TEM evidence for eukaryotic diversity in mid-Proterozoic oceans

Biomarker molecular fossils in 2770 Ma shales suggest that the Eucarya diverged from other principal domains early in Earth history. Nonetheless, at present, the oldest fossils that can be assigned to an extant eukaryotic clade are filamentous red algae preserved in ca. 1200 Ma cherts from Arctic Canada. Between these records lies a rich assortment of potentially protistan microfossils. Combined light microscopy, scanning electron microscopy, and transmission electron microscopy on 1500‐1400 Ma fossils from the Roper Group, Australia, and broadly coeval rocks from China show that these intermediate assemblages do indeed include a moderate diversity of eukaryotic remains. In particular, preserved cell wall ultrastructure, observed using transmission electron microscopy (TEM), can help to bridge the current stratigraphic gap between the unambiguous eukaryotic morphologies of later Proterozoic assemblages and molecular biomarkers in much older rocks.     

Defaecation by African elephants (Loxodonta africana africana (Blumenbach))

A study of defaecation in the African elephant was carried out at the Voi headquarters of the Tsavo (East) National Park. Four orphaned animals aged between 1 and 10 years were observed for 4 days and 3 nights. During the day the time and weight of each individual's defaecation was recorded while at night only the time of defaecation. Details of all the records are presented. Analysis has shown that the amount of dung produced with each defaecation bears a similar characteristic to that of the growth curve of these animals. The rate of defaecation does not vary significantly with age. Records of defaecation arranged by time demonstrate an apparent periodicity with a low peak mid-morning and a high peak mid-afternoon. The potential use of this information in feeding and population studies is discussed.     

Auxin Transport in Roots: VI. MOVEMENT OF IAA THROUGH DIFFERENT ZONES OF ZEA ROOTS

The movement of IAA through 6-mm segments excised 1 mm, 7 mm,and 13 mm behind the apex of the primary root of Zea mays seedlingshas been investigated at temperatures between 10 and 25°C. In all segments, and at all temperatures, the movement of IAAwas polarized acropetally, more IAA being found in apical receiverblocks than in basal ones after transport periods of up to 24h. The amounts of IAA which moved acropetally through a segmentdecreased as the segment was taken at an increasing distancebehind the root apex. Similarly, at least after transport periodsof 8 h, more IAA moved basipetally through the apical segmentthan through the basal ones. At 10°C the velocity of acropetal movement was similar inall three segments, but the acropetbut the acropetal flux wasgreatest in the apical segment and smallest in the most basalone. The same situation appears to exist at the other temperatures. The flux and velocity of the acropetal movement of IAA througha 6-mm segment taken 7 mm behind the apex of the root were similarto those previously reported for the acropetal movement througha 12-mm segment excised 1 mm behind the apex. The smaller amountsof IAA which move acropetally through longer root segments aretherefore attributable to a limitation of the flux in the mostbasal regions of the segment.     

STATISTICAL COVARIANCE AS A MEASURE OF PHYLOGENETIC RELATIONSHIP

Abstract— The method of parsimony in phylogenetic inference is often taken to mean two things: (1) that one should favor the genealogical hypothesis that minimizes the required number of homoplasies ( matchings of independently evolved derived character states ), and (2) that symplesiomorphies (matchings of primitive character states) have little or no evidential value for phylogenetic relationship. This paper shows both theses to be false by undermining recent likelihood arguments for them and by providing a more secure likelihood proof of a new method, which is incompatible with both (1) and (2).     

The Geoelectric Effect in Plant Shoots: II. SENSITIVITY OF CONCENTRATION CHAIN ELECTRODES TO REORIENTATION

A concentration chain, static-drop electrode system has beenused by several investigators to measure the geoelectric effectin plant shoots. This paper describes investigations of theinherent sensitivity of this electrode system to reorientationwith respect to gravity. When the gelatine plug of the electrodeis made up with distilled water, and the contact solution is0.1 mM KCl, a potential difference develops immediately afterelectrodes in direct contact are rotated through 90° intothe vertical plane. A similar response is found when the contactsolution is 5 mM CaCl₂. Increasing the concentration of thecontact solution, or incorporating KCl, K₂SO₄, or ZnSO₄ intothe gelatine plug, drastically reduces the potential differencedeveloped after reorientation. The potential difference acrosselectrodes in direct contact decreases as the electrodes age.The potential difference measured with these electrodes acrossa decapitated, horizontally placed, hypocotyl of Helianthusarmuus also decreases as the electrodes age. The polarity ofthe charge is reversed as compared with that found when theelectrodes are in direct contact. The kinetic characteristicsof the geoelectric potential difference developed across a non-decapitated,horizontal coleoptile of Zea mays change as the electrodes age.With fresh electrodes the potential develops immediately afterreorientation and continues to increase with time. With 4-day-oldelectrodes, however, no potential difference develops until9 min after the moment of reorientation, but then it increaseswith time. The characteristics of the geoelectric potentialdifference developed with the aged concentration-chain, static-dropelectrodes are similar to those found with several other typesof electrodes which do not themselves have an inherent sensitivityto reorientation with respect to gravity. The results supportour earlier suggestion that the potential difference which apparentlydevelops with the static-drop electrode system, immediatelyafter a shoot is turned through 90° in reality developsin the electrode system itself and not in the plant tissue.The geoelectric effect which arises in the living plant shootbegins to develop approximately 10 min after reorientation.     

Oviposition by Danaus plexippus in relation to cardenolide content of three Asclepias species in the southeastern U.S.A.

Abstract. 1. Female monarchs were observed in the field ovipositing on a native North American milkweek host, Asclepias humistrata L. As in a comparable Australian study on an introduced novel host ( Asclepias fruticosa L.) we found post-alighting rejection of plants with low and high cardiac glycoside concentration (CG).
2. Most oviposition took place on plants with CG in the range 200–500 μg/0.1 g dry weight. Thin-layer chromatography showed no obvious qualitative difference in cardenolide types between accepted and rejected plants, excepting an indication that rejected plants may have a higher level of more polar cardenolides.
3. In a controlled laboratory experiment comparing oviposition on a low ( A.incarnata L.) vs high ( A.curassavica L.) CG host plant species we found no relationship between CG and oviposition on the low CG species, but a negative relationship in the high CG species. This corroborates our findings on oviposition on single host species in the field.
4. We also record the first indication of a physiological cost of monarch larvae feeding on plants high in CG. There was a significant negative relationship between survival of first instar larvae and CG levels in plants. This study opens the way for further work on the association of monarch butterflies and their toxic milkweed hosts.