Number Of Reproductive Events Research Articles

Reproductive characteristics of American bullfrogs (Lithobates catesbeianus) in their invasive range of the Pacific Northwest, USA

Invasive species pose a major threat to global biodiversity. The effects of invasive species can be strongly influenced and potentially mediated by their reproductive characteristics, such as fecundity, egg production, and duration and number of reproductive events. Selection for smaller body size at first reproduction can also play a role in their establishment, facilitating colonization and spread. The American bullfrog, native to the eastern U.S. (Lithobates catesbeianus), is a species that has invaded more than 40 countries across 4 continents. This species has become especially prevalent in the western United States since its introduction in the early 1900s. This study characterized reproductive characteristics of bullfrogs with emphasis on the minimum size at which males and females reach sexual maturity in the Willamette Valley, Oregon, USA invasion range. We collected and dissected 121 individuals in 2013 and 2017, quantifying characteristics of sexual maturity including snout-vent length, total length, sex, tympanum diameter, presence of distended oviducts or eggs for females, and testes length and sperm activity in males. Our results showed that the minimum reproductive size of both males and females was smaller relative to bullfrogs in their native range as well as in populations across their invasive range. Reduction in size at reproductive maturity is likely impacting the invasive success of American bullfrogs and this study gives us insight on management actions to control the invasion. Applying this insight, managers can adjust their definition of reproductively active adults, increasing the target population of culling and other control methods.

Host‐plant‐based restoration as a potential tool to improve conservation status of odonate specialists

Abstract Several species worldwide show rapid range retraction due to habitat degradation, and some of them have restricted distribution and specific resource needs. Such cases deserve particular attention and need urgent conservation actions to avoid extinction, and one way is to facilitate colonisation of new habitats by resource supplementation. Here, we investigate the changes in range distribution, during the last decade (2007–2016), of an endangered endemic damselfly, Calopteryx exul Selys, and assess the importance of its favourite host‐plant (Potamogeton nodosus) in colonisation and population dynamics in the last existing population of Algeria. We first used dynamic occupancy models to assess range distribution dynamics and we found that both occupancy and colonisation probabilities of the species were positively dependent on the occurrence of P. nodosus. There was also evidence that extinction probability increased with habitat disturbance but decreased with the occurrence of P. nodosus. Our experimental restoration showed that the augmentation of patches of P. nodosus increased the total number of individuals, the number of reproductive events and philopatry. Our study highlights the importance of insect–plant relationship in the establishment of effective restoration plans because of their implication in colonisation and extinction processes and population dynamics. Since most insect species from different orders and ecosystems are ecologically dependent on plants, our restoration approach may benefit a large range of threatened species and improve their conservation status.

Thinking beyond organism energy use: a trait‐based bioenergetic mechanistic approach for predictions of life history traits in marine organisms

AbstractThe functional trait‐based bioenergetic approach is emergent in many ecological spectra, from the conservation of natural resources to mitigation and adaptation strategies in a global climate change context. Such an approach relies on being able to exploit mechanistic rules to connect environmental human‐induced variability to functional traits (i.e. all those specific traits defining species in terms of their ecological roles) and use these to provide estimates of species life history traits (LH;e.g. body size, fecundity per life span, number of reproductive events).LHs are species‐specific and proximate determinants of population characteristics in a certain habitat. They represent the most valuable quantitative information to investigate how broad potential distributional boundaries of a species are, and to feed predictive population models. There is much to be found in the current literature that describes mechanistic functional trait‐based bioenergetics models, using them to test ecological hypotheses, but a mathematical framework often renders interpretation and use complicated. Here, we wanted to present a simpler interpretation and description of one of the most important recent mechanistic bioenergetic theories: the dynamic energy budget theory by Kooijman (Dynamic Energy Budget Theory for Metabolic Organisation, 2010, Cambridge University Press, Cambridge). Our main aim was to disentangle those aspects that at first reading may seem too mathematically challenging to many marine biologists, ecologists and environmental scientists, and present them for use in mechanistic applications.

Linking sub-individual and population level toxicity effects in Daphnia schoedleri (Cladocera: Anomopoda) exposed to sublethal concentrations of the pesticide α-cypermethrin

Synthetic pyrethroids are classified as moderately toxic to mammals and birds; nevertheless, they are highly toxic to non-target aquatic organisms such as fish and zooplankters. Chemical pollutants produce different effects in exposed organisms, ranging from biochemical to population responses. Cladocerans can modify the energy content of their offspring according to the surrounding medium as a way to improve their odds in case they have to cope with stressful conditions at birth. In this study, the effect of a synthetic pesticide on two levels of response in a Daphnia species different from those traditionally used as test organisms was evaluated. With this aim, Daphnia schoedleri neonates (<24 h) were exposed for 21 days to three sublethal concentrations of α-cypermethrin, 0.54, 5.4, and 54 ng L(-1), which correspond to 48-h EC1/100, EC1/10, and EC1, respectively. Effects were measured through a life table analysis for fecundity and survivorship. For effects on progeny, protein, carbohydrates, and lipids were determined and then transformed to caloric content. Biomarkers (BM) were expected to be the most sensitive evaluated response; nevertheless, population parameters such as survivorship and net reproductive rate (R0) were more sensitive since they presented significant differences with respect to controls at the lowest tested concentration. Neonates' caloric content varied during the reproductive period assessed and was negatively correlated to fecundity: as more neonates were born, less energy was provided by the adult females. Macromolecules concentration and caloric content values in cypermethrin-exposed adults were not different from those recorded in the control at the end of exposure time. The results herein presented suggest that stressed daphnids allocate more energy reserves to their offspring, although this strategy can vary depending on the number of reproductive events during the lifecycle, and on the toxicant's concentration. Sub-individual approaches to assess toxicant effects should be accompanied by demographic studies, which support population effect predictions inferred from BMs assessment.

Effects of recruiting age on senescence, lifespan and lifetime reproductive success in a long-lived seabird

Theories of ageing predict that early reproduction should be associated with accelerated reproductive senescence and reduced longevity. Here, the influence of age of first reproduction on reproductive senescence and lifespan, and consequences for lifetime reproductive success (LRS), were examined using longitudinal reproductive records of male and female blue-footed boobies (Sula nebouxii) from two cohorts (1989 and 1991). The two sexes showed different relationships between age of first reproduction and rate of senescent decline: the earlier males recruited, the faster they experienced senescence in brood size and breeding success, whereas in females, recruiting age was unrelated to age-specific patterns of reproductive performance. Effects of recruiting age on lifespan, number of reproductive events and LRS were cohort- and/or sex-specific. Late-recruiting males of the 1989 cohort lived longer but performed as well over the lifetime as early recruits, suggesting the existence of a trade-off between early recruitment and long lifespan. In males of the 1991 cohort and females of both cohorts, recruiting age was apparently unrelated to lifespan, but early recruits reproduced more frequently and fledged more chicks over their lifetime than late recruits. Male boobies may be more likely than females to incur long-term costs of early reproduction, such as early reproductive senescence and diminished lifespan, because they probably invest more heavily than females. In the 1991 cohort, which faced the severe environmental challenge of an El Niño event in the first year of life, life-history trade-offs of males may have been masked by effects of individual quality.

Population persistence in a landscape context: the case of endangered arctic fox populations in Fennoscandia

Anthropogenic fragmentation of habitat and populations is recognized as one of the most important factors influencing loss of biodiversity. Since it is difficult to quantify demographic parameters in small populations, we need alternative methods to elucidate important factors affecting the viability of local populations. The Fennoscandian arctic fox inhabits a naturally fragmented alpine tundra environment, but historic anthropogenic impacts have further fragmented its distribution. After almost 80 yr of protection, the population remains critically endangered. Both intrinsic factors (related to the isolation and size of sub‐populations) and extrinsic factors (related to environmental conditions influencing patch quality and interspecific competition) have been proposed as explanations for the lack of population growth. To distinguish between these hypotheses, we conducted a spatially explicit analysis that compares areas where the species has persisted with areas where it has become locally extinct. We used characteristics of the fragments of alpine tundra habitat and individual arctic fox breeding dens (including both currently active dens and historically active dens) within the fragments to evaluate the importance of habitat characteristics and connectivity in explaining variation in persistence within a fragment. The number of reproductive events in a fragment was related to the size of the fragment, but not more than expected following a 1:1 relationship, suggesting little effect of fragment size on the relative number of reproductions. The likelihood of a den being used for breeding was positively associated with factors minimising interspecific competition as well as increasing within‐fragment connectivity. These results support the idea that the failure of Fennoscandian arctic fox to recover is caused by demographic factors that can be related to fine‐scale Allee or Allee‐like effects, as well as environmental influences related to increased competition and exclusion by red foxes.

Decline in the frequency and benefits of multiple brooding in great tits as a consequence of a changing environment.

For multiple-brooded species, the number of reproductive events per year is a major determinant of an individual's fitness. Where multiple brooding is facultative, its occurrence is likely to change with environmental conditions, and, as a consequence, the current rates of environmental change could have substantial impacts on breeding patterns. Here we examine temporal population-level trends in the proportion of female great tits (Parus major) producing two clutches per year ('double brooding') in four long-term study populations in The Netherlands, and show that the proportion of females that double brood has declined in all populations, with the strongest decline taking place in the last 30 years of the study. For one of the populations, for which we have data on caterpillar abundance, we show that the probability that a female produces a second clutch was related to the timing of her first clutch relative to the peak in caterpillar abundance, and that the probability of double brooding declined over the study period. We further show that the number of recruits from the second clutch decreased significantly over the period 1973-2004 in all populations. Our results indicate that adjustment to changing climatic conditions may involve shifts in life-history traits other than simply the timing of breeding.

Longevity in cheetahs: the key to success?

An understanding of the factors governing reproductive success has fundamental implications for population demography, conservation, selection and adaptation. Although a consistent positive correlation between lifetime reproductive success and longevity has been reported for many iteroparous organisms, few studies have explored how longevity influences annual individual performance. In this study we show (1) that longevity and lifetime reproductive success are positively but not linearly correlated, (2) that short-lived individuals have higher annual reproductive success, (3) that the generally lower success of the last breeding occasion increased with females' longevity, and (4) that long-lived females have higher chances of rearing long-lived females. We suggest that experience and the increase in the number of reproductive events with longevity are key processes leading to a strong correlation between (1) lifetime reproductive success and longevity and (2) mother and daughter longevities. Our results demonstrate the importance of long term studies that follow multiple generations in gaining a full understanding of the factors affecting reproductive success.

Longevity in cheetahs: the key to success?

An understanding of the factors governing reproductive success has fundamental implications for population demography, conservation, selection and adaptation. Although a consistent positive correlation between lifetime reproductive success and longevity has been reported for many iteroparous organisms, few studies have explored how longevity influences annual individual performance. In this study we show (1) that longevity and lifetime reproductive success are positively but not linearly correlated, (2) that short‐lived individuals have higher annual reproductive success, (3) that the generally lower success of the last breeding occasion increased with females’ longevity, and (4) that long‐lived females have higher chances of rearing long‐lived females. We suggest that experience and the increase in the number of reproductive events with longevity are key processes leading to a strong correlation between (1) lifetime reproductive success and longevity and (2) mother and daughter longevities. Our results demonstrate the importance of long term studies that follow multiple generations in gaining a full understanding of the factors affecting reproductive success.

Allocation to reproduction following experimental defoliation in Platanthera bifolia (Orchidaceae)

The roles of herbivory and pollination success in plant reproduction have frequently been examined, but interactions between these two factors have gained much less attention. In three field experiments, we examined whether artificial defoliation affects allocation to attractiveness to pollinators, pollen production, female reproductive success and subsequent growth in Platanthera bifolia L. (Rich.). We also recorded the effects of inflorescence size on these variables. We studied the effects of defoliation on reproductive success of individual flowers in three sections of inflorescence. Defoliation and inflorescence size did not have any negative effects on the proportion of opened flowers, spur length, nectar production or the weight of pollinia. However, we found that hand-pollination increased relative seed production and defoliation decreased seed set in most cases. Interactions between hand-pollination and defoliation were non-significant indicating that defoliation did not affect female reproductive success indirectly via decreased pollinator attraction. Plants with a large inflorescence produced relatively more seeds than plants with a small inflorescence only after hand-pollination. The negative effect of defoliation on relative capsule production was most clearly seen in the upper sections of the inflorescence. In addition to within season effects of leaf removal, defoliated P. bifolia plants may also have decreased lifetime fitness as a result of lower seed set within a season and because of a lower number of reproductive events due to decreased plant size (leaf area) following defoliation. Our study thus shows that defoliation by herbivores may crucially affect reproductive success of P. bifolia.

Molecular clocks: when timesare a-changin'

The molecular clock has proved to be extremely valuable in placing timescales on evolutionary events that would otherwise be difficult to date. However, debate has arisen about the considerable disparities between molecular and palaeontological or archaeological dates, and about the remarkably high mutation rates inferred in pedigree studies. We argue that these debates can be largely resolved by reference to the "time dependency of molecular rates", a recent hypothesis positing that short-term mutation rates and long-term substitution rates are related by a monotonic decline from the former to the latter. Accordingly, the extrapolation of rates across different timescales will result in invalid date estimates. We examine the impact of this hypothesis with respect to various fields, including human evolution, animal domestication and conservation genetics. We conclude that many studies involving recent divergence events will need to be reconsidered.

A COMPARATIVE APPROACH TO UNDERSTANDING CAUSES AND CONSEQUENCES OF MOLLUSC–DIGENEAN SIZE RELATIONSHIPS: A CASE STUDY WITH ALLOCREADIID TREMATODES AND CYCLOCALYX CLAMS

Allocreadiid flukes often parasitize and castrate sphaeriid freshwater clams. The effects of parasitic castrators on host population life history can lead to earlier reproductive onset, changes in body size, or changes in the number of reproductive events per year. However, little is known about whether species- or clade-level traits are associated with parasite prevalence. In this study, we examine if phenotypic effects, e.g., size change, seen at the population level, sort to the species or clade level. To answer this question, we determined if different-sized host species in the ecologically important, widespread, and common sphaeriid subgenus Cyclocalyx have different prevalences of allocreadiid infection. After showing that large species are more than 12 times more likely to have patent infections than small species, we examined the evolution of size within Cyclocalyx lineages. Transitions from large size to small size or vice versa have occurred at least twice and probably many times during lineage diversification, perhaps relating to trade-offs between clutch size and parasite risk. Finally, based on existing data, we show that it is unlikely that age and body size are correlated; therefore, a simple age-exposure model is not a sufficient explanation for parasite prevalence in this clade.

Low proportions of reproducing hemiclonal females increase the stability of a sexual parasite–host system (Rana esculenta, R. lessonae)

Summary 1. The number of reproductive events per lifetime affects all levels of ecological complexity, including the structure and dynamics of species communities. Here we investigate a sexual parasite‐host system with two water frog species of which one ( Rana esculenta , E) is a hemiclonal hybrid that depends on one of its parental species ( R. lessonae , L) for successful reproduction. Previous theoretical models have shown that relative fecundities are important for the species composition and stability of this system, but empirical data from natural mixed LE-populations were lacking. 2. We used three different methods to estimate the proportion of annually reproducing hybrid and parental females: (a) screening for eggs through a tiny incision into the belly skin, (b) measuring plasma hormone titres from blood samples and (c) counts of egg clumps deposited into the pond. 3. After accounting for the respective adult population sizes of the two female types ‐ calculated from mark‐recapture analyses ‐ we found that all three estimates revealed a higher proportion of reproducing L- than E-females. Ratios ranged from 1·43 (method c), to 1·90 (a) to 2·38 (b), with an average of 1·90. 4. We also investigated three potential causes for the fecundity difference (age structure, hybrid sterility and differences in reproductive costs) but could not find compelling evidence for any of them. We hypothesize that size-related differences in energy budgets offer the most probable explanation. 5. The consequences of the observed species differences in annual reproductive success were analysed with a theoretical model. The higher proportion of reproducing R. lessonae females increases the possibilities for stable coexistence in mixed LE-populations under a variety of combinations of mating patterns, relative fecundity and larval performance. The results, however, also indicate new limits for coexistence and highlight the paramount importance of larval competition for explaining the composition and dynamics of mixed LE-populations.

Energy allocation patterns inBufo marinusfrom two habitats in Venezuela

ABSTRACTPatterns of energy allocation in the cane toad,Bufo marinus, were explored by analysing the seasonal variations in fat bodies and gonads in two populations subjected to different rainfall regimes and water permanency. In both populations, fat deposition occurred shortly after the rainy season due to an increase in feeding activity. In contrast, the timing of reproduction varied between sites according to the availability of suitable water bodies. Nevertheless, females with mature oocytes were predominant during the dry season, even in populations that bred throughout the year in permanent ponds. This suggests that seasonal variations in the nutritional condition of adults may also result in a tendency towards cyclicity in the reproduction ofB. marinusin tropical regions. Analyses of allometric relationships of reproductive and storage tissues with body weights indicated that the fractions of weights in reproductive tissues did not vary either with the size of females or between populations. On the contrary, not only did larger toads have proportionally larger fat bodies, but those from wet sites had greater fractions of weight allocated to fat bodies than those from dry sites. This suggests that reproductive output may be fixed in this species and, therefore, excess energy is allocated to fat bodies. Given that the initiation of ovarian cycles depends on the restoration of proper nutritional levels, energy stored in fat bodies during breeding may allow females to resume a new ovarian cycle shortly after spawning and thus maximize the number of reproductive events.