Age and season impact resource allocation to eggs and nesting behavior in the painted turtle

Theory predicts that in long-lived organisms females should invest less energy in reproduction and more in growth and self-maintenance early in life, with this balance shifting as females age and the relative value of each reproductive event increases. We investigated this potential trade-off by characterizing within-population variation in resource allocation to eggs by female painted turtles (Chrysemys picta) and relating this variation to their nesting ecology and life history. We examined lipid and protein allocation to yolks, accounting for both relative female age and seasonal effects (first vs. second clutches within a female). Older females appear to increase their investment in reproduction by producing larger eggs, but these eggs are not disproportionately more lipid or protein rich than the smaller eggs from younger females. Within the nesting season, first clutches have more lipid and protein than second clutches. We also found that younger females nest closer to the water than older females. Our results indicate that trade-offs involving resource allocation and nesting behavior do occur both seasonally and with age, suggesting ontogenetic variation in life-history strategies in this long-lived organism.     

Females allocate differentially to offspring size and number in response to male effects on female and offspring fitness

Female investment in offspring size and number has been observed to vary with the phenotype of their mate across diverse taxa. Recent theory motivated by these intriguing empirical patterns predicted both positive (differential allocation) and negative (reproductive compensation) effects of mating with a preferred male on female investment. These predictions, however, focused on total reproductive effort and did not distinguish between a response in offspring size and clutch size. Here, we model how specific paternal effects on fitness affect maternal allocation to offspring size and number. The specific mechanism by which males affect the fitness of females or their offspring determines whether and how females allocated differentially. Offspring size is predicted to increase when males benefit offspring survival, but decrease when males increase offspring growth rate. Clutch size is predicted to increase when males contribute to female resources (e.g. with a nuptial gift) and when males increase offspring growth rate. The predicted direction and magnitude of female responses vary with female age, but only when per-offspring paternal benefits decline with clutch size. We conclude that considering specific paternal effects on fitness in the context of maternal life-history trade-offs can help explain mixed empirical patterns of differential allocation and reproductive compensation.     

Experience pays: offspring survival increases with female age

Life-history theory predicts that, in long-lived organisms, effort towards reproduction will increase with age, and research from oviparous vertebrates largely supports this prediction. In reptiles, where parental care occurs primarily via provisioning of the egg, older females tend to produce larger eggs, which in turn produce larger hatchlings that have increased survival. We conducted an experimental release study and report that maternal age positively influences offspring survivorship in the painted turtle (Chrysemys picta) and predicts offspring survival at least as well as hatchling body size does. These data suggest that, although increasing hatchling size is a major component of reproductive success in older individuals, other factors also contribute.     

Sexual dimorphism in resource acquisition and deployment: both size and timing matter

Background and Aims

The males and females of many dioecious plant species differ from one another in important life-history traits, such as their size. If male and female reproductive functions draw on different resources, for example, one should expect males and females to display different allocation strategies as they grow. Importantly, these strategies may differ not only between the two sexes, but also between plants of different age and therefore size. Results are presented from an experiment that asks whether males and females of Mercurialis annua, an annual plant with indeterminate growth, differ over time in their allocation of two potentially limiting resources (carbon and nitrogen) to vegetative (below- and above-ground) and reproductive tissues.

Methods

Comparisons were made of the temporal patterns of biomass allocation to shoots, roots and reproduction and the nitrogen content in the leaves between the sexes of M. annua by harvesting plants of each sex after growth over different periods of time.

Key Results and Conclusions

Males and females differed in their temporal patterns of allocation. Males allocated more to reproduction than females at early stages, but this trend was reversed at later stages. Importantly, males allocated proportionally more of their biomass towards roots at later stages, but the roots of females were larger in absolute terms. The study points to the important role played by both the timing of resource deployment and the relative versus absolute sizes of the sinks and sources in sexual dimorphism of an annual plant.     

Temporal variation in reproductive allocation in a shield bug Elasmostethus interstinctus

We investigated changes in the reproductive output and the effect of female phenotype on reproductive parameters in a shield bug Elasmostethus interstinctus (L.) (Heteroptera: Acanthosomatidae) over the whole reproductive period. At the beginning and the middle of the reproductive period eggs were smaller than at the end of the period. Clutch mass and number of eggs per clutch decreased in laying sequence, first clutches being much larger than any of the later ones. Lifetime fecundity correlated positively with female size: large females produced more eggs and lived longer than small ones. Egg size did not vary with female size. Offspring survival until adulthood increased with egg weight. Individuals overwinter before reproduction, and because the nymphs from later-laid eggs have the least time to gather resources before overwintering, it may be important for later-laid eggs to be of high quality. Reproductive allocation varies during the reproductive period; females allocate resources relatively more to offspring number at the beginning of the reproductive period and more to offspring quality at the end of their life.     

A lengthy solution to the optimal propagule size problem in the large-bodied South American freshwater turtle, <Emphasis Type="Italic">Podocnemis unifilis</Emphasis>

In oviparous vertebrates lacking parental care, resource allocation during reproduction is a major maternal effect that may enhance female fitness. In general, resource allocation strategies are expected to follow optimality models to solve the energy trade-offs between egg size and number. Such models predict that natural selection should optimize egg size while egg number is expected to vary with female size, thus maximizing offspring fitness and consequently, maternal fitness. Deviations from optimality predictions are commonly attributed to morphological constraints imposed by female size, such as reported for small-bodied turtle species. However, whether such anatomical constraints exist in smaller-bodied females within large-bodied clades remains unstudied. Here we tested whether resource allocation of the river turtle Podocnemis unifilis (a relatively smaller member of the large-bodied Podocnemididae) follows optimality theory, and found a pattern of egg elongation in smaller females that provides evidence of morphological constraints and of a reproductive trade-off with clutch size, whereas egg width supports the existence of an optimal egg size and no trade-off. Moreover, larger females laid larger clutches composed of rounder eggs, while smaller females laid fewer and relatively more elongated eggs. Elongated eggs from smaller females have larger volume relative to female size and to round eggs of equal width. We propose that elongated eggs represent a solution to a potential morphological constraint suffered by small females. Our results suggest that larger females may optimize fitness by increasing the number of eggs, while smaller females do so by producing larger eggs. Our data supports the notion that morphological constraints are likely more widespread than previously anticipated, such that they may not be exclusive of small-bodied lineages but may also exist in large-bodied lineages.     

Reproductive investment is connected to innate immunity in a long-lived animal

Life-history theory predicts that organisms optimize their resource allocation strategy to maximize lifetime reproductive success. Individuals can flexibly reallocate resources depending on their life-history stage, and environmental and physiological factors, which lead to variable life-history strategies even within species. Physiological trade-offs between immunity and reproduction are particularly relevant for long-lived species that need to balance current reproduction against future survival and reproduction, but their underlying mechanisms are poorly understood. A major unresolved issue is whether the first-line innate immune function is suppressed by reproductive investment. In this paper, we tested if reproductive investment is associated with the suppression of innate immunity, and how this potential trade-off is resolved depending on physiological state and residual reproductive value. We used long-lived capital-breeding female eiders (Somateria mollissima) as a model. We showed that the innate immune response, measured by plasma bacteria-killing capacity (BKC), was negatively associated with increasing reproductive investment, i.e., with increasing clutch size and advancing incubation stage. Females in a better physiological state, as indexed by low heterophil-to-lymphocyte (H/L) ratios, showed higher BKC during early incubation, but this capacity decreased as incubation progressed, whereas females in poorer state showed low BKC capacity throughout incubation. Although plasma BKC generally declined with increasing H/L ratios, this decrease was most pronounced in young females. Our results demonstrate that reproductive investment can suppress constitutive first-line immune defence in a long-lived bird, but the degree of immunosuppression depends on physiological state and age.     

A Review for Life-history Traits Variation in Frogs Especially for Anurans in China

Environmental variation can promote differentiation in life-history traits in species of anurans. Increased environmental stress usually results in larger age at sexual maturity, older mean age, longer longevity, slower growth, larger body size, and a shift in reproductive allocation from offspring quantity to quality, and a stronger trade-off between offspring size and number. However, previous studies have suggested that there are inconsistent geographical variations in life-history traits among anuran species in China. Hence, we here review the intraspecific patterns and differences in life-history traits(i.e., egg size, clutch size, testes size, sperm length, age at sexual maturity, longevity, body size and sexual size dimorphism) among different populations within species along geographical gradients for anurans in China in recent years. We also provide future directions for studying difference in sperm performance between longer and shorter sperm within a species through transplant experiments and the relationships between metabolic rate and brain size and life-history.     

Sexual differences in biomass and nutrient allocation of first-year Silene dioica plants

Reproductive and somatic biomass, nitrogen (N), and phosphorus (P) pools were compared between females and males in 1st-year plants of Silene dioica. We estimated irretrievable resources allocated to seeds, pollen, flowers, and unrecovered summer leaf investment by collecting plant parts at abscission throughout the season. At the end of the season, we determined resources lost through senescent stems and autumn leaf turnover and resources stored in perennial roots and overwintering buds. Sexual differences in allocation patterns depended on the resource used for comparison, and whether absolute or proportional resource pools were assessed. Total resource pools in terms of biomass and N were similar for females and males. However, male plants acquired relatively more P. The proportional reproductive investment, i.e., reproductive effort, was similar for males and females in terms of biomass and N. In terms of P, male reproductive effort was higher. There was no difference between sexes in the proportional and relative biomass allocated to perennial roots and overwintering buds. However, in terms of absolute and relative N allocation to below-ground parts, females had larger reserves than males. Females, moreover, had a larger proportion of their P in below-ground parts. However, as male total P pools were larger, absolute P reserves did not differ between sexes. The high reproductive effort and N depletion of below-ground parts in males resulted largely from higher flower production compared to females. In females, seeds were the major component of reproductive effort. These results show that if biomass and nutrient allocation are assessed in parallel for dioecious plants, we obtain a more complete view of their sexual differences. Received: 07 May 1998 / Accepted: 30 October 1998     

Age at mating and male quality influence female patterns of reproductive investment and survival

The trade‐off between the allocation of resources toward somatic maintenance or reproduction is one of the fundamentals of life history theory and predicts that females invest in offspring at the expense of their longevity or vice versa. Mate quality may also affect life history trade‐offs through mechanisms of sexual conflict; however, few studies have examined the interaction between mate quality and age at first mating in reproductive decisions. Using house crickets (Acheta domesticus), this study examines how survival and reproductive trade‐offs change based on females’ age at first reproduction and exposure to males of varying size. Females were exposed to either a large (presumably high‐quality) or small male at an early (young), middle (intermediate), or advanced (old) age, and longevity and reproductive investment were subsequently tracked. Females mated at a young age had the largest number of eggs but the shortest total lifespans while females mated at older ages produced fewer eggs but had longer total lifespans. The trade‐off between age at first mating and eggs laid appears to be mediated through higher egg‐laying rates and shorter postmating lifespans in females mated later in life. Exposure to small males resulted in shorter lifespans and higher egg‐laying rates for all females indicating that male manipulation of females, presumably through spermatophore contents, varies with male size in this species. Together, these data strongly support a trade‐off between age at first reproduction and lifespan and support the role of sexual conflict in shaping patterns of reproduction.     

Resource allocation in a simultaneously hermaphroditic slug with phally polymorphism

The theory of resource allocation assumes that a resource not allocated to one function may be reallocated to another. Thus, in hermaphroditic species, an individual that suppresses the use of one sex function may free resources for the other sex function. We determined the relative importance of male copulatory organs in terms of their fraction of the total dry body weight and tested whether in the pulmonate land slug Deroceras laeve (Müller), individuals that lack the male copulatory organs (aphallics) reallocate this resource towards the female structures and/or towards life-history traits. To this end, we raised 13 families under uniparental reproduction and compared growth, length of the juvenile period, number of eggs produced, percentage of hatched eggs and hatching time among a- and euphallics. We also measured the reproductive and sex allocation of all individuals. Six out of 13 families contained no euphallic individuals. In the other seven families, the proportion of euphallic individuals ranged from 0.13 to 0.43. There was an enormous variation in life-history traits and reproductive and sex allocation among individuals, even among individuals of the same family. Allocation to the male function was very low in euphallic slugs (i.e. 1.35% of the total body dry mass and 12.33% of the total reproductive dry mass). Our results did not reveal a reallocation from the lost male function towards the female function, nor towards one of the life-history traits. Finally, we propose a scenario that could explain the maintenance of phally polymorphism in D. laeve.     

Allocation from capital and income sources to reproduction shift from first to second clutch in the flesh fly, Sarcophaga crassipalpis

Understanding how resources are allocated between survival and reproduction is fundamental to the study of the evolution of life histories. Reproductive resources can come from two intrinsic resource pools, stored reserves (capital) acquired before reproduction or income acquired during reproduction. The variety of reproductive strategies in insects is remarkable and reproductive allocation encompasses the complete range of allocation strategies from pure capital breeders to pure income breeders. However, most organisms probably use a blend of capital and income and this blend is likely dynamic, changing between reproductive bouts in response to internal and external conditions. We used stable isotopes to quantify the allocation of capital and income resources to reproduction in the flesh fly, Sarcopha crassipalpis and assessed how allocation patterns change over multiple bouts of reproduction. Sarcophaga crassipalpis shifts from a slight investment of capital in the first clutch to an almost pure income breeder in the second clutch. We discuss the relationship between activity and allocation, and the potential for this system to understand how allocation patterns change in response to environmental stress.     

Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish

Fish are known for their high phenotypic plasticity in life‐history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade‐offs in phenotypic plasticity between life‐history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long‐term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high fishing mortality.     

Species traits and shoot-root biomass allocation in 20 dry-grassland species

Aims A plant has a limited amount of resources at any time and it allocates them to different structures. In spite of the large number of previous studies on allocation patterns within single species, knowledge of general patterns in species allocation is still very limited. This is because each study was done in different conditions using different methodology, making generalization difficult. We investigate intraspecific above- versus below-ground biomass allocation among individuals across a spectrum of dry-grassland plant species at two different developmental stages and ask whether allocation is age- and species specific, and whether differences among species can be explained by their life-history traits and phylogeny.Methods We collected data on above- and below-ground biomass of seedlings and adult plants of 20 species from a common garden experiment. We analysed data on shoot–root biomass allocation allometrically and studied the relationship between the allometric exponents (slopes on log–log scale), species life-history traits and phylogenetic distances.Important findings We found isometric as well as allometric patterns of biomass allocation in the studied species. Seedlings and adult individuals of more than half of the species differed in their above- versus below-ground biomass allometric exponents. Seedlings and adult individuals of the remaining species differed in their allometric coefficients (intercepts). Annual species generally allocated proportionally more to above- than below-ground biomass as seedlings than as adults, whereas perennial species showed the opposite pattern. Plant life-history traits, such as plant life span, age of first flowering, month in which the species begin flowering and specific leaf area were much more important in explaining differences in shoot–root allometry among species than were phylogenetic relationships. This suggests that allocation patterns vary greatly among closely related species but can be predicted based on species life-history traits.     

Magellanic penguin telomeres do not shorten with age with increased reproductive effort,investment, and basal corticosterone

All species should invest in systems that enhance longevity; however, a fundamental adult life‐history trade‐off exists between the metabolic resources allocated to maintenance and those allocated to reproduction. Long‐lived species will invest more in reproduction than in somatic maintenance as they age. We investigated this trade‐off by analyzing correlations among telomere length, reproductive effort and output, and basal corticosterone in Magellanic penguins (Spheniscus magellanicus). Telomeres shorten with age in most species studied to date, and may affect adult survival. High basal corticosterone is indicative of stressful conditions. Corticosterone, and stress, has been linked to telomere shortening in other species. Magellanic penguins are a particularly good model organism for this question as they are an unusually long‐lived species, exceeding their mass‐adjusted predicted lifespan by 26%. Contrary to our hypothesis, we found adults aged 5 years to over 24 years of age had similar telomere lengths. Telomeres of adults did not shorten over a 3‐year period, regardless of the age of the individual. Neither telomere length, nor the rate at which the telomeres changed over these 3 years, correlated with breeding frequency or investment. Older females also produced larger volume clutches until approximately 15 years old and larger eggs produced heavier fledglings. Furthermore, reproductive success (chicks fledged/eggs laid) is maintained as females aged. Basal corticosterone, however, was not correlated with telomere length in adults and suggests that low basal corticosterone may play a role in the telomere maintenance we observed. Basal corticosterone also declined during the breeding season and was positively correlated with the age of adult penguins. This higher basal corticosterone in older individuals, and consistent reproductive success, supports the prediction that Magellanic penguins invest more in reproduction as they age. Our results demonstrate that telomere maintenance may be a component of longevity even with increased reproductive effort, investment, and basal corticosterone.     

Phenotypic plasticity of life-history traits in clonal and sexual fish (Poeciliopsis) at high and low densities

Models of resource allocation strategies predict an array of life-history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal strains) in high and low density treatments. To examine the plasticity of life-history traits in females raised in these two environments, I measured survival, growth, egg production, egg size, and proportion mature at 10 weeks of age. Survival was not affected by density treatment. However, both growth and overall egg production were lower in females from the high density treatments, and reproductive maturity was significantly delayed at the high density for all strains. Egg production per unit size was not affected by density in any strain, signifying that differences in the numbers of eggs produced was merely a reflection of the differences in size of fish in the two density treatments. Egg size was also unaffected by density in all strains. These results are related to models of resource allocation in stressful environments. There was a consistent pattern of increased reproductive investment in the sexual strain relative to the two clonal strains. The sexual strain matured earlier, produced more eggs per unit body weight, and had larger eggs than either clone at both densities. These results are interpreted by considering the predicted adaptive responses of these three strains to the long-term environmental differences in their natural habitats.     

Mating modifies female life history in a haplodiploid spider mite

Mating usually modifies females' resource allocation pattern, often as a result of conflicts between male and female partners. Can such a switch occur even in the absence of sexual conflicts? We addressed this issue in the haplodiploid spider mite Tetranychus urticae, whose biology and population structure considerably reduce conflicts between males and females over reproductive decisions. Comparing virgin and mated females, we tested the hypothesis that mated females modify their allocation pattern so as to maximize their probability of producing daughters. Mated females produced fewer but larger eggs, resulting in an overall similar reproductive effort but an increased probability of producing daughters, since in this species larger eggs are more likely to be fertilized and thus to become female. Moreover, mated females concentrated their reproduction early in life. Again, this might be a way to produce more daughters, since sperm is more abundant early in life. For virgins, spreading reproductive investment might be a way to save resources to extend life span, thus increasing their probability of encountering a sexual partner. Females with multiple opportunities for mating produced fewer eggs and a less female-biased sex ratio than once-mated females, raising the question of why multiple mating often occurs in this species.     

Influence of Male Dominance on Egg Testosterone and Antibacterial Substances in the Egg of Grey Partridges

Maternal effects play an important role in mediating reproductive success; the different allocation of resources in eggs is considered a primary maternal effect. In oviparous vertebrates, there are several substances (hormones, immunoglobulins, antioxidants, antibacterial molecules) that females may allocate differentially. Mate choice is a key factor influencing female reproductive decisions and investment in eggs, but it is not clear to what extent the dominance status of the partner can influence the decision to invest differentially in the quality of eggs. In the grey partridge Perdix perdix, we ranked males for their social status after pairwise dominance tests. Then, females were paired experimentally with dominant or subordinate individuals. We measured testosterone, lysozyme and ovotransferrin concentrations in their eggs. Females paired with dominant males laid eggs with higher testosterone concentration, while egg mass, lysozyme and ovotransferrin concentrations did not differ. With regard to testosterone, because this hormone has been shown to elicit beneficial effects in offspring hatching from grey partridge eggs, our results are in line with the differential allocation hypothesis that females paired with high‐quality males should invest more in the current reproductive event.     

Individual and population sex allocation patterns

A variety of sex allocation models is considered in which the reproductive returns on investment in males differ from the returns on investment in females, the amounts of resources available for reproduction vary in the population, the costs of making male and female reproductive structures differ, and the conception sex ratio may be fixed and there may be an initial minimum investment per offspring. Results of these models include quantitative predictions for both individual- and population-level sex allocation, an opportunity to study the magnitude of changes in predicted patterns as key variables change, and therefore an analysis of the robustness of Fisher's equal investment theory. One example is that Fisher's argument is extremely robust for high fecundity organisms, but, in low fecundity organisms, is sensitive to differences between the sexes in reproductive returns on investment per offspring, a situation that occurs in many vertebrates to which Fisher's theory is often applied. A second example is that individual- and population-level patterns often depend strongly on the distribution of resources available for reproduction among individuals in the population.     

Developmental trade-offs and life histories: strategic allocation of resources in caddis flies

Resource allocation trade-offs during development are potentially very important in the evolution of organism morphology and life-history strategy However, they have rarely been demonstrated empirically. To what extent the division of limited resources between growing organs is a consequence of particular developmental pathways or varies strategically in line with life-history predictions is unknown. It has been demonstrated in a number of holometabolous insects that altering the resources available at pupation changes the pattern of allocation to adult tissues, but this has not been examined in a life-history context. Using caddis flies (Trichoptera), we show here that the effect of depleted larval resources on the pattern of somatic and reproductive investment is not fixed but varies between species with different life-history patterns. In particular, we demonstrate that, in a long-lived species, thorax size is preserved, which contrasts with the pattern previously observed in a short-lived species. That the adult body can be differentially altered by the same resource depletion in the larvae demonstrates that the allocation of resources amongst body parts is not a consequence of fixed pathways during development. Rather, the allocation of resources during development can occur in a manner consistent with the minimization of the effects on adult fitness.