Graham J. Holloway

The effect of new environment on adapted genetic architecture

Central to the study of life cycle evolution is the concept of genetic trade-offs. Genetic trade-offs between life cycle characters develop as a result of the accumulation of genes with antagonistic pleiotropic effects. In the present study a comparison was made between the genetic architecture that had evolved in the ancestral environment and the way that this genetic architecture was disrupted following transfer to a new environment. It was predicted that, in the ancestral environment, genetic trade-offs should have evolved between each life cycle character and, as a result of these genetic trade-offs, significant levels of additive genetic variation should remain despite many generations of selection.Following transfer to a new environment different genes might be expressed. Therefore, it was predicted that in the new environment the levels of additive genetic variation should increase and that the genetic trade-offs should break down. The predictions were well supported by the data.

Life histories and parasite pressure across the major groups of social insects.

Animal societies are aggregations of cooperating individuals that are isolated from other societies by limitations of dispersal and/or hostile exclusion mechanisms. The individuals within them are more related to the members of their own society than to random individuals in the population at large and quite often this relatedness is high because societies are families or groups of families. For parasites and diseases, however, animal societies are merely patches of suitable hosts to be colonized and exploited and to ultimately produce dispersing propagules to reach other similar patches (Freeland, 1979). Living in groups or societies has generally been thought to be associated with increased parasitism (Alexander, 1974; Freeland, 1976; Hamilton, 1987; Sherman et al., 1988; Schmid-Hempel, 1998; Côté and Poulin, 1995). However, several recent studies have questioned the generality of this assertion (Watve and Jog, 1997; Lewis, 1998; Naug and Camazine, 2002; Wilson et al., 2003). Others have provided data to show that social behaviour can also be associated with reduced parasite load, due to either behavioural interactions providing an effective defence (Rosengaus et al., 1998; Hughes et al., 2002; Traniello et al., 2002), or density-dependent immune responses (Reeson et al., 1998, Barnes and Siva-Jothy, 2000, Wilson et al., 2003). These discrepancies may result from the exact mode of transmission. In fact, a meta-analysis by Côté and Poulin (1995) has shown that rates of parasitism tend to be positively correlated with group size

Chemical defence in ladybird beetles (Coccinellidae). I. Distribution of coccinelline and individual variation in defence in 7-spot ladybirds (Coccinella septempunctata)

Summary7-spot ladybirds secrete alkaloid (coccinelline)-rich fluid (reflex blood) from leg joints as a defence mechanism against predators. A technique is described that enables the collection and accurate quantification of reflex blood produced, and the amount of coccinelline therein. Coccinelline was found distributed throughout the body, although concentrated in the reflex blood. Reflex blood was collected from a large set of beetles at several time points. Significant variation was found among beetles in the amount of reflex blood produced (for males and for females corrected for body weight) and the coccinelline concentration of the reflex blood. The results are discussed in relation to automimicry and the maintenance of variation through energy trade-offs. The relationships between tendency to aggregate, ability to reflex bleed and the possession of aposematic coloration are also considered.

Evolution in toxin-stressed environments.

Here we briefly consider how organisms may evolve in toxin-stressed environments, and illustrate our ideas with data from our work on Sitophilus oryzae (L.), the rice weevil. This animal was selected for study as a model organism because of its short generation time (c 6 weeks), the ease with which its natural environment (stored seeds) can be replicated in the laboratory, and for ease of culture and environmental control. We begin by considering what happens in a constant environment containing low levels of toxins, and then proceed to consider the evolutionary changes that occur in response to the introduction of further toxins. Thus these two environments differ in toxin content.

Chemical defence in ladybird beetles (Coccinellidae). II. Amount of reflex fluid, the alkaloid adaline and individual variation in defence in 2-spot ladybirds (Adalia bipunctata).

Summary2-spot ladybirds secrete alkaloid (adaline)-rich defence fluid (reflex blood) in response to predator attack. Reflex fluid was collected from individual ladybirds and weighed and the alkaloid content measured by GC. The amount of fluid produced built up rapidly following winter hibernation in animals feeding on aphids. The concentration of adaline in the fluid was highest in the first bleeding after winter hibernation. A large sample of beetles was reflex bled several times. Significant among beetle variation was found in the amount of fluid produced and the concentration of the reflex blood. The results are discussed in relation to the possibility that 2-spot ladybirds are Batesian mimics of 7-spot ladybirds and to the possible functions of adaline.

THE EFFECT OF NOVEL ENVIRONMENT AND SEX ON THE ADDITIVE GENETIC VARIATION AND COVARIATION IN AND BETWEEN EMERGENCE BODY WEIGHT AND DEVELOPMENT PERIOD IN THE COWPEA WEEVIL, CALLOSOBRUCHUS MACULATUS (COLEOPTERA, BRUCHIDAE)

Progeny from full-sib/half-sib families of a population of Callosobruchus maculatus near genetic equilibrium were reared either in an ancestral (30°C, 70 per cent relative humidity) or in a novel (25°C, 45 per cent relative humidity) environment. The life history traits, emergence body weight and development period were measured in both sexes. Insects developed faster and emerged heavier at a higher temperature and humidity. For both sexes, in the ancestral environment additive genetic variation and ‘narrow-sense’ heritability estimates were higher for body weight, the morphological trait, than for development period, the primary fitness trait. For both sexes, matrix analyses revealed significant differences between the estimated additive genetic variance-covariance (G) matrices from each environment. In the novel environment, the evolved genetic architecture appeared to break down, possibly as a result of novel gene expression; the trade-off between emergence body weight and development period was disrupted with an associated increase in additive genetic variation for both life history traits. In both environments, female insects developed more slowly and emerged heavier than male insects. Matrix analyses show significant differences between the G-matrices of each sex, suggesting that different constraints may operate in the two sexes.

THE GENETICS AND COST OF CHEMICAL DEFENSE IN THE TWO-SPOT LADYBIRD (ADALIA BIPUNCTATA L.)

Ladybirds (Coccinellidae) defend themselves against attack by vertebrate predators by exuding a fluid from the femero‐tibial joints. This fluid carries a noxious or toxic alkaloid. The amount of fluid produced during a single attack can be very high (up to 20% of fresh body weight), and the weight of the self‐synthesized alkaloid can amount to several percent of the weight of the fluid. A study was carried out on these two defense characters and two other fitness characters (body weight and growth rate) to demonstrate a cost to defense in the form of genetic trade‐offs between characters. The two sexes were analyzed separately, and a jackknife procedure was used to attach errors to the estimates of Va and cova. All four characters were associated with high levels of Va, but the cova values were mixed, some being negative and others positive. Principal‐component analysis indicated the operation of factors constraining the cova values in males, and further possible reasons for the appearance of so many positive values are explored. A matrix analysis showed that the genetic variance/covariance matrices of the two sexes were significantly different from each other. Breeding values derived from sons plotted on breeding values from daughters had correlation coefficients significantly less than +1. This finding indicated that a substantial amount of sex‐dependent gene expression was occurring.

A comparison of the effects of organophosphate insecticide exposure and temperature stress on fluctuating asymmetry and life history traits in Culex quinquefasciatus

Effects of exposure to a non-chemical (temperature) or chemical (organophosphate insecticide) stressor during larval development were compared in Culex quinquefasciatus mosquitoes. Stress was measured in two ways: using conventional life history traits (survival, development time and a measure of body size) and by calculating the degree of developmental instability from the departure from bilateral symmetry of wing characters (fluctuating asymmetry). Increasing insecticide dose, but not temperature, was observed to elevate wing fluctuating asymmetry in male but not female mosquitoes. Insecticide treatment reduced survival and was associated with a significant reduction in wing trait sizes in both females and males but did not significantly affect development time. Temperature was associated with a significant reduction in all life history traits in both sexes. Therefore wing fluctuating asymmetry in C. quinquefasciatus cannot be used as a general biomonitor of all stress, although it may have potential as a more specific monitor of chemical stress. It needs to be complimented with other measures such as life history and biochemical methods. The significant differences in response between sexes may impact on results of short-term larval exposures to insecticides.

Phenotypic plasticity in hoverflies: the relationship between colour pattern and season in Episyrphus balteatus and other Syrphidae

1. The abdominal colour patterns of some multivoltine species of hoverfly are phenotypically plastic and change through the flying season.

The genetics of wing pattern elements in the polyphenic butterfly, Bicyclus anynana

The tropical butterfly, Bicyclus anynana, is highly polyphenic in response to seasonal changes (temperature and rainfall) in Malawi. The wing pattern varies considerably between the wet and dry season forms, particularly with respect to the background colour and the size of many of the wing pattern elements (e.g. eyespots). A selection experiment was carried out to determine the heritability of one of the ventral wing surface eyespots. The degree of genetic covariation among the various polyphenic ventral surface pattern elements and two non-polyphenic dorsal surface eyespots was also investigated. Selection to both increase and decrease the relative size of the second eyespot on the ventral surface was successful and indicated a heritability of more than 0.4. Other eyespots and the transverse wing band on the ventral surface all showed correlated responses. On the dorsal surface only the second eyespot showed a correlated response to selection. The results indicate that response to selection occurred at two levels: (i) the genes affecting the size of the eyespot directly and (ii) the eyespot biochemical determination mechanism. The fact that not all of the dorsal surface features showed correlated responses suggests that subtle differences may exist between the ways in which the production of eyespots on the ventral and dorsal surface is controlled.