Population Genetics and Spawning Time of Lake Taupo Rainbow Trout

<p>The rainbow trout (Oncorhynchus mykiss) of Lake Taupo, New Zealand provide an exceptional opportunity to explore the contemporary adaptation of an introduced aquatic species. Recently it has become evident that their spawning migration time has shifted to later in the season. I investigated the genetic basis of these changes in spawning time by (1) using genetic markers to determine the origins of Taupo trout in California, (2) determining the pattern and extent of spatial population genetic variation throughout the Lake Taupo catchment and in comparison to nearby Lake Tarawera in the Rotorua district, (3) analysing genetic variation at the OtsClock1b spawning time gene in temporal replicates from several sites from Taupo, and (4) comparing contemporary genetic variation at this gene and microsatellite markers to genetic variation from three Taupo tributaries in 1980s. I compared the ability of single nucleotide polymorphism (SNP) and microsatellite markers to determine the origins of Lake Taupo rainbow trout, translocated from California around 120 years ago. Data were collected from 15 microsatellite and 93 SNP markers, using samples from the Lake Taupo population and ten populations throughout California, which included all historically indicated populations of origin. Results revealed that the Lake Taupo population has significantly diverged from Californian populations at both microsatellite and SNP loci. These analyses also showed that the Lake Taupo population was probably derived from several sources in California (the most likely origins being the McCloud River and Lake Almanor), and an indeterminate California coastal population. This conclusion was supported with simulations of founder events, which suggested that the genetic patterns of a single source of introduction would still be detectable 100 years post-founding, but with multiple introductions exact source populations become more difficult to detect. Approximately 50 individuals from 10 locations throughout the catchment were then analysed using 15 microsatellite loci to determine if there was any spatial population genetic differentiation. There was no significant difference in genetic distance between locations within Lake Taupo, although there was a significant difference between these populations and Rotorua and Waipakihi, which are isolated by geographic barriers. Lake Taupo rainbow trout do appear to diverge at markers potentially under selection, though, because genotyping of the poly-Q region of the timing locus OtsClock1b shows significant differentiation between individuals sampled at different times in the Waipa River. Two other sites, however, did not show the same pattern of significant seasonal variation in OtsClock1b allele frequencies. This suggests that genotypes at this locus could be influencing spawning migration time, but that this variation could also be site specific, and therefore have a strong environmental component. Scale samples from the 1980s show no significant divergence at 5 microsatellites and OtsClock1b, indicating that allele frequencies have not changed significantly over the last 20 years at neutral markers or markers under selection. I therefore conclude that while Taupo rainbow trout have diverged from their origins in California, they have only slightly diverged within their new environment, and do not show a consistent pattern of genetic change over time. This information will contribute not only to the management of the Taupo fishery but also to the current understanding of the population genetic structuring of introduced salmonids.</p>

Population Genetics and Spawning Time of Lake Taupo Rainbow Trout

<p>The rainbow trout (Oncorhynchus mykiss) of Lake Taupo, New Zealand provide an exceptional opportunity to explore the contemporary adaptation of an introduced aquatic species. Recently it has become evident that their spawning migration time has shifted to later in the season. I investigated the genetic basis of these changes in spawning time by (1) using genetic markers to determine the origins of Taupo trout in California, (2) determining the pattern and extent of spatial population genetic variation throughout the Lake Taupo catchment and in comparison to nearby Lake Tarawera in the Rotorua district, (3) analysing genetic variation at the OtsClock1b spawning time gene in temporal replicates from several sites from Taupo, and (4) comparing contemporary genetic variation at this gene and microsatellite markers to genetic variation from three Taupo tributaries in 1980s. I compared the ability of single nucleotide polymorphism (SNP) and microsatellite markers to determine the origins of Lake Taupo rainbow trout, translocated from California around 120 years ago. Data were collected from 15 microsatellite and 93 SNP markers, using samples from the Lake Taupo population and ten populations throughout California, which included all historically indicated populations of origin. Results revealed that the Lake Taupo population has significantly diverged from Californian populations at both microsatellite and SNP loci. These analyses also showed that the Lake Taupo population was probably derived from several sources in California (the most likely origins being the McCloud River and Lake Almanor), and an indeterminate California coastal population. This conclusion was supported with simulations of founder events, which suggested that the genetic patterns of a single source of introduction would still be detectable 100 years post-founding, but with multiple introductions exact source populations become more difficult to detect. Approximately 50 individuals from 10 locations throughout the catchment were then analysed using 15 microsatellite loci to determine if there was any spatial population genetic differentiation. There was no significant difference in genetic distance between locations within Lake Taupo, although there was a significant difference between these populations and Rotorua and Waipakihi, which are isolated by geographic barriers. Lake Taupo rainbow trout do appear to diverge at markers potentially under selection, though, because genotyping of the poly-Q region of the timing locus OtsClock1b shows significant differentiation between individuals sampled at different times in the Waipa River. Two other sites, however, did not show the same pattern of significant seasonal variation in OtsClock1b allele frequencies. This suggests that genotypes at this locus could be influencing spawning migration time, but that this variation could also be site specific, and therefore have a strong environmental component. Scale samples from the 1980s show no significant divergence at 5 microsatellites and OtsClock1b, indicating that allele frequencies have not changed significantly over the last 20 years at neutral markers or markers under selection. I therefore conclude that while Taupo rainbow trout have diverged from their origins in California, they have only slightly diverged within their new environment, and do not show a consistent pattern of genetic change over time. This information will contribute not only to the management of the Taupo fishery but also to the current understanding of the population genetic structuring of introduced salmonids.</p>

Allopatric origin of sympatric whitefish morphs with insights on the genetic basis of their reproductive isolation

The European whitefish (Coregonus lavaretus) species complex is a classic example of recent adaptive radiation. Here we examine a whitefish population introduced to northern Finnish Lake Tsahkal in late 1960s, where three divergent morphs (viz. littoral, pelagic and profundal feeders) were found ten generations after. Using demographic modelling based on genomic data we show that whitefish morphs evolved during a phase of strict isolation, refuting a rapid symmetric speciation scenario. The lake is now an artificial hybrid zone between morphs originated in allopatry. Despite their current syntopy, clear genetic differentiation remains between two of the three morphs. Using admixture mapping three quantitative trait loci associated with gonad weight variation, a proxy for sexual maturity and spawning time, were identified. We suggest that ecological adaptations in spawning time evolved in allopatry are currently maintaining partial reproductive isolation in the absence of other barriers to gene flow.

Effect of Photoperiod Manipulation on Spawning Time and Performance of Turbot (Scophthalmus maximus)

Temperature and photoperiod are known as the main stimuli of seasonal reproduction in fish. Turbot (Scophthalmus maximus) is a spring spawning teleost fish species with a promising aquaculture potential and high market value. This study was conducted to assess the effect of photoperiod manipulation on spawning time and spawning performance of turbot. A total of 28 mature turbots from the Black Sea population were subjected to manipulated photoperiod (a photoperiod regime that fish would naturally receive three months later) and natural photoperiod for almost a year. While the fish exposed to natural photoperiod spawned in May, the fish exposed to manipulated photoperiod spawned almost three months earlier compared to the natural photoperiod group. Reproductive and hatchery performance of the manipulated photoperiod and natural photoperiod groups were similar. It can be emphasized that photoperiod play an important role in accelerating maturation and spawning. The findings of this study could be implemented in the turbot aquaculture industry to advance production.

Networks of marine protected areas under fluctuating connectivity: The importance of within-MPA dynamics

The design of marine protected areas (MPAs) has been optimized under assumptions of spatially and temporally homogeneous larval dispersal, despite complex spatiotemporal patterns displayed by ocean currents. Here we studied the effect of dispersal variability on the effectiveness of MPA networks across scales. We adopted a nested approach integrating the dynamics of both within and among MPA connectivity into a stochastic metapopulation model and first derived metapopulation persistence (required reproductive effort) and stability over MPA networks by partitioning within and among MPA contributions in relation to the spatial resolution of within-MPA connectivity. We applied this framework over a range of dispersal traits (spawning time and pelagic larval duration) and MPA network configurations, based on simulated biophysical connectivity along the northeast Pacific coast. Our results show how within-MPA dynamics affect predictions based on parameters of MPA networks such as MPA size, spacing, and pelagic larval duration. Increasing within-MPA spatial resolution predicted increasing population persistence and stability independently of other network properties. High-resolution within-MPA dynamics also predicted a negative relationship between species persistence and MPA spacing while that relationship was non-monotonic under low-resolution within-MPA dynamics. Our analysis also resolved the role of pelagic larval duration for scaling up within-MPA dynamics to MPA networks: species with short larval duration led to increasing network stability with MPA spacing while the opposite was observed for species with long larval duration. Our study stresses the importance of integrating fluctuating larval connectivity, both within and among MPAs, and more specifically suggest the benefit of small and nearby MPAs under increasing ocean variability.

Spawning season movements of transported landlocked Atlantic salmon in a newly restored river habitat

Certain spawning areas of the critically endangered Lake Saimaa landlocked Atlantic salmon (Salmo salar m. sebago) have been recently restored by excavator- and helicopter-scattered gravel, but the success of applied methodologies has remained open. Here, we monitored the spawning-related movements and redds occurrence of transported semi-wild and hatchery-reared salmon in the restored River Ala-Koitajoki, Eastern Finland using radiotelemetry and snorkelling. Nearly all fish accepted the newly-restored spawning habitats in the river that maintains a low flow rate (only 4 m3 s-1). The movements of females released up to two weeks before spawning time were restricted mainly to the closest rapids from the release site, and most of the movements were directed downstream. Semi-wild and hatchery background fish exhibited similar mobility, which was more variable among males. A majority of redds were found in restored areas, and both helicopter- and excavator-scattered gravels were accepted as spawning substrates. Our results indicate that natural reproduction of the studied landlocked salmon population can be successfully returned to its original spawning river by restoration of habitats and transfer of spawners.

Reproduction aspect of green swordtail, Xiphophorus hellerii Heckel 1848 in Tamblingan Lake, Bali

Eco-biological information of green swordtail in Tamblingan Lake is unknown. This research aimed to reveal sex ratio, gonadosomatic index, viviparity, spawning time and location of green swordtail in Tamblingan Lake. Fish was collected by gill nets with a mesh size of 0.5 and 1.0 cm in five sampling stations from January to June 2019. Total length and body weight of all fish samples were measured then dissected to observe the level of gonad maturity and viviparity in female fish. A total of 373 green swordtail with total length ranged and body weight ranged from 30.4-69.2 mm and 0.7935 – 7.6612 g, respectively. The results showed that males outnumberd of females in all sampling periods. Gonadosomatic index of male and female ranged from 0.159-1.239 and 0.204-13.592, respectively. The mature individuals were captured in all sampling stations and observation times. This species has a good reproductive potential with viviparity ranges between 6-54 juveniles.