Maternal investment and size-specific reproductive output in carcharhinid sharks

1.  Life-history theory predicts that organisms will provide an optimal level of parental investment for offspring survival balanced against the effects on their own survival and future reproductive potential.
2.  Optimal resource allocation models also predict an increase in reproductive output with age as expected future reproductive effort decreases. To date, maternal investment in sharks has received limited attention.
3.  We found that neonatal dusky sharks ( Carcharhinus obscurus ) are not independent from maternal resource allocation at the point of parturition but instead are provisioned with energy reserves in the form of an enlarged liver that constitutes approximately 20% of total body mass.
4.  Analysis of long-term archived data sets showed that a large proportion of this enlarged liver is utilized during the first weeks or months of life suggesting that the reported weight loss of newborn sharks signifies a natural orientation process and is not necessarily related to prey abundance and/or indicative of high mortality rates.
5.  Interrogation of near-term pup mass in two carcharhinids, the dusky and spinner shark ( Carcharhinus brevipinna ), further revealed an increase in reproductive output with maternal size, with evidence for a moderate decline in the largest mothers.
6.  For the dusky shark, there was a trade-off between increasing litter size and near-term pup mass in support of optimal offspring size theory.
7.  For both the dusky and spinner shark, there was a linear increase in near-term pup mass with month, which may indicate variable parturition strategies and/or that carcharhinids are able to adjust the length of the gestation period.
8.  The identification of optimal size-specific reproductive output has direct implications for improving the reproductive potential of exploited shark populations and for structuring future management strategies.     

Experimental food supplementation reveals habitat-dependent male reproductive investment in a migratory bird

Environmental factors can shape reproductive investment strategies and influence the variance in male mating success. Environmental effects on extrapair paternity have traditionally been ascribed to aspects of the social environment, such as breeding density and synchrony. However, social factors are often confounded with habitat quality and are challenging to disentangle. We used both natural variation in habitat quality and a food supplementation experiment to separate the effects of food availability—one key aspect of habitat quality—on extrapair paternity (EPP) and reproductive success in the black-throated blue warbler, Setophaga caerulescens. High natural food availability was associated with higher within-pair paternity (WPP) and fledging two broods late in the breeding season, but lower EPP. Food-supplemented males had higher WPP leading to higher reproductive success relative to controls, and when in low-quality habitat, food-supplemented males were more likely to fledge two broods but less likely to gain EPP. Our results demonstrate that food availability affects trade-offs in reproductive activities. When food constraints are reduced, males invest in WPP at the expense of EPP. These findings imply that environmental change could alter how individuals allocate their resources and affect the selective environment that drives variation in male mating success.     

Habitat and the evolution of social and reproductive behavior in callitrichidae

The numerous remarkable traits characterizing the ecology and behavior of callitrichids have inspired considerable research and discussion of the flexible mating system (cases of monogamy, polygyny, and polyandry), cooperative breeding, reproductive inhibition by dominant females, rapid reproductive rate, significance of dietary differences (gum feeding, frugivory, and insectivory), and demographics and social characteristics of the four genera, Cebuella, Callithrix, Saguinus, and Leontopithecus. The majority of functional explanations evaluate costs, benefits, and alternative strategies but do not address the critical selective forces that led to the behaviors in the first place. In this paper, it is argued that Callithrix and Saguinus evolved to occupy a small insectivore/frugivore niche in secondary growth forest patches (gaps arising from tree falls), and other successional forests and edge habitats; that Cebuella evolved to occupy a gum-feeding/insectivore niche in inundated forest; and that Leontopithecus is above all a small animal predator/frugivore and a mature forest genus. The keys to explanations concerning the evolution of the social and reproductive systems of these animals lie in an understanding of the resource base in these different habitats. Finally, it should be remembered that studies of callitrichids have in the main part been carried out in habitats highly altered by human activities (especially the Brazilian Atlantic forest, home to marmosets and lion tamarins) and are not the environments in which their social and breeding behavior evolved. © 1996 Wiley-Liss, Inc.     

Growth, maturation and reproductive investment in Arctic charr

Size and rates of growth in a cohort of 1 + Arctic charr housed in standard conditions were tracked over 12 months (December to December) and mature and immature males and females compared retrospectively. In both sexes, maturing fish were larger than non-maturing ones. In males, this size differential was the result of differences in growth in winter and early spring, but not in the remainder of the study period. In females, size differentials resulted mainly from growth rate differences immediately prior to breeding. In females but not in males, gonadosomatic index was predicted by growth rates in the months leading up to maturation, and among the females that matured, faster growing fish produced more eggs. Lipid reserves in July were correlated negatively with growth during the previous 7 months and, in females only, lipid reserves were significantly lower in maturing fish than in non-maturing fish, indicating that mobilization of lipid energy reserves in maturing fish had commenced by this time. Variation in investment in gonadal tissue, measured as gonadosomatic index, was not explained by variation in July lipid reserves for either males or females. However, July lipid reserves were negatively correlated with egg number, so females investing more in ova exhibited greater depletion of lipid reserves. These results are discussed in the context of the relationship between body condition and the onset of maturation in salmonids, relative investment in reproduction and sexual differences in the cost of reproduction.     

Reproductive senescence and terminal investment in female Barbary macaques (Macaca sylvanus) at Salem

The reproductive history of 207 female Barbary macaques, living in a large outdoor enclosure in Southwest Germany, was studied during an 11-year period. The results yielded a significant relationship between female age and fecundity, with fertility rates lower than expected among young and old females. Analysis of the reproductive history of individual females revealed a significant decline in fertility from prime age (7–12 years) to mid age (13–19 years), and from mid age to old age (20–25 years). The proportion of long interbirth intervals increased steadily among aging females. Infant survival was not significantly related to maternal age, but offspring of old females showed the highest survivorship. Behavioral observations revealed that old mothers weaned their offspring significantly later than younger mothers, suggesting that prolongation of interbirth intervals is due not only to deteriorating physical condition but also to increased maternal investment, as life history theory predicts. Reproduction ceased during the middle of the third decade of life. Final cessation of estrous cycling invariably occurred 3 or 4 years after the birth of the last offspring, but a postreproductive life span of 5 years appears to be common in this population. Available data suggest that reproductive senescence and menopause are more common among nonhuman primates than widely believed and that both traits are part of an adaptive life history strategy.     

Effect of the nutritional environment and reproductive investment on herbivore-parasite interactions in grazing environments

Parasitism is a serious challenge to herbivore health and fitness.To avoid parasites, herbivores avoid grazing near feces, creatinga mosaic of contaminated tall avoided areas (tussocks) and noncontaminatedshort grazed areas (gaps). The mosaic represents a nutritionversus parasitism trade-off in that feces-contaminated tussocksare localized concentrations of both forage resources and parasites.Here, we use a grazing experiment with a natural tussock–gapmosaic to determine how the nutritional environment and reproductiveeffort affect sheep grazing decisions when faced with this trade-off.There were 3 animal treatments (Barren ewes, ewes suckling asingle lamb, and ewes suckling twin lambs) and 2 environmenttreatments (low and high nitrogen). Sward selection and grazingbehavior were measured using focal observations on grazing ewes.Sheep showed an overall strong and significant avoidance oftussocks across all treatments. However, there was a reductionin the avoidance of tussocks by ewes on the low-nitrogen (low-N)plots. Ewes suckling twins showed a reduced avoidance of tussockscompared with barren ewes. Lactating ewes in low-N environmentsfurther reduced their avoidance of tussocks. Ewes with twins,which are at greatest risk from parasites, had the greatestcontact with feces and thus parasites, especially in low-N environments.We conclude that twin-bearing ewes accept the increased riskof parasitism in order to gain the nutrients required to supportincreased reproductive effort, thus increasing their investmentin current offspring at the cost of increased risk of parasitismand thus future potential reproductive attempts.     

Maternal environment and variation in ovariole number among populations of Melanoplus femurrubrum and M. scudderi scudderi

Ovariole number in univoltine populations of the grasshoppers Melanoplus femurrubrum (De Geer) and M. scudderi scudderi (Uhler) (Orthoptera: Acrididae) from Virginia was studied. Ovariole number in M. femurrubrum was found to vary among three geographic populations, and between years. Ovariole number did not vary between years in one population of M. s. scudderi. Ovariole number in M. femurrubrum was positively correlated with the mean length of the growing season at each site and precipitation during August-September of the previous year (adult season of the maternal generation). In the laboratory, nymphal rearing temperatures did not affect ovariole number in M. femurrubrum, but it was found to be weakly correlated with egg size.

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Résumé Le nombre d'ovarioles des criquets détermine le nombre maximum d'oeufs par ponte. Si la variabilité du nombre d'ovarioles des criquets a souvent été signalée, l'origine de ces variations n'a été examinée que pour quelques espèces migratrices, et cela, au laboratoire.Le nombre d'ovarioles des populations monovoltines de M. femurrubrum a changé suivant les populations et suivant les années. Une étude par régressions multiples a montré que le nombre d'ovarioles est lié à des caractéristiques écologiques de la génération maternelle: durée de la saison de développement, indiquée par la somme des températures au-dessus de 10°C, et précipitations en août et septembre. La durée de la saison de développement détermine le temps disponible pour la reproduction: les populations, aux saisons de développement les plus longues, ont plus de temps pour former une oothèque, et ainsi disposent des moyens métaboliques pour avoir plus d'ovarioles. Août-septembre est l'époque où les criquets deviennent adultes, commencent à s'alimenter avant la ponte, et pondent la majorité de leurs oothèques. On estime que l'effet des précipitations est indirect, par son action sur la quantité et la qualité des plantes-hôtes disponibles. Le nombre d'ovarioles n'est pas lié à la taille de M. femurrubrum ou de M. scudderi scudderi.Les effectifs de M. s. scudderi étaient insuffisants pour permettre de telles analyses; cependant, nous n'avons observé dans une station aucune modification du nombre d'ovarioles au cours des années.

     

Male genotype influences female reproductive investment in Drosophila melanogaster

In many species, males can influence the amount of resources their mates invest in reproduction. Two favoured hypotheses for this observation are that females assess male quality during courtship or copulation and alter their investment in offspring accordingly, or that males manipulate females to invest heavily in offspring produced soon after mating. Here, we examined whether there is genetic variation for males to influence female short-term reproductive investment in Drosophila melanogaster, a species with strong sexual selection and substantial sexual conflict. We measured the fecundity and egg size of females mated to males from multiple isofemale lines collected from populations around the globe. Although these traits were not strongly influenced by the male's population of origin, we found that 22 per cent of the variation in female short-term reproductive investment was attributable to the genotype of her mate. This is the first direct evidence that male D. melanogaster vary genetically in their proximate influence on female fecundity, egg size and overall reproductive investment.     

Ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae

The ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae was studied using light microscopy, scanning and transmission electron microscopy. The results revealed that the female reproductive system of M. matsumurae is composed of a pair of ovaries, a common oviduct, a pair of lateral oviducts, a spermatheca and two pairs of accessory glands. Each ovary is composed of approximately 50 telotrophic ovarioles that are devoid of terminal filaments. Each ovariole is subdivided into an apical tropharium, a vitellarium and a short pedicel connected to a lateral oviduct. The tropharium contains 8–10 trophocytes and two early previtellogenic oocytes termed arrested oocytes. The trophocytes degenerate after egg maturation, and the arrested oocytes are capable of further development. The vitellarium contains 3–6 oocytes of different developmental stages: previtellogenesis, vitellogenesis and choriogenesis. The surface of the vitellarium is rough and composed of a pattern of polygonal reticular formations with a center protuberance. The oocyte possesses numerous yolk spheres and lipid droplets, and is surrounded by a mono-layered follicular epithelium that becomes binucleate at the beginning of vitellogenesis. Accessory nuclei are observed in the peripheral ooplasm during vitellogenesis.     

Age-related decrease in male reproductive success and song quality in Drosophila montana

In the present paper, we have studied the effects of aging onmale reproductive success and song quality in Drosophila montana.We analyzed the reproductive success of wild-caught males attheir normal breeding age during the mating season and aftermaintaining the males in laboratory from 1 to 5 months. In linewith the mutation accumulation theory of aging, none of thefactors affecting the reproductive success of wild-caught malesduring the mating season were related to male longevity. However,mating activity and progeny production of the males decreasedwith male age. Interestingly, there was no significant variationin progeny production between males at their normal breedingage, whereas at older age, the variation between males becomessignificant. The quality of sexually selected song traits deterioratedwith male age in concert with the decrease in male reproductivesuccess. The size of the males did not have an effect on malereproductive success at the normal breeding age, but at olderage, larger males were able to maintain the sexually selectedcarrier frequency of the song at higher level than the smallermales. We conclude that by experimentally extending the reproductiveage of the males beyond that which they normally experiencein nature, it is possible to expose relationships between reproductivesuccess, sexually selected characters, and body size that arenot apparent when analyzed for the males at their normal breedingage.     

Initial reproductive investment and parental body size in Cryptocercus punctulatus (Dictyoptera: Cryptocercidae)

Abstract. Females of the subsocial woodroach Cryptocercus punctulatus Scudder generally have a single oviposition period during which they produce one to four oöthecae. Monogamous pairs and their recently deposited oöthecae were collected in the field, and measured, weighed and analysed for nitrogen in the laboratory. Females put 9.8 ± 2.4% (mean ± SD) of their dry weight and 11.6 ±0.5% of their body nitrogen into oöthecae. The total nitrogen and dry weight of the brood were positively related to the post-oviposition total nitrogen and dry weight of the mother. A female's investment, on a per nymph basis, averaged 0.06% of her post-oviposition dry weight. Females may be able to recover up to 58.7% of the nitrogen invested into a brood by consuming the egg cases after hatch. Overall, there was little variation in the width of head capsules of adults in this species, and this parameter was not significantly different between the sexes. Females were heavier than males (dry weight) (P = 0.06). Within pairs, the weights and nitrogen contents of males and females were positively correlated, probably because they feed together in the same log for nearly a year prior to reproduction.     

Resource tracking in aphids: programmed reproductive strategies anticipate seasonal trends in habitat quality

Most aphids show cyclical parthenogenesis, have short generation times and complete several generations each season. Two hypotheses have been proposed to account for the adaptive seasonal trends observed in the reproductive strategies of aphids. Firstly, individuals of each generation modify their reproductive strategy in direct response to the conditions they experience during their development. Secondly, the reproductive strategies of the different generations are to a large extent programmed and anticipate seasonal trends in habitat quality. These hypotheses were tested by rearing individuals of three generations of the host-alternating willow-carrot aphid, Cavariella aegopodii, on both willow and carrot. This revealed that the way this aphid allocates resources to gonads and lipid reserves is independent of an aphid's weight and the host plant on which it is reared. In addition each generation shows a specific relationship between offspring size and adult size, which tends to keep the absolute investment in individual offspring relatively constant from generation to generation, inspite of the big differences in adult size between generations. That is, through programmed allometric engineering aphids anticipate the predictable seasonal trends in habitat quality and so more closely track their resources, investing relatively more in gonads when food quality is high and relatively more in lipoidal reserves when food quality is poor. Received: 25 August 1997 / Accepted: 19 October 1997     

Unequal maternal investment in offspring quality in relation to predation risk

Equal investment within broods does not always maximize parental reproductive value if the reproductive value of some of the young is low. We examined maternal investment in terms of offspring size in relation to the prospects of survival from predation within broods of the shield bug Elasmucha ferrugata Fabr. (Heteroptera; Acanthosomatidae). Shield bug females guard eggs and first instar nymphs against invertebrate predators by covering the clutch with their body and by behaving aggressively towards their enemies. Survival of eggs was not possible without maternal care. When females were allowed to guard their brood, eggs at the periphery were more vulnerable to predators than eggs at the centre. We found that females laid significantly larger eggs in the safest, central part of the clutch. There seems to be an advantage of large nymph size, since when nymphs were reared separately with low food resources, the larger ones were more likely to survive. Larger nymphs were also more likely to push themselves to the safest, central part of the clutch. Females seem to allocate their resources more to the offspring with the highest probability of avoiding predation. Thus our study supports unequal maternal investment within broods of E.ferrugata.     

Interactions between habitat heterogeneity and food affect reproductive output in a top predator

1. Habitat heterogeneity has important repercussions for species abundance, demography and life-history patterns. While habitat effects have been more thoroughly studied in top-down situations (e.g. in association with predation), their role in bottom-up situations (e.g. in association with food abundance) has been less explored and the underlying mechanism(s) behind the ecological patterns have not commonly been identified. 2. With material from 1993 to 2003, we test the hypothesis that the reproduction of Finnish northern goshawks Accipiter gentilis (L.) is bottom-up limited by habitat composition, especially in situations where the density of their main prey (grouse) is low. Special emphasis was placed on identifying the mechanism(s) behind potential habitat effects. 3. While laying date and large-scale variation in the main prey density (but not habitat composition) were related to the number of eggs goshawks laid, small-scale differences in alternative prey density between different territories later influenced how many young were fledged via the mechanism of habitat-dependent partial-brood loss. As a result of this mechanism, a difference in nestling condition also arose between goshawk territories with differing habitat compositions. 4. As the relative proportions of different landscape elements in a given landscape is a function of large-scale differences in geomorphology and land use, this means that the reproductive performance of goshawks as averaged over larger scales can be understood correctly only in respect to the fact that habitat gradients differ across landscapes. 5. In addition to being one of the first papers identifying the mechanism of partial brood loss as being primarily responsible for the habitat-specific differences in the production of young, this study further illustrates the need to identify small-scale mechanisms to correctly understand the large-scale patterns of reproductive performance in territorial species. The repercussions of the observed habitat effect for local population development are discussed.     

Adaptive allocation of resources and life-history trade-offs in aphids relative to plant quality

The need to allocate a limited amount of energy between different life-history traits is a fundamental assumption in life-history theory. However, it has often turned out to be extremely difficult to measure the competing processes that contribute to costs or benefits for individual organisms. The present investigation begins by analysing how an aphid clonal lineage adapts its reproductive investment to moderate changes in host plant quality (e.g. during the life cycle of its host). Using Centaurea jacea and Uroleucon jaceae as a model plantaphid system, I show that reproductive investment can be far more complex than indicated by dry or wet mass of the gonads alone. The number of embryos of a particular size class or developmental state present in the reproductive system of an aphid is highly flexible and is influenced by the quality of the host plant. Next, the effects of a particular reproductive investment on survival during periods of food deprivation are analysed for aphids originating from host-plants of different qualities. When food stress is severe the ability to rapidly resorb and reallocate resources committed to offspring is important for survival. However, this ability is limited. I argue that, in periods of food stress, young, unsclerotized embryos might serve as a kind of energy buffer similar to a fat body and are therefore not relevant to cost-benefit calculations. However, embryos that are beginning to sclerotize within the ovarioles are not available for resorption and resource reallocation. They compete for nutrients with their mother and contribute to costs. Therefore, it is suggested that the reproductive investment of an aphid should not be equated with reproductive costs in a general al way. The dynamics of adaptive resource allocation and resorption are a key feature of an aphid's life history, and the implications for life-history theory are discussed.     

Survival costs of reproduction predict age-dependent variation in maternal investment

Life-history theory predicts that older females will increase reproductive effort through increased fecundity. Unless offspring survival is density dependent or female size constrains offspring size, theory does not predict variation in offspring size. However, empirical data suggest that females of differing age or condition produce offspring of different sizes. We used a dynamic state-variable model to determine when variable offspring sizes can be explained by an interaction between female age, female state and survival costs of reproduction. We found that when costs depend on fecundity, young females with surplus state increase offspring size and reduce number to minimize fitness penalties. When costs depend on total reproductive effort, only older females increase offspring size. Young females produce small offspring, because decreasing offspring size is less expensive than number, as fitness from offspring investment is nonlinear. Finally, allocation patterns are relatively stable when older females are better at acquiring food and are therefore in better condition. Our approach revealed an interaction between female state, age and survival costs, providing a novel explanation for observed variation in reproductive traits.     

Maternal investment and reproductive success in Chinese water deer

Among cervids, maternal investment, estimated as the amount of resources and care allocated to the offspring, was expected to be related to species body size. Therefore, maternal investment in a herd of captive Chinese water deer Hydropotes inermis, a relatively small species of cervid, was investigated over 3 years. Except during the lactation period, reproductive females spent about 2-fold more time resting than feeding. During lactation, the amount of time spent feeding increased highly (25.3 min/h during lactation vs 17.3 min/h during the gestation period). Females spent less than 30% of time in communal behaviours with offspring. They did not reject alien fawns during this care period. Frequency and duration of suckling events decreased exponentially from the second week onwards. More than 10% of suckling bouts were non-filial. Prenatal investment leads to a mean litter mass (about 12% of maternal mass) higher than in most cervid species. Postnatal investment in fawns represents a daily mass gain of ca. 85 g/d during the first 2 weeks, without any sexual difference. Female production, timing and synchrony of births and survival of fawns characterized reproductive success. Seventy percent of mature females gave birth, with a mean of 1.9 offspring per female. The sex ratio was even. Births were synchronous, 80% of births occurring in 25 days. In this herd, 0.74 fawn per female was successfully weaned and 0.56 fawn per female survived through their first year. Based on these results we conclude that reproductive strategy of Chinese water deer was efficient and characterized by mother-offspring relationships typical of hiders and high levels of pre- and postnatal investments. This strategy seems typical of small species of cervids without marked sexual dimorphism.[Current Zoology 55(2):102-110,2009].