Journal of Evolutionary Biology

Sgrò and, C. M.; Hoffmann, A. A.

doi: 10.1046/j.1420-9101.1998.11010001.xpmid: N/A

Parent‐offspring comparisons were used to investigate the effects of temperature extremes on genetic variances for two life history traits and one morphological trait in Drosophila melanogaster. We considered three temperatures (14 °C, 25 °C and 28 °C) for culturing and testing flies, and considered heritabilities, coefficients of additive variation (CVA) and evolvabilities (IA) for fecundity, development time and wing length. For fecundity, heritabilities and evolvabilities were higher when parents were exposed to 14 °C compared to 28 °C. Parent‐offspring comparisons suggested that genetic correlations among environments were close to 1, although lower correlations were obtained in comparisons of family means. Parent‐offspring correlations across environments seemed to depend on parental temperature. For development time, heritabilities and evolvabilities were low at 14 °C compared to 28 °C. However, parent‐offspring correlations were relatively high when the progeny of parents tested at 14 °C were raised at the opposite extreme, suggesting that genetic variation can be enhanced when parents and offspring experience different conditions. CVAs and IAs for development time were lower than for fecundity, even when heritability estimates were similar in magnitude. Genetic variation for wing length was generally not affected by the temperature extremes, and genetic correlations across the extremes estimated from the parent‐offspring comparison were close to 1. There was no evidence for tradeoffs between traits; rapid development time was associated with high fecundity at both the phenotypic and genetic levels. The findings highlight inherent difficulties of estimating genetic parameters from parent‐offspring comparisons when two generations experience different environmental extremes and also show how parent‐offspring comparisons can lead to unexpected findings about the expression of genetic variation.

Gotthard, K.

doi: 10.1046/j.1420-9101.1998.11010021.xpmid: N/A

This study addresses the general hypothesis that insects living in seasonal environments should shorten development times at progressively later dates in the growth season, and that insects living outside equatorial areas should use daylength as a cue to determine the date. Diapause strategies and reaction norms relating the duration of larval development to daylength was investigated in a French population of the butterfly, Lasiommata petropolitana. The results are compared with those of an earlier study of the species in Sweden. Because of the diapausing strategy and phenology of the population, it was expected that an adaptive reaction norm relating larval time to daylength should have a positive slope, i.e. relatively shorter daylengths induce faster growth and development. This prediction was supported, and the reaction norm was qualitatively similar to the one found in Swedish populations. In the French population it was, however, shifted to a range of shorter photoperiods which corresponds to the regime of shorter daylengths in southern Europe. Shorter larval development times and high growth rates were associated with a reduction in pupal size, suggesting a trade off between time and size at pupation. There was no evidence of a trade off between growth rate and starvation endurance. The results suggests that the daylength‐dependent decision of what growth trajectory an individual larva will follow, is not made continuously but rather at one or a few occasions during larval development.It is clear that larvae of L. petropolitana make developmental decisions in relation to the daylength they experience during larval growth. The result is a reaction norm that agrees closely to what is predicted by some life history models, suggesting that it is an adaptation for optimising life history traits in a seasonal environment.

Van Dooren, T. J. M.; Metz, J. A. J.

doi: 10.1046/j.1420-9101.1998.11010041.xpmid: N/A

In this paper we study the evolutionary dynamics of delayed maturation in semelparous individuals. We model this in a two‐stage clonally reproducing population subject to density‐dependent fertility. The population dynamical model allows multiple — cyclic and/or chaotic — attractors, thus allowing us to illustrate how (i) evolutionary stability is primarily a property of a population dynamical system as a whole, and (ii) that the evolutionary stability of a demographic strategy by necessity derives from the evolutionary stability of the stationary population dynamical systems it can engender, i.e., its associated population dynamical attractors.Our approach is based on numerically estimating invasion exponents or “mutant fitnesses”. The invasion exponent is defined as the theoretical long‐term average relative growth rate of a population of mutants in the stationary environment defined by a resident population system. For some combinations of resident and mutant trait values, we have to consider multi‐valued invasion exponents, which makes the evolutionary argument more complicated (and more interesting) than is usually envisaged. Multi‐valuedness occurs (i) when more than one attractor is associated with the values of the residents' demographic parameters, or (ii) when the setting of the mutant parameters makes the descendants of a single mutant reproduce exclusively either in even or in odd years, so that a mutant population is affected by either subsequence of the fluctuating resident densities only.Non‐equilibrium population dynamics or random environmental noise selects for strategists with a non‐zero probability to delay maturation. When there is an evolutionarily attracting pair of such a strategy and a population dynamical attractor engendered by it, this delaying probability is a Continuously Stable Strategy, that is an Evolutionarily Unbeatable Strategy which is also Stable in a long term evolutionary sense. Population dynamical coexistence of delaying and non‐delaying strategists is possible with non‐equilibrium dynamics, but adding random environmental noise to the model destroys this coexistence. Adding random noise also shifts the CSS towards a higher probability of delaying maturation.

Qualls, C. P.; Shine, R.

doi: 10.1046/j.1420-9101.1998.11010063.xpmid: N/A

Many factors, both environmental and biotic, have been suggested to facilitate or hinder the evolution of viviparity (live‐bearing) in reptiles. Viviparity has evolved recently within the Australian scincid lizard Lerista bougainvillii and the species includes oviparous, viviparous, and reproductively intermediate (with prolonged egg retention) populations; thus, it offers an exceptional opportunity to evaluate the validity of these hypotheses. We carried out such tests by (i) comparing environmental conditions over the geographic ranges occupied by oviparous, viviparous, and intermediate populations (to identify possible selective forces for the evolution of viviparity), and (ii) comparing morphological, reproductive and ecological traits of L. bougainvillii with those of other sympatric scincid species (to identify traits that may have predisposed this taxon to the evolution of viviparity). The areas occupied by viviparous L. bougainvillii are significantly colder than those occupied by both their intermediate and oviparous conspecifics, in accord with the “cold‐climate” hypothesis for reptilian viviparity. Rainfall is similar over the ranges of the three forms. Climatic unpredictability (as assessed by the magnitude of year‐to‐year thermal variation) is lower for viviparous animals, in contradiction to published speculations. Comparison with 31 sympatric scincid species showed that L. bougainvillii is not atypical for most of the traits we measured (e.g., body size, clutch size, thermal preferenda and tolerances). However, oviparous L. bougainvillii do display several traits that have been suggested to facilitate the evolution of viviparity. For example, pregnancy does not reduce locomotor ability of females; the lizards are semi‐fossorial; even the oviparous females produce only a single clutch of eggs per year; and they ovulate relatively late in summer, so that the time available for incubation is limited.

Müller, J.

doi: 10.1046/j.1420-9101.1998.11010079.xpmid: N/A

Previous studies have revealed inconsistent results about the taxonomic status of European Gammarus fossarum forms. The variability in morphology and hybridization ability has not shown clear geographic patterns, whereas on a genetical basis two Central European G. fossarum forms have been proposed.In the present study the genetic structure of G. fossarum populations was investigated across a natural contact zone. For the first time direct comparisons of allotopic versus syntopic populations were feasible. 24 Populations of G. fossarum plus 4 populations of G. pulex (as outgroup) were sampled along 2 transects across the contact zone. The genotypes of about 60 individuals per population were revealed by allozyme electrophoresis at 6 polymorphic loci.Parallel step ‘clines’ in allele frequencies indicate secondary contact of the two G. fossarum forms. The level of genetic variation between the forms was comparable to an interspecific level (G. pulex versus G. fossarum). The pronounced genetic bipartition in syntopic G. fossarum populations and the lack of potential F1‐hybrids further corroborated the taxonomic status of the G. fossarum types. The geographic patterns of the genetic differentiation between and within the G. fossarum types, the allelic diversities and the genotypic disequilibria revealed recent introgression at the analysed loci to be insignificant. In addition it is shown that the population structure of the western G. fossarum type is out of equilibrium, which suggest a recent colonization of this type probably by displacement of the other type.

Bourguet, D.; Raymond, M.

doi: 10.1046/j.1420-9101.1998.11010103.xpmid: N/A

A controversial debate in evolutionary biology has been to explain why deleterious mutations are usually recessive to their wild‐type allele. For Fisher, dominance of the wild‐type is the result of selection, whereas for Wright it is a mere consequence of the biochemical properties of physiological pathways. Over time, Wright's theory has appeared as the most appropriate, and Kacser and Burns explained why the widespread occurrence of recessive mutants is the inevitable consequence of the kinetic structure of enzyme networks. Does Wright and Kacser and Burns (W‐K‐B)'s theory apply for newly arisen adaptive genes? A survey of more than 70 studies shows that pesticide resistance conferred by mutations decreasing the affinity of the pesticide target‐sites varies from complete recessivity to complete dominance. This review shows that dominance always has a purely physiological explanation that can be roughly, but not simply, predicted by W‐K‐B's theory. Thus, although W‐K‐B's theory remains powerful for predicting the recessivity of deleterious mutations involved in enzymatic pathways, no general theory emerges from the study of other situations, and molecular explanations are to be sought on a case by case basis.

Wills, Matthew A.

doi: 10.1046/j.1420-9101.1998.11010123.xpmid: N/A

Benton, Michael J.

doi: 10.1046/j.1420-9101.1998.11010126.xpmid: N/A

Bekoff, Marc

doi: 10.1046/j.1420-9101.1998.11010128.xpmid: N/A