaptation, Physiological↗
PubMed2004

Marine dinoflagellates show induced life-history shifts to escape parasite infection in response to water-borne signals.

Many dinoflagellate species form dormant resting cysts as a part of their life cycle, and in some freshwater species, hatching of these cysts can be delayed by the presence of water-borne signals from grazing zooplankton. Some marine dinoflagellates can form temporary cysts, which may function to resist unfavourable short-term environmental conditions. We investigated whether the marine dinoflagellate Alexandrium ostenfeldii is able to induce an increased resistance to the parasitic flagellate Parvilucifera infectans by forming temporary cysts. We performed several laboratory experiments where dinoflagellates were exposed either to direct contact with parasites or to filtered water from cultures of parasite-infected conspecifics (parasite-derived signals). Infection by P. infectans is lethal to motile A. ostenfeldii cells, but temporary cysts were more resistant to parasite infection. Furthermore, A. ostenfeldii induced a shift in life-history stage (from motile cells to temporary cysts) when exposed to parasite-derived water-borne signals. The response was relaxed within a couple of hours, indicating that A. ostenfeldii may use this behaviour as a short-term escape mechanism to avoid parasite infection. The results suggest that intraspecies chemical communication evoked by biotic interactions can be an important mechanism controlling life-history shifts in marine dinoflagellates, which may have implications for the development of toxic algal blooms.

Adaptation, Physiological↗
PubMed1989

Natural extinction on islands.

Almost all recent extinction of species or subspecies on islands comes from human activities. On the other hand, in local populations there is much natural extinction and immigration, i.e. turnover, on small islands. Most of this turnover occurs in locally rare species, and attests to the phenomenon of minimum viable population size. The MacArthur-Wilson theory is based on this turnover which, from an ecological point of view, is generally trivial. More useful theories of minimum viable population size are being developed. Rarity is the precursor of extinction, and species can be rare in several ways. Models of these phenomena are still primitive, particularly those that relate habitat availability to population density. Models of interactive communities show phenomena that may be relevant to the understanding of extinction in the geological record. Lotka-Volterra equations indicate considerable sensitivity to invasions, sometimes producing a cascade of extinction. Chemostat equations show that the behaviour of food chains can change dramatically with small changes in parameters, suggesting that small environmental effects can sometimes cause large ecological changes, including extinctions, in interactive biotic communities.

Animals↗