Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: Trace fossil evidence

Endosymbionts are organisms that live within the growing skeleton of a live host organism, producing a cavity called a bioclaustration. The endosymbiont lives inside the bioclaustration, which it forms by locally inhibiting the normal skeletal growth of the host, a behaviour given the new ethological category, impedichnia. As trace fossils, bioclaustrations are direct evidence of past symbioses and are first recognized from the Late Ordovician (Caradoc). Bioclaustrations have a wide geographic distribution and occur in various skeletal marine invertebrates, including tabulate and rugose corals, calcareous sponges, bryozoans, brachiopods, and crinoids. Ten bioclaustration ichnogenera are recognized and occur preferentially in particular host taxa, suggesting host-specificity among Palaeozoic endosymbionts. The diversity of bioclaustrations increased during the Silurian and reached a climax by the late Middle Devonian (Givetian). A collapse in bioclaustration diversity and abundance during the Late Devonian is most significant among endosymbionts of host coral and calcareous sponge taxa that were in decline leading up to the Frasnian-Famennian mass extinction.     

Island isolation and habitat heterogeneity correlate with DNA variation in a marine snail (Littorina saxatilis)

The null assumption of molecular variation is that most of it is neutral to natural selection. This is in contrast to variation in morphological traits that we generally assume is maintained by selection, and therefore often by selection coupled to environmental heterogeneity in time and space. Examples of molecular variation that vary over habitat-shifts, particularly in allozymes, show that the relative impact of non-neutral variation as compared to neutral variation might be substantial in some systems. To assess the importance of habitat-generated variation in relation to variation generated by random processes in nuclear DNA markers at small spatial scales, we compared the effects of island isolation and habitat heterogeneity on genetic substructuring in a rocky shore snail ( Littorina saxatilis ). This species has a restricted migration among islands owing to the lack of free-floating larvae. Earlier studies show that allozymes vary extensively as a consequence of isolation by water barriers among islands, but also as a consequence of divergent selection among different microhabitats within islands. In the DNA markers we observed genetic differentiation owing to island isolation at three of nine loci. In addition, variation at three loci correlated with habitat type, but the correlation for two of the loci was weak. Overall, isolation contributed slightly more to the genetic variation among populations than did habitat-related factors but the difference was small. It is concluded that both island isolation, which interrupts gene flow, and a heterogeneous habitat cause genetic substructuring at the DNA level in L. saxatilis in the studied area, and thus in this species we need to be somewhat concerned about habitat heterogeneity also at DNA loci.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 377–384.     

Annual and seasonal reproductive trends in the Lesser Spotted Woodpecker Dendrocopos minor

Annual and seasonal variation in reproductive timing and performance were studied in a population of the Lesser Spotted Woodpecker Dendrocopos minor over 10 years in southern Sweden. The median laying date of the first egg varied by up to 17 days between years, being generally larger than the variation of laying dates within years. Neither clutch size, brood size in successful nests, fledging success in successful nests nor mean nestling weight differed significantly between years. There was no trend for mean clutch size to vary between early and late years. In spite of a more than threefold variation in population size, no reproductive variable demonstrated an apparent density-dependence. Within the season, clutch size declined steeply with increasing clutch initiation date, whereas fledging success and nesting success did not, leading to a trend in brood size almost identical to the trend in clutch size. The survival prospects of fledged young declined with increasing clutch initiation date, and it is argued that the clutch size laid is a strategic adjustment to laying date. Out of 124 breeding attempts, 34% did not produce fledged young. In 9% of the breeding attempts, pairs laid no eggs. At least 20% of the breeding attempts failed after egg-laying. The most common cause of breeding failure was loss of the breeding partner followed by nest abandonment (40% of the failures). Only 16–28% of the failures were due to predation on the nest. Most complete failures, and also partial losses from nests, occurred at the early breeding stages. It is argued that the early nestling phase may be a critical stage, which the woodpeckers adjust to coincide with the seasonal food peak, explaining the strikingly late breeding season compared with other non-migrant species.     

pH-Dependent Effects of 2,4-Dinitrophenol (DNP) on Proliferation, Endocytosis, Fine Structure and DNP Resistance in Tetrahymena

ABSTRACT. In view of the importance of external pH on cytotoxic effects of ionizable agents, the pH-dependent effects of 2,4-dinitrophenol (DNP) were investigated. As uncoupler of oxidative phosphorylation. DNP interferes with the proton gradient across the inner mitochondrial membrane. DNP was added to proliferating Tetrahymena pyriformis in media of different initial pH. Effects studied were rates of cell proliferation and endocytosis, and fine structure. Findings correlated with the calculated concentration of undissociated DNP, taking into account that pH changes with time and cell density in Tetrahymena cultures. A linear relationship thus emerged between initial concentrations of undissociated DNP and lengths of the lag preceding cell proliferation. Once resumed, the rate of proliferation corresponded to that of control cells, even in different concentrations of undissociated DNP, presumably indicating an adaptation mechanism. Endocytosis was elevated throughout a wide range of undissociated DNP concentrations with a sharp transition towards inhibition at high DNP concentrations causing lethality with time. Changes in fine structure of DNP-treated cells (mitochondria, peroxisomes, nucleoli) also depended on the concentration of undissociated DNP.     

The effect of climate change on partial migration – the blue tit paradox

Climate change has proven to affect various aspects of the migration of birds. In response to milder winters making the habitat more profitable and increasing the survival of residents, the migratory fraction of partially migratory populations has been predicted to decline. We studied the blue tit Parus caeruleus , a common partial migrant in southern Sweden. The numbers migrating at Falsterbo, a migratory passage site in SW Sweden, has increased during the last decades, in parallel with increasing winter and annual temperatures. Migration data from Falsterbo were compared with yearly indices of the size of the breeding population as estimated by the Swedish National Bird Monitoring Programme. Over the study period 1975–2004, also the breeding population has increased in size. The proportion of blue tits migrating each year did not change over the study period, or possibly even increased slightly, which is in contrast to how climate change has been predicted to influence populations containing both migratory and resident individuals. The most important factors determining the intensity of blue tit migration in a given year was the size of an important winter food source, the beech mast crop (more migrants at lower crops) and the size of the breeding population (more migrants at higher densities).     

Macro-alga population shows low but significant heterogeneity in developmental instability with no detectable association with individual fitness

We studied among-individual variation in developmental instability (DI) and fitness-related parameters in 80 individual plants of Fucus vesiculosus (Phaeophyta). To minimize differential environmental effects, plants were sampled from one environmentally homogenous population. DI was measured as fluctuating asymmetry (FA) of four bilaterally symmetric traits (branch length, receptacle length and width, and bladder width) for an average total of 30 structures per individual. FA levels varied significantly among individual plants, consistent with a coefficient of variation of 0.12 for organism-wide DI or 0.13–0.21 for trait-specific DI. These values are lower than estimates for other organisms, suggesting that the genetic heterogeneity in DI was low. The data provide some evidence for organism-wide DI, but simulations show that organism-wide and trait-specific variation cannot be conclusively separated. Growth rate of branch tips was determined experimentally, demonstrating significant variation among individuals. FA was not significantly correlated with growth rate or with morphological variables associated with fecundity, age, size, and health. At the same time, the signs of all the correlation coefficients were consistent with the expectation of a negative relationship between DI and fitness. The simulations indicated that the correlation between FA and the underlying DI was comparatively strong (high hypothetical repeatability), implying that the lack of significant associations between FA and fitness variables reflected a weak relationship between DI and these fitness parameters. This weak relationship may be related to the low amount of DI variation in the study population.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 277–286.     

Distribution patterns and dispersal strategies of Galiciales

In Caliciales both passive and active spore dispersal occurs. A review of the distribution of 162 species is given. Species with small spores have wider distribution than species with large spores, irrespective of dispersal strategy. In antitropical species there is only rarely a differentiation between Northern and Southern Hemisphere populations. It is concluded that in several small-spored genera long-distance dispersal has been instrumental in dispersing the species and range extensions have been much more frequent than in large-spored species for which vicariance explanations are more appropriate. Comparisons with bryophyte distributions show differences in dispersal strategies and distribution patterns.     

Structural Aspects of Digestion of Escherichia coli in Tetrahymena1

Tetrahymena pyriformis ingested Escherichia coli for 15–20 min and the fine structure of food vacuoles was analyzed 5, 15, 30, 60, 90, 120, and 180 min after uptake began. From this analysis, eight vacuolar stages could be defined, and three to four stages were found in each sample. Stage 1 represents forming and newly detached vacuoles with a random distribution of bacteria. Stage 2 is the “dehydration” vacuole in which the bacteria are compacted and a few may lyse. Stage 3, corresponding to the acid phosphatase-positive stage, has an electron-dense vacuolar matrix revealing components of lysed bacteria and the translucent coat of intact bacteria. Stage 4 is the “halo” stage where centrally located, intact bacteria are surrounded by lysed material being removed by pinocytic activity of the vacuolar membrane. Stage 5 represents lysis of bacteria remaining intact until this stage; the stage is apparently followed by a second stage 4. Stage 6 contains few bacterial profiles in a smeared homogeneous mass. Stage 7 contains numerous vesicular membranous structures which apparently become transferred to the cytoplasm as such. Stage 8 represents defecation vacuoles derived from fusion of smaller vacuoles. The main findings are as follows: I) Bacterial lysis may occur during acidification of the vacuole prior to fusion with lysosomes. II) Digestion of bacteria apparently occurs in “bursts” as indicated by the extended time that vacuoles in stages 4 and 5 are present. III) Bacterial membranous structures seem to be transferred directly to the cytoplasm of Tetrahymena. IV) Mass defecation occurs 2 h after uptake begins.