1,720,983 research outputs found
Experimental and comparative analyses of maternal age and senescence
No full textSenescence is often described as an age-related physiological deterioration accompanied
with declining fertility and increasing mortality, and it is believed to be the result of
declining forces of natural selection. A manifestation of senescence that has attracted
much recent interest is the detrimental effect of increasing maternal age acting on
offspring traits. However, uncertainty arises when attempting to describe the prevalence
and ubiquity of this third form of ageing and the evolutionary causes for diversity in
ageing trajectories. Here I address the following questions: (1) How are maternal age
effects distributed across taxa? And (2) Can an evolutionary perspective help us to
understand the observed diversity in maternal age effects and demographic senescence?
I addressed these through (i) a cross-fostering ageing experiment using a laboratory
population of burying beetle, Nicrophorus vespilloides to decouple the separate effects
of increasing pre- and postnatal maternal age, whilst accounting for the potential bias
of selective disappearance. I found no evidence for maternal age effects or effects deriving
from selective disappearance. These results suggest that current theory may be
insufficient to account for the true diversity in ageing patterns. (ii) A meta-analytical
review of maternal effect senescence to investigate the prevalence and diversity of
maternal effect ageing patterns and the performance of an evolutionary model to predict
observed patterns. We found taxa-wide evidence for maternal age effects on offspring
survival. However the direction of these effects was based on phylogenetic constraints
with laboratory and natural-mammal species showing a decline, but natural-bird species
showing an ambiguous effect of maternal age. The evolutionary model was shown to
improve in performance compared to evolution-agnostic demographic models when
describing maternal effect ageing in natural populations. This result suggests an
evolutionary cause to maternal effect senescence. (iii) Lastly, I performed a comparative
analysis of vital rate selection across the tree of life. Using extensive existing databases
of life history data coupled with predictions from two evolutionary theories, I derived
correlations between predicted and observed vital rates across multiple animal species.
I found that whilst natural selection had weak predictive power when describing
patterns of mortality, age-specific fertility patterns showed extensive departures from
evolutionary predictions. Additionally, I found that several biological processes were
readily contributing to non-conformance of Hamilton-like ageing. Taken together, we
provide convincing evidence to suggest that both natural selection and biological
processes have helped shape the vast diversity of observed ageing rates that exist across
the tree of life
Data from: Disentangling pre- and post-natal maternal age effects on offspring performance in an insect with elaborate maternal care
No full textMaternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and post-natal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of burying beetle, Nicrophorus vespilloides, to examine both the effects of female pre- and post-natal maternal age on offspring life history traits and the post-care outcomes of mothers while accounting for selective disappearance of post-natal caregivers. Neither pre- nor post-natal maternal age affected offspring longevity or larval weight at hatching, and post-natal age had no effect upon post-care maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg-producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care
Triparental ageing in a laboratory population of an insect with maternal care
No full textParental age at reproduction influences offspring size and survival by affecting prenatal and postnatal conditions in a wide variety of species, including humans. However, most investigations into this manifestation of ageing focus upon maternal age effects; the effects of paternal age and interactions between maternal and paternal age are often neglected. Furthermore, even when maternal age effects are studied, pre- and postnatal effects are often confounded. Using a cross-fostered experimental design, we investigated the joint effects of pre-natal paternal and maternal and post-natal maternal ages on five traits related to offspring outcomes in a laboratory population of a species of burying beetle, Nicrophorus vespilloides. We found a significant positive effect of the age of the egg producer on larval survival to dispersal. We found more statistical evidence for interaction effects, which acted on larval survival and egg length. Both interaction effects were negative and involved the age of the egg-producer, indicating that age-related pre-natal maternal improvements were mitigated by increasing age in fathers and foster mothers. These results agree with an early study that found little evidence for maternal senescence, but it emphasizes that parental age interactions may be an important contributor to ageing patterns. We discuss how the peculiar life history of this species may promote selection to resist the evolution of parental age effects, and how this might have influenced our ability to detect senescence
The diversity of maternal-age effects upon pre-adult survival across animal species
No full textMaternal senescence is the detrimental effect of increased maternal age on offspring performance. Despite much recent interest given to describing this phenomenon, its distribution across animal species is poorly understood. A review of the published literature finds that maternal age affects pre-adult survival in 252 of 272 populations (93%) representing 97 animal species. Age effects tended to be deleterious in invertebrates and mammals, including humans, confirming the presence of senescence. However, bird species were a conspicuous exception, as pre-adult survival tended to increase with maternal age in surveyed populations. In all groups, maternal-age effects became more negative in older mothers. Invertebrates senesced faster than vertebrates, and humans aged faster than non-human mammals. Within invertebrates, lepidopterans demonstrated the most extreme rates of maternal-effect senescence. Among the surveyed studies, phylogeny, life history and environment (e.g. laboratory versus wild populations) were tightly associated; this made it difficult to make confident inferences regarding the causes of diversity for the phenomenon. However, we provide some testable suggestions, and we observe that some differences appear to be consistent with predictions from evolutionary theory. We discuss how future work may help clarify ultimate and proximate causes for this diversity
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fitness benefits of dietary restriction
No full textDietary restriction (DR) improves survival across a wide range of taxa yet remains poorly understood. The key unresolved question is whether this evolutionarily conserved response to temporary lack of food is adaptive. Recent work suggests that early-life DR reduces survival and reproduction when nutrients subsequently become plentiful, thereby challenging adaptive explanations. A new hypothesis maintains that increased survival under DR results from reduced costs of overfeeding. We tested the adaptive value of DR response in an outbred population of Drosophila melanogaster fruit flies. We found that DR females did not suffer from reduced survival upon subsequent re-feeding and had increased reproduction and mating success compared to their continuously fully fed (FF) counterparts. The increase in post-DR reproductive performance was of sufficient magnitude that females experiencing early-life DR had the same total fecundity as continuously FF individuals. Our results suggest that the DR response is adaptive and increases fitness when temporary food shortages cease
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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