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.     

Neuromuscular Systems in Molluscs

Molluscs have become increasingly popular in the study of centralneural mechanisms. More recently, there have been attempts torelate activity in central neurons with behavior in animalsof this phylum. The latter studies necessitate an understandingof the effectors of such behaviors. This requires not only informationabout the neuromuscular junction, but also an awareness of thecapabilities of the muscles themselves. Therefore, we have discussedsome structural and related functional characteristics of molluscanmuscle. We suggest that invertebrate mucles might be comparedon three scales: the amount of myofilament organization, theamount of vesicular specialization and organization, and theamount of paramyosin. We have considered some characteristicsof the widely-studied sustained contraction, known as "catch."Finally, we have discussed the neuromuscular junction—thetypes of junctions, the multiplicity of innervation, and someaspects of pharmacology. The results of such a study indicatedmany areas in which further research is essential before wecan understand behavior in terms of activity in the centralnervous system.     

Neotropical Frog Biogeography: Paradigms and Problems

SYNOPSIS. The distributions and relationships of exemplary speciesgroups of the Neotropical frog genera Cycloramphus and Leptodactylusare discussed in terms of current biogeographic models. Fromthis exercise, the following conclusions emerge: (1) frog biogeographyis and will remain primarily a correlative science; (2) bothmorphological and genetic data are required to choose amongalternate biogeographic models; (3) frog speciation events significantlypredate recent distributional events complicating the understandingof past and recent distributions; (4) both data and theory areinadequate to completely understand Neotropical frog biogeographyat present.     

Impact of soluble sugar concentrations on the acquisition of freezing tolerance in accessions of Arabidopsis thaliana with contrasting cold adaptation – evidence for a role of raffinose in cold acclimation

In the present study the cold acclimation potential of two accessions of Arabidopsis thaliana was investigated. Significant variation was found for basic tolerance as well as the capacity to acclimate to freezing temperatures. During cold acclimation, levels of soluble sugars increased in both genotypes, but raffinose accumulation discriminated the more tolerant accession Col‐0 from C24. Concentrations of other compatible solutes such as proline and glutamine were also higher in cold‐acclimated Col‐0 than C24 plants. Changes of invertase activity during cold exposure corresponded to changes in sucrose and fructose, but not glucose concentrations and were consistent with an initial chilling response and a later decline in hexose metabolization. When vacuolar invertase was suppressed by siRNA expression, reduced sucrolytic activity resulted in elevated leaf sucrose concentration, whereas the fructose content was strongly reduced. This led to elevated freezing tolerance in the cold‐tolerant genotype Col‐0, but not in C24. The most pronounced metabolic changes in invertase‐inhibited Col‐0 plants occurred for proline and glutamine concentrations, indicating indirect metabolic effects of altered sugar concentrations.