Showing papers by "Graham J. Holloway published in 2002"

Phenotypic Plasticity: Beyond Nature and Nurture

Abstract: The concept of phenotypic plasticity has been popular in evolutionary biology over the last two decades or so. It really provides something for the theoreticians to get their teeth into, lying, as it does, at the interface of physiology, morphology, behaviour and genetics, probably contributing significantly to the level of phenotypic variation noted in wild populations and influencing rates of evolution. As is so often the case in evolutionary biology, this is a field in which empiricists have struggled to keep up with the pace of theoretical development. Phenotypic plasticity research has produced controversy; how do the genes affecting the plastic response operate, indeed do genes for plasticity really exist, how should plasticity be described and quantified, and so on? This has provided the stuff for some fascinating conflicts in the scientific press and the development of a number of phenotypic plasticity ‘camps’. The appearance of Phenotypic Plasticity: Beyond Nature and Nurture by Massimo Pigliucci is timely. The study of phenotypic plasticity is probably due for new input and it is possible that this publication could provide the necessary stimulus. A comparison of this book with an earlier text by CD Schlichting and M Pigliucci (Phenotypic Evolution: A Reaction Norm Perspective, Sinauer, 1998) is inevitable. As expected, there is a fair amount of overlap in the material covered by the two books. However, Phenotypic Plasticity: Beyond Nature and Nurture gets my vote. I found it considerably easier to read and to digest the information provided. In fact, I would expect Phenotypic Plasticity to appeal to students at all levels of development and sophistication. The text is nicely laid out (although the reproduction of many of the figures is quite poor) and well written. After three chapters introducing phenotypic plasticity, Pigliucci presents separate chapters on genetics, molecular biology, developmental biology, ecology, behaviour, evolution and theoretical biology. One of the great strengths of the book is that Pigliucci is making real efforts to ensure that the subject moves forward by discussing lines of research that still need to be addressed. It is difficult to see how any student of phenotypic plasticity will be able to get by without a copy of this book on their shelf. In fact, I highly recommend Phenotypic Plasticity to anybody interested in evolution. It is a fascinating read and will not fail to stimulate new insight into this most important topic.

Temperature and genotypic effects on life history and fluctuating asymmetry in a field strain of Culex pipiens.

Abstract: Fluctuating asymmetry (FA) has been proposed as a tool to measure levels of stress experienced by populations of organisms during development. To be of value as a bio-marker to highlight conditions at particular sites, it is important that variation in FA is due to environmental (eg pollution) variation and not genetic variation among populations and families, in other words heritability for FA should be very close to zero. A full-sib design was set up in which families of Culex pipiens mosquitoes collected from the field were reared at three different developmental temperatures. The effects of temperature and family on developmental rate, egg to adult survival and four wing morphological measures were assessed. There was both a temperature and a family effect on development rate and survival. Temperature affected all four wing traits, but an influence of family was only evident in two of the wing traits. Two separate measures of FA for each of the wing traits were obtained. The mean estimates of FA were mainly around 1% of the value of the character measured. There was evidence of an increase in FA with increase in temperature stress. Heritability was estimated for the wing traits and wing trait FA's using restricted estimation maximum likelihood. The estimates of heritability for the wing traits were small and, individually, did not differ significantly from zero. There was also no evidence of heritable genetic variation for any of the wing trait FA's. The results are discussed in relation to other studies where FA heritabilities have been estimated and in relation to the use of FA as an indicator of environmental stress.

The relationship between mimetic imperfection and phenotypic variation in insect colour patterns

Abstract: Many hoverflies (Syrphidae) mimic wasps or bees through colour or behavioural adaptations. The relationship between phenotypic variation in colour pattern and mimetic perfection (as determined by pigeons) was investigated in three species of Mullerian mimics (Vespula spp.) and 10 Batesian hoverfly mimics, plus two non-mimetic species of flies. Four predictions were tested: (i) Batesian mimics might be imperfect because they are in the process of evolving towards perfection, hence there should be a positive relationship between variation and imperfection; (ii) some Batesian mimics are imperfect because they do not have the appropriate genetic variation to improve and have evolved to be as good as possible, hence there should be no differences between species, all displaying a low level of variation; (iii) very common hoverflies should show the highest levels of variation because they outnumber their models, resulting in high predation and a breakdown in the mimetic relationship; and (iv) social wasps (Vespula) have such a powerful defence that anything resembling a wasp, both Mullerian and perfect Batesian mimics, would be avoided, resulting in relaxed selection and high variance. Poor mimics may still evolve to resemble wasps as well as possible and display lower levels of variation. The data only provided support for the fourth prediction. The Mullerian mimics, one of the most perfect Batesian mimics, and the non-mimetic flies displayed much higher levels of variation than the other species of Batesian mimics.

Effects of temperature and genetic stress on life history and fluctuating wing asymmetry in Culex pipiens mosquitoes

Abstract: Fluctuating asymmetry (FA) of bilaterally symmetrical organisms has been introduced as a promising indicator of environmental stress. Stress factors reported to contribute to developmental stability include inbreeding and the presence of resistance genes. In the current study we examined the effect of stress derived from high developmental temperatures, resistance genes and low genetic variation on life history variables and wing FA in Culex pipiens mosquitoes. Three strains were compared: two inbred laboratory strains sharing a similar genetic background but differing in that one strain contained organophosphate (OP) resistance genes, and a third strain that was an outbred OP resistant field strain recently collected from India. There were no strong and general trends that suggested that the OP resistant lab strain was less fit than the OP susceptible strain, although there were some specific among strain differences for some treatments. Fluctuating asymmetry (FA) of wing traits was higher in the laboratory strains than the field strain, suggesting that inbreeding may cause elevated FA in the study species. There was no evidence that the resistance genes were associated with increased wing FA. Wing FA increased with increasing developmental temperature in females, but the association was less strong in males. There was a significant difference between the sexes in this respect. The results are discussed with reference to the value of FA as a biomonitor of environmental stress.