Optimal Timing Of Reproduction Research Articles

Climate warming may affect the optimal timing of reproduction for migratory geese differently in the low and high Arctic

Rapid climate warming is driving organisms to advance timing of reproduction with earlier springs, but the rate of advancement shows large variation, even among populations of the same species. In this study, we investigated how the rate of advancement in timing of reproduction with a warming climate varies for barnacle goose (Branta leucopsis) populations breeding at different latitudes in the Arctic. We hypothesized that populations breeding further North are generally more time constrained and, therefore, produce clutches earlier relative to the onset of spring than southern populations. Therefore, with increasing temperatures and a progressive relief of time constraint, we expected latitudinal differences to decrease. For the years 2000–2016, we determined the onset of spring from snow cover data derived from satellite images, and compiled data on egg laying date and reproductive performance in one low-Arctic and two high-Arctic sites. As expected, high-Arctic geese laid their eggs earlier relative to snowmelt than low-Arctic geese. Contrary to expectations, advancement in laying dates was similar in high- and low-Arctic colonies, at a rate of 27% of the advance in date of snowmelt. Although advancement of egg laying did not fully compensate for the advancement of snowmelt, geese laying eggs at intermediate dates in the low Arctic were the most successful breeders. In the high Arctic, however, early nesting geese were the most successful breeders, suggesting that high-Arctic geese have not advanced their laying dates sufficiently to earlier springs. This indicates that high-Arctic geese especially are vulnerable to negative effects of climate warming.

Flowering schedule in a perennial plant; life-history trade-offs, seed predation, and total offspring fitness.

Optimal timing of reproduction within a season may be influenced by several abiotic and biotic factors. These factors sometimes affect different components of fitness, making assessments of net selection difficult. We used estimates of offspring fitness to examine how pre-dispersal seed predation influences selection on flowering schedule in an herb with a bimodal flowering pattern, Actaea spicata. Within individuals, seeds from flowers on early terminal inflorescences had a higher germination rate and produced larger seedlings than seeds from flowers on late basal inflorescences. Reproductive value, estimated using demographic integral projection models and accounting for size-dependent differences in future performance, was two times higher for intact seeds from early flowers than for seeds from late flowers. Fruits from late flowers were, however, much more likely to escape seed predation than fruits from early flowers. Reproductive values of early and late flowers balanced at a predation intensity of 63%. Across 15 natural populations, the strength of selection for allocation to late flowers was positively correlated with mean seed predation intensity. Our results suggest that the optimal shape of the flowering schedule, in terms of the allocation between early and late flowers, is determined by the trade-off between offspring number and quality, and that variation in antagonistic interactions among populations influences the balancing of this trade-off. At the same time they illustrate that phenotypic selection analyses that fail to account for differences in offspring fitness might be misleading.

Pathogenic bacteria and timing of laying

Pathogenic bacteria constitute a serious threat to viability of many organisms. Because growth of most bacteria is favored by humid and warm environmental conditions, earlier reproducers in seasonal environments should suffer less from the negative consequences of pathogenic bacteria. These relationships, and the effects on reproductive success, should be particularly prominent in predators because they are frequently exposed to pathogenic microorganisms from sick prey. Here, we presented and tested this hypothesis by sampling bacteria on adult and nestling goshawks Accipiter gentilis. We predicted that early breeders and their offspring should have fewer bacteria than those reproducing later during the breeding season. Adult goshawks with a high abundance of Staphylococcus on their beak and claws were easier to capture and their laying date was delayed. Moreover, goshawks that laid their eggs later had offspring with more Staphylococcus on their beaks and claws. The strength of the association between laying date and bacterial density of nestlings was stronger during the warm spring of 2013, when nestlings suffered from a higher abundance of pathogenic bacteria. Hatching failure and fledging failure were more common in nests with a higher abundance of Staphylococcus independently of the number of years occupied, laying date, and age of the female nest owner. These findings imply that timing of reproduction may be under the influence of pathogenic bacteria. Because early breeding goshawks produce more recruits than later breeders, our results suggest a role for pathogenic bacteria in the optimal timing of reproduction.

Foraging and reproductive behavior of Arizona gray squirrels (Sciurus arizonensis): impacts of climatic variation

Optimal timing of reproduction is critical to ensure adequate conditions for raising young. However, factors influencing timing of reproduction may differ between sexes. Harsh seasonal environments offer unique opportunities to link timing with resource availability and strategies of the sexes. The Arizona gray squirrel (Sciurus arizonensis) inhabits arid forests in which precipitation is highly seasonal and exceptionally variable; however, no data are available on diet or reproduction. We investigated annual variation in foraging and reproductive habits of Arizona gray squirrels to assess responses to extreme seasonality. We found that Arizona gray squirrels have a diverse diet, with consumption of major food items shifting between years. Reproduction also varies between years. Reproductive output was greater in 2008, with more females successfully reproducing and males remaining in reproductive condition for extended periods. Males shifted timing of reproductive behaviors in response to female receptivity, which tracked food availability. This shift likely reflects variation in food production due to precipitation, because rainfall varied greatly, with most years prior to and during our study recording below-average rainfall. With drought conditions and extreme rainfall events predicted to increase with climate change, understanding the relationship between climatic events, phenology of food production, and impacts on reproduction is critical when attempting to manage and conserve species.

Predation risk and reproduction in the bank vole

Context Life-history strategies are the means that organisms use to achieve successful reproduction in environments that vary in time and space. Individual animals maximise life-time reproductive success (LRS) through optimal timing of reproduction and investment in offspring. A crucial factor affecting LRS is predation risk in a highly seasonal environment. According to the breeding-suppression hypothesis (BSH), females should delay breeding under short periods of high predation risk. Delayed breeding under risk is suggested to have substantial consequences for females’ fitness. Aims We tested the BSH in an iteroparous boreal small rodent, the bank vole, Myodes glareolus. Methods We used caged-live weasels and spread weasel scent to simulate increased predation risk in four of eight 0.25-ha outdoor enclosures. We monitored females’ reproduction in three periods (May, July, August), i.e. during the breeding season over the course of summer. Key results Contrary to our main prediction, predation risk did not affect timing of mating, pregnancy rate or litter size in any study period. Conclusions and implications We conclude that during the short but resource-rich breeding season of boreal summer, postponing breeding does not seem to be an optimal strategy for females, even under high risk of predation. Under favourable summer condition, i.e. in circumstances without any constraining factors such as food or conspecific density, females manage to balance the costs of predation against benefits of resource availability and do not suppress breeding. Although the BSH has been studied widely, also our results reveal the intricacies of this adaptive behaviour.

An Empirical Model of the Optimal Timing of Reproduction for Female Amphipods Infected by Trematodes

An Empirical Model of the Optimal Timing of Reproduction for Female Amphipods Infected by Trematodes

The effects of density-dependent offspring mortality on the synchrony of reproduction

Mortality rates often depend on the size of a population. Using ideal free theory to model the optimal timing of reproduction in model populations, I considered how the specific relationship between density-dependent offspring mortality and population size affects the optimal temporal distribution of reproduction. The results suggest that the specific form of the relationship between density-dependent mortality and the number of offspring produced determines the degree to which reproduction within a population is synchronous. Specifically, reproductive synchrony decreases as density-dependent mortality becomes increasingly inversely related to the number of offspring produced and is highest when density-dependent mortality is directly density-dependent. These findings support the suggestion that predation pressure selects for greater reproductive synchrony in species where mortality is directly density-dependent, but does not affect the timing of reproduction in species with density-independent rates of mortality.

Genotypic and Plastic Variation in Plant Size: Effects on Fecundity and Allocation Patterns in Lychnis Flos-Cuculi Along a Gradient of Natural Soil Fertility

1 Genotypic and plastic variation in plant size, and trade-offs among components of reproduction were studied using cloned individuals from 24 parental plants of the perennial hay-meadow species Lychnis-flos-cuculi, planted in four sites along a gradient of natural soil fertility. 2 Plant biomass, survival and fecundity differed significantly among clones and sites. Differences in survival and early components of fecundity among clones were strongly average rosette biomass attained during the first year. 3 There were significant clone-site interactions. However, a small number of clones which ranked high for plant biomass and fruit production at all sites, made a large contribution to local fruit production within a year across the entire gradient. 4 Patterns of biomass allocation and timing of first reproduction differed significantly among clones. A large part of this variation could be explained by clonal differences in average plant biomass attained during the first year. We conclude therefore that clonal variation in allocation patterns reflected differences in resource acquisition, rather than differences in partitioning strategies underlying life-history evolution. 5 Consequences of delaying first reproduction varied among sites. Precocity was favoured in the least productive site, whereas at intermediate soil fertility individuals that postponed reproduction gained a three-fold increase in fecundity at first reproduction, with no significant reduction in survival to this stage. Optimal timing of reproduction may thus vary at a small scale. 6 Genetically based trade-offs between only observed in the less productive sites. Costs of reproduction were also only apparent at such sites, supporting the idea that the expression of trade-offs and costs is most likely under low resource conditions. 7 In the more productive sites, within- and among-clone correlations between etative and generative reproduction, and among five components of fecundity were generally insignificant or positive. This available, differences in both microsite quality and resource a governed patterns of covariance. 8 Fruit predation by caterpillars of the noctuid Hadena bicruris was dependant on plant size. In the site with lowest individual fecundity, conferring a relative advantage to smaller sized individuals. [KEYWORDS: Allocation trade-offs; fecundity components; hadena bicruris; phenotypic plasticity; size hierarchies Reproductive characteristics; seedling performance; impatiens-capensis; viola-sororia; lanceolata l; selection; population;environment; yield; variability]

On the Optimal Timing of Reproduction

Previous articleNext article No AccessNotes and CommentsOn the Optimal Timing of ReproductionShmuel AmirShmuel Amir Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 114, Number 3Sep., 1979 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/283495 Views: 3Total views on this site Citations: 2Citations are reported from Crossref Copyright 1979 The University of ChicagoPDF download Crossref reports the following articles citing this article:Theodore G. Wong, David D. Ackerly Optimal reproductive allocation in annuals and an informational constraint on plasticity, New Phytologist 166, no.11 (Mar 2005): 159–172.https://doi.org/10.1111/j.1469-8137.2005.01375.xSimon A. Levin Some Models for the Evolution of Adaptive Traits, (Jan 1980): 56–72.https://doi.org/10.1007/978-3-642-93161-1_4