No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of 70 years of freshwater residency on survival, growth, early maturation, and smolting in a stock of anadromous rainbow trout from southeast Alaska
Abstract
Progeny of wild, freshwater sequestered (resident) rainbow trout Oncorhynchus mykiss, descendants of a stocking of steelhead (anadromous rainbow trout) in 1926, and progeny of the wild, ancestral steelhead lineage and their reciprocal crosses were compared for two brood years in a hatchery environment to determine the effects of 70 years of freshwater residency on growth, survival, early maturity, and smolting proportion. Resulting smolts were tagged, released, and recovered as maturing adults to evaluate marine survival. For the 1996 brood, 75 families were maintained in separate freshwater raceways for 10 months. Approximately 100 fish from each family were tagged with passive integrated transponder tags, pooled by type, and cultured until age 2. An additional group was tagged with coded-wire tags and reared in the same manner. For the 1997 brood, 80 families were coded-wire-tagged, separated by breeding type, and cultured at different densities. Size-at-age and survival were reduced significantly in progeny of resident females when compared with progeny from anadromous females during the first 2 months after first feeding. No significant differences were observed in subsequent growth or survival through age 2. A higher proportion of smolting at age 2 and a lower proportion of early male maturity was observed in families from anadromous parents. Smolts produced by anadromous parents had four to five times higher marine survival than those from resident parents. While smolting proportions and smolt survival were lower for the progeny of freshwater resident fish, the results indicate that significant numbers of smolts and adults can still be produced by populations landlocked for up to 70 years and 20 generations. The results have substantial implications for the use of natural freshwater environments for the preservation of endangered anadromous stocks of rainbow trout, the rehabilitation of anadromous stocks, and the actual effective breeding size of anadromous rainbow trout populations.
... The proportion of each phenotype is influenced by genotype (Nichols et al., 2008;Hecht et al., 2013), individual condition (size, growth rate, energy storage) (McMillan et al., 2012) and environmental factors . Regardless, efforts to produce a strain with a single phenotype, either selecting the sea-run (Sharpe et al., 2007;Christie et al., 2011;Sloat and Reeves, 2014) or the freshwater-resident (Thrower and Joyce, 2005;Hayes et al., 2012), have failed. ...
... Although the proportion of each phenotype is influenced by genotype (Nichols et al., 2008;Hecht et al., 2013), individual condition (size, growth rate, energy storage) (McMillan et al., 2012) and environmental factors , the current knowledge is not enough to completely explain their smoltification patterns (Kendall et al., 2015). Efforts to produce a strain with a single phenotype, either selecting the sea-run (Sharpe et al., 2007;Christie et al., 2011;Sloat and Reeves, 2014) or the freshwater-resident (Thrower and Joyce, 2005;Hayes et al., 2012), have proved unsuccessful. Therefore, it is likely that the fish that performed poorly in seawater would have been natural freshwater-residents, while the others would have been the sea-run phenotype. ...
... Furthermore, rainbow trout have a unique life-history, with their wild population being naturally divided into freshwater residents and sea-run animals, which is in turn related to smoltification rates (Christie et al., 2011;Kendall et al., 2015). Efforts to produce a strain with a single phenotype, either selecting the sea-run (Sharpe et al., 2007;Christie et al., 2011;Sloat and Reeves, 2014) or the freshwater-resident (Thrower and Joyce, 2005;Hayes et al., 2012), have proved unsuccessful so far. From here arises the hypothesis that the fish that performed well in seawater could be natural migrants to seawater, while the ones that die or become GS could be natural freshwater-residents but were forcefully transferred to seawater. ...
Seawater-transferred rainbow trout (Oncorhynchus mykiss) has become an attractive aquaculture product in recent years. Industrial interest is mainly due to its resistance to infectious pancreatic necrosis and its adaptability to brackish water, which allows farming in otherwise unexploited locations. However, most practices for the aquaculture of this species have been imported from Atlantic salmon (Salmo salar) without evidence data supporting their suitability for the species. These include protocols to induce their preadaptation to seawater (smoltification). As a result, following seawater transfer, large numbers of fish die (around 10%) or become growth-stunted (GS; 10-60%). Therefore, species-specific rearing protocols and seawater-readiness biomarkers are needed.
In the present PhD thesis, the effects of different photoperiod and temperature protocols for rearing in freshwater were assessed on the development of smoltification traits and subsequent seawater performance. This was achieved by using an array of molecular tools to measure osmoregulation-, growth- and haematopoiesis-related genes, proteins and hormones. Moreover, the discovery of potential seawater-readiness biomarkers and the study of smoltification, seawater adaptation and GS fish development were performed using several mass spectrometry proteomic and lipidomic approaches.
Results suggest that winter light signals are inadvisable for the species, while all tested summer signals produced similar good results. Moreover, increased temperature protocols not only failed to improve smoltification and growth but potentially compromised the immune system of the fish. Overall, continuous light seems an advisable light regime, irrespective of temperature. Moreover, new promising potential biomarkers for seawater-readiness were identified using proteomics, while also suggesting a previously unknown role of these proteins in smoltification and seawater adaptation. Finally, GS development was shown to be related to low insulin-like growth factor 1 levels following seawater transfer. Moreover, other related factors to the phenotype were higher stress levels, possibly caused by bullying by bigger fish, and hepatic anomalies related to oxidative stress.
... The Sashin Creek system on Baranof Island in southeastern Alaska has become a model population for studying the genetic basis of migration in rainbow trout, as previous quantitative genetic, QTL, and GWAS analyses all confirm a strong genetic basis to life history development (e.g., [27,29,30]). The Sashin Creek drainage is composed of a native, largely anadromous population in Sashin Creek, and a resident population in Sashin Lake that was founded by transplants from Sashin Creek (individuals originating below the two large barrier waterfalls that separate the creek and the lake; [31,32]). Since founding, strong selective pressures against the production of migrants in the lake have resulted in the development of a largely resident lake population [29]. ...
... As already stated, the lake population was founded by transplanting fish from the creek above two barrier waterfalls in the 1920s. Since that event there have been no additional introductions [31]. Therefore, samples within the lake have been through a substantial genetic bottleneck as supported by lower observed and expected heterozygosity (Fig 3) and higher estimates of LD (S2 Table) in the R x R samples compared to the A x A samples. ...
... Therefore, samples within the lake have been through a substantial genetic bottleneck as supported by lower observed and expected heterozygosity (Fig 3) and higher estimates of LD (S2 Table) in the R x R samples compared to the A x A samples. Although our sampling confirms that resident samples can produce migrants and vice versa, it is important to note that previous studies have found that migrants produced by residents are less likely to return to spawn than migrants produced from migratory samples [31]. These differences between adjacent populations add to a growing body of literature that suggests life history development is controlled by population specific genetic effects. ...
In studying the causative mechanisms behind migration and life history, the salmonids–salmon, trout, and charr–are an exemplary taxonomic group, as life history development is known to have a strong genetic component. A double inversion located on chromosome 5 in rainbow trout (Oncorhynchus mykiss) is associated with life history development in multiple populations, but the importance of this inversion has not been thoroughly tested in conjunction with other polymorphisms in the genome. To that end, we used a high-density SNP chip to genotype 192 F1 migratory and resident rainbow trout and focused our analyses to determine whether this inversion is important in life history development in a well-studied population of rainbow trout from Southeast Alaska. We identified 4,994 and 436 SNPs–predominantly outside of the inversion region–associated with life history development in the migrant and resident familial lines, respectively. Although F1 samples showed genomic patterns consistent with the double inversion on chromosome 5 (reduced observed and expected heterozygosity and an increase in linkage disequilibrium), we found no statistical association between the inversion and life history development. Progeny produced by crossing resident trout and progeny produced by crossing migrant trout both consisted of a mix of migrant and resident individuals, irrespective of the individuals’ inversion haplotype on chromosome 5. This suggests that although the inversion is present at a low frequency, it is not strongly associated with migration as it is in populations of Oncorhynchus mykiss from lower latitudes.
... Stream residency is also common for this species, with resident individuals remaining in fresh water throughout their life cycle, often moving between suitable habitats (Gowan et al. 1994), but never venturing to the ocean. In watersheds with ocean access, researchers have found that in addition to interbreeding (McMillan et al. 2007), resident rainbow trout and steelhead can produce progeny of the alternate lifehistory form (Pascual et al. 2001; Thrower and Joyce 2004; Korman et al. 2010). These findings indicate that life-history trajectories of partially anadromous salmonid populations are driven by a combination of genetic predispositions and environmental cues (Jonsson and Jonsson 1993; Hendry et al. 2004). ...
... There is need for resolution concerning the question of whether resident rainbow trout and steelhead are reproductively isolated in the majority cases (Behnke 2002) to inform whether population assessments should be expected to quantify the impact of resident rainbow trout on the persistence of steelhead. Observational studies (McMillan et al. 2007 ), breeding experiments (Thrower and Joyce 2004), genetic analyses (Olsen et al. 2006; McPhee et al. 2007; Christie et al. 2011 ), and otolith microchemistry (Zimmerman and Reeves 2002) are used to examine partial anadromy in rainbow trout populations. Otolith primordial chemistry, specifically the strontium to calcium (Sr/Ca) ratio, is a well-established method of determining maternal life history of partially anadromous salmonids (Kalish 1990; Rieman et al. 1994; Volk et al. 2000). ...
... Conversely, juveniles may be less likely to exhibit anadromy in habitats favorable to a nonmigratory life history, such as areas with low migration success (Narum et al. 2008 ) or stream flow conditions suited for residency (Mills et al. 2012). Available genetic and observational data collected on rainbow trout populations throughout the Pacific Rim (Pascual et al. 2001; Thrower and Joyce 2004; McPhee et al. 2007 ) suggest that in habitats with ocean access, resident rainbow trout produce some anadromous offspring that survive and return as adult steelhead. To test this hypothesis, we quantified the proportion of steelhead produced by native female resident rainbow trout in the Yakima Basin, Washington, using otolith primordial Sr isotope ratios. ...
Rainbow trout (Oncorhynchus mykiss) have diverse life histories, including both freshwater-resident and anadromous “steelhead” life-history forms. Here, we demonstrate that female resident rainbow trout produce anadromous offspring that survive and return to spawn as adult steelhead. This study represents the first successful attempt to quantify steelhead production rates from female resident rainbow trout across a large watershed. Otolith microchemistry (⁸⁷Sr/⁸⁶Sr) techniques were used to determine the maternal life history (resident or anadromous) of 498 emigrating steelhead kelts in the Yakima Basin, Washington. Five geochemically distinct freshwater rearing regions were identified within the basin. All five regions were predicted to produce steelhead with resident maternal life histories. Basin-wide, 20% and 7% of steelhead collected in 2010 and 2011, respectively, had resident maternal life histories. Cross-life-history form production may be critical to persistence of anadromous life histories within partially anadromous salmonid populations, particularly in areas where anadromous fish abundance is low due to natural or anthropogenic influences.
... There is growing evidence that expression of anadromy is influenced by both sex and genetics, where anadromy is more common in females (Rundio et al. 2012;Ohms et al. 2014;Kendall et al. 2015) and, at least for southern populations, in individuals with the migration-associated haplotype of a large multigene complex on chromosome Omy05 (Kelson et al. 2019;Pearse et al. 2019). Anadromy is also associated with maternal life history, with progeny of anadromous females more likely to migrate than progeny of nonanadromous females, although progeny of both forms can express the alternative life history (Zimmerman and Reeves 2000;Thrower and Joyce 2004;Courter et al. 2013). ...
... Finally, six of the adults in our study were progeny of anadromous mothers but one had a nonanadromous mother, demonstrating that nonmigratory forms can produce migrants that stray and provide connectivity among basins on the Big Sur coast. Previous studies have shown that although O. mykiss often express the same migratory type as their mother, both forms can produce offspring of the alternative life history (e.g., Zimmerman and Reeves 2000;Thrower and Joyce 2004;Courter et al. 2013). However, our study is the first, to our knowledge, to document straying by an anadromous offspring of a nonanadromous mother into a neighboring basin. ...
Straying has been difficult to study directly in natural steelhead Oncorhynchus mykiss populations. We analyzed an opportunistic sample of seven adult steelhead from a small basin on the Big Sur coast of California to determine life‐history traits including whether fish were strays. Otolith natural tags (87Sr/86Sr) and genetic stock identification (GSI) indicated that all seven adults were strays from at least six different sources. Three adults strayed from nearby streams (<72 km) on the Big Sur coast, while three strayed from distant sources including the Klamath River (680 km to the north); the source of one stray could not be identified. Six strays were progeny of steelhead mothers but one was the offspring of a nonanadromous mother. Six were female and one was male, and all that could be genotyped were homozygous (n = 4) or heterozygous (n = 2) for the anadromy‐associated haplotype in a migration‐associated genomic region. While the opportunistic nature and small size of the sample prevents us from inferring the rate of straying into the basin, our study nonetheless demonstrates that steelhead may stray across greater distances than generally appreciated and that nonanadromous females can produce anadromous offspring that stray and hence provide connectivity among basins.
... Life history strategies in diadromous fishes are diverse within species and populations (Walther et al. 2011;Kendall et al. 2015;Hodge et al. 2016), yet this diversity has been substantially reduced by anthropogenic alterations to critical habitats, most notably by the loss of ecological connectivity through damming of rivers (Dauble and Watson 1997;Bunn and Arthington 2002). However, in a few cases, migratory phenotypes that had seemingly been lost due to dam construction have been found to have persisted over generations in isolated populations of rainbow/steelhead trout (Oncorhynchus mykiss) (Thrower and Joyce 2004), redband trout (O. mykiss gairdneri) (Holecek et al. 2012), and sockeye salmon (O. ...
... The removal of hydroelectric dams on the Elwha River, Washington, USA, resulted in the resumption of anadromy and the expansion of foraging opportunities in bull trout (S. confluentus) after being almost entirely land-locked for over a century (Quinn et al. 2017). Rainbow trout transplanted to a lake in Alaska above large waterfalls in the 1920s continued to produce smolts that returned as adult steelhead to the base of the waterfalls 70 years later (Thrower and Joyce 2004). Adfluvial redband trout (a subspecies of rainbow trout) land-locked in a reservoir in southwestern Idaho for over 40 years retained the potential for anadromy and continued to undergo smoltification, although unlike in the Table 3 for fish IDs present study the fish did not actually emigrate from the reservoir to undertake a seaward migration (Holecek et al. 2012). ...
The conservation of land-locked populations of migratory fishes is increasingly important in the era of dam removal and habitat reconnection. We used an otolith strontium (Sr) tracer (⁸⁷Sr/⁸⁶Sr) to test the hypothesis that a land-locked population of an endangered salmonine species, Sakhalin taimen (Parahucho perryi), retains the capacity for anadromy, and that some individuals out-migrate from the reservoir to the sea. Years later, these individuals return but are blocked by the migration barrier of the reservoir dam and are denied reproduction in their natal streams. Juvenile taimen collected from the reservoir and two nearby regions were classified based on their otolith Sr isotopic signatures to their regions of origin with an overall accuracy of 88%. When the same classifier was applied to ocean-caught adult taimen, we predicted some individuals had originated from the reservoir with high posterior probabilities (> 0.9). Whether the land-locked Sakhalin taimen can help sustain the metapopulation dynamics of the species at the watershed scale may depend on whether, and how soon, the disrupted migration pathway is restored.
... The two forms can interbreed and contribute to the genetic pool of the population. Anadromous parents can produce non-anadromous progeny and vice-versa (Docker and Heath 2003;Thrower and Joyce 2004;Thrower et al. 2004;Boughton et al. 2006;Thrower et al. 2008;Olsen et al. 2006;Girman and Garza 2006;Garza and Clemento 2007;Christie et al. 2011). Studies have shown that wild steelhead and rainbow trout from different parts of their range exhibit distinct ecological traits and genetic characteristics (Thorgaard 1983;Nielsen et al. 1994Nielsen et al. , 1997Nielsen et al. , 1998Girman and Garza 2006;Pearse and Garza 2008;Clemento et al. 2009). ...
... The two forms can interbreed and contribute to the genetic pool of the population. Anadromous parents can produce non-anadromous progeny and vice-versa (Docker and Heath 2003;Thrower and Joyce 2004;Thrower et al. 2004;Boughton et al. 2006;Thrower et al. 2008;Olsen et al. 2006;Girman and Garza 2006;Garza and Clemento 2007;Christie et al. 2011). Studies have shown that wild steelhead and rainbow trout from different parts of their range exhibit distinct ecological traits and genetic characteristics (Thorgaard 1983;Nielsen et al. 1994Nielsen et al. , 1997Nielsen et al. , 1998Girman and Garza 2006;Pearse and Garza 2008;Clemento et al. 2009). ...
This study explores the historical distribution and abundance of anadromous steelhead and associated freshwater rainbow trout in the Santa Ynez River watershed of northern Santa Barbara and western Ventura counties, California, prior to the completion of Bradbury Dam in 1953. Steelhead and rainbow trout once occurred throughout the Santa Ynez River basin, which supported one of the largest steelhead runs in central and southern California. The size of the Santa Ynez River's steelhead runs varied dramatically due to climatic and hydrologic cycles. Yet the river still supported an important recreational steelhead fishery until the early 1950s, when the population collapsed following the construction of Bradbury Dam. Few steelhead spawn in the Santa Ynez today, but the river remains a crucial focus for the recovery of southern California steelhead, which since 1997 have been listed as endangered under the U.S. Endangered Species Act (ESA).
... The Cowichan River is home to one of the most significant winter-run steelhead (Oncorhynchus mykiss) stocks on Vancouver Island and is used as an indicator stock for the East Coast of Vancouver Island. O. mykiss exhibit multiple life-history strategies, including anadromous (steelhead) and non-anadromous (rainbow trout) forms (Pascual et al. 2001;McMillan et al. 2007;Thrower and Joyce 2004). Both anadromous and non-anadromous rainbow trout are known to occupy the Cowichan River, with the expectation that resident rainbow trout are likely to represent individuals of both fluvial life history and adfluvial life history in association with Cowichan Lake. ...
In 2015 the British Columbia Ministry of Forests, Lands, and Natural Resource Operations and Rural Development contracted the British Columbia Conservation Foundation to initiate a preliminary study of the maternal origin of rainbow trout/steelhead (Oncorhynchus mykiss) fry from the Cowichan River, Vancouver Island, British Columbia, using otolith microchemistry methods. Microchemical analysis of the Sr/Ca ratios in the otolith primordium from O. mykiss fry were used to distinguish the life history, anadromy vs non-anadromy of maternal fish.
... In the Nisqually River, the resident form of O. mykiss is known to be abundant in some years and may contribute to smolt production. Smolts derived from resident Rainbow Trout may have lower marine survival than those originating from anadromous mothers (Kostow et al. 2003;Thrower and Joyce 2004;Pearse et al. 2009). If smolt trap estimates are inaccurate, redds are missed, and estimates of anadromous smolts are comprised of a large proportion of fish originating from resident Rainbow Trout, the compounded sources of error could result in underestimates of marine survival and inflated estimates of production. ...
We highlight the uncertainty that exists around estimating productivity and survival for one population of threatened steelhead Oncorhynchus mykiss with the goal of strengthening our understanding of the well documented poor marine survival of Puget Sound steelhead. We evaluated how sensitive estimates of productivity and survival were to the uncertainty associated with smolt trap, redd survey methodology, estimates of fish per redd, and smolt production by resident O. mykiss in order to clarify causes of poor steelhead survival in this area. We show that from 2004 to 2014 estimates of both freshwater productivity and marine survival were highly sensitive to estimates of fish per redd used to expand redd counts as well as error around smolt abundance estimates. Regardless, uncertainty associated with these inputs did not explain the low survival and high productivity observed for Nisqually River steelhead relative to other populations. In addition, we identified progeny from anadromous mothers upstream of what was previously considered a barrier and we also documented that a proportion of steelhead smolts (N= 4/43) originated from resident mothers (rainbow trout). While these results indicated an under‐estimation in the total number of steelhead redds counted each year, and overestimation of steelhead progeny enumerated at smolt traps, they had little impact on estimates of survival and productivity. Results from the current study supports previous work reporting poor marine survival for populations of Puget Sound steelhead and highlights the sympatric relationship between resident and anadromous life histories of O. mykiss. Overall, our study supports a management strategy that protects both the anadromous and fluvial forms of O. mykiss, prioritizes habitat improvements that promote freshwater productivity and increases research focused on identifying causes of poor marine survival.
... For example, flooding and increased food availability resulted in elevated rates of freshwater maturation (residency) in Salmo salar [52]. Similarly, O. mykiss isolated in a reservoir for 70 years are still able to express migration [53]. In summary, indirect genetic control may facilitate opportunistic responses to environmental conditions and also encourage the persistence of life-history diversity, contributing to population stability [54]. ...
Migration is a complex trait that often has genetic underpinnings. However, it is unclear if migratory behaviour itself is inherited (direct genetic control), or if the decision to migrate is instead the outcome of a set of physiological traits (indirect genetic control). For steelhead/rainbow trout ( Oncorhynchus mykiss ), migration is strongly linked to a large genomic region across their range. Here, we demonstrate a shared allelic basis between early life growth rate and migratory behaviour. Next, we demonstrate that early life growth differs among resident/migratory genotypes in wild juveniles several months prior to migration, with resident genotypes achieving a larger size in their first few months of life than migratory genotypes. We suggest that the genetic basis of migration is likely indirect and mediated by physiological traits such as growth rate. Evolutionary benefits of this indirect genetic mechanism likely include flexibility among individuals and persistence of life-history diversity within and among populations.
... The short length of rivers and large estuaries on PEI are highly conducive to anadromy. The innate flexibility of the species also promotes anadromy, as the traits associated with it can remain latent within freshwater populations for decades (Thrower and Joyce 2004;Quinn et al. 2017). Furthermore, mothers of either phenotype (anadromous or freshwater) can give rise to a mix of both phenotypes (Christie et al. 2011;Courter et al 2013). ...
This study examined the migratory patterns of introduced rainbow trout (Oncorhynchus mykiss) in three rivers in Prince Edward Island, Canada, using acoustic telemetry and otolith microchemistry. Only 6% of acoustically tagged fish in three river systems left coastal embayments. A cohort of rainbow trout in all three rivers entered saline waters. Habitat use differed among migrants in the three rivers, as Montague River fish occupied estuary habitat (mean 20.79 PSU) more often than West River and Dunk River fish that tended to occupy both riverine tidal (mean 1.27 and 4.29 PSU, respectively) and freshwater habitats (<0.5 PSU), particularly during summer months (July and August). A second cohort of rainbow trout remained exclusively in fresh water. Migratory individuals were more likely to arise from anadromous mothers, but freshwater mothers produced migratory offspring in all sites. Migratory individuals were significantly larger than nonmigratory freshwater residents. This study suggests that partial residency was the primary strategy, with prominent tidal occupation, while secondary marine and freshwater contingents were included in the full range of successful migratory strategies.
... This species is partially migratory, meaning that some individuals migrate to the ocean (i.e., anadromous "steelhead" trout) whereas others complete their entire life history in freshwater (i.e., resident "rainbow" trout). In general, migratory O. mykiss occupy lower elevation streams with easy access to the ocean, while resident O. mykiss dominate further upstream (Berejikian, Campbell, & Moore, 2013;Kendall, McMillan, & Sloat, 2014;Narum, Zendt, Graves, & Sharp, 2008) and above impassible barriers (Pearse et al., 2009;Thrower & Joyce, 2004). Like other migratory salmonid fishes, steelhead trout migrate from the ocean to freshwater to breed, and swim upstream to seek out breeding sites, ideally where their offspring will experience reduced competition and densities (Fleming & Reynolds, 2003). ...
Landscape permeability is often explored spatially, but may also vary temporally. Landscape permeability, including partial barriers, influences migratory animals who move across the landscape. Partial barriers are common in rivers where barrier passage varies with streamflow. We explore the influence of partial barriers on the spatial and temporal distribution of migration-linked genotypes of Oncorhynchus mykiss, a salmonid fish with co-occurring resident and migratory forms, in tributaries to the South Fork Eel River, California, USA, Elder and Fox Creek. We genotyped >4,000 individuals using RAD-capture and classified individuals as resident, heterozygous, or migratory-genotypes using life history-associated loci. Across four years of study (2014-2017), the permeability of partial barriers varied across dry and wet years. In Elder Creek the largest waterfall was passable for up-river migrating adults 4-39 days/year. In this stream, the overall spatial pattern, with fewer migratory genotypes above the waterfall, remained true across dry and wet years (67-76% of migratory alleles were downstream of the waterfall). We also observed a strong relationship between distance upstream and proportion of migratory alleles. In Fox Creek, the primary barrier is at the mouth, and we found that the migratory allele frequency varied with the annual timing high flow events. In years when rain events occurred during the peak breeding season, migratory allele frequency was high (60-68%), and otherwise it was low (30% in two years). We highlight that partial barriers and landscape permeability can be temporally dynamic, and this effect can be observed through changing genotype frequencies in migratory animals.
... Most salmonid populations that have been landlocked for several thousand years (i.e., post-glacially) do show decreased osmoregulatory ability in salt water (e.g., Staurnes et al. 1992;Nilsen et al. 2003), but other populations have shown no apparent decrease in this ability (e.g., McCormick et al. 1985;Nilsen et al. 2007). Conversely, there are examples where salmonid populations isolated above recently constructed barriers soon showed reduced ability to osmoregulate in salt water and reduced rates of smoltification (e.g., Thrower and Joyce 2004;Holecek et al. 2012). Moreover, there are multiple examples of rapid freshwater evolution in other fishes. ...
Despite their highly conserved body plan and larval stage, adult life history type in lampreys diverges on two main axes related to migration and feeding. Of the 41–45 recognized lamprey species, 18 species feed parasitically after metamorphosis and their juvenile (sexually immature) feeding phase lasts from 3–4 months to 2–4 years. Nine of these species are exclusively freshwater resident; five are exclusively or almost exclusively anadromous, and four (sea lamprey, European river lamprey, Arctic lamprey, and, to a lesser extent, Pacific lamprey) are largely anadromous but with established freshwater populations. The other 23–27 described species are non-parasitic “brook” lampreys which remain within their natal streams. They initiate sexual maturation during metamorphosis, and, because the non-trophic periods of metamorphosis and sexual maturation are superimposed, the parasitic feeding phase is eliminated; this makes them the only vertebrates known to have non-trophic adults. Body size at maturity varies dramatically among life history types, ranging from ~110 to 150 mm total length (TL) in non-parasitic species to 800–900 mm TL in the anadromous sea lamprey. Freshwater forms are typically intermediate in size, although those that inhabit small systems may be no larger than non-parasitic lampreys and others (particularly the Great Lakes sea lamprey) are quite large. Some anadromous species (most notably European river lamprey, Pacific lamprey, and Arctic lamprey) show considerable intraspecific variation, consisting of typical large-bodied forms and dwarf or “praecox” forms that appear to feed at sea for a reduced period of time. Establishment in fresh water is more common in species that are consistently small-bodied or those with praecox forms. The only exceptions are the very small-bodied western river lamprey (mean TL at maturity ~200 mm), which does not produce freshwater parasitic forms (although it has given rise to innumerable non-parasitic freshwater populations), and the sea lamprey which, despite its very large size, has successfully colonized the Great Lakes. Abundant prey of a suitable size range is critical for establishment of freshwater parasitic populations. However, even with abundant prey, abandonment of anadromy is expected only under circumstances where decreases in mortality and the costs associated with migration make the reduction in size at maturity, and the accompanying reduction in fecundity, worthwhile. Pacific lamprey generally fail to establish when isolated above recently constructed barriers, likely because the reservoirs in which they have been isolated are relatively small and because they appear to osmoregulate poorly in fresh water. However, because colonization of fresh water appears to select for individuals “pre-adapted” to feed and grow to maturity in fresh water (i.e., relying on existing genetic variation within the source population), probability of establishment would likely increase with the number of founders. The existence of three closely related freshwater parasitic species suggests that Pacific lamprey successfully colonized fresh water in the past. Whether sea lamprey colonized Lake Ontario and Lake Champlain post-glacially or in historic times is debated. At present, the “invasion-by-canal” hypothesis appears to be the most convincing, but definitive resolution should be possible with genome-level analyses. Given the decimation of the Great Lakes ecosystem by sea lamprey, it is critical to be able to predict the potential for anadromous lampreys to become invasive in other freshwater systems. Migratory type is rarely considered a species-specific character unless it is accompanied by identifiable morphological differences. In contrast, variability in feeding type has long been considered a species-specific character because size-assortative mating was thought to result in reproductive isolation between parasitic and non-parasitic forms. However, not all parasitic and non-parasitic forms appear to be reproductively isolated, and different species show different degrees of divergence from their presumed parasitic ancestor. “Paired” non-parasitic species are defined as those that are morphologically similar to a particular parasitic species in all aspects other than body size, and “relict” brook lampreys are those that cannot be obviously paired with extant parasitic forms. However, molecular analyses have: (1) identified the closest extant parasitic relative to these relict species (although a few “orphan” species still remain, where identification of the closest living relative still sheds little light on the identity of the parasitic ancestor); (2) shown that the distinction between paired and relict species is sometimes unclear; and (3) demonstrated that there is also considerable variation among paired species in the degree to which they are morphologically and genetically differentiated from their parasitic ancestors. We review this “speciation continuum,” particularly in European river and brook lamprey populations where recent genetic and genomic studies show significant gene flow between these species where they co-occur (i.e., refuting assumptions of complete reproductive isolation resulting from size-assortative mating) while also showing that there are genome-level differences between the feeding types (i.e., refuting the hypothesis of phenotypic plasticity). In sympatry, European river and brook lampreys appear to be partially reproductively isolated ecotypes that nevertheless maintain distinct phenotypes, because regions of the genome involved in reproductive isolation and local adaptation resist the homogenizing effect of introgression. Interestingly, the results of analyses used to reconstruct the demographic history of divergence in this species pair are inconsistent with recent and rapid divergence in sympatry following the recent glacial retreat; rather, they support divergence in allopatry ~200,000–250,000 years ago and re-establishment of secondary contact ~90,000 years ago. Some loci have been identified that differ between the forms (e.g., the vasotocin and gonadotrophin-releasing hormone 2 precursor genes), but an understanding of the genetic basis of life history evolution in lampreys remains elusive. There appear to be strong parallels between factors that promote or constrain loss of anadromy in parasitic species (and reduction in duration of the feeding phase) and those that lead to or limit the evolution of non-parasitism (i.e., total elimination of the feeding phase). Smaller-bodied parasitic species have been far more prolific in producing non-parasitic derivatives than others; western river lamprey are already so small at maturity that “skipping” right to a non-parasitic form represents a more profitable trade-off between mortality and fecundity than freshwater parasitism. In contrast, there is a conspicuous absence of brook lamprey derivatives from the large-bodied sea, pouched, and Caspian lampreys. Our comparisons suggest that 300 mm TL (with a 10–12× reduction in fecundity) is the cut-off above which shifts to non-parasitism would not be beneficial. Therefore, we predict that Great Lakes sea lamprey is not an “intermediate” freshwater parasitic form that will give rise to a non-parasitic derivative, because complete elimination of the parasitic feeding phase would represent too large (~40×) a reduction in fecundity.
... Although the proportion of each phenotype is influenced by genotype (Hecht et al., 2013;Nichols et al., 2008), individual condition (size, growth rate, energy storage) (McMillan et al., 2012) and environmental factors , the current knowledge is not enough to completely explain their smoltification patterns (Kendall et al., 2015). Efforts to produce a strain with a single phenotype, either selecting the sea-run (Christie et al., 2011;Sharpe et al., 2007;Sloat and Reeves, 2014) or the freshwater-resident (Hayes et al., 2012;Thrower and Joyce, 2005), have proved unsuccessful. Therefore, it is likely that the fish that performed poorly in seawater would have been natural freshwater-residents, while the others would have been the sea-run phenotype. ...
Photoperiod is thought to be the main zeitgeber that induces smoltification in salmonids. However, its effects on the smoltification of rainbow trout (Oncorhynchus mykiss) are not fully understood and no published data documents the effects of the photoperiod regime currently used commercially, continuous light (LL). The present study compared the effect of four different photoperiod regimes (i.e. advanced phase photoperiod (APP), delayed phase photoperiod (DPP), LL and simulated natural photoperiod (SNP)) on the smoltification and growth of juvenile rainbow trout during their freshwater phase of winter-spring and the following summer post-smolt phase. Smoltification was evaluated by monitoring gill Na+,K+–ATPase (NKA) activity and transcription of NKA α-subunit isoforms 1a and 1b, and Na+,K+,2Cl- cotransporter 1a. Growth was measured as specific growth rate of both length and weight, and through molecular growth proxies such as the levels of circulating insulin-like growth factor 1 (IGF-I) in plasma and transcription of igf-I, igf binding protein 1b (igfbp1b), growth hormone receptor 1 (ghr1) and cathepsin L (ctsl) in the liver. Results indicate that APP induces a longer smolt window and higher levels of plasma IGF-I in both freshwater and seawater (two months post transfer), while DPP led to a shorter smolt window, lower plasma IGF-I levels in freshwater and seawater, an earlier decrease in liver igf-I and ctsl transcription in freshwater (as seen by modelling over time) and lower specific growth rate in freshwater. The transcription analysis of osmoregulatory genes complemented NKA activity and allowed for the detection of a transient response to light and of differences between the osmoregulatory capacity of parr and desmolted fish. Furthermore, an upregulation of the liver transcription of igf-I, ghr1 and ctsl was found in all treatments during the smolt window, which corresponded to the periods with highest growth. Finally, both plasma IGF-I and liver igf-I in seawater were found to be significantly correlated to fish growth in seawater. However, our data did not show that plasma IGF-I prior to seawater transfer could be used as a reliable predictor of growth in seawater. Overall, and especially when compared with other salmonid species, photoperiod seems to be a weaker inducer of smoltification in rainbow trout, according to the parameters that were tested, suggesting that other environmental cues might be more important drivers of this process.
... By contrast, offspring from the anadromous population maybe more variable in their timing of sexual maturation. Smoltification (the physiological transition leading to migration to the sea) is highly heritable in this population [27,32]; moreover, although both migrant and resident fish can produce migrants, migrants produced from resident parents have lower hypo-osmotic capability and reduced ocean survival relative to conspecifics with anadromous parents [76]. Therefore, it seems likely that female offspring produced from anadromous parents (A x A cross) are more predisposed to migrate than female offspring produced from resident parents (R x R cross). ...
Sex-bias in gene expression is a mechanism that can generate phenotypic variance between the sexes, however, relatively little is known about how patterns of sex-bias vary during development, and how variable sex-bias is between different populations. To that end, we measured sex-bias in gene expression in the brain transcriptome of rainbow trout (Oncorhynchus mykiss) during the first two years of development. Our sampling included from the fry stage through to when O. mykiss either migrate to the ocean or remain resident and undergo sexual maturation. Samples came from two F1 lines: One from migratory steelhead trout and one from resident rainbow trout. All samples were reared in a common garden environment and RNA sequencing (RNA-seq) was used to estimate patterns of gene expression. A total of 1,716 (4.6% of total) genes showed evidence of sex-bias in gene expression in at least one time point. The majority (96.7%) of sex-biased genes were differentially expressed during the second year of development, indicating that patterns of sex-bias in expression are tied to key developmental events, such as migration and sexual maturation. Mapping of differentially expressed genes to the O. mykiss genome revealed that the X chromosome is enriched for female upregulated genes, and this may indicate a lack of dosage compensation in rainbow trout. There were many more sex-biased genes in the migratory line than the resident line suggesting differences in patterns of gene expression in the brain between populations subjected to different forces of selection. Overall, our results suggest that there is considerable variation in the extent and identity of genes exhibiting sex-bias during the first two years of life. These differentially expressed genes may be connected to developmental differences between the sexes, and/or between adopting a resident or migratory life history.
... Steelhead also express variations in age and timing of juvenile migrations to the ocean, years spent in the ocean, and seasonal timing of adult returns (Savvaitova et al. 2003;Kuzishchin et al. 2007; Moore et al. 2014). Life history expressions among O. mykiss are described as conditional strategies in which individuals have the capacity to express all life histories regardless of parentage or previous selective pressures (Thrower and Joyce 2004;McPhee et al. 2007;Kendall et al. 2014;Phillis et al. 2016). Expression of these strategies have been linked to interactions between genetically controlled thresholds and body size, growth rate, and lipid stores at particular times of the year (Beakes et al. 2010;McMillan et al. 2011;Tattam et al. 2013;Evans et al. 2014;Kendall et al. 2014; Thompson and Beauchamp 2014). ...
We used PIT tags implanted in juvenile Oncorhynchus mykiss to monitor movement into and out of two coastal Washington State rivers, East Twin River and West Twin River. Movement patterns revealed at least 18 life histories of steelhead O. mykiss with variations in age and seasonal migration of juveniles, juvenile use of the ocean prior to migration, years spent in the ocean, season of adult return, and iteroparity. While most migrants left the river in their first fall or winter, we did not detect any returning adults from these age-0 migrants. Adults were only produced from age-1 and older migrants, of which most were age-2 spring migrants that returned after two summers in the ocean. Our results indicated a positive relationship between fish length at tagging and the probability of being detected as a migrant, while the probability of a migrant leaving at age 1 and older decreased with increasing length at tagging among fish that were detected as migrants. We hypothesize that fish attaining a large enough size early in life to survive over the winter but not big enough to trigger migration at age 0 were more likely to remain in the river to become age-1 migrants, which were more likely to produce a returning adult steelhead. We also found evidence that density-dependent growth may influence juvenile steelhead migration patterns and production of migrants as evidenced by increasing contributing-adult steelhead escapement being negatively related to average cohort body size, probabilities of fish being detected as migrants, and production of age-1 and older migrants. We anticipate that the findings of this study can be used to inform the development of steelhead recovery strategies for East Twin and West Twin rivers, which have experienced recent declines in adult returns much like other North Pacific Ocean stocks.
Received January 20, 2016; accepted May 18, 2016
... Steelhead also express variations in age and timing of juvenile migrations to the ocean, years spent in the ocean, and seasonal timing of adult returns (Savvaitova et al. 2003;Kuzishchin et al. 2007; Moore et al. 2014). Life history expressions among O. mykiss are described as conditional strategies in which individuals have the capacity to express all life histories regardless of parentage or previous selective pressures (Thrower and Joyce 2004;McPhee et al. 2007;Kendall et al. 2014;Phillis et al. 2016). Expression of these strategies have been linked to interactions between genetically controlled thresholds and body size, growth rate, and lipid stores at particular times of the year (Beakes et al. 2010;McMillan et al. 2011;Tattam et al. 2013;Evans et al. 2014;Kendall et al. 2014; Thompson and Beauchamp 2014). ...
Understanding life history diversity and factors influencing expression of resident (rainbow trout) and anadromous (steelhead) Oncorhynchus mykiss life histories are essential pre-requisites for O. mykiss population conservation and recovery. To this end, we monitored migration, growth, and survival of Oncorhynchus mykiss in two coastal watersheds using passive integrated transponder (PIT) tags. Our results indicated that these populations expressed a diversity of anadromous life histories with no evidence of resident life history types. A majority of juveniles migrate to the ocean in their first fall or winter, although these parr migrants do not produce adults. Adults were only produced from fish that reared in the river for at least one winter, with rearing at least two winters producing most adults. Our results indicated that body size early in life affected the probability of fish expressing an early or late migration strategy. Fish that attained larger body size early in life were more likely to migrate early and ultimately fail to produce adults. In contrast, smaller fish were more likely to rear in the river at least one winter to produce smolt migrants that ultimately had a greater chance of producing an adult.
... This is because body size correlates strongly with fitness components, such as habitat-specific survival (Ward et al. 1989;Bond 2006;Evans et al. 2014;Thompson and Beauchamp 2014) and female fecundity (Shapovalov and Taft 1954), and such fitness components evolutionarily favor anadromy in some environments and freshwater residency in others (Satterthwaite et al. 2009. Thus, although life histories are partly under genetic control (Thrower and Joyce 2004;McPhee et al. 2007;Heath et al. 2008;Pearse et al. 2014), natural selection should favor a conditional life history strategy that uses body size as an internal cue for whether and when to switch from freshwater habitat to marine habitat (Mangel and Satterthwaite 2008;Satterthwaite et al. 2009;McMillan et al. 2012;Sloat et al. 2014). At the same time, the growth and body size necessary to cue the switch are expected to (1) differ for males and females (Sloat et al. 2014); (2) vary regionally as a function of local survival in both the marine and freshwater environments; and (3) depend on the maximum attainable body size (asymptotic body size) in the two environments . ...
... Most salmonid populations that have been landlocked for several thousand years (i.e., post-glacially) do show decreased osmoregulatory ability in salt water (e.g., Staurnes et al. 1992;Nilsen et al. 2003), but other populations have shown no apparent decrease in this ability (e.g., McCormick et al. 1985;Nilsen et al. 2007). Conversely, there are examples where salmonid populations isolated above recently constructed barriers soon showed reduced ability to osmoregulate in salt water and reduced rates of smoltification (e.g., Thrower and Joyce 2004;Holecek et al. 2012). Moreover, there are multiple examples of rapid freshwater evolution in other fishes. ...
In North America, at least seven lamprey species pairs are recognized in which the filter-feeding larvae are morphologically similar but the adults differ dramatically, becoming either parasitic or non-parasitic (i.e. non-trophic) following metamorphosis. It is widely accepted that non-parasitism arose independently in each pair. Conspicuous morphological differences (particularly adult body size) distinguish non-parasitic adults from parasitic forms, and most lamprey taxonomists (applying the Morphological Species Concept) consider each a distinct species. Due to size assortative mating, it is assumed that reproductive isolation between parasitic and non-parasitic lampreys would be absolute and immediate; thus the Biological Species Concept would also dictate that each be recognized as distinct species. However, a growing body of molecular data is demonstrating that wide-ranging non-parasitic species are invariably polyphyletic (supporting an insightful suggestion by Carl Hubbs and Milton Trautman in 1937 that non-parasitism has evolved repeatedly within individual pairs) but are frequently genetically indistinguishable from their sympatric parasitic counterpart. Thus, according to the Phylogenetic Species Concept, paired species are NOT distinct species. Furthermore, in at least one pair, even high-resolution genetic markers have been unable to distinguish between parasitic and non-parasitic lampreys when sympatric, questioning the previous assumptions of reproductive isolation. What’s a taxonomist to do?
... What followed in such systems can be thought of as a hard selection sweep in which alleles associated with residency were selected to a much greater frequency than the same alleles in the migrant population. Further support for selection against residents producing migrants comes from Thrower and Joyce (2004), who examined the survivability of migrant fish produced from crosses between resident fish and migrant fish. They found that migrant offspring produced by migrant fish had a greater proportion of returns than migrant offspring from resident fish, suggesting migrants are inheriting alleles that promote ocean survivability. ...
Next generation sequencing and the application of population genomic and association approaches have made it possible to detect selection and unravel the genetic basis to variable phenotypic traits. Using the two approaches in parallel is an especially attractive approach in non-models organisms that lack a sequenced and annotated genome, but only works well when population structure is not confounded with the phenotype of interest. Herein, we use population genomics in a non-model fish species, rainbow trout (Oncorhynchus mykiss), to better understand adaptive divergence between migratory and non-migratory ecotype, and to further our understanding about the genetic basis of migration. RAD tag sequencing was used to identify Single Nucleotide Polymorphisms (SNPs) in migrant and resident O. mykiss from two systems, one in Alaska and the other in Oregon, USA. A total of 7,920 and 6,755 SNPs met filtering criteria in the Alaska and Oregon, data sets respectively. Population genetic tests determined that 1,423 SNPs were candidates for selection when loci were compared between resident and migrant samples. Prior linkage mapping studies using RAD tag SNPs were available to determine the position of 1,990 markers. Several significant SNPs are located in genome regions that contain QTL for migratory related traits, reinforcing the importance of these regions in the genetic basis of migration/residency. Annotation of genome regions linked to significant SNPs revealed genes involved in processes known to be important in migration (such as osmoregulatory function). This study adds to our growing knowledge on adaptive divergence between migratory and non-migratory ecotypes of this species; across studies, this complex trait appears to be controlled by many loci of small effect, with some in common, but many loci not shared between populations studied.
... Most salmonid populations that have been landlocked for several thousand years (i.e., post-glacially) do show decreased osmoregulatory ability in salt water (e.g., Staurnes et al. 1992;Nilsen et al. 2003), but other populations have shown no apparent decrease in this ability (e.g., McCormick et al. 1985;Nilsen et al. 2007). Conversely, there are examples where salmonid populations isolated above recently constructed barriers soon showed reduced ability to osmoregulate in salt water and reduced rates of smoltification (e.g., Thrower and Joyce 2004;Holecek et al. 2012). Moreover, there are multiple examples of rapid freshwater evolution in other fishes. ...
In most lamprey genera, "paired" species exist in which the larvae (which are microphagous filter feeders) are morphologically similar but the adults differ dramatically, becoming parasitic on teleost fishes or nonparasitic (i.e., do not feed at all) following metamorphosis. Parasitic lampreys feed for several months to several years (either in their natal stream or after migrating to larger fresh or marine water bodies) before embarking on a nontrophic upstream migration, sexual maturation, and spawning (followed by death); nonparasitic lampreys eliminate the parasitic phase, begin sexual maturation toward the end of metamorphosis, and spawn and die within 6-10 months of metamorphosis. In each species pair, the reduction in the length of postlarval life in nonparasitic lampreys is generally accompanied by an increase in the length of the larval period (and size at metamorphosis) so that the evolution of nonparasitism appears to have occurred without a change in the overall life span. Rather, nonparasitism appears to have evolved as a result of a change in the timing of metamorphosis relative to the timing of sexual maturation. Conspicuous morphological (e.g., adult body size, relative eye and oral disk size) and histological (e.g., lack of a functional digestive tract) differences distinguish nonparasitic adults from parasitic forms, and most lamprey taxonomists recognize life history type as a species-specific characteristic. However, plasticity of feeding type (e.g., facultative parasitism) has been observed in some lamprey populations, and molecular data on a number of paired species show no genetic differentiation between sympatric species pairs and suggest a polyphyletic origin for several nonparasitic species. This paper reviews the paired species concept, the repeated and independent evolution of nonparasitism in different genera and even within species, the evidence for facultative parasitism or facultative nonparasitism in some lamprey species, and the potential for hybridization between paired species and attempts to answer the question, are brook lampreys "real" species? The tentative answer is that there likely is not a single answer for all lamprey species pairs; different species pairs represent speciation at different stages. Some pairs appear to be distinct species according to both the biological and phylogenetic species concepts (i.e., they are reproductively isolated and show reciprocal monophyly), although each is not necessarily fixed for feeding type. In contrast, other pairs may represent incipient speciation and others yet may be experiencing ongoing gene flow. Parallels are therefore drawn between different lamprey species pairs and the divergent life history types found in other animal taxa (e.g., echinoderms and amphibians) and other temperate fish species (e.g., anadromous and freshwater-resident salmonids)
... This makes the A. nobilis system unique, even in relation to well-known programs, such as those for red drum Sciaenops ocellatus (McEachron et al. 1993;Smith et al. 2003;Tringali et al. 2008), Pacific salmonids Oncorhynchus spp. (Waples 1994;Reisenbichler et al. 2004;Thrower and Joyce 2004), and Atlantic cod Gadus morhua (Jørstad 2004). Beyond its general interest to those that study marine mating systems, we anchor this research in specific context by comparing knowledge gained of A. nobilis spawning to that of the closely related S. ocellatus, arguably the most comprehensively assessed sciaenid (family Sciaenidae; drums, grunts, and croakers) in terms of genetics (e.g., Gold 2004;Gold et al. 2008Gold et al. , 2010. ...
The evolutionary effects captive-bred individuals that can have on wild conspecifics are necessary considerations for stock enhancement programs, but breeding protocols are often developed without the knowledge of realized reproductive behavior. To help fill that gap, parentage was assigned to offspring produced by a freely mating group of 50 white seabass (Atractoscion nobilis), a representative broadcast spawning marine finfish cultured for conservation. Similar to the well-known and closely related red drum (Sciaenops ocellatus), A. nobilis exhibited large variation in reproductive success. More males contributed and contributed more equally than females within and among spawns in a mating system best described as lottery polygyny. Two females produced 27% of the seasonal offspring pool and female breeding effective size averaged 1.85 per spawn and 12.38 seasonally, whereas male breeding effective size was higher (6.42 and 20.87, respectively), with every male contributing 1–7% of offspring. Further, females batch spawned every 1–5 weeks, while males displayed continuous reproductive readiness. Sex-specific mating strategies resulted in multiple successful mate pairings and a breeding effective to census size ratio of ≥0.62. Understanding a depleted species’ mating system allowed management to more effectively utilize parental genetic variability for culture, but the fitness consequences of long-term stocking can be difficult to address.
Oncorhynchus mykiss is a partially migratory salmonid species, and many migratory populations (known as steelhead) have declined in recent decades in the western United States and Canada. Closely related resident populations (known as rainbow trout) may be an effective resource in the recovery of these declining migratory populations. However, the extent to which different populations of resident rainbow trout produce migratory individuals and how likely these individuals are to return as adults to spawn remains unknown. One limitation to answering these questions is the identification of loci that accurately segregate between migratory and resident populations. To address this limitation, we used existing genomic data from a well‐studied population of O. mykiss from Southeastern Alaska (Sashin Creek) to identify loci that segregate between phenotypes. We then utilized Double Mismatch Allele‐Specific qPCR (DMAS‐qPCR) to genotype 233 smolts out‐migrating from Sashin Creek and 99 returning adult steelhead trout across a five‐year period to determine (a) the origin of out‐migrating smolts and returning adults and (b) to quantify the extent to which the resident population contributes to the migratory population. Our results show that 37.3% of out‐migrating smolts were produced from resident parents, whereas 19.3% of returning adults had resident parents. Ultimately, these results demonstrate that resident populations of rainbow trout produce migrant offspring that successfully complete their migration and return to spawn, increasing population sizes and likely improving genetic diversity. Therefore, conservation efforts should consider landlocked resident populations for producing smolts when developing recovery plans for migratory steelhead populations.
Rainbow trout (Oncorhynchus mykiss) are a partially migratory species wherein some individuals undergo long-distance anadromous migrations, and others stay as residents in their native freshwater streams. The decision to migrate is known to be highly heritable, and yet, the underlying genes and alleles associated with migration are not fully characterized. Here we used a pooled approach of whole-genome sequence data from migratory and resident trout of two native populations-Sashin Creek, Alaska and Little Sheep Creek, Oregon-to obtain a genome-wide perspective of the genetic architecture of resident and migratory life history. We calculated estimates of genetic differentiation, genetic diversity, and selection between the two phenotypes to locate regions of interest and then compared these associations between populations. We identified numerous genes and alleles associated with life history development in the Sashin Creek population with a notable area on chromosome 8 that may play a critical role in the development of the migratory phenotype. However, very few alleles appeared to be associated with life history development in the Little Sheep Creek system, suggesting population-specific genetic effects are likely important in the development of anadromy. Our results indicate that a migratory life history is not controlled by a singular gene or region but supports the idea that there are many independent ways for a migratory phenotype to emerge in a population. Therefore, conserving and promoting genetic diversity in migratory individuals is paramount to conserving these populations. Ultimately, our data add to a growing body of literature that suggests that population-specific genetic effects, likely mediated through environmental variation, contribute to life history development in rainbow trout.
The construction of dams and water diversions has severely limited access to spawning habitat for anadromous fishes.
To mitigate for these impacts, hatchery programs rear and release millions of juvenile salmonids, including steelhead,
the anadromous ecotype of the species Oncorhynchus mykiss. These programs sometimes use nonindigenous
broodstock sources that may have negative effects on wild populations. In California, however, only one anadromous
fish hatchery program currently uses nonnative broodstock: the steelhead program at Nimbus Fish Hatchery on the
American River, a tributary of the Sacramento River in the California Central Valley. The goal of this study was to
determine if potentially appropriate sources to replace the broodstock for the Nimbus Hatchery steelhead program
exist in the Upper American River, above Nimbus and Folsom dams. We show that all Upper American River O. mykiss
sampled share ancestry with other populations in the Central Valley steelhead distinct population segment, with
limited introgression from out-of-basin sources in some areas. Furthermore, some Upper American River populations
retain adaptive genomic variation associated with a migratory life history, supporting the hypothesis that these
populations display adfluvial migratory behavior. Together, these results provide insights into the evolution of trout
populations above barrier dams. We conclude that some Upper American River O. mykiss populations represent
genetically appropriate sources from which fisheries managers could potentially develop a new broodstock for the
Nimbus Hatchery steelhead program to reestablish a native anadromous population in the Lower American River and
contribute to recovery of the threatened Central Valley steelhead distinct population segment.
The construction of dams and water diversions has severely limited access to spawning habitat for anadromous fishes. To mitigate for these impacts, hatchery programs rear and release millions of juvenile salmonids, including steelhead, the anadromous ecotype of the species Oncorhynchus mykiss. These programs sometimes use nonindigenous broodstock sources that may have negative effects on wild populations. In California, however, only one anadromous fish hatchery program currently uses nonnative broodstock: the steelhead program at Nimbus Fish Hatchery on the American River, a tributary of the Sacramento River in the California Central Valley. The goal of this study was to determine if potentially appropriate sources to replace the broodstock for the Nimbus Hatchery steelhead program exist in the Upper American River, above Nimbus and Folsom dams. We show that all Upper American River O. mykiss sampled share ancestry with other populations in the Central Valley steelhead distinct population segment, with limited introgression from out-of-basin sources in some areas. Furthermore, some Upper American River populations retain adaptive genomic variation associated with a migratory life history, supporting the hypothesis that these populations display adfluvial migratory behavior. Together, these results provide insights into the evolution of trout populations above barrier dams. We conclude that some Upper American River O. mykiss populations represent genetically appropriate sources from which fisheries managers could potentially develop a new broodstock for the Nimbus Hatchery steelhead program to reestablish a native anadromous population in the Lower American River and contribute to recovery of the threatened Central Valley steelhead distinct population segment.
Partial migration is a common phenomenon wherein populations include migratory and resident individuals. Whether an individual migrates or not has important ecological and management implications, particularly within protected populations. Within partially migratory populations of Oncorhynchus mykiss, migration is highly correlated with a specific genomic region, but it is unclear how well this region predicts migration at the individual level. Here, we relate sex and life history genotype, determined using >400 single nucleotide polymorphisms (SNPs) on the migratory-linked genomic region, to life history expression of marked juvenile O. mykiss from two tributaries to the South Fork Eel River, northern California. Most resident fish were resident genotypes (57% resident, 37% heterozygous, 6% migratory genotype) and male (78%). Most migratory fish were female (62%), but were a mixture of genotypes (30% resident, 45% heterozygous, 25% migratory genotype). Sex was more strongly correlated with life history expression than genotype, but the best-supported model included both. Resident genotypes regularly migrated, highlighting the importance of conserving the full suite of life history and genetic diversity in partially migratory populations.
Steelhead (Oncorhynchus mykiss) populations in the Puget Sound Distinct Population Segment are far below their historic abundance and are currently listed as Threatened under the Endangered Species Act. Despite the declines in steelhead abundance, resident O. mykiss populations appear to be relatively abundant and little is known about how resident O. mykiss above anadromous barriers interact with steelhead downstream. This study evaluated the dispersal and gene flow of above-barrier Oncorhynchus mykiss in the Duckabush and Hamma Hamma Rivers, Washington into below-barrier reaches that were accessible to anadromous salmonids. As well as the abundance, sex ratio and annual survival rate of O. mykiss above and below the barriers, and their influence on gene flow. We also evaluated the annual and summer growth potential of Oncorhynchus mykiss at various life stages (age 1-2, age 2-3 and age 3-4) above and below anadromous barriers in rivers to determine whether growth was limited by environmental conditions within the watershed, and if so, whether the greatest influence over growth was the availability of food or the thermal regime. Although a three year mark-recapture study did not detect any dispersal from the above the barrier populations into the below-barrier populations, microsatellite DNA analysis detected gene flow from the above-barrier populations into the below barrier populations. Gene flow was more pronounced in the Duckabush River, where 90% of the below-barrier fish were assigned to the above-barrier population. The Hamma Hamma River populations were more distinct, with 41% of the below-barrier population assigning to the above-barrier population. Abundance was estimated for O. mykiss ≥130 mm FL in the Duckabush River, with 150 trout per km in the lower below-barrier reach, 907 per km in the middle reach below the barrier and 1,165 per km above the barrier. Catch per unit effort in the Duckabush River above the barrier was 5.4 fish per angler hour compared to 2.0 in the Hamma Hamma River above the barrier, suggesting much lower relative abundance in the Hamma Hamma River. These results indicate that the gene flow from the above-barrier populations into the below-barrier population is strongly tied to abundance. Annual survival rates were low ranging from 5.7% to 21.4%, with 2013-2014 generally having better survival than 2014-2015. Survival declined with age in the middle (below-barrier) and above-barrier reaches, but improved with age in the lower reaches. Bioenergetic modeling was used with empirical data on growth, diet, and thermal experience to estimate the feeding rate, growth trajectory and the amount of food required to attain the growth observed between life stages in the, middle and lower reaches below the barrier and above the barrier in both watersheds. Model outputs indicated that consumption rates were low throughout the watersheds, ranging from 20% (age-2) to 32% (age-4) of their maximum consumption rate (%Cmax) annually. Food was insufficient to support adequate growth for age-2 and older O. mykiss in the middle and upper reaches in the Duckabush and Hamma Hamma Rivers. Food availability and quality appeared to limit growth of juvenile O. mykiss in the middle and upper reaches in the Duckabush and Hamma Hamma Rivers with little scope for growth beyond age-2, making these populations vulnerable to density-dependent effects on growth and production. Prey supply and quality were less limiting in the lower reaches below the barriers, largely due to marine subsidies from spawning salmon; however it appears that other factors might limit the populations in these reaches. These results suggest that high mortality rates in freshwater caused by delayed smoltification due to low growth rates may be significant factors limiting these steelhead populations. With steelhead facing declines across their range, this study highlights the importance of identifying factors limiting growth and survival during critical life stages in freshwater.
Oncorhynchus mykiss form partially migratory populations with anadromous fish that undergo marine migrations and residents that complete their life cycle in fresh water. Many populations’ anadromous components are threatened or endangered, prompting interest in understanding ecological and evolutionary processes underlying anadromy and residency. In this paper, we synthesize information to better understand genetic and environmental influences on O. mykiss life histories, identify critical knowledge gaps, and suggest next steps. Anadromy and residency appear to reflect interactions among genetics, individual condition, and environmental influences. First, an increasing body of literature suggests that anadromous and resident individuals differ in the expression of genes related to growth, smoltification, and metabolism. Second, the literature supports the conditional strategy theory, where individuals adopt a life history pattern based on their conditional status relative to genetic thresholds along with ultimate effects of size and age at maturation and iteroparity. However, except for a generally positive association between residency and high lipid content plus a large attainable size in fresh water, the effects of body size and growth are inconsistent. Thus, individuals can exhibit plasticity in variable environments. Finally, patterns in anadromy and residency among and within populations suggested a wide range of possible environmental influences at different life stages, from freshwater temperature to marine survival. Although we document a number of interesting correlations, direct tests of mechanisms are scarce and little data exist on the extent of residency and anadromy. Consequently, we identified as many data gaps as conclusions, leaving ample room for future research.
Little information has been gathered regarding the ontogenetic changes that contribute to differentiation between resident and migrant individuals, particularly before the onset of gross morphological and physiological changes in migratory individuals. The aim of this study was to evaluate gene expression during early development in Oncorhynchus mykiss populations with different life histories, in a tissue known to integrate environmental cues to regulate complex developmental processes and behaviors. We sampled offspring produced from migrant and resident parents, collecting whole embryos prior to the beginning of first feeding, and brain tissue at three additional time points over the first year of development. RNA sequencing for 32 individuals generated a reference transcriptome of 30,177 genes that passed count thresholds. Differential gene expression between migrant and resident offspring was observed for 1,982 genes. The greatest number of differentially expressed genes occurred at eight months of age, in the spring a full year before the obvious physiological transformation from stream-dwelling parr to seawater-adaptable smolts begins for migrant individuals. Sex and age exhibited considerable effects on differential gene expression between migrants and resident offspring. Differential gene expression was observed in genes previously associated with migration, but also in genes previously unassociated with early life history divergence. Pathway analysis revealed coordinated differential expression in genes related to phototransduction, which could modulate photoperiod responsiveness and variation in circadian rhythms. The role for early differentiation in light sensitivity and biological rhythms is particularly intriguing in understanding early brain processes involved in differentiation of migratory and resident life history types. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Oncorhynchus mykiss populations with ocean access display considerable life history plasticity. Resident (rainbow trout) and anadromous (steelhead) adults commonly produce offspring of the alternate ecotype, but environmental drivers of this life history variability are not well understood. To explore potential environmental factors influencing the distribution of resident and anadromous O. mykiss in the Yakima River basin, we used a life-cycle modeling approach to simulate flow and temperature effects on relative reproductive success of each ecotype. As a supplement to more traditional hypotheses about declining steelhead abundance, we propose a theory that more closely resembles evidence from pristine rivers. We hypothesize that flow regimes providing cool temperatures and maintaining depth and velocities necessary to sustain adult O. mykiss throughout the summer and fall seasons result in increased resident rainbow trout abundance and decreased steelhead abundance. Model results indicated a correlation between flow and temperature conditions and relative reproductive success of the two ecotypes and appear to explain in part why the upper Yakima Basin supports renowned resident rainbow trout populations, while tributaries in the lower basin continue to produce predominantly steelhead. Location within the basin also played a central role in determining the life history composition of O. mykiss. Upper basin sites, having a higher mortality cost for migration, favored a resident life history even when local environmental conditions promoted a migratory life history strategy. Channel type was also an important determinant of ecotypic dominance, with higher relative reproductive success of anadromous spawners occurring in tributary habitats. Alteration of flow conditions in mainstem habitats had little effect on the relative reproductive success of anadromous O. mykiss. Our modeling demonstrated that tributary habitats were most likely to support an anadromous ecotype, and management actions that improve tributary habitats have the greatest potential to increase abundance of steelhead in the Yakima Basin.
In this study we collected information on abundance, age structure, migration, and exploitation to characterize the population demographics and reproductive characteristics of a historically anadromous Columbia River Redband Trout Oncorhynchus mykiss gairdneri population now isolated in a southwestern Idaho reservoir and limited to resident and adfluvial life histories. We estimated there were 3,905 adfluvial individuals in Mann Creek Reservoir in October 2008 based on a mark–recapture population estimate. The adfluvial population sex ratio of 2.78 females per male captured at a weir, peak spawn timing near the peak of the hydrograph (late April), age at spawning (4–6 years), and growth patterns (slow growth in the stream followed by rapid growth in the reservoir) were all characteristic of an anadromous population. Resident fish abundance was not estimated, but the fish were characterized by relatively slow growth, earlier sexual maturity, and a reverse sex ratio (0.23 females per male) compared with the adfluvial fish. The two life histories (resident and adfluvial) and their differential use by the sexes are consistent with life history theory, which suggests female salmonids maximize fitness by increasing body size and fecundity while males attempt to maximize survival at the expense of growth. The migratory fish in this drainage that could have historically exercised an anadromous life history appear to be exercising the next-best option, an adfluvial life history, which has relatively similar costs and benefits to the anadromous form as distinct from the stream-resident form. Future studies should evaluate other similar native populations isolated in reservoir systems because these populations could play a role in recovery of endangered steelhead (anadromous Rainbow Trout) populations in the western USA.
Received December 4, 2012; accepted April 18, 2013
Steelhead trout (Oncorhynchus mykiss) historically occurred in all major watersheds along the west coast of the United States. They can be a vital part of a healthy riverine ecosystem, are highly valued for fishing, and have been greatly affected by human activities. Given these traits, and that the San Joaquin River in the Central Valley of California is under consideration for steelhead reintroduction, emphasis has recently been placed on conservation efforts to reintroduce steelhead into streams in which they were once native. There are many issues to consider when deciding how, where, and in what manner to reintroduce steelhead, including genetic considerations. One primary factor is determining the source population for reintroduction. In this paper, we consider the many important genetic aspects to consider when determining the source for steelhead reintroduction, and outline the genetic data needs when determining sources for reintroduction. We discuss the lessons learned from previous reintroductions in relation to a reintroduction scenario in the San Joaquin River, and recommend potential source populations.
Memorandum NMFS-NWFSC series to issue scientific and technical publications. Manuscripts have been peer reviewed and edited. Documents published in this series may be cited in the scientific and technical literature. The NMFS-NWFSC Technical Memorandum series of the Northwest Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest & Alaska Fisheries Science Center, which has since been split into the Northwest Fisheries Science Center and the
We investigated the interaction among genetically identified origin, behavioral tendency to emigrate, and Na ⁺ , K ⁺ ‐ATPase enzyme activity in recently diverged subpopulations of resident (above‐barrier) rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) in Scott Creek, California. Genetic assignment tests found that the frequency of resident and anadromous origin fish varied by sampling location within the watershed. Individuals immediately below barriers assigned to both above‐barrier (37%) and anadromous (63%) subpopulations, and distinct differences in size and age were observed. However, the majority of downstream migration behavior occurred in fish of anadromous ancestry, which represented 97% of the fish sampled as outmigrating smolts. Nonmigratory fish of both life history types and origins typically had low Na ⁺ , K ⁺ ‐ATPase activity levels throughout most of the year, but significantly elevated levels were observed in individuals from both groups during the spring smolt migration period. Conversely, many fish sampled in the upper watershed with anadromous genotypes were greater than typical smolt size thresholds for this population yet appeared unlikely to migrate based on low Na ⁺ , K ⁺ ‐ATPase activity. Life history pathways of O. mykiss in this population are strongly influenced but not entirely determined by origin in the resident or anadromous subpopulation, and this relationship has implications for recovery of populations impacted by dams, water diversions, and residualized hatchery fish. Further, this work demonstrates the need to consider resident rainbow trout as potentially important resources for recovery of threatened and endangered steelhead populations.
Received September 4, 2011; accepted April 12, 2012
Otolith Sr:Ca ratios near primordia (Sr:CaCore) have been used to distinguish progeny of resident and anadromous Oncorhynchus mykiss and to estimate rates of exchange between the two forms however, the influences of confounding variables on Sr:CaCore have not been quantified. We analyzed Sr:CaCore in juvenile O.mykiss produced at 13 California hatcheries that spawn primarily resident or anadromous broodstock. Mean Sr:CaCore of progeny of resident females increased with increasing Sr:Ca ratio of the stream (Sr:CaWater) in which the mother spawned (r² = 0.71). Mean Sr:CaCore of progeny of anadromous females averaged 1.0 10³ higher, also increased with Sr:CaWater, and decreased with increasing migratory difficulty (distance elevation) of the mother (r² = 0.96). Model results predict that discrimination of sympatric progeny is equally good among streams where Sr:CaWater is less than 5mmolmol¹, but limited at higher Sr:CaWater or when anadromous females return to freshwater 6 months or more before spawning (e.g., summer steelhead). The models also provide an alternative method of interpreting Sr:CaCore data that can improve discrimination between sympatric progeny. Analysis of adults from one stream and eight hatchery sites suggested that resident females made little or no contribution to populations of anadromous adults, but anadromous females contributed to populations of resident adults.
Removal of two hydroelectric dams on the Elwha River, Washington, one of the largest river restoration projects in the United States, represents a unique opportunity to assess the recovery of fish populations and aquatic ecosystems at the watershed scale. The current project implementation does not contain sufficient funding to support comprehensive monitoring of restoration effectiveness. As a result, current monitoring efforts are piecemeal and uncoordinated, creating the possibility that project managers will not be able to answer fundamental questions concerning salmonid and ecosystem response. We present the initial elements of a monitoring framework designed to assess the effectiveness of dam removal on the recovery of Elwha River salmonids, their aquatic habitats, and the food webs of which they are an integral component. The monitoring framework is linked to the Elwha Fisheries Restoration Plan, which outlines the restoration of native stocks of salmon and relies upon a process of adaptive management. The monitoring framework includes two areas of emphasis—salmonid population recovery and ecosystem response. We provide study design considerations and make recommendations for additional monitoring efforts prior to dam removal. Based on a power analysis, we determined that a minimum of 3–11 years and up to 50 years of monitoring will be required to capture potential ecosystem responses following dam removal. The development of a monitoring plan will be a significant step forward in objectively evaluating the success of Elwha River dam removal.
Innate predator recognition and fright response behaviours were compared in a laboratory study between second generation offspring from two related populations of steelhead trout Oncorhynchus mykiss from Sashin Creek, Alaska. The stream population was anadromous and co-occurred with Dolly Varden Salvelinus malma, a piscivore and salmonid predator. Sashin Lake, formerly fishless, was stocked with fish from the stream population in 1926 and that population has been isolated from heterospecific piscine predation ever since. Fish from the lake population were predicted to show diminished innate fright response to Dolly Varden scent relative to the stream population. The behaviour of 60 individual juvenile O. mykiss from each population was measured and observed in aquaria before and after exposure to chemical cues of Dolly Varden, conspecific skin extract, or a control of distilled water. The alarm substances caused significant behavioural changes in both populations in the amount of time spent motionless, time spent in the lower water column and feeding frequency. No significant differences were observed between the stream and lake populations in the change in behaviour between pre- and post-stimulus observation periods for any of the measured fright responses, indicating that the sequestered lake population has not lost the ability to detect or respond to conspecific alarm substances or Dolly Varden scent.
growth, precocious maturation and smolting were measured in 75 families of juvenile steelhead or rainbow trout Oncorhynchus mykiss, progeny of within and between line matings (crosses) of wild, anadromous steelhead and wild, resident (lake) rainbow trout originally derived from the same anadromous stock 70 years earlier. The tagged yearling progeny were combined by line in common freshwater rearing containers and graded into three categories: mature, smolt or rearing (undifferentiated) at age 2 years. Heritabilities of precocious male maturity, smolting and growth were moderate to high, and the genetic correlation between growth and smolting was low. Smolting and precocious male maturity were highly variable among families within lines and significantly different between lines. Each of the four lines produced significant numbers of smolts at age two. Smolting and maturation were negatively genetically correlated, which may explain the persistence of smolting in the lake population despite strong selection against lake smolts; balancing selection on male maturation age may help to maintain variation for smolting. The high heritability of smolting, coupled with the inability of smolts that leave the lake to return to it indicates that the genetic potential for smolting can lie dormant or be maintained through a dynamic interaction between smolting and early maturation for decades despite com plete selection against the phenotype. The results have significant implications for the preservation of threatened anadromous stocks in fresh water and the inclusion of resident fish of formerly anadromous populations, currently trapped behind long-standing barriers to migration, as one component of the same population.
For two populations of Alaskan steelhead (Oncorhynchus mykiss) of common ancestry we evaluated effects of inbreeding in second-generation descendants of wild fish by comparing progeny
of full-sibling matings to those of non-inbred controls to determine if a single event of close inbreeding has significant
effects on survival and growth in captivity or the wild. In captivity, both survival and size were highly variable between
inbred and control types within each line and among the five broods during five periods of freshwater culture. However, no
consistent patterns of inbreeding enhancement or depression between types within lines across years were evident. In contrast,
in the wild marine environment, 34 of 34 pairwise comparisons between inbred and control types in body size of returning adults
after 2 or 3years at liberty in the ocean were consistent with inbreeding depression with significant inbreeding depression
varying from 2.9% for female length to 20.0% for female weight. Survival of marked juveniles (smolts) to adults in the wild
marine environment was consistently and significantly lower in inbred types for both lines, for an average inbreeding depression
of 78.8%. The results underscore the potential problems that can arise from using protective culture technologies, including
captive broodstocks, to supplement endangered populations, and they highlight the genetic hazards that can be faced by small
wild populations. This study demonstrates that high natural mortality or selection increases the amount of inbreeding depression
detected in survival. Inbreeding effects on survival and growth in captivity can be poor indicators of survival and growth
in a wild marine environment.
Effective population size and inbreeding rates are derived in terms of the variability of broodstock replacement; the parameters are more useful for extensive aquaculture than the usual formulation. It is shown that response to mass selection may improve if variability in birth date and age is reduced by weight-specific rather than age-specific selection for growth rate. Current studies on domestication selection in Asia suggest that traditional broodstock management may be causing stocks to deteriorate.
We describe a micro-vertical raceway, a small floating container, for rearing small populations of fish. The container is a 170.6-L polyethylene drum fitted to a controlled water supply. An array of these containers was used to rear juvenile salmon simultaneously in 60 groups (200 fish each) to 6.0-g size. We compared growth rates of juvenile chinook salmon (Oncorhynchus tshawytscha) reared in these containers with those reared in large (70.8-m) vertical raceways and conclude that micro-vertical raceways do not adversely affect fish growth.
Twelve polymorphic allozyme loci were employed to assess the genetic change in a captive breeding population of the endangered killifish Aphanius baeticus in the Doñana National Park, south-western Spain. The initial founder event did not significantly reduce the allelic richness or the expected heterozygosity. No genetic bottleneck signature was detected by tests for deviation from mutation-drift equilibrium. The FST between the wild source and captive population, however, was relatively high (0·053 or 0·122 when excluding or including the locus IDHP-1* respectively), after just two to three generations in captivity. Two generations after the incorporation of 68 new wild specimens (greater than five generations after founding) decreased the genetic differences and the FST(0·041 excluding IDHP-1*). The restoration efforts appeared to be helpful and the study of 12 polymorphic loci and a sensitive parameter such as FST were useful for monitoring genetic changes in captivity. Nonetheless, future monitoring should include additional highly polymorphic loci (microsatellites) to achieve higher power to detect genetic change. Such restoration and monitoring efforts should help to avoid rapid inbreeding, adaptation to captivity, and to maintain the long-term evolutionary potential in small isolated populations.
We studied patterns of allozymic variation among wild and captive populations of endangered desert pupfish Cyprinodon m. macularius. Much of the existing variation can be attributed to different founder sources, founder and bottleneck effects, or a combination of all three. Local isolation, either natural or artificial, promotes divergence of both wild and captive populations. Divergence was countered over the natural long-term condition of drought by dispersal and population mixing during brief wetter periods. Such gene flow among populations is now precluded by anthropogenic control of hydrologic pattern. Recovery of this species to self-sufficiency will likely require re-establishment of a natural hydrology, which, for the foreseeable future, is unlikely in the lower Colorado River basin. If this charismatic desert species is to survive, resource managers must combine knowledge of ecological and genetic patterns with political realities. Until natural habitats are re-established, a captive management program that more closely mimics patterns of alternating gene flow and isolation should be implemented.
A floating vertical raceway was developed to culture salmon (Oncorhynchus spp.), and tested for 12 years. The structure is composed of a durable, impervious liner suspended from a rigid flotation collar. Notable features of the raceway include low construction and maintenance costs, adaptability to sites that are remote or without suitable area for shore-based raceways, and high water quality in the rearing environment.