Life History Implications Research Articles

The Distribution and Biogenic Origins of Zinc in the Mineralised Tooth Tissues of Modern and Fossil Hominoids: Implications for Life History, Diet and Taphonomy.

Zinc is incorporated into enamel, dentine and cementum during tooth growth. This work aimed to distinguish between the processes underlying Zn incorporation and Zn distribution. These include different mineralisation processes, the physiological events around birth, Zn ingestion with diet, exposure to the oral environment during life and diagenetic changes to fossil teeth post-mortem. Synchrotron X-ray Fluorescence (SXRF) was used to map zinc distribution across longitudinal polished ground sections of both deciduous and permanent modern human, great ape and fossil hominoid teeth. Higher resolution fluorescence intensity maps were used to image Zn in surface enamel, secondary dentine and cementum, and at the neonatal line (NNL) and enamel-dentine-junction (EDJ) in deciduous teeth. Secondary dentine was consistently Zn-rich, but the highest concentrations of Zn (range 197-1743 ppm) were found in cuspal, mid-lateral and cervical surface enamel and were similar in unerupted teeth never exposed to the oral environment. Zinc was identified at the NNL and EDJ in both modern and fossil deciduous teeth. In fossil specimens, diagenetic changes were identified in various trace element distributions but only demineralisation appeared to markedly alter Zn distribution. Zinc appears to be tenacious and stable in fossil tooth tissues, especially in enamel, over millions of years.

Effects of data sources and biological criteria on length-at-maturity estimates and spawning periodicity of the commercially important Hawaiian snapper, Etelis coruscans

Reproductive characteristics of a fish stock provide important tools for assessing population health. Change in length-at-maturity (L50) is a potential indicator of exploited fish populations but when criteria for determining maturity classifications are inconsistent, it is difficult to accurately assess change over time and space. Etelis coruscans is a commercially important eteline snapper found throughout the Indo-Pacific, but its region-specific reproductive information in the main Hawaiian Islands (MHI) is sparse. The present study describes length-specific (fork length: FL) female reproductive characteristics of this deep water snapper in the context of a data-limited fishery. We explored the use of six maturity classification criteria based on a functionally mature (containing vitellogenic oocytes and capable of spawning within the season of collection) or physiologically mature (gonadotropin-dependent maturation initiation) designation combined with seasonality and inclusion of additional reproductive phases. Of these classifications, the largest and therefore most conservative estimate was for functional maturity during the spawning period, September-December (L50F = 65.8 cm). Progressively smaller L50 estimates occurred as we incorporated additional reproductive phases and seasonality, the smallest being for physiological maturity during the entire year (L50PY = 50.0 cm). Both functional and physiological maturity criteria are valid for estimating L50 but can yield drastically different parameter estimates based on the definition of mature or immature reproductive phases. Fish that are relatively slow growing, late to mature, and whose fisheries encompass a wide size range, such as E. coruscans, may be more subject to unreliability in the development of their reproductive indicators (length-at-maturity and spawning period) when inconsistent maturity classification criteria are executed over time. We discuss the reproductive characteristics of E. coruscans in the MHI, the use of alternative maturity classification criteria in L50 estimation, the impact on resultant parameters estimates, and the life history implications for the future fishery.

Parental methyl-enhanced diet and in ovo corticosterone affect first generation Japanese quail (Coturnix japonica) development, behaviour and stress response

The role of maternal investment in avian offspring has considerable life history implications on production traits and therefore potential for the poultry industry. A first generation (G1) of Japanese quail (Coturnix japonica) were bred from a 2 × 2 factorial design. Parents were fed either a control or methyl-enhanced (HiBET) diet, and their eggs were treated with a vehicle or corticosterone injection during day 5 of incubation. A subset of G1 birds were subjected to an open field trial (OFT) and capture-restraint stress protocol. Significant effects of HiBET diet were found on parental egg and liver weights, G1 hatch, liver and female reproductive tract weights, egg productivity, latency to leave the OFT central zone, male baseline 11-dehydrocorticosterone, and female androstenedione plasma concentrations. In ovo treatment significantly affected latency to return to the OFT, male baseline testosterone and androstenedione, and change in androstenedione plasma concentration. Diet by treatment interactions were significant for G1 liver weight and male baseline plasma concentrations of corticosterone. These novel findings suggest significant positive effects on reproduction, growth, precociousness, and hypothalamic–pituitary–adrenal axis function from enhanced methyl diets, and are important in understanding how in ovo stressors (representing maternal stress), affect the first offspring generation.

Hidden Markov models identify major movement modes in accelerometer and magnetometer data from four albatross species

BackgroundInertial measurement units (IMUs) with high-resolution sensors such as accelerometers are now used extensively to study fine-scale behavior in a wide range of marine and terrestrial animals. Robust and practical methods are required for the computationally-demanding analysis of the resulting large datasets, particularly for automating classification routines that construct behavioral time series and time-activity budgets. Magnetometers are used increasingly to study behavior, but it is not clear how these sensors contribute to the accuracy of behavioral classification methods. Development of effective classification methodology is key to understanding energetic and life-history implications of foraging and other behaviors.MethodsWe deployed accelerometers and magnetometers on four species of free-ranging albatrosses and evaluated the ability of unsupervised hidden Markov models (HMMs) to identify three major modalities in their behavior: ‘flapping flight’, ‘soaring flight’, and ‘on-water’. The relative contribution of each sensor to classification accuracy was measured by comparing HMM-inferred states with expert classifications identified from stereotypic patterns observed in sensor data.ResultsHMMs provided a flexible and easily interpretable means of classifying behavior from sensor data. Model accuracy was high overall (92%), but varied across behavioral states (87.6, 93.1 and 91.7% for ‘flapping flight’, ‘soaring flight’ and ‘on-water’, respectively). Models built on accelerometer data alone were as accurate as those that also included magnetometer data; however, the latter were useful for investigating slow and periodic behaviors such as dynamic soaring at a fine scale.ConclusionsThe use of IMUs in behavioral studies produces large data sets, necessitating the development of computationally-efficient methods to automate behavioral classification in order to synthesize and interpret underlying patterns. HMMs provide an accessible and robust framework for analyzing complex IMU datasets and comparing behavioral variation among taxa across habitats, time and space.

Life-history implications of migratory Lesser Sandhill Cranes replacing adjacent blocks of primaries synchronously

Abstract Using the patterns of fault bars in their primaries, we studied the mode of primary replacement in non-molting Lesser Sandhill Cranes (Antigone c. canadensis) salvaged from hunters in southwestern Saskatchewan. About 80% of their primaries are used for 2 yr and 20% for 3 yr. Primaries are replaced during the breeding season and are lost in synchronous blocks representing about half the primaries, suggesting that most adults probably can fly weakly during flight feather replacement. Cranes are large, aggressive birds, and this interesting, and undescribed mode of flight feather replacement seems adapted to the ability of adult cranes to defend their precocial chicks from predators. Strikingly, juvenile Sandhill Cranes showed no fault marks in their primaries, suggesting that their parents’ ability to protect them shields them from the fright of predator attacks, which, in most birds, causes fault bars to be more prevalent and strongly expressed in juveniles than adults. Adults show interesting variation in the number of primaries replaced annually, which seems likely related to whether or not they are caring for chicks. Further, single primaries may or may not be replaced preferentially, suggesting sensitivity to feather function. Evaluating these observations must await field studies of molting adults.

Quantification of the full lifecycle bioenergetics of a large mammal in the high Arctic

Energy is a critical driver of animal life-history traits and Darwinian fitness, with direct implications for population dynamics. In the Arctic, extreme seasonal climatic conditions dictate energy flow and physiology of resident species. Consequently, vital rates of animal populations in the Arctic are tightly linked to climatic factors influencing food availability and quality. The muskox (Ovibos moschatus) is a capital breeder and the largest herbivore in the Arctic. Seasonal changes in energy intake influence body reserve dynamics of this species, impacting inter-annual and spatial variations in survival and recruitment. Yet, little is known about the full lifecycle bioenergetics of this and other Arctic species, and the impact of extreme seasonal conditions on life-history traits have never been quantified. By integrating energetic and physiological processes throughout the full lifecycle of individuals, we developed an individual-based model using dynamic energy budget theory (DEB-IBM) of the muskox that covers all aspects of mammalian life-history. We parameterized a baseline muskox model using data from a well-studied captive research herd, and then explored its application to a wild population in the high Arctic to assess the life-history implications of seasonal food availability. Our baseline DEB-IBM, which for the first time explicitly characterized fetal development using DEB theory, successfully predicted life-history traits as well as patterns of growth, body condition, feeding, metabolic rates, and reproduction of captive muskoxen. Adaptation of the model to the wild population required re-parameterization of only three variables that controlled seasonal food availability and upregulated assimilation. The wild model successfully captured inter-annual costs of reproduction, such that lactating females were in poorer body condition than females without calves. Arctic seasonal food limitations reduced fecundity in wild muskoxen by 42% compared to annual reproduction in well-fed captive individuals. We have developed a mechanistic energy-based framework to study life-history processes of muskoxen but the model is broadly applicable also for other mammals in the Arctic. Our study quantifies and highlights the strong interplay between energetics and individual fitness components, opening the door to future applications of the model in assessments of population dynamics and climate change impacts.

Seasonal differences in body mass and circulating metabolites in a wing‐dimorphic pygmy grasshopper: implications for life history?

1. Functional wing polymorphism in insects is an intriguing topic, especially with respect to the adaptive advantage of each wing morph. The common pygmy grasshopper in Germany, Tetrix subulata, displays wing polymorphism skewed towards macropterous (LW) individuals capable of flight. Furthermore, T. subulata is known to undergo adult diapause in winter and reproduce in spring.2. Morphometric and biochemical parameters were examined in field‐collected grasshoppers during autumn and spring to obtain a ‘snapshot’ from the same/one cohort of grasshoppers in the wild.3. Flight muscles are largely reduced in brachypterous (SW) specimens, whereas they are well developed in LW individuals. Body mass measurements indicated gain in female T. subulata in spring, especially in LW morphs, which could be attributed to increased reproductive activity (egg production).4. Metabolic fuel in haemolymph is differentially distributed in autumn: the concentration of lipids is highest in males, while carbohydrates are most abundant in LW specimens. The metabolic data imply that dispersal in T. subulata is predominantly in autumn, by flight in the case of LW specimens and by hopping/walking in males.5. The season seems to be an important factor for the reproductive versus dispersal trade‐off in this species. Moreover, this study shows that morphological differences in T. subulata individuals are reflected in physiological differences that may ultimately affect behaviour and ecology.

Polyploid lineages in the genus Porphyra

Whole genome duplication is now accepted as an important evolutionary force, but the genetic factors and the life history implications affecting the existence and abundance of polyploid lineages within species are still poorly known. Polyploidy has been mainly studied in plant model species in which the sporophyte is the dominant phase in their life history. In this study, we address such questions in a novel system (Porphyra, red algae) where the gametophyte is the dominant phase in the life history. Three Porphyra species (P. dioica, P. umbilicalis, and P. linearis) were used in comparisons of ploidy levels, genome sizes and genetic differentiation using flow cytometry and 11 microsatellite markers among putative polyploid lineages. Multiple ploidy levels and genome sizes were found in Porphyra species, representing different cell lines and comprising several cytotype combinations among the same and different individuals. In P. linearis, genetic differentiation was found among three polyploid lineages: triploid, tetraploid and mixoploids, representing different evolutionary units. We conclude that the gametophytic phase (n) in Porphyra species is not haploid, contradicting previous theories. New hypotheses for the life histories of Porphyra species are discussed.

Longevity and life history of cave bears – a review and novel data from tooth cementum and relative emergence of permanent dentition

Longevity and other life history variables are key to understanding evolutionary processes and the biology of extinct animals. For the past 20 years, the lifespan of cave bears received an increased interest. Studies focusing on incremental lines of tooth cementum resulted in detailed mortality patterns from different localities. In this review, we summarise literature on age estimation as well as mortality of different European cave bear localities and present novel data on longevity from 94 teeth originating from 20 European localities. Additionally, the relative tooth emergence pattern of the permanent dentition is investigated under the Schultz’s rule framework of possible life history implications. For this, the known sequences of extant bear species are compared with the one of cave bears. Our results suggest that the typical duration of the life of cave bears was 19 years but data from literature show that in rare cases ages of up to 30–32 years were achieved. Additionally, we present the oldest known age for the Middle Pleistocene cave bear Ursus deningeri, 29 years. The tooth eruption pattern of cave bears exhibits a heterochronic shift that implies, under the assumption of Schulz’ rule, a slightly faster life history than closely related species.

Implications of life history for control and eradication

Implications of life history for control and eradication

Diversity and Ecology of Pulmonary Metastrongyloidosis in Coyotes (Canis latrans) of Nova Scotia, Canada

Coyotes (Canis latrans) are widely distributed in North America and were first recorded in Nova Scotia, Canada, in 1977. Although coyotes are host to a number of parasitic helminths, the parasite fauna of coyotes from Nova Scotia has not been previously investigated. The objectives of this study were to determine geographical range, prevalence, mean intensity, and abundance of metastrongyloid helminth parasites of the pulmonary system (Crenosoma vulpis, Oslerus osleri) in coyotes from Nova Scotia and to investigate whether prevalence, mean intensity, and abundance were consistent among different age classes of this mammal. In addition, hearts and pulmonary arteries were examined for the presence of Angiostrongylus vasorum (French heartworm) and Dirofilaria immitis (heartworm) to determine whether these heartworms had spread to Nova Scotia. A total of 235 coyotes were collected from trappers in the 2010–2011 season. Heart and lungs were removed from coyotes and examined for parasites by gross examination and lungflush. Canine teeth from lower jaws were removed to assess the age class of each coyote. Crenosoma vulpis and O. osleri were found in 31% and 37% of coyotes, respectively. There was a mean intensity of 8.8 adult C. vulpis and 9.5 nodules of O. osleri in infected coyotes across all age classes, with a tendency toward higher worm burdens in juvenile animals; significant differences were observed only for C. vulpis. There was a mean abundance of 2.7 adult C. vulpis and 3.5 nodules of O. osleri in coyotes sampled across all age classes, with significantly higher numbers of each species of worm in juveniles. Dirofilaria immitis and A. vasorum were not detected. The life history implications of these findings are discussed in relation to the possibility of parasite transmission to domestic dogs.

Life-history implications of the allometric scaling of growth

Several phenomenological descriptions, such as the von Bertalanffy growth model, have been widely used to describe size-at-age and individual growth across a diverse range of organisms. However, for modelling life histories, as opposed to just growth, biologically and mechanistically meaningful growth models, based on allocation decisions, have become increasingly important. This is because fitness is determined by survival and reproduction, which are not addressed directly in phenomenological growth models. To elucidate these considerations, we take as a starting point the biphasic growth model by Quince et al. (2008a, J. Theor. Biol. 254:197) which has the advantage that the underlying allometric scaling of net energy intake can be freely chosen. First, we reformulate this model such that individual size is given in meaningful units of length and weight, facilitating the model׳s interpretation and application. Second, we show that even though different allometric scaling relationships can produce practically identical growth trajectories, the accompanying reproductive investments are highly dependent on the chosen allometric exponent. Third, we demonstrate how this dependence has dramatic consequences for evolutionary predictions, in particular with regard to the age and size at maturation. These findings have considerable practical relevance, because empirically observed allometric exponents are often uncertain and systematically differ from those assumed in current standard growth models.

Primate energy expenditure and life history

Humans and other primates are distinct among placental mammals in having exceptionally slow rates of growth, reproduction, and aging. Primates' slow life history schedules are generally thought to reflect an evolved strategy of allocating energy away from growth and reproduction and toward somatic investment, particularly to the development and maintenance of large brains. Here we examine an alternative explanation: that primates' slow life histories reflect low total energy expenditure (TEE) (kilocalories per day) relative to other placental mammals. We compared doubly labeled water measurements of TEE among 17 primate species with similar measures for other placental mammals. We found that primates use remarkably little energy each day, expending on average only 50% of the energy expected for a placental mammal of similar mass. Such large differences in TEE are not easily explained by differences in physical activity, and instead appear to reflect systemic metabolic adaptation for low energy expenditures in primates. Indeed, comparisons of wild and captive primate populations indicate similar levels of energy expenditure. Broad interspecific comparisons of growth, reproduction, and maximum life span indicate that primates' slow metabolic rates contribute to their characteristically slow life histories.

Differential thermal bleaching susceptibilities amongst coral taxa: re-posing the role of the host

It is well established that different coral species have different susceptibilities to thermal stress, yet it is less clear which biological or physical mechanisms allow some corals to resist thermal stress, whereas other corals bleach and die. Although the type of symbiont is clearly of fundamental importance, many aspects of coral bleaching cannot be explained solely by differences in symbionts amongst coral species. Here, I use the CO2 (sink) limitation model of coral bleaching to repose various host traits believed to influence thermal tolerance (e.g. metabolic rates, colony tissue thickness, skeletal growth form, mucus production rates, tissue concentration of fluorescent pigments and heterotrophic feedings capacity) in terms of an integrated strategy to reduce the likelihood of CO2 limitation around its intracellular photosymbionts. Contrasting observational data for the skeletal vital effect on oxygen isotope composition (δ18O) partitions two alternate evolutionary strategies. The first strategy is heavily reliant on a sea water supply chain of CO2 to supplement respiratory CO2(met). In contrast, the alternate strategy is less reliant on the sea water supply source, potentially facilitated by increased basal respiration rates and/or a lower photosynthetic demand for CO2. The comparative vulnerability of these alternative strategies to modern ocean conditions is used to explain the global-wide observation that corals with branching morphologies (and thin tissue layers) are generally more thermally sensitive than corals with massive morphologies (and thick tissue layers). The life history implications of this new framework are discussed in terms of contrasting fitness drivers and past environmental constraints, which delivers ominous predictions for the viability of thin-tissued branching and plating species during the present human-dominated (“Anthropocene”) era of the Earth System.

Long Bone Histology and Growth Patterns in Ankylosaurs: Implications for Life History and Evolution

The ankylosaurs are one of the major dinosaur groups and are characterized by unique body armor. Previous studies on other dinosaur taxa have revealed growth patterns, life history and evolutionary mechanisms based on their long bone histology. However, to date nothing is known about long bone histology in the Ankylosauria. This study is the first description of ankylosaurian long bone histology based on several limb elements, which were sampled from different individuals from the Ankylosauridae and Nodosauridae. The histology is compared to that of other dinosaur groups, including other Thyreophora and Sauropodomorpha. Ankylosaur long bone histology is characterized by a fibrolamellar bone architecture. The bone matrix type in ankylosaurs is closest to that of Stegosaurus. A distinctive mixture of woven and parallel-fibered bone together with overall poor vascularization indicates slow growth rates compared to other dinosaurian taxa. Another peculiar characteristic of ankylosaur bone histology is the extensive remodeling in derived North American taxa. In contrast to other taxa, ankylosaurs substitute large amounts of their primary tissue early in ontogeny. This anomaly may be linked to the late ossification of the ankylosaurian body armor. Metabolically driven remodeling processes must have liberated calcium to ossify the protective osteodermal structures in juveniles to subadult stages, which led to further remodeling due to increased mechanical loading. Abundant structural fibers observed in the primary bone and even in remodeled bone may have improved the mechanical properties of the Haversian bone.

Standard metabolic rate is associated with gestation duration, but not clutch size, in speckled cockroaches Nauphoeta cinerea

SummaryMetabolic rate varies significantly between individuals, and these differences persist even when the wide range of biotic and abiotic factors that influence metabolism are accounted for. It is important to understand the life history implications of variation in metabolic rate, but they remain poorly characterised despite a growing body of work examining relationships between metabolism and a range of traits. In the present study we used laboratory-bred families (one sire to three dams) of Nauphoeta cinerea (Olivier) (speckled cockroaches) to examine the relationship between standard metabolic rate (SMR) and reproductive performance (number of offspring and gestation duration). We show that SMR is negatively associated with female gestation duration. Age at mating is negatively associated with gestation duration for females, and mass is negatively associated with the average gestation duration of the females a male was mated with. In addition to the results in the current literature, the results from the present study suggest that the association between metabolism and life history is more complex than simple relationships between metabolism and various fitness traits. Future work should consider longitudinal, ontogenetic as well as selective and quantitative genetic breeding approaches to fully examine the associations between metabolism and fitness.

COCKROACHES THAT EXCHANGE RESPIRATORY GASES DISCONTINUOUSLY SURVIVE FOOD AND WATER RESTRICTION

Metabolic rate and respiratory gas exchange patterns vary significantly both between and within species, even after a number of biotic and abiotic factors are taken into account. This suggests that such variation is of evolutionary importance, but the life history implications of this variation remain relatively poorly characterized. In the present study, we examine the effect of metabolic variation on starvation and desiccation resistance in the speckled cockroach Nauphoeta cinerea. We also compare the starvation and desiccation resistance of individuals that exchange respiratory gases continuously with those that breathe discontinuously. We show that metabolic rate has no effect on survival during food and water restriction, but cockroaches exhibiting discontinuous gas exchange cycles (DGCs) live longer than those that do not and those provisioned with water lived longer than those that were not. This finding represents the first demonstration that DGCs confer a fitness benefit, and supports the oldest hypothesis for the evolution of DGCs (which suggests that DGCs arose or are maintained to reduce respiratory water loss) as we also reveal reduced water loss (both respiratory and total) in cockroaches exhibiting discontinuous gas exchange.

Adaptive changes in size and age at metamorphosis can qualitatively vary with predator type and available defenses

In many taxa the timing of metamorphosis is plastic in response to predation risk during the pre-metamorphic stage, and trends in both age and body size at metamorphosis have been the subject of much study. The responses to cues of predators are predominantly to be larger or equal-sized at the same age or older at metamorphosis. These observations are in direct contrast with existing theoretical treatments of this plasticity, which mostly predict earlier and smaller metamorphosis and never later and larger metamorphosis without invoking indirect effects on growth rate. Here we resolve the discrepancy between theory and observation using a dynamic state-dependent model that incorporates morphological and behavioral responses to predation risk. We allow prey to choose the optimal activity level and/or investment in defense over the growth period. We show that under certain conditions, metamorphosis at a larger size and later time is likely to be optimal. Our analysis allows us to make testable predictions about the changes in activity level of prey as they grow and how the effect of providing refuges will vary with predator type. Several of these predictions are supported by a meta-analysis of metamorphic responses to caged predators by larval amphibians and insects. Our predictions lead to insights about the feedback effects of antipredator responses on growth and subsequent implications for life history.

Parental Care Trade‐Offs and Life‐History Relationships in Insects

Insect parental care is extensive and varied, but its life-history implications have never been comparatively tested. Using original and literature data, we tested predictions about egg size, egg number (lifetime fecundity), and body size under different parental care modes across a phylogeny of 287 insect species. Life-history theory and both comparative and intraspecific evidence from ectotherms suggest parental care should select for bigger, fewer eggs, but that allometric scaling of egg size and lifetime fecundity may depend on whether care consists of provisioning (density-dependent offspring survival) or merely guarding (density-independent offspring survival). Against expectation, egg size was indistinguishable among parental care modes, covarying only with body size. This refutes most theory of egg size evolution under parental care. Lifetime fecundity scaled differently depending on parental investment-positively under no care and guarding, as in most ectotherms, but negatively under provisioning. Reproductive allocation in provisioning insects resembled that in mammals and birds, also groups with obligate provisioning. We propose that the metabolic demands of multiple offspring must scale with species body size more steeply than the parent's provisioning capacity, resulting in larger females laying fewer eggs. These patterns lay the groundwork for a more general understanding of parental care and life history.

Exploring the life-history implications of colour variation in offshore Gulf of Maine cod (Gadus morhua)

Abstract Sherwood, G. D., and Grabowski, J. H. 2010. Exploring the life-history implications of colour variation in offshore Gulf of Maine cod (Gadus morhua). – ICES Journal of Marine Science, 67: 1640–1649. The evolution of alternative life-history strategies in fish has largely been overlooked by fisheries managers, although differences in the biology of life-history variants can have important implications for the scale and productivity of fisheries. Cod display strikingly variable colouration in the Gulf of Maine, with red- and olive-coloured cod found in close sympatry. Colour types from Cashes Ledge, a shallow, offshore (∼100 km) feature, are examined to see whether they differ in key life-history traits including diet, depth distribution, growth, and body morphology. Red cod consumed significantly more crabs, lobsters, and demersal fish, whereas olive cod consumed more shrimp. Stable carbon isotope signatures (δ13C) varied significantly among colour types, but are thought to reflect baseline differences in δ13C at Cashes Ledge (potentially useful for residence estimates). Red cod were confined to a small area of shallow water (<20 m) and were significantly smaller at age than olive cod. Body shape was used to classify colour types correctly with 84% accuracy; red cod had shorter snouts, deeper bodies, and more slender tails than olive cod. Collectively, the results suggest that red cod are resident at Cashes Ledge and represent a life-history strategy distinct from olive cod.