Variation In Reproductive Patterns Research Articles

Life-history characteristics and historical factors are important to explain regional variation in reproductive traits and genetic diversity in perennial mosses.

Plants have evolved an unrivalled diversity of reproductive strategies, including variation in the degree of sexual vs. clonal reproduction. This variation has important effects on the dynamics and genetic structure of populations. We examined the association between large-scale variation in reproductive patterns and intraspecific genetic diversity in two moss species where sex is manifested in the dominant haploid generation and sex expression is irregular. We predicted that in regions with more frequent realized sexual reproduction, populations should display less skewed sex ratios, should more often express sex and should have higher genetic diversity than in regions with largely clonal reproduction. We assessed reproductive status and phenotypic sex in the dioicous long-lived Drepanocladus trifarius and D. turgescens, in 248 and 438 samples across two regions in Scandinavia with frequent or rare realized sexual reproduction, respectively. In subsets of the samples, we analysed genetic diversity using nuclear and plastid sequence information and identified sex with a sex-specific molecular marker in non-reproductive samples. Contrary to our predictions, sex ratios did not differ between regions; genetic diversity did not differ in D. trifarius and it was higher in the region with rare sexual reproduction in D. turgescens. Supporting our predictions, relatively more samples expressed sex in D. trifarius in the region with frequent sexual reproduction. Overall, samples were mostly female. The degree of sex expression and genetic diversity differed between sexes. Sex expression levels, regional sex ratios and genetic diversity were not directly associated with the regional frequency of realized sexual reproduction, and relationships and variation patterns differed between species. We conclude that a combination of species-specific life histories, such as longevity, overall degree of successful sexual reproduction and recruitment, and historical factors are important to explain this variation. Our data on haploid-dominated plants significantly complement plant reproductive biology.

Reproduction of white-tailed deer in a seasonally dry tropical forest of Costa Rica: a test of aseasonality

Abstract The reproductive season of white-tailed deer (Odocoileus virginianus) has been hypothesized to be aseasonal south of about 14°–18°N latitude, where annual variation in day length is low. We tested this idea by using camera-trap data (1,336 photographed individuals identified by age and sex) collected during 2011–2017 in the dry tropical forest of Santa Rosa National Park, northwest Costa Rica, where wet and dry seasons are well-defined. We identified variation in monthly occurrence of spotted deer fawns, as well as the status of antler growth of male deer, specifically related to the very seasonal environment of the region. Year-round reproduction likely occurs, but the rainfall pattern in the area greatly influences the relative frequency of reproductive indicators, with most births occurring during the dry season, and a second peak occurring toward the latter part of the wet season. We speculate that food resources are the major influence on reproductive patterns, and that variation in types and timing of food resource availability likely account for the variation in reproductive patterns.

Cumulative estrogen exposure, number of menstrual cycles, and Alzheimer's risk in a cohort of British women

The effect of estrogen on Alzheimer's Disease (AD) risk has received substantial research and media attention, especially in terms of hormone replacement therapy. But reproductive history is also an important modifier of estrogenic exposure, and deserves further investigation. Importantly, there is wide variation in reproductive patterns that modifies estrogen exposure during the reproductive span, which previous AD studies have not incorporated into their calculations. We measured degree of Alzheimer's-type dementia in a cohort of elderly British women, and collected detailed reproductive and medical history information, which we used to estimate number of months with estrogen exposure and number of months with menstrual cycles. Using Cox proportional-hazards models, we find that longer duration of estrogen exposure may have a protective effect against AD risk, such that for every additional month with estrogen, women experienced on average a 0.5% decrease in AD risk (N=89, p=0.02). More menstrual cycles may also have a protective effect against AD risk, although this result was of borderline statistical significance (p<0.10). These results build upon previous methodologies by taking into account a variety of parameters including oral contraceptive use, breastfeeding, post-partum anovulation, abortions, and miscarriages. Additionally, Cox models revealed that longer reproductive span, age>21 at first birth, and more months in lifetime spent pregnant had protective effects against AD risk.

Variation in floral sex allocation, female success, and seed predation within racemiform synflorescence in the gynomonoecious Ligularia virgaurea (Asteraceae)

Studies of diclinous species have showed that floral sex allocation and female reproductive success were quite variable within inflorescences. However, little attention has been paid to gynomonoecious species, in which individuals produce both female and bisexual flowers. The purpose of this study was to investigate the variations in reproductive patterns at different capitulum positions within racemiform synflorescence in Ligularia virgaurea, and to determine selective mechanisms of variations in reproductive patterns. We conducted observational and experimental studies in natural populations of the gynomonoecious composite L. virgaurea. Floral sex allocation, seed production and pre-dispersal seed predation were quantified in the field. The results showed several patterns of variation from top to bottom capitula, including an increase in bisexual flowers and flower number per capitulum, but a decrease in seed set and size. Removing earlier capitula during bud stage did not change floral sex allocation in later capitula. And no effect was found on seed set under supplemental pollination. Thus, although it has been reported many times in previous studies, the variation of floral sex allocation in L. virgaurea may not result from architectural effect or mating environment, and the variation of seed production could not be fully explained by pollination success. Additionally, our results showed that L. virgaurea was susceptible to high levels of bisexual biased predation, which was greater for top capitula. We therefore suggest that these variations may help to enhance reproductive success of L. virgaurea in the face of bisexual-biased seed predation.

Monitoring population and gene pool dynamics of the annual species Capsella bursa-pastoris (Brassicaceae): a review of relevant species traits and the initiation of a long-term genetic monitoring programme

Species that colonise habitats on an annual basis are important for studying and understanding evolutionary changes and adaptations in the course of environmental shifts, caused, for instance, by global change phenomena. These species are characterised by a weedy ecology enabling them to react fast to environmental changes. As a model species, we selected Capsella bursa-pastoris (Brassicaceae, Shepherd’s Purse), which is annual to biennial, predominantly selfing and closely related to the genetic model plant Arabidopsis thaliana. Differentiation and adaptation in C. bursa-pastoris are shortly reviewed. Based on this knowledge, two Botanical Gardens are currently arranging long-term sites characterised by annual ploughing for the genetic monitoring of C. bursa-pastoris. Demographic parameters will be monitored as well, i.e. different life-cycle phases such as flowering, fruiting, and the soil seed bank. Furthermore, seeds of at least 20 individuals will be sampled per year. Isozyme analyses, flow cytometry, AFLPs, SNPs as well as microsatellites will be utilised to characterise changes in genetic diversity patterns over time. In general, the objective of our genetic monitoring of C. bursa-pastoris is to address the following questions: In the light of future research, our objectives are to study whether the genetic structure and diversity of C. bursa-pastoris alter over time, whether a possible invasion of ecotypes/genotypes of Sheperd’s purse is traceable using genetic markers, and whether it is possible to relate variation in reproductive patterns to respective candidate genes, which may be useful for monitoring.

Reproductive biology of three hydrothermal vent peltospirid gastropods (Nodopelta heminoda, N. subnoda and Peltospira operculata) associated with Pompeii worms on the East Pacific Rise

The gonad morphology and gametogenesis of three peltospirid gastropods (Nodopelta heminoda, N. subnoda and Peltospira operculata) from hydrothermal vents in the East Pacific Rise were analysed using histological techniques. Samples were collected on different hydrothermal structures from three chemically distinct sites in vent fields along the north East Pacific Rise (13°N) to assess spatial variation in oocyte size–frequency distributions. The three species revealed the same gonad morphology. The ovary, which occupies a large part of the body, is confined to the dorsal area of the visceral mass and is located between the dorsal gill lamellae and the digestive gland that appear progressively from the posterior part. The oogonia develop into previtellogenic oocytes, and when they grow to a size of 50–70 µm, vitellogenesis begins. Maximal egg size ranges between 129 µm for P. operculata and 150 µm for N. heminoda. The presence of oocytes at all stages of development, in all females, suggested a continuous gametogenesis within those species. Continuous reproduction appears to be a common trait in vent gastropods and may be adaptive in relation to constant energy supply and the ephemeral and unstable vent environment. Percentage of vitellogenic oocytes (i.e. gametogenic maturity) was independent of shell length. The slight variability observed between gametogenetic maturity of females from different localities is likely due to random individual variations in reproductive patterns rather than variation in environmental conditions or food availability.

Seasonal reproductive patterns of female Gambusia holbrooki from two Florida lakes

Lake Apopka in central Florida (USA) is significantly contaminated with a variety of chemicals including anthropogenic nutrients, organochlorine pesticides like dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE), and multiple congeners of polychlorinated biphenyls (PCBs). Our laboratory has previously documented a number of reproductive abnormalities in alligators from Lake Apopka, compared with alligators captured from Lake Woodruff, a nearby reference lake. We conducted the present study to investigate if another native vertebrate, Gambusia holbrooki (eastern mosquitofish), is similarly affected. Adult female mosquitofish were collected from Lake Apopka and Lake Woodruff monthly for 16 months to document seasonal and lake-associated variation in reproductive patterns. In contrast to fish from Lake Woodruff (reference), females from Lake Apopka exhibited earlier and more synchronized spring ovarian recrudescence, increased body size, increased fecundity, increased adjusted hepatic weight, and more extreme fluctuations in muscle estradiol concentrations in most months. Endocrine disruption, consistent with other studies and Lake Apopka's pollution profile, is one explanation for these findings. Other environmental and physiological factors are also addressed. However, the higher fecundity among Apopka females suggests that, unlike Apopka alligators, Apopka mosquitofish are not impacted at the population level.

Reproduction and life history of the green alga Prasiola linearis Jao (Trebouxiophyceae, Chlorophyta)

Abstract Marine species of Prasiola are most common on rocky shores of the North Atlantic and North Pacific Oceans. Prasiola linearis is a little-known member of this group, whose known distribution is restricted to coastal marshes of Pacific North America. The little information available on this species is mostly based on the original description; its life history has not been previously reported. Reproduction and life history were investigated in a series of experiments conducted in different combinations of culture medium, temperature, daylength and photon irradiance. The alga reproduced by aplanospores that were produced in the apical part of the blade. Upon release, each aplanospore reproduced a new thallus; sexual reproduction, which occurs in other marine species of Prasiola (P. stipitata and P. meridionalis) was not observed in P. linearis. No variation in reproductive patterns was observed between different combinations of factors tested; however, the alga showed very weak growth at 20°C. The life history of Prasiola linearis consists of a repetition of the same morphological phase reproducing by aplanospores. The diversity of life histories observed in marine species of Prasiola is illustrated and discussed.

Variation in Reproductive Patterns of Antelope Ground Squirrels, Ammospermophilus leucurus, from Oregon to Baja California

Abstract Clines of biological variation result from variation in physical environmental conditions. We report new reproductive data for a population of antelope ground squirrels, Ammospermophilus leucurus, at the northern geographic limit of this species. We then analyze reproductive patterns at 3 sites spanning the entire north–south extent of the geographic range, covering more than 2,500 km and 21 degrees of latitude. The overall breeding season of populations is relatively short in Oregon (42°N) and California (37°N), but in Baja California (24°N) it encompasses half a year. Mean litter size decreases significantly from north to south, from 9.3 (SD = 1.8) per litter in Oregon to 5.9 (SD = 1.5) in Baja California. Major shifts in seasonality of precipitation and ecosystem composition and diversity are associated with longer breeding season and lower litter size at the southern geographic extreme of A. leucurus. The environmental predictability for the northern populations is due to “constancy,” whereas...

Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, North-western Mediterranean Sea

Pasiphaea multidentata is a deep-water caridean shrimp fished in the Mediterranean in association with the commercially exploited red-shrimp Aristeus antennatus. A previous study describes seasonality in the reproductive pattern of P. multidentata using external morphological parametres. This study assesses the spatio-temporal variations in the population structure, sex ratio, ovary cycle and gametogenesis of P. multidentata from three different fishing grounds in the Blanes canyon and adjacent margin (North-western Mediterranean) over an annual cycle. The oogenetic pattern of this species is typical of a caridean shrimp. There is a pool of previtellogenic oocytes at all times that develop from the periphery of the gonad towards the centre during maturation. Previtellogenic oocytes grow to approximately 200 μm before undergoing vitellogenesis. The vitellogenic oocytes are surrounded by a monolayer of accessory cells. The maximum size observed for a mature oocyte was 1420 μm. The oocyte-size distribution confirmed the seasonal reproductive pattern of this species; in winter, the ovaries contained mainly previtellogenic oocytes, some of which start maturing in spring, resulting in a slightly bimodal distribution. In summer, the vitellogenic oocytes reach approximately 1000 μm and in late autumn the ovaries are fully mature and ready to spawn. There were no significant differences in the reproductive and population structure patterns of P. multidentata among the three sites, suggesting that the population’s distribution is not affected by the geomorphology of the area, in particular the presence of the canyon. The populations are dominated by females at all sites and all seasons, with the arrival of juveniles in spring. The seasonal variations in the reproduction and recruitment of P. multidentata and the lack of spatial segregation within the population are discussed in terms of the species’ known biology, the effects of canyons in energy supply to the deep-sea floor and the relationships of this species with the red-shrimp A. antennatus.

Sexual maturity, factors affecting the breeding season and breeding in consecutive seasons in populations of overabundant Victorian koalas (Phascolarctos cinereus)

It is important to have knowledge of basic population parameters to understand how these vary geographically and temporally and how they contribute to population dynamics. This paper investigates three of these parameters in Victorian koala populations: sexual maturity, aspects of the breeding season, and the continuity of individuals’ breeding. The investigation was carried out in koalas of known-age in two free-living (Redbill Creek on French Island and Brisbane Ranges) and one semi-captive (the Koala Conservation Centre on Phillip Island) population as well as koalas of unknown age in four Victorian populations of overabundant koalas: Mt Eccles and Framlingham in south-west Victoria, French Island in Western Port and Snake Island in south Gippsland. At sexual maturity, female koalas had a mean age (±95% confidence interval) of 24.4 months (23.5–25.3 months), a mean head length of 125 mm (124–127 mm) and a mean body mass of 6.6 kg (6.3–6.8 kg). Only 7.4% of independent females (of unknown age) were carrying young when they weighed less than 6 kg. The breeding season was more restricted in the south-west populations. At Framlingham and Mt Eccles 85% and 91% of births, respectively, occurred between December and March. At Snake and French Islands only 46% and 53% of births, respectively, were recorded in the same period. In the Chlamydia-free population (Red Bill Creek) none of the koalas that were monitored stopped breeding and then resumed breeding in a subsequent season whereas many females from Chlamydia-infected populations (Brisbane Ranges and the Koala Conservation Centre) did so. This variation in reproductive patterns is likely to make an important contribution to the variation in the demography observed in different koala populations.

Population dynamics and life history of the oribatid mite Ameronothrus lineatus (Acari, Oribatida) on the high arctic archipelago of Svalbard

Summary Ameronothrus lineatus was studied in the northernmost part of its distribution range in the high Arctic. Survey sampling was carried out on two sites on West Spitsbergen: a Carex saltmarsh and a smooth layer of cyanobacteria, where the species was the only oribatid mite collected. On the latter substrate all mites were visible and could be sampled by hand, making it ideal for demographic studies. An experimental population was established in microcosms based on the mite-cyanobacteria system, and all three populations were sampled regularly during summer 1998. Our results suggested spatial variation in reproductive patterns between local populations. Influence of climatic variation on demography was illustrated by comparing reproduction in 1997 and 1998. Synchronous larviposition was observed in early summer, but recruitment also occurred throughout the season, and gravid females were found on all sampling dates. Both the saltmarsh and the cyanobacteria populations were female biased. A highly synchronous moulting involving at least 80% of the juveniles was observed in July, and it seems that juveniles moult once per season on average. The synchronous moult is suggested to be a phenological strategy to exploit the short arctic summer by timing moulting with the warmest part of the season. A generation time of 5 years was estimated. Juvenile stages of one year, continuous recruitment, and high adult longevity (2–3 years) give stable stage structures and stable population dynamics.

Postponed reproduction as an adaptation to winter conditions in Drosophila melanogaster: evidence for clinal variation under semi-natural conditions.

Patterns of climatic adaptation in drosophila and other insects have largely been inferred from laboratory comparisons of traits that vary clinally. Here, we extend this research to comparisons under semi-natural conditions. To test for clinal variation in reproductive patterns and survival over winter, Drosophila melanogaster populations were initiated from seven collection sites along the eastern coast of Australia, ranging from tropical to temperate regions. The fecundity and survival of these populations were monitored in field cages at a temperate location until all adults had died more than 5 months later. Total fecundity showed a curvilinear relationship with latitude, due to higher egg production by high- and low-latitude populations. Adults from temperate locations survived winter conditions better than those from subtropical populations but not tropical ones. There was a linear cline in the timing of egg production: temperate populations produced eggs later than populations from lower latitudes. This cline is likely to be adaptive because egg-to-adult viability experiments indicated that only eggs laid in spring developed successfully to the adult stage. There was no evidence for climatic adaptation in the immature stages. The adult mortality rate increased gradually over winter, and in some populations was also correlated with the minimum ambient temperature. These results indicate that adaptation to winter conditions in D. melanogaster has involved shifts in reproductive patterns.

On the enigmatic brown alga Acinetospora crinita (Ectocarpales, Fucophyceae)

The present paper reports on the study of French and Danish strains of Acinetospora crinita (Harvey) Kornmann and their responses in growth and reproduction to various combinations of temperature and salinity. The distribution of the species in both hemispheres may be explained by the temperature requirements for growth and reproduction. The limit at lower latitudes in both hemispheres is a lethal limit, at higher latitudes it is probably a growth and reproduction limit. Acinetospora crinita is a stenohaline species and only occurs in high salinity areas in Danish waters. This paper also discusses the status of the genus Acinetospora, which has been considered to be a phase in the life history of some Feldmannia and Hincksia species. We conclude that there are several characters that justify independent status at the genus and species level. The large variation in reproductive patterns is enigmatic and adds to the taxonomic confusion. In A. crinita various reproductive structures occur: megasporangia/acinetosporangia, unilocular sporangia (some are apomeiotic), monosporangia, plurilocular sporangia which are presured to be gametangia, and a strain is known from the United States with reproduction solely by fragmentation. The combination of reproductive structures appears to be unique to specific strains.

Plasticity, Constraint, and Optimality in Reproductive Timing

Synchronous release of gametes or larvae by marine animals may be controlled as many as four environmental cycles thereby enabling an array of reproductive timing patterns. Cohesive scenarios that account for the diversity of reproductive patterns are rare and tests of their adaptive significance have been even rarer. By exploiting plasticity in the timing of larval release, we isolated proximate factors regulating reproductive synchrony and provided evidence that predation ultimately may best explain the diversity of hatching patterns by brachyuran crabs. Tides entrain reproductive rhythms by many crabs, and therefore spatial and temporal variation in tides produces intraspecific variation in reproductive patterns. This was demonstrated by determining the timing of larval release of the same or sibling species of intertidal crabs in Pacific semidiurnal and Caribbean mixed semidiurnal tidal regimes on the two coasts of the Republic of Panama. The time of larval release varied during the year in the Caribbean, where entraining physical cycles exhibited complicated changes in phase, but not along the Pacific coast, where the phase relationships among physical cycles varied little year—round. Crabs timed larval release relative to the light—dark, tidal phase, and tidal amplitude cycles, but not the lunar cycle, suggesting that three rhythms determined when larvae were released. For each species we ranked these rhythms by the degree to which larval release kept phase with their entraining physical cycles. The species—specific hierarchies of rhythms we observed match those expected if the time of larval release minimizes predation on females, embryos, and newly hatched larvae. Such hierarchies enable crabs to track phase shifts of cycles in variable tidal environments and may enhance reproductive success across tidal regimes. However, larval release may be timed better in some tidal regimes than others due to differences in the phasing of environmental cycles. In some tidal regimes, larval release cannot be synchronized with all three physical during the year, and hierarchies of rhythms may determine the timing and duration of breeding.

Testing generalizations about latitudinal variation in reproduction and recruitment patterns with sicyoniid and caridean shrimp species

Summary Study of latitudinal variation in seasonality of reproduction and recruitment of benthic marine invertebrates is useful in generating and testing hypotheses about causal factors acting on reproduction such as temperature and larval food supply that might be altered by changes in world climate. Analysis of latitudinal variation in reproductive patterns might be made with comparisons (a) among species with a common phylogenetic history from different latitudes and habitats and (b) among phylogenetically different taxa from the same location. Hypotheses on variation of reproductive seasonality with latitude are tested here with results of a study on nine species of caridean and two species of sicyoniid shrimp sampled from a tropical seagrass meadow in Puerto Rico. Breeding condition was determined by the presence or absence of incubated embryos (carideans) and the state of ovarian development in both carideans and sicyoniids. Recruitment was estimated from the percentage of individuals of monthly population samples in the juvenile size classes. Comparison of reproductive patterns among tropical, subtropical, and cool temperate Sicyonia spp. supports the paradigm of continuous reproduction in the tropics with increased restriction of breeding season with an increase in latitude. A greater intensity of breeding effort appears to accompany the shorter breeding period associated with an increase in latitude. At the tropical site most females of all caridean species carried embryos during all months of the year. With the onset of sexual maturity, caridean females produced consecutive broods for the rest of their relatively short (< 6 month) life span. In both sicyoniid and caridean species, recruitment occurred throughout the year but was highly variable, i.e., episodic rather than truly continuous or seasonal. Patterns of recruitment were highly concordant among but not between sicyoniid and caridean species, indicating that different sets of environmental factors controlled recruitment in the two groups. It is suggested that simultaneous study of adult reproduction and larval ecology is necessary to understand patterns of reproduction and recruitment. Coordinated effort on a global scale in studying latitudinal variation in reproduction and recruitment is suggested in order to predict the consequences of climate change on commercially and ecologically important marine invertebrate species.

Factors affecting the reproductive ecology of Thalassia testudinum (Hydrocharitaceae)

Morpho-anatomical studies of short-shoots of Thalassia testudinum Banks ex König collected in Tampa Bay, Florida from February 1979 to October 1980 ( n = 5394) demonstrated the presence of sexually reproductive short-shoots during all months, except August and September. Mean inflorescence lengths (MIL) indicated that little inflorescence development occurs during autumn and winter (MIL 0.2–1.0 mm); MIL's in 1979 increased rapidly during April (19.47 mm ± 17.04 mm SD) and May (74.10 mm ± 27.11 mm SD), peaking in June (110.17 mm ± 8.88 mm SD). Large standard deviations reflect the presence of early stage inflorescences throughout the reproductive season. This suggests possible genetic diversity and aseasonality for floral induction. Quantitative in situ observations from 1981 to 1985 detected significant temporal and spatial variations in reproductive patterns. Annual variations in flowering (anthesis) may be explained by the influence of environmental factors, such as water temperature and salinity, on inflorescence development and survival. Spatial patchiness in reproductive effort, negative correlations between male and female short-shoot distributions and sex-related differences in the number of leaf scars short-shoot −1 may reflect clonal variation and/or a possible interaction of ramet age with sex expression in this species.

Observations on the reproductive ecology of Thalassia testudinum (Hydrocharitaceae). III. Spatial and temporal variations in reproductive patterns within a seagrass bed

Spatial and temporal variations in the reproductive patterns of a population of Thalassia testudinum Banks ex König in Tampa Bay, Florida were observed from 1981 to 1983. Reproductive densities of 11.4, 20.7 and 10.0% were observed in 1981, 1982 and 1983, respectively. The significantly higher reproductive density in 1982 was due to a 3-fold increase in the temporally labile male phenotype. Sex ratios were male-biased only in 1982. In contrast, female short-shoot densities did not vary significantly during the study. Total and reproductive short-shoot densities generally decreased from the shoreward (shallower) fringe to the seaward (deeper) fringe of the bed. Spatial variations in female short-shoot densities were significant. Female short-shoots were prevalent near fringing areas of the bed, while males were predominant in the interior. This distribution pattern resulted in a negative correlation between male and female densities. The distribution and spatial separation of the sexes suggest an interaction of age with sex expression in this Thalassia testudinum population.