1,721,020 research outputs found
Hopwood-etal-male reproductive competition in burying beetles JEB-2015-00671-data
No full textThese data relate to "The effect of size and sex-ratio experiences on reproductive competition in Nicrophorus vespilloides burying beetles in the wild." Hopwood, Paul E., Moore, Allen J., Tregenza, Tom, Royle, Nick J
Phenotypic Plasticity in Female Burying Beetle's: Individual Responses in a Multidimensional Environment
Get PDFPhenotypic plasticity is defined as the environmentally sensitive expression of alternative phenotypes produced within a single genotype. The majority of research on plasticity has been demonstrating its evolutionary implications, specifically highlighting how plasticity can drive, direct and constrain genetic evolution and how plasticity will evolve. However, our current understanding of plasticity and evolution is limited by a lack of empirical studies investigating individuals and how multiple environmental variables interact influencing the direction or the degree of the plastic response. Yet, this is important to consider in future research as population level responses are determined by how individuals respond, furthermore by studying individuals rather than populations we can quantify the extent of variation amongst individuals in which selection acts upon. Studying the response on a multivariate environment also has significant benefits if we want to improve our knowledge of phenotypic plasticity. This is because generally studies focus on manipulating only one environmental variable, yet interactions between environments alter the benefits and costs of plasticity/the optimal response to environmental change, thus potentially changing the direction or the magnitude of selection acting on plasticity.
In this thesis, I address this gap by investigating how individuals in a multivariate environment respond to environmental change using burying beetles (Nicrophorus vespilloides) as our model system. Burying beetles are considered highly plastic, largely because they reproduce exclusively on carrion, a resource that is unpredictable in space and time, meaning the environment is never consistent between breeding attempts. The aim of this thesis was therefore to explore further and in more detail, how burying beetles respond to environmental change and to investigate the importance and potential benefits of plasticity in burying beetles. Additionally, this thesis also aimed to answer two overlooked questions in research. Firstly, looking at how females respond to changes in the competitive environment and variation in resource quality, predicting that plasticity in maternal behaviour would aim to maximise offspring traits (i.e. offspring size) in a competitive environment. And secondly, assessing how individual age affects the plastic response to reproductive resource quality, in which I expected our data to follow theoretical predictions that it would be adaptive for old individuals to be unresponsive.
The results in chapter 2 revealed that parental behaviour, whether it being direct care (feeding offspring) or indirect care (carcass maintenance), significantly declined in a competitive environment, following more closely with a costly competitive hypothesis. This suggests that competitive stress limited the level of energetic resources available for maternal investment, and that evolution between the traits is potentially negatively correlated. However, contrary to the above result, the chapter also found that female burying beetles adjusted brood size adaptively, by reducing offspring number and increasing larval mass in a competitive environment, thus matching offspring phenotypes with the environment, a form of adaptive transgenerational plasticity.
In chapter 3 I demonstrate that to a certain extent plasticity is age-dependant. It was found that, on average, old individuals do not adjust their reproductive traits in relation to the size of the breeding resource (carrion), while young individuals do. However, this pattern in response is only illustrated within certain environmental conditions, as the chapter found that the results above are dependent on a population’s current and previous breeding environment. The chapter also reveals that there is substantial variation in the plastic response amongst individuals. Specifically illustrating that old individuals are responsive, demonstrating that studying at a population level doesn’t provide sufficient information to fully understand how individuals are responding to the environment. This result would therefore indicate that while age may have some effect on influencing the plastic response to environmental change, shown at a population level, it is only likely to play a minor role influencing plasticity, as individuals of the same age substantially differed in their plastic response.
In this thesis, I conclude by discussing how the results have improved our understanding of plasticity in female burying beetles and how selection may be expected to act on plasticity in such a species given our results. I also talk about how the theses has improved our broader understanding of phenotypic plasticity and how it may develop research for the future
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
The effect of the social environment on the parental care and offspring performance of burying beetles, Nicrophorus vespilloides.
Get PDFThis thesis details two experiments on burying beetles, Nicrophorus
vespilloides, examining the evolutionary consequences of different elements of
the social environment for parental care and offspring performance.
The first experiment (Chapter 2) followed on from a previous study which found
that, under biparental conditions, females burying beetles from lines selected for
a high mating rate provide less parental care and have lower offspring
performance than those from a low mating rate line. This suggested that
selection on females in the high mating rate line due to the costs of mating lead
to the evolution of a reduction in their parental care. In contrast, selection on
mating rate had no effect on male parental care, suggesting the costs to a high
mating rate are greater for females than males. Male and female burying
beetles in the wild also commonly display uniparental care, where they care for
their larvae in the absence of a partner. Chapter 2 investigated whether the
costs to a high mating rate for parental care are also greater for females than
males under uniparental conditions. The results of the experiment suggest that
the costs of a high mating rate are indeed higher for females than males under
uniparental conditions. Few studies have investigated the impact of the social
environment on parental care across different non-social environments. The
other aim of this experiment was to investigate whether the impact of a high
mating rate (social environment) on parental behaviour was dependent upon
the non-social environment (carcass size). This is important because, if this is
the case, the evolution of plasticity in parental care in response to the social
environment will be heavily impacted by the non-social environment
experienced (e.g. resource availability). The size of the carcass on which
burying beetles breed is an important element of their non-social environment,
as it has a large impact on the number of larvae that can be raised and on larval
mass. Costs of a high mating rate on the number of larvae initially produced and
the proportion of larvae surviving to dispersal were found to be greater when
breeding on a large carcass, suggesting high mating rate line individuals are
unable to take advantage of the extra resources available.
3
Few studies have investigated the impact of female-female competition for
resources on the expression of parental care, especially in species other than
mammals. One of the reasons that female-female competition has received little
attention is that it was perceived to be of less evolutionary significance than
male-competition, as in many species males show more aggression and have
more elaborate ornaments and weapons. However, in recent years the
significance of female-female competition for female fitness has become more
appreciated. The second experiment in this thesis (Chapter 3) investigated the
impact of the presence of a rival female prior to reproduction on female parental
care and offspring performance. An earlier study had found that female burying
beetles that experience competition increase their expression of parental care. I
therefore predicted in my study that females may be able to alter the phenotype
of their offspring to best match them to the competition environment they are
likely to experience. My study differed from the previous study by using beetles
from genetically diverged selection lines. This enabled me to investigate
whether there is a genetic variability for this plasticity in parental care behaviour
(a GxE) in response to the social environment. Whether there is a GXE for
plasticity in behaviour has important implications for the speed at which the
extent of plasticity will evolve in response to selection. The results of my
experiment showed that females that experienced a rival produced heavier
offspring. This is potentially an example of an anticipatory parental effect, as
heavier larvae are expected as adults to be better able to compete for access to
a carcass. There was no GxE for plasticity in parental care behaviours,
suggesting that the extent of plasticity of parental care behaviours may not
evolve quickly in response to selection, such as due to climate change
The evolution and regulation of cooperation in the wild
No full textIn cooperatively breeding societies, where individuals (termed ‘helpers’) provide care to young which are not their own, group members can vary substantially in their contributions to cooperative activities. Individuals are expected to exhibit higher levels of cooperative investment if the benefit of performing that behaviour greatly outweighs the cost of performing that behaviour. This may be achieved by directing investment towards kin (thereby maximising indirect fitness benefits) and/or attaining large direct fitness benefits. In this thesis, I explore whether direct fitness benefits shape patterns of helping behaviour in the cooperatively breeding white-browed sparrow weaver (Plocepasser mahali). White-browed sparrow weavers live in year round territorial groups with high reproductive skew, comprising a dominant pair and subordinates of both sexes. Although all group members contribute to a wide range of highly conspicuous cooperative activities, there is large inter-individual variation in investment. In chapter 2, I use simulated territorial intrusions to show that sexually-selected direct benefits shape the expression of sentinel behaviour. In chapter 4, I provide evidence that the direct benefits associated with either the pay-to-stay or social prestige hypotheses are unlikely to modulate patterns of provisioning in male white-browed sparrow weavers. Evidence of marked individual differences in contributions to offspring care in cooperative societies is also generating increased interest in the proximate causes of such variation. In chapter 5, I use within-individual measurements to demonstrate that variation in provisioning effort is not directly regulated by variation in circulating levels of prolactin (a pituitary hormone). The evidence does suggest, however, that provisioning behaviour may be induced by exceeding a threshold hormone level. Individual contributions to parental behaviours (as opposed to alloparental) may be shaped by constraints associated with life-history traits. In chapter 3, I show that parents in white-browed sparrow weaver societies perform different provisioning rates yet employ similar food allocation tactics, and that these patterns are expected in tropical living bird species. Combined, these findings provide insights into the selection pressures that may shape individual contributions to cooperative activities
Variations on the Author
Get PDF“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
Nutritional and Social Environmental Effects on Parental Care
No full textParental care is likely to evolve when benefits of care are greater than costs. Provision of parental care may buffer vulnerable offspring against unpredictable or hazardous environments permitting parents to breed in situations too hostile for unassisted juvenile survival. The nature of environmental unpredictability faced by parents and their offspring (e.g., availability of nutritional resources, breeding resources and/or the strength of competition) provides the ecological context in which costs and benefits of parental traits are defined. Therefore investigations about how the environment might shape parental traits ought not only to be conducted in the laboratory but also in a natural setting where unanticipated parameters may have profound effects on theoretical predictions. I conducted a series of manipulative experiments and observational studies in the laboratory and in the field using burying beetles, Nicrophorus vespilloides, to examine the effects of environmental variation on parental competitive ability, reproductive productivity, longevity and the expression of parental sex-role differences and alternative reproductive tactics. In these beetles a relative size advantage confers success in contests for scarce and vital breeding resources so a central prediction was that reproductive success would be positively correlated with body size. In contrast I found that reproductive performance was favoured over contest success when nutritional resources were delayed temporarily during a developmental window. Larger beetles do win contests for breeding-resources but the benefits of being large depend on the quality of the social environment experienced (i.e., the relative size of an opponent). In a naturalistic setting, smaller males avoided direct contests because they attracted proportionately more females and as a result their breeding associations were more often monogamous. This has potential benefits for females because they avoid female-female contests and brood parasitism. Variation in the nutritional environment provided by parents (the carcass size on which offspring are reared) directly influences body size creating a dynamism between the nutritional and social environments experienced by these beetles depending on their size, which has ramifications for their individual success and maintenance of alternative strategies in the population as a whole.Natural Environment Research Counci
Food, sex and death: costs of reproduction and the mechanistic basis of ageing.
No full textAgeing is the progressive decline in physiological performance with age, which is almost universal amongst multicellular organisms. While understanding ageing is an important aim in biological research, our current understanding of how and why we age is incomplete. In this thesis, I examine how sexual selection affects the evolution and mechanistic basis of ageing. I then explore how diet affects lifespan and reproduction in either sex. Finally, I test the hypotheses that oxidative stress, which occurs when cellular levels of Reactive Oxygen Species exceed circulating antioxidant defences causes ageing (i.e. the free radical theory of ageing) and/or constrains life-history strategies.
To ask these questions, I employ quantitative genetics in decorated crickets Gryllodes sigillatus to examine the genetic co(variance) of ageing, lifespan, reproductive effort, oxidative damage and antioxidant protection. In the Australian field cricket, Teleogryllus commodus, I apply the geometric framework of nutrition to examine how lifespan, reproductive effort, oxidative damage and antioxidant capacity respond to dietary manipulation.
In G. sigillatus, I found that sexual selection caused divergent strategies of age-dependent reproductive effort across the sexes and that this, in turn, promoted different rates of ageing in males and females. I found a trade-off between early reproductive effort and ageing rate in both sexes, although this trade-off was more pronounced in females (Chapter 3). I then explored the mechanistic basis of these sex-specific life-history strategies and, in support of the free radical theory of ageing, I found that oxidative damage was greatest in the shortest lived sex (females) and was negatively genetically correlated with lifespan. Additionally, oxidative damage was a cost of female reproductive effort that accelerated ageing, showing that oxidative stress may mediate sex-specific life-history strategies in decorated crickets (Chapter 4).
If sexual selection affects reproduction and lifespan it should promote sex-specific life-history responses to dietary manipulation. In Australian black field crickets Teleogryllus commodus, I found that males and females have distinct dietary optima for lifespan and reproductive effort and that diet mediated a trade-off between these traits. I found that mating affected responses to dietary manipulation and caused sexual dimorphism in dietary intake under choice (Chapter 5). However, oxidative stress did not explain these life-history responses to dietary manipulation across the sexes (Chapter 6): although oxidative damage was greatest in the shortest lived sex (i.e. females), diets that extended lifespan did not reduce oxidative damage.
My thesis illustrates the importance of considering sexual selection when considering the evolution and mechanistic basis of ageing. It offers equivocal support for the free radical theory of ageing but shows that oxidative stress may help underpin sex-specific life-history strategies. However, my results highlight that unravelling the relationship between oxidative stress and life-history strategies across the sexes will be a very difficult task.NER
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
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