Population genetics and conservation of critically small cycad populations: a case study of the Albany Cycad,Encephalartos latifrons (Lehmann)

Declining populations of less than 250 mature individuals are symptomatic of many Critically Endangered cycads, which, globally, comprise the most threatened group of organisms as a result of collecting and habitat loss. Survival plans focus on law enforcement, reintroduction, and augmentation programmes using plants from the wild and botanical gardens. Augmentation is one of the few remaining options for cycad populations, although the assumed benefits remain untested and there is a possibility that augmentation from different sources could compromise the genetic integrity of existing populations, especially when garden plants have no provenance data. We studied Encephalartos latifrons, a South African endemic, which is a typical Critically Endangered cycad. We studied the extent and structure of genetic diversity in wild and ex situ populations to assess the potential benefits and risks associated with augmentation programmes. We examined 86 plants using amplified fragment length polymorphisms (AFLPs). The 417 AFLP markers thus generated yielded a unique DNA ‘fingerprint’ for each plant. Wild populations retain high levels of genetic diversity and this is reflected among the ex situ holdings at the Kirstenbosch Botanical Garden. No population differentiation is evident, indicating a single panmictic population, consistent with moderately high levels of gene flow between subpopulations and a sexual mode of reproduction. Bayesian clustering identified four genotype groups in the wild, as well as a genotype group only found in ex situ collections. Our results indicate that E. latifrons would benefit from augmentation programmes, including the use of undocumented collections, and careful management of breeding plants would increase the heterogeneity of propagules. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 293–308.     

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.     

Programmed cell death during development of cowpea (Vigna unguiculata (L.) Walp.) seed coat

The seed coat develops primarily from maternal tissues and comprises multiple cell layers at maturity, providing a metabolically dynamic interface between the developing embryo and the environment during embryogenesis, dormancy and germination of seeds. Seed coat development involves dramatic cellular changes, and the aim of this research was to investigate the role of programmed cell death (PCD) events during the development of seed coats of cowpea [Vigna unguiculata (L.) Walp.]. We demonstrate that cells of the developing cowpea seed coats undergo a programme of autolytic cell death, detected as cellular morphological changes in nuclei, mitochondria, chloroplasts and vacuoles, DNA fragmentation and oligonucleosome accumulation in the cytoplasm, and loss of membrane viability. We show for the first time that classes 6 and 8 caspase‐like enzymes are active during seed coat development, and that these activities may be compartmentalized by translocation between vacuoles and cytoplasm during PCD events.     

Complete sequences of the rRNA genes of Drosophila melanogaster

In this, the first of three papers, we present the sequence of the ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S (123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat of D. melanogaster is AT rich (65.9% overall), with the spacers being particularly AT rich. Analysis of DNA simplicity reveals that, in contrast to the intergenic spacer (IGS) and the external transcribed spacer (ETS), most of the rRNA gene regions have been refractory to the action of slippage-like events, with the exception of the 28S rRNA gene expansion segments. It would seem that the 28S rRNA can accommodate the products of slippage-like events without loss of activity. In the following two papers we analyze the effects of sequence divergence on the evolution of (1) the 28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary structures among eukaryotic species, respectively. Our detailed analyses reveal, in addition to unequal crossing-over, (1) the involvement of slippage and biased mutation in the evolution of the rDNA multigene family and (2) the molecular coevolution of both expansion segments and the nucleotides involved with compensatory changes required to maintain secondary structures of RNA.      

新的端粒酶活性抑制蛋白LPTS-L的制备

LPTS基因是利用定位候选克隆策略克隆的一个新的肝相关候选肿瘤抑制基因。LPTS基因编码一个全长为328氨基酸的蛋白质(LPTS-L),该蛋白具有抑制细胞端粒酶活性的功能。为了进一步研究LPTS-L蛋白的结构与功能,利用DNA重组技术,将LPTS-L的cDNA克隆到表达载体pET-24a中构建重组克隆pET-24-LPTS,并在大肠杆菌BL-21中进行融合表达,获得可溶形式的LPTS-L融合蛋白。采用Ni Sepharose4B柱亲和层析,可以获得纯度较高的蛋白,但不适合大量制备。通过设计引物去掉了pET-24a载体上的6×His tag将LPTS-L基因进行了非融合表达,然后采用磷酸纤维素P11阳离子交换层析纯化LPTS-L蛋白,纯度可达到55%。再经Sephadex G-100凝胶过滤,LPTS-L蛋白的纯度可达到80%。Western blot实验显示经纯化后的LPTS-L蛋白可与兔抗GST-LPTS-L的多抗发生特异性结合。采用TRAP法测定蛋白质活性,结果显示纯化得到的LPTS-L蛋白可抑制端粒酶的活性,与采用Ni Sepharose4B纯化获得的LPTS-L融合蛋白比较,其抑制效率基本一致。因此,所建立的技术可以有效地制备LPTS-L蛋白。     

Microsatellite loci for the stingless bee Melipona rufiventris (Hymenoptera: Apidae)

Eight microsatellite primers were developed from ISSR (intersimple sequence repeats) markers for the stingless bee Melipona rufiventris. These primers were tested in 20 M. rufiventris workers, representing a single population from Minas Gerais state. The number of alleles per locus ranged from 2 to 5 (mean = 2.63) and the observed and expected heterozygosity values ranged from 0.00 to 0.44 (mean = 0.20) and from 0.05 to 0.68 (mean = 0.31), respectively. Several loci were also polymorphic in M. quadrifasciata, M. bicolor, M. mandacaia and Partamona helleri and should prove useful in population studies of other stingless bees.