Genetic population structure of Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) and evidence of temporal variation in structure.

Surubim (Pseudoplatystoma corruscans, Pimelodidae) are migratory catfish native to the rivers in the La Plata and São Francisco basins. They are piscivores that attain considerable body sizes and are a valuable economic resource. Surubim exhibits extensive migrations during its life cycle that may affect the population structure at vast geographic scales. The authors examined the genetic diversity and population genetic structure of P. corruscans using microsatellite markers from a comprehensive sampling of 260 individuals from the Upper and Lower Paraná River. They identified two well-differentiated genetic clusters corresponding to a natural geographic barrier historically separating Upper and Lower Paraná regions. They also demonstrated temporal variation in population genetic structure at a site in Lower Paraná close to the confluence with the Paraguay River, most likely explained by the influx of migrant fishes at certain times of the year.

Mating System of Caiman yacare (Reptilia: Alligatoridae) Described from Microsatellite Genotypes.

The yacare caiman (Caiman yacare) is a reptile from South America and 1 of the 2 crocodilian species present in Argentina. The degradation of their natural habitat and strong hunting pressure led to a sharp numerical decline of wild populations. Nowadays, C. yacare is included in Appendix II of CITES, and ranching practices in some areas in Argentina are helping hatching success. In this context, it is important to better understand the population structure and mating system of the species. To do this, we amplified 10 microsatellite markers (SSRs) in 148 individuals of 13 C. yacare nests. All of the markers were polymorphic with 2­12 alleles per locus, with allelic sizes ranging between 154 and 400 bp and medium levels of polymorphism (Ho = 0.152­0.551 and He = 0.221­0.621). We were able to determine the maternal genotype in 9 out of 13 nests. In 6 of them we found more than 1 paternal genotype, with a maximum of 3 fathers for a single nest. This study is the first to provide evidence of multiple paternity behavior. These findings will be useful to improve management and conservation strategies for the species.

Hahb-10, a sunflower homeobox-leucine zipper gene, is regulated by light quality and quantity, and promotes early flowering when expressed in Arabidopsis.

Homeodomain-leucine zipper proteins constitute a family of transcription factors found only in plants. Expression patterns of the sunflower homeobox-leucine zipper gene Hahb-10 (Helianthus annuus homeobox-10), that belongs to the HD-Zip II subfamily, were analysed. Northern blots showed that Hahb-10 is expressed primarily in mature leaves, although expression is clearly detectable in younger leaves and also in stems. Considerably higher expression levels were detected in etiolated seedlings compared with light-grown seedlings. Induction of Hahb-10 expression was observed when seedlings were subjected to treatment with gibberellins. Transgenic Arabidopsis thaliana plants that express Hahb-10 under the 35S cauliflower mosaic virus promoter show special phenotypic characteristics such as darker cotyledons and planar leaves. A reduction in the life cycle of about 25% allowing earlier seed collection was also observed, and this phenomenon is clearly related to a shortened flowering time. When the number of plants per pot increased, the difference in developmental rate between transgenic and non-transformed individuals became larger. After gibberellin treatment, the relative difference in life cycle duration was considerably reduced. Several light-regulated genes have been tested as possible target genes of Hahb-10. One of them, PsbS, shows a different response to illumination conditions in transgenic plants compared with the response in wild-type plants while the other genes behave similarly in both genotypes. We propose that Hahb-10 functions in a signalling cascade(s) that control(s) plant responses to light quality and quantity, and may also be involved in gibberellin transduction pathways.