Cortical Pattern in Non-dividers, Dividers and Reorganizers of an Austrian Population of Paraurostyla weissei (Ciliophora, Hypotrichida): A Comparative Morphological and Biometrical Study

The morphology and the regulation of cortical pattern associated with the cell size, division, and reorganization of Paraurostyla weissei (Stein, 1859) were investigated. The ranges of variation of the Austrian, Polish, and American strains were compared by biometrical analyses. The Austrian population most frequently shows 4 frontal cirri in the anteriormost and 2 in the posterior row, 4 ventral rows, 8 transverse cirri, and 7 dorsal kineties. The oral primordium originates next to the postoral ventral row. The undulating membrane field and 3 frontal-ventral-transverse(FVT)-streaks for the opisthe develop as a result of the dispersion of the basal bodies of 1 or 2 cirri of the 1st ventral row. The farthest-right ventral row is of composite origin from 2 FVT-streaks. Three short dorsal bristle rows originating beside the right marginal row are a constant feature. In reorganizers the oral primordium characteristically possesses a group of kinetosomes extending toward the anterior right, fusing with the undulating membrane field. The development of dorsal primordia always starts in the 3rd dorsal kinety. These results provide important criteria for future species discrimination, if the examination of non-morphological characters supplies evidence that P. weissei is a complex of sibling species.     

Environmental, demographic, and genetic mating system variation among five geographically distinct dusky pipefish (Syngnathus floridae) populations

Genetic mating systems are expected to vary among and within populations in response to environmental and demographic factors. Despite the fact that mating system variation theoretically can have profound effects on important evolutionary processes such as sexual selection, extensive intraspecific surveys of geographical variation in mating systems are rare. We used microsatellite markers to characterize genetic mating systems of dusky pipefish, Syngnathus floridae , from five populations distributed from the mid-Atlantic Coast to the Western Gulf of Mexico. We also measured a number of environmental and demographic variables to examine correlations between the ecological setting and mating behaviour. Our results show that dusky pipefish are polygynandrous throughout their USA distribution, but they exhibit a wide range of quantitative variation in male mating behaviour. In addition, these five populations varied substantially with respect to environmental and demographic variables, and some of these were significantly correlated with aspects of the genetic mating system. While causal relationships cannot be firmly diagnosed from this type of comparative study, our results do identify several ecological factors, such as water temperature, adult sex ratio, and seagrass biomass, which should be considered in future experimental and comparative work. Overall, this study confirms the expectation that geographical variation in mating systems is widespread and shows that the dusky pipefish is an excellent model for continued research into the factors affecting mating systems in nature.     

The relative importance of birds and bees in the pollination of Metrosideros excelsa (Myrtaceae)

Exclusion experiments were used to assess the effect of different pollinator groups on outcrossing and seed production in Metrosideros excelsa. The main study site was Little Barrier Island, New Zealand where indigenous bird and native solitary bees are the main flower visitors. Our results showed that native birds were more important pollinators of M. excelsa than native bees. Seed production was much higher in open pollination than in two exclusion experiments where either birds were excluded and native bees only had access to flowers, or where all pollinators had been excluded. The number of fertile seeds per capsule was 45% higher after open pollination than in treatments with bee visitation only and 28% higher than in treatments where all flower visitors were excluded. Estimated outcrossing rates were significantly higher (t_m = 0.71) for open pollination in the upper canopy (>4 m above‐ground level) where bird visitation is presumed to be more frequent than for a treatment with native bee access only (t_m = 0.40). Our results also suggest that a large proportion of seeds (66%) arise from autonomous self‐pollination when all pollinators are excluded. In four trees of a modified mainland population with predominantly introduced birds and a mixture of introduced and native bees there was no decrease in seed production for the treatment allowing bee access only, indicating that – in contrast to native bees – honeybees may be more efficient pollinators of M. excelsa. Observation of the foraging behaviour of both groups of bees showed that native bees contact the stigma of flowers less frequently than honeybees. This is likely to be a consequence of their smaller body size relative to honeybees.     

Reproductive traits of riverine shrimps may explain the impact of altered flow conditions

1. The response of a species to environmental disturbance is largely mediated by its life history traits that have evolved within a particular habitat template. Altered flow seasonality, as a direct consequence of river regulation, is a major environmental disturbance and has been implicated in the redistribution of a range of riverine organisms. An understanding of the reasons for species‐specific responses, however, has proved elusive. 2. Here, we investigated the reproduction of three riverine shrimp species (Paratya australiensis, Caridina mccullochi and Macrobrachium australiense) that show contrasting patterns in distribution and abundance in regulated Australian rivers. 3. In all three species, breeding females were largest, and fecundity was greatest early in the breeding season (November–December). Fecundity and egg size subsequently declined, with lower investment (overall and per offspring) perhaps indicating that conditions for larvae were more favourable later in the breeding season (a time normally characterised by low flow, warm water and high productivity). 4. Interspecific differences in absolute values of reproductive traits were, however, striking. Paratya australiensis has typically ‘opportunistic’ traits (small body size, small eggs and high fecundity), whereas M. australiense has more ‘equilibrium’ traits (larger body size, larger eggs and moderate fecundity). Caridina mccullochi is intermediate, having neither high fecundity nor large size, and has limited swimming ability when young. This species is now absent from at least one heavily regulated river in south‐eastern Australia, and we hypothesise that its life history may explain this absence. 5. Studies involving aspects of life history, such as reproductive traits, are likely to improve our understanding of a range of organisms and assist in the management of disturbed or altered environments.     

Scale‐dependent genetic structure of the Idaho giant salamander (Dicamptodon aterrimus) in stream networks

The network architecture of streams and rivers constrains evolutionary, demographic and ecological processes of freshwater organisms. This consistent architecture also makes stream networks useful for testing general models of population genetic structure and the scaling of gene flow. We examined genetic structure and gene flow in the facultatively paedomorphic Idaho giant salamander, Dicamptodon aterrimus, in stream networks of Idaho and Montana, USA. We used microsatellite data to test population structure models by (i) examining hierarchical partitioning of genetic variation in stream networks; and (ii) testing for genetic isolation by distance along stream corridors vs. overland pathways. Replicated sampling of streams within catchments within three river basins revealed that hierarchical scale had strong effects on genetic structure and gene flow. amova identified significant structure at all hierarchical scales (among streams, among catchments, among basins), but divergence among catchments had the greatest structural influence. Isolation by distance was detected within catchments, and in‐stream distance was a strong predictor of genetic divergence. Patterns of genetic divergence suggest that differentiation among streams within catchments was driven by limited migration, consistent with a stream hierarchy model of population structure. However, there was no evidence of migration among catchments within basins, or among basins, indicating that gene flow only counters the effects of genetic drift at smaller scales (within rather than among catchments). These results show the strong influence of stream networks on population structure and genetic divergence of a salamander, with contrasting effects at different hierarchical scales.     

Morphology of Pinus uliginosa (Pinaceae) needles from populations exposed to and isolated from the direct influence of Pinus sylvestris

Eleven needle traits of two contrasting populations of Pinus uliginosa ( P. mugo complex), one located in a Pinus sylvestris forest, the other isolated from the influence of this species, were compared to quantify the degree of hybridization. Statistically significant differences between the studied populations were found, but both of them differed by a similar degree from P. sylvestris . Surprisingly, the P. uliginosa population surrounded by the P. sylvestris forest, which was expected to consist of individuals with intermediate traits, appeared to be more closely related to P. mugo than those isolated from the direct influence of P. sylvestris . Large differences in the distances between the analysed pair of populations of P. uliginosa and P. sylvestris have not influenced the morphological traits of the species. Gene flow from P. sylvestris to P. uliginosa is possible, but is likely to be small and does not differ compared with populations of P. uliginosa . The decline observed during the last three decades in both populations of the species has not influenced their needle morphological traits.  © 2003 The Linnean Society of London , Botanical Journal of the Linnean Society , 2003, 142, 83–91.     

Pinus mugo (Pinaceae) in the Abruzzi Mountains: high morphological variation in isolated populations

Thirty-three individuals of Pinus mugo from the Abruzzian Apennines (Italy), the most isolated population of the species, were examined biometrically to verify the range of trait variation and compared with six other populations sampled in the north-eastern part of the species range. Ten needles and ten cones from each individual were measured and quantified on the basis of 31 traits. The interpopulation comparison revealed a close affinity of the Abruzzian population of P. mugo to three of the six other populations. The other three north-eastern populations, one from the Tatra Mountains and two from the Chornokhora Mountains, appeared to be different. This suggests that these populations originated from other Pleistocene centres of occurrence. The intrapopulation variation of the population from the Abruzzian Apennines is comparable with those of all six populations of P. mugo from the Sudety and Carpathian Mountains. These findings support the hypothesis that isolated but locally abundant plant populations do not necessarily show a reduction in variability resulting from isolation.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 309–316.     

Differential taphonomy of modern brachiopods (San Juan Islands, Washington State): effect of intrinsic factors on damage and community-level abundance

The differences in shell structure and population turnover between organic-poor, impunctate (Hemithiris) and organic-rich, punctate brachiopod (Terebratalia) in a mixed-bottom, siliciclastic setting (San Juan Islands, WA) lead to different taphonomic damage and fidelity with respect to community-level abundance in death assemblages. In comparing shell interiors of similar-sized specimens, Terebratalia is predominantly affected by fibre detachment and shows almost no microbioerosion at the SEM scale; whereas, Hemithiris shows less marked fibre detachment at the SEM scale and is more intensely affected by microbioerosion both at SEM and light microscope (LM) scales. Fibre detachment related to rapid, microbially-induced organic matter decay appears to be the main destructive process acting on Terebratalia. Higher bioerosion levels in Hemithiris at SEM and LM scales are probably related to a combination of a low maceration rate and a preferential settlement by borers. From their vastly different abundances in life assemblages it can be deduced that Terebratalia produces dead shells at a much higher rate than Hemithiris. Therefore, the proportion of altered Terebratalia, relative to Hemithiris, is expected to be decreased due to its higher production of recently dead cohorts. That Terebratalia is also characterized by high damage levels shows that differential population turnover alone is not responsible for the differences in taphonomic damage. This shows that organic-rich and organic-poor shells are characterized by differential post-mortem durability. Although very few Hemithiris are present in the life assemblages, high durability ensures its relative over-representation in death assemblages. Terebratalia is not strongly under-represented in death assemblages, despite its high destruction rate, because of large production of recently dead shells. Even with the biasing effect of differential durability, the good fidelity reported in previous live-dead studies can be enhanced by higher population turnover of numerically dominant taxa, leading to constant input of recently dead shells into death assemblages.