Onset Of Reproductive Maturity Research Articles

Morphological features of the poultry thymus

This article reviews the literature on the morphological features of the poultry thymus. Since the preservation of livestock and disease prevention is a constant problem, the issue of poultry care will always remain in the forefront. Efforts to preserve the population and increase their productivity are directly related to strengthening poultry immunity and the state of their immune system. The study of the morphology of immune system organs allows us to objectively assess the effectiveness of methods for the prevention and treatment of various diseases, as well as to identify critical periods of development of the immune system and the body as a whole. When assessing the immune status of poultry, much attention is paid to the state of lymphoid organs, including the thymus. Currently, aspects related to the dynamics of development of immunocompetent organs during the postnatal period of ontogenesis and the time frame of their involution remain unresolved. Understanding the morphological features of the thymus and its changes is a key element in assessing the function of the immune system. It was found that with the growth and development of chicks, the absolute and relative weight of the thymus increases. However, at the onset of reproductive maturity, these values decrease significantly. Involution of the thymus mass occurs, the boundary between cortical and cerebral substances becomes less distinct, and the cellular composition of the thymus changes. The process of age-related involution is accompanied by a decrease in lymphoid tissue and T-lymphocytes. It is worth noting that the total number of circulating T-lymphocytes remains stable, as this population includes long-lived cells that do not require constant renewal. In this context, there is a change in the ratio of cortical and cerebral substances, the growth of connective tissue stroma and adipose tissue. It is noted that stress factors are one of the causes of early thymic involution, and the degree of development and morphological state of the thymus significantly affect the body's resistance to infections. Changes in the structure and morphometry of the chicken thymus can be an important criterion for the morphological diagnosis of immunodeficiencies in poultry.

Osteohistology and taphonomy support social aggregation in the early ornithischian dinosaur Lesothosaurus diagnosticus

AbstractLesothosaurus diagnosticus is a small ornithischian dinosaur from the Lower Jurassic Massospondylus Assemblage Zone of the upper Elliot Formation of the Karoo Basin of South Africa and Lesotho. The Early Jurassic age, comparatively large sample size, and multiple growth stages of Lesothosaurus make it an excellent taxon for investigating the plesiomorphic condition of ornithischian growth. Here, we examine the osteohistology of an ontogenetic series of Lesothosaurus diagnosticus using multiple limb elements to assess the maximum body size, life history, growth dynamics and potential for sociality in one of the earliest‐branching ornithischian dinosaurs. We found that Lesothosaurus grew rapidly during early and mid‐ontogeny (as shown by its highly vascularized woven‐parallel complex) with its growth rate decreasing between 2–4 years of age, possibly indicating the onset of reproductive maturity. However, an external fundamental system, indicating a cessation in growth, could not be confirmed in any of the individuals studied, suggesting that at 6 years of age, this taxon was still not fully grown. The presence of multiple individuals of varying ontogenetic stages in a monodominant bone bed strongly suggests that it lived in multigenerational herds, indicating that, along with the Venezuelan Laquintasaura venezuelae, social behaviour developed very early in ornithischian evolutionary history.

Modeling the Individual Growth of the Bonnethead Shark Sphyrna tiburo of the Western Gulf of Mexico Using the Multimodel Approach

To describe the growth pattern of the bonnethead shark (Sphyrna tiburo) in the Gulf of Mexico, a von Bertalanffy (VB) model has been automatically fit, which indicated a single−phase continuous growth without oscillations, though this would generate biases if this hypothesis is not confirmed. The objective of this research was to describe the growth pattern of S. tiburo under a multimodel approach based on information theory and contrasting single−phase models (VB, Gompertz, logistic models, and variants) and biphasic models (Soriano model and variants). The VB model was not supported. The Soriano model, with the variant in growth rate (k) and including length at birth (L0), was selected with 100% supporting evidence. The hypothesis of the two−phase growth of S. tiburo with an increase in k, more than L∞, fitted to L0, is confirmed, and a correspondence was identified between growth−phase change sizes and the sizes reported in the literature for change in the juvenile–adult stages in females and for onset of reproductive maturity in males and both sexes.

Sexually dimorphic control of gene expression in sensory neurons regulates decision-making behavior in C. elegans

Animal behavior is directed by the integration of sensory information from internal states and the environment. Neuroendocrine regulation of diverse behaviors of Caenorhabditis elegans is under the control of the DAF-7/TGF-β ligand that is secreted from sensory neurons. Here, we show that C. elegans males exhibit an altered, male-specific expression pattern of daf-7 in the ASJ sensory neuron pair with the onset of reproductive maturity, which functions to promote male-specific mate-searching behavior. Molecular genetic analysis of the switch-like regulation of daf-7 expression in the ASJ neuron pair reveals a hierarchy of regulation among multiple inputs-sex, age, nutritional status, and microbial environment-which function in the modulation of behavior. Our results suggest that regulation of gene expression in sensory neurons can function in the integration of a wide array of sensory information and facilitate decision-making behaviors in C. elegans.

Developmental energetics, sibling death, and parental instability as predictors of maturational tempo and life history scheduling in males from Cebu, Philippines.

Cross-species comparisons show that high extrinsic mortality favors the evolution of "faster" life histories. There is interest in applying this principle to human life history plasticity, based on the idea that psychosocial stressors that correlate with extrinsic mortality accelerate reproductive pace. Most prior studies have been conducted in settings in which psychosocial stressors co-occur with the maturation-accelerating influence of nutritional abundance. We evaluate cues of local mortality (sibling death) or low parental investment (paternal instability; maternal absence) and energetic measures during development as predictors of life history scheduling among males (n = 754) in a Philippine population with marginal developmental nutritional. Males who had more favorable nutritional status during childhood, as reflected in linear growth, skinfold thickness, and caloric intake, were more maturationally advanced in adolescence (all P < 0.05). Taller stature and higher caloric intake during childhood also predicted earlier ages at first sex (both P < 0.01), which persisted after controlling for the effect of nutrition on pubertal maturation. While psychosocial stressors did not predict accelerated maturation, males who as children grew up with an unstable paternal presence had sex earlier (P < 0.05) and tended to become fathers sooner than those with a stable fatherly presence. Those who had a sibling die became fathers sooner than those who did not (P < 0.05). Our findings point to important energetic constraints on the onset of reproductive maturity, while psychosocial stressors accelerate entry to parenthood, which may be comparatively more socially, rather than biologically, constrained. Am J Phys Anthropol 158:175-184, 2015. © 2015 Wiley Periodicals, Inc.

Repression of the Heat Shock Response Is a Programmed Event at the Onset of Reproduction

The heat shock response (HSR) is essential for proteostasis and cellular health. In metazoans, agingisassociated with a decline in quality control, thusincreasing the risk for protein conformational disease. Here, we show that in C.elegans, the HSR declines precipitously over a 4hr period in early adulthood coincident with the onset of reproductive maturity. Repression of the HSR occurs due to an increase in H3K27me3 marks at stress gene loci, the timing of which is determined by reduced expression of the H3K27 demethylase jmjd-3.1. This results in a repressed chromatin state that interferes with HSF-1 binding and suppresses transcription initiation in response to stress. The removal of germline stem cells preserves jmjd-3.1 expression, suppresses the accumulation of H3K27me3 at stress gene loci, and maintains the HSR. These findings suggest that competing requirements of the germline and soma dictate organismal stress resistance as animals begin reproduction.

Physiologic Course of Female Reproductive Function: A Molecular Look into the Prologue of Life.

The genetic, endocrine, and metabolic mechanisms underlying female reproduction are numerous and sophisticated, displaying complex functional evolution throughout a woman's lifetime. This vital course may be systematized in three subsequent stages: prenatal development of ovaries and germ cells up until in utero arrest of follicular growth and the ensuing interim suspension of gonadal function; onset of reproductive maturity through puberty, with reinitiation of both gonadal and adrenal activity; and adult functionality of the ovarian cycle which permits ovulation, a key event in female fertility, and dictates concurrent modifications in the endometrium and other ovarian hormone-sensitive tissues. Indeed, the ultimate goal of this physiologic progression is to achieve ovulation and offer an adequate environment for the installation of gestation, the consummation of female fertility. Strict regulation of these processes is important, as disruptions at any point in this evolution may equate a myriad of endocrine-metabolic disturbances for women and adverse consequences on offspring both during pregnancy and postpartum. This review offers a summary of pivotal aspects concerning the physiologic course of female reproductive function.

Growth Performance, Fillet Quality, and Reproductive Maturity of Rainbow Trout (Oncorhynchus mykiss) Cultured to 5 Kilograms within Freshwater Recirculating Systems

Rainbow trout are commonly cultured within aquaculture systems to one pound or less and marketed as pan- sized fillets. Production of larger rainbow trout provides a distinguishable product. Research that describes the growth performance and fillet quality of large rainbow trout is limited, particularly for trout cultured in recirculating aquaculture systems. A study was conducted evaluating the growth performance and fillet quality attributes of all- female rainbow trout reared using freshwater recirculating systems operated at a mean water temperature of 13°C, under constant lighting, and with around-the-clock feeding. Rainbow trout grew to 4.8 kg in 22 months post-hatch. Growth rates declined with the onset of reproductive maturity. Rainbow trout weighed 5.2 kg at 26 months. The mean ratio of feed provided to biomass gain was 1.36:1 from first feeding to 22 months but increased substantially from 23-25 months. As rainbow trout approached reproductive maturity, 10 fish were collected at specified intervals for assessment of fillet quality attributes. Fillet yield peaked at 20-22 months when trout were 3.8-4.8 kg. Cook yield, cooked fillet firmness, and crude fat decreased; while fillet moisture and raw fillet firmness increased from 24-26 months. Changes in fillet quality coincided with reduced growth rates, decreased feed efficiency, and increasing gonadosomatic index. Two principal components were identified that explained more than 73% of the variation in growth and fillet attribute responses: principal component 1, the growth variable (length, weight, fillet thickness, belly flap thickness, and cook yield) and principal component 2, the quality variable (fillet moisture, fillet fat, and cooked fillet firmness). This research provides rainbow trout growth performance and fillet quality results that can be referenced for the development of recirculating system production plans and for selection of harvest endpoints that balance the requirements of fish farmers and the food industry sector .

Toxicity of magnesium pulses to tropical freshwater species and the development of a duration‐based water quality guideline

Six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Hydra viridissima, Moinodaphnia macleayi, and Mogurnda mogurnda) were exposed to 4-h, 8-h, and 24-h Mg pulses in natural creek water. Magnesium toxicity to all species increased with exposure duration; however, the extent of increase and the nature of the relationship differed greatly between species. Based on median inhibitory concentrations (IC50s), and compared with continuous exposure data from a previous study, the increase in toxicity with increasing exposure duration from 4 h to continuous (72-144 h) ranged from approximately 2-fold for Chlorella sp. and H. viridissima to greater than 40-fold for A. cumingi. Moreover, the form of the relationship between Mg toxicity and duration ranged from linear or near-linear to exponential for different species. The life-stage at which M. macleayi was exposed was important, with cladocerans pulsed at the onset of reproductive maturity being approximately 4 times more sensitive (based on IC50s) than younger than 6-h-old neonates. Species sensitivity distributions were constructed for the 4-h, 8-h, and 24-h pulse durations, from which 99% species protection guideline values (95% confidence limits [CLs]) of 94 (6.4-1360) mg/L, 14 (0.5-384) mg/L, and 8.0 (0.5-144) mg/L Mg, respectively, were derived. These values were plotted against exposure duration (h) and polynomial interpolation used to derive a guideline value for any pulse duration within the range assessed.

Fractionation of stigmasterol derivative and study of the effects of Celsia coromandelina aerial parts petroleum ether extract on appearance of puberty and ovarian steroidogenesis in immature mice

Context: Celsia coromandelina Vahl (Scrophulariaceae) is a shrub found throughout Bangladesh and India, and it is distributed widely in the plains of West Bengal. It is used by the tribal people to treat diarrhea, dysentery, insomnia, skin eruption, fever, syphilis, helminthes infection, and to control fertility.Objective: The objective of this study was to fractionate stigmasterol derivative and to investigate the effects of petroleum ether extract of C. coromandelina (PECC) aerial parts on the onset of reproductive maturity and the ovarian steroidogenesis in immature female mice.Materials and methods: PECC was prepared by hot extraction process and one compound was isolated by preparative TLC from it. PECC was completely freed from solvent and administered in immature female mice intraperitoneally once on every alternate day for nine doses. The sexual maturity was observed by means of vaginal opening, first estrus (days), rate of body growth, changes in weight of ovary, uterus and pituitary. The content of ascorbic acid, cholesterol, Δ5-3β-hydroxy steroid dehydrogenase (Δ5-3β-HSD) and glucose 6-phosphate dehydrogenase (G 6-PDH) activities in ovaries and carbonic anhydrase activity in uterus were measured by means of biochemical technique in control and treated mice. The activity of PECC was compared with standard marker compound ethinyl estradiol.Results: The isolated compound was characterized as stigmasterol derivative. PECC treatment caused a remarkable delay (30.27 and 18.56%, respectively, by low dose) in sexual maturity compared to vehicle control as evidenced by the age of vaginal opening and appearance of first estrus (cornified smear). PECC treatment also caused a significant fall (58.6 and 50.0%, respectively, by low dose) in Δ5-3β-HSD and G 6-PDH activities involved in ovarian steroidogenesis compared to vehicle control. Total cholesterol and ascorbic acid content in ovaries and carbonic anhydrase activity in uterus were increased significantly (low dose by 49.3, 424.6 and 82.4%, respectively) along with a reduction in the weight of ovary, uterus and pituitary in comparison to that of control.Discussion and conclusion: Overall, these results demonstrate that PECC has a good antifertility effect and is responsible for the delayed development of sexual maturity, suppression of ovarian steroidogenesis and elevation of carbonic anhydrase activity in uterus of immature mice. This supports the claim by tribal people as a potential remedy for birth control.

Development of foraging strategies with age in a long-lived marine predator

The development of foraging strategies as animals mature depends upon experience, stage-specific physiology, the onset of reproductive maturity and the reproductive costs incurred by each sex. To understand the ontogeny of foraging behaviour, we compared movement behaviour of 24 young-of-year (YOY) juveniles (12 male, 12 female) with 6 subadult (4 male, 2 female) and 81 adult (43 male, 38 female) grey seals Halichoerus grypus. We used a behaviour discriminating state-space model followed by a series of mixed-effects models to examine trip structure and habitat use in these age classes. In foraging trips, tortuosity and speed of outbound travel were not different in YOY, subadults and adults, suggesting that YOY navigate as well as older animals. On average, however, YOY trips lasted 1.2 to 3.5 d longer and required up to twice as much transit time to reach foraging areas that were 1.5 to 3 times farther from haul-out sites than those of subadults and adults. This sug- gests an overall apparent higher foraging effort for YOY. Differences, however, were highly season- ally dependent. In all groups, apparent foraging effort decreased in the summer and increased in the winter, which is consistent with seasonal changes in prey distribution and energy content. Adult for- aging patterns showed complex seasonal patterns influenced by both reproductive cycles and sea- sonal environmental variation, whereas annual foraging patterns of YOY and subadults, neither of which invest in reproduction, were simpler and appeared more closely tied to seasonal changes in prey availability and condition. Although foraging in the same habitats, male and female YOY showed small but significant differences in movement behaviour and trip structure. These differences are unlikely to be due to size difference, which is minimal at this age, and suggest that sex-related differences in foraging develop early before sexual size dimorphism is significantly expressed.

Brothers delay menarche and the onset of sexual activity in their sisters

The higher costs of sons compared with daughters extends to a negative effect of brothers on the lifetime reproductive success of their siblings in subsistence and preindustrial societies. In societies with fewer resource constraints, one might expect that these effects would be limited or non-existent. This study investigates the costs of brothers and sisters in a contemporary western society of adult Australians. Girls with elder brothers had a delayed age at menarche. Younger brothers were associated with delayed onset of sexual activity in sisters, but not in brothers. Neither younger nor elder brothers influenced fitness parameters (number of pregnancies, number of children, age at first pregnancy or age at first birth) in siblings of either sex. This study provides evidence that brothers negatively affect their sisters' onset of reproductive maturity and sexual activity; however, this delay is not associated with a fitness cost in contemporary Australia. We suggest this is due to the long period of independence prior to child bearing.

Body size dependence of euphausiid spatial patchiness

We analyzed size‐dependent variations in spatial patchiness of the eight numerically dominant euphausiid species in the California Current System (Euphausia pacifica, Nematoscelis difficilis, Nyctiphanes simplex, Thysanoessa gregaria, Euphausia recurva, Euphausia gibboides, Thysanoessa spinifera, and Euphausia eximia). Patchiness was measured by using a count‐based statistic using euphausiid densities and applied to 11 yr of detailed size‐specific enumerations from the California Cooperative Oceanic Fisheries Investigations program. We rejected the hypothesis of size‐independent patchiness for seven of the eight species. The most common pattern observed was a “U‐shaped” curve, showing elevated patchiness in the smallest size classes, a rapid decrease in patchiness of intermediate‐sized euphausiids, and a later increase in patchiness of adults following the onset of reproductive maturity. These size‐dependent changes parallel ontogenetic changes in spatial dispersion observed for some marine fishes. The initial descending limb of the patchiness curve appears to be caused by turbulent diffusion, while the later ascending limb of the curve is consistent with the onset of predator‐induced aggregation behavior. The patterns were surprisingly consistent across years and different reproductive characteristics (egg‐brooding vs. broadcast spawning euphausiids).

Blue sucker stock characteristics in the Wabash River, Indiana–Illinois, USA

Abstract  Blue sucker, Cycleptus elongatus (Lesueur), populations have declined because of habitat degradation and overharvest, and little information exists on the population characteristics and stock dynamics of this species. We examined size and age structure, mortality, growth and condition of blue sucker in the Wabash River, Indiana–Illinois, USA. A total of 356 fish collected by electric fishing from June 2003 to April 2006 ranged from 238 to 775 mm total length and 85 to 5288 g wet weight. Age ranged from 3 to 16 years and annual mortality ranged from 22 to 25%. Annual growth was greatest among younger age classes (range 48–141 mm yr−1) and declined after age 6, likely at the onset of reproductive maturity. Variation in the relative condition factor (range 66–141) was heteroscedastic over the size range of fish sampled, perhaps attributable to seasonal differences in reproductive condition among mature fish.

Affiliative Behavior, Ultrasonic Communication and Social Reward Are Influenced by Genetic Variation in Adolescent Mice

Social approach is crucial for establishing relationships among individuals. In rodents, social approach has been studied primarily within the context of behavioral phenomena related to sexual reproduction, such as mating, territory defense and parental care. However, many forms of social interaction occur before the onset of reproductive maturity, which suggests that some processes underlying social approach among juvenile animals are probably distinct from those in adults. We conducted a longitudinal study of social investigation (SI) in mice from two inbred strains to assess the extent to which genetic factors influence the motivation for young mice to approach one another. Early-adolescent C57BL/6J (B6) mice, tested 4–6 days after weaning, investigated former cage mates to a greater degree than BALB/cJ (BALB) mice, irrespective of the sex composition within an interacting pair. This strain difference was not due to variation in maternal care, the phenotypic characteristics of stimulus mice or sensitivity to the length of isolation prior to testing, nor was it attributable to a general difference in appetitive motivation. Ultrasonic vocalization (USV) production was positively correlated with the SI responses of mice from both strains. Interestingly, several USV characteristics segregated with the genetic background of young mice, including a higher average frequency and shorter duration for the USVs emitted by B6 mice. An assessment of conditioned place preference responses indicated that there was a strain-dependent difference in the rewarding nature of social contact. As adolescent mice aged, SI responses gradually became less sensitive to genetic background and more responsive to the particular sex of individuals within an interacting pair. We have thus identified a specific, genetic influence on the motivation of early-adolescent mice to approach one another. Consistent with classical theories of motivation, which propose a functional relationship between behavioral approach and reward, our findings indicate that reward is a proximal mechanism through which genetic factors affect social motivation during early adolescence.

Sex identification in Encephalartos natalensis (Dyer and Verdoorn) using RAPD markers

All cycads are strictly dioecious with a long juvenile stage. Currently, there is no method available to determine the sexuality of seedlings prior to the onset of cone formation. This study aimed to develop a sex specific Random Amplified Polymorphic DNA (RAPD) marker for Encephalartos natalensis. Initially, 140 primers were used to amplify the bulk DNA of five individuals each of known male and female sexuality. While a high degree of polymorphism was observed in the amplification profiles of male and female plants, only primer OPD-20 generated a specific band (∼850 bp) in female DNA. To validate this observation, this primer was re-tested with 69 individuals of E. natalensis. The 850 bp DNA band was present in all 38 female individuals tested and it was consistently absent in all 31 male plants tested. The result offers a rapid and simple test to determine sexuality of E. natalensis seedlings at early stages of development, before the onset of reproductive maturity thereby saving time and economic resources when cultivating these specimens.

Onset of puberty and ovarian steroidogenesis following adminstration of methanolic extract of Cuscuta reflexa Roxb. stem and Corchorus olitorius Linn. seed in mice

The effect of methanolic extract (ME) of Cuscuta reflexa stem Roxb. and Corchorus olitorius Linn. seed on the onset of reproductive maturity and the ovarian steroidogenesis was studied by means of biochemical techniques. ME of Cuscuta reflexa stem and Corchorus olitorius seed treatment causes a remarkable delay in sexual maturation as evidenced by the age at vaginal opening and apperance of first estrus (cornified smear). The same treatment also results in a significant diminution of Δ 5-3β-hydroxysteroid dehydrogenase (HSD) and glucose-6-phosphate dehydrogenase (G-6-PD) activity along with a reduction in the weight of ovary, uterus and pituitary. On the basis of above data, it is assumed that the probable cause of delayed maturation in ME of Cuscuta reflexa stem and Corchorus olitorius seed treated mice is due to the suppressed ovarian steroidogenesis.

Different early post-settlement strategies between American lobsters Homarus americanus and rock crabs Cancer irroratus in the Gulf of Maine

The abundance of many invertebrates with planktonic larval stages can be determined shortly after they reach the benthos. In this study, we quantified patterns of abundance and habitat utilization of early benthic phases of the American lobster Homarr~s americanus and the rock crab Cancer irroratus. These 2 decapods are among the most common and abundant macroinvertebrates in coastal zones of the Gulf of Maine, with similar densities of larger individuals. Settlement and early postsettlement survival indicate that lobsters are highly substrate-specific early in life, settling predominantly in cobble beds. Crabs appear to be less selective, settling both in cobble and sand. Cumulative settlement of crabs, inferred from weekly censuses over the summer, was an order of magnitude greater than that of lobsters over the same time period. However, only crabs showed significant postsettlement losses. Although the identity of specific predators is unknown, predator exclusion experiments and placement of vacant uninhabited nursery habitat suggested that post-settlement mortality rather than emigration was respons~ble for these losses. The selectlve habitat-seeking behavior and lower post-settlement mortality of lobsters is consistent with their lower fecundity and later onset of reproductive maturity. The patterns observed for crabs, however, suggest a different strategy which is more in accordance with their hlgher fecundity and earlier onset of maturity. It is possible that lower fecundity but greater per-egg investment, along with strict habitat selection at settlement and lower post-settlement mortality, allows adult lobster populations to equal adult populations of crabs. This occurs despite crabs being more fecund and less habitat-selective settlers but sustaining higher postsettlement mortality.

Seasonal Changes in Resightings of Marked, Wild Rhagoletis pomonella (Diptera: Tephritidae) Flies in Nature

We observed individually marked, wild male and female apple maggot flies (AMF) on a host apple tree for 24 days. Although we resighted a fairly high proportion (30.6%) of 599 marked flies, we observed most flies (74.9%) only during the first week after marking and release. Following the onset of reproductive maturity, as evidenced by mating and oviposition, we saw males over more consecutive days than females. This presumably occurred due to male arrestment following contact with female marking pheromone deposited on fruit. Peak diel time of mating by unmarked flies corresponded more closely with peak time of observation of marked males rather than marked females. We estimate some adult AMF may live up to 4 weeks in nature.

LABORATORY EVOLUTION OF POSTPONED SENESCENCE IN DROSOPHILA MELANOGASTER.

Evolutionary genetics seems to have found the fundamental cause of senescence: the decline in the sensitivity of natural selection to gene effects expressed at later ages in most populations of organisms with separate somatic and germline tissue. (Here refers to decline in age-specific fitness-components after the onset of reproductive maturity.) This idea traces back to Haldane (1941) and Medawar (1946, 1952), with considerable elaboration and elucidation since then (Williams, 1957; Hamilton, 1966; Edney and Gill, 1968; Emlen, 1970; Charlesworth and Williamson, 1975; Charlesworth, 1980; Rose, 1983a). While there are still clear limitations to the mathematical formulation of this theory (cf. Hamilton, 1966; Charlesworth, 1980), the basic formal analysis leads to a straightforward conclusion: the first partial derivative of fitness with respect to appropriately scaled changes in age-specific life-history characters usually declines in magnitude with the age of these changes. The force of natural selection thus declines with age. This overall theory and its particular subsidiary variants lead to a number of empirically testable corollaries (Rose, 1983a, 1983b). Some of these corollaries are specific to the subsidiary variants of the theory (Rose and Charlesworth, 1980, 1981a, 1981b; Rose, 1983b), sothattests of them individually do not test the theory as a whole. Fortunately, there are two corollaries which follow from the general theory itself: the reproductive schedule of an outbred population will give rise to natural selection acting to (i) accelerate senescence in populations with a relatively earlier age of reproduction and (ii) postpone senescence in populations with a relatively later age of reproduction (Edney and Gill, 1968; Rose, 1983a). The former prediction has been corroborated by Sokal (1970) using Tribolium castaneum, while the latter has been corroborated by Wattiaux (1968a, 1968b) and by Rose and Charlesworth (1980, 198 lb), using Drosophila species. Once a theory has been well-developed mathematically and then empirically corroborated, attention turns to experiments in which the theory either is not clearly corroborated or is ostensibly refuted. It would be misleading to claim that all relevant experimental results directly corroborate the evolutionary theory of senescence. Sokal (1 970) and Mertz (1975) using Tribolium castaneum and Taylor and Condra (1980) using Drosophila pseudoobscura found heterogeneity between lines in experiments with replication, such that some lines did not exhibit the predicted response to the imposed selective regime. Taylor and Condra (1980) also found a difference in the response of the sexes which was later attributed to the pattern of female mating preference (Taylor et al., 1981). More problematic still are the studies from the Lints laboratory, one of which failed to obtain a direct response to artificial selection for longevity (Lints et al., 1979), while another gave puzzling fluctuations in life-history attributes (Lints and Hoste, 1974, 1977). Lints (1978, 1983) has made a great deal of these problems, contending that they cast doubt on all proposed evolutionary theories of senescence. While it can be argued that these puzzling results are due to technical artifacts such as inbreeding, genetic disequilibrium, and inadequate controls (cf. Rose and Charlesworth, 1981b), the only ef-