Somatic Investment Research Articles

Sexual cannibalism increases male material investment in offspring: quantifying terminal reproductive effort in a praying mantis.

Models of the evolution of sexual cannibalism argue that males may offset the cost of cannibalism if components of the male body are directly allocated to the eggs that they fertilize. We tested this idea in the praying mantid Tenodera sinensis Males and females were fed differently radiolabelled crickets and allowed to mate. Half of the pairs progressed to sexual cannibalism and we prevented cannibalism in the other half. We assess the relative allocation of both male-derived somatic materials and ejaculate materials into the eggs and soma of the female. Our results show that male somatic investment contributes to production of offspring. The eggs and reproductive tissues of cannibalistic females contained significantly more male-derived amino acids than those of non-cannibalistic females, and there was an increase in the number of eggs produced subsequent to sexual cannibalism. Sexual cannibalism thus increases male material investment in offspring. We also show that males provide substantial investment via the ejaculate, with males passing about 25% of their radiolabelled amino acids to females via the ejaculate even in the absence of cannibalism.

Temporal Uncoupling between Energy Acquisition and Allocation to Reproduction in a Herbivorous-Detritivorous Fish.

Although considerable knowledge has been gathered regarding the role of fish in cycling and translocation of nutrients across ecosystem boundaries, little information is available on how the energy obtained from different ecosystems is temporally allocated in fish bodies. Although in theory, limitations on energy budgets promote the existence of a trade-off between energy allocated to reproduction and somatic growth, this trade-off has rarely been found under natural conditions. Combining information on RNA:DNA ratios and carbon and nitrogen stable-isotope analyses we were able to achieve novel insights into the reproductive allocation of diamond mullet (Liza alata), a catadromous, widely distributed herbivorous-detritivorous fish. Although diamond mullet were in better condition during the wet season, most reproductive allocation occurred during the dry season when resources are limited and fish have poorer body condition. We found a strong trade-off between reproductive and somatic investment. Values of δ13C from reproductive and somatic tissues were correlated, probably because δ13C in food resources between dry and wet seasons do not differ markedly. On the other hand, data for δ15N showed that gonads are more correlated to muscle, a slow turnover tissue, suggesting long term synthesis of reproductive tissues. In combination, these lines of evidence suggest that L. alata is a capital breeder which shows temporal uncoupling of resource ingestion, energy storage and later allocation to reproduction.

Disposable Soma Theory and the Evolution of Maternal Effects on Ageing.

Maternal effects are ubiquitous in nature and affect a wide range of offspring phenotypes. Recent research suggests that maternal effects also contribute to ageing, but the theoretical basis for these observations is poorly understood. Here we develop a simple model to derive expectations for (i) if maternal effects on ageing evolve; (ii) the strength of maternal effects on ageing relative to direct environmental effects; and (iii) the predicted relationships between environmental quality, maternal age and offspring lifespan. Our model is based on the disposable soma theory of ageing, and the key assumption is thus that mothers trade off their own somatic maintenance against investment in offspring. This trade-off affects the biological age of offspring at birth in terms of accumulated damage, as indicated by biomarkers such as oxidative stress or telomere length. We find that the optimal allocation between investment in maternal somatic investment and investment in offspring results in old mothers and mothers with low resource availability producing offspring with reduced life span. Furthermore, the effects are interactive, such that the strongest maternal age effects on offspring lifespan are found under low resource availability. These findings are broadly consistent with results from laboratory studies investigating the onset and rate of ageing and field studies examining maternal effects on ageing in the wild.

Environment-specific and sex-specific allocation strategies among gonadal, somatic, and immune indices in a marine fish

We examined the relative investment in somatic, gonadal, and liver growth, as well as a measure of immune function, in a marine species of fish (cabezon, Scorpaenichthys marmoratus (Ayres, 1854)) reared under different ambient temperature regimes (mean temperatures: 14.8 °C in Santa Barbara and 12.7 °C in Cayucos; both in California, USA). We predicted that fish reared in colder water would exhibit more pronounced trade-offs among growth, development, and immune parameters than fish in warmer water, and that females would have more pronounced trade-offs than males due to increased energy requirements for ovary development. We found immune function and liver investment were positively related in cold-water fish, but unrelated in warmer water fish. Immune function positively covaried with gonadal investment, but was not associated with somatic investment. Gonadal investment was negatively related to somatic investment, but this was driven by females, as there was no relationship between gonad development and somatic growth in males. We also found that the sexes differed in the relationship between gonadal and liver investments, in which females again exhibited a negative association but males exhibited a positive association. These results indicate that developmental investment strategies in cabezon are flexible and may be both context-specific and sex-specific.

Exploring simultaneous allocation to mating effort, sperm production, and body growth in male guppies

In several species, males increase their mating and sperm investment in the presence of unfamiliar females, the so-called Coolidge effect. Such an elevated reproductive effort is expected to be associated with a decreased investment in other costly traits, such as somatic growth and maintenance. How precopulatory, postcopulatory, and somatic investments interact one with each other, however, has been rarely evaluated simultaneously. We used the guppy (Poecilia reticulata), a polyandrous livebearing fish with alternative male mating tactics, to compare these 3 investments between males whose encounter rate with unfamiliar females was experimentally maintained at either high (high mate encounter rate [HER]) or low rate (low mate encounter rate [LER]) for 4 months. At the end of this period, HER males showed an increased sperm production as compared with their LER counterparts. This increment was accompanied with a reduction in the time spent following the female and by a shift from costly courtship displays to gonopodial thrusting, a less expensive coercive mating tactic. This effect may indicate a trade-off between these 2 components of male reproductive investment or may reflect a change in male optimal reproductive strategy associated with different mate encounter rate. In contrast, body growth was positively correlated with the increase in sperm production, and did not differ between experimental groups. Collectively, these results suggest that males did not vary their overall reproductive investment in response to their encounter rate with unfamiliar females, but differed significantly in the amount of resources available individually.

Masuda's Central Serous Chorioretinopathy (C.S.C.R.) and its somatic investment in Narcissism: our observations on new psychiatric nosography

Case report. Co-morbidity between central serous chorioretinopathy (C.R.S.C.) and narcissistic personality disorder. A reflection on the importance of an integrated approach to this ophthalmological disease through the description of its psychosomatic aspects and the evaluation of the nosographic definition in psychiatry. The central serous chorioretinopathy (C.R.S.C.) is a transudative disease affecting the posterior pole of the eye, that rapidly compromises the visual acuity, although it is a self-limited disease. Narcissism is a personality disorder characterised by an extreme gratification of self, without actually taking care of other people. In the current work both the diseases, along with the respective psychosomatic consequences the patient received, are examined.

Removal control of the highly invasive fish Gambusia holbrooki and effects on its population biology: learning by doing

Context For the success of future conservation and management programs, it is necessary to better understand the resilience mechanisms of invasive species and their invasive potential. In this sense, the study of the effects that management actions have on their biological traits is essential. Aims The present study aimed to assess the effects of removal control on the abundance and biology of an isolated population of the top invasive fish Gambusia holbrooki (eastern mosquitofish). Methods Experimental removal control with traps and handnets was carried out on a population of mosquitofish inhabiting a small semiarid stream in south-eastern Spain. Mosquitofish were periodically captured for more than 3 years. Temporal variations in abundance, fish somatic condition and reproductive investment, percentage of mature females, size at maturity and population recruitment were analysed. Key results Individuals of the 1+ age class increased their reproductive investment when population abundance was lower, thus increasing recruitment rate during the first months of the recruitment period. Individuals of the 0+ age class were responsible for expanding the reproductive period in conditions of low fish abundance. Conclusions The mosquitofish population showed variations of reproductive parameters that could indicate a compensatory density-dependent phenotypic response under diminished abundance conditions. However, its removal by the constant use of a combination of active and passive capture methods, reinforced by increased extraction effort according to its local biology, has led to an eradication of the population. The target mosquitofish population showed distinct ecological features that may have contributed to the effectiveness of local control, namely, low initial fish density, isolation in a headwater stretch and the prevalence of individuals in sunlit shallow ponds. Implications The compensatory mechanisms of this invasive species in low-density conditions should be considered in the design of management programs. Moreover, further research into removal control methods for mosquitofish or similar species is also needed.

Testes Investment along a Vertical Depth Gradient in an Herbivorous Fish

AbstractMales are expected to adjust testes investment according to the varying level of sperm competition that they experience. Spatial and temporal variation in population density likely influences sperm competition. In herbivorous aquatic organisms, densities often decrease along a vertical depth gradient, because their food is photosynthetic and thus becomes less abundant in deeper regions where less light penetrates. This decrease should be dramatic on a steep slope, which allows testing of the association between density and testes investment at the within‐population level. We tested the effect in the socially monogamous herbivorous cichlid fish Variabilichromis moorii living on a steep slope in Lake Tanganyika. We examined competitor density and food abundance as ecological factors, territory defense behaviors and phenotypic traits (testes investment and somatic investment), and compared them between shallow (4–6 m depth) and deep habitats (10–13 m depth) separated by several dozen meters. We found that food availability drastically decreased with increasing depth and that V . moorii was much more abundant in shallower habitats. Males in shallower habitats were in better physical condition (based on fat and liver mass) despite experiencing greater costs in terms of territory defense. Testes investment differed in areas with different competitor density and food abundance along a vertical depth gradient, but competitor density was the most explanatory factor of the difference. This suggests that this herbivorous fish would change testes investment in response to population density.

Effects of Ration on Growth and Reproductive Investment from Larva to Sexual Maturity in the Female Cyprinid Minnow, Tanichthys albonubes

AbstractSomatic growth and reproductive investment in female Tanichthys albonubes (Cyprinidae) individually cultured at the laboratory from larva to sexual maturity were examined under low, medium, and satiation food rations. All the 72‐day post‐hatch fish reached sexual maturity under all rations. The standard length, wet body mass, dry ovarian mass, dry liver mass, condition factor, energy content, and number of vitellogenic oocytes were all increased with ration levels. However, food conversion efficiency decreased with ration. There were no significant differences in total number of oocytes per female between rations. The species is a continuous batch‐spawner. The size‐frequency distributions of oocyte diameters showed a continuous pattern, ranging from 0.03 to 0.70 mm, at different rations. The proportion of energy intake allocated to growth decreased with ration levels. Only 3.29–4.60% of energy intake was stored in the ovary. These biological and energetic characteristics allow this fish to reach first maturity with low food intake, although it produced fewer vitellogenic oocytes at lower rations. This property enables T. albonubes survive in its native habitats where food is not only scarce, but also variable temporally and spatially. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Similar offspring production by normal and intersex females in two populations of Gammarus minus (Malacostraca, Amphipoda) with high levels of intersexuality

Two Virginia (U.S.A.) populations of the freshwater amphipod Gammarus minus (Say, 1818) exhibit high frequencies of females with male genital papillae (60 to 75% in one population and 100% in the other) that have been observed for over 30 years. This observation is surprising because sex-allocation theory predicts that such intersex individuals should have lower evolutionary fitness than ‘normal’ males or females. Here we tested this theory by comparing a major component of reproductive fitness (offspring production, as estimated by number and total mass of offspring in a brood) between intersex and normal females. Although intersex females tend to brood slightly fewer, but larger embryos than those of normal females, these differences were not significant overall, and moreover they resulted in nearly identical mean production of total offspring mass per brood. Maternal somatic investment (body mass and body condition) during brooding also did not differ significantly between intersex and normal females. These results suggest that intersex females may not have lower reproductive fitness than that of normal females, which may help explain their high frequencies in the Virginia populations. Consistent with this hypothesis, available literature data on four amphipod species show a positive association between intersex frequency and the offspring production of intersex females relative to that of normal females. However, this hypothesis needs to be tested further by examining other reproductive and survival traits related to fitness, and by examining other amphipod populations with varying intersex frequencies. Moreover, the cause(s) of the intersex condition in the Virginia populations (and most other amphipod populations) remains largely unknown.

Diet restriction and life history trade‐offs in short‐ and long‐lived species of Daphnia

The life-extending effects of diet restriction are well documented. One evolutionary model that accounts for this widespread conservation is the resource allocation model, where the selected individuals are those that can delay reproduction during periods of resource limitation. In this study, we use closely related species of a model organism, Daphnia, with widely divergent lifespans to address the relationship between diet restriction and longevity and assess whether the relationships are owing to trade-offs between reproductive and somatic investment. Specifically, we conducted a common garden experiment and constructed reaction norms for lifespan, fecundity, and body size as a function of food concentration. Our study provides evidence that the short-lived species in our study, D. pulex, shows the classically observed relationship of enhanced lifespan in response to reduced diet intake, but does not divert resources to somatic maintenance at the expense of reproduction during chronic diet restriction. In contrast, we find no evidence that the long-lived species in our study, D. pulicaria, gains any life-extending effects through diet restriction. Combined, our results provide evidence that the resource allocation model is not sufficient to explain the evolution of diet-mediated lifespan plasticity.

ORIGINAL ARTICLE: Leptin associations with age, weight, and sex among chimpanzees (Pan troglodytes)

AbstractBackground Leptin is a hormone secreted primarily by adipocytes, a lipostatic signal to the hypothalamus, and is often correlated with adiposity. Associations between leptin, age, and development are unknown in human’s closest evolutionary relative, the common chimpanzee (Pan troglodytes).Methods Serum leptin was assessed cross sectionally in association with age, weight, and sex in healthy captive chimpanzee males (n = 47) and females (n = 49) to test hypotheses related to predicted differences in leptin levels with body mass, development, and sexual dimorphism.Results Leptin increased with age and weight among females, but not in males. Leptin was overall higher in females compared to males.Conclusions Sex differences in leptin were most evident during adolescence and adulthood, despite similar increases in weight in both sexes indicating that sexual maturation is a key divergence point for differential somatic investment in adiposity and leptin levels between male and female chimpanzees.

Mechanisms of aging in the naked mole-rat: The case for programmed aging

Maximum lifespan is an important species trait that generally scales with body size. Never the less there are many mammals that deviate from this allometric relationship and live more than double the expected lifespan predicted on the basis of body size. These exceptionally long-lived species appear to defy the expected rate of aging and provide powerful tools with which to elucidate if maximum species lifespan is indeed encoded in the genome; determine possible biological clocks and their downstream molecular mechanisms that may abrogate or regulate rates of aging. One such mammal is the naked mole-rat [NMR]. This, the longest-lived rodent known, lives 8.6-times longer than similar-sized mice, yet it maintains cancer-free, good health for more than 85% of its astonishing 30-year lifespan. NMRs, like other long-lived species, show pronounced resistance to most cellular stressors. This may be due to enhanced cellular protection and/or better maintenance of somatic integrity. In contrast, short-lived species generally direct many of their resources into rapid growth and early reproduction rather than fend off threats to their soma. Although the mechanisms facilitating this species divergence in somatic maintenance are poorly understood, these most likely represent an evolutionary trade-off between partitioning energy and resources into somatic maintenance (thereby contributing to the survival of the individual) versus investments in growth and reproduction and ensuring the rapid attainment of sexual maturity and the long-termsurvival of the species. This species-specific difference in resource and somatic management must be encoded in the genome, thus enabling cells and the organism to mount the appropriate level of cytoprotection, commensurate with their expected longevity. We explore this premise by reevaluating the various theories of aging in the light of what is known from the biology of the longest-living rodent, the naked mole-rat.

Maternal characteristics and environment affect the costs of reproduction in female mountain goats

Reproduction should reduce resources available for somatic investment and result in fundamental trade-offs among life-history traits. Using 18 years of longitudinal data from marked mountain goats (Oreamnos americanus), we assessed whether reproductive status affected female survival and future reproduction when accounting for parity, age, individual quality, population density, and environmental conditions. Reproduction reduced the probability of parturition and offspring survival in the following year. Female survival, however, was independent of previous reproduction, suggesting that females favored their own survival over that of their offspring. The lower probability of parturition in females that had a kid the previous year was only detected at high population density and among young and prime-aged females, suggesting that fitness costs of reproduction can be masked by variations in resource availability and individual characteristics. Primiparous females were less likely than multiparous females to reproduce in the subsequent year. Offspring survival was reduced at high density and after severe winters. Environmental conditions mainly influenced offspring survival, whereas female survival and fecundity were principally modulated by female characteristics. Our study highlights how different intrinsic and environmental factors can affect the probability of future reproduction and also underlines the value of long-term monitoring of known individuals.

New insights on the biology of the jumbo squid Dosidicus gigas in the Northern Humboldt Current System: Size at maturity, somatic and reproductive investment

Based on size at maturity and standardized residuals from mantle length (ML)–total weight (TW) and mantle length–gonad weight (GW) relationships, this paper describes the interannual variability of the size at maturity (SM), somatic and reproductive investment of mature males and females of Dosidicus gigas during the spawning peak (October–March) for the period 1994–2006 in the Northern Humboldt Current Ecosystem (Peruvian waters). Significant changes occurred in the SM in females as well in males: before 2001 the average did not exceed 47 cm ML, while from 2001 onwards the average MS varied between 62 and 96 cm ML. The average SM was generally higher in females. There was a great individual variability of somatic and reproductive investment, being higher in large-sized mature squids. No relationship was found between SM and somatic condition. The presence of small-sized mature squids in good somatic condition under different scenarios of sea surface temperature (normal, warm or cold periods; El Niño and La Niña events) does not indicate a relationship between somatic condition and SST. The relationship between reproductive and somatic investment was variable and independent of the sex. It also varied among different years. This would indicate that females and males may respond differently under the same environmental conditions. Considering the relationship between fecundity and ML, mature females at larger sizes had a lower reproductive condition, but also a higher potential fecundity. Lower fertility potential for some small mature females is offset by greater investment in reproduction, particularly under adverse environmental conditions. The positive correlation between the abundance (CPUE) and SM shows that the biomass was greater in periods dominated by the presence of large-sized mature squid.

Flight feather shaft structure of two warbler species with different moult schedules: a study using high‐resolution X‐ray imaging

Plumage constitutes a significant component of the somatic investment of birds. A detailed investigation of feathers and moult can help to uncover trade-offs involved in somatic investment decisions, the sources of some of the costs birds have to pay and the potential fitness consequences. We used micro-computed tomography imaging to study the second moment of area, a structural parameter that is one determinant of bending stiffness and the cortex volume of flight feather shafts of two sister taxa, the willow warbler Phylloscopus trochilus, a migratory species with two annual moults, and the chiffchaff Phylloscopus collybita, a migrant with one annual post-nuptial moult. Juvenile and adult willow warbler and chiffchaff feathers, all grown on the breeding grounds, are structurally very similar to each other. Willow warbler feathers grown during moult on the wintering grounds, however, have a significantly higher second moment of area and a significantly larger cortex volume than all the other feather types. We discuss the possibility that the seasonal variability of willow warbler feathers may be an adaptive structural reflection of a moult-migration strategy that has allowed this species to occupy large breeding and wintering ranges.

A potential function for oocyte apoptosis in unmated Nauphoeta cinerea

AbstractStarvation and enforced virginity induce apoptosis (programmed cell death) in the oocytes of female cockroaches of Nauphoeta cinerea, yet the life‐history outcome differs among fed and starved virgins. Consistent with the hypothesis that oocytes are absorbed to reallocate resources, apoptosis is followed by an increase in future reproduction and longevity in starved virgins. However, apoptosis induction by enforced virginity in fed females results in reduced fecundity and longevity. It is predicted that this life‐history outcome occurs because oocyte apoptosis under these conditions is not part of an adaptive reproductive strategy but simply is the result of cellular ageing and clearance to maintain reproductive synchrony. In the present study, reproductive and somatic allocation are examined over time to test whether resources are recouped by the fat body, reinvested in reproduction or lost altogether when apoptosis is associated with enforced virginity. To assay reproductive investment, the number of ovarioles is counted, apoptosis levels are analysed and the size of all oocytes within the vitellaerium is measured. To assay somatic investment, dry fat body mass is measured. In conjunction with apoptosis, the number of ovarioles declines, whereas the size of surviving oocytes increases. By contrast to the cellular ageing hypothesis, apoptosis associated with enforced virginity appears to be adaptive if resources from sacrificed oocytes are recycled into the survivors to maintain the quality of ageing oocytes. This reinvestment in current reproduction may trade‐off with future reproductive capacity.

Separate and combined effects of nutrition during juvenile and sexual development on female life-history trajectories: the thrifty phenotype in a cockroach

We have yet to understand fully how conditions during different periods of development interact to influence life-history structure. Can the negative effects of poor juvenile nutrition be overcome by a good adult diet, or are life-history strategies set by early experience? Here, we tested the influence and interaction of different nutritional quality during juvenile and sexual development on female resource allocation physiology, life history and courtship behaviour in the cockroach, Nauphoeta cinerea. Nymphs were raised on either a good-quality or poor-quality diet. After adult eclosion, females were either switched to the opposite diet or remained on their original diet. We assessed mating behaviour and lifetime reproductive success for half of the females from each treatment. We evaluated reproductive investment, somatic investment and resource reallocation from reproduction to the soma via oocyte apoptosis in the remaining females. We found that poor juvenile conditions resulted in a fat phenotype with slow juvenile growth and short reproductive lifespan that could not be retrieved with a change in diet. Good juvenile conditions resulted in the converse, but again fixed, phenotype in adulthood. Thus, juvenile nutrition sets adult patterns of resource allocation.

Waterborne cues from crabs induce thicker skeletons, smaller gonads and size-specific changes in growth rate in sea urchins

Indirect predator-induced effects on growth, morphology and reproduction have been extensively studied in marine invertebrates but usually without consideration of size-specific effects and not at all in post-metamorphic echinoids. Urchins are an unusually good system, in which, to study size effects because individuals of various ages within one species span four orders of magnitude in weight while retaining a nearly isometric morphology. We tracked growth of urchins, Strongylocentrotus droebachiensis (0.013–161.385 g), in the presence or absence of waterborne cues from predatory Jonah crabs, Cancer borealis. We ran experiments at ambient temperatures, once for 4 weeks during summer and again, with a second set of urchins, for 22 weeks over winter. We used a scaled, cube-root transformation of weight for measuring size more precisely and for equalizing variance across sizes. Growth rate of the smallest urchins (summer: <17 mm diameter; winter: <7 mm diameter) decreased by 40–42% in response to crab cues. In contrast, growth rate of larger urchins was unaffected in the summer and increased in response to crab scent by 7% in the winter. At the end of the 22-week experiment, additional gonadal and skeletal variables were measured. Cue-exposed urchins developed heavier, thicker skeletons and smaller gonads, but no differences in spine length or jaw size. The differences depended on urchin size, suggesting that there are size-specific shifts in gonadal and somatic investment in urchins.

THE GENETIC ARCHITECTURE OF A FEMALE SEXUAL ORNAMENT

Understanding the evolution of sexual ornaments, and particularly that of female sexual ornaments, is an enduring challenge in evolutionary biology. Key to this challenge are establishing the relationship between ornament expression and female reproductive investment, and determining the genetic basis underpinning such relationship. Advances in genomics provide unprecedented opportunities to study the genetic architecture of sexual ornaments in model species. Here, we present a quantitative trait locus (QTL) analysis of a female sexual ornament, the comb of the fowl, Gallus gallus, using a large-scale intercross between red junglefowl and a domestic line, selected for egg production. First, we demonstrate that female somatic investment in comb reflects female reproductive investment. Despite a trade-off between reproductive and skeletal investment mediated by the mobilization of skeletal minerals for egg production, females with proportionally large combs also had relatively high skeletal investment. Second, we identify a major QTL for bisexual expression of comb mass and several QTL specific to female comb mass. Importantly, QTL for comb mass were nonrandomly clustered with QTL for female reproductive and skeletal investment on chromosomes one and three. Together, these results shed light onto the physiological and genetic architecture of a female ornament.