The genetic consequences of fluctuating inbreeding depression and the evolution of plant selfing rates

The magnitude of inbreeding depression, a central parameter in the evolution of plant mating systems, can vary depending on environmental conditions. However, the underlying genetic mechanisms causing environmental fluctuations in inbreeding depression, and the consequences of this variation for the evolution of self‐fertilization, have been little studied. Here, we consider temporal fluctuations of the selection coefficient in an explicit genetic model of inbreeding depression. We show that substantial variance in inbreeding depression can be generated at equilibrium by fluctuating selection, although the simulated variance tends to be lower than has been measured in experimental studies. Our simulations also reveal that purging of deleterious mutations does not depend on the variance in their selection coefficient. Finally, an evolutionary analysis shows that, in contrast to previous theoretical approaches, intermediate selfing rates are never evolutionarily stable when the variation in inbreeding depression is due to fluctuations in the selection coefficient on deleterious mutations.     

Anthropogenic changes to the landscape resulted in colonization of koalas in north‐east New South Wales,Australia

Significant changes in the distribution and persistence of species have been driven by Pleistocene cyclical climate changes and, more recently, by human modification of the environment. In eastern Australia, Pleistocene cyclical patterns in temperature and aridity led to the expansion and retraction of rainforest and likely affected the distribution of the koala (Phascolarctos cinereus, family Phascolarctidae), a species preferring dry or open woodland. More recently, anthropogenic landscape modification has led to a large‐scale change in distribution of the koala following the destruction of approx. 75 000 ha of subtropical rainforest in north‐east New South Wales termed the ‘Big Scrub’. Sharing of the control region haplotypes to the north and south of this region indicate historical connectivity of coastal koala populations. However, the majority (110/115) of sampled koalas from this region shared a single mitochondrial control region haplotype, suggesting that koalas did not persist in multiple refugial pockets within a heterogenous rainforest but expanded into the region following deforestation. Bayesian cluster analysis of microsatellite data consistently identified two clusters of koalas. One cluster, in the north of the area, had high microsatellite diversity (10 alleles per locus, He = 0.79) and clustered with koalas further to the north, thus suggesting a southerly expansion into the cleared area. To the south was a cluster with significantly lower diversity (six alleles per locus, He = 0.59, P < 0.001). It is possible there has been restricted or filtered movement of koalas between these clusters, which coincides with a cleared river valley and associated roads or immigration from populations both to the north and to the south. This study gives an insight into the timescale of changes in species distribution following rapid alterations to suitable habitat.     

The biology in Jamaica of the adults of the sphecid wasp Sceliphron assimile Dahlbom

Abstract. 1. The adult biology of the solitary mud-wasp Sceliphron assimile Dahlbom was studied in Jamaica.
2. Adults were active from sunrise until they finally settled in roosting groups a little before sunset. Nesting took place during an 8.5 h period commencing about 3 h after sunrise but individuals rarely spent > 4 h nesting per day, the remainder being spent in resting and feeding.
3. Males sought females in all places in the habitat.
4. The number of cells per nest was positively correlated to high cell density per unit area but negatively correlated to illuminance.
5. The number of pellets used to build a cell, but not cell length, was negatively correlated to the body length of the builder. There is evidence that females that build multiple nests locate them within a few metres of each other.
6. Incompletely stored cells were closed with an externally concave lamella of mud at the onset of rain or at 16.00—17.00 hours E.S.T. and never reopened the same day.
7. Like other species of Sceliphron studied in this respect S. assimile collected spiders belonging to the Argiopidae (particularly), and also mainly to the Thomisidae, Salticidae and Oxyopidae.
8. The consequences of the nest architecture on mortality and the method of building on distribution are discussed.
9. Protarrhenotoky and proterandry occur and probably influence the sex ratio through differential mortality and fecundity. A suggested interaction between the flight motor and the ovaries could regulate egg production.     

The utilization of bicarbonate ions by the macroalga Ascophyllum nodosum (L.) Le Jolis

Abstract A comparison of some of the methods used to determine whether aquatic plants have the ability to utilize bicarbonate ions as a source of inorganic carbon for photosynthesis has been applied to the intertidal macroalga Ascophyllum nodosum. These include: observing photosynthesis at a high pH (below the alga's CO₂ compensation point), pH compensation point determinations, comparing the photosynthetic characteristics at low pH (5.20) and at high pH (7.95), estimating the maximal rates at which CO₂ can diffuse through the unstirred layer and the rate at which CO₂ can be produced from bicarbonate dehydration in the unstirred layer. All indicated that Ascophyllum nodosum can use bicarbonate ions for photosynthesis, though some were not always consistent. Calculating the total inorganic carbon concentration from pH measurements and acidification CO₂ determinations revealed that the assumption that the alkalinity remains constant during pH drift experiments is not always valid.     

Evidence for DNA Synthesis in Pneumocystis carinii Trophozoites Treated with the β‐1,3‐Glucan Synthesis Inhibitor Pneumocandin L‐693,989

ABSTRACT. Pneumocandins inhibit β‐1,3‐glucan synthesis preventing the development of Pneumocystis cysts that are absent from the lungs of treated rats. To determine whether treated trophozoites are capable of DNA replication, cytochemical analyses were performed on 4′,6‐diamidino‐2‐phenylindole (DAPI)‐ and DB181‐stained Pneumocystis carinii isolated from pneumocandin L‐693‐989‐treated rats. Fluorescence intensities of trophozoite nuclei from drug‐treated rats were greater than those of untreated controls, suggesting that DNA replication was not inhibited but that cytokinesis and perhaps karyokinesis were blocked.     

Free Sugars and Organic Acids in the Leaves of Various Plant Species and their Compartmentation Between the Tissues4

The distribution of free sugars and organic acids between theepidermis and mesophyll of Tulipa gesneriana L., Vicia fabaL., and Commelina communis L. leaves was studied using mainlygas-liquid chromatography. Fructose, glucose, sucrose, and myo-inositol were found in theepidermis and mesophyll of all three species. In T. geenerianaleaf tissues arabinose (trace levels), stachyose, tuliposidesA and B (mainly in the mesophyll), and xylose (trace levelsalso in V. faba tissues) were also detected. The acids were more difficult to detect and identify, beingat considerably lower concentrations than the sugars in bothtissues. Fumaric, citric, malic, ascorbic (trace levels), andan unidentified acid were common to the epidermis and mesophyllof all three species. Of special interest was the detectionof large amounts of glyceric acid in the epidermis and mesophyllof V. faba; this acid was not detected in the tissues from theother species. Fumaric acid was also very abundant in the epidermisof V.faba. A special study was made of the compartmentation of acids andsugars between the epidermis and mesophyll of T. geenerianaleaves after light and dark treatments. No changes in free acidor sugar levels were detected in the epidermis or mesophyllafter these treatments. Except for suceinic acid (P < 0·05),there were no statistically significant differences in acidlevels between the epidermis and mesophyll but for most of thesugars (myo-inositol, arabinose, and xylose being exceptions)differences were highly significant (P < 0·001), highestlevels occurring in the mesophyll. The differences in sugarlevels and the similarity in acid levels between epidermis andmesophyll of tulip leaves were considered to be essentiallydue to the different CO₂ fixing mechanisms and capacities ofthe two tissues. The energy source for the essentially non-greenepidermal tissue was discussed.     

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5–7% relative humidity (RH)] and moist air (90–97% RH) by means of flow‐through CO₂ respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO₂ gas is released in bursts, with a low level of CO₂ release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO₂ production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).