Life History Forms Research Articles

Somatostatin signaling and the regulation of growth and metabolism in fish

The study of the somatostatins (SS) signaling system in fish has provided important information about the structure, function, and evolution of SSs and their receptors. The SS signaling system elicits widespread biological actions via multiple hormone variants, numerous receptor subtypes, and a variety of signal transduction pathways. SSs alter growth via both direct and indirect actions, including inhibiting growth hormone release at the pituitary, decreasing hepatic GH sensitivity, and lowering plasma IGF-I levels. Metabolism also is significantly influenced by SSs. SSs stimulate the breakdown of energy stores and influences digestion, food intake, nutrient absorption, and food conversion both directly and through the modulation of other hormonal systems. The study of fish, which display a diversity of habitat types and life history forms, reveals that the SS signaling system helps regulate energy partitioning and integrate metabolism with growth and other biological processes.

BURNING PHYLOGENIES: FIRE, MOLECULAR EVOLUTIONARY RATES, AND DIVERSIFICATION

Mediterranean-type ecosystems are among the most remarkable plant biodiversity "hot spots" on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters-which did not agree with theoretical predictions-may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems.

Mating system and individual reproductive success of sympatric anadromous and resident brook charr, Salvelinus fontinalis, under natural conditions

Salmonids are known for the occurrence in sympatry of two life-history forms, one that undergoes migration to sea before returning to freshwater to reproduce (anadromous) and one that inhabits freshwater without a migration phase (resident). Whereas one breeding population is often suggested by population genetic studies, mating patterns have rarely been directly assessed, especially when both sexes are found within each life-history form. By using highly polymorphic microsatellite loci and parentage analysis in a natural population of sympatric anadromous and resident brook charr (Salvelinus fontinalis), we found that gene flow occurred between the two forms and was mediated by resident males mating with both resident and anadromous females. Determinants of reproductive success, estimated by the number of surviving juveniles (ages 1 and 2 years), differed between the sexes. No strong evidence of the influence of size on individual reproductive success was found for males, whereas larger females (and hence most likely to be anadromous) were more successful. The higher individual reproductive success of anadromous fish compared to residents was mainly explained by this higher reproductive success of anadromous females. We suggest that resident males adopt a “sneaking” reproductive tactic as a way of increasing their reproductive success by mating with females of all sizes in all habitats. The persistence of the resident tactic among females may be linked to their advantage in accessing spatially constrained spawning areas in small tributary streams unavailable to larger females.

Variation of vertebral number in juvenile Oncorhynchus mykiss in relation to upstream distance from the ocean

Vertebral counts in fishes are set early in development by a complex interaction of genetic and environmental factors. Recently, R. M. McDowall showed that vertebral counts can differ between diadromous and non-diadromous galaxiids, and suggested similar life history-based variation might also occur in the closely related Salmonidae. We examined variation in vertebral counts of juvenile rainbow trout, Oncorhynchus mykiss, from within a single large basin where anadromous and non-anadromous forms co-occur. Juveniles were collected at 29 sites within the Klamath River basin using a nested sampling design. Mean vertebral counts varied among regions, among complexes within regions, and among sites within complexes. Regression showed that mean vertebral counts decreased with increasing distance from the ocean. This decrease could not be explained by differences in temperature within the basin during early development. However, the decrease is consistent with the expectation that non-anadromous forms have fewer vertebrae and are more common at sites distant from the ocean, and suggests that further study of the relationship between vertebral counts and life history form in O. mykiss is warranted.

Distribution and Characteristics of Native and Exotic Plants on Cut Slopes and Rest Areas along Korean Highway Lines

Vegetation surveys were performed at 45 plots along 10 highways cut slopes in South Korea. Total floral inventory, species richness and exotic plant percentage were obtained within each plot. Life history and life form of each species appeared were analyzed. Community types were classified using hierarchical cluster analysis and detrended correspondence analysis and non-metric multidimensional scaling were conducted from vegetation matrix. 292 species of vascular plants were discovered and the number of natives and exotics were 226 and 66, respectively. There were no significant differences of species richness and exotic plant percentage between cut slopes and rest areas. Hierarchical cluster analysis indicated five clear vegetation associations in cut slopes and rest areas. Detrended correspondence analysis indicated that species composition of total and native plants were similar along the highway cut slopes whereas exotic plants were distributed differentially along the highway cut slopes. in non-metric multidimensional scaling, the studied sites were more separated from each other on the basis of their species composition than the results of detrended correspondence analysis with respect to total, native and exotic plants. The both ordination represented that exotic plants have not been made uniform yet on cut slopes and rest areas by highway corridor in spite of diverse chronosequences after highway construction termination (1 to 22 years). This study showed that the distribution of species composition in exotic plants was different and localized on cut slopes and rest areas of highway in this representative peninsula area of North East Asia and the invasion of exotic plants can retard the process of plant species homogenization.

Evolutionary history of lamprey paired speciesLampetra fluviatilis(L.) andLampetra planeri(Bloch) as inferred from mitochondrial DNA variation

A remarkable trend in the evolution of lampreys is the occurrence in most genera of 'paired species', in which the parasitic anadromous lampreys are believed to have given rise to nonparasitic freshwater resident populations. The present work examines the phylogeography of the European paired species Lampetra fluviatilis and Lampetra planeri, in an attempt to elucidate species pair evolutionary history. We studied sequence variation in cytochrome b and ATPase 6, 8 mitochondrial genes in 63 individuals from 21 localities of the paired species throughout their distribution range. Results from the phylogenetic and nested clade analyses were largely consistent, suggesting the existence of three major evolutionary lineages: lineage I and possibly lineage II are widespread throughout Europe, while the most ancestral lineage III is apparently restricted to the Iberian Peninsula. The high genetic diversity observed in the Iberian Peninsula is probably the result of refugial persistence and subsequent accumulation of variation over several ice ages, whereas the low levels of genetic diversity observed in central and northern Europe should reflect a rapid postglacial colonization. Results suggest that L. planeri originated within at least two distinct evolutionary lineages, rejecting the single origin hypothesis. The observed lack of taxa monophyly within lineage I may be the result of ongoing gene flow if the two taxa are alternate life-history forms of a single species. However, structure within lineage I is also consistent with the hypothesis of divergence of taxa after postglacial dispersion (around 2000 generations ago) with incomplete lineage sorting. Further testing of the alternative hypotheses is warranted.

Effective population size of steelhead trout: influence of variance in reproductive success, hatchery programs, and genetic compensation between life‐history forms

The effective population size is influenced by many biological factors in natural populations. To evaluate their relative importance, we estimated the effective number of breeders per year (Nb) and effective population size per generation (Ne) in anadromous steelhead trout (Oncorhynchus mykiss) in the Hood River, Oregon (USA). Using demographic data and genetic parentage analysis on an almost complete sample of all adults that returned to the river over 15 years (>15,000 individuals), we estimated Nb for 13 run years and Ne for three entire generations. The results are as follows: (i) the ratio of Ne to the estimated census population size (N) was 0.17-0.40, with large variance in reproductive success among individuals being the primary cause of the reduction in Ne/N; (ii) fish from a traditional hatchery program (Htrad: nonlocal, multiple generations in a hatchery) had negative effects on Nb, not only by reducing mean reproductive success but also by increasing variance in reproductive success among breeding parents, whereas no sign of such effects was found in fish from supplementation hatchery programs (Hsupp: local, single generation in a hatchery); and (iii) Nb was relatively stable among run years, despite the widely fluctuating annual run sizes of anadromous adults. We found high levels of reproductive contribution of nonanadromous parents to anadromous offspring when anadromous run size is small, suggesting a genetic compensation between life-history forms (anadromous and nonanadromous). This is the first study showing that reproductive interaction between different life-history forms can buffer the genetic impact of fluctuating census size on Ne.

Distinct temporal patterns of Transaldolase 1 gene expression in future migratory and sedentary brown trout ( Salmo trutta)

The occurrence of sedentary and migratory life-history forms is common in several salmonid fish species. A cDNA microarray study, investigating differences between these life-history forms at the level of the transcriptome, identified the transaldolase 1 gene (Taldo1) as being differently expressed in liver between sedentary and migratory brown trout populations just before the onset of migration. The aim of the study presented here was to gain further knowledge about the potential role of this gene during preparatory changes associated with the migratory life-history and the time of onset of this expression difference by investigating its expression levels in several juvenile age stages of sedentary and freshwater-migratory brown trout. A quantitative real-time PCR assay was established for the Taldo1 gene to measure its expression levels in liver samples of brown trout and Atlantic salmon. Taldo1 transcript levels were significantly lower in migratory brown trout and Atlantic salmon at the onset of migration compared to sedentary trout of the same age, confirming the results obtained by cDNA microarray technology. Comparison of Taldo1 expression patterns with changes in body condition factor led to the hypothesis that the observed lower levels of Taldo1 expression in migratory individuals are associated with the depletion of lipid stores during premigratory adaptations, potentially related to the smoltification process observed in anadromous salmonids, and a joint reduction in de novo lipid synthesis. Analysis of three juvenile stages of morphologically undifferentiated future migratory and sedentary brown trout revealed a significantly elevated expression level of the Taldo1 gene in future migratory trout compared to sedentary individuals three and a half month before the onset of migration, indicating an early signal potentially useful for predicting the future life-history of an individual. These results suggest that physiological differences between life-history forms might be measurable before morphological differentiation and that further study of such younger age stages could reveal new insights into the regulation and initiation of life-history related physiological, morphological and behavioural changes.

ARE LIFE HISTORY CHARACTERISTICS GOOD PREDICTORS OF GENETIC DIVERSITY AND STRUCTURE? A CASE STUDY OF THE INTERTIDAL ALGA FUCUS SPIRALIS (HETEROKONTOPHYTA; PHAEOPHYCEAE)1

Characteristics of an organism's life history are often good predictors of genetic diversity and genetic structure. We tested hypotheses about genetic structure and diversity in an intertidal alga based on life history and life form. Fucus spiralis L. is a perennial monoecious alga that is abundant on the shores of Maine. Reproduction in fucoids is highly sensitive to water motion, resulting in fertilization success close to 100%. Given these life history characteristics, we predicted genetic structure among populations to be high and genetic diversity within populations to be low. We used five microsatellite loci to analyze genetic structure and diversity in F. spiralis from four sites on each of two coastal points, Maine, USA. Observed heterozygosities were relatively low (0.23 to 0.56), and FIS estimates were usually significantly large, ranging from 0.021 to 0.476. This suggests that selfing and/or inbreeding may occur. Contrary to predictions, genetic differentiation between the two coastal points was insignificant. Moreover, few sites were genetically different from one another. Pairwise tests revealed complex patterns among sites. Genetic differentiation was not correlated with distance (P>0.05). Life history characteristics are good predictors of genetic diversity but not of population genetic structure in F. spiralis. We suggest that long distance dispersal of F. spiralis via drifting algal rafts increases gene flow. In addition, low levels of genetic structure may arise due to episodic recruitment or recent recolonization events. We discuss the implications of our results in terms of using life history characteristics as predictors of genetic diversity and structure in algae.

Extent of Anadromy in Bull Trout and Implications for Conservation of a Threatened Species

AbstractThe use of radiotelemetry revealed that adult bull trout Salvelinus confluentus moved between freshwater and the Pacific Ocean and between watersheds along coastal Washington. Forty‐seven of 82 radio‐tagged bull trout implanted in the Hoh River and Kalaloch Creek basins were anadromous, and 23 fish were relocated in five different estuaries up to 47 km south of their tagging locations. Anadromous bull trout typically entered the Hoh River from May to July, ascended as far as 78 km upstream to spawning areas by September, and returned to the ocean to overwinter. This is the first study to verify that anadromy is a primary life history form in coastal bull trout. The presence of anadromy and the irregular periods of freshwater, estuarine, and marine residence observed in this study are consistent with observations reported for other Salvelinus species. These results also demonstrate that anadromous bull trout inhabit a diverse range of estuarine, freshwater, and marine habitats. Their affinity to estuaries and their observed temporal movements suggest that bull trout optimize winter refugia and forage opportunities and are susceptible to incidental mortality in gill‐net and recreational fisheries directed at other Pacific salmonids. An understanding of the extent of anadromy, sources of mortality, and diversity of habitats occupied by bull trout is informative in the establishment of appropriate conservation and recovery strategies for this species.

Population Structure of Columbia River Basin Chinook Salmon and Steelhead Trout

The population structure of chinook salmon and steelhead trout is presented as an assimilation of the life history forms that have evolved in synchrony with diverse and complex environments over their Pacific range. As poikilotherms, temperature is described as the overwhelming environmental influence that determines what life history options occur. The different populations represent ecological types referred to as spring-, summer-, fall, and winter-run segments, as well as stream- and ocean-type, or stream- and ocean-maturing life history forms. However, they are more correctly described as a continuum of forms that fall along a temporal cline related to incubation and rearing temperatures that determine spawn timing and juvenile residence patterns. Population structure of chinook salmon and steelhead in the Columbia Basin, therefore, is the reflection of the genetic composition of the founding source or sources within the respective region, shaped by the environment, principally temperature, that defines life history evolutionary strategy to maximize fitness under the conditions delineated. The key in developing an effective recovery program for chinook salmon and steelhead is to recognize that measures taken must address the genetic and biological requirements of the population unit within the environmental template identified.

Simple traits do not predict grazing response in Australian dry shrublands and woodlands

Summary Plant species composition and species response to grazing are fundamental to the management of grazing lands. Reliable prediction of grazing responses from species’ traits would be a major step forward in generalizing knowledge and management beyond the locality. Recently results have been presented showing that plant species’ responses to grazing in subhumid grasslands in Argentina and Israel could be predicted from simple traits: height, leaf size, life history and specific leaf area (SLA). This study assessed whether those relationships between traits and grazing responses hold for Australian semi‐arid and arid shrublands and woodlands. Eleven lists of grazing responses from five published grazing studies were matched with a plant trait data set. Trait distributions were compared between response groups pooled across studies. Relationships between traits and grazing response were also assessed, both within and across studies, using meta‐analysis. Overall there was little evidence for predictability of grazing responses with simple traits in the semi‐arid and arid shrublands and woodlands. There were relationships between grazing response and life history and growth form, and some weak evidence for grazing increasers having high SLA. Synthesis and applications. It was concluded that prediction of grazing responses with simple traits is less clear in semi‐arid and arid rangelands, which are characterized by openness at ground level and high diversity of growth forms, compared with subhumid grasslands that have structurally simple, continuous swards. The finding that species’ traits may have differing predictive capacity for grazing responses in different situations means that we need more empirical studies in different situations. The most important contrasts between situations for investigation are likely to be on axes of rainfall/productivity and evolutionary history of grazing.

Reconnecting a Fragmented River: Movements of Westslope Cutthroat Trout and Bull Trout after Transport Upstream of Milltown Dam, Montana

Abstract Milltown Dam annually impedes the migration of 11 fish species, and data suggest that fish that migrate to the dam do not spawn once their migration is impeded. Densities of westslope cutthroat trout Oncorhynchus clarki lewisi and bull trout Salvelinus confluentus are low near Milltown Dam, but their annual presence at the dam suggests the potential to reestablish fluvial life history forms and enhance local or upriver populations. Operating a fish trap at Milltown Dam in 2000 and 2001, I captured westslope cutthroat trout and bull trout, implanted 42 with radio transmitters, and transported them upstream of Milltown Dam. I monitored the implanted fish to determine posttransport movements and spawning. Most of the fish captured continued upstream to spawn, and many migrations exceeded 100 km after transport. Several fish encountered pre- or postspawning problems, including entrainment in irrigation ditches, predation by nonnative northern pike Esox lucius, angler harvest, and fallback over Millto...

Temporal variation in synchrony among chinook salmon (Oncorhynchus tshawytscha) redd counts from a wilderness area in central Idaho

Metapopulation dynamics have emerged as a key consideration in conservation planning for salmonid fishes. Implicit to many models of spatially structured populations is a degree of synchrony, or correlation, among populations. We used a spatially and temporally extensive database of chinook salmon (Oncorhynchus tshawytscha) redd counts from a wilderness area in central Idaho to examine patterns in synchrony as these fish underwent a sixfold decrease in abundance. Our results suggested that populations became strongly synchronous as abundances decreased and that the range, or diversity of correlations, exhibited among populations also decreased. These changes indicate that the likelihood of simultaneous extirpations has increased, which could have long-term detrimental consequences for metapopulation persistence. Implications for management are that the resilience of many metapopulations to large-scale disturbance and anthropogenic suppression may not depend solely on attempts to maintain large and productive component populations, but also on efforts to desynchronize populations that have become strongly correlated. Such efforts could entail promoting the existence of a broad distribution and diversity of habitats that support a wide array of life-history forms and ensuring that some habitats are sufficiently spatially disjunct so that risks from catastrophic stochastic events are minimized.

Reproductive Behaviors Related to Life History Forms in Male Masu Salmon, Oncorhynchus masou Breboort, in Lake Toya, Japan

ABSTRACT We observed the spawning behaviors of male masu salmon (Oncorhynchus masou) to examine whether the life history forms of males were related to the reproductive tactics. Standard males (mean ± SD = 43.0 ± 7.1 cm), which migrate into the lake and return to the natal creek for spawning, fought with other males to become the dominant male in the reproductive group. The male that became dominant in the reproductive group intensively attacked males of a similar sue and defended an area around a spawning female against other males. Puerile males (22.3 ± 6.3 cm), which grow in the lake and mature while retaining parr marks, attempted to gain a higher hierarchical position in the subordinate group, while being attacked frequently by the dominant male. Precocious males (mature male parr, 11.5 ± 3.3 cm), which mature without migrating to the lake, had a tendency to occupy positions near the females and attempted to use sneaking mating tactics. These males were not attacked by the dominant male. This indicates that the different life history forms of males are associated with different reproductive tactics.

Comment: First Documented Case of Anadromy in a Population of Introduced Rainbow Trout in Patagonia, Argentina

Pascual et al. (2001) contributes important information on the basis for anadromous and resident life history forms of rainbow trout Oncorhynchus mykiss introduced into a new environment. I agree w...

Content/Construct Approaches in Life History Form Development for Selection

Life history, or biodata, inventories are attractive alternatives to cognitive ability tests for selection, but they have been frequently criticized for their low construct validity and the a‐theoretical nature of their items. Little guidance in the literature is provided for developing good construct‐valid biodata measures. Using a content/construct‐oriented approach, a biodata form was developed and validated. The methods for developing and validating the form are thoroughly described so as to provide guidelines for future researchers, and evidence for the meaningfulness of the scales is presented.

Genetic contribution of three introduced life history forms of sockeye salmon to colonization of Frazer Lake, Alaska

Colonization of Frazer Lake (Kodiak Island, Alaska) by sockeye salmon (Oncorhynchus nerka) represents a rare, successful introduction of this species into a new environment. Eggs, fry, and adults were introduced repeatedly into Frazer Lake from 1951 to 1971. Donors originated from three source populations, each with different life histories: late-run lake shoreline spawners (Karluk Lake), early-run inlet tributary spawners (Red Lake), and late-run lake outlet spawners (Ruth Lake). We used six nuclear DNA (nDNA) microsatellite loci and mitochondrial DNA (mtDNA) to determine which donor population(s) had colonized the principal spawning habitats of Frazer Lake: three shoreline areas and four inlet tributaries. Based on nDNA comparisons, two shoreline-spawning populations were most similar to the shoreline donor, and the four tributary-spawning populations were most similar to the tributary donor. However, five of the seven Frazer Lake populations appeared to be influenced genetically by more than one donor. Genetic distances based on mtDNA were independent of life histories with high (relative to nDNA) interpopulation variation, suggesting significant female founder effects and poststocking drift. Our data suggest that life history adaptations of donor populations were critically important for successful colonization of Frazer Lake, thus underscoring the need to consider life history traits in other introduction and recovery programs.

Genetic contribution of three introduced life history forms of sockeye salmon to colonization of Frazer Lake, Alaska

Colonization of Frazer Lake (Kodiak Island, Alaska) by sockeye salmon (Oncorhynchus nerka) represents a rare, successful introduction of this species into a new environment. Eggs, fry, and adults were introduced repeatedly into Frazer Lake from 1951 to 1971. Donors originated from three source populations, each with different life histories: late-run lake shoreline spawners (Karluk Lake), early-run inlet tributary spawners (Red Lake), and late-run lake outlet spawners (Ruth Lake). We used six nuclear DNA (nDNA) microsatellite loci and mitochondrial DNA (mtDNA) to determine which donor population(s) had colonized the principal spawning habitats of Frazer Lake: three shoreline areas and four inlet tributaries. Based on nDNA comparisons, two shoreline-spawning populations were most similar to the shoreline donor, and the four tributary-spawning populations were most similar to the tributary donor. However, five of the seven Frazer Lake populations appeared to be influenced genetically by more than one donor....

Genetic relationships among populations of wild resident, and wild and hatchery anadromous brook charr

To determine the genetic relationship of anadromous and resident life-history types within and among drainages, and compare several hatchery strains to their progenitor populations, brook charr Salvelinus fontinalis were examined for allozyme and mitochondrial DNA variation. Greater genetic similarity of sympatric anadromous and resident charr was found compared to similar life-history forms allopatrically, suggesting the two life-history types are not reproductively isolated. Low divergence among the mtDNA haplotypes suggests that the two life-history types are members of the same evolutionary lineage. Population differentiation from mtDNA data exceeded that from estimates based on allozymes. Genetic deviations from expectations suggest that the hatchery strains were derived from few individuals. 1997 The Fisheries Society of the British Isles