Intestinal disaccharidases are key determinants of carbohydrate assimilation in fish. Here, we characterized maltase and sucrase activity in juveniles of Oligosarcus jenynsii (Günther, 1864) and evaluated the modulation of maltase activity by dopamine. Maltase activity was detected across a broad pH (6.0–8.0) and temperature (4–45 °C) range and followed Michaelis–Menten kinetics (Km :1.22 mM), whereas sucrase activity was not detected. In vitro assays showed that dopamine significantly stimulated maltase activity in a concentration-dependent manner, with increases at 10-4 and 10-3 M. This stimulatory effect was not observed in the presence of the D1 receptor antagonist SCH-23390 or the D2 receptor antagonist chlorpromazine. These results demonstrate that intestinal maltase activity is responsive to dopaminergic stimulation under in vitro conditions and suggest the participation of dopaminergic pathways in this response. The physiological significance of this modulation in vivo remains to be established. These findings contribute to the understanding of the biochemical regulation of intestinal disaccharidases in a freshwater fish species.
Ontogenetic dietary shifts are common in freshwater fishes, typically occurring due to growth and gape widening that allow for an increasing breadth of dietary options. Identifying when changes occur can help quantify energetic and resource demands between life stages, and is particularly important for at-risk fishes by identifying the timing and extent of dietary shifts. Silver shiner (Notropis photogenis (Cope, 1865)), a Threatened species in Canada, has limited available ontogenetic dietary information. Here, stable isotope and gut content analyses were used to investigate the species' size-specific dietary shifts in Sixteen Mile Creek, one of five occupied watersheds in Canada. We hypothesized that ontogenetic niche shifts would be related to age/size and reflected in differing stable isotope values and gut contents. Ontogenetic dietary shifts occurring by size-classes were found, with trophic compression suggesting increased feeding specialization at the smallest and largest size-classes. The greatest dietary overlap and similarity were observed among intermediate size-classes and were lowest at both ends of the size range. The trophic shift observed in the larger size classes emphasizes the importance of maintaining sufficient terrestrial food resources for this species in Canada.
Understanding adaptation requires detecting selection at both phenotypic and genotypic levels. However, detecting selection at the genotypic level is challenging when selection is weak and/or when the genetic basis of phenotypes under selection is polygenic. Here, we investigated selection on genotypes in threespine stickleback fish (Gasterosteus aculeatus Linnaeus, 1758) from a mark-recapture experiment performed in the outlet stream of Misty Lake on Vancouver Island, Canada. We performed restriction site associated DNA sequencing (RAD-seq) on 190 fish that were recaptured in the experiment (“survivor” fish) and 192 fish that were not recaptured (“random” fish). Although we did not identify individual loci with strong differentiation between survivor and random fish, we found that survival was associated with a multi-locus genetic signature of ancestry in a "mystery" population. These loci were distributed across the genome and were not found at high frequency in the inlet stream of Misty Lake, suggesting that Misty Inlet is not the source of the mystery population. Fish that survived in Misty Outlet tended to be female and have wider pectoral fins. Our findings highlight the complexities of detecting weak and polygenic selection and the importance of integrating genomic approaches with ecological studies to elucidate adaptive mechanisms in natural populations.
The relative contributions of selection and genetic drift to phenotypic evolution remain difficult to disentangle. Although often framed as alternative causes of evolution, both operate simultaneously, particularly during population bottlenecks, range expansions, and extreme climatic events. Motivated by previous findings where a population of threespine stickleback (Gasterosteus aculeatus Linnaeus, 1758) experienced a severe drought, we explore how selection and drift interact to produce phenotypic change during a bottleneck. We implement forward-time Wright-Fisher simulations across a range of selection coefficients and bottleneck population sizes to assess the plausibility of different causal scenarios. We use this case study to highlight that single-generation phenotypic responses to selection are constrained, but that bottlenecks expand the variance, making extreme phenotypic shifts possible. Critically, the simulations also illustrate a fundamental non-identifiability problem, where a wide range of parameter combinations produce indistinguishable patterns, making definitive causal inference from a single evolutionary episode inherently challenging. We discuss how genomic data, long-term monitoring programs, and experimental approaches can help resolve the causal contributions of selection and drift. As contexts involving strong selection and severe bottlenecks become increasingly frequent, such as range expansions and extreme climatic events, developing such tools is essential for understanding evolutionary responses.
Sexual dimorphism (SD) can contribute to local adaptation and evolutionary diversification, but species-wide comparisons are hindered by heterogeneous published datasets. We developed the Sexual Dimorphism Ternary Index (SDTI), coding each trait–sample comparison as −1 (significant female bias), 0 (no significant difference), or +1 (significant male bias), to integrate heterogeneous data on threespine stickleback, Gasterosteus aculeatus Linnaeus, 1758, into a comparative dataset. Correlation-guided hierarchical aggregation reduced 11 overlapping traits to four weakly correlated variables: standard length (SL), the head–posterior composite (HPC), body depth (BD1), and the dorsal-spine composite (DSs). PERMANOVA detected a significant ecotype effect, with the clearest contrast occurring between marine and freshwater populations; BD1 showed the clearest single-variable separation. Marine populations tended to exhibit more male-biased body-depth and dorsal-spine dimorphism, whereas SL was consistently female-biased across ecotypes. The framework also allowed the White Sea samples to be positioned relative to the major ecotypes: their mean profile was closest to the anadromous centroid, while their high signed mean SDTI reflected a net predominance of significant male-biased comparisons across the traits examined. Although SDTI does not measure effect magnitude and is sensitive to statistical power, it identifies patterns in direction and organization of sexual dimorphism.
