Presumed hybrids between Haliotis rufescens and H. fulgens abalones, produced in a commercial abalone laboratory, were evaluated for progeny viability, gonad characteristics and for their 'true' status as hybrids by means of allozyme and microsatellite analyses. Four out of 10 evaluated allozyme loci proved to be useful for the genetic certi¢cation of hybrids, Gpi, Mdh-1, Mdh-2 and Sod, as they had exclusive alleles for each of the abalone reference species from which the presumed hybrids were produced. Three microsatellite loci were also evaluated for their usefulness in abalone hybrid certi¢cation. Two were not useful for hybrid certi¢cation as the reference abalone species shared some of the same alleles. The third loci (Hka 56) also had shared alleles between the two species, but at very di¡erent frequencies. Therefore, this permitted a presumptive certi¢cation of hybrids, which, however, was not error-proof as two allozyme certi¢ed hybrids were wrongly classi-¢ed as H. rufescens rather than as hybrids. Progeny viability of the only female certi¢ed to be a hybrid was signi¢cantly lower compared with one viability of the other females spawned, which were certi¢ed as H. rufescens. However, the number of eggs spawned by the only certi¢ed hybrid female was as large as those spawned by females certi¢ed as H. rufescens. Gonads of abalones sampled for the macroscopic appearance of sterility indicated that in the absence of any gonad development, no distinctive difference allows for hybrid identi¢cation, as there were undi¡erentiated individuals that were both hybrid and non-hybrid. On the other hand, two certi¢ed hybrid males were characterized by spermatocytes being the most abundant gamete type, although one had some spermatozoa present, indicating only partial sterility. Among the two female hybrids found, vitellogenesis was observed to proceed up to vitellogenic oocytes.

The SalI satellite repeat previously identified in Haliotis L. (abalone) was thought to be present in H. rufescens and absent in H. fulgens. However, we show here that SalI is also found in H. fulgens and is not useful for screening hybrid individuals bred in aquaculture or occurring naturally in the wild. SalI is a family of predominantly subtelomeric tandemly repeated sequences, and sequenced clones revealed clustering to species and little intraspecific variation. Analysis of SalI sequence divergence between Haliotis species of the Northeast Pacific revealed that evolutionary distances correlate well with bathymetric and latitudinal species distributions. Analysis of the structure of the tandem repeats revealed two regions of high sequence conservation that may contain conserved transcription factor binding sites, a surprise for an apparently "non-coding" tandem repeat. We speculate that these regions might be involved in heterochromatin silencing, perhaps mediated via transcriptional activity and RNA interference. The repeats show substantial differences in their chromosomal distributions, even between individuals of the same species, indicating a dynamic organization of repeats, perhaps mediated via sequence homogenization.

Abalone species are different from most mollusks utilized in aquaculture as they are known to hybridize in laboratory-induced matings. Allotriploidization of hybrid abalone has not yet been studied, and methodology useful in verifying the genotypic condition of such allotriploids do not exist. Genotypic verification of hybridization and allotriploidization in a cross of Haliotis fulgens and Haliotis rufescens was performed utilizing 6 crossamplifying microsatellite loci. Five H. rufescens spawns were used in this experiment, dividing each spawn into control and experimental hybrid groups and further into diploids and triploids. Two microsatellite loci developed for H. fulgens and H. rufescens allowed for the genotypic identification of hybrids within diploid and triploids. To further verify the percentage of allotriploids within the genotypic hybrids in the triploid hybrid groups, microsatellite loci originally developed in Haliotis corrugata and Haliotis kamtschatkana were tested for crossamplification in H. fulgens and H. rufescens. Of 21 loci, 4 were chosen for this study based on their crossamplification, heterozygosity in the females, and centromere recombination frequencies. Allotriploids in triploid-hybrid larvae were then detected by identifying larvae with recombinant genotypes at any of those loci. One family had low success verification associated with reduced recombination frequencies for all loci in that family. These results demonstrate that allotriploid verification at larval stages is feasible but depends on the number of loci available, their crossamplification in the species, and their recombination frequencies.

No abstract

La información sobre la estructura cromosómica es básica dentro del conocimiento biológico de cualquier especie y fundamental para la comprensión de fenómenos citogenéticos que subyacen a procesos fisiológicos, ontogénicos y evolutivos. En este último ámbito, el conocimiento del grado de similitud de los cromosomas de especies filogenéticamente cercanas complementa la información necesaria para plantear hipótesis causales sobre procesos de divergencia evolutiva. El objetivo del presente estudio fue determinar la similitud citogenética entre Paralabrax maculatofasciatus y P. nebulifer, especies filogenéticamente cercanas que se distribuyen en el Pacífico oriental, mediante la comparación del número, tipo y tamaño de los cromosomas. El examen de células mitóticas de eleuteroembriones en ambas especies mostró un cariotipo constituido por 48 cromosomas acrocéntricos (2n = 48A; número fundamental = 48), sin la presencia de cromosomas heteromórficos. No se detectaron diferencias significativas entre especies, tanto en el tamaño promedio, como en la longitud relativa (LR) de los pares cromosómicos homeólogos que presentaron un valor máximo de 4 μm (LR = 5.5 %; par 1) y un mínimo de 1.7 μm (LR = 2.3 %; par 24). Este cariotipo es considerado ancestral dentro del Orden Perciformes y está presente en la mayoría de las especies de la Familia Serranidae. Con base en estos resultados se sustenta la hipótesis de que la divergencia evolutiva entre P. maculatofasciatus y P. nebulifer se originó a través del establecimiento de barreras reproductivas precopulatorias sin alteración cariotípica ni formación de barreras postcopulatorias, tanto precigóticas como postcigóticas. Evidencen of karyotypic stasis during the evolutionary divergence between Paralabrax maculatofasciatus and P. nebulifer (Perciformes: Serranidae) Information on chromosome structure is basic within the biological knowledge of any species and fundamental to the understanding of the cytogenetic phenomena underlying physiological, ontogenic and evolutionary processes. Knowledge on the degree of similarity of chromosomes in phylogenetically close species supplements the necessary information to raise causal hypotheses on the processes of evolutionary divergence. The objective of this study was to determine the cytogenetic similarity between Paralabrax maculatofasciatus and P. nebulifer, closely (phylogenetically) related species distributed in the Eastern Pacific, by comparing number, type and size of chromosomes of these taxa. The examination of mitotic cells from eleutheroembryos of both species showed a karyotype consisting of 48 acrocentric chromosomes (2n = 48A; fundamental number = 48), without the presence of heteromorphic chromosomes. No significant differences between species were observed in size and relative length (RL) of homeologous chromosome pairs which showed maximum and minimum values of 4 μm (RL = 5.5 %; pair 1) and 1.7 μm (RL = 2.3 %; pair 24), respectively. This karyotype is considered ancestral within the Order Perciformes and is present in most of the species of the Family Serranidae. The results found in this study supported the hypothesis that evolutionary divergence between P. maculatofasciatus and P. nebulifer occurred through the establishment of pre-mating reproductive barriers, without karyotype modification or formation of post-mating barriers, either pre-zygotic or post-zygotic.