Life history strategy of Leptinaria unilamellata (d'Orbigny, 1835) (Mollusca,Pulmonata, Subulinidae)

Abstract

Life history theory predicts that the patterns of resource allocation in animals are associated with different strategies, selected in the course of evolution. In the present study, the life history of Leptinaria unilamellata was characterized under laboratory conditions. We determined the growth, reproduction, and longevity patterns of this species and elucidated the strategy related to the development of embryos, through direct observations and examination of the morphology of the gravid uterus. Furthermore, we attempted to analyze the glycogen and galactogen contents of the albumen gland, digestive gland and cephalopedal mass in order to understand energy allocation to life history traits, for three life stages. Leptinaria unilamellata's life history is characterized by great longevity, a short juvenile phase, early sexual maturity, and repeated reproductive events, with little reproductive effort at each event and some mortality shortly after the first reproduction. In the terraria, we found juveniles but no eggs. However, the results of the anatomical study showed no morphological connection between the embryos and the parental organism. Thus, this species should be described as ovoviviparous rather than viviparous. Egg retention in the parent organism is the primary cause of the release of juveniles, instead of eggs, enabling the offspring to withstand environmental stress. The higher quantity of galactogen found in the adults' albumen gland, as compared to juveniles and senescent individuals, as well as the ratio of glycogen to galactogen, reveal the allocation of energy to reproduction rather than to growth. The remaining energy is directed to the maintenance of omeostasis. Such pattern was confirmed by the low levels of glycogen and galactogen observed in the senescent stage, compared to the juvenile and adult stages. In the life strategy of L. unilamellata, the distribution of the reproductive effort among many events associated with ovoviviparity indicates a long-term investment in reproductive success.     

The Effects of Kinetin, Gibberellic Acid, and Light on Expansion and Cell Division in Leaf Disks of Dwarf Bean (Phaseolus vulgaris)

The effects of kinetin (Kn), gibberellic acid (G), and light(L) on cell expansion and division in disks from 6-day-old etiolatedprimary leaves of dwarf bean are described. Cell number wasdetermined by direct counting after disks were digested in apectinase/EDTA mixture to separate the cells. Kn increased leafexpansion wholly by increasing cell size. G also increased cellsize; it increased cell division in the dark but not in thelight. Light also increased cell size and cell division; iteliminated the effect of G on cell division but enhanced theeffect of G on cell expansion.     

Growth Activity of the Gibberellins of Dwarf French Bean, Potato, and Lettuce

Zones with similar Rf to gibberellic acid (GA) on chromatogramsof ethylacetate extracts of dwarf French bean and potato leavesand stems and lettuce heads all promoted growth of disks ofetiolated dwarf French bean leaves in darkness. The presence of a gibberellin was confirmed by tests with stemsof dwarf pea, but that the substance was not GA was shown bythe lack of effect in the tests with lettuce hypocotyls. Thetests with dwarf maize, effects on d-3 and d-5, but not d-1,identified it as gibberelliin A₅ (bean factor II). Materialthat promoted the growth of lettuce hypocotyls occurred in zonesclose to the starting-line of chromatograms of extracts of beanand lettuce leaves. Calibration of the growth tests with GA gave an estimate ofthe gibberellin content of the tissues extracted. In the dwarf-peatest the apparent gibberellin contents were similar to the valuesin the leaf-disk test, but very low values occurred in the maizetests.     

DNA SYNTHESIS AND CELL TURNOVER IN RANA PIPIENS TADPOLE LIVER DURING SPONTANEOUS METAMORPHOSIS1

The relationship of DNA synthesis and cellular turnover to biochemical differentiation during metamorphosis of R. pipiens liver was investigated. Average DNA/cell was constant at 11.6 pg/ nucleus through stage XXV; but increased during juvenile growth; during metamorphosis stages, changes in total DNA content must correspond to changes in cell number. Rates of DNA synthesis were estimated by rates of ³H-thymidine incorporated into the acid-precipitable fractions, corrected for both precursor uptake into the acid-soluble pool, and for endogenous thymine pool size. DNA content increased steadily from premetamorphosis until late prometamorphosis; at preclimax stages XVIII and XX there were two successive decreases in DNA content of approximately 30%. Fluctuations in synthesis rates preceded corresponding fluctuations in content; DNA synthesis was maximal at stages XVI and XVIII, decreased nearly ten-fold at metamorphic climax, and then gradually rose again during late climax stages. The size of the endogenous thymine pool increased transitorily during spontaneous metamorphosis corresponding to a stage of maximal DNA synthesis. These results indicate that both DNA synthesis and cellular turnover play a significant role in determining net DNA synthesis rates and content during metamorphosis. Metamorphosis of the tadpole liver appears to be associated with both proliferation and cellular death, perhaps a replacement of “larval” by “adult” cells. Metamorphosis of the liver cannot be occuring in a “fixed population of cells” as is commonly assumed. An interpretation of the population dynamics of the metamorphic liver is presented.     

Molecular systematics of mantelline frogs from Madagascar and the evolution of their femoral glands

Several genera of frogs from Madagascar, classified in the family Mantellidae, subfamily Mantellinae, possess structures commonly called 'femoral glands' on the ventral side of their shanks. The question arises as to the origin and phylogenetic significance of these glands. A molecular phylogeny based on 3601 nucleotide DNA sequences of three mitochondrial and two nuclear genes of 30 mantellid species provided strong support for monophyly of the included mantellines, all characterized by enlarged femoral gland clusters, as well as for those with gland clusters of coordinated central arrangement of secretion ducts. However, the phylogeny also strongly supported the hypothesis of convergent evolution of structurally similar glands in unrelated frogs ( Indirana , Petropedetes ), and several trends of convergent evolution of gland structure within mantellines. We studied the light microscopic structure of the femoral glands in a representative array of 18 mantellid species. Males of all species of the subfamily Mantellinae were characterized by clusters of distinct single glands. Each was structurally similar to an enlarged granular gland and secreted independently, probably through a single duct. By contrast, the largely semi-aquatic frogs in the genus Mantidactylus had a specialized cluster of glands, in which the secretion ducts led into a macroscopically recognizable central depression. In Boophis opisthodon , a mantellid species of the subfamily Boophinae without externally recognizable femoral glands, we observed a large number of enlarged granular glands of various sizes in the ventral skin of the shank. This observation is consistent with the hypothesis that the large and more uniform organs of mantellines are derived granular glands.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 529–539.     

Design and field methods for sighting surveys of cetaceans in coastal and riverine habitats

• 1 Dolphins and porpoises in coastal and/or riverine habitats face serious conservation threats, yet surveys of their abundance are often especially difficult due to the challenges imposed by the habitats. Because many of these species occur in developing countries, lack of resources imposes a further set of challenges.
• 2 We offer advice on designing and conducting line‐transect surveys with a focus on sound, practical, design rather than analytical sophistication, and we attempt, where possible, to offer simple, inexpensive solutions.
• 3 We guide the reader through the questions of what kind of survey should be done, whether by boat or aircraft, and we discuss ways to avoid bias and increase precision.
• 4 Our treatment of field methods focuses especially on robust, but low‐cost, approaches. We provide two case studies to illustrate the implementation of these ideas.

     

Time course of uptake of 14C-abscisic acid by Lemna gibba in relation to growth

The time course of growth of Lemna gibba L. in low concentrations of abscisic acid (ABA) and of uptake of ¹⁴C-labelled ABA into the plants was followed for up to 15 days. Fresh weight increase was arrested when the plants were transferred to ABA solutions. This inhibition was greatest during the first days after which a marked recovery took place. Dry matter production was only slightly affected by ABA. On a culture basis, the uptake of ABA was almost linear with time during the experimental period. The rate of uptake on a fresh weight basis was highest during the first two days but decreased rapidly from the third day. Most of the applied ¹⁴C remained in the culture solution throughout the experiments. Plants transferred to a solution without ABA retained most of their accumulated ¹⁴C. Possible explanations for the decrease in rate of ABA uptake and restoration of growth are discussed.     

Occurrence of Endogenous Indol-3yI-Aspartic Acid in Light and Dark-Grown Bean Seedlings (Phaseolus vulgaris)

An acid ether-soluble, strongly growth-stimulating substance revealed by the Avena coleoptile straight-growth test in methanol extracts from bean seedlings (Phaseolus vulgaris L.) was identified as indol-3yl-aspartic acid (IAAsp). Points of agreement between synthetic IAAsp and the investigated growth stimulator were indicated by chromatographic behavior, elution volume in gel filtration, mobility in paper electrophoresis, “colour reaction” with DMCA reagent, ability to form indol-3yl-acetic acid (IAA) and aspartic acid after hydrolysis and, finally, biological activity in the Avena test. Furthermore, some experiments demonstrated the occurrence of an inhibitor in extracts from light-grown tissue. This masked the stimulation of IAAsp in the Avena test when the extracts had been chromatographed in isopropanol: NH₃:H₂ O. A comparison of the levels of IAAsp between green and etiolated tissue did not reveal any distinct difference, demonstrating that the IAA conjugate IAAsp does not participate in the regulation of the photomorphogenesis.