Urbanization drives contemporary evolution in stream fish

Human activities reduce biodiversity but may also drive diversification by modifying selection. Urbanization alters stream hydrology by increasing peak water velocities, which should in turn alter selection on the body morphology of aquatic species. Here, we show how urbanization can generate evolutionary divergence in the body morphology of two species of stream fish, western blacknose dace (Rhinichthys obtusus) and creek chub (Semotilus atromaculatus). We predicted that fish should evolve more streamlined body shapes within urbanized streams. We found that in urban streams, dace consistently exhibited more streamlined bodies while chub consistently showed deeper bodies. Comparing modern creek chub populations with historical museum collections spanning 50 years, we found that creek chub (1) rapidly became deeper bodied in streams that experienced increasing urbanization over time, (2) had already achieved deepened bodies 50 years ago in streams that were then already urban (and showed no additional deepening over time), and (3) remained relatively shallow bodied in streams that stayed rural over time. By raising creek chub from five populations under common conditions in the laboratory, we found that morphological differences largely reflected genetically based differences, not velocity–induced phenotypic plasticity. We suggest that urbanization can drive rapid, adaptive evolutionary responses to disturbance, and that these responses may vary unpredictably in different species.     

The effects of allospecific mitochondrial genome on the fitness of northern redbelly dace (Chrosomus eos)

Instantaneous mitochondrial introgression events allow the disentangling of the effects of hybridization from those of allospecific mtDNA. Such process frequently occurred in the fish Chrosomus eos, resulting in cybrid individuals composed of a C. eos nuclear genome but with a C. neogaeus mtDNA. This provides a valuable model to address the fundamental question: How well do introgressed individuals perform in their native environment? We infer where de novo production of cybrids occurred to discriminate native environments from those colonized by cybrids in 25 sites from two regions (West‐Qc and East‐Qc) in Quebec (Canada). We then compared the relative abundance of wild types and cybrids as a measure integrating both fitness and de novo production of cybrids. According to mtDNA variation, 12 introgression events are required to explain the diversity of cybrids. Five cybrid lineages could not be associated with in situ introgression events. This includes one haplotype carried by 93% of the cybrids expected to have colonized West‐Qc. These cybrids also displayed a nearly complete allopatric distribution with wild types. We still inferred de novo production of cybrids at seven sites, that accounted for 70% of the cybrids in East‐Qc. Wild‐type and cybrid individuals coexist in all East‐Qc sites while cybrids were less abundant. Allopatry of cybrids restricted to the postglacial expansion suggests the existence of higher fitness for cybrids in specific conditions, allowing for the colonization of different environments and expanding the species’ range. However, allospecific mtDNA does not provide a higher fitness to cybrids in their native environment compared to wild types, making the success of an introgressed lineage uncertain.     

Otolith Sr : Ca ratios of the freshwater and anadromous cyprinid genus Tribolodon

The ratio of strontium to calcium concentration in the otolith of four species of Tribolodon (Cyprinidae) was examined to reveal their migratory histories. The ratio was relatively stable from the core to the edge of the otolith in fluvial Tribolodon ezoe and T. hakonensis, whereas it changed from a low level to a higher level in anadromous T. brandtii and T. hakonensis. Four specimens of T. nakamurai from the Mogami River, Yamagata Prefecture, northern Japan, showed relatively stable ratios, indicating a fluvial life mode. On the other hand, the ratio increased once in only one specimen of T. nakamurai from the Koyoshi River of Akita Prefecture, suggesting the possibility that it was born in the Mogami River, the nearest major habitat of this species, and accidentally migrated to the Koyoshi River through the sea.     

Interaction between the roach, Rutilus rutilus, and dace, Leuciscus leuciscus, populations in a river catchment in south-west England

The ecology of roach, Rutilus rutilus (L.), and dace, Leuciscus leuciscus (L.), populations from different regions of the R. Exe catchment was studied. Dace were the predominant cyprinid in the middle reaches whilst roach dominated in the slow-flowing lower reaches. Each species showed maximum growth rate and reproductive effort in its preferred habitat, i.e. where it dominated the fish community. The diet of roach consisted mainly of vegetable material, whilst dace were omnivorous. Although each species had a characteristic diet, there was considerable overlap. There was little evidence that variability between regions in growth rates of each species resulted from competition for food.     

Assessing phylogeographic variation in the Rosyside Dace (Teleostei,Leuciscidae), a widespread morphologically variable taxon

Clinostomus (Leuciscidae) is a wide-ranging freshwater fish genus that occurs throughout eastern North America and southern portions of Canada with two species currently recognized: C. elongatus and C. funduloides. A previous taxonomic study of C. funduloides recognized two subspecies (estor and funduloides) and one diagnosed, but undescribed subspecies based on morphological characteristics and geographic distribution. In this study, we used three molecular markers (cytochrome b, S7 intron 1 and growth hormone intron 4) to test the three lineage hypothesis and evaluate genetic variation of C. funduloides across the range using Bayesian inference. Our results indicate that C. funduloides is not monophyletic, as individuals of C. elongatus nest within C. funduloides in both the mtDNA and nDNA phylogenetic analyses, although the position of C. elongatus varies between data sets. In addition, some of the recovered clades are deeply divergent from one another, further supporting the distinctiveness of many of the populations. Overall, these results suggest that subspecies designations are not warranted and a taxonomic revision is needed as Clinostomus is likely more diverse than is currently recognized.     

Intraspecific aggression in rosyside dace, a drift-feeding stream cyprinid

Individual rosyside dace Clinostomus funduloides in a semi-natural, artificial stream displayed substantial differences in their aggressiveness and could be classified as: (1) non-aggressive (NA, 18 of 30 rosyside dace), (2) moderately aggressive (MA, 9 of 30) and (3) highly aggressive (HA, 3 of 30). Rosyside dace groups, however, did not exhibit linear dominance hierarchies and fish size was only weakly correlated with the number of aggressive acts performed per individual. Small rosyside dace (<56 mm L_F) were always non-aggressive, but larger fish were present in all three aggression classes. The difference in size between the contestants was significantly, although not very strongly, correlated with the probability of winning an agonistic interaction (r ²=0·39). Aggressive rosyside dace may have ultimately gained higher fitness than less aggressive ones. HA individuals occupied the upstream-most position within foraging groups significantly more often than other rosyside dace. This location should be the most profitable one because its occupant will be the first to encounter prey. HA rosyside dace also occupied significantly higher focal velocities that were closer to energetic optima than MA and NA ones. They also had greater foraging rates and were less solitary than less aggressive fish, but these differences only were significant at the P=0·066 and P=0·081 level, respectively. Finally, HA fish performed significantly more aggressive acts and feedings backwards than other individuals. Despite these differences, the effects of intraspecific aggression in rosyside dace appeared less substantial than those that have been observed in stream salmonids.     

Characterization of microsatellite loci in longnose dace (Rhinichthys cataractae) and interspecific amplification in five other Leuciscinae species

The longnose dace (Rhinichthys cataractae) appears as a relevant model to address environmental and ecological issues in an evolutionary perspective. Eleven microsatellite markers were characterized for this species. Eight of these loci were highly polymorphic for populations of this species. Between four to 10 loci were also successfully amplified in five closely related species. These markers are believed to be valuable tools for genetic analysis of populations of longnose dace and other Leuciscinae species.     

Small founding number and low genetic diversity in an introduced species exhibiting limited invasion success (speckled dace, Rhinichthys osculus)

Molecular evaluations of successful invaders are common, however studies of introduced species that have had limited invasion success, or have died out completely, are rare. We studied an introduced population of speckled dace (Rhinichthys osculus) from northern California, USA that has rapidly increased in abundance but remained restricted to a 25-km stretch of river since its introduction in the mid-1980s. Field and laboratory analyses indicate that invasion success of speckled dace is constrained by the combined effects of multiple predators. The role of bottleneck effects associated with the introduction has not been studied. We assayed variation in seven microsatellite loci and one mitochondrial DNA gene in the introduced population and nine putative source populations to identify the source population and evaluate bottleneck effects. The Trinity River system was supported as the source owing to its genetic similarity and geographic proximity to the introduced population. Consistent with a bottleneck, the introduced population exhibited reduced allelic and haplotype richness in comparison to source populations. Estimates of the genetically effective number of individuals founding the introduced population using nuclear coalescent analyses and a mitochondrial simulation procedure were highly concordant in suggesting that the initial colonizing group was comprised of about 10 individuals. A bottleneck effect in an exotic species exhibiting limited invasion success has rarely been documented and thus introduction of speckled dace represents an important model system for future investigation. Establishing a relationship between genetic diversity and factors limiting invasion success in this system (e.g., predator avoidance) will help determine the extent to which genetic diversity loss has constrained invasion success in speckled dace.