Reproduction Rate Of Increase Research Articles

Impact of temperature and prey type on biology and life-table parameters of Cheyletus malaccensis Oudemans (Acari: Cheyletidae)

ABSTRACT This study deals with biology and life table parameters of the predatory mite, Cheyletus malaccensis Oudemans were evaluated on three astigmatid mites as prey (i.e. Acarus siro (Linnaeus), Caloglyphus berlesei (Michael) and Tyrophagus putrescentiae (Schrank)) under laboratory conditions. Three constant temperatures (22, 27 and 32 ± 2°C) and constant relative humidity 80 ± 5% were used. Statistical analysis indicated significant difference between prey types and the three different temperatures. The shortest life cycle was recorded on A. siro (11.60 and 8.0 days) at 32°C, while the longest was on C. berlesei (29.5 and 21.2) at 22°C for females and males, respectively. Longest female longevity was on A. siro (43.6 days) at 22°C and shortest was 20.65 days on T. putrescentiae at 32°C. Highest fecundity was found on A. siro (196.50 eggs/female) at 27°C and lowest one was 69.10 eggs/female on C. berlesei at 22°C. The highest net reproduction rate of increase (R0) was 113.2 ♀/♀/generation at 27°C on A. siro. Obtained results suggested that C. malaccensis could develop and reproduce within a wide range of temperatures and prey types. It can also be used as a biological control agent to reduce the amount of acarid mite pests that infest stored commodities.

Influence of temperature on development, reproduction and regeneration in the flatworm model organism, Macrostomum lignano

BackgroundThe free-living marine flatworm Macrostomum lignano is a powerful model organism for use in studying mechanisms of regeneration and stem cell regulation due to its combination of biological and experimental properties, including the availability of transgenesis methods, which is unique among flatworm models. However, due to its relatively recent introduction in research, many aspects of this animal’s biology remain unknown. One such question is the influence of culture temperature on Macrostomum biology.ResultsWe systematically investigated how different culture temperatures affect development time, reproduction rate, regeneration, heat shock response, and gene knockdown efficiency by RNA interference (RNAi) in M. lignano. We used marker transgenic lines to accurately measure the regeneration endpoint, and to establish the stress response threshold for temperature shock. We found that compared to the culture temperature of 20 °C commonly used for M. lignano, temperatures of 25 °C–30 °C substantially increase the speed of development and regeneration, lead to faster manifestation of RNAi phenotypes, and increase reproduction rate without detectable negative consequences for the animal, while temperatures above 30 °C elicit a heat shock response.ConclusionsWe show that altering temperature conditions can be used to reduce the time required to establish M. lignano cultures, perform RNAi experiments, store important lines, and optimize microinjection procedures for transgenesis. These findings will help to optimize the design of experiments in M. lignano, and thus facilitate future research using this model organism.

Influence of Prey Type on the Biology and Life-Table Parameters of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae)

Biological characteristics, life table parameters and predation rate of the predatory mite Neoseiulus californicus (McGregor) under the laboratory conditions of 25 ± 2°C, 75% R.H. and photoperiod of 12L: 12D was studied. Prey types were Brevipalpus phoenicis (Geijskes) motile stages, Tetranychus urticae Koch eggs and motile stages and Tegolophus guavae (Boczek) motile stages. The predator completed developmental stages on tested prey types with a life cycle of 7.02 to 10.25 days. Its developmental time was significantly affected by prey species as T. urticae motile stages shortened its development more than other ones. Female longevity ranged between 16.70 and 28.2 days. Longest female longevity and highest fecundity one was recorded on T. urticae motile stages (49.3 eggs/female), whereas lowest fecundity (12.6 eggs/female) was recorded on motile stages of T. guavae. The highest consumption rate of adult female was 496.2 individuals when fed on T. guavae; while the lowest was 161.2 individuals on T. urticae motile stages. Net reproduction rate of increase (Ro), intrinsic rate of natural increase (rm) and finite rate of increase (λ) were highest on T. urticae motile stages as 35.59, 0.272 and 1.31, respectively.

Male internal reproductive structures of european pea crabs (Crustacea, Decapoda, Brachyura, Pinnotheridae): Vas deferens morphology and spermatozoal ultrastructure

Pea crabs of the subfamily Pinnotherinae (Pinnotheridae) have a high investment in reproduction and an outstanding reproductive output, probably as an adaptation to the required increase in reproductive rate due to the pinnotherids small size and their parasitic, host-dependant way of life. In the present study, we investigate the male internal reproductive structures and the ultrastructure of spermatozoa of Pinnotheres pisum and Nepinnotheres pinnotheres by histological methods and both scanning- and transmission electron microscopy. In the Brachyura, the male internal reproductive systems generally consist of paired testes and corresponding vasa deferentia where spermatozoa develop and mature. Spermatozoal ultrastructure of the investigated pinnotherids conforms to the thoracotreme type, however, N. pinnotheres has an accessory opercular ring and a periopercular rim, neither of which are present in spermatozoa of P. pisum. Spermatozoa are enclosed within spermatophores in the secretory proximal vas deferens. Two types of secretions were observed in P. pisum and N. pinnotheres: an electron dense substance secreted in the proximal vas deferens involved in spermatophore formation, and large electron-luscent vesicles constituting the seminal plasma in the medial and distal vas deferens. The medial vas deferens is strongly widened compared to other brachyurans to purpose storing spermatophores embedded in seminal plasma. Tubular appendices, which produce and store large amounts of seminal plasma, arise from the distal region of the vas deferens. The appendices extend into the ventral cephalothorax and also in the first pleomere. The latter being an exceptional location for reproductive structures among male brachyurans.

Ecological factors driving the higher hedgehog ( Erinaceus europeaus) density in an urban area compared to the adjacent rural area

Our objective was to explore the effect of natural food (earthworms and arthropods) and anthropogenic food (pet food) availability and the risk of predation by badgers on the density and recruitment of the European hedgehog in an urban area and the adjacent rural area located in northeastern France. Hedgehog density was estimated from distance sampling surveys applied to 43 line-transects visited monthly in 2006 and 2007. Hedgehogs were detected by using infrared binoculars. They were captured to be sexed, age-classified and marked. Earthworm, arthropod and pet food availability as well as distance to the nearest badger sett were assessed per transect through field sampling. Hedgehog population density, estimated from the detection of 127 hedgehogs, was 4.4 ± 1.3 individuals km −2 in the rural area and 36.5 ± 15.2 individuals km −2 in the urban area, where transects had lower arthropod biomass, higher pet food availability, and a greater distance from badger setts than in rural area. Adult hedgehog abundance was predicted by earthworm biomass and pet food availability. The number of young per adult female was predicted by arthropod biomass and distance to the nearest badger sett. The high urban hedgehog density did not seem to be mainly induced by an increase in reproductive rate and cannot be fully explained by food resource availability. The effect of variations in road kills and winter mortality factors between urban and rural area are discussed. We concluded that the combination of anthropogenic food and sheltered climatic conditions may provide good situations for hedgehogs and other hibernator species in urbanised environment.

17β-Oestradiol may prolong reproduction in seasonally breeding freshwater gastropod molluscs

Whilst the effects of oestrogenic contaminants in the aquatic environment are well documented in fish, effects in invertebrate species has been subject to debate, possibly due to differences in experimental conditions (temperature, timing and duration of exposure) between studies. It has been suggested that molluscs are only susceptible to oestrogens in periods either following the main spawning or leading up to the maturation of gametes. To investigate this possibility, two temperate, seasonally reproducing gastropods ( Planorbarius corneus and Viviparus viviparus) were exposed to two concentrations of 17β-oestradiol (E2; 10 ng/l and 100 ng/l nominal) in an outdoor mesocosm (subject to natural seasons). In addition, P. corneus was also exposed to E2 (1, 10 and 100 ng/l) in the laboratory at temperatures and photoperiods to simulate summer and autumn. In the mesocosm, both snail species produced similar numbers of eggs/embryos as reference groups in the summer, but the groups exposed to 10 ng E2/l (nominal) had significantly higher productivities after the onset of autumn, when entering their quiescent phase, whilst the snails exposed to a higher concentration (100 ng/l, nominal) had an increased rate of mortality, and did not experience increased reproduction. In the laboratory, the rate of egg laying in P. corneus was unaffected in simulated summer (20 °C, 16 h photoperiod), but snails exposed to 10 and 100 ng/l (nominal) in simulated autumn (15 °C, 12 h photoperiod) showed a concentration-dependent inhibition of the natural decline in egg laying observed in the control snails. Overall, rather than an increase in reproductive rate, the response of this species was a perpetuation of summer reproductive rates into autumn. We conclude that exposure to E2 can affect reproduction in the freshwater gastropods studied, but in P. corneus at least, this is dependent on the seasonal conditions (temperature and photoperiod) at which exposures are made.

Grazing willow ( Salix spp.) fodder blocks for increased reproductive rates and internal parasite control in mated hoggets

A grazing experiment, conducted for 116 days from 19 January to 15 May in the late summer/autumn of 2006 at Massey University's Riverside dry-land Farm, near Masterton (New Zealand), compared effects of grazing willow ( Salix spp.) fodder blocks or perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) pasture, during the pre-mating and mating periods, on gastrointestinal nematode parasite control and reproductive rates in 7-month old ewe hoggets. A rotational grazing system with 348 weaned Romney ewe hoggets was used, with 116 hoggets per treatment (control pasture with regular anthelmintic drenching, control pasture with trigger drenching and willow fodder blocks with trigger drenching). Hogget live weights (LW), dag scores (DS), faecal nematode egg counts (FEC) and reproductive rates at foetal ultrasound scanning, lambing, tail docking and weaning were measured. Total N concentration (35 g/kg dry matter; DM), organic matter digestibility (OMD; 0.68) and metabolisable energy (ME; 10 MJ/kg DM) were similar for fodder block pasture and control pasture; the selected tree fodder had lower concentrations of N (24 g/kg DM) and was higher in OMD (0.74) and ME (10.4 MJ/kg DM). Tree fodder contained higher concentrations of condensed tannins (CT; 22.9 g/kg versus 1.6 g/kg DM) than control pasture and herbage in willow fodder blocks. Grazing willow fodder blocks increased LW gain (approximately 97 g/day versus 86 g/day) and increased reproductive rate corrected to equal LW by approximately 17 lambs/100 hoggets mated, due to increases in both oestrus activity and conception rates (hoggets pregnant/100 mated). Calculated daily DM (1.41 kg) and ME (14 MJ) intakes were similar in all groups. Calculated daily CT intake (6.0 g versus 2.1 g) and CT intake/100 g CP intake (2.2 g versus 0.7 g) were higher for willow fodder block hoggets than for the control pasture groups, and this may have increased the flow of undegraded dietary protein to the small intestine leading to increases in reproductive rates of this group. Grazing willow fodder blocks failed to reduce the number of anthelmintic drenches (3) needed to maintain FEC below 1000 eggs/g wet faeces, but was successful in reducing DS compared to grazing conventional ryegrass/white clover pastures. Grazing willow fodder blocks can be beneficial in sustainable farming systems since tree fodder can sustain growth rates, increase reproductive rates and reduce dag formation in parasitized hoggets.

Ospreys of the Chesapeake Bay: Population Recovery, Ecological Requirements, and Current Threats

The Chesapeake Bay supports the largest Osprey (Pandion haliaetus) breeding population in the world. The population experienced a dramatic reduction due to biocide-induced reproductive suppression in the post World War II era and reached an estimated low of 1,450 pairs by the early 1970s. By the mid 1990s, the population recovered to an estimated 3,500 pairs and breeding was documented on 427 of 878 named tributaries of the tidal Bay. Recovery has been exponential but spatially variable with average doubling times for defined geographic areas varying by more than an order of magnitude. Rates of population growth have been negatively related to salinity with the highest rates occurring within tidal fresh reaches suggesting that recovery has progressed from the main stem of the Bay toward the fall line. Virtually nothing is known about the breeding ecology of Ospreys in the lower saline waters of the Bay. The increase and diversification of man-made structures used for nesting has made a fundamental contribution to recovery and current distribution. A synthesis of information from several field sites throughout the Bay shows a collective increase in reproductive rate (young/active pair) from less than 0.8 in the 1960s to more than 1.2 by the mid-1980s followed by a reduction to below 1.0 in the late 1980s. Threats to the population continue to be the release of new classes of contaminants into the estuary and anthropogenic activities that have the potential to suppress reproductive rates and juvenile/adult survivorship.

Biology and life table of the predatory mite Euseius aizawai (Acari: Phytoseiidae)

Pollens of 19 plant species were used as diets in a laboratory study of the life history of Euseius aizawai (Ehara & Bhandhufalck) (Acari: Phytoseiidae). The mite ingested pollens of all tested plant species and produced eggs. On eight of them the predator completed all developmental stages, with a life cycle of 5.47±0.88 to 6.95±1.61 days. The longest life-span of adults was observed when feeding on pollens of Coriaria sinica , Zea mays , mixed species and Punica granatum . Larvae had a higher survival rate (70% to 82%) when reared with the pollens of Luffa cylindrica , Trachycarpus excelsa , punica granatum and Betula platyphylla. Longevity of adult females was longer with pollens of Coriaria sinica , Zea mays and mixed species . The oviposition period was from 15.05±4.05 to 25.55±15.25 days, the longest when feeding on pollens of Zea mays , mixed species and Coriaria sinica . Fecundity ranged from 23.50±13.50 to 54.50±19.50 per female and the highest was on pollens of mixed species, Luffa cylindrica and Punica granatum . The sex ratio (proportion of females) was highest when feeding on pollen of Luffa cylindrica . The most suitable range of humidities for egg hatching was 70% to 90%. The net reproduction rate of increase (R0) was the highest on the pollen of Luffa.cylindrica , and the intrinsic rate of natural increase (rm) and finite rate of increase (λ) were the highest on the pollen of Trachycarpus excelsa .

Female modulation of reproductive rate and its role in postmating prezygotic isolation in Callosobruchus maculatus

Summary Mechanisms that come into play after mating but prior to fertilization can prevent hybrid formation and thus promote reproductive isolation. Recent research indicates that the evolution of such barriers to gene exchange between incipient forms appears to be common and is essential for speciation. We aimed to test if female Bean Weevils (Callosobruchus maculatus) modulate their reproductive rate and/or remating propensity in response to mating with males with varying degrees of relatedness in a manner that limits the number of ‘hybrids’ produced. We also tested if remating with a male from a female's own population, following a first mating with a foreign male, would elevate egg production. Females varied their egg‐production rate depending on the relatedness of their mates, but this effect was not in the predicted direction. Heterospecific C. analis males actually elicited the strongest reproductive response in females, which resulted in up to 9% higher egg production. Male relatedness did not significantly affect female propensity to remate with a second male. Further, females did not generally show a compensatory increase in reproductive rate following rematings with males from their own population. The mechanisms documented here do not act to limit gene flow and are costly to females, as they suffer reduced life span and egg production late in life following a high reproductive rate early in life. We suggest that sexually antagonistic coevolution within species may have caused the pattern observed.

Effects of willow ( Salix) versus poplar ( Populus) supplementation on the reproductive performance of ewes grazing low quality drought pasture during mating

An 87 days grazing experiment, in the late summer/autumn of 2002 in Masterton (New Zealand), compared the effects of willow ( Salix) versus poplar ( Populus) supplementation (1.3 kg fresh/ewe/day), during mating, on reproductive performance and wool production in ewes grazing low quality drought pasture. A rotational grazing system with 285 mixed age Romney ewes (55.2 ± 0.54 kg) was used, with 95 ewes per treatment (control, willow-supplemented and poplar-supplemented). All ewes were offered about 0.70 kg dry matter (DM)/day of low quality pasture, containing 62% dead matter, with pre- and post-grazing pasture masses of 941 and 456 kg DM/ha. Pasture consumed was typical of drought pasture; 571 g neutral detergent fibre (NDF)/kg DM, 0.540 organic matter digestibility (OMD). Both the willow and poplar diets selected were higher in OMD and metabolisable energy (ME) and had a higher ratio of readily fermentable carbohydrate (CHO) to structural CHO, than the pasture diet selected. Willow contained higher concentrations of condensed tannin (CT; 52 g/kg versus 19 g/kg; P < 0.001) and total phenolic glycosides (34 g/kg versus 17 g/kg; P < 0.001) than poplar. The concentration of total phenolic glycosides increased curvilinearly over time with peak values between 51 and 61 days, corresponding to the mating period. Reproductive rate was low in the control ewes (133 lambs born/100 ewes mated), with willow supplementation reducing live weight (LW) loss (−86 g/day versus −103 g/day) and increasing ewe reproductive rate by 15, 17, 21 and 20% units at ultrasound scanning, lambing, docking and weaning, respectively, through an increase in the proportion of multiple pregnancies (fecundity). Poplar supplementation had no affect on reproductive rate, probably due to contamination with poplar leaf rust ( Melampsora larici-populina), which may produce an unknown oestrogenic substance. There were no treatment effects on wool production and only small treatment effects on the LW of single- and twin-born lambs at birth and weaning. Willow tree trimmings are a beneficial supplement for increasing the reproductive rate of ewes grazing drought pasture during the pre-mating and mating periods and they may be superior to poplar tree trimmings, due to higher concentrations of both CT and phenolic glycosides. Willow supplementation increased the intakes of DM and ME, but this did not explain all of the increase in reproductive rate. The increased concentration of total N, CT, phenolic glycosides and water-soluble CHO in the diet of supplemented ewes would be likely to increase amino acid absorption and this may explain the remainder of the increase in ewe reproductive rate from willow supplementation.

The effect of different levels of poplar ( Populus) supplementation on the reproductive performance of ewes grazing low quality drought pasture during mating

A grazing experiment, conducted for 71 days from 31 January to 12 April in the late summer/autumn of 2001 at Massey University’s Riverside Farm, in Masterton (New Zealand), compared the effect of poplar supplementation ( Populus deltoides × nigra, clone Veronese), during mating, on ewe production and reproduction when grazing low quality drought pasture. A rotational grazing system with 300 mixed age Romney ewes ( 57.1±0.68 kg ) was used, with 100 ewes per treatment. All ewes were offered 0.70 kg dry matter (DM)/day of low quality pasture, containing 84% dead matter, with pre- and post-grazing pasture masses of 1040 and 531 kg DM/ha. Ewes were randomly allocated to three treatment groups, being: high supplementation, low supplementation and control. The high and low treatment groups were offered 1.50 kg/ewe/day (fresh) and 0.75 kg/ewe/day (fresh) poplar cuttings, respectively. The effect of poplar supplementation on liveweight (LW) and body condition score (BCS) change; reproductive rate at pregnancy scanning, lambing, docking and weaning; and wool production and staple length was measured. The poplar diet selected contained 22 g/kg DM of phenolic glycosides and higher levels of nitrogen (N; 28.4 g/kg DM versus 17.8 g/kg DM) and condensed tannin (CT; 7.0 g/kg DM versus 1.5 g/kg DM) and was of higher organic matter digestibility (0.66 versus 0.52) than the pasture diet selected. Voluntary DM intake of poplar progressively increased with time of supplementary feeding for both treatments ( P<0.01), due to increases in both DM content and the diameter of stem consumed. Reproductive rate was low in the control ewes (121 lambs born/100 ewes mated), and poplar supplementation increased ewe reproductive rate by approximately 20 and 30% units for the low and high treatment groups, respectively, compared to the control group, at scanning, lambing, docking and weaning. The increase in reproductive rate in supplemented ewes was due to increases in both conception rate and fecundity, with a higher proportion of pregnant ewes, and a higher proportion of multiple pregnancies, in the supplemented groups. Ewes in the high and low treatments lost slightly less LW (−67 and −71 g/day versus −82 g/day; P<0.05) and BCS (−0.78 and −1.27 units versus −1.31 units; P<0.05) as a result of poplar supplementation, but these differences did not occur in the post-treatment period. There were no treatment effects on wool production or staple length, and only small treatment effects on the LW of single- and twin-born lambs at birth and weaning. Poplar cuttings are a beneficial supplement for increasing the reproductive rate of ewes grazing drought pasture during the pre-mating and mating periods. Poplar supplementation increased intakes of DM, metabolisable energy (ME) and crude protein (CP), and increased the estimated g CP/MJ ME eaten during the mating period. Increased concentrations of total N, CT and water-soluble carbohydrate (WSC) in the diet of supplemented ewes would also be likely to increase outputs of undegradable dietary protein and microbial protein from the rumen, per unit of CP consumed. A combination of these mechanisms, especially the likely increased absorption of protein, probably explains the increased ewe reproductive rate from poplar supplementation.

The effect of different levels of poplar (Populus) supplementation on the reproductive performance of ewes grazing low quality drought pasture during mating

A grazing experiment, conducted for 71 days from 31 January to 12 April in the late summer/autumn of 2001 at Massey University’s Riverside Farm, in Masterton (New Zealand), compared the effect of poplar supplementation (Populus deltoides × nigra, clone Veronese), during mating, on ewe production and reproduction when grazing low quality drought pasture. A rotational grazing system with 300 mixed age Romney ewes (57.1±0.68kg) was used, with 100 ewes per treatment. All ewes were offered 0.70 kg dry matter (DM)/day of low quality pasture, containing 84% dead matter, with pre- and post-grazing pasture masses of 1040 and 531 kg DM/ha. Ewes were randomly allocated to three treatment groups, being: high supplementation, low supplementation and control. The high and low treatment groups were offered 1.50 kg/ewe/day (fresh) and 0.75 kg/ewe/day (fresh) poplar cuttings, respectively. The effect of poplar supplementation on liveweight (LW) and body condition score (BCS) change; reproductive rate at pregnancy scanning, lambing, docking and weaning; and wool production and staple length was measured. The poplar diet selected contained 22 g/kg DM of phenolic glycosides and higher levels of nitrogen (N; 28.4 g/kg DM versus 17.8 g/kg DM) and condensed tannin (CT; 7.0 g/kg DM versus 1.5 g/kg DM) and was of higher organic matter digestibility (0.66 versus 0.52) than the pasture diet selected. Voluntary DM intake of poplar progressively increased with time of supplementary feeding for both treatments (P<0.01), due to increases in both DM content and the diameter of stem consumed. Reproductive rate was low in the control ewes (121 lambs born/100 ewes mated), and poplar supplementation increased ewe reproductive rate by approximately 20 and 30% units for the low and high treatment groups, respectively, compared to the control group, at scanning, lambing, docking and weaning. The increase in reproductive rate in supplemented ewes was due to increases in both conception rate and fecundity, with a higher proportion of pregnant ewes, and a higher proportion of multiple pregnancies, in the supplemented groups. Ewes in the high and low treatments lost slightly less LW (−67 and −71 g/day versus −82 g/day; P<0.05) and BCS (−0.78 and −1.27 units versus −1.31 units; P<0.05) as a result of poplar supplementation, but these differences did not occur in the post-treatment period. There were no treatment effects on wool production or staple length, and only small treatment effects on the LW of single- and twin-born lambs at birth and weaning. Poplar cuttings are a beneficial supplement for increasing the reproductive rate of ewes grazing drought pasture during the pre-mating and mating periods. Poplar supplementation increased intakes of DM, metabolisable energy (ME) and crude protein (CP), and increased the estimated g CP/MJ ME eaten during the mating period. Increased concentrations of total N, CT and water-soluble carbohydrate (WSC) in the diet of supplemented ewes would also be likely to increase outputs of undegradable dietary protein and microbial protein from the rumen, per unit of CP consumed. A combination of these mechanisms, especially the likely increased absorption of protein, probably explains the increased ewe reproductive rate from poplar supplementation.

Acceleration of senescence in the collared flycatcher Ficedula albicollis by reproductive costs

SENESCENCE is the innate deterioration of an organism that leads to a decline in its fitness components such as fecundity and survival expectations with advancing age1,2. Williams3 proposed that the evolution of senescence could be understood in terms of age-specific pleiotropic gene action, where a mutation increases fitness early in life at the expense of reducing it later on. The basic idea, first proposed by Medawar1, is that mutations acting early in life are more sensitive to selection than those acting later, as the early effects would be expressed in more individuals than would the late effects. A cost of reproduction, where an increase in reproductive rate reduces future survival or fecundity, could be the kind of pleiotropic gene action that generates senescence2,3. Evidence exists for such costs in animals and plants4–8, but their role in the evolution of senescence is so far not clear2. Most empirical work has been with fruit-flies in laboratory studies, where selection experiments indicate negative genetic correlations between early and late fitness components9–12. But it is not certain how applicable the results of such studies are to natural populations. Here we report that the clutch size of older individuals in the collared flycatcher Ficedula albicollis is affected by their reproductive effort early in life. This provides empirical support for Williams's idea that costly reproduction accelerates senescence for fertility in a vertebrate species under natural conditions.

Estimation of fertility and fitness in Huntington disease in New England

The advent of presymptomatic and prenatal testing in Huntington disease (HD) may change the reproductive behavior of persons at risk for HD. In order to assess future change, an analysis of fertility and reproductive fitness was carried out on 999 affected and 2,253 unaffected offspring from 235 New England families. Ascertainment biases observed for persons born before 1910 and after 1929 reduced the sample to 250 HD cases and 201 unaffected sib controls born between 1910 and 1929. No increase in reproductive rate was found in HD-affected men compared to male control sibs. A small increase in fertility averaging 0.5 child was seen in HD-affected females compared to unaffected females, but this difference was not significant. The increase in mean number of children for HD females is accounted for in part by a small number of affected women who had very large families. No evidence was found to suggest that any increase in reproductive rate for affected persons was related to offspring being born after HD onset. The fitness of both HD-affected and unaffected females was not significantly different from that of the general population of Massachusetts.

A cost of mating in female fruitflies

COSTS of reproduction occur when an increase in reproductive rate reduces future reproduction by increasing mortality or reducing fertility. Such costs have been demonstrated in plants and animals in laboratory and field studies1–5. Their importance lies in their possible role in the evolution of life histories and of senescence6–15. An understanding of their mechanisms will also reveal the nature of the physiological constraints on longevity and fertility. Most accounts assume that these occur as a result of competition for nutrient allocation between growth, storage, somatic maintenance and reproduction16–21. An increase in reproductive rate would then result in a denial of nutrients to other processes, resulting in a drop in life expectancy or future fertility. Some support for this point of view comes from the finding that lifespan is lengthened in female Drosophila melanogaster that have inactive or absent ovaries22–23 or that are experimentally induced to produce fewer eggs24. Increased exposure to males, however, also results in a drop in lifespan24–26. We show here that mating with males greatly reduces lifespan in female fruitflies whose rates of egg-production and egg-fertility do not differ, suggesting both that simple nutrient allocation to reproduction is not its only physiological cost, and that males can cause females to remate at a frequency that results in reduced female lifetime reproductive success.

Optimal age and size at maturity in annuals and perennials with determinate growth

A model predicting optimal age and size at maturity is presented, exploring the conflict between growth and energy allocation to reproduction. According to the model, the factors promoting delayed maturity and large adult body size are as follows: (1) high rate of somatic growth, (2) high percentage increase in reproductive rate with body size increase, (3) long life expectancy at maturity for annuals or large number of expected productive days (when either growth or reproduction is possible) for perennials with growth ceasing at maturity, (4) life expectancy increasing with body size. All these factors are combined in the mathematical formula predicting optimal age and size at maturity, which allows for quantitative predictions. The optimal schedule of growth and reproduction may be achieved by natural selection, developmental plasticity, or when one species replaces another. Sexual size dimorphism is also discussed, resulting from different optimal age at maturity for either sex.

Is there an increase of reproductive rates in schizophrenics? II. An investigation in Nordbaden (SW Germany): methods and description of the patient sample.

For an investigation on the question of whether fertility rates of schizophrenics have been increasing in recent times, two cohorts of patients were defined on an epidemiological basis. The patients were first admissions during either 1949-50 (n = 183) or 1965-67 (n = 228). The conditions of case definition as well as their demographic and psychiatric characteristics are described. These data are necessary for the evaluation of reproductive rates observed in the patient sample. Furthermore, the two cohorts of patients may be of general interest, because they comprise patients first admitted to a hospital who were completely ascertained in a certain region and time period. They reflect certain changes in hospitalization practice in Germany.

Is there an increase of reproductive rates in schizophrenics? III. An investigation in Nordbaden (SW Germany): results and discussion.

Two cohorts of schizophrenic patients admitted to a psychiatric hospital for the first time either during 1949-50 or 1965-67 were compared with matched controls for reproductive rates before and 13 years after onset of psychosis. Patients of both admission periods had reduced marriage rates. After onset of the disease the rate of reproduction was decreased in males of both periods, but not in females. Patients of both periods did not differ from control values with respect to marital fertility. It has repeatedly been reported that fertility of schizophrenics has been increasing in recent times. Comparison of total reproduction, rate of marriage and marital fertility in patients of the two admission periods and matched controls did not yield any evidence for increasing rates. Instead, the results favour the idea that the patients parallel at a lower level the general decline of birth rates observed in Western Germany.

Is there an increase of reproductive rates in schizophrenics? I. Critical review of the literature.

It is well-known that the fertility of schizophrenic patients, particularly males, is below the population average. The main measures of fertility (reproductivity) are marriage rate, marital fertility, and rate of reproduction. A review of the literature reveals the rate of reproduction of schizophrenic patients to be 30% to 80% of the general population, the reduction being mainly due to reduced probability of marriage. At least one investigation presented evidence for an increase in marriage rate and rate of reproduction in schizophrenic patients relative to the general population in recent time. If this increase were to be confirmed it would undoubtedly have practical as well as theoretical implications. The hypothesis of a compensatory higher fertility of healthy relatives of schizophrenics based on a physiological advantage is empirically unproven. Additionally, the concept of a balanced polymorphism in schizophrenia rests on a superficial analogy with Mendelian traits.