Population Reproductive Output Research Articles

Short- and long-term toxicity of nano-sized polyhydroxybutyrate to the freshwater cnidarian Hydra viridissima

The accumulation of increasingly smaller plastic particles in aquatic ecosystems is a prominent environmental issue and is causing a significant impact on aquatic biota. In response to this challenge, biodegradable plastics have emerged as a potential ecological alternative. Nevertheless, despite recent progress in polymer toxicology, there is still limited understanding of the ecological implications of biodegradable plastics in freshwater ecosystems. This study evaluated the toxicity of polyhydroxybutyrate nano-sized particles (PHB-NPLs) on the freshwater cnidarian Hydra viridissima assessing individual and population-level effects. Data revealed low toxicity of PHB-NPLs to H. viridissima in the short-term, as evidenced by the absence of significant malformations and mortality after the 96-h assays. In addition, hydras exhibited rapid and complete regeneration after 96 h of exposure to PHB-NPLs. Feeding assays revealed no significant alterations in prey consumption behavior in the 96-h mortality and malformations assay and the regeneration assay. However, significantly increased feeding rates were observed after long-term exposure, across all tested concentrations of PHB-NPLs. This increase may be attributed to the organisms' heightened energetic demand, stemming from prolonged activation of detoxification mechanisms. These changes may have a cascading effect within the food web, influencing community dynamics and ecosystem stability. Furthermore, a dose-dependent response on the hydras' populational growth was found, with an estimated 20 % effect concentration (EC20,8d) on this endpoint of 10.9 mg PHB-NPLs/L that suggests potential long-term impacts on the population's reproductive output and potential depression and local extinction upon long-term exposure to PHB-NPLs on H. viridissima. The obtained data emphasizes the importance of evaluating sublethal effects and supports the adoption of long-term assays when assessing the toxicity of novel polymers, providing crucial data for informed regulation to safeguard freshwater ecosystems. Future research should aim to unravel the underlying mechanisms behind these sublethal effects, as well as the impact of the generated degradation products.

Changes in Population Demography and Reproductive Output of the Invasive Hemigrapsus sanguineus (Asian Shore Crab) in the Long Island Sound from 2005 to 2017

Cross-intertidal transects at a western Long Island Sound estuary site provided estimates of the density of the non-native Hemigrapsus sanguineus (Asian Shore Crab) from 1998 to 2017, and measurements of crab size (carapace width; CW) from 2005 to 2017. Since 2001, average intertidal density declined by ∼5% per year. This decline was driven by decreases in the density of larger crabs, with consequent reductions in average and maximum sizes of both males and females. The proportion of the largest crabs (>24 mm CW) dropped from 10.1% of the population in 2005 to 1.4% in 2017. Individual reproductive output scales with size; thus, I estimate the loss of the largest females to have reduced population reproductive output by half between 2005 and 2017. Also, the frequency of ovigerous females in the smallest reproductively mature classes (12–14 mm CW) increased. Though the density and average size of Asian Shore Crab have declined significantly, resident and native crab populations have still not recovered.

Sexual selection, phenotypic plasticity and female reproductive output.

In a rapidly changing environment, does sexual selection on males elevate a population's reproductive output? If so, does phenotypic plasticity enhance or diminish any such effect? We outline two routes by which sexual selection can influence the reproductive output of a population: a genetic correlation between male sexual competitiveness and female lifetime reproductive success; and direct effects of males on females' breeding success. We then discuss how phenotypic plasticity of sexually selected male traits and/or female responses (e.g. plasticity in mate choice), as the environment changes, might influence how sexual selection affects a population's reproductive output. Two key points emerge. First, condition-dependent expression of male sexual traits makes it likely that sexual selection increases female fitness if reproductively successful males disproportionately transfer genes that are under natural selection in both sexes, such as genes for foraging efficiency. Condition-dependence is a form of phenotypic plasticity if some of the variation in net resource acquisition and assimilation is attributable to the environment rather than solely genetic in origin. Second, the optimal allocation of resources into different condition-dependent traits depends on their marginal fitness gains. As male condition improves, this can therefore increase or, though rarely highlighted, actually decrease the expression of sexually selected traits. It is therefore crucial to understand how condition determines male allocation of resources to different sexually selected traits that vary in their immediate effects on female reproductive output (e.g. ornaments versus coercive behaviour). In addition, changes in the distribution of condition among males as the environment shifts could reduce phenotypic variance in certain male traits, thereby reducing the strength of sexual selection imposed by females. Studies of adaptive evolution under rapid environmental change should consider the possibility that phenotypic plasticity of sexually selected male traits, even if it elevates male fitness, could have a negative effect on female reproductive output, thereby increasing the risk of population extinction. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Dual-stressor selection alters eco-evolutionary dynamics in experimental communities.

Recognizing when and how rapid evolution drives ecological change is fundamental for our understanding of almost all ecological and evolutionary processes such as community assembly, genetic diversification and the stability of communities and ecosystems. Generally, rapid evolutionary change is driven through selection on genetic variation and is affected by evolutionary constraints, such as tradeoffs and pleiotropic effects, all contributing to the overall rate of evolutionary change. Each of these processes can be influenced by the presence of multiple environmental stressors reducing a population's reproductive output. Potential consequences of multistressor selection for the occurrence and strength of the link from rapid evolution to ecological change are unclear. However, understanding these is necessary for predicting when rapid evolution might drive ecological change. Here we investigate how the presence of two stressors affects this link using experimental evolution with the bacterium Pseudomonas fluorescens and its predator Tetrahymena thermophila. We show that the combination of predation and sublethal antibiotic concentrations delays the evolution of anti-predator defence and antibiotic resistance compared with the presence of only one of the two stressors. Rapid defence evolution drives stabilization of the predator-prey dynamics but this link between evolution and ecology is weaker in the two-stressor environment, where defence evolution is slower, leading to less stable population dynamics. Tracking the molecular evolution of whole populations over time shows further that mutations in different genes are favoured under multistressor selection. Overall, we show that selection by multiple stressors can significantly alter eco-evolutionary dynamics and their predictability.

High fishing intensity reduces females’ sperm reserve and brood fecundity in a eubrachyuran crab subject to sex- and size-biased harvest

Abstract Size-selective male fisheries may result in sperm limitation whereby the number of sperm is insufficient to fertilize all oöcytes produced by females. In eubrachyuran crabs, females have seminal receptacles for sperm storage which may reduce the risk of sperm limitation over their lifetime. In this study on the commercially exploited eubrachyuran Metacarcinus edwardsii, we evaluate the sperm limitation hypothesis by measuring female reproductive success in five Chilean populations subjected to low or high fishing intensity. The quantity and viability of sperm stored by females was measured in each season and population, and related to resulting brood fecundity. Females’ sperm reserve was larger when fishing intensity was low than when it was high—paralleling previously demonstrated differences in males’ sperm reserve—and especially in the season before oviposition. Sperm viability was in general high (92%) and independent of fishing intensity. Mean brood fecundity adjusted to constant female size was about 60% greater under low compared with high fishing intensity. Thus, in M. edwardsii, population reproductive output could be depressed by male-biased fishing in spite of female sperm storage capability.

Reproductive investment and multiple spawning evidence in the redfinger rubble crab Eriphia gonagra (Brachyura, Eriphioidea)

Abstract The variation in reproductive investment (RI) and the hypothesis of multiple spawning were evaluated in the redfinger rubble crab Eriphia gonagra (Fabricius, 1781). The gonads and embryos showed synchronous development, and fecundity and RI varied widely among females of the same size class. The mean RI value recorded was 11.31%, with no significant differences among the means for different size classes. The allometric analysis of fecundity indicated RI decrease while body size increase, but we suggested that this occurs due to size overestimation where the largest width of carapace was used as body size reference in these analyzes. In addition, we found an isometric relationship for “female weight vs. egg number”, and also for “female weight vs. egg weight”, indicating that RI ​​increased proportionally with size of females. Relatively high frequencies both of smaller females with rudimentary gonads, and of larger females with developed gonads were observed. This indicates that larger females take place more frequently in the population reproductive output over time. This difference could not be observed by means of RI analyses of captured and fixed crabs, for which only one stage of gonad development and/or one spawning is usually recorded.

Chronic Intake of Green Propolis Negatively Affecting the Rat Testis.

Background:Human and animal evidence suggests that environmental toxicants may have an adverse impact on male reproductive health, reducing the population's reproductive output. Owing to the renewed attraction for natural products, some of them constitute effective alternatives to mitigate these effects. Propolis is a candidate for this use because of its intrinsic properties. In many situations, it improved the testicular damage and alleviated the toxic effects induced by environmental contaminant exposure.Objective:The aim of this study was to investigate possible alterations of testicular parameters and certify if its use is really advantageous to the testis, since this could affect rat reproductive function.Materials and Methods:Forty-eight adult male Wistar rats were divided into four groups (Co = control, T1 = 3 mg propolis/kg/day, T2 = 6 mg/kg/day, T3 = 10 mg/kg/day) and were exposed during 56 days. The testes were assessed with morphometrical, stereological, and ultrastructural analyses. Cell proliferation and death were diagnosed, respectively, by immunocytochemistry. Connexin 43 (Cx43) and N-cadherin transcript levels were determined by reverse transcription-polymerase chain reaction.Results:Increased cell proliferation and Leydig cell volume were observed in T2, and in contrast, Cx43 upregulation and cell death were observed in T3. Both T2 and T3 showed ultrastructural abnormalities in testicular parenchyma.Conclusion:We recommend a cautious intake of propolis to avoid deleterious effects.SUMMARY Chronic intake of Brazilian green propolis induced N.-cadherin downregulation and decreased on seminiferous tubule volumeIncrease on connexin 43 expression and cell death and decrease in Leydig cell.(LC) number/testis with the concentration of 10 mg/kg/day were observedIncrease on cell proliferation, cytoplasmic proportion, and volume of LC with the concentration of 6 mg/kg/day was detectedThe presence of empty spaces between spermatids and malformed spermatozoa in the lumen of seminiferous tubule was showedThis male reproductive disruption can be linked to phenolic compounds present in Brazilian green propolis. Abbreviation Used: AEC: 3-amino-9-ethylcarbazole; AJ: Adherens junction; AME: Aromadendrin-40-methyl ether; CAPE: Caffeic acid phenethyl ester; Co: Control group; C×43: Connexin 43; DAB: Diaminobenzidine; dNTP: Deoxyribonucleotide phosphate; DSP: Daily sperm production; FA: Ferulic acid; FSH: Follicle-stimulating hormone; GJ: Gap junction; GJIC: Gap junction intercellular communication; HPLC: High-performance liquid chromatography; LC: Leydig cell; LH: Luteinizing hormone; N-cad: N-cadherin; PCNA: Proliferating cell nuclear antigen; PCR: Polymerase chain reaction; RT-PCR: Reverse transcription-polymerase chain reaction; SDM: Standard deviation of mean; T1: Group exposed to 3 mg of propolis/kg/day; T2: Group exposed to 6 mg of propolis/kg/day; T3: Group exposed to 10 mg of propolis/kg/day; TUNEL: Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling; WB-ras 2 cells: Ras-transformed rat liver epithelial cell line.

The relative importance of reproduction and survival for the conservation of two dolphin populations.

It has been proposed that in slow‐growing vertebrate populations survival generally has a greater influence on population growth than reproduction. Despite many studies cautioning against such generalizations for conservation, wildlife management for slow‐growing populations still often focuses on perturbing survival without careful evaluation as to whether those changes are likely or feasible. Here, we evaluate the relative importance of reproduction and survival for the conservation of two bottlenose dolphin (Tursiops cf aduncus) populations: a large, apparently stable population and a smaller one that is forecast to decline. We also assessed the feasibility and effectiveness of wildlife management objectives aimed at boosting either reproduction or survival. Consistent with other analytically based elasticity studies, survival had the greatest effect on population trajectories when altering vital rates by equal proportions. However, the findings of our alternative analytical approaches are in stark contrast to commonly used proportional sensitivity analyses and suggest that reproduction is considerably more important. We show that in the stable population reproductive output is higher, and adult survival is lower;the difference in viability between the two populations is due to the difference in reproduction;reproductive rates are variable, whereas survival rates are relatively constant over time;perturbations on the basis of observed, temporal variation indicate that population dynamics are much more influenced by reproduction than by adult survival;for the apparently declining population, raising reproductive rates would be an effective and feasible tool to reverse the forecast population decline; increasing survival would be ineffective. Our findings highlight the importance of reproduction – even in slow‐growing populations – and the need to assess the effect of natural variation in vital rates on population viability. We echo others in cautioning against generalizations based on life‐history traits and recommend that population modeling for conservation should also take into account the magnitude of vital rate changes that could be attained under alternative management scenarios.

Effects of gastropod predation on the reproductive output of an overexploited deep octocoral

The study presented herein is aimed at quantifying the effects of the partial predation exerted by the gastropod Pseudosimnia carnea on the reproductive features of the highly valuable, slow-growing, and long-lived red coral, Corallium rubrum. Seventy-five colonies were collected just before annual spawning from a red coral population living between 85 and 90 m deep in the NW Mediterranean; of these, 35 % were affected by P. carnea. Female colonies were more frequently preyed upon than males (3:1 ratio). Overall, 1,100 polyps were dissected and examined for their reproductive content. The mean number of polyps per colony and the mean fecundity of female polyps and colonies were significantly reduced by gastropod predation, which affected colonies independently of their size; in particular, colony fecundity was reduced by 81 %. The consequent reduction in population reproductive output is likely to have long-term effects on preyed-upon populations and thereby limit their resilience to intense commercial harvesting.

Demographic responses of a site‐faithful and territorial predator to its fluctuating prey: long‐tailed skuas and arctic lemmings

Environmental variability, through interannual variation in food availability or climatic variables, is usually detrimental to population growth. It can even select for constancy in key life-history traits, though some exceptions are known. Changes in the level of environmental variability are therefore important to predict population growth or life-history evolution. Recently, several cyclic vole and lemming populations have shown large dynamical changes that might affect the demography or life-histories of rodent predators. Skuas constitute an important case study among rodent predators, because of their strongly saturating breeding productivity (they lay only two eggs) and high degree of site fidelity, in which they differ from nomadic predators raising large broods in good rodent years. This suggests that they cannot capitalize on lemming peaks to the same extent as nomadic predators and might be more vulnerable to collapses of rodent cycles. We develop a model for the population dynamics of long-tailed skuas feeding on lemmings to assess the demographic consequences of such variable and non-stationary prey dynamics, based on data collected in NE Greenland. The model shows that populations of long-tailed skua sustain well changes in lemming dynamics, including temporary collapses (e.g. 10 years). A high floater-to-breeder ratio emerges from rigid territorial behaviour and a long-life expectancy, which buffers the impact of adult abundance's decrease on the population reproductive output. The size of the floater compartment is affected by changes in both mean and coefficient of variation of lemming densities (but not cycle amplitude and periodicity per se). In Greenland, the average lemming density is below the threshold density required for successful breeding (including during normally cyclic periods). Due to Jensen's inequality, skuas therefore benefit from lemming variability; a positive effect of environmental variation. Long-tailed skua populations are strongly adapted to fluctuating lemming populations, an instance of demographic lability in the reproduction rate. They are also little affected by poor lemming periods, if there are enough floaters, or juveniles disperse to neighbouring populations. The status of Greenland skua populations therefore strongly depends upon floater numbers and juvenile movements, which are not known. This reveals a need to intensify colour-ringing efforts on the long-tailed skua at a circumpolar scale.

Sexual structure of a highly reproductive, recovering gorgonian population: quantifying reproductive output

A population of the Mediterranean red gorgonian Paramuricea clavata has exhibited unexpected resilience after being impacted by 2 anomalous mortality events in 1999 and 2003. To understand the recovery mechanisms, we examined the population reproductive structure and reproductive output based on data collected via non-destructive sampling techniques. The overall population sex ratio was balanced, though the spatial distribution of sexes was significantly segregated. Dividing the population into 14 size classes on the basis of their measured average annual growth revealed a decreasing monotonic trend of abundance of larger classes. The Recruitment class was consistently dominant. The minimum size at first reproduction was 8.5 cm in height, corresponding to an age of ~3 yr. The percentage of fertile colonies increased with size, reaching 90% in size Class 9. Polyp fecundity increased with colony size and did not differ signif- icantly between healthy and damaged colonies. As the number of mature oocytes produced by a colony is a function of polyp fecundity and of the number of reproductive polyps, colony reproduc- tive output increased exponentially with size. The population reproductive output (145 × 10 3 mature oocytes m �2 yr �1 ) was one-fifth of that measured in stable, undamaged populations and came mainly from the medium size classes. After the catastrophic mortality, the population has been recovering, albeit with reduced reproductive output. Moreover, it has exhibited a 2-fold increase in recruitment rate, 3-fold greater than that measured in other, undisturbed populations. Our findings are consistent with a strict density-dependent recruitment control operating in crowded, stable P. clavata populations.

Growth and population dynamic model for the non-zooxanthellate temperate solitary coral Leptopsammia pruvoti (Scleractinia, Dendrophylliidae)

In corals where complex life history processes decoupling age from size (e.g., fragmentation, fusion, partial colony mortality) are rare or clearly detectable, individual age may be determined from size, and age-based growth and population dynamic models may be applied. One example is the solitary Mediterranean coral Leptopsammia pruvoti Lacaze-Duthiers 1897, whose population size and structure, and growth rates were determined at Calafuria (43°28′N and 10°20′E), Ligurian Sea, from December 2007 to June 2009. Growth rate decreased with increasing size. The growth curve derived from field measurements confirmed the one obtained by growth band analysis. The frequency of individuals decreased exponentially with age, indicating a steady state population. Turnover time was 2.3 years. Maximum life span was 13 years. Most reproductive output was from intermediate age classes (6 years), while older individuals (>7 years), although having higher fecundity, were rare and accounted for a minority of population reproductive output. In comparison with other solitary dendrophylliids, L. pruvoti life strategy was characterized by a reproduction with r-strategy correlates (high fecundity, short embryo incubation, small planula size, fast achievement of sexual maturity), and a rate of demographic renewal occurring halfway along the r–K continuum (intermediate turnover time and maximum longevity).

Realistic nitrate concentration alters the expression of sexual traits and olfactory male attractiveness in newts

Summary The occurrence of endocrine disruption is increasing and may now affect most, if not all, ecosystems. Owing to its impact on survival and reproduction, it is increasingly important to consider this factor in ecological studies. The study of secondary sexual traits is of particular interest because they are under strong hormonal control and play a crucial role in mating. A neglected sub‐lethal effect of endocrine disruption is the reduction of male attractiveness, and the distortion of the sexual selection process. Nitrate is one of the most widespread endocrine disruptors because of its extensive use in agriculture. Studies, especially in amphibians, have mostly focused on early developmental stages, probably because these were considered critical for population dynamics. However, negative effects on adult survival or reproductive success may also affect population demography. We surveyed nitrate concentration in a large sample of ponds. We then exposed male palmate newts, Triturus helveticus, to high (75 mg L−1) but realistic concentration of sodium nitrate to investigate the effect of nitrate on the expression of secondary sexual traits and male attractiveness. Exposure to nitrate for 3 weeks was found to limit the expression of sexual traits and to reduce body growth; exposure for 10 days reduced male attractiveness. Female preferred males unexposed to nitrate in olfactory tests but not in visual tests. The expression of secondary sexual characteristics and body size is reduced in males exposed to realistic nitrate concentration. However, a drop in male attractiveness may first be caused by disruption of the production of olfactory cues. Depending on the frequency of contaminated breeding sites, the disruption of male ability to express sexual signals might affect the sexual selection process in palmate newts and eventually reduce population reproductive output. We discuss the ecological and evolutionary implications of this result.

Influence of depth on sex-specific energy allocation patterns in a tropical reef fish

The effect of depth on the distribution and sex-specific energy allocation patterns of a common coral reef fish, Chrysiptera rollandi (Pomacentridae), was investigated using depth-stratified collections over a broad depth range (5–39 m) and a translocation experiment. C. rollandi consistently selected rubble habitats at each depth, however abundance patterns did not reflect the availability of the preferred microhabitat suggesting a preference for depth as well as microhabitat. Reproductive investment (gonado-somatic index), energy stores (liver cell density and hepatocyte vacuolation), and overall body condition (hepato-somatic index and Fulton’s K) of female fish varied significantly among depths and among the three reefs sampled. Male conspecifics displayed no variation between depth or reef. Depth influenced growth dynamics, with faster initial growth rates and smaller mean asymptotic lengths with decreasing depth. In female fish, relative gonad weight and overall body condition (Fulton’s K and hepato-somatic index) were generally higher in shallower depths (≤10 m). Hepatic lipid storage was highest at the deepest sites sampled on each reef, whereas hepatic glycogen stores tended to decrease with depth. Depth was found to influence energy allocation dynamics in C. rollandi. While it is unclear what processes directly influenced the depth-related patterns in energy allocation, this study shows that individuals across a broad depth gradient are not all in the same physiological state and may contribute differentially to the population reproductive output.

Nest-site characteristics and breeding biology of the Black-cheeked Lovebird Agapornis nigrigenis in Zambia

The nest-site characteristics and breeding biology of the Black-cheeked Lovebird Agapornis nigrigenis in their natural habitat and in captivity were investigated as part of a wider study of the ecology of the species. Seventy-eight nests were found. Black-cheeked Lovebirds nested inside naturally formed cavities in live Mopane trees Colophospermum mopane, in localities which were used for roosting during the non-breeding season. Nest-site fidelity was suspected. Most nests were found in a loosely clumped distribution. Nest-site characteristics including cavity dimensions, height from ground, distance to three nearest nest trees, cavity entrance orientation and nest shape are presented. No nesting requirement appeared to be limiting, or to affect the population's reproductive output. Reproductive data were necessary to elucidate factors affecting reproductive success and to assist with the development of a conservation management plan for this Vulnerable species. Breeding occurred from January to May, coinciding with annual maximum rainfall and the early dry season, when a single clutch was raised by most pairs. Nesting chronology was correlated with mean monthly rainfall and major food source availability. Behavioural data on nest building, location, defence and breeding success are presented. Courtship, copulation, parental care and juvenile behaviours are reported, and clutch size, laying intervals and hatching successes of captive birds are discussed.

Intertidal distribution, population dynamics and production of the amphipod Uhlorchestia spartinophila in a Georgia, USA, salt marsh

The talitrid amphipod Uhlorchestia spartinophila Bousfield and Heard occurs in close association with the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the U.S. Atlantic coast. In order to assess its potential as a prey resource for secondary consumers, we followed the population and production dynamics of this amphipod from 3 November 1990 to 2 October 1991 in a salt marsh on Sapelo Island, Georgia. Semimonthly samples were taken along an intertidal transect, which extended from a vegetated creekbank levee landward 140 m to a site near the upland edge of the marsh. Amphipod densities ranged from 9 to 826 indm-2 and were greatest in the levee and high marsh habitats at opposite ends of the transect. The highest densities occurred in March to May and the lowest in November and December. Specific growth rates, which ranged from 0.001 to 0.024 mm mm-1 d-1 length and 0.003 to 0.068 mg mg-1 d-1 AFDW (ash-free dry weight), were least in winter and decreased with increasing amphipod size. Although some reproduction occurred year-round, most of the population's reproductive output was from January to May, when adults had the greatest size-specific mass. Sex ratio usually favored females, which were larger than males. Minimum adult female size was 5.4 mm total length (TL). Broods included from 1 to 28 eggs or young and increased with increasing body size, averaging 7.4 young for an average-size female of 7.6 mm TL. Annual production, which ranged from 0.769 to 1.444 g AFDW m-2, was least in the low marsh and greatest in the levee habitat. Production:biomass ratios were 15.4 to 17.3 in different habitats. Such high turnover rates, together with the population's broad intertidal distribution, suggest a greater contribution to trophic dynamics than is implied by the relatively low standing stock biomass of U. spartinophila in this marsh system.