Abstract. Six Anemia populations from coastal and inland sites in Chile, ranging from 20 to 50 degrees latitude south, were compared morphologically. The study included reference samples of A. franciscana (San Francisco Bay, California-USA) and A. persimilis (Buenos Aires, Argentina). These species are likely to be found in Chile. Samples from Peru (Piura) and Brazil (Macau, Rio Grande do Norte) are two known examples of deliberate introduction of A. franciscana. The hypothesis ofA. franciscana being the dominant species in South America was tested by multivariate morphological analysis based on ten body measurements. In addition, laboratory cross-fertility tests were performed in order to evaluate levels of reproductive isolation among these widely distributed populations.The analysis showed that A. franciscana and A. persimilis are morphologically divergent. A number of populations overlap with the San Francisco Bay sample, two are morphologically close to Buenos Aires, whilst others lie morphologically in between. Interpopulation morphological differences along with geographical and, probably, ecological divergence do not reflect reproductive isolation, at least of the pre-mating type. The morphological similarity of two Chilean samples with A. persimilis suggests that the distribution ofA. persimilis should be further investigated. A multi-trait approach for Anemia characterization is stressed as a way to obtain better descriptions and interpretations of the biological diversity in the genus.

The brine shrimp Artemia, a typical inhabitant of hypersaline environments and characterized by a highly subdivided population structure, was used as a model to evaluate, under standardized laboratory conditions (at 65 ppt), primary reproductive traits (offspring quality and quantity) along with levels of reproductive isolation and degrees of divergence among populations. Intrapopulation experimental crosses and cross-fertility tests were evaluated in ®ve populations (mostly A. franciscana) from coastal and inland environments in Chile, and in reference samples of A. franciscana (San Francisco Bay, U.S.A.) and A. persimilis (Buenos Aires, Argentina), which are the species likely to be found in Chile. The populations compared displayed signi®cant variability in fecundity (total offspring, brood size) as well as in the ratio encystment/oviviparity. Hybrid offspring, produced abundantly in cross-fertility tests with reference populations, showed a pronounced switch to the encystment mode, particularly in crosses with A. persimilis. Exposure to a broad range of ecological conditions seems to have optimized a generalist reproductive strategy in the Artemia populations studied that combines variation in both the quantity and quality of zygotes. Laboratory cross-fertility tests evaluated prime reproductive characteristics in individual crosses with fair repeatability, as well as testing barriers to laboratory reproductive isolation. The lack of ef®cient mechanisms for reproductive isolation in the allopatric Artemia populations studied follows a trend often seen in other anostracods. Formerly allopatric populations have not achieved sympatry later as required by the allopatric speciation paradigm, and this is a probable explanation for production of the laboratory hybrids.

Back, flank (reddish band along the lateral line and below the lateral line), and belly regions of cultured rainbow trout Oncorhynchus mykiss were characterized in terms of skin coloration, spottiness, and darkness by using computerbased image analysis as an approach to separate fish into desirable back color categories for market and export. Three highly represented colors were observed on the back (mean ± SE percentage of area covered by the given color): blue or sky-blue, 18.0 ± 1.8%; yellow, 13.4 ± 1.5%; and green, 66.1 ± 2.0%. Individuals with a high frequency of these colors on the back (at least 50% of area covered by a given color) were reclassified into groups exhibiting a yellowish back color (YB), a bluish back color (BB), or a greenish back color (GB) to determine whether the BB group presented differences in various skin color variables when compared with the other back color groups; an undefined back color (UB) group (fish for which all colors had less than 50% coverage) was also used in these comparisons. The number and size of dark spots (mean ± SE) on the back was significantly smaller in the BB group (2.3 ± 0.3 spots/cm 2 ; 1.3 ± 0.2% of area covered by spots/cm 2 ) than in the YB group (3.4 ± 0.2 spots/cm 2 ; 1.9 ± 0.1% of area covered by spots/cm 2 ); furthermore, skin darkening on the back as measured in grayscale space (where 0 = black, 255 = white) was slightly greater in the BB group (58.2 ± 3.9) than in the GB group (80.7 ± 2.8). In the lateral band along the flank, the percentage of area covered by purple was significantly lower in the BB group (7.1%) than in the UB group (27.5%). Skin darkening of the back and darkening of the belly demonstrated a significant positive correlation in the BB group (r = 0.558, P < 0.05). Discriminant function analysis clearly distinguished the BB group from the other back color groups based on color profile. These results support the fact that the BB group, more commonly referred to as "blue back" rainbow trout, presents a color pattern of high commercial interest that can be used to improve the external appearance of farmed rainbow trout. Furthermore, computer-based image analysis was shown to be an effective technique for objectively measuring skin color to categorize rainbow trout into particular color patterns.

Chromosomal rearrangements have played a key role in the speciation of the New World sexual Artemia species (Crustacea, Anostraca) A. franciscana and A. persimilis. The species differ by a chromosome duplication (2n+2=44 in A. persimilis vs 2n=42 in A. franciscana), and a greater amount of heterochromatin (HCH) in A. franciscana. To investigate this difference in HCH, four parameters were compared for the first time in Artemia: 1) the absolute sizes of one A. persimilis and four A. franciscana karyotypes; 2) the relative lengths of all chromosome; 3) the number of heterochromatic bands and 4) the relative amounts of HCH per chromosome and its position. The two A.franciscana karyotypes with the largest HCH amount (26%), have twice (139.26 microm and 134.05 microm) the absolute size of the A.persimilis karyotype (64.91 microm; HCH: 1.97%). Interspecific and intraspecific (A. franciscana) differences in chromosome size and HCH were observed, although the two sets of information are not positively correlated. While A. persimilis shares plesiomorphic karyological traits with Old World species, A. franciscana has apomorphic features such as longer chromosomes and greater HCH content, mainly dispersed towards telomeres. The impacts of such chromosome rearrangements are discussed in relation to the wider geographic distribution, greater colonizing ability, and life history plasticity of A. franciscana. An additional, though preliminary, point of this paper is the observation that the female would be the heterogametic sex.

This study describes the genetic structure of five naturalized populations of brown trout in southern Chile using allozyme and microsatellite markers to establish levels of intra‐ and interpopulation genetic variability and divergence. Fourteen enzymatic systems were used comprising 20 loci and three microsatellite loci specific to brown trout. The genetic variability values (allozymes, P=20–35%, average=27%, HO=0.118–0.160, average=0.141; microsatellites, P=33.3–100%, average=66.66%, HO=0.202–0.274, average=0.229) are similar to values described in other naturalized populations of brown trout present in Chile, but higher than those observed in European populations of this species. Values of total genetic diversity (HT) (allozymes=0.1216 and microsatellites=0.3504) and relative genetic divergence (GST) (allozymes=9.5% and microsatellites=15%) were also similar to the results obtained in previous studies of Chilean populations of brown trout. These values, when compared with those obtained in Europe, proved to be similar for HT but lower for GST. The low interpopulational genetic differentiation was in accordance with the small genetic distance observed between the populations analysed (D Nei=0.004–0.025). On the other hand, the high frequency of one of the two alternative alleles of the phylogeographic marker locus LDH‐5* in the populations analysed (LDH‐5*90>0.84) would indicate a European origin, in particular Atlantic as opposed to Mediterranean, for the brown trout introduced into Chile. The high levels of genetic variability suggest a mixed origin for the naturalized brown trout in Chile, which could have originated either before or during the introduction process. Nevertheless, the low level of genetic differentiation between populations could reflect the short lapse of time in evolutionary terms, during which populations introduced into Chile have been exposed to different evolutionary forces, and which has not been sufficiently long to produce greater genetic differentiation between populations.