Artículo de publicación ISIFor 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.FONDECYT 1110445 1150388 Direction de Investigacion y Desarrollo of the Universidad Austral de Chile Basal Grant PFB 02

How organisms adapt to unfavorable environmental conditions by means of plasticity or selection of favorable genetic variants is a central issue in evolutionary biology. In the Maipo River basin, the fish Basilichthys microlepidotus inhabits polluted and non-polluted areas. Previous studies have suggested that directional selection drives genomic divergence between these areas in 4% of Amplified Fragment Length Polymorphism (AFLP) loci, but the underlying genes and functions remain unknown. We hypothesized that B. microlepidotus in this basin has plastic and/or genetic responses to these conditions. Using RNA-Seq, we identified differentially expressed genes in individuals from two polluted sites compared with fish inhabiting non-polluted sites. In one polluted site, the main upregulated genes were related to cellular proliferation as well as suppression and progression of tumors, while biological processes and molecular functions involved in apoptotic processes were overrepresented in the upregulated genes of the second polluted site. The ornithine decarboxylase gene (related to tumor promotion and progression), which was overexpressed in both polluted sites, was sequenced, and a parallel pattern of a heterozygote deficiency and increase of the same homozygote genotype in both polluted sites compared with fish inhabiting the non-polluted sites was detected. These results suggest the occurrence of both a plastic response in gene expression and an interplay between phenotypic change and genotypic selection in the face of anthropogenic pollution.

To understand the role of gene expression in adaptive variation, it is necessary to examine expression variation in an ecological context. Quantitative real-time PCR (qPCR) is considered the most accurate and reliable technique to measure gene expression and to validate the data obtained by RNA-seq; however, accurate normalization is crucial. In Chile, the freshwater silverside fish Basilichthys microlepidotus inhabits both polluted and nonpolluted areas, showing differential gene expression related to pollution. In this study, we infer the stability of six potential reference genes (tubulin alpha, hypoxanthine-guanine phosphoribosyltransferase, glyceraldehyde-3-phosphate dehydrogenase, beta-actin, 60S ribosomal protein L13, and 60S ribosomal protein L8) in the gills and liver of silverside individuals inhabiting polluted and nonpolluted areas. To validate the reference genes selected, the most and least stable reference genes were used to normalize two target transcripts, one for each organ. The RefFinder tool was used to analyze and identify the most stably expressed genes. The 60S ribosomal protein L8 gene was ranked as the most stable gene for both organs. Our results show that reference gene selection influences the detection of differences in the expression levels of target genes in different organs and, also highlighting candidate reference genes that could be used in field studies.

Human activity has caused a deterioration in the health and population size of riverine species; thus, public policies have been implemented to mitigate the anthropogenic impacts of water use, watercourse transformation, and pollution. We studied the Maipo River Basin, one of the most polluted with untreated wastewater in Chile, for a period of 12 years (2007‐2019). Since the implementation of new public policies, including the operation of a wastewater collector (2012), the Maipo River Basin is currently much less polluted by untreated water than before. To analyze the impact of wastewater reduction in this river basin, we studied the native silverside (Basilichthys microlepidotus), which inhabits both polluted and unpolluted areas of the river basin. Previous studies reported the overexpression of the ornithine decarboxylase (odc) gene, heterozygote deficit, and high frequency of a homozygote odc genotype in silverside populations that inhabit wastewater‐polluted sites, suggesting a phenotypic change and genotypic selection in response to pollution. Here, a population affected and another population unaffected by wastewater were studied before and after implementing the wastewater collector. The physicochemical data of water samples, changes in odc expression and microsatellite variability, and odc genotype frequencies were analyzed. The results showed physicochemical changes in the affected site before and after the operation of the wastewater collector. The microsatellite loci showed no changes in either population. The odc expression in the affected site was higher before the operation of the wastewater collector. Significant changes in the genotype frequencies of the odc gene before and after the wastewater collector operation were detected only at the affected site, wherein the homozygous dominant genotype decreased from >59% to <25%. Our results suggest that public policies aimed at mitigating aquatic pollution can indirectly affect both gene expression and genotype frequencies of important functional genes.

For marine invertebrates with a benthic adult form and a planktonic larva phase, the connectivity among populations is mainly based on larval dispersal. While an extended larval phase will promote gene flow, other factors such as an intensive fishery and geographical barriers could lead to changes in genetic variability. In this study, the population genetic structure of the commercial crab Metacarcinus edwardsii was analyzed along 700 km of the Chilean coast. The analysis, based on eight microsatellite loci genotyped from megalopae and adult crabs, considered temporal and spatial patterns of genetic variation. The results showed no evidence of spatial patterns in genetic structure, suggesting high connectivity among the sampling sites. The temporal analysis showed no evidence of changes in allele frequencies and no evidence of a recent bottleneck. The lack of spatial structure and allele variation over time could be explained by the interaction of factors such as i) low reproductive variance due to the capability of females to store sperm in the seminal receptacle, which can be used for successive broods, ii) high larval dispersal and iii) high individual reproductive output. Using our data as priors, a genetic modelling approach coincided, predicting this temporal and spatial stability. The same analysis showed that a reduction in population size leads to the loss of genetic variability in populations, as well as of the genetic cohesiveness between populations, pointing out the importance management for species under exploitation, such as M. edwardsii.

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1. The presence of a dam disturbs river flow, which in turn directly affects the communities and evolutionary potential of riverine species. To detect the ecological effects of a dam on genetic diversity, genetic structure, and their progress in time, two riverine fishes living upstream and downstream of an irrigation reservoir were studied at two periods after its construction in 2004 in central Chile. 2. Samples of the Neotropical silverside Basilichthys microlepidotus and the pencil catfish Trichomycterus areolatus were obtained 2 and 7 years after the Corrales Dam was built. The microsatellite DNA variability of both species upstream and downstream of the dam was analysed. 3. Fish analysed 2 years after dam construction did not show genetic differences between upstream and downstream populations; however, fish obtained 7 years after dam construction showed differences between populations above and below the dam and differences from individuals collected 5 years earlier. 4. The current effective population sizes of both species were smaller in samples obtained upstream than in samples obtained downstream. Simulations showed a migration equal to zero as most probable after reservoir construction, suggesting that the dam is an impermeable barrier to the movement of individuals of these species. These results showed that population fragmentation in time could be related to the barrier imposed by the dam. 5. In a scenario of no new contact between populations located upstream and downstream of the dam, the simulation predicts a reduction of genetic diversity ranging from 3.98 to 8.09% over the next 60 years. 6. Analyses suggest that the Corrales Reservoir may be affecting the evolutionary potential of the populations upstream and downstream from the dam.

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