Survival of the Richest: The Malthusian Mechanism in Pre-Industrial England

Fundamental to the Malthusian model of pre-industrial society is the assumption that higher income increased reproductive success. Despite the seemingly inescapable logic of this model, the empirical support for this vital assumption in the preindustrial world is weak. Here we examine the relationship between income and net fertility using a large new cross-sectional data set on reproductive success, social status and income for England between 1585 and 1638. We find that for early seventeenth century England, a society seemingly close to a Malthusian equilibrium, wealth at death robustly predicts reproductive success. The richest male testators left behind double the number of children of the poorest. Consequently in the static English economy of this period social mobility was generally downwards. The strong association in England between wealth and reproductive success seems to also extend back to at least 1250.england and economy

Modelling temperature-dependent larval development and\ud subsequent demographic Allee effects in adult populations of the alpine butterfly Parnassius smintheus

Climate change has been attributed as a driver of changes to ecological systems worldwide and understanding the effects of climate change at individual, population, community, and ecosystem levels has become a primary concern of ecology. One avenue toward understanding the impacts of climate change on an ecosystem is through the study of environmentally sensitive species. Butterflies are sensitive to climatic changes due to their reliance on environmental cues such as temperature and photoperiod, which regulate the completion of life history stages. As such, the population dynamics of butterflies may offer insight into the impacts of climate change on the health of an ecosystem. In this paper we study the effects of rearing temperature on the alpine butterfly Parnassius smintheus (Rocky Mountain Apollo), both directly through individual phenological changes and indirectly through adult reproductive success at the population level. Our approach is to formulate a mathematical model of individual development parameterized by experimental data and link larval development to adult reproductive success. A Bernoulli process model describes temperature-dependent larval phenology, and a system of ordinary differential equations is used to study impacts on reproductive success. The phenological model takes field temperature data as its input and predicts a temporal distribution of adult emergence, which in turn controls the dynamics of the reproductive success model. We find that warmer spring and summer temperatures increase reproductive success, while cooler temperatures exacerbate a demographic Allee effect, suggesting that observed yearly fluctuations in P. smintheus population size may be driven by inter-annual temperature variability. Model predictions are validated against mark-recapture field data from 2001 and 2003 − 2009

Integrated behavioural and stable isotope data reveal altered diet linked to low breeding success in urban-dwelling blue tits (Cyanistes caeruleus)

Animals often show reduced reproductive success in urban compared to adjacent natural areas. The lower availability and quality of natural food in cities is suggested as one key limiting factor. However, only few studies have provided conclusive support by simultaneously assessing food availability, diet and fitness. We consolidate this evidence by taking a holistic approach, comparing blue tits breeding in forest, suburban and urban areas. We (a) assessed arthropod availability, (b) investigated parental provisioning behaviour, (c) inferred diet through stable isotope analysis, and (d) measured reproductive success. At the urban site, we found a significant reduction in caterpillar availability, the main food source of blue tits, and consequently urban tits fed their offspring with fewer caterpillars than forest and suburban birds. Stable isotope analysis confirmed that diet in the urban area was fundamentally different than in the other sites. Reproductive success was lower in both urban and suburban sites compared to the forest site, and was positively associated with volume of provisioned caterpillars. Our findings provide strong integrative evidence that urban blue tit nestlings are not receiving a suitable diet, and this may be an important limiting factor for urban populations of this and potentially many other species

Early maternal experience shapes offspring performance in the wild

Both the environments experienced by a mother as a juvenile and an adult can affect her investment in offspring. However, the implications of these maternal legacies, both juvenile and adult, for offspring fitness in natural populations are unclear. We investigated whether the juvenile growth rate and adult reproductive traits (length, body condition, and reproductive investment at spawning) of female wild Atlantic salmon (Salmo salar) were related to the growth and survival of their offspring. Adult salmon captured on their upstream migration were used to create experimental full-sib clutches of eggs, which were mixed and then placed in artificial nests in a natural stream that lacked salmon due to a migration barrier. Four months later we resampled the stream to obtain family-level estimates of offspring size and survival. Mothers that had grown slowly as juveniles (as determined by scalimetry) but had invested heavily in reproduction (egg production for a given body length) and were in relatively poor body condition (somatic mass for a given body length) at spawning produced the largest eggs. Larger eggs resulted in larger juveniles and higher juvenile survival. However, after controlling for egg size, offspring growth was positively related to maternal juvenile growth rate and reproductive investment. The predictors of offspring survival (i.e., reproductive success) varied with the juvenile growth rate of the mother: If females grew slowly as juveniles, their reproductive success was negatively related to their own body condition. In contrast, the reproductive success of females that grew quickly as juveniles was instead related positively to their own body condition. Our results show that maternal influences on offspring in the wild can be complex, with reproductive success related to the early life performance of the mother, as well as her state at the time of breeding

Divorce in cooperatively breeding long-tailed tits: a consequence of inbreeding avoidance?

The decision of whether to divorce a breeding partner between reproductive attempts can significantly affect individual fitness. In this paper, we report that 63% of surviving pairs of long-tailed tits Aegithalos caudatus divorced between years. We examine three likely explanations for the high divorce rate in this cooperative breeder. The 'better option' hypothesis predicts that divorce and re-pairing increases an individual's reproductive success. However, divorcees did not secure better partners or more helpers and there was no improvement in their reproductive success following divorce. The 'inbreeding avoidance' hypothesis predicts that females should disperse from their family group to avoid breeding with philopatric sons. The observed pattern of divorce was consistent with this hypothesis because, in contrast to the usual avian pattern, divorce was typical for successful pairs (81%) and less frequent in unsuccessful pairs (36-43%). The 'forced divorce' hypothesis predicts that divorce increases as the number of competitors increases. The pattern of divorce among failed breeders was consistent with this hypothesis, but it fails to explain the overall occurrence of divorce because divorcees rarely re-paired with their partners' closest competitors. We discuss long-tailed tits' unique association between divorce and reproductive success in the context of dispersal strategies for inbreeding avoidance

The contribution of differential hatching success to the fitness of species and interspecific hybrids

Resting egg banks of microcrustaceans have been used to reconstruct the evolutionary and ecological history of species. However, recent studies provided evidence for a discrepancy between dormant propagules in the sediment and the planktonic population. This pattern raises two questions: First, what is the value of data on resting egg banks for population dynamics over time and second, which component of the reproductive cycle causes the observed inconsistency? In our study we focussed on the second question by comparing the taxon composition of a resting egg bank with the reproductive success of ex-ephippial hatchlings. Species and interspecific hybrid identification of dormant and hatched stages was achieved through the application of restriction fragment length polymorphism analysis of an internal transcribed spacer region. We found no significant deviation between the proportion of hatched Daphnia galeata, D. galeata x hyalina and D. hyalina individuals and the observed taxon composition of the resting egg bank. However, species and hybrids differed in their mode and relative success of reproduction. We conclude that the components of reproductive success in Daphnia contribute differentially to the fitness of species and interspecific hybrids. The discrepancy between resting egg banks and "active" planktonic populations results not from differential hatching of species but from the reproductive success of ex-ephippial females and the timing and frequency of sexual reproduction of the different taxa

Postnatal depression and reproductive success in modern, low-fertility contexts

Background and objectives: Postnatal depression (PND) presents a puzzling phenomenon to evolutionary anthropologists as it is highly prevalent and yet detrimental to child development and maternal health. Adaptive explanations have been proposed, but have not been tested with data that directly link PND to female fertility. Methodology: A survey was designed to gather complete reproductive histories and retrospective measures of PND to measure the effects of PND on fitness. Respondents were born between 1930 and 1967, with the majority based in the UK during their childrearing years. The hypothesis that PND is detrimental to fitness is assessed using Mann–Whitney U tests on completed fertility. Binary logistic regression modelling is used to test the hypothesis that PND reduces the likelihood of parity progression. Results: Women experiencing PND at their first or second birth have lower completed fertility, with PND at the first birth leading to lowered fertility. Logistic regression analyses show that this is the result of reductions in the likelihood of parity progression to a third birth when PND is experienced at the first birth or when repeat bouts occur. Conclusions and implications: Our results call into question adaptationist arguments, contribute to the growing understanding of the importance of emotional wellbeing to fertility decision making, and given the economic consequences of markedly below replacement fertility, highlight a potential new source of financial incentive to invest in screening and preventative measures to ensure good maternal mental health

REPRODUCTIVE SUCCESS IN HATCHERY-PRODUCED EASTERN OYSTER, CRASSOSTREA VIRGINICA (GMELIN)

The eastern oyster (Crassostrea virginica Gmelin 1791) has great ecological and economic importance but populations have declined, especially in Chesapeake Bay, to historically low numbers. Hatcheries strive to produce oysters with beneficial characteristics for supplementation and commercial purposes, both natural and stimulated mass spawning. Unequal contribution of parents in mass spawnings potentially can lead to high levels of inbreeding and a loss of beneficial characteristics in offspring. In this study, we determined microsatellite genotypes for parents (n^parents =24, 49, and 77 parents) and progeny (n=96 each) of three hatchery-produced families and used the data for parental assignment. We observed the presence of more than two alleles per locus for some offspring, yet because genetic analysis software only allows for a maximum of two alleles per locus, we chose the two alleles with the strongest signals. For the three parent “populations,” 71% of alleles had frequencies of \u3c0.05 and observed heterozygosities were lower than expected by an average factor of 0.27. Inbreeding within the various parent populations was similar across the three families ranging from F^IS 0.26–0.43. In all three families, the offspring exhibited greater levels of genetic diversity and lower inbreeding levels than the parents (F^IS 0.14–0.21), and in some cases offspring exhibited alleles that were not present in the parents. Variance in the number of offspring produced per parent was observed for all families and in general, \u3c10% of potential parents (generally 2-5 females and 1-3 males) produced \u3e10% of the offspring. Reproductive success for spawning parents, N^b, determined by three methods, ranged from 0.07 to 0.27. As the number of parents per family increased, a higher proportion of parents failed to produce offspring. Across all three families, the average effective number of breeders was N^b = 7.1 and the level of reproductive success was inversely proportional to the number of potential parents. This finding implies that to maintain high levels of diversity and beneficial characteristics in the offspring (and to avoid the chance of unintentional inbreeding), hatcheries should perform more spawnings with fewer parents

Selecting habitat to what purpose? The advantage of exploring the habitat-fitness relationship

Measures of reproductive success have been recognized in many fields as essential tools to assess the status of populations, species, and communities. However, difficulties in gathering data on reproductive success often prevent researchers from taking advantage of the information offered by those measures. For example, most of habitat selection studies do not include reproductive success in their analysis even though doing so would highly improve our understanding of the habitat selection process. In our study, we aimed to assess to what extent habitat selection choices made by adult individuals are directed to increase their annual reproductive success. We tested this idea by first developing habitat selection models and then relating the results of those models to two measures of reproductive success. Using wolves, Canis lupus, as the study species, we determined that not all habitat selection choices performed by adult wolves were related to their annual reproductive success. The results varied also in relation to the measure of reproductive success used in the analysis and other individual-, group-, and population-level factors. Likely, adult female wolves select habitat characteristics to increase not only their annual reproductive success but also their lifetime reproductive success, for example, by ensuring their own survival and reproductive abilities in subsequent years. Our study suggests that a variety of motivations may govern habitat choices performed by adult individuals and including different measures of fitness in habitat selection studies can improve our understanding of these complex processes