Correlative Changes in Life-History Variables in Response to Environmental Change in a Model Organism

Global change alters the environment, including increases in the frequency of (un)favorable events and shifts in environmental noise color. However, how these changes impact the dynamics of populations, and whether these can be predicted accurately has been largely unexamined. Here we combine recently developed population modeling approaches and theory in stochastic demography to explore how life history, morphology, and average fitness respond to changes in the frequency of favorable environmental conditions and in the color of environmental noise in a model organism (an acarid mite). We predict that different life-history variables respond correlatively to changes in the environment, and we identify different life-history variables, including lifetime reproductive success, as indicators of average fitness and life-history speed across stochastic environments. Depending on the shape of adult survival rate, generation time can be used as an indicator of the response of populations to stochastic change, as in the deterministic case. This work is a useful step toward understanding population dynamics in stochastic environments, including how stochastic change may shape the evolution of life histories

The role of dispersal in life history and population dynamics: an experimental and theoretical approach

Understanding the evolution and maintenance of phenotypic and genetic variation within populations is a key challenge in population biology. Discrete phenotypic variation such as alternative reproductive strategies and dispersal strategies are extreme forms of this. To understand phenotypic variations, such as male dimorphisms and dispersal expression, requires investigating the costs and benefits of these different phenotypes. In this thesis I do so. First, at the individual level, I determine trade-offs between life-history traits and phenotypic expression. The influence of male morph expression is assessed by determining whether male morph survival is frequency dependent. Costs of dispersal expression were assessed by comparing individuals that expressed the dispersal phenotype during their ontogeny with individuals that did not. Second, at the population level, I specifically investigate costs of phenotype expression to the natal population when dispersers fail to disperse. To determine any demographic costs to natal populations, I used structured integral population models to calculate population biology quantities, which I compared between populations that produced dispersers that fail to disperse and populations that produced no dispersers. I show that expressing a dispersal morph is costly to life-history traits and skews the male morph ratio, indicating that these two conditional strategies interact during ontogeny. This questions whether current models explaining single conditional strategies, such as the environmental threshold model, should consider interactions between different conditional strategies. In natal populations where dispersal is expressed, but dispersers fail to disperse, populations suffer reduced fitness and this demographic cost is enhanced in stochastic environments. These results do not include benefits of successful dispersal or other costs such as inbreeding. However, they do provide a cost of dispersal expression which indicates what the benefits of dispersal would need to be for dispersal to evolve. One aspect that the results do not inform on is possible eco-evolutionary dynamics in populations. Future work should look to incorporate eco-evolutionary feedback, within a metapopulation structure, to identify the maintenance and evolution of male dimorphism and dispersal

Acclimation effects on thermal tolerance in ameronothrid mites at sub-Antarctic Marion Island

Thesis (MSc)--Stellenbosch University, 2005.ENGLISH ABSTRACT: Evidence for widespread ecological impacts due to rapid climate change is on the increase, with further warming predicted over the next century. This increase in warming has lead to organisms adjusting their distribution range and where this is not possible organisms must cope with the stressful environments in a different way. One potential way to handle environmental stress is via a mechanism known as phenotypic plasticity, which allows an organism to express different phenotypes depending on the biotic or abiotic environment in a way that may alter that organism's fitness. Acclimation temperatures can potentially cause plastic (reversible and irreversible) changes in the response of individuals to stressful experimental conditions that could increase their survival. The issue of whether this acclimation will be beneficial to the organism or not remains contentious, with support offered both for and against the idea of beneficial acclimation. The aims of the investigation were to determine the thermal limits of five ameronothrid mite species (Halozetes marinus, H marionensis, H belgicae, H. fulvus and Podacarus auberti) from varying terrestrial habitats and to test whether there is beneficial acclimation on the thermal traits. Along with the beneficial acclimation hypothesis several alternative hypotheses were also tested. In addition, locomotor performance was determined as it has been suggested that locomotion performance is a reliable and practical measure of potential fitness of animals. The same hypotheses testing the effects of acclimation temperature on the thermal limits were tested on three performance traits; performance breadth, optimum speed and optimum temperature. Support for beneficial acclimation was found in the performance breadth and optimum speed traits for all species except for Halozetes marinus. For the optimum temperature trait the prediction for the compensation hypothesis was met and that of the beneficial acclimation hypothesis rejected, with the only exception again being that of H marinus. In the case of the locomotor performance traits the prediction for the beneficial acclimation hypothesis in the performance breadth and optimum speed traits are the same for that of the compensation hypothesis, therefore the overall response of the more terrestrial mite species is one of compensation. However, support for beneficial acclimation was not found in the thermal limit traits of all five species, with the higher acclimation temperatures (specifically 150 C) resulting in negative responses in LLT in H. marinus and H. belgicae, and in ULT in H. fulvus. Phenotypic flexibility varied between marine and terrestrial species. The less variable marine environment showed lower flexibility than that of terrestrial species in the performance breadth trait and optimum temperature trait, but there was a lack of variation between the marine and terrestrial species in the temperature tolerance traits. These results show that the effects of acclimation on various traits, especially fitness related traits, are complex and require more attention if the consequences are to be fully explained. This study therefore provides insight into the effects of acclimation on performance traits and thermal limit traits and has implications for the evolution of plastic responses in terrestrial arthropods.AFRIKAANSE OPSOMMING: Bewys vir wye ekologiese impakte as gevolg van vinnige klimaatsverandering is aan die toeneem, met verdere verwarming wat voorspel word gedurende die volgende eeu. Dié toename in verwarming het alreeds veroorsaak dat organismes hulle verspreidings verander, of waar dit nie moontlik is nie, moet hulle stresvolle omgewingstoestande op 'n ander wyse hanteer. Een moontlike manier om omgewingsstres te hanteer is deur gebruik te maak van 'n meganisme wat bekend staan as fenotipiese plastisiteit, wat dit vir 'n organisme moontlik maak om ander fenotipes te toon afhangende van die biotiese of abiotiese omgewing in 'n wyse wat die organisme se fiksheid beinvloed. Temperatuur akklimasie kan moontlik plastisiteit (omkeerbaar of onomkeerbaar) veranderinge in die reaksie van individue tot stresvolle eksperimentele toestande tot gevolg hé, wat gevolglik hulle oorlewing kan verhoog. Die kwessie of hierdie akklimasie wel voordelig vir die organisme is of nie is steeds betwisbaar, met beide steun vir en teen die idee van voordelige akklimasie. Die doel van hierdie ondersoek was om vas te stel wat die termiese limiete van vyf ameronothrid myt spesies (Halozetes marinus, H marionensis, H belgicae, H fulvus en Podacarus auberti) van verskeie terrestriële habitatte is, en om te toets of daar voordelige akklimasie in die termiese eienskappe voorkom. Tesame met die voordelige akklimasie hipotese is daar verskeie alternatiewe hipoteses ook getoets. Verder, is bewegings prestasie vasgestelomdat dit al voorgestel is dat bewegings prestasie 'n betroubare en praktiese mate van die potensiële fiksheid van 'n dier aantoon. Dieselfde hipotese wat die effek van akklimasie temperatuur op die termiese limiete toets, is op drie prestasie eienskappe getoets; prestasie wydte, optimale spoed en optimale temperatuur. Bewyse vir voordelige akklimasie is gevind in die prestasie wydte en optimale spoed eienskappe vir alle spesies behalwe Halozetes marinus. Vir die optimale temperatuur eienskap was die voorspelling vir die kompensasie hipotese korrek maar dié van die voordelige akklimasie verkeerd, met H. marin us die enigste uitsondering. In die geval van die bewegings prestasie eienskappe is die voorspelling vir die voordelige akklimasie hipotese in die prestasie wydte en optimale spoed eienskappe die selfde as vir die kompensasie hipotese. Daarom is die algemene reaksie vir die meer terrestriële spesies een van kompensasie. Bewyse vir voordelige akklimasie is egter nie gevind in die termiese limiet eienskappe van die vyf spesies nie, met die hoér akklimasie temperature (spesifiek 15° C) wat 'n negatiewe reaksie in LLT in H. marin us en H. belgicae, en in UL T in H. fulvus veroorsaak het. Fenotipiese buigsaamheid het verskil tussen mariene en terrestriële spesies. Die minder variërende mariene omgewing het 'n laer buigsaamheid in die prestasie wydte en optimale temperatuur eienskappe getoon as die van terrestriële spesies, maar daar was geen variasie tussen mariene en terrestriële spesies in die temperatuur toleransie eienskappe nie. Die resultate wat hier voorgelê word wys dat die gevolge van akklimasie op verskeie eienskappe, veral fiksheids verwante eienskappe, ingewikkeld is en vereis meer aandag om die gevolge volledig te verduidelik. Hierdie studie verskaf dus insig in die gevolge van akklimasie vir prestasie eienskappe en termiese limiet eienskappe en het gevolge vir die evolusie van plastiese reaksies in terrestriële arthropoda

The role of dispersal in life history and population dynamics: an experimental and theoretical approach

Understanding the evolution and maintenance of phenotypic and genetic variation within populations is a key challenge in population biology. Discrete phenotypic variation such as alternative reproductive strategies and dispersal strategies are extreme forms of this. To understand phenotypic variations, such as male dimorphisms and dispersal expression, requires investigating the costs and benefits of these different phenotypes. In this thesis I do so. First, at the individual level, I determine trade-offs between life-history traits and phenotypic expression. The influence of male morph expression is assessed by determining whether male morph survival is frequency dependent. Costs of dispersal expression were assessed by comparing individuals that expressed the dispersal phenotype during their ontogeny with individuals that did not. Second, at the population level, I specifically investigate costs of phenotype expression to the natal population when dispersers fail to disperse. To determine any demographic costs to natal populations, I used structured integral population models to calculate population biology quantities, which I compared between populations that produced dispersers that fail to disperse and populations that produced no dispersers. I show that expressing a dispersal morph is costly to life-history traits and skews the male morph ratio, indicating that these two conditional strategies interact during ontogeny. This questions whether current models explaining single conditional strategies, such as the environmental threshold model, should consider interactions between different conditional strategies. In natal populations where dispersal is expressed, but dispersers fail to disperse, populations suffer reduced fitness and this demographic cost is enhanced in stochastic environments. These results do not include benefits of successful dispersal or other costs such as inbreeding. However, they do provide a cost of dispersal expression which indicates what the benefits of dispersal would need to be for dispersal to evolve. One aspect that the results do not inform on is possible eco-evolutionary dynamics in populations. Future work should look to incorporate eco-evolutionary feedback, within a metapopulation structure, to identify the maintenance and evolution of male dimorphism and dispersal

Life history data for Rhizoglyphus robini

<p>Data are for individual life history of the bulb mite (Rhizoglyphus robini). Growth measurements, survival, and offspring data were collected daily and for both sexes until death of individuals. Mites were fed ad libitum oats and kept in unlit incubators at 24°C and >70%. Data were collected between August 2012 and May 2013. Data file is in Microsoft excel format that includes a sheet with raw data and a detailed metafile sheet.</p

Data from: Correlative changes in life history variables in response to environmental change in a model organism

Global change alters the environment, including increases in the frequency of (un)favorable events and shifts in environmental noise color. However, how these changes impact the dynamics of populations, and whether these can be predicted accurately has been largely unexamined. Here we combine recently developed population modeling approaches and theory in stochastic demography to explore how life history, morphology, and average fitness respond to changes in the frequency of favorable environmental conditions and in the color of environmental noise in a model organism (an acarid mite). We predict that different life-history variables respond correlatively to changes in the environment, and we identify different life-history variables, including lifetime reproductive success, as indicators of average fitness and life-history speed across stochastic environments. Depending on the shape of adult survival rate, generation time can be used as an indicator of the response of populations to stochastic change, as in the deterministic case. This work is a useful step toward understanding population dynamics in stochastic environments, including how stochastic change may shape the evolution of life histories

Growth and survival data of R. robini

Data on growth and survival of Rhizoglyphus robini females raised in a good (yeast) or a bad (filter paper) environment. Mites were reared individually and always had ad lib access to their food. These data were used to estimate the Gompertz functions (see Methods) and character-demography functions of the Integral Projection Model (see Methods)

Thermal tolerance in a south-east African population of the tsetse fly Glossina pallidipes (Diptera, Glossinidae) : implications for forecasting climate change impacts

The original publication is available at http://www.journals.elsevier.com/journal-of-insect-physiology/For tsetse (Glossina spp.), the vectors of human and animal trypanosomiases, the physiological mechanisms linking variation in population dynamics with changing weather conditions have not been well established. Here, we investigate high- and low-temperature tolerance in terms of activity limits and survival in a natural population of adult Glossina pallidipes from eastern Zambia. Due to increased interest in chilling flies for handling and aerial dispersal in sterile insect technique control and eradication programmes, we also provide further detailed investigation of low-temperature responses. In wild-caught G. pallidipes, the probability of survival for 50% of the population at low-temperatures was at 3.7, 8.9 and 9.6 °C (95% CIs: ±1.5 °C) for 1, 2 and 3 h treatments, respectively. At high temperatures, it was estimated that treatments at 37.9, 36.2 and 35.6 °C (95% CIs: ±0.5 °C) would yield 50% population survival for 1, 2 and 3 h, respectively. Significant effects of time and temperature were detected at both temperature extremes (GLZ, p0.5 in all cases). However, flies with low chill coma values had the highest body water and fat content, indicating that when energy reserves are depleted, low-temperature tolerance may be compromised. Overall, these results suggest that physiological mechanisms may provide insight into tsetse population dynamics, hence distribution and abundance, and support a general prediction for reduced geographic distribution under future climate warming scenarios. © 2007 Elsevier Ltd. All rights reserved.Publishers' Versio

Life cycle of the bulb mite.

<p>The life cycle has six life stages; the deutonymph stage is the facultative dispersal stage that develops under unfavourable conditions. Male morph determination is dependent on the size of the tritonymph stage. Here, we found that adult males that had expressed the dispersal stage all matured as fighters (see <i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136872#sec011" target="_blank">Results</a></i>).</p