Reduction In Reproductive Output Research Articles

Photosynthetic Characteristics of the C4Invasive Exotic Grass Miscanthus sinensis Andersson Growing Along Gradients of Light Intensity in the Southeastern United States

Miscanthus sinensis, a C4 grass, is an emerging invasive species in open and edge habitats throughout the eastern United States. To assess its ability to invade forest understories, we examined photosynthetic responses of Miscanthus sinensis grown under natural light gradients (5% to 100% full sunlight). Although there was a slight reduction in reproductive output under lower light, Miscanthus sinensis was able to maintain high rates of photosynthesis and positive carbon gain along the entire light gradient. Positive carbon gain at low light was likely due to an increased quantum yield. Photosynthetic induction for all plants was rapid, while stomatal opening during induction was slower. Rates of induction loss were slower than induction gain, and were slower than another major C4 invasive exotic grass, Microstegium vimineum that is shade tolerant. During transient high light events, the combination of rapid induction, maintenance of induction state between sunflecks, and high photosynthetic rates, may allow for greater carbon gain than native understory plants. Miscanthus sinensis possesses some characteristics that allow it to persist in forest understories and to rapidly utilize increases in light availability, rendering it a potentially important invader of southeastern United States forest understories.

An experimental test of body volume constraint on female reproductive output

The body volume constraint hypothesis is a widely accepted notion that explains proximate limitation of female reproductive output, but lacks empirical support. To examine how body volume determines reproductive output, we experimentally manipulated the body volume of female lacertid lizard (Takydromus septentrionalis), to examine whether a reduction in body volume caused a reduction in reproductive output. Clutch size and mass decreased with a reduction in body volume. Reproductive output (residual clutch mass, R(CM)) was negatively related to body volume reduction (BVR) (R(CM)=-0.008BVR+0.225). In contrast, neither egg size nor offspring size was affected by the manipulation. Relative clutch mass was lower in manipulated females than in control females, but the actual physical burden (egg plus pearls) carried by manipulated females was much bigger than that of the control females. A normal clutch of eggs only filled 55% of maternal body volume, whereas manipulated females used 75% of body volume to contain eggs and pearls. Therefore, females are capable of carrying more eggs than a normal clutch. Our observations provide unequivocal empirical support for the maternal body volume constraint hypothesis. In addition, these results suggest that female T. septentrionalis may produce a clutch of eggs that fill the available abdomen space to an optimal level rather than the physical limit.

Reduction in reproductive output and leaf size in Sanguinaria canadensis as a cost of reproduction

Abstract When resources are limited, plants must partition their energetic resources among life history traits such as maintenance, growth, and reproduction. Thus reproduction in a given year may result in lowered growth rates or reproductive rates in subsequent years. This is known as the Principle of Allocation or the Cost of Reproduction hypothesis. In this study, flowering, fruiting, and leaf output were evaluated during two consecutive growing seasons in a population of Sanguinaria canadensis in Fairfax, Virginia. The objective of this field study was to determine if the energetic investments by plants that reproduced in two consecutive years (2003 and 2004 growing seasons) were sufficient to reduce reproduction and leaf size as compared to plants that only reproduced in a single year (2004 growing season). The study area is situated on the west campus of George Mason University on a slope of 11.9% and is divided into three 10 m × 100 m rows, with each row separated from the adjacent row by an unsamp...

The Effects of Artificial Beach Nourishment on Marine Turtles: Differences between Loggerhead and Green Turtles

Abstract Marine turtle reproductive success is correlated with the stability and quality of the nesting environment. Female marine turtles show fidelity to nesting beaches, making artificial beach nourishment practices directly relevant to their recovery. We evaluated the impacts of artificial beach nourishment on Loggerhead (Caretta caretta) and Green turtles (Chelonia mydas) between artificially nourished and nonnourished beaches. We observed reduced nesting success (ratio of nesting emergences to emergences not resulting in nest deposition) for both species. This negative effect lasted for one season in Loggerheads and for at least one season in Green turtles. Physical attributes of the fill sand did not impede nesting attempts. We argue that the decrease in nesting success resulted from an altered beach profile not favorable for nest deposition, which subsequently improved in later seasons as the beach equilibrated to a more natural slope. We observed a 52.2% decrease in reproductive output (hatchlings km−1 yr−1) for Loggerheads one year postnourishment, with a 44.1% increase observed the two seasons postnourishment. In Green turtles, a 0.8% reduction was observed the first season postnourishment, despite a 13% increase in the nonnourished area. The reduction in reproductive output in both cases was primarily a consequence of decreased nesting success, lowering nest numbers. These results reveal stronger negative effects of beach nourishment on Loggerheads compared to Green turtles and the importance of minimizing excessive nonnesting emergences associated with artificial beach nourishment. Nourished areas also experienced more than 600% increase in the number of Loggerhead hatchlings disoriented by artificial lighting over two years postnourishment.

Effect of Ligula intestinalis on the reproductive capacity of Rastrineobola argentea in Lake Victoria

This study examined the potential effect of the cestode Ligula intestinalis on the reproduction of the indigenous cyprinid Rastrineobola argentea in Lake Victoria. Ligula intestinalis had a marked effect on the breeding cycle of R. argentea. The proportion of the infected population in advanced stages of maturation prior to spawning was considerably reduced compared with uninfected fish. Infection by L. intestinalis significantly reduced the fecundity of individual fish, particularly in the 45–60 mm size range; the component of the population that makes the greatest contribution to reproductive output. The reduction in reproductive output of the R. argentea population could potentially affect replenishment of stocks in this important fishery.

Effects of the NMDA receptor antagonist MK-801 on female reproduction and juvenile hormone biosynthesis in the cricketGryllus bimaculatusand the butterflyBicyclus anynana

Apart from regulating insect development, juvenile hormones (JHs) play an important role in insect reproduction, where they initiate vitellogenin synthesis and regulate the uptake of yolk by the ovary. JH synthesis is a tightly regulated process controlled by neurons and peptidergic neurosecretory cells. One of the known stimulatory regulators of JH biosynthesis is glutamate, and its N-methyl-d-aspartate (NMDA) receptor has been recently found in the cockroach Diploptera punctata. In this study we demonstrate a strong reduction in reproductive output in the tropical butterfly Bicyclus anynana and the Mediterranean field cricket Gryllus bimaculatus caused by the NMDA receptor antagonist MK-801. Such inhibiting effects on reproduction could be overruled by the application of JH mimics. In G. bimaculatus, MK-801 inhibits in vitro JH biosynthesis in the corpora allata and reduces in vivo JH haemolymph titres in a dose-dependent manner. These results suggest that JH biosynthesis in the corpora allata is at least in part controlled by an NMDA receptor with Ca2+ as a second level messenger. Based on our findings we consider NMDA receptor antagonists as important tools for manipulating juvenile hormone biosynthesis and therefore for gaining a better understanding of the mechanistic basis of reproduction.

Loss of caudal autotomy during ontogeny of Balkan Green Lizard, Lacerta trilineata

Tail loss is an effective antipredator strategy in many lizards. After loss the tail continues to thrash vigorously and may distract predators away from the escaping lizard. However, autotomy imposes energetic and survival costs (loss of lipid reserves, reduction of reproductive output, impairment of locomotor performance). Autotomy may have been lost when costs exceed benefits, while a substantial reduction or full loss may occur during ontogeny. The Balkan green lizard, Lacerta trilineata is a skilful sprinter despite its robust structure. Predation was simulated in a total of 83 individuals (48 juveniles and 35 adults). All juveniles shed their tail readily while none of the adults autotomized their tails. Post‐autotomy duration of movement and levels of involving metabolites in shed tails were measured. No differences were found on comparison to other Greek lacertids. These findings suggest that autotomic ability is lost ontogenetically in L. trilineata while post‐autotomy energetics seems to be a conservative character.

The effect of transplantation on reproduction in clonal ramets of Goniopora columna on Singapore's coral reefs

Summary Ramets of the coral Goniopora columna (Dana, 1846–1849) were excised from five large colonies at one site south of mainland Singapore and transplanted within the same site and depth (2.3 m); to a more disturbed site closer to the mainland at a similar depth (2.2 m); and to greater depth at both sites (8.9 m and 7.6 m, respectively). Ramets were left for one year, then harvested before the predicted spawning periods. Fecundity (average number of oocytes polyp−1), reproductive effort (average oocyte diameter), and polyp tissue diameter were compared among transplanted clonal ramets, control ramets, and parent colonies. Typically, fragmentation in corals results in reductions in reproductive output because energy is diverted into tissue repair, but in this case reproductive effort and fecundity did not change significantly when ramets were transplanted within the same site and depth. Clonal fragments transplanted to the more disturbed site had significantly fewer oocytes, smaller oocytes and smaller polyps after one year suggesting that energy was diverted away from normal functions in response to stressors in the new environment. Ramets transplanted to 7–9 m bleached at both sites after acute periods of reduced irradiance, resulting in high mortality and reproductive failure in surviving ramets.

Effects of tail autotomy on survival, growth and territory occupation in free‐ranging juvenile geckos (Oedura lesueurii)

Abstract Many animals autotomize their tails to facilitate escape from predators. Although tail autotomy can increase the likelihood of surviving a predatory encounter, it may entail subsequent costs, including reduced growth, loss of energy stores, a reduction in reproductive output, loss of social status and a decreased probability of survival during subsequent encounters with predators. To date, few studies have investigated the potential fitness costs of tail autotomy in natural populations. I investigated whether tail loss influenced survival, growth and territory occupation of juvenile velvet geckos Oedura lesueurii in a population where predatory snakes were common. During the 3‐year mark–recapture study, 32% of juveniles voluntarily autotomized their tails when first captured. Analysis of survival using the program mark showed that voluntary tail autotomy did not influence the subsequent survival of juvenile geckos. Survival was age‐dependent and was higher in 1‐year‐old animals (0.98) than in hatchlings (0.76), whereas recapture probabilities were time‐dependent. Growth rates of tailed and tailless juveniles were very similar, but tailless geckos had slow rates of tail regeneration (0.14 mm day−1). Tail autotomy did not influence rock usage by geckos, and both tailed and tailless juveniles used few rocks as diurnal retreat sites (means of 1.64 and 1.47 rocks, respectively) and spent long time periods (85 and 82 days) under the same rocks. Site fidelity may confer survival advantages to juveniles in populations sympatric with ambush foraging snakes. My results show that two potential fitness costs of tail autotomy – decreased growth rates and a lower probability of survival – did not occur in juveniles from this population. However, compared with juveniles, significantly fewer adult geckos (17%) voluntarily autotomized their tails during capture. Because adults possess large tails that are used for lipid storage, the energetic costs of tail autotomy are likely to be much higher in adult than in juvenile O. lesueurii.

Changes in population biology of two succulent shrubs along a grazing gradient

Summary Heavy livestock grazing in Namaqualand, South Africa, is threatening the region's unique diversity of succulent shrubs. This is especially true in the communally managed lands, where grazing is centred around fixed enclosures (stockposts) in which animals stay overnight. In this study we set out to determine the effects of a semi‐permanent stockpost on the composition of the surrounding vegetation and the mechanisms by which grazing limits the persistence of leaf‐succulent shrub populations. We used the grazing gradient created by a stockpost to examine the impacts of grazing on vegetation composition and changes in mortality, reproductive output and seedling establishment for the leaf‐succulent species Ruschia robusta and Cheiridopsis denticulata. Vegetation composition was found to change from a community dominated by the unpalatable shrub Galenia africana at high grazing intensities to a community dominated by the palatable leaf‐succulent shrub R. robusta at lower grazing intensities. Mortality of the leaf‐succulents R. robusta and C. denticulata was high at the sites closest to the stockpost, while fruit production and seedling germination were substantially reduced over distances of 800 m and 2 km for the two species, respectively. Seedling establishment was not limited by either grazing or microsite availability. Thus reduction in reproductive output is the greatest impact of heavy grazing on these two species. Synthesis and applications. This study demonstrates that marked zonation in vegetation composition and population biology can develop around a fixed stockpost and that the greatest impact of grazing on the two leaf‐succulent species studied is the suppression of flower and fruit production. Consistent suppression of reproductive output could have long‐term consequences for the persistence of succulent shrub populations in the heavily grazed communal lands of Namaqualand. We recommend that (i) herders should be encouraged to relocate their stockposts regularly to prevent the development of centres of degradation, and (ii) areas should be relieved periodically of all grazing pressure to allow for successful seed set of native shrubs.

A longitudinal study of age-specific reproductive output and body condition among male rhesus macaques, Macaca mulatta.

In many mammalian species, male reproductive success appears to climb sharply at young adulthood, form a brief plateau during prime ages, and decline among older animals, a pattern often attributed to reduced physical condition with ageing. However, solid evidence to either substantiate or refute this profile among nonhuman primates is lacking. Here, we combine a decade of genetic analysis of paternity among free-ranging rhesus macaques, Macaca mulatta, with information about body condition in order to evaluate how changes in morphology might govern age-specific reproduction among males. We show that age-specific reproductive success traverses the same life history profile as found in other mammals, but reductions in reproductive output with advanced age were associated with reduced chances of survivorship rather than accompanied by diminished body condition. We demonstrate that variance in male age at onset of reproduction is three times greater than variance in female age at onset of reproduction. We provide the first evidence from primates that age-specific reproductive output among males is not a consequence of age-related changes in body condition, but reflects social and demographic factors.

Effects of eight polycyclic aromatic compounds on the survival and reproduction ofEnchytraeus crypticus(Oligochaeta, Clitellata)

The effects of eight polycyclic aromatic compounds (PACs) on the survival and reproduction of the enchytraeid worm Enchytraeus crvpticus were investigated in an agricultural soil with an organic carbon content of 1.6%. With the exception of acridine, which showed a strong binding to the test soil and a subsequent low toxicity, polycyclic aromatic hydrocarbons and neutral N-, S-, O-monosubstituted analogues showed a similar toxicity to the enchytraeids. Concentrations estimated to give a 10% reduction of reproductive output (EC10 values) were based on measured initial concentrations and were, for acridine, 310 mg/kg; for carbazole, 19 mg/kg; for dibenzofuran, 36 mg/kg, for dibenzothiophene, 40 and 45 mg/kg (two tests); for fluoranthene, 15 mg/kg; for fluorene, 25 mg/kg; for phenanthrene, 40 mg/kg; and for pyrene, 11 mg/kg. Using reported soil-pore-water partitioning coefficients for the substances in question, equilibrium pore-water concentrations could be estimated from the total soil concentrations. Calculated EC10 values, expressed as log10(mmol/L pore water), were negatively related to the lipophilicity (log Kow) of the compounds (r2 = 0.58; p = 0.027, n = 8), thus indicating a rather nonspecific (narcotic) mode of toxic action for these compounds. When compared with literature ecotoxicity data for a springtail (Folsomia fimetaria) tested in the same soil type, enchytraeids generally seem less sensitive.

Effects of eight polycyclic aromatic compounds on the survival and reproduction of the springtail Folsomia fimetaria L. (collembola, isotomidae)

AbstractThe effects of eight polycyclic aromatic compounds on the survival and reproduction of the collembolan Folsomia fimetaria L. were investigated in a well‐characterized Danish agricultural soil. With the exception of acridine, polycyclic aromatic hydrocarbons (PAHs) and neutral N‐, S‐, and O‐monosubstituted analogues showed similar toxicities to soil collembolans when the results were expressed in relation to total soil concentrations (mg/kg). The estimated concentrations resulting in a 10% reduction of reproductive output (EC10 values) were based on measured initial concentrations and were for acridine 290 mg/kg, carbazole 10 mg/kg, dibenzofuran 19 mg/kg, dibenzothiophene 7.8 mg/kg, fluoranthene 37 mg/kg, fluorene 7.7 mg/kg, phenantrene 23 mg/kg, and pyrene 10 mg/kg. When the EC10 values were converted to soil pore‐water concentrations, they showed a highly significant correlation (r2 = 0.71, p < 0.01) to no‐observed‐effect concentrations for the freshwater crustacean Daphnia magna, as estimated by a quantitative structure activity relation (QSAR) for baseline toxicity (nonpolar narcosis). Only carbazole and acridine were more than two times more toxic (4.9 and 3.1, respectively) than expected from the Daphnia QSAR data. The latter result indicates that the toxicity of the tested substances is close to that expected for compounds with nonpolar narcosis as the mode of action. However, the relatively large uncertainties in the extrapolation method prevent final conclusions from being drawn.

Hypotheses of aging in a long-lived vertebrate, Blanding's turtle (Emydoidea blandingii).

For 35 of the past 47 years, Blanding's turtles were studied on the University of Michigan's E.S. George Reserve in southeastern Michigan. Blanding's turtle is one of the longest-lived emydid turtles with individuals reaching ages greater than 75 years. We compared body sizes, reproductive traits and survival of Young, Middle, and Oldest age groups of Blanding's turtles to test predictions from two contrasting hypotheses of aging. The relative reproductive rate hypothesis predicts traits that increase the reproductive output or survival rates of older compared to younger individuals, whereas the senescence hypothesis predicts a reduction in reproductive output or survival in older versus younger individuals. Body size did not increase with age among groups; therefore, indeterminate growth was not a mechanism for increased reproductive output of the oldest individuals. Survivorship, reproductive frequency and size-adjusted mean clutch size were all higher in the Oldest age group compared to the younger age groups. Nest predation rate was highest in the Young age group compared to either group of older turtles. In nests that survived predation, the proportion of nests that failed entirely due to developmental problems was lowest in the Young, intermediate in the Middle, and highest in the Oldest age group. Successful nests produced similar numbers of hatchlings and similar sized hatchlings in all three age groups. Traits such as egg and offspring size, and offspring produced per nest did not support either the relative reproductive rate or the senescence hypothesis of aging. Increased embryo mortality in nests of older females compared to younger turtles supports predictions from the senescence hypothesis. Three traits; increased clutch size, reproductive frequency, and survivorship of individuals in the Oldest age group compared to younger turtles support the relative reproductive rate hypothesis for evolution of longevity.

Effects of eight polycyclic aromatic compounds on the survival and reproduction of the springtail Folsomia fimetaria L. (Collembola, isotomidae).

The effects of eight polycyclic aromatic compounds on the survival and reproduction of the collembolan Folsomia fimetaria L. were investigated in a well-characterized Danish agricultural soil. With the exception of acridine, polycyclic aromatic hydrocarbons (PAHs) and neutral N-, S-, and O-monosubstituted analogues showed similar toxicities to soil collembolans when the results were expressed in relation to total soil concentrations (mg/kg). The estimated concentrations resulting in a 10% reduction of reproductive output (EC10 values) were based on measured initial concentrations and were for acridine 290 mg/kg, carbazole 10 mg/kg, dibenzofuran 19 mg/kg, dibenzothiophene 7.8 mg/kg, fluoranthene 37 mg/kg, fluorene 7.7 mg/kg, phenantrene 23 mg/kg, and pyrene 10 mg/kg. When the EC10 values were converted to soil pore-water concentrations, they showed a highly significant correlation (r2 = 0.71, p < 0.01) to no-observed-effect concentrations for the freshwater crustacean Daphnia magna, as estimated by a quantitative structure activity relation (QSAR) for baseline toxicity (nonpolar narcosis). Only carbazole and acridine were more than two times more toxic (4.9 and 3.1, respectively) than expected from the Daphnia QSAR data. The latter result indicates that the toxicity of the tested substances is close to that expected for compounds with nonpolar narcosis as the mode of action. However, the relatively large uncertainties in the extrapolation method prevent final conclusions from being drawn.

Environmental Stress as an Evolutionary Force

Stressful environmental conditions can be defined as those that lead to a sharp reduction in fitness in populations. That is, when changed environmental con­ ditions cause a drastic reduction in reproductive output, and when persistence of the conditions leads to permanent damage, these conditions constitute an environmental stress. Physical stresses that are encountered rarely in populations-such as periods of drought or extreme cold­ or that are encountered by a minority of a species-such as in populations that are located at distribution borders or are exposed to local chemical stresses arising from human activities-can, through their direct or indirect effects, lead to marked reductions in the size of populations (Glynn 1988, Hoffmann and Parsons 1991) and to repeated cycles of colonization and extinction (Andrewartha and Birch 1954).

Rapid population growth of Great Skuas Catharacta skua at St Kilda: implications for management and conservation

The St Kilda archipelago is a World Heritage Site holding internationally important populations of a number of seabird species. Great Skuas first bred at St Kilda in 1963, and numbers there rose steadily until 1990. Since then, a rapid expansion has occurred, with the population size increasing on Hirta, the main island in the archipelago, at a rate of 22.1% per annum between 1994 and 1997. In total, 233 pairs were occupying territories at St Kilda in 1997. A simple model suggests that as many as 50% of the birds recruited to Hirta between 1994 and 1997 were immigrants from other colonies. Comparison of breeding data collected in different areas gave no indication that the higher nest density resulting from the recent influx was having any detrimental effect on annual productivity and it seems likely that Great Skuas will continue to increase, at least in the near future. Given the importance of seabird prey in the diet of Great Skuas at St Kilda, the continued expansion in numbers of this species gives some cause for concern. However, because immigration plays a large role in the population dynamics of Great Skuas at this site, any attempts to limit population growth by small-scale culling of adults or reduction of reproductive output is unlikely to succeed, and might result in a decline in recruitment at other colonies of this rare and vulnerable species.

Effects of temperature and food quantity on the reproduction of Tisbe battagliai (Copepoda: Harpacticoida)

There are relatively few reports of the influence of environmental factors on the development and reproduction of harpacticoid copepods. In this study, we establish the effect of temperature (15, 20 and 25°C) and food concentration (83–3250 μg of carbon per litre of the alga Isochrysis galbana Parke) on the reproduction of the marine harpacticoid Tisbe battagliai Volkmann-Rocco. Reproductive lifespan, total number of broods and total number of offspring produced were recorded from females reared individually in the laboratory. Reduction in algal concentration from 3250 to 1300 μg C l −1 resulted in significant decreases in the number of broods and offspring produced at 15 and 20°C, but not at 25°C. Algal concentrations lower than 1300 μg C l −1 elicited significant reductions in reproductive output throughout the temperature range. There was an inverse relationship between female lifespan and temperature; females reared at 15°C lived approximately twice as long as those reared at 25°C. Increases in temperature (15–25°C) and algal concentration (520–3250 μg C l −1) resulted in a reduction in the time interval between hatching of successive broods. Larger brood sizes were observed with increased algal concentration, however, there was no clear trend of temperature on brood size. The implication of these results to the development of harpacticoid populations in the natural environment is discussed.

Reproductive effort and success are related to haematozoan infections in blue tits

The associations between reproductive effort, as assessed by variation in natural clutch size and experimentally altered brood size, breeding success, and prevalence of blood parasite infections were studied in blue tits, Parus caeruleus. Females infected with blood parasites during incubation had laid significantly smaller clutches than non-infected females, irrespective of female age and laying date. Infected and non-infected females did not differ in the length of incubation delay, the time spent incubating eggs, or in fledging success. However, nestlings reared by females that had infections during incubation fledged in significantly poorer condition than nestlings reared by non-infected females. These findings are consistent with the interpretation that parasites had a negative impact on their blue tit hosts, but they do not exclude the possibility that the prevalence of haematozoans and reduction in reproductive output (clutch size) and success (fledging condition) were independently triggered by some third factor (e.g., energetic stress caused by variation in territory quality). However, the prevalence of parasites at day 14 posthatch was related to experimentally altered brood size: adult females and males rearing enlarged broods were more likely to be infected than those rearing control or reduced broods, although the opposite was true for juvenile females and males. From our results, we suggest that a naturally low reproductive output (clutch size) may be an indicator of low individual quality, and that there may be a trade-off between reproductive effort and immunocompetence.

Interactions between Halipegus occidualis and Its Ostracod Second Intermediate Host: Evidence for Castration?

Interactions between metacercariae of Halipegus occidualis and ostracod second intermediate hosts (Cypridopsis sp.) were examined over 5 wk using female ostracods exposed to 4 cercariocysts each and maintained in isolation. Control ostracods were subjected to the same manipulations but were not exposed to cercariae. Growth of metacercariae over 4 wk was not constrained by either infection intensity or ostracod size. The number of eggs produced by ostracods was significantly reduced by the presence of metacercariae in an intensity-dependent manner. This reduction in reproductive output, combined with a significantly higher survivorship of exposed ostracods, suggests infection by H. occidualis may result in ostracod castration. These effects are considered to be the result of persistent ancestral traits rather than adaptation.