An analysis of G matrix variation in two closely related cricket species,Gryllus firmus and G. pennsylvanicus

An important issue in evolutionary biology is understanding the pattern of G matrix variation in natural populations. We estimated four G matrices based on the morphological traits of two cricket species, Gryllus firmus and G. pennsylvanicus, each reared in two environments. We used three matrix comparison approaches, including the Flury hierarchy, to improve our ability to perceive all aspects of matrix variation. Our results demonstrate that different methods perceive different aspects of the matrices, which suggests that, until more is known about these methods, future studies should use several different statistical approaches. We also found that the differences in G matrices within a species can be larger than the differences between species. We conclude that the expression of the genetic architecture can vary with the environment and that future studies should compare G matrices across several environments. We also conclude that G matrices can be conserved at the level of closely related species.     

Evolutionary epistemology as science

What credentials does evolutionary epistemology have as science? A judgement based on past performance, both in terms of advancing an empirical programme and further ng theory construction, is not much. This paper briefly outlines some of the research areas, both theoretical and empirical, that can be developed and that might secure for evolutionary epistemology a future in evolutionary biology.     

The typology of syncretisms and the status of feature structure. Verbal paradigms across 355 Dutch dialects

In this article syncretic patterning in the present indicative paradigm of the verb kloppen (‘to knock’) is described for 355 Dutch dialects taken from the morphological atlas of Dutch dialects (Van den Berg 2003). Following Baerman et al. (2005, The syntax-morphology interface. A study of syncretism. Cambridge: Cambridge University Press), I distinguish syncretisms driven by (universal) feature structure and language specific sources of syncretism. I present independent evidence for the role of phonology, pragmatics and amplification in the formation of syncretic patterns of Dutch. The benefit of the study of the interaction between language specific routes to syncretism and feature structure is threefold. We know language specific routes to syncretism can obscure feature structure. By distinguishing the different routes to syncretism we canalsorevealthe strength of feature structure. Secondly, distinguishing sources of syncretisms enables us to understand similarities and differences in the cross-linguistic patterning of syncretisms. Thirdly, we can link typological data to language acquisition patterns.     

Oviposition preferences of aphidophagous hoverflies

1. Oviposition preferences of two predatory hoverflies, Episyrphus balteatus and Syrphus ribesii (Diptera, Syrphidae), were studied in the laboratory. 2. There was broad agreement between the two species: two of the top three preferred prey for oviposition in both hoverflies were pea and rose aphids; nettle aphids were consistently the least preferred. 3. Discrimination decreased with age.     

Hierarchy,spatial configuration,and nutrient cycling in a desert stream

Abstract Recent studies of nutrient cycling in Sycamore Creek in Arizona, USA, suggest that a thorough understanding requires a spatially explicit, hierarchical approach. Physical configuration determines the path that water follows as it moves downstream. Water follows flowpaths through surface stream components, the hyporheic zone beneath the surface stream, and the parafluvial (sand bar) zone. Characteristic biogeochemical processes in these subsystems alter nitrogen (N) species in transport, in part as a function of available concentrations of N species. At several hierarchical levels, substrate materials are an important determinant of nitrogen dynamics in desert streams. Sand is present in bars of variable size and shape, each of which can be considered a unit, interacting with the surface stream. Groups of these stream-sandbar units form a higher level, the reach. At the next higher scale, sandy reaches (runs) alternate with riffles. Where flowpaths converge, rates of N transformation are high and, as a result, change in concentration is a non-linear function of flowpath length. Disturbance by flash floods alters sandbar configuration. Between floods, the interaction of subsurface and surface flowpaths shapes configuration in each, thus a self-organizing element of spatial structure exists. Sandy runs are dominated by subsurface processes and are likely to be net nitrifiers while riffles are dominated by surface flow and are nitrogen fixers. Whether a stream ecosystem retains nitrogen, or transports it to downstream recipient systems, or is a net emitter of gaseous forms of N, depends upon the dynamics of a spatial mosaic of interacting elements. An understanding of the net effect of this mosaic requires a spatially explicit, hierarchical, multi-scale approach.     

Zonation of Ribosomal DNA Transcription Defines a Stem Cell Hierarchy in Colorectal Cancer

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Sibling competition, size variation and frequency-dependent outcrossing advantage in Plantago coronopus

Many plants display limited seed dispersal, thereby creating an opportunity for sibling competition, i.e. fitness-determined interactions between related individuals. Here I investigated the consequences of intra-specific competition, by varying density and genetic composition of neighbors, on the performance of seedlings derived by selfing or outcrossing of the partially self-fertilizing plant Plantago coronopus (L.). Seedlings from eight plants, randomly selected from an area of about 50 m² in a natural population, were used in (i) a density series with either one, four or eight siblings of each cross type per pot and (ii) a replacement series with eight plants per pot where selfed and outcrossed siblings were grown intermixed in varying frequencies. Density had a pronounced effect on plant performance. But, except for singly grown individuals, no differences were detected between selfed and outcrossed progenies in vegetative and reproductive biomass. When grown intermixed, selfed offspring were always inferior to their outcrossed relatives. The magnitude of reduction in performance was dependent on the number of outcrossed relatives a selfed seedling had to compete with, giving rise to a frequency-dependent fitness advantage to outcrossed seedlings. The major result of this study is (i) that the relative fitness of inbred progeny is strongly affected by the type of competitors (inbred or outbred) and (ii) that inbreeding depression varies according to the density and frequency of outbred plants and could be considered as a density- and frequency-dependent phenomenon. It is argued that sibling competition, due to the small genetic neighborhood of P. coronopus, might be an important selective force in natural populations of this species.     

Allorecognition and xenorecognition in reef corals: a decade of interactions

Xenorecognition phenomena in coral reefs are expressed by a striking array of morphological and cytological responses. Corals encountering conspecifics further elicit additional repertoires of effector mechanisms, specific to allogeneic challenges. Both inducible sets of antagonistic machineries of allo- and xenoresponses are highly specific. In many cases, they are predictable, reproducible, and reveal the hallmark of coral tissue capacity to distinguish between self and non-self. This essay summarizes a decade (1992 –2002) of published results on reef coral immune features. While studies on xenorecognition uncovered the existence of established, non-transitive hierarchies and the importance of antibacterial/cytotoxic compounds secreted by corals, allorecognition assays disclosed the presence of specific and complex non-transitive hierarchies dictated by the expression of a variety of effector mechanisms (‘tailored’ against different conspecifics), the existence of gradual maturation of alloresponses (important in the formation of natural chimeras), the debatable issue of allorecognition memory, and the appearance of delayed, second sets of alloresponses. A critical evaluation of historecognition reveals that expressed responses in different coral systems are phenotypically matched with counterpart outcomes recorded in the mammalian immune systems. Histocompatibility in corals, as in vertebrates, relies on recognition elements (not yet disclosed on the molecular level) as well as on effector mechanisms.