Cell Division in Gonyaulax catenella,A Marine Catenate Dinoflagellate*

Mitosis and cytokinesis are described and illustrated for the first time in the mesokaryotic, catenate dinoflagellate Gonyaulax catenella. A structure similar to the central body of G. tamarensis and G. monilata is shown by light and electron microscopy to be situated intranuclearly near the arms of the U-shaped interphase nucleus, and is suggested to function in the segregation of daughter chromosomes. This structure has the fine structure of a nucleolus, and it is suggested that the term central body be replaced by persistent nucleolus (= endosome). The time required for the completion of mitosis is 4–6 hr, while cytokinesis requires at least 2 hr. Cytokinesis begins during the mitotic cycle, and the plane of fission is perpendicular to the mitotic plane of division. Parental fission moieties are retained and shared by the daughter cells while either a new antero-sinistral moiety or a posterodextral moiety is synthesized by the dividing cell.     

Some Aspects of Regeneration in the Scyphistoma of Cassiopea (Class Scyphozoa) as Revealed by the Use of Antimetabolites and Microspectrophotometry

As a continuation of studies of the regenerative capacitiesof the scyphistoma of Cassiopea, a series of experiments wasundertaken in which (i) regenerating fragments were culturedin the presence of various antimetabolites and (ii) Feulgenstainednuclei from control animals and regenerating fragments weremeasured by scanning, integrating microspectrophotometry. Theresults of the antimetabolite experiments were complex and variablebut nonetheless suggested that normal regeneration of functionalheads from fragments requires the synthesis of DNA, RNA, andprotein. Regardless of the type of antimetabolite, the mostfrequently observed morphological effect was prolonged or arresteddevelopment. None of the antimetabolites produced characteristicor unique abnormalities, although variation was observed inthe ability of the inhibited fragments to recover from the variousantimetabolites. Microspectrophotometric measurements of Feulgen-stainednuclei from control animals revealed that approximately 25%of the nuclei contained more than the diploid amount of DNAand thus were in either the S or G₂ phases of the cell cycle.In regenerating fragments, the frequency of nuclei in this categorydropped progressively to less than 6% by the end of 3 days butreturned nearly to control levels by the end of six days. Thenuclei also became somewhat enlarged and less dense during regeneration.     

Prevalence of Sarcocystis in Grackles in Maryland

SYNOPSIS. One hundred and fifty-nine grackles (Quiscalus quiscula) in Maryland were examined grossly and microscopically for Sarcocystis sp. Of 98 mature birds, 91 had Sarcocystis. None of 51 juvenile birds and none of 10 birds hatched in the laboratory had Sarcocystis. More mature females had Sarcocystis than did mature males. However, the number of intramuscular cysts (per bird) was greater in male grackles than in females. Both male and female grackles had more infections in the leg and thigh muscles than in breast muscles. No tongue or heart muscles contained Sarcocystis. No seasonal fluctuation in the number of infected birds was apparent.     

Potential for host range expansion in Ceratitis capitata flies: impact of proximity of adult food to egg-laying sites

Abstract.

• 1 In field cage and field tests, female Mediterranean fruit flies, Ceratitis capitata (Wiedemann), in trees alighted in significantly greater numbers upon sticky-coated (non-odour-emitting) kumquats, Fortunella japonica, that were in the vicinity of odorous natural proteinaceous food (bird faeces) or synthetic food odour than on similar kumquats distant from bird faeces or synthetic food odour.
• 2 In field cage tests, oviposition in non-sticky kumquats nearby bird faeces was significantly greater than in non-sticky kumquats distant from bird faeces.
• 3 In field tests, medflies laid significantly more eggs in host kumquat and non-host hawthorn, Crataegus mollis, fruit adjacent to bird faeces and synthetic food odour than in fruit of these types distant from food-type stimuli.
• 4 These findings suggest that odour of natural food of medflies could lure flies to plants whose fruit emit little or no attractive odour and are not permanent hosts but which are nonetheless susceptible to egg-laying and larval development, resulting in temporary expansion of host range.

     

Phylogenetic analyses of mtDNA sequences reveal three cryptic lineages in the widespread neotropical frog Leptodactylus fuscus (Schneider, 1799) (Anura, Leptodactylidae)

Leptodactylus fuscus is a neotropical frog ranging from Panamá to Argentina, to the east of the Andes mountains, and also inhabiting Margarita, Trinidad, and the Tobago islands. We performed phylogenetic analyses of 12S rRNA, 16S rRNA, tRNA-Leu, and ND1 mitochondrial (mt) DNA sequences from specimens collected across the geographic distribution of L. fuscus to examine two alternative hypotheses: (i) L. fuscus is a single, widely distributed species, or (ii) L. fuscus is a species complex. We tested statistically for geographic association and partitioning of genetic variation among mtDNA clades. The mtDNA data supported the hypothesis of several cryptic species within L. fuscus. Unlinked mtDNA and nuclear markers supported independently the distinctness of a 'northern' phylogenetic unit. In addition, the mtDNA data divided the southern populations into two clades that showed no sister relationship to each other, consistent with high differentiation and lack of gene flow among southern populations as suggested by allozyme data. Concordance between mtDNA and allozyme patterns suggests that cryptic speciation has occurred in L. fuscus without morphological or call differentiation. This study illustrates a case in which lineage splitting during the speciation process took place without divergence in reproductive isolation mechanisms (e.g. advertisement call in frogs), contrary to expectations predicted using a biological species framework.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 325–341. No claim to original US government works.     

Diagnostic Genetic Marker That Differentiates Eastern Fox Squirrels From Eastern Gray Squirrels

Abstract The Delmarva fox squirrel (Sciurus niger cinereus) has been listed as endangered by the United States Department of Interior since 1967. A high-priority task for the recovery of this taxon is to determine its current geographic distribution. Toward this end, we have identified a microsatellite locus that unambiguously differentiates Delmarva fox squirrels from eastern gray squirrels (S. carolinensis), which frequently co-occur with Delmarva fox squirrels. Analysis of this marker in noninvasively collected hair samples will allow unequivocal identification of localities occupied by Delmarva fox squirrels with a minimum investment of funds, time, and effort because handling individuals will be unnecessary. This protocol will expedite site review in connection with the Endangered Species Act consultation process.