The genus Pikea (Dumontiaceae, Rhodophyta) in England and the North Pacific: Comparative morphological, life history, and molecular studies

A Pikea species attributed to Pikea californica Harvey has been established in England since at least 1967. Previously, this species was believed to occur only in Japan and Pacific North America. Comparative morphological studies on field-collected material and cultured isolates from England, California, and Japan and analysis of organellar DNA restriction fragment length polymorphisms, detected using labeled organellar DNA as a non-radioactive probe, showed that English Pikea is conspecific with P. californica from California. Both populations consist of dioecious gametophytes with heteromorphic life histories involving crustose tetrasporophytes; 96% of organellar DNA bands were shared between interoceanic samples. A second dioecious species of Pikea, P. pinnata Setchell In Collins, Holden et Setchell, grows sympatrically with P. californica near San Francisco but can be distinguished by softer texture, more regular branching pattern, and elongate cystocarpic axes. Pikea pinnata and P. californica samples shared 49-50% of organellar DNA bands, consistent with their being distinct species. Herbarium specimens of P. robusta Abbott resemble P. pinnata in some morphological features but axes are much wider; P. robusta may represent a further, strictly subtidal species but fertile material is unknown. Pikea thalli from Japan, previously attributed to P. californica and described here as Pikea yoshizakii sp. nov., are monoecious and show a strikingly different type of life history. After fertilization, gonimoblast filaments grow outward through the cortex and form tetrasporangial nemathecia; released tetraspores develop directly into erect thalli. Tetrasporoblastic life histories are characteristic of certain members of the Phyllophoraceae but were previously unknown in the Dumontiaceae. Japanese P. yoshizakii shared 55 and 56% of organellar DNA bands with P. californica and P. pinnata, respectively phylogenetic analysis indicated equally distant relationships to both species. Pikea yoshizakii or a closely similar species with the same life history occurs in southern California and Mexico.

A MOLECULAR AND MORPHOLOGICAL ANALYSIS OF THE GYMNOGONGRUS-DEVONIENSIS (RHODOPHYTA) COMPLEX IN THE NORTH-ATLANTIC

The Gymnogongrus devoniensis (Greville) Schotter complex in the North Atlantic Ocean was elucidated by comparative molecular, morphological, and culture studies. Restriction fragment length patterns and hybridization data on organellar DNA revealed two distinct taxa in samples from Europe and eastern Canada. Nucleotide sequences for the intergenic spacer between the large and small subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and the adjoining regions of both genes, differed by 12.5-13.4% between the two taxa. One of the taxa, which included material from the type locality of G. devoniensis at Torbay, Devon, England, was taken to represent authentic G. devoniensis. Within this taxon, samples from Ireland, England, northern France, northern Spain, and southern Portugal showed great morphological variation, particularly in habit, but their Rubisco spacer sequences were identical or differed by only a single nucleotide. Constant morphological features included the development, from a single auxiliary cell, of the spherical cystocarp with a thick mucilage sheath that appears to be typical of Gymnogongrus species with internal cystocarps. Two life-history types were found. Northern isolates underwent a direct-type life history, recycling apomictic females by carpospores, whereas the Portuguese isolate followed a heteromorphic life history in which carpospores gave rise to a crustose tetrasporophyte.

Phenotypic plasticity affects the response of a sexually selected trait to anthropogenic noise

Sexually selected traits are shaped by an interaction between sexual selection and other natural selection pressures in the environment. However, there is little understanding of how recent anthropogenic environmental change affects the elaboration of sexually selected traits. Most sexually selected traits are complex displays comprising multiple components that interact in a functional way, thereby affecting overall trait expression. To understand how environmental change may shape the expression of sexually selected traits, we have to consider not only (i) the phenotypic plasticity of individual components of traits but also their (ii) phenotypic integration, that is, the correlations among trait components, as well as (iii) plasticity integration, that is, the correlations among the plasticities of trait components. Here, we show that background noise is a considerable pressure in shaping a sexually selected multicomponent acoustic signal, bird song. We compared singing behavior of European robins (Erithacus rubecula) in territories that differed in levels of anthropogenic noise and conducted noise-exposure experiments to test if behavioral plasticity caused immediate changes in song components, for example, minimum frequency, song complexity, and song length. We found that song components differed in their plasticity to background noise and that plasticity integration between components may further restrict the elaboration of song. Thus, the altered expression of song components under noise exposure leads to increased phenotypic integration, which is linked with reduced song complexity. Our findings demonstrate that plasticity integration restricts the elaboration of a sexually selected trait, which raises the question of how changing environments may modify sexual selection.

Convergent evolutionary processes driven by foraging opportunity in two sympatric morph pairs of Arctic charr with contrasting post-glacial origins

The expression of two or more discrete phenotypes amongst individuals within a species (morphs) provides multiple modes upon which selection can act semi-independently, and thus may be an important stage in speciation. In the present study, we compared two sympatric morph systems aiming to address hypotheses related to their evolutionary origin. Arctic charr in sympatry in Loch Tay, Scotland, exhibit one of two discrete, alternative body size phenotypes at maturity (large or small body size). Arctic charr in Loch Awe segregate into two temporally segregated spawning groups (breeding in either spring or autumn). Mitochondrial DNA restriction fragment length polymorphism analysis showed that the morph pairs in both lakes comprise separate gene pools, although segregation of the Loch Awe morphs is more subtle than that of Loch Tay. We conclude that the Loch Awe morphs diverged in situ (within the lake), whereas Loch Tay morphs most likely arose through multiple invasions by different ancestral groups that segregated before post-glacial invasion (i.e. in allopatry). Both morph pairs showed clear trophic segregation between planktonic and benthic resources (measured by stable isotope analysis) but this was significantly less distinct in Loch Tay than in Loch Awe. By contrast, both inter-morph morphological and life-history differences were more subtle in Loch Awe than in Loch Tay. The strong ecological but relatively weak morphological and life-history divergence of the in situ derived morphs compared to morphs with allopatric origins indicates a strong link between early ecological and subsequent genetic divergence of sympatric origin emerging species pairs. The emergence of parallel specialisms despite distinct genetic origins of these morph pairs suggests that the effect of available foraging opportunities may be at least as important as genetic origin in structuring sympatric divergence in post-glacial fishes with high levels of phenotypic plasticity. (c) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, , .

Parallel and nonparallel ecological, morphological and genetic divergence in lake-stream stickleback from a single catchment

Parallel phenotypic evolution in similar environments has been well studied in evolutionary biology; however, comparatively little is known about the influence of determinism and historical contingency on the nature, extent and generality of this divergence. Taking advantage of a novel system containing multiple lake-stream stickleback populations, we examined the extent of ecological, morphological and genetic divergence between three-spined stickleback present in parapatric environments. Consistent with other lake-stream studies, we found a shift towards a deeper body and shorter gill rakers in stream fish. Morphological shifts were concurrent with changes in diet, indicated by both stable isotope and stomach contents analysis. Performing a multivariate test for shared and unique components of evolutionary response to the distance gradient from the lake, we found a strong signature of parallel adaptation. Nonparallel divergence was also present, attributable mainly to differences between river locations. We additionally found evidence of genetic substructuring across five lake-stream transitions, indicating that some level of reproductive isolation occurs between populations in these habitats. Strong correlations between pairwise measures of morphological, ecological and genetic distance between lake and stream populations supports the hypothesis that divergent natural selection between habitats drives adaptive divergence and reproductive isolation. Lake-stream stickleback divergence in Lough Neagh provides evidence for the deterministic role of selection and supports the hypothesis that parallel selection in similar environments may initiate parallel speciation.

Freshwater pearl mussels show plasticity of responses to different predation risks but also show consistent individual differences in responsiveness

Animals often show behavioural plasticity with respect to predation risk but also show behavioural syndromes in terms of consistency of responses to different stimuli. We examine these features in the freshwater pearl mussel. These bivalves often aggregate presumably to reduce predation risk to each individual. Predation risk, however, will be higher in the presence of predator cues. Here we use dimming light, vibration and touch as novel stimuli to examine the trade-off between motivation to feed and motivation to avoid predation. We present two experiments that each use three sequential novel stimuli to cause the mussels to close their valves and hence cease feeding. We find that mussels within a group showed shorter closure times than solitary mussels, consistent with decreased vulnerability to predation in group-living individuals. Mussels exposed to the odour of a predatory crayfish showed longer closures than control mussels, highlighting the predator assessment abilities of this species. However, individuals showed significant consistency in their closure responses across the trial series, in line with behavioural syndrome theory. Our results show that bivalves trade-off feeding and predator avoidance according to predation risk but the degree to which this is achieved is constrained by behavioural consistency. © 2011 Elsevier B.V.

Morphological cladistic analysis as a model for character evaluation in primitive living chitons (Polyplacophora, Lepidopleurina)

Chitons are often referred to as "living fossils" in part because they are proposed as one of the earliest-diverging groups of living molluscs, but also because the gross morphology of the polyplacophoran shell has been conserved for hundreds of millions of years. As such, the analysis of evolution and radiation within polyplacophorans is of considerable interest not only for resolving the shape of pan-molluscan phylogeny but also as model organisms for the study of character evolution. This study presents a new, rigorous cladistic analysis of the morphological characters used in taxonomic descriptions for chitons in the living suborder Lepidopleurina Thiele, 1910 (the earliest-derived living group of chitons). Shell-based characters alone entirely fail to recover any recognized subdivisions within the group, which may raise serious questions about the application of fossil data (from isolated shell valves). New analysis including characters from girdle armature and gill arrangements recovers some genera within the group but also points to the lack of monophyly within the main genus Leptochiton Gray, 1847. Additional characters from molecular data and soft anatomy, used in combination, are clearly needed to resolve questions of chiton relationships. However, the data sets currently available already provide interesting insights into the analytical power of traditional morphology as well as some knowledge about the early evolution and radiation of this group.

Genetic and morphological characterization of Cladobotryum species causing cobweb disease of mushrooms

Cladobotryum dendroides (= Dactylium dendroides) has hitherto been regarded as the major causal agent of cobweb disease of the cultivated mushroom, Agaricus bisporus. Nucleotide sequence data for the internal transcribed spacer (ITS) regions of four Cladobotryum/Hypomyces species reported to be associated with cobweb disease, however, indicate that the most common pathogen is now C. mycophilum. This cobweb pathogen varies somewhat in conidial septation from published descriptions of C. mycophilum and lacks the distinctive colony odor. ITS sequencing revealed minor nucleotide variation which split isolates of the pathogen into three subgroups, two comprising isolates that were sensitive to methylbenzimidazole carbamate (MBC) fungicides and one comprising MBC-resistant isolates. The MBC-resistant isolates, which were only obtained from Ireland and Great Britain, clustered together strongly in randomly amplified polymorphic DNA (RAPD) PCR analysis, suggesting that they may be clonal. The MBC-sensitive isolates were more diverse. A RAPD fragment of 800 to 900 bp, containing a microsatellite and found in the MBC-resistant isolates, also indicated their clonal nature; the microsatellites of these isolates contained the same number of GA repeats. Smaller, polymorphic microsatellites, similarly comprising GA repeats, in the MBC-sensitive isolates in general correlated with their geographic origin.