David Véliz

Molecular Phylogenetic and Embryological Evidence That Feeding Larvae Have Been Reacquired in a Marine Gastropod

Evolutionary transitions between different modes of development in marine invertebrates are thought to be biased toward the loss of feeding larvae. Because the morphology of feeding larvae is complex and nonfeeding larvae or encapsulated embryos with benthic development often have simplified morphologies, it is presumed to be easier to lose a larval stage than to reacquire it. Some authors have gone so far as to suggest that feeding larvae, morphologically similar to the ancestral feeding larvae, cannot be reacquired. However, the larval structures of some groups, most notably gastropods, are often retained in the encapsulated embryos of species that hatch as benthic juveniles. Therefore the re-evolution of feeding larvae using the same structures may be possible in these groups. Here we present the first well-substantiated case for the recent re-evolution of feeding larvae within a clade of direct-developers. DNA sequence data show that Crepipatella fecunda, a species of calyptraeid gastropod with planktotrophic development, is nested within a clade of species with direct development, and that Crepipatella dilatata, a species with direct development, appears to be paraphyletic with respect to C. fecunda. Observation of the embryos of C. dilatata shows that the features necessary for larval feeding and swimming are retained in the encapsulated veligers, suggesting that heterochronic shifts in hatching time and changes in nurse-egg allotment could have resulted in the re-evolution of feeding larvae in this species.

Phylogenetic and phylogeographic analysis of the genus Orestias (Teleostei: Cyprinodontidae) in the southern Chilean Altiplano: the relevance of ancient and recent divergence processes in speciation

This study presents phylogenetic molecular data of the Chilean species of Orestias to propose an allopatric divergence hypothesis and phylogeographic evidence that suggests the relevance of abiotic factors in promoting population divergence in this complex. The results reveal that diversification is still ongoing, e.g. in the Ascotán salt pan, where populations of Orestias ascotanensis restricted to individual freshwater springs exhibit strong genetic differentiation, reflecting putative independent evolutionary units. Diversification of Orestias in the southern Altiplano may be linked to historical vicariant events and contemporary variation in water level; these processes may have affected the populations from the Plio-Pleistocene until the present.

Comparative population genetics of Basilichthys microlepidotus (Atheriniformes: Atherinopsidae) and Trichomycterus areolatus (Siluriformes: Trichomycteridae) in north central Chile.

To describe comparative population genetic structure of the Chilean silverside Basilichthys microlepidotus and the catfish Trichomycterus areolatus, four rivers and three sites within each river were investigated by the analysis of haplotype polymorphisms of the mitochondrial Control Region. For both species, analyses revealed significant differentiation among rivers and low differences within rivers. However, the species differ in haplotype composition; individuals of B. microlepidotus shared some haplotypes in all four rivers, while individuals of T. areolatus showed a different haplotype composition in most rivers. This difference may be explained by the different ecological features of the species. Assuming that both silversides and catfish were present before the separation of the rivers, B. microlepidotus migrated after river isolation, probably using coastal water, while T. areolatus has probably never migrated between these rivers. The long times that the studied rivers have been separated should be taken into account in future conservation plans for the freshwater fish of Chile.

An effective sperm competition avoidance strategy in crabs drives genetic monogamy despite evidence of polyandry

For polyandrous species where females have sperm storage structures, males develop several strategies to avoid sperm competition and thus to maximize the number of eggs fertilized. On the other hand, females may receive several benefits from multiple paternity (indirect and directly), and a potential sexual conflict can arise. This research describes the mating systems of an exploited crab species (Metacarcinus edwardsii), integrating (1) the individual level by assessing the mating behavior in a scenario of potential polyandry, (2) the organ level by examining histological sections of seminal receptacles from localities with scenarios of contrasting sex ratios, and (3) the genetic level by measuring the number of parents involved in egg clutches. We found that females can mate with multiple males under experimental conditions. Further, in all localities, we found histological evidences that sperm receptacles stored ejaculates from more than one male. However, contrary to expectations, genetic analysis revealed high probability of single male paternity of all progeny in each egg clutch. In this mating system, males compete to be the single male that mates with a receptive female, investing energy in guarding behavior and foregoing opportunities to mate with other females, all in order to ensure their paternity. However, females benefit from multiple mating (or potential for it) by prolonged guarding behavior, protecting them from predation after molt (soft-shelled period). The mating system of M. edwardsii can be defined as polygamous (where both sexes can mate multiple times) with genetic monogamy.

The Larval Development of Petrolisthes Violaceus (Guérin, 1831) (Decapoda, Anomura, Porcellanidae) From Chilean Waters, Cultivated Under Laboratory Conditions

[The complete larval development of Petrolisthes violaceus (Guerin, 1831), a porcellanid crab endemic to the south-eastern Pacific, is described and illustrated. The development comprises a prezoea, two zoeal stages and a megalopa. The megalopal stage was reached under laboratory conditions (19°C; 34‰ s) after an average of 25.2 days. We compare zoeal and megalopal features of P. violaceus with those of other species of Petrolisthes from the coast of the Americas, and indicate characteristics that distinguish P. violaceus larvae from those of P. granulosus and P. laevigatus, the other two Chilean species of Petrolisthes for which larval descriptions are available., The complete larval development of Petrolisthes violaceus (Guerin, 1831), a porcellanid crab endemic to the south-eastern Pacific, is described and illustrated. The development comprises a prezoea, two zoeal stages and a megalopa. The megalopal stage was reached under laboratory conditions (19°C; 34‰ s) after an average of 25.2 days. We compare zoeal and megalopal features of P. violaceus with those of other species of Petrolisthes from the coast of the Americas, and indicate characteristics that distinguish P. violaceus larvae from those of P. granulosus and P. laevigatus, the other two Chilean species of Petrolisthes for which larval descriptions are available.]

Development and characterization of nine polymorphic microsatellite markers in the Chilean kelp Lessonia nigrescens

A total of nine microsatellite loci were isolated and characterized in the Chilean kelp Lessonia nigrescens Bory. Using two different enriched libraries, we observed 1–14 alleles per locus in two samples of 21 kelp individuals each. The observed heterozygosities ranged from 0.05 to 0.80 and all loci are in Hardy–Weinberg equilibrium for one or both samples. Seventeen samples collected from different sites showed high allele diversity along the species distribution. The variation detected at these markers is currently being used for the study of populations of Lessonia nigrescens at different geographical scales.

The trochidae family (Mollusca : Gastropoda) in northern Chile: taxonomic and ecological considerations

Este estudio describe la diversidad, y la distribucion latitudinal y batimetrica de los caracoles de la Familia Trochidae en el norte de Chile, mediante muestreos intermareales y submareales someros, realizados entre 1996 y 1999 entre Arica (18o S) y Los Vilos (31o S), y de muestras de profundidad provenientes de la pesca de arrastre del camaron nylon, Heterocarpus reedi. En el norte de Chile, la Familia Trochidae esta representada por cuatro generos: Tegula y Diloma de distribucion intermareal y submareal somero hasta los 20 m de profundidad, y Bathybembix y Calliostoma presentes en profundidades superiores a los 200 m. El genero Tegula tiene seis especies (T. quadricostata, T. luctuosa, T. ignota, T. atra, T. tridentata y T. euryomphala) distribuidas en sustratos rocosos intermareales y submarales someros. El genero Diloma esta representado por una especie, D. nigerrima, de distribucion intermareal hasta pocos metros de profundidad. El genero Calliostoma tiene dos especies C. chilena y C. delli, las que se distribuyen entre 200 y 750 m de profundidad. Finalmente, el genero Bathybembix esta representado por B. humboldti y B. macdonaldi distribuidas entre 200 y 1480 m de profundidad. Esta segregacion batimetrica parece estar relacionada a las estrategias alimentarias de cada uno de los generos de la familia Trochidae. Diloma y Tegula son herbivoros, las especies del genero Bathybembix son alimentadoras de deposito y las de Calliostoma son carnivoras

Description, seasonal morphological variation, and molecular identification of Paraxanthus barbiger megalopae obtained from the natural environment

Larval identification represents a powerful tool for detailed studies on recruitment and population dynamics in marine invertebrates. However, intra-specific morphological variation can become a serious limitation for the correct identification at species level. High morphological variation can be expected in species with continuous breeding periods because larvae are exposed to seasonal fluctuations in physical and biological factors during their development in the plankton. We describe, for the first time, the megalopae of Paraxanthus barbiger, one of the most common and abundant brachyuran crabs along the coast of Chile. To validate larvae identification, the 16S rRNA gene was sequenced from both megalopae and adults, and was compared with sequences of three sympatric species. In addition, size, body shape, and appendage setation pattern variations were analyzed with a year-round sampling scheme. The results demonstrated high seasonal phenotypic plasticity in size. Despite these differences, certain conservative characteristics exist which can be very useful for identification at species level.

Use of novel microsatellite markers for population and paternity analysis in the commercially important crab Metacarcinus edwardsii (Brachyura: Cancridae)

Abstract In order to study fishery stocks and the effect of the male-biased fishery on multiple paternity, new genetic resources were developed for Metacarcinus edwardsii, the most important crab of artisanal fishery in Chile. A total of eight microsatellite loci were isolated and characterized in this crab, using an enriched library. Six to 27 alleles per locus were observed in two samples of 24 crab individuals. The observed heterozygosity ranged from 0.58 to 1.00 and all loci showed no deviation from Hardy–Weinberg equilibrium for either. Two sampling sites separated by 300 km showed no differences in allele frequencies, indicating that both sites are a part of the same population. Further, the genotypes of five ovigerous females and their newly hatched larvae showed that only one male was involved in the fertilization of each clutch. The variation detected in these markers is currently being used both for the study of populations of Metacarcinus edwardsii in a highly exploited geographic area and in order to elucidate the mating system of this species.

Genetic effects of living in a highly polluted environment: the case of the silverside Basilichthys microlepidotus (Jenyns) (Teleostei: atherinopsidae) in the Maipo River basin, central Chile

Freshwater systems are one of the environments most impacted by human activity, with pollution being a highly important factor. In Chile, several rivers exhibit varied levels of pollution, one of which is the Maipo River basin where the city of Santiago is located. The silverside Basilichthys microlepidotus (Jenyns) is an endemic fish species that inhabits this basin, thus we hypothesized that pollution has affected gene diversity and migration in populations of B. microlepidotus from the Maipo River basin. The aim of this study was to identify the population structure of B. microlepidotus in this basin and to determine if the populations of the silverside inhabiting polluted sites present differences in gene diversity and gene flow compared to populations inhabiting non-polluted areas. Using the variability of eight microsatellites, five populations of silverside were detected; three inhabiting non-polluted sites and two inhabiting polluted sites. From this, it was inferred that B. microlepidotus has been able to tolerate pollution in the Maipo River basin. No differences in gene diversity or migration were detected between polluted and non-polluted sites but comparison with historical estimation revealed an increase in the current migration rate when all the data from the basin were compared. A reduction in current effective population size was also observed when compared to historical values, and this is probably due to river degradation. Despite the disappearance of other fish species recorded at this basin, our results suggest that B. microepidotus is tolerant to pollution, thus indicating that native species respond differently to this environmental factor.