Meteorite impact and the mass extinction of species at the Cretaceous/Tertiary boundary.
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Biological Evolution↗
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The tempo of mass extinction and recovery: the end-Permian example.
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Animals↗
Dynamics of Pleistocene population extinctions in Beringian brown bears.
The climatic and environmental changes associated with the last glaciation (90,000 to 10,000 years before the present; 90 to 10 ka B.P.) are an important example of the effects of global climate change on biological diversity. These effects were particularly marked in Beringia (northeastern Siberia, northwestern North America, and the exposed Bering Strait) during the late Pleistocene. To investigate the evolutionary impact of these events, we studied genetic change in the brown bear, Ursus arctos, in eastern Beringia over the past 60,000 years using DNA preserved in permafrost remains. A marked degree of genetic structure is observed in populations throughout this period despite local extinctions, reinvasions, and potential interspecies competition with the short-faced bear, Arctodus simus. The major phylogeographic changes occurred 35 to 21 ka B.P., before the glacial maximum, and little change is observed after this time. Late Pleistocene histories of mammalian taxa may be more complex than those that might be inferred from the fossil record or contemporary DNA sequences alone.
Animals↗
The effects of a pool of dispersers on host-parasitoid systems.
When individuals migrate in a multi-patch environment, a considerable proportion of their lifetime might be spent in transit between patches. We investigate the effects such a pool of dispersers can have on local stability and dynamics for a variety of multi-patch host-parasitoid models. When an arbitrary number of patches with internal Lotka-Volterra dynamics is coupled via a global pool of dispersers, the equilibrium is globally stable. The global pool is stabilising if dispersal is by hosts only, by parasitoids only, or by both hosts and parasitoids. If dispersal is local such that individuals first enter a pool close to the patch where they originate and then disperse to adjacent pools, the equilibrium is locally stable. We also analyse the situation where the functional response of parasitoids within a patch is Holling type II which is known to destabilise host-parasitoid systems. Coupling this single patch to a pool of dispersers can produce a locally stable interaction, provided the handling time of hosts is not too long. However, the pool provides a biologically realistic example of an interaction that is locally stable but not permanent. The longer the handling time, the smaller the region of population densities within which populations converge to the equilibrium state. In a multi-patch environment with a global disperser pool, the dynamics of the system are not qualitatively different from the single patch case (i.e. the equilibrium can be locally stable but the system is not permanent). In a multi-patch environment with local disperser pools, true spatial interactions between patches can develop. In contrast to the global pool, local pools can destabilise the stable equilibrium of the single patch case. Limit cycles develop around this unstable equilibrium that lead to extremely complicated dynamics. In contrast to the global pool, a system of local pools can exhibit bounded fluctuations so that populations do not go extinct.
Animals↗
Heumann-Hötzel model for aging revisited.
Since its proposition in 1995, the Heumann-Hötzel model has remained as an obscure model of biological aging. The main arguments used against it were its apparent inability to describe populations with many age intervals and its failure to prevent a population extinction when only deleterious mutations are present. We find that with a simple and minor change in the model these difficulties can be surmounted. Our numerical simulations show a plethora of interesting features: the catastrophic senescence, the Gompertz law and that postponing the reproduction increases the survival probability, as has already been experimentally confirmed for the drosophila fly.
Aging↗
Sensitivity of transmission surface plasmon resonance (T-SPR) spectroscopy: self-assembled multilayers on evaporated gold island films.
The distance dependence of the localized surface plasmon (SP) extinction of discontinuous gold films is a crucial issue in the application of transmission surface plasmon resonance (T-SPR) spectroscopy to chemical and biological sensing. This derives from the usual sensing configuration, whereby an analyte binds to a selective receptor layer on the gold film at a certain distance from the metal surface. In the present work the distance sensitivity of T-SPR spectroscopy of 1.0-5.0 nm (nominal thickness) gold island films evaporated on silanized glass substrates is studied by using coordination-based self-assembled multilayers, offering thickness tuning in the range from approximately 1 to approximately 15 nm. The morphology, composition and optical properties of the Au/multilayer systems were studied at each step of multilayer construction. High-resolution scanning electron microscopy (HRSEM) showed no apparent change in the underlying Au islands, while atomic force microscopy (AFM) indicated flattening of the surface topography during multilayer construction. A regular growth mode of the organic layers was substantiated by X-ray photoelectron spectroscopy (XPS). Transmission UV-visible spectra showed an increase of the extinction and a red shift of the maximum of the SP band upon addition of organic layers, establishing the distance dependence of the Au SP absorbance. The distance sensitivity of T-SPR spectroscopy can be varied by using characteristic substrate parameters, that is, Au nominal thickness and annealing. In particular, effective sensitivity up to a distance of at least 15 nm is demonstrated with 5 nm annealed Au films. It is shown that intensity measurements, particularly in the plasmon intensity change (PIC) presentation, provide an alternative to the usually measured plasmon band position, offering good accuracy and the possibility of measuring at a single wavelength. The present distance sensitivity results provide the basis for further development of T-SPR transducers based on receptor-coated Au island films.
Journal Article↗
The paradox of the parasites: implications for biological invasion.
The enemy-release hypothesis for biological invasions supposes that invasive species may be more successful in their introduced ranges than in their native ranges owing to the absence of coevolved natural enemies. Recent studies supporting this hypothesis have found that introduced plants and animals are less parasitized in their introduced ranges than in their native ranges. Expanding on this theory, I hypothesize that the role of enemy release may differ among the introduction, establishment and spread phases of an invasion. I present a simple model indicating that parasite release is unlikely to greatly affect the chance of establishment in populations with and without an immune subpopulation. The specific numerical relationship between the number of individuals introduced and the chance of establishment depends on a relationship between virulence, here conceptualized as the chance for the extinction of a lineage, and the fraction of the population infected at introduction. These results support the idea of a 'filter effect' in which different biological processes regulate the different phases of an invasion.
Adaptation, Physiological↗
Regularity in irregular echinoids.
Using the mathematical concept of eutactic star, we prove that it is possible to define a morphospace for irregular echinoids by using a single parameter. In particular, we have found an extraordinary geometric property in the flower-like patterns of the five ambulacral petals of these animals. This property is fulfilled with great accuracy for a large collection of fossil specimens and provides new insights in the study of the viable skeletal designs of extinct and/or living organisms.
Animals↗
Interplay of causation between suppliers and consumers in evolutionary trophic dynamics.
Natural selection, conceived as the process of small causes making small effects on the level of molecular evolutionary dynamics of a population, can yield global effects on the level of evolutionary trophic dynamics of populations, including those of mass extinctions. Occurrence of mass extinctions is due to the interplay of causation between suppliers and consumers in trophic dynamics. If the case of supplier causation is available such that resource exploitation by consumers on the upper trophic level follows in time resource presentation by suppliers on the lower, instead of resource exploitation followed by resource presentation, mass extinctions could be a norm of the evolutionary trophic dynamics.
Biological Evolution↗
Introductory conference: on the relevance of protected areas for the research on conservation ecology: from fundaments to applications.
Regarding the present rate of species extinction, preservation of biodiversity has become a prerequisite to achieve sustainable development. Among major challenges an urgent need in research in biological conservation is required to reach this goal. Protected areas deserve special importance due to their relevance for development of research both in fundamental and applied ecology. This papers aims at making a critical review of possibilities and priorities in conservation ecology in these areas.
Biodiversity↗
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↗
Comparison and evolution of the lagena in various animal species.
The structure of the vestibular organs of the teleost fish (bluegill), newts (Japanese fire-belly newt), frogs (black-spotted pond frog), snapping turtles and birds (chicks) was morphologically compared, with particular attention to the lagena macula, and the differences between animal species with relation to evolution were considered. Teleost fish had no striola on the lagena macula. The striola of newts were short and restricted to the central area of the macula, but those of frogs, snapping turtles and chicks extended from the anterior to posterior edges of the macula. This indicates that the frog is more highly evolved than the newt. The length of the kinocilium of sensory hairs was equal to that of the longest stereocilium in teleost fish and newts, but the kinocilia of frogs, snapping turtles and chicks were longer than the longest stereocilium. This indicates that the function of the lagena of teleost fish and newts is for hearing whilst in the other animals they are for posture. The diameter of the sensory hair bundles is small in teleost fish and frogs, but large in newts and snapping turtles. This indicates that the sensitivity of the sensory cells of the lagena towards outer force is low in teleost fish and frogs, high in newts and snapping turtles and intermediate in birds. The lagena of snapping turtles protrudes from the basilar papilla into the vestibule but the lagena of chicks lies on the tip of the long projecting basilar papilla. From observation of the locations of lagenae it is natural to speculate that there must have been some species of animal now extinct that had the evolving location of the lagena prior to that of chicks. In future it will be very interesting and useful to identify this extinct animal using DNA techniques.
Acoustic Maculae↗
Sperm competition and the dynamics of X chromosome drive: stability and extinction.
Several empirical studies of sperm competition in populations polymorphic for a driving X chromosome have revealed that Sex-ratio males (those carrying a driving X) are at a disadvantage relative to Standard males. Because the frequency of the driving X chromosome determines the population-level sex ratio and thus alters male and female mating rates, the evolutionary consequences of sperm competition for sex chromosome meiotic drive are subtle. As the SR allele increases in frequency, the ratio of females to males also increases, causing an increase in the male mating rate and a decrease in the female mating rate. While the former change may exacerbate the disadvantage of Sex-ratio males during sperm competition, the latter change decreases the incidence of sperm competition within the population. We analyze a model of the effects of sperm competition on a driving X chromosome and show that these opposing trends in male and female mating rates can result in two coexisting locally stable equilibria, one corresponding to a balanced polymorphism of the SR and ST alleles and the second to fixation of the ST allele. Stochastic fluctuations of either the population sex ratio or the SR frequency can then drive the population away from the balanced polymorphism and into the basin of attraction for the second equilibrium, resulting in fixation of the SR allele and extinction of the population.
Animals↗
Prehistoric bird extinctions and human hunting.
Holocene fossils document the extinction of hundreds of bird species on Pacific islands during prehistoric human occupation. Human hunting is implicated in these extinctions, but the impact of hunting is difficult to disentangle from the effects of other changes induced by humans, including habitat destruction and the introduction of other mammalian predators. Here, we use data from bones collected at a natural sand dune site and associated archaeological middens in New Zealand to show that, having controlled for differences in body mass and family membership (and hence for variation in life-history traits related to population growth rate), birds that were more intensively hunted by prehistoric humans had a higher probability of extinction. This result cannot be attributed to preservation biases and provides clear evidence that selective hunting contributed significantly to prehistoric bird extinctions at this site.
Animals↗
Population on the verge of a mutational meltdown? Fitness costs of genetic load for an amphibian in the wild.
The fitness costs of high genetic load in wild populations have rarely been assessed under natural conditions. Such costs are expected to be greatest in small, bottlenecked populations, including those occurring near range edges. Britain is at the northwesterly range limit of the natterjack toad Bufo calamita. We compared fitness attributes in two populations of this amphibian with very different recent histories. Key larval fitness attributes in B. calamita, notably growth rate and metamorph production, were substantially higher in the large outbreeding population (Ainsdale) than in the small and isolated one (Saltfleetby). These differences were manifest under seminatural conditions, when larvae were reared in mesh cages within breeding ponds at the site of the small population, and were exacerbated by high stress treatments. The results indicate that genetic load effects can be sufficiently severe enough to predispose extinction over relatively short time frames, as predicted by extinction vortex models.
Animals↗
Metapopulation persistence with age-dependent disturbance or succession.
Simple metapopulation models with random disturbances are used in species conservation or management, relying on the condition for persistence that the per-patch colonization rate be greater than the per-patch extinction rate. For a general model incorporating the role of succession or patch age-dependent extinction, I show that persistence requires the per-patch colonization rate to be greater than the inverse of mean patch age, where age is the time since the patch became available for colonization. Because mean patch age can be arbitrarily large relative to the extinction rate, currently persisting metapopulations may be persisting despite small colonization rates, and management approaches that do not consider the role of mean patch age may unnecessarily doom populations to extinction.
Animals↗
New methods for competitive coevolution.
We consider "competitive coevolution," in which fitness is based on direct competition among individuals selected from two independently evolving populations of "hosts" and "parasites." Competitive coevolution can lead to an "arms race," in which the two populations reciprocally drive one another to increasing levels of performance and complexity. We use the games of Nim and 3-D Tic-Tac-Toe as test problems to explore three new techniques in competitive coevolution. "Competitive fitness sharing" changes the way fitness is measured; "shared sampling" provides a method for selecting a strong, diverse set of parasites; and the "hall of fame" encourages arms races by saving good individuals from prior generations. We provide several different motivations for these methods and mathematical insights into their use. Experimental comparisons are done, and a detailed analysis of these experiments is presented in terms of testing issues, diversity, extinction, arms race progress measurements, and drift.
Algorithms↗
C-values of seven marine mammal species determined by flow cytometry.
C-values, which estimate genome size, have puzzled geneticists for years because they bear no relationship to organismal complexity. Though C-values have been estimated for thousands of species, considerably more data are required in order to better understanding genome evolution. This is particularly true for mammals, in which C-values are known for less than 8% of the total number of mammalian species. Among marine mammals, a C-value has been estimated only for the bottlenose dolphin (Tursiops truncatus). Thus examination of additional species of marine mammals is necessary for comparative purposes. It will enable a better understanding of marine mammal genome evolution, and it is also relevant to conservation, because larger genome size has been linked to increased likelihood of extinction in some plant and animal groups. Our study presents C-values of seven marine mammal species, including five cetacean species that are endangered to varying degrees. Similarly to the results for other groups, our results suggest that larger genome size in cetaceans is related to an increased likelihood of extinction.
Animals↗