EVIDENCE FOR SYMPATRIC GENETIC DIVERGENCE OF ANADROMOUS AND NONANADROMOUS MORPHS OF SOCKEYE SALMON (ONCORHYNCHUS NERKA)

Anadromous and nonanadromous morphs of the Pacific salmon Oncorhynchus nerka spawn in close physical proximity in tributaries to Takla Lake, British Columbia, yet differ in morphology, gill raker number, allozyme allele frequencies, and reproductive traits. Both morphs are semelparous typically maturing at age four, the anadromous morph (sockeye) at fork lengths of 38-65 cm and the nonanadromous morph (kokanee) at 17-22 cm. When reared together, pure and hybrid morphs also exhibited different growth rates and maturity schedules. Collectively, these large differences between the morphs confirm that sockeye and kokanee exist as reproductively isolated populations. Average gene flow (m) was estimated to be 0.1-0.8% between morphs, 1.7-3.7% among tributaries for kokanee, and 0.3-5.6% among tributaries for sockeye. We conclude that divergence has occurred in sympatry and examine potential isolating mechanisms.

MOLECULAR GENETIC EVIDENCE FOR PARALLEL LIFE-HISTORY EVOLUTION WITHIN A PACIFIC SALMON (SOCKEYE SALMON AND KOKANEE, ONCORHYNCHUS NERKA)

The Pacific salmon Oncorhynchus nerka typically occurs as a sea-run form (sockeye salmon) or may reside permanently in lakes (kokanee) thoughout its native North Pacific. We tested whether such geographically extensive ecotypic variation resulted from parallel evolutionary divergence thoughout the North Pacific or whether the two forms are monophyletic groups by examining allelic variation between sockeye salmon and kokanee at two minisatellite DNA repeat loci and in mitochondrial DNA (mtDNA) Bgl II restriction sites. Our examination of over 750 fish from 24 populations, ranging from Kamchatka to the Columbia River, identified two major genetic groups of North Pacific O. nerka: a "northwestern" group consisting of fish from Kamchatka, western Alaska, and northwestern British Columbia, and a "southern" group consisting of sockeye salmon and kokanee populations from the Fraser and Columbia River systems. Maximum-likelihood analysis accompanied by bootstrapping provided strong support for these two genetic groups of O. nerka; the populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity. The two major genetic groups resolved in our study probably stem from historical isolation and dispersal of O. nerka from two major Wisconsinan glacial refugia in the North Pacific. There were significant minisatellite DNA allele frequency differences between sockeye salmon and kokanee populations from different parts of the same watershed, between populations spawning in different tributaries of the same lake, and also between sympatric populations spawning in the same stream at the same time. MtDNA Bgl II restriction site variation was significant between sockeye salmon and kokanee spawning in different parts of the same major watershed but not between forms spawning in closer degrees of reproductive sympatry. Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific. We conclude that sockeye salmon and kokanee are para- and polyphyletic, respectively, and that the present geographic distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye (divergences between them) thoughout the North Pacific.

Recurrent evolution of life history ecotypes in sockeye salmon: implications for conservation and future evolution

We examine the evolutionary history and speculate about the evolutionary future of three basic life history ecotypes that contribute to the biocomplexity of sockeye salmon (Oncorhynchus nerka). The ‘recurrent evolution’ (RE) hypothesis claims that the sea/river ecotype is ancestral, a ‘straying’ form with poorly differentiated (meta)population structure, and that highly structured populations of lake-type sockeye and kokanee have evolved repeatedly in parallel adaptive radiations between recurrent glaciations of the Pleistocene Epoch. Basic premises of this hypothesis are consistent with new, independent evidence from recent surveys of genetic variation in mitochondrial and microsatellite DNA: (1) sockeye salmon are most closely related to pink (O. gorbuscha) and chum (O. keta) salmon with sea-type life histories; (2) the sockeye life history ecotypes exist as polyphyletic lineages within large drainages and geographic regions; (3) the sea/river ecotype exhibits less genetic differentiation among populations than the lake or kokanee ecotypes both within and among drainages; and (4) genetic diversity is typically higher in the sea/river ecotype than in the lake and kokanee ecotypes. Anthropogenic modification of estuarine habitat and intensive coastal fisheries have likely reduced and fragmented historic metapopulations of the sea/river ecotype, particularly in southern areas. In contrast, the kokanee ecotype appears to be favoured by marine fisheries and predicted changes in climate.

Comparison of health-related quality of life between patients with end-stage ankle and hip arthrosis

BACKGROUND

End-stage ankle arthrosis is one of the leading causes of chronic disability in North America. Information on this condition is limited. The amount of pain and the reduction in health-related quality of life and function have not been quantified with use of universal outcome measures. The purpose of the present study was to compare the extent of pain, loss of function, and health-related quality of life in two cohorts of patients waiting for the surgical treatment of end-stage ankle or hip arthrosis.

METHODS

One hundred and thirty patients with end-stage ankle arthrosis who were awaiting total ankle arthroplasty or ankle arthrodesis were recruited through a Canadian Orthopaedic Foot and Ankle Society multicenter study. All patients prospectively completed the Short Form-36 (SF-36) generic outcome instrument. This cohort was compared with a similar cohort of 130 patients with end-stage hip arthrosis, randomly selected from an existing prospective joint replacement database, who had completed an SF-36 questionnaire prospectively from 2000 to 2005.

RESULTS

In both groups, the scores for all SF-36 subscales were approximately two standard deviations below normal population scores. Patients with ankle arthrosis had significantly worse mental component summary scores (p < 0.05), role-physical scores (p < 0.05), and general health scores (p < 0.05). Patients with hip arthrosis reported significantly lower physical function scores (p < 0.05), although the SF-36 physical component summary score was not significantly different between the two groups. The SF-36 physical component summary, bodily pain, vitality, role-emotional, social functioning, and mental health subscale scores were equally affected in both cohorts.

CONCLUSIONS

The mental and physical disability associated with end-stage ankle arthrosis is at least as severe as that associated with end-stage hip arthrosis.

Comparison of health-related quality of life between patients with end-stage ankle and hip arthrosis

BACKGROUND

End-stage ankle arthrosis is one of the leading causes of chronic disability in North America. Information on this condition is limited. The amount of pain and the reduction in health-related quality of life and function have not been quantified with use of universal outcome measures. The purpose of the present study was to compare the extent of pain, loss of function, and health-related quality of life in two cohorts of patients waiting for the surgical treatment of end-stage ankle or hip arthrosis.

METHODS

One hundred and thirty patients with end-stage ankle arthrosis who were awaiting total ankle arthroplasty or ankle arthrodesis were recruited through a Canadian Orthopaedic Foot and Ankle Society multicenter study. All patients prospectively completed the Short Form-36 (SF-36) generic outcome instrument. This cohort was compared with a similar cohort of 130 patients with end-stage hip arthrosis, randomly selected from an existing prospective joint replacement database, who had completed an SF-36 questionnaire prospectively from 2000 to 2005.

RESULTS

In both groups, the scores for all SF-36 subscales were approximately two standard deviations below normal population scores. Patients with ankle arthrosis had significantly worse mental component summary scores (p < 0.05), role-physical scores (p < 0.05), and general health scores (p < 0.05). Patients with hip arthrosis reported significantly lower physical function scores (p < 0.05), although the SF-36 physical component summary score was not significantly different between the two groups. The SF-36 physical component summary, bodily pain, vitality, role-emotional, social functioning, and mental health subscale scores were equally affected in both cohorts.

CONCLUSIONS

The mental and physical disability associated with end-stage ankle arthrosis is at least as severe as that associated with end-stage hip arthrosis.

MDR1 C3435T polymorphisms correlate with cyclosporine levels in de novo renal recipients

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the multidrug resistance (MDR1) gene correlate with the intestinal function of P-glycoprotein (PGP). PGP serves as a hydrophobic export pump that extrudes cyclosporine (CsA) across the luminal membrane thus preventing CsA absorption. These genetic variants may predict CsA exposure levels in the early posttransplantation period.

METHODS

CsA absorption profiles were established in 75 renal transplant patients using total daily dose and body weight adjusted 4-hour area under the time-concentration curve, AUC(0-4)/mg dose/kg body weight, on posttransplant day 3. These patients were subsequently genotyped for C3435T and G2677T polymorphisms using real-time polymerase chain reaction. An analysis was conducted to assess the independent impact of C3435T and G2677T SNPs on CsA bioavailability.

RESULTS

C3435T polymorphisms were found to be an independent predictor of CsA AUC(0-4)/mg dose/kg levels on postoperative day 3. An inverse correlation was found between the number of T alleles and AUC values such that every T allele was associated with an approximate 15% decrement in AUC(0-4)/mg dose/kg (P = .034). A similar nonsignificant trend was observed for G2677T polymorphisms.

CONCLUSIONS

MDR1 SNPs are correlated with CsA exposure in the early post-transplant period. Polymorphisms, in conjunction with other criteria, may become a useful tool to optimize initial drug dosing in renal transplantation.

Concurrent natural and sexual selection in wild male sockeye salmon, Oncorhynchus nerka

Concurrent natural and sexual selection have been inferred from laboratory and comparative studies in a number of taxa, but are rarely measured in natural populations. Because the interaction of these two general categories of selection may be complex when they occur simultaneously, empirical evidence from natural populations would help us to understand this interaction and probably give us greater insight into each separate episode as well. In male sockeye salmon, sexual selection for larger body size has been indicated in both deep and shallow water habitats. However, in shallow habitats male sockeye are generally smaller and less deep-bodied than in deep habitats, a difference that has been ascribed to natural selection. We measured concurrent natural and sexual selection in two years on breeding male sockeye salmon with respect to body size, body shape, and time of arrival to the breeding grounds. Natural selection was variable in effect and sexual selection was variable in intensity in these two years. The patterns of selection also appear to be interdependent; areas where predation on spawning adults is not intense have yielded different patterns of sexual selection than those measured here. It appears that some of the body shape differences in sockeye salmon associated with different spawning habitats, which were previously attributed to selective mortality, may be a result of different patterns of sexual selection in the different habitats. Total selection resulting from the combination of both natural and sexual selection was less intense than either natural or sexual selection in most cases. Measurement of concurrent selection episodes in nature may help us to understand whether the pattern of differential sexual selection is common, and whether observed patterns of habitat-related differentiation may be due to differences in sexual selection.

Countergradient variation and secondary sexual color: phenotypic convergence promotes genetic divergence in carotenoid use between sympatric anadromous and nonanadromous morphs of sockeye salmon (Oncorhynchus nerka)

Genetically distinct anadromous (sockeye) and nonanadromous (kokanee) morphs of the Pacific salmon, Oncorhynchus nerka, develop identical, brilliant red color at maturity during sympatric breeding in freshwater streams. The marine and lacustrine environments they occupy prior to maturity, however, appear to differ in the availability of dietary carotenoid pigments necessary to produce red coloration. We tested the hypothesis that kokanee, which occupy carotenoid-poor lakes, are more efficient at using the dietary pigments than are sockeye, which occupy the more productive North Pacific Ocean. In a 2-year controlled breeding study, flesh and skin color of mature and immature crosses fed a low-carotenoid diet were quantified with both a chromameter and by chemical extraction of carotenoid pigments. Results revealed striking countergradient variation in carotenoid use, with kokanee approximately three times more efficient at sequestering the pigments to the flesh musculature than similar age sockeye. This difference translated into virtually nonoverlapping differences between pure crosses in secondary sexual color at maturity, when the pigments are mobilized and transported to the skin. Kokanee crosses turned pinkish red over most of their body, whereas sockeye turned olive green. The olive green was similar to the breeding color of residuals in the wild, the progeny of anadromous sockeye that remain in fresh water and are believed to have given rise to kokanee on numerous independent occasions. Reciprocal hybrids were similar to each other and intermediate to the pure crosses, indicating additive genetic inheritance. Mate choice trials with sockeye males in the wild showed the ancestral morph strongly preferred red over green models. These results suggest a preference for red mates maintained in nonanadromous breeding populations drove the reevolution of the red phenotype in kokanee via more efficient use of dietary carotenoid pigments. This is a novel, yet hidden, mechanism by which sexual selection promotes the genetic differentiation of these sympatric populations.

The role of chemoreception in salmon-egg predation by coastrange (Cottus aleuticus) and slimy (C. cognatus) sculpins in Iliamna Lake, Alaska

Egg predation by coastrange sculpins (Cottus aleuticus) and slimy sculpins (C. cognatus) may be a major factor affecting sockeye salmon (Oncorhynchus nerka) production in Iliamna Lake, Alaska. In this study, we examined the potential roles of visual and chemosensory cues in egg predation by sculpins. A field study tested whether sculpins were differentially attracted to minnow traps baited with eggs that were (i) visible with no odours present, (ii) visible with odours present, or (iii) not visible with odours present. Our results indicated that sculpins do not require visual cues for detecting salmon eggs. However, attraction to sockeye eggs did require chemical cues emanating from the eggs. To characterize the chemical attractants that emanate from salmon eggs, we tested whether sculpins were attracted to test odours in a two-choice maze. Test odours were prepared by soaking eggs in lake water. Sculpins preferred egg wash to lake water but demonstrated no attraction to ovarian fluid versus lake water, suggesting that the attractive substances are derived directly from egg material. These results are discussed in relation to the known sensory mechanisms involved in feeding by sculpins as well as to the ecological relationship between spawning sockeye salmon and sculpins.

Fish age, nematode (Philonema oncorhynchi) infection, and development of sexual dimorphism by the adult male sockeye salmon, Oncorhynchus nerka, in western Alaska

Of 255 mature male sockeye salmon (Oncorhynchus nerka) from two Alaskan lakes (Aleknagik and Iliamna), 254 (99.6%) were infected with the nematode Philonema oncorhynchi with a mean wet mass of 3.1 g (SD = 3.4 g) of nematodes. Fish that had spent 1 year in the lake prior to seaward migration had significantly lower parasite masses than those that had spent 2 years in the lake (2.7 vs. 4.1 g). However, there was no significant difference in parasite masses between lakes or among spawning populations within the lakes for fish of a given age or of all ages combined, even though the populations differed in age composition. The variation in relative parasite mass (mass of parasite (g)/mass of fish (kg)) was mainly explained by the significant variation in total mass of the parasites and the sea age of the fish. Thus, total parasite mass was correlated with the duration of residence in fresh water, while the relative parasite mass was correlated with fish size, and hence with the duration of residence in the sea. In spite of heavy infections (up to 28 g of nematodes) in many salmon, there were no corresponding reductions in mass/length or in the development of two sexually dimorphic features, body depth and snout length. Thus, parasite infection did not appear to affect traits under sexual selection, as hypothesized by Hamilton and Zuk.

On the developmental pathway to nonanadromy in sockeye salmon, Oncorhynchus nerka

The evolution of nonanadromous forms of salmonids has been linked to adaptive similarities between migration to the sea and migration to lakes, and to inhibition of smoltification by rapid development rates and early maturation. We examined the seasonal cycle of seawater adaptability in a landlocked (10 000 years) population of kokanee, Oncorhynchus nerka, to determine if the typical anadromous cycle persists in the absence of recent gene flow from sockeye salmon, as would be expected if components of smoltification are beneficial to a lacustrine existence. We also monitored the effects of maturation on seawater adaptability, to determine if they had an inhibitory effect on smoltification, as would be expected if a developmental conflict was responsible for the evolution of nonanadromous forms. Maturation was measured through the growth of gonadal tissue and the increase in circulating testosterone and 11-ketotestosterone. Landlocked kokanee showed the seawater adaptability cycle typical of sockeye salmon, and maturation had no inhibitory effect on seawater adaptability until near, or at, full maturity. We conclude that at least some components of smoltification must be beneficial to a life in lakes to account for the continued maintenance of the cycle. Further, rapid development and maturation on their own do not appear to account for the evolution of nonanadromous populations of O. nerka.

Endocrine changes associated with spawning behavior in male kokanee salmon (Oncorhynchus nerka) and the effects of anosmia

This study examines the relationship between social status, behavioral activity, and hormone levels through the spawning cycle in male kokanee salmon (Oncorhynchus nerka). Shortly after arrival at the spawning grounds, male kokanee undergo dramatic changes in morphological and physiological condition: there is an increase in body depth, a bright silvery appearance is replaced by an intense red coloration, and spermiation commences. Males become associated with nesting females which they defend against other males. The androgens, testosterone and 11-ketotestosterone, decline slowly over the spawning period from high levels observed in the silvery males; gonadotropin (GtH II) and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one increase as males approach final maturation. Androgen and GtH levels in males placed in pens with females over the spawning bed were higher than those in males penned without females. Among males competing for females, amounts of milt and plasma concentrations of GtH were higher in those males that were successful in gaining access to nesting females. A marked reduction in milt and plasma hormones following cauterization of the olfactory nares indicates that olfactory stimuli play a role in mediating endocrine and spermiation responses to the nesting females. Anosmic males were less vigorous and persistent in their courtship, suggesting that, either a female pheromone and/or high levels of hormone are necessary to maintain full reproductive behavior in male kokanee. The role of socially induced hormone changes in modulating reproductive behavior is discussed.

Inhibition of smolting in precocious male chinook salmon, Oncorhynchus tshawytscha

The ontogeny of precocious maturation in chinook salmon from Nicola River, British Columbia, was examined in conjunction with the effects of such maturation on smoltification and growth. A high proportion (56%) of male parr matured as yearlings. The growth patterns of precocious males and nonmaturing individuals of both sexes differed significantly. Precocious males appeared to grow rapidly relative to nonmaturing individuals in the early spring, but thereafter displayed a decreasing specific growth rate. In addition, precocious individuals gained more weight per increment of body length than nonmaturing individuals. The seawater adaptability of precocious individuals was lower than that of nonmaturing individuals at the three monthly sampling periods and decreased steadily as maturation proceeded.