Start Of Reproduction Research Articles

Effects of the temperature during embryonic development on adult reproduction and the phenotype of the second generation in zebra finches

Across taxa, the temperature experienced by individuals early in life can have large effects on their development. However, comparatively little is known about whether the effects of this thermal developmental environment can be long-lasting or transgenerational. In birds, one important aspect of the developmental environment is incubation and, in general, eggs incubated at low temperatures produce offspring with smaller morphology, suboptimal physiology, and even lower long-term survival. Yet, little is known about whether incubation temperature may affect avian reproduction in adulthood, and nothing is known about whether the effects of avian incubation temperature may be transgenerational. To investigate this, we incubated zebra finch (Taeniopygia guttata) eggs at two different temperatures: 37.5 °C (‘control’) and 36.3 °C (‘low’), raised nestlings until adulthood, and allowed same-temperature treatment pairs to reproduce. We found that F1 individuals incubated at the low temperature had shorter beaks at the start of reproduction than those incubated at the control temperature. Further, compared to those from control parents, F2 offspring from parents incubated at the low temperature had lighter body masses at 5 days-old and had shorter beaks at 30 days-old. However, we found little evidence that incubation temperature affected other aspects of reproduction, with no effect on latency to lay, clutch size, egg mass, incubation period, hatching success/asynchrony, fledging, or the number of offspring that ultimately survived until independence. Overall, we found some evidence that a difference in the early thermal developmental environment can have lasting morphological effects into the next generation. However, future work is needed to determine whether the incubation temperature that birds experience as embryos may influence parental care behaviors or lifetime reproductive success.

Dissociable neural indices for time and space estimates during virtual distance reproduction

The perception and measurement of spatial and temporal dimensions have been widely studied. Yet, whether these two dimensions are processed independently is still being debated. Additionally, whether EEG components are uniquely associated with time or space, or whether they reflect a more general measure of magnitude quantity remains unknown. While undergoing EEG, subjects performed a virtual distance reproduction task, in which they were required to first walk forward for an unknown distance or time, and then reproduce that distance or time. Walking speed was varied between estimation and reproduction phases, to prevent interference between distance or time in each estimate. Behaviorally, subject performance was more variable when reproducing time than when reproducing distance, but with similar patterns of accuracy. During estimation, EEG data revealed the contingent negative variation (CNV), a measure previously associated with timing and expectation, tracked the probability of the upcoming interval, for both time and distance. However, during reproduction, the CNV exclusively oriented to the upcoming temporal interval at the start of reproduction, with no change across spatial distances. Our findings indicate that time and space are neurally separable dimensions, with the CNV both serving a supramodal role in temporal and spatial expectation, yet an exclusive role in preparing duration reproduction.

Contribution of Reproduction Management and Technologies to Genetic Progress in Horse Breeding

Reproductive technologies aim at improving fertility with the ultimate result of improving genetic selection. In equidae, the respective contribution of different methods of horse management and breeding to genetic progress remain difficult to evaluate as breeding strategies affect the number of offspring per mare or stallion whereas different selection methods (based on pedigree, performance, genomics or progeny’s performance) will be applicable at different ages, leading to different accuracy in the estimation of the breeding value. Here, a mathematical model was applied to evaluate theoretical genetic progress depending on breeding conditions in horses. The model showed that for breeding systems ranging from 0.6 to 2 foals/year/mare and from 10 to 150 foals/year for stallions, when selection of the best animals is strictly made by a truncation, the genetic progress is accelerated by (1) increasing the number of offspring per year, (2) the start of reproduction as soon as the age of 2 in both sexes, and (3) reducing the number of years of use for stallions from 10 to 5 years. The calculation showed that using all ways of improvement could provide an increase in genetic progress of up to +270% and +226% in mares and stallions, respectively, above the basal reference situation of 100%. In the Selle Français breed, the observed reproductive management parameters (10 years generation interval, 10 foals/stallion and 0.55 foals/mare) are close to the worst conditions of the model. In addition, the best mares are not selected for breeding. In conclusion, new reproductive technologies, genomic selection, and breeding younger animals will increase genetic gain.

Структура разнообразия по вегетативной и генеративной структуре кроны кедра сибирского на плантации с разреженной посадкой

Studies of the diversity of economically valuable traits in forest tree species are of great interest not only for forest selection and practical silviculture, but also important as a general biological problem. Among the objects of attention of breeders, a special place is occupied by cone-bearing species such as Siberian stone pine. Its cultivation through the forest tree plantations for wood and for cone-bearing will allow in the future to reduce the damage for natural ecosystems significantly. The purpose of this work was to analyze the structure of diversity in growth and generative development of the Siberian stone pine crown on a specially created plantation, where a low level of natural selection makes it possible to more efficiently select for early reproduction, growth and seed productivity. This plantation is located in the south of the area (Western Siberia, south of Tomsk region). It was created from stone pine seeds of the local population, that were sown in 1977 as forest crops with standard density (0,75 х 3 м). At the age of 10, they were planted out at a distance of 8 x 8 m. The vegetative and generative development of 89 trees aged 40 years was analyzed. We used a retrospective method that allows reconstructing of the tree organogenesis and growth on the scars on the bark of the shoots. The start of sexual reproduction has been reconstructed; a comparative characteristic of the vegetative and generative development of the tree crown has been carried out. The results show that, in general, the initial idea of the dependence of the efficiency of selection on the conditions in which the trees were formed is confirmed. In the natural dense stands, many of the leader trees in cone-bearing, which we found in our study, could fall behind due to slow growth and did not live to reproductive age. On the plantation where sparse tree planting was applied, they survived and became the leaders in cone-bearing. Early start of reproduction, even under conditions of sparse tree planting, is positively correlated with the growth rate in the pre-generative period of ontogenesis (r = + 0.65). The level of variations in the generative development of trees was much higher than in the vegetative one. The abundance of male shoots in the crown and the relative length of the male generative zone of crown were determined primarily by the height of the trees. On the contrary, the active growth of the tree in height did not have a noticeable influence on the development of the female shoots and the female generative zone of crown. Contrasting differences in the traits of male and female crown development with growth traits are very interesting result, in our opinion. Tall trees with a narrow crown are most promising for pollen productivity breeding, since they have a longer male generative zone and because of this they have more male shoots in the crown. Trees with a broad crown are promising for seed production breeding. Although seed productivity is not in all cases a direct function of the size of the crown, but depends on the specific genotype of the tree. This is confirmed by the fact that in each group (high, medium and low trees) there are individuals of high-cone-bearing and low-cone-bearing, which is promising for seed production breeding in groups of different growth levels. Using the calculated relative traits «1 m2 of the area of the horizontal projection of the crown onto the ground surface» made it possible to select the best trees for seed production (combining the minimum size of the crown with the number of cones per unit area of the crown) and growth (combining greater height and narrow crown).For citation: Velisevich S.N., Popov A.V. Pattern of diversity in the vegetative and generative crown structure of the siberian stone pine on a seed orchard with sparse tree planting. Lesnoy Zhurnal [Forestry Journal], 2019, no. 5, pp. 35–47. DOI: 10.17238/issn0536-1036.2019.5.35Funding: This work is supported by the Russian Science Foundation under grant no. 18-16-00058. The article is published within the framework of implementation of the scientific journals development program in 2019, based on proceedings of XIX International conference of the young scholars “Forests of Euro-Asia – The Southern Ural” (August 25-30, 2019. Chelyabinsk).

Exposure to the azo dye Direct blue 15 produces toxic effects on microalgae, cladocerans, and zebrafish embryos.

Aquatic pollution caused by dyes has increased together with the growth of activities using colorants such as the textile, leather, food, and agrochemicals industries. Because most popular azo dyes are synthesized from benzidine, a carcinogenic compound, a threat to aquatic biota could be expected. The use of single species for toxicity assessment provides limited data, so a battery of test organisms, including representatives of different trophic levels such as algae, zooplankters, and fish, could undoubtedly provide more information. Therefore, our study was aimed at evaluating the toxic effect of the azo dye Direct blue 15 (DB15) on a battery of bioassays using a primary producer (Pseudokirchneriella subcapitata), a primary consumer (Ceriodaphnia dubia), and a secondary consumer (Danio rerio). P. subcapitata was more sensitive to DB15 (IC50 = 15.99 mg L-1) than C. dubia (LC50: 450 mg L-1). In the algae exposed to DB15, chlorophyll-a and -b were significantly increased, and carotenoids were reduced. The concentrations of protein, carbohydrates, and lipids per cell in P. subcapitata exposed to all DB15 concentrations were significantly higher than that measured in control. At 25 mg L-1 of DB15, survival, total progeny, and the number of released clutches were significantly decreased, and the start of reproduction was delayed in C. dubia. DB15 did not induce lethal or sublethal effects in D. rerio embryos at any of the tested concentrations from 24 to 72 h post-fertilization (hpf), but from 96 to 144 hpf, the larvae exposed to 100 and 500 mg L-1 developed yolk sac edema, curved tail, and skeletal deformations. After 144 hpf, DB15 produced a significant increase in embryos without a heartbeat, as the concentration of dye raised. The textile-used, azo dye DB15, caused toxic effects of different magnitude on microalgae, cladocerans, and zebrafish embryos; for this reason, the discharge of this colorant into waterbodies should be regulated to prevent environmental impacts.

Variación espacial de la unión conyugal de los jóvenes en México

La unión conyugal es un eje organizador de la vida de las personas y de una sociedad. En México este evento es clave en el proceso de transición a la vida adulta. En muchos casos articula la salida del hogar y el inicio de la reproducción. Se sabe que en el ámbito nacional su temporalidad se ha postergado, pero poco se sabe sobre ella a nivel subnacional. En esta investigación se analiza la variación espacial de la proporción de jóvenes unidos conyugalmente. Se busca identificar la manera como influyen la desigualdad regional y la heterogeneidad cultural sobre la asunción de los roles adultos.

Variability in reproductive effort of a keystone species: age and height of branch establishment

Carnegiea gigantea (saguaro, Cactaceae) is a protected and keystone species in the Sonoran Desert upon which nearly all of the ecosystem’s fauna rely. Little is known about its branching habits, which are particularly important as branching is directly related to seed production. This study assessed the ages and heights of plants when branching commenced under four different environmental regimes. Significant variations were observed in the onset of branching across the populations by both age (78–139 years) and height (4.4–5.5 m), likely related to the interplay between summer precipitation (and thus growth rate) and winter precipitation, which increases branching in any given individual. In all four populations, branches developed from areoles that are themselves reproductive (past or present); i.e., the lower areoles that pre-date the start of reproduction do not appear to contribute to branch production. Further, unlike the wide range of ages at the start of branching, the delay between the start of fruiting and the production of branches appears to be relatively consistent across populations, hovering around a 30-year time lag. Of greatest concern is the advanced age (around 140 years) at which branching begins at the most marginal, arid site, which is around the same time that old-age mortality may set in for the species (generally), dramatically diminishing reproductive output in an already marginal population. If this keystone species declines in this already arid to hyper-arid environment, it would have dramatic and irreversible consequences for the fauna and the ecosystem in this region.

Spatial Ecology ofScaphiophryne gottlebeiin the Canyons of the Isalo Massif, Madagascar

The Rainbow Frog Scaphiophryne gottlebei lives within the humid canyons that cross the Isalo Massif, central-southern Madagascar. Knowing that a single haplotype dominates the largest part of its distribution range raised questions about the dispersal ability of the species. We affixed external radio transmitters to 36 individuals of S. gottlebei to understand whether the adults of this species actively displaced from the canyon they inhabit. We studied 13 males and 7 females in 2009 and 7 males and 9 females in 2011 over two periods (November-December 2009 and January-February 2011). Study sessions were chosen due to the different meteorological conditions: the first is the beginning of the rainy season, which corresponds to the start of reproduction; and the second being the end of the rainy season, which corresponds to a wetter period during which individuals are more likely to be feeding in order to increase body weight. Our results revealed that there is no significant difference in the activity patterns between sexes and that rain and temperature stimulate the dispersal rate. The distance covered by the individuals did not differ between males and females; the range varied from a few centimeters to approximately 50 m, although two individuals displaced more than 100 m in a single day. These data suggest that individuals of this species are quite phylopatric to the canyons they inhabit. The generalized haplotype sharing observed might then be explained by passive dispersal of larvae and metamorphosed individuals during the intense cyclonic floods.

Baltic Dunlin (Calidris alpina schinzii Brehm) on Kurgalsky Peninsula: features of biology, the annual cycle, and factors of the environment limiting its distribution in the eastern part of the Gulf of Finland

This paper presents the description of the breeding biology of Baltic Dunlin on the Kurgalsky Peninsula (eastern part of the Gulf of Finland). Variability of terms of the arrival and start of reproduction and their dependence from the process of spring events in the Baltic region was studied. These parameters were compared with data from other parts of the area. The essential delay of terms of the arrival and start of reproduction of Baltic Dunlins is observed in process of movement to the north-east of the breeding area. At that, the time of the termination of eggs laying everywhere is dated for the last dates of May – beginning of June, and flying away of young and adult birds everywhere finished by the end of June – beginning of July. In north-east areas, there is an essential reduction of the period of eggs laying and, especially, the prebreeding period. Important factors of dynamics of natural habitats of Baltic Dunlins are the effect of winter shearing of ice and of the autumn storms, interrupting vegetative successions at early stages of their development. Recommendations to the protection of this subspecies are given.

Resource use for reproduction depends on spring arrival time and wintering area in an arctic breeding shorebird

Resources for egg production may come from body reserves stored before breeding (“capital breeders”) or from food acquired at the breeding site (“income breeders”). Arctic migrants were long thought to be capital breeders, because they often arrive at a time when local food availability is still limited. However, later evidence suggested that arctic breeding shorebirds are primarily income breeders, or that they use a mixed strategy depending on laying date. We explored the relationship between laying date and resource use for reproduction in the pectoral sandpiper Calidris melanotos breeding in the Alaskan arctic by contrasting carbon isotope (δ13C) values of the local diet and of maternal plasma, cellular blood, feather and claw with those of the eggs produced. Our results revealed that early breeding females utilize resources for egg production that were acquired recently at staging areas, whereas later breeding females mostly relied on nutrients derived from local food sources. These findings suggest that the resource allocation strategy used for reproduction differs among females, and varies depending on the timing of arrival and the start of reproduction. The arrival date at the breeding ground and laying date may critically depend on non‐breeding season events such as winter habitat choice, staging areas or migration routes. By comparing maternal feather δ13C, claw δ13C and feather δD, we examined whether non‐breeding season events influenced the use of resources for egg production through variation in capture date or clutch initiation date. Female pectoral sandpipers originating from moulting areas characterized by higher (more positive) δD signatures were caught earlier and started laying earlier, and they used stored resources for reproduction. Using regional maps of δD values for precipitation in the wintering sites in South America, we compared the spatial variation in the observed feather δD signatures. This analysis indicated that female pectoral sandpipers with higher δD signatures, presumably coming from more north‐easterly wintering sites in southern America, started laying earlier and used mostly stored resources for egg production, compared to females that wintered (or at least moulted) further south. Our results thus show that winter moulting habitat is linked to breeding resource allocation strategy in this high‐arctic breeding shorebird.

A comparison of the response of Simocephalus mixtus (Cladocera) and Daphnia magna to contaminated freshwater sediments

The southeast region of Mexico is characterized by intensive oil industry activities carried out by the national public enterprise Petróleos Mexicanos (PEMEX). The freshwater lagoon “El Limón”, located in the municipality of Macuspana, state of Tabasco, Mexico, has received over 40 years discharges of untreated waste waters from the Petrochemical Complex “Ciudad PEMEX”, located on the border of the lagoon. To assess the toxicity of the sediments and, hence, to obtain information on the biological effects of these contaminating discharges, the cladoceran Simocephalus mixtus was used as a test organism in acute (48 h) and chronic (12 d) toxicity assays. For comparison purposes, bioassays were also conducted with the reference cladoceran Daphnia magna. The sediments of this lagoon contain important amounts of metals and hydrocarbons that have been accumulated over time; however, the acute tests only registered reduced lethal effects on the test organisms (maxima of 10% and 17% mortality for D. magna and S. mixtus, respectively). This may be due to low bioavailability of the pollutants present in the sediments. On the other hand, partial or total inhibition and delay in the start of reproduction, reduction in clutch sizes, reduced survival, as well as reduction in the size of adults and offspring were recorded in the chronic assays. The most evident chronic effects were found in S. mixtus; in this species, reproduction was inhibited up to 72%, whereas D. magna was only affected by 24%. We determined that S. mixtus is a more sensitive test organism than D. magna to assess whole-sediment toxicity in tropical environments, and that chronic exposure bioassays are required for an integrated sediment evaluation. The sediments from “El Limón” lagoon induced chronic intoxication responses and, therefore, remediation measures are urgently needed to recover environmental conditions suitable for the development of its aquatic biota.

Start of reproduction and allozyme heterozygosity in Pinus sibirica under different techniques of artificial forest stand establishment

Siberian stone pine (Pinus sibirica Du Tour) is one of the main forest-forming tree species in boreal forests of Eurasia. Large edible seeds of this species have an important resource value because of their high nutritious properties. Development of approaches to establishment of early cone producing Siberian stone pine stands including utilization of corresponding genetic background is one of the priorities of forest resource management. The goal of our study was to evaluate the effect of stand density on the differentiation of trees by the age of first reproduction and the relationship of allozyme heterozygosity and morphological traits variability in Siberian stone pine. Morphological and allozyme variability in artificial Pinus sibirica stands with high and low density was investigated. In the high-density stand the distance between trees was 0.7 and 3 meters (4080 trees per ha) while in the lowdensity stand it was 8 and 8 meters (144 trees per ha). Age of formation of first male and female cones was evaluated by retrospective method based on analysis of tracks of cones on a shoot bark. Tree height, diameter and number of male, female and vegetative shoots in a crown of model trees were measured. Genotypes of the trees were determined by 29 isozyme loci coding for 16 enzymes (ADH, FDH, FEST, GDH, GOT, IDH, LAP, MDH, MNR, PEPCA, 6-PGD, PGI, PGM, SDH, SKDH, SOD). In the low-density stand, the portion of generative trees was higher and differentiation of trees by age of reproduction starting was lower in spite of the smaller age of trees as compared to the high-density stand. In both samples, the age of formation of first generative organs was related negatively with stem height, stem diameter and number of female shoots. In the high-density stand, positive relation of age of first reproduction with total number of shoots and number of male shoots was found. In both samples nonreproductive trees were less heterozygous at isozyme loci as compared to trees starting cone production. Allozyme heterozygosity correlated positively with the age of first cone production in the high-density stand only. We conclude that the degree of competition between trees due to different stand density determined age and timing of first reproduction and development of tree crowns. The relationship of allozyme heterozygosity and the age of first reproduction was expressed more in the high-density stand of Siberian stone pine.

Variation in age and height of onset of reproduction in the saguaro cactus (Carnegiea gigantea) in the Sonoran Desert

The objective of this study is to determine the height and age at which reproduction begins (i.e., production of flowers and fruits; the transition to adulthood) in the giant saguaro cactus (Carnegiea gigantea) in four geographically and environmentally distinct populations, and to relate observed variability to environmental differences. The onset of reproduction has been estimated at a height of 2.2 m in near optimal conditions. This value has been widely accepted and applied to populations in less optimal conditions, although variations under less ideal conditions have not been investigated. In addition, previous research has demonstrated that Carnegiea growth rates are highly variable over their range. Thus, even if 2.2 m is a consistent transition height to adulthood over their range, the age of individuals in different populations would be different. I investigate the age and height at which this transition occurs. The author sampled the heights of the shortest reproductive individuals and the tallest non-reproductive individuals to estimate the mean height of the onset of flowering in each of four locales in the northern Sonoran Desert. Using a previously published age-height-growth model, the mean age of the start of reproduction was also computed for the four sites. ANOVA and t-tests were used to compare the average transition to adulthood across sites by both age and height. Statistical results are robust and significant variations in the onset of reproduction are observed by both age and height across the four sites. Saguaro National Park and Organ Pipe Cactus National Monument individuals are transitioning to adulthood, on average, at younger ages and shorter heights than the other two locales. At the arid and marginal Kofa site, individuals that established during the regeneration peak of the late 1800s-early 1900s are only now becoming reproductive (individuals that established around 1899), while at Saguaro National Park, on average, individuals that established in the 1950s are already transitioning to adulthood. These results have implications for regeneration, particularly in marginal locales where regeneration is already limited.

Functional change in the swimbladder with fish size in Coryphaenoides acrolepis

One common macrourid fish, Coryphaenoides acrolepis, was analyzed to examine the relationship between the length of the rete mirabile (RmL) and water depth with fish size. The relationships differed when specimens were divided into two size classes based on pre-anal fin length (PAF). The RmL in specimens with PAF >15 cm became longer with greater depth, while in specimens with PAF <15 cm it was not affected by depth. On the other hand, the RmL became longer with fish size in the small-size class, while in the large-size class it was not affected by fish size. These differences suggest that the function of the swimbladder in C. acrolepis changes with fish size. The swimbladder of larger specimens would provide more buoyancy than that of smaller ones, and the RmL of C. acrolepis would become longer with growth when PAF is <15 cm. This functional change in the swimbladder at a PAF of 15 cm was in agreement with results on both changes in feeding habits and the start of reproduction. Our findings suggest that C. acrolepis experiences a decisive life cycle change when PAF reaches 15 cm. This study also suggests the possibility that a functional change in the swimbladder might be widespread among deep-sea demersal species in which the diet changes with fish size.

The reproductive program of female Varroa destructor mites is triggered by its host, Apis mellifera.

Reproducing Varroa females begin oviposition on a host larva by laying an unfertilized (male) egg, followed by fertilized (female) offspring. Using transfer experiments, we examined whether the sequence of sexes in the brood cell is triggered by a host stimulus. When reproducing Varroa females were transferred from white-eyed pupae (worker brood) into freshly capped worker brood cells, 77% (n = 22 fertile mites after the transfer) began a new reproductive cycle by laying a male egg. The proportion of brood cells with male offspring was similar to naturally infested brood cells. Varroa females transferred into brood cells with young pupae reproduced, but only 6% (n = 16 fertile mites after the transfer) produced male offspring. This was significantly different from male production in naturally reproducing Varroa females and those transferred into freshly capped brood cells. We conclude that a host stimulus present in freshly capped brood cells triggers both the start of reproduction and the sequence of sexes.

Ecology and social structure of the Gobi khulan Equus hemionus subsp. in the Gobi B National Park, Mongolia

The status of the Gobi khulan Equus hemionus subsp. is recorded as “insufficiently known” in the Species Survival Commission's Equid Action Plan. Recent counts confirm that Mongolia holds the most important population of the whole species. Since 1953, the animals have benefited from a protected status, but this is now challenged. A 5-year study in the B part of the Gobi National Park on one subpopulation showed that it has remained stable over the past 15 years with an adequate mean reproductive rate of 15% and a 50% survival rate over the first year. Age/sex related mortality and prey analysis indicate that wolf predation probably has some impact on the population, in particular for 4–6-year-olds of both sexes at the start of reproduction. Desert and mountain steppes are the khulan's year-round preferred habitat, but ‘oases’, play an important role at the beginning of lactation. Anthropogenic factors affect both home range and habitat use through direct intervention or permanent occupation of the scarce water sources. Khulans of this subpopulation, unlike other Asian and African wild asses, form year-round stable, non-territorial families. These families and all-male groups join together into “bands” in winter, and herds of several hundred animals, where reproductive rate is highest, form throughout the year. The existence of such herds may thus be critical for the breeding success of the population. Our study provides the first detailed quantitative data for this subspecies, which will help to monitor changes in the future.

Diversity of age-specific reproductive rates may result from ageing and optimal resource allocation.

This paper reports the results of a dynamic programming model which optimizes resource allocation to growth, reproduction and repair of somatic damage, based on the disposable soma theory of ageing. Here it is shown that different age-dependent patterns of reproductive rates are products of optimal lifetime strategies of resource partitioning. The array of different reproductive patterns generated by the model includes those in which reproduction begins at the maximum rate at maturity and then declines to the end of life, or increases up to a certain age and then drops. The observed patterns reflect optimal resource allocation shaped by the level of extrinsic mortality. A continuous decline in the reproductive rate from the start of reproduction is associated with high extrinsic mortality, and an early increase in the reproductive rate occurs under low extrinsic mortality. A long-lived organism shows a low reproductive rate early in life, and short-lived organisms start reproduction at the maximum rate.

Reproductive behaviour of female Siberian lemmings during the increase and peak phase of the lemming cycle.

The reproduction of female Siberian lemmings in the increase and peak phases of the lemming cycle was investigated in connection with a ship-borne expedition along the Siberian arctic tundra. The cycle phase of each studied lemming population was determined using demographic analyses, i.e. current density indices (captured lemmings per 100 traps per 24 h), information on previous density (frequency of old lemming faeces and runways), and information from dendrochronological analyses revealing the most recent winters with a high intensity of willow-stem scarring caused by lemmings. The cycle phase determination was corroborated with data on the age profiles of the populations. The reproductive behaviour of female lemmings differed markedly in relation to cycle phase. In increase-phase populations, all captured females (including young and winter born) were reproducing (had embryos or were lactating), and females started to reproduce early in life, i.e. when <2 months old. By contrast, in peak-phase populations, only 6% of the young females and 63% of the winter-born ones were reproducing, and females did not start to reproduce until they were 5-6 months old. The average number of embryos per reproducing female was significantly higher in increase-phase populations than in peak-phase ones. It is concluded that the rapid population growth in lemmings during the increase phase can largely be explained by the early (young age) reproductive start and, consequently, the shorter generation time, the high proportion of females taking part in reproduction, and the large litters produced. Similarly, a delay in the start of reproduction, a lower proportion of reproducing females, and smaller litter sizes produced by peak-phase lemming populations can contribute substantially to the deceleration in the population increase and possibly lead to a decline.

Gender and social differences in adolescent sexuality and reproduction in Nicaragua

The aim of this research was to study gender and social differences in adolescent sexuality and reproduction, as reflected in age at first intercourse and age at first pregnancy, as a basis for future interventions in the municipality of León, Nicaragua. In a community-based cross-sectional study including 7789 households, all women aged 15-49 years (n = 10,867) were interviewed about socioeconomic, sexual, and reproductive issues. A random subsample of men (n = 388) and women (n = 413) aged 15-49 years was interviewed in more detail about sexual patterns and reproduction. The median age at first intercourse for women and men was 17.8 and 16.2 years, respectively. Women's average latency period to end of first pregnancy was 22 months. There was a significant tendency to start active sexual life later among today's girls aged 15-20 years, compared to the groups 21-27, 28-35, and 36-49 years old. A similar trend was found in age at first pregnancy. These secular trends were not found among men. Age at first pregnancy for current adolescents was lower among those having less formal education. The short latency period between first sexual intercourse and end of first pregnancy, probably reflecting lack of access to counseling and contraception, is worrying in light of the growing sexually transmitted disease/human immunodeficiency virus threat. The secular trend of later start of reproduction, however, is a positive sign which partly may be an effect of increasing education in the Nicaraguan society.

Influence of Food Quantity and Lead Exposure on Maturation in Daphnia magna; Evidence for a Trade-Off Mechanism

1. The start of reproduction is an important life-history trait in both ecology and ecotoxicology. Effects of food availability and toxic stress on maturation in female Daphnia magna are presented. 2. Five instars to maturation were observed under conditions of moderate to high food levels. Age and size at subsequent stages of the maturation process, i.e. ovary provisioning and egg deposition, depended on the rate of body growth. 3. At low food, a trade-off between reproduction and growth occurred. Within the same environment, some females reproduced at early age and small size, whereas others gave priority to growth over reproduction. In the latter resorption of yolk from the ovaries was observed. 4. Except for the production of malformed young, effects of lead on maturation resembled increased food stress. With abundant food, toxic effects were different to effects at low food. The results of standardized laboratory tests may therefore underestimate toxic effects at reduced food availability. 5. The phenomena observed in our studies can only partly be explained by a food-independent size threshold for maturation, which initiates resource allocation to reproduction; a minimum food uptake is required to enable the production of eggs