A Century of Sea Urchin Development

SYNOPSIS. In the last quarter of the nineteenth century severalinvestigators including Richard and Oskar Hertwig, Theodor Boveri,Hans Driesch, Curt Herbst, T. H. Morgan and others turned theirattention to sea urchin eggs and early embryos. This favorablecombination of outstanding investigators and the sea urchinembryo as an experimental organism contributed to a fundamentalunderstanding of the cell, fertilization and heredity. The advantagesof the sea urchin continued to be recognized as experimentalembryologists used these embryos to develop the concepts ofgradients, regulative development and inductive interactions.Then, as developmental biology arose from chemical embryology,the sea urchin embryo once again emerged as an ideal experimentalanimal, pivotal in the understanding of the molecular and developmentalbiology of eukaryotic organisms.     

The effect of methanogen growth on mineral substrates: will Ni markers of methanogen‐based communities be detectable in the rock record?

Methanogens, thought to be present on early Earth, have a high requirement for Ni, suggesting that Ni utilization could be a potential biosignature for methanogens if enhanced Ni extraction from surrounding minerals accompanies methanogenic growth. To test the potential for such Ni extraction from minerals by methanogens, Ni release from Ni‐containing silicate glass was measured in Ni‐free growth medium in the presence of the methanogen Methanothermobacter thermoautotrophicus (average pH ∼7.0) and observed to be higher than an abiotic control (average pH ∼6.8). However, batch dissolution experiments and a siderophore assay indicate that cell exudates such as siderophores, low molecular weight organic acids, or lysates accompanying cell death are not responsible for the observed increase in Ni release rate. In addition, scanning electron microscopy (SEM) shows little to no evidence of direct microbe–mineral interactions such as biofilms or pitting. Instead, comparison with abiotic experiments suggests that changes in pH due to CO₂ uptake may be responsible for enhanced dissolution in the presence of metabolizing cells. These results document that methanogens may not preferentially extract Ni from surrounding minerals although they may indirectly affect mineral reaction rates that are pH sensitive. Thus identifiable Ni biosignatures may not exist in the rock record to document the presence of methanogens on early Earth or Mars.     

Untaming the Frontier in Anthropology, Archaeology, and History

Untaming the Frontier in Anthropology, Archaeology, and History. Bradley J. Parker and Lars Rodseth, eds. Tucson: University of Arizona Press, 2005. 294 pp.     

Multidecadal to millennial-scale shifts in drought conditions on the Canadian prairies over the past six millennia: implications for future drought assessment

Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between ∼1700–2000 cal. yr bp and ∼3600–3900 cal. yr bp , as well as at ∼5400–5500 cal. yr bp for the two sites which extend back to at least 6000 cal. yr bp . The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanic–atmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies.     

Water Deficit Enhanced Cotton Resistance to Spider Mite Herbivory

We investigated the responses of cotton (Gossypium hirsutumL.)to the combined effects of soil water deficit and two-spottedspider mite (Tetranychus urticaeKoch) infestation. Two mitetreatments (-M: uninfested, +M: artificially infested 83 d aftersowing), and two water regimes (+W: well watered, -W: waterstressed) were combined factorially in four treatments. Mitecolonies developed at similar rates in well-watered and water-stressedcrops. Despite the similar intensity of infestation, visualsymptoms of mite injury were more marked in well-watered hostplants (+M+W) than in their water-stressed counterparts (+M-W).Lint yield of unstressed controls (-M+W) was 175 g m^-2. In uninfestedcrops, water deficit reduced yield by 30%, mites reduced theyield of well-watered crops by 92%, and the combination of miteinfestation and water deficit reduced yield by 72% (water effect:P<0.01;mite and interaction effect:P<0.0001). Differences in yieldresponses to mites between well-watered and water-stressed cropswere mostly related to differences in reproductive partitioning.The interaction between mites and water deficit was also significantfor other crop variables including canopy temperature, leafwater potential, concentration of nitrogen in reproductive structuresand seed oil concentration. The magnitude and consistency ofthe interaction between both stresses indicates that, underour experimental conditions, mechanisms of adjustment to waterdeficit may have enhanced cotton resistance to mites. This isfurther supported by (a) an increase in specific leaf weightand a parallel increase in leaf penetration resistance due towater deficit; (b) a negative association between macroscopicsymptoms of mite injury and leaf penetration resistance; and(c) a choice test showing that adult female mites preferredto feed and oviposit on leaves from well-watered plants.Copyright1998 Annals of Botany Company Gossypium hirsutumL.;Tetranychus urticaeKoch; leaf water potential; leaf penetration resistance; canopy temperature; multiple stresses; specific leaf weight; radiation use efficiency; nitrogen concentration; reproductive allocation.     

Phylogenetic analysis of eleven species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae) based on comparisons of allozymes

Freshwater snails in the genus Biomphalaria transmit Schistosoma mansoni in Africa, South America and the Caribbean region. Although considerable attention has been given to the identification of species, little is known of evolutionary relationships among the species. A phylogenetic analysis of 25 populations representing 11 species was performed on 25 enzyme loci examined using starch gel electrophoresis. A phylogenetic analysis of the individual populations produced 60 trees of equal length. The 60 trees have a consistency index value of 75.9% and a retention index value of 76.5%. The phylogenetic analysis provided strong support for the monophyly of Biomphalaria with either 14 or 15 synapomorphies uniting all of the species included and separating them from the outgroup, two species of Helisoma. Four nominal species represented by multiple populations formed monophyletic groups. Populations of B. sudanica, B. choanomphala, and B. alexandrina were interspersed. Ten arrangements were obtained for the populations of these three species. A variety of ingroup taxa were used to root the trees, and all provided support for the use of Helisoma species as an outgroup. In all of the trees obtained, the African species together formed a monophyletic group. In none of the trees obtained did the neotropical species form a monophyletic group. A constrained analysis requiring the monophyly of the neotropical species as well as the African species resulted in 90 trees just two steps longer than the shortest trees. Analysis of the species from either hemisphere alone resulted in decreased resolution, as measured by an increase in the number of trees obtained. This finding suggests that further comparisons of species from the two hemispheres will be of considerable value. Finally, two species which are resistant to infection with S. mansoni were included among the eleven studied. Neither of these species formed the sister group to all of the other species included, indicating that susceptibility is the plesiomorphic state, and that resistance is derived. Similarly, in none of the trees obtained did the two resistant species fall out as sister taxa, indicating that resistance arose independently twice.     

Breeding strategies of Antarctic Petrels Thalassoica antarctica and Southern Fulmars Fulmarus glacialoides in the high Antarctic and implications for reproductive success

Breeding strategies of two closely related fulmarine petrels were studied on Ardery Island, on the continental coast of East Antarctica, where short summers are expected to narrow the time-window for reproduction. Both species had a similar breeding period (97 days from laying to fledging) but Antarctic Petrels Thalassoica antarctica bred up to 16 days earlier than Southern Fulmars. During the pre-laying exodus, all Antarctic Petrels deserted the colony, whereas some Southern Fulmars Fulmarus glacialoides remained. Antarctic Petrels exhibited stronger synchronization in breeding, made longer foraging trips and spent less time guarding their chicks than Southern Fulmars. Overall breeding success of both species was similar but failures of Antarctic Petrels were concentrated in the early egg-phase and after hatching, when parents ceased guarding. Southern Fulmars lost eggs and chicks later in the breeding cycle and so wasted more parental investment in failed breeding attempts. Different breeding strategies may be imposed by flight characteristics; Southern Fulmars are less capable of crossing large expanses of pack ice and need to delay breeding until the sea ice retreats and breaks up. However, due to the short summer they risk chick failure when weather conditions deteriorate late in the season.     

AN EARLY HERBIVOROUS LIZARD FROM THE LOWER CRETACEOUS OF JAPAN

Abstract:  The Lower Cretaceous Tetori Group of Japan has yielded diverse freshwater and terrestrial vertebrate assemblages. The most productive small vertebrate locality is the 'Kaseki-Kabe' or 'fossil-bluff' at Kuwajima, Hakusan City, Ishikawa Prefecture. These deposits have produced at least six distinct lizard taxa of which one, described and named here as Kuwajimalla kagaensis , has lanceolate denticulate teeth convergent on those of the living Iguana . This type of dentition is rare among living lizards and is usually considered indicative of herbivory and, more specifically, folivory. Kuwajimalla kagaensis provides the earliest unambiguous record of squamate herbivory. Comparisons with modern and fossil lizards suggest that Kuwajimalla may be an early relative of the macrocephalosaurines, a group of large herbivores well represented in the Upper Cretaceous of Mongolia.     

Extended gestation with late‐autumn births in a cool‐climate viviparous gecko from southern New Zealand (Reptilia: Naultinus gemmeus)

Abstract Female viviparous lizards from temperate locations in the Southern Hemisphere (New Zealand, Tasmania (Australia), South Africa and South America) often have reproductive activity spanning many months of the year. In contrast, vitellogenesis and pregnancy are often confined to the spring/summer months in viviparous species from temperate zones of the Northern Hemisphere. An extreme Southern Hemisphere example is the nocturnal common gecko from New Zealand, Hoplodactylus maculatus (Gray 1845), in which females exhibit biennial reproduction with pregnancy lasting up to 14 months in a cool‐climate population. Here, we examined whether such an extended reproductive cycle also occurs in a diurnal species, the jewelled gecko Naultinus gemmeus (McCann 1955), at a similar latitude. Palpation was used to assess reproductive condition non‐invasively. In contrast to the nearby higher‐altitude population of H. maculatus, N. gemmeus reproduces annually. Vitellogenesis occurs from autumn to spring in both species, but pregnancy ends after about 7 months in N. gemmeus. Birth occurs in the seemingly unpropitious season of mid‐ to late autumn, a pattern that may be unique for lizards from cool‐temperate zones. We hypothesize that there are major differences between populations of N. gemmeus and H. maculatus with respect to survival of autumn‐born neonates and/or costs to females from remaining pregnant over winter. Museum specimens of N. gemmeus support anatomical inferences from palpation; they also suggest that vitellogenesis may begin before the end of pregnancy (which may be essential to completing each reproductive cycle within a year) and that some populations may show gestation in utero over winter, as in H. maculatus. Extended gestation appears to be a common response to cool climates for Southern Hemisphere lizards that have independently evolved viviparity.