CARACTERIZACIÓN GENÉTICA DE LA POBLACIÓN DE Heliconius sara (Nymphalidae) EN LA ISLA GORGONA, COLOMBIA / Genetic characterization of the Heliconius sara (Nymphalidae) population in the Gorgona Island, Colombia

RESUMEN La estructura genética de poblaciones de mariposas con distribución en islas y sus pares continentales ha sido poco documentada para el neotrópico. Este estudio presenta la caracterización de una población de Heliconius sara con distribución en la Isla Gorgona, ubicada en la región del Pacífico Oriental Colombiano. Para esto se examinaron secuencias parciales de un marcador mitocondrial incluyendo información obtenida del GenBank. Se comparó la diversidad y estructura genética con sus conespecíficos continentales y también con congéneres, con los que comparte un ancestro común cercano en el clado Sapho-Sara. Para el análisis de diversidad y estructura genética se realizó un análisis de varianza molecular. Este análisis muestra que la distancia entre la población de la isla y sus pares en el continente es consistente con la variación intraespecífica observada en otras especies del género Heliconius. Para la reconstrucción de la genealogía y datación reciente en el Pleistoceno superior del grupo monofilético de secuencias de H. sara, se realizó un análisis de inferencia bayesiana, así como una de máxima verosimilitud. Del análisis demográfico se seleccionó un modelo histórico de flujo asimétrico desde la isla hacia el continente que sugiere baja resistencia de la discontinuidad geográfica a la dispersión de esta mariposa diurna desde la isla. Este es el primer estudio en examinar un posible evento de aislamiento de una población insular de mariposas en Colombia.

ABSTRACT The genetic structure of butterfly populations among islands and mainland has been poorly documented for the neotropics. This study shows a characterization of the Heliconius sara population with distribution on Gorgona Island in the Colombian Eastern Tropical Pacific region. We obtained partial sequences of a mitochondrial DNA, including information obtained from GenBank. The genetic diversity and structure were compared among the island population and their mainland conspecific, but also with congenerics, with those shared by a recent common ancestor within the Sapho/Sara clade. For the analysis of diversity and genetic structure, an analysis of molecular variance was performed. This analysis shows that the genetic distance between the island's population and that of the mainland is consistent with the intraspecific variation observed in other species of the Heliconious genus. For the reconstruction of the genealogy and the recent dating calibration in the upper Pleistocene of the monophyletic group of H. sara, a Bayesian inference was carried out as well as one of maximum likelihood. From the demographic analysis, an asymmetric gene flow model from the island to the mainland was selected. This model suggests low historical resistance of the geographic discontinuity to dispersal of this small and diurnal butterfly from the island. This is the first study to examine a possible event of local isolation of an island population of a butterfly in Colombia.

Population structure and genetic diversity in yellow catfish (Pelteobagrus fulvidraco) assessed with microsatellites

Yellow catfish (Pelteobagrus fulvidraco) is an important aquaculture species which is widely distributed, especially in the Yangtze River of China. To facilitate its conservation and stock improvement, 273 yellow catfish samples from the Yangtze River (seven populations) and Baiyangdian (BYD) Lake were genotyped using eight microsatellites in combination with capillary electrophoresis. A total of 250 alleles were detected at eight loci in eight populations showing high allelic (Na= 31.25 ± 7.38) and genetic diversity (He = 0.888–0.944). Both FST and clustering analyses revealed the presence of subtle population differences between the species of Yangtze River and the BYD lake. Mantel tests suggest that genetic distance is significantly correlated with geographical distance (R = 0.9294 and P < 0.05). The results of genetic diversity and population structure will help in conservation and improvement of yellow catfish.

Geographical variation in the genetic diversity and composition of the endangered Queen Conch Strombus gigas (Mesogastropoda: Strombidae) from Yucatán, México

In Mexico and elsewhere in the Caribbean, the queen conch Strombus gigas is an endangered species. Understanding the genetic connectivity of their populations will support management strategies for long term conservation of the species. Genetic diversity and population differentiation was assessed from samples collected at Banco Chinchorro and Isla Cozumel in the Mexican Caribbean and at Arrecife Alacranes in the Gulf of Mexico. Samples were obtained from the commercial capture at Banco Chinchorro (n=50) and Isla Cozumel (n=40) on March 2004. On November 2004, a non-invasive method for the Arrecife Alacranes sampling was applied, taking the hemolymph of live animals (n=65) and releasing them to the wild. The mitochondrial DNA variation at two genes (COI and Cyt-b) was analyzed. Genetic diversity at the three locations ranged between 0.55-0.65 in COI and 0.87-0.94 in Cyt-b, showing no bottleneck evidences. A non-significant fixation index (F ST=0.019, p=0.161) and a Maximum Parsimony Network tree that did not show particular clades associated with any of the geographical locations, suggested a lack of statistically significant genetic differentiation among populations. Nevertheless, the cline patterns observed in both genetic diversity and haplotypic frequencies from Banco Chinchorro through Arrecife Alacranes, and the larger genetic distance between these locations from those between Isla Cozumel, Banco Chinchorro and Arrecife Alacranes, suggest the possibility of a pattern of isolation-by distance. The role of the main current systems over the potential genetic differences in S. gigas populations along the Mexican Caribbean, and the conservation management of S. gigas at these locations as discrete units is discussed. Rev. Biol. Trop. 59 (3): 1115-1126. Epub 2011 September 01.

El caracol rosado Strombus gigas es una especie amenzada en México y otros sitios del Caribe. Su conservación a largo plazo requiere la comprensión de la conectividad entre sus poblaciones. En este estudio se evaluó la diversidad y diferenciación genética de muestras recolectadas en tres sitios del Caribe y Golfo de México adyacentes a la Península de Yucatán. Las muestras se obtuvieron de la captura comercial en Banco Chinchorro (n=50) e Isla Cozumel (n=40) en marzo de 2004. En noviembre de 2004 se obtuvieron muestras de Arrecife Alacranes (n=65) de animales vivos, mediante un método no invasivo diseñado para la obtención de hemolinfa; los organismos muestreados se liberaron de vuelta al medio natural. Se analizó la diversidad genética de dos genes del ADN mitocondrial (COI y Cyt-b). La diversidad genética en las tres localidades varió entre 0.55 - 0.65 en COI y 0.87 - 0.94 en Cyt-b no indicando reducción por cuello de botella. Un índice de fijación no significativamente diferente de cero (F ST=0.019, p=0.161) y un árbol en Red de Máxima Parsimonia que no mostró clados particulares asociados con localidades específicas, sugiere que no hay diferencias genéticas significativas entre sitios. Sin embargo, los patrones clinales observados en la diversidad genética y en las frecuencias haplotípicas, así como la mayor distancia genética registrada entre las localidades más alejadas (Banco Chinchorro y Arrecife Alacranes) sugiere un posible un patrón de aislamiento por distancia. Se discute el papel de los sistemas de corrientes principales del Caribe mexicano sobre la posible diferenciación genética de S. gigas. Asimismo, se discute el manejo de las localidades estudiadas como unidades discretas.

Evidence of geographical structuring in the Malaysian Snakehead, Channa striata based on partial segment of the CO1 gene

Channa striata, locally known as "haruan", is economically important in fisheries and aquaculture industries in several Asian countries. DNA sequencing, based on a partial segment of the Cytochrome oxidase c subunit 1 (CO1) gene, was used to determine genetic variation in C. striata samples from four different populations on the west coast of Peninsular Malaysia. The highest nucleotide and haplotype diversities were observed in the Linggi population (π = 0.0067, h = 0.835), and the lowest in the Timah Tasoh population (π = 0.0008, h = 0.286). Apart from Kajang-Linggi, which was insignificant, F ST values were significant (p < 0.05) in all pairwise-population comparisons. Consequently, it is inferred that genetic structuring C. striata populations in this region was largely shaped by a common origin, with secondary influences from geographical factors and isolation.

A review of techniques for spatial modeling in geographical, conservation and landscape genetics

Most evolutionary processes occur in a spatial context and several spatial analysis techniques have been employed in an exploratory context. However, the existence of autocorrelation can also perturb significance tests when data is analyzed using standard correlation and regression techniques on modeling genetic data as a function of explanatory variables. In this case, more complex models incorporating the effects of autocorrelation must be used. Here we review those models and compared their relative performances in a simple simulation, in which spatial patterns in allele frequencies were generated by a balance between random variation within populations and spatially-structured gene flow. Notwithstanding the somewhat idiosyncratic behavior of the techniques evaluated, it is clear that spatial autocorrelation affects Type I errors and that standard linear regression does not provide minimum variance estimators. Due to its flexibility, we stress that principal coordinate of neighbor matrices (PCNM) and related eigenvector mapping techniques seem to be the best approaches to spatial regression. In general, we hope that our review of commonly used spatial regression techniques in biology and ecology may aid population geneticists towards providing better explanations for population structures dealing with more complex regression problems throughout geographic space.

Multiple Mantel tests and isolation-by-distance, taking into account long-term historical divergence

Mantel tests of matrix correspondence have been widely used in population genetics to examine microevolutionary processes, such as isolation-by-distance (IBD). We used partial and multiple Mantel tests to simultaneously test long-term historical effects and current divergence and equilibrium processes, such as IBD. We used these procedures to calculate genetic divergence among Eugenia dysenterica (Myrtaceae) populations in Central Brazil. The Nei's genetic distances between pairs of local populations were strongly correlated with geographic distances, suggesting an IBD process, but field observations and the geographic distribution of the samples suggest that populations may have been subjected to more complex evolutionary processes of genetic divergence. Partial Mantel regression was used to partition the effects of geographic structure and long-term divergence associated with a possible historical barrier. The R(2) of the model with both effects was 73.3%, and after the partition 21.9% of the variation in the genetic distances could be attributed to long-term historical divergence alone, whereas only 1.5% of the variation in genetic distances could be attributed to IBD. As expected, there was a large overlap between these processes when explaining genetic divergence, so it was not possible to entirely partition divergence between historical and contemporary processes.