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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50236 |
| Date | 12 1900 |
| Creators | Deere, Jacques Andries |
| Contributors | Chown, S. L., Marshall, D. J., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | ix, 161p. : ill. |
| Rights | Stellenbosch University |
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