Climatic data and collection records for the 'cactophilic Drosophila aldrichi' and 'Drosophila buzzatii' for 97 localities were used to examine the effects of geographical location, season, host plant species and climatic factors on their range and relative abundance. Temporal variation in relative abundance was assessed from monthly collections over 4 years at one locality. Effects of weather variables over the 28 days before each collection were examined. A generalized linear model of the spatial data showed significant geographical variation in relative abundance, and significant climatic effects, with the proportion of 'D. aldrichi' higher in the warm season, and increasing as temperature variation decreased and moisture indices increased. The temporal data gave generally concordant results, as D. aldrichi proportion was higher in summer and autumn, and increased as maximum and minimum temperatures increased, and as variation in maximum temperature decreased. In a laboratory competition experiment, 'D. aldrichi' eliminated 'D. buzzatii' at 31°C, but was itself eliminated at 18°C and 25°C. The range of 'D. buzzatii' is constrained only by availability of its host plant, Opuntia species, although its relative abundance is reduced in the northern part of its distribution. The range of 'D. aldrichi', from central Queensland to northern NSW, Australia, is entirely within that of 'D. buzzatii', and its relative abundance decreases from north to south. Both climate and weather, particularly temperature variability, have direct effects on the relative abundances of the two species, and both likely act indirectly by influencing the outcome of interspecific competition.

'Scaptodrosophila hibisci' (Cook et al., 1977) and 'S. aclinata' (McEvey and Barker, 2001) are endemic Australian species that breed in the flowers of a number of 'Hibiscus' species belonging to the section 'Furcaria'. 'Scaptodrosophila hibisci' has been bred from the flowers of five species in eastern Australia, and 'S. aclinata' from 11 species in the Northern Territory. For non-'Furcaria Hibiscus' species, 'H. tiliaceus' is common within the distributions of both 'Scaptodrosophila' species, and 'H. panduriformis' is present within the distribution of 'S. aclinata'. In addition, the introduced species 'H. sabdariffa' (also sect. 'Furcaria') is widespread within the distribution of 'S. aclinata'. These three species are often in close proximity to section 'Furcaria' species with 'S. hibisci' or 'S. aclinata' present, but no adult 'Scaptodrosophila' have been seen in hundreds of flowers of each of these species. Thus an apparently strict hostplant association of both 'S. hibisci' and 'S. aclinata' with endemic Australian 'Hibiscus' species of the section 'Furcaria' has evolved. However, as both 'Scaptodrosophila' species use a range of different 'Hibiscus' species (only 'H. meraukensis' common to both), it seems likely that 'Furcaria' specialization pre-dated the speciation of 'S. hibisci' and 'S. aclinata'.

In drosophilid flies, male recombination and neo-sex chromosome formation are rare. Following the genotyping of full-sib families with 20 microsatellite markers and subsequent cytological work, we found evidence of both male recombination and neo-sex chromosome formation in Scaptodrosophila hibisci. As far as we are aware, this is the first report of male recombination and neo-sex chromosome formation co-occurring in a drosophilid fly. Two autosomal loci, Sh29c and Sh90, showed aberrant segregation of male parental alleles. We describe how an autosomal fission followed by fusion of one of the autosomal fragments to the Y chromosome to create a Y1Y2X1X2/X1X1X2X2 sex determination system provides the most parsimonious explanation of the patterns we observe. Male recombination was observed in three families, including autosomal linkage groups and the Y1/X2 linkage group. In addition to the X1 linkage group, two autosomal linkage groups were identified.

Species colonizing new areas disjunct from their original habitat may be subject to novel selection pressures, and exhibit adaptive genetic changes. However, if colonization occurs through a small number of founders, the genetic composition of the colonized population may differ from that of the original population simply due to genetic drift. Disentangling the effects of founder drift and selection after colonization is crucial to understanding the adaptive process. 'Drosophila buzzatii' colonized Australia some 600–700 generations ago, and spread rapidly over a wide geographical range. Genetic variation for 15 microsatellite loci in each of nine populations in eastern Australia was used to estimate the size of the bottleneck, and to determine if any of these microsatellites marked genomic regions subject to recent selection. We estimate that on its introduction to Australia, 'D. buzzatii' went through a moderate bottleneck (approximately 30–40 founders).

'Scaptodrosophila hibisci' is an endemic Australian Drosophilidae that breeds in the flowers of native 'Hibiscus'. Here we report the isolation and amplification of 20 polymorphic microsatellite loci. We cloned these microsatellites because loci developed for 'Drosophila melanogaster' failed to amplify in 'S. hibisci'. Null alleles were detected at six loci, and five were X-linked. Two of the primer pairs amplified an unlinked 'bonus' locus. One locus containing juxtaposed microsatellite loci was suitable for designing an additional set of primers. Mean number of alleles per locus was 10, mean Ho and HE per locus were 0.532 and 0.636, respectively.

Prospects for estimation of parameters of models of sperm competition from field data have improved recently with the development of methods that employ multilocus genotype data from brood-structured samples. Sperm competition in Drosophila buzzatii is of special interest because it is possible to directly observe the breeding behaviour of this species in its natural habitat of rotting cactus. Previous laboratory experiments showed that this species exhibits an unusual pattern of frequent remating and sperm partitioning. This paper reports the first attempt to estimate the frequency of female remating and sperm competition in natural populations of D. buzzatii. For the Australian population studied, the mean remating frequency was lower (α = 2.12–2.20) than previously estimated in laboratory experiments with the same population, whereas mean sperm displacement (β = 0.69–0.71) fell within the limits of previous laboratory results. The evolution of the D. buzzatii mating system is discussed.

The red deer ('Cervus elaphus') population in Denmark became almost extinct in recent historical times due to over-hunting. The species has subsequently recovered within remote areas, but non-Danish individuals have been introduced at several localities. To assess genetic structure, past demographic history, and the possibility of a still existing original stock, we analysed 349 specimens from 11 geographically separate areas and from three enclosed areas, genotyping 11 microsatellite loci. Moreover, an 826-bp fragment of the control region of the mitochondrial DNA was sequenced for 116 recent specimens and seven museum specimens. There was a significant difference in mean expected heterozygosity (HE) between the three enclosed areas and the 11 unenclosed areas. Significant departures from Hardy–Weinberg equilibrium were observed in the three enclosed areas and in nine of the unenclosed areas. The overall degree of genetic differentiation among all 14 areas was significant (FST = 0.09, P < 0.01), primarily because the mean pairwise FST for the three enclosed areas was significantly higher than that for the 11 unenclosed areas. A Bayesian clustering procedure detected three genetically distinct populations and indicated reduced gene flow between the enclosed and unenclosed areas. The individuals in the unenclosed areas show genotypic mixture, presumably as a result of gene flow among them. Markov Chain Monte Carlo simulations, based on the genealogical history of the microsatellite alleles, suggest a drastic decline in the effective population size of the enclosed areas some 188–474 years ago. Mitochondrial DNA analysis of the recent specimens showed seven haplotypes. Individuals from the enclosed Jægersborg Dyrehave contain haplotypes that occur all over Denmark and also are found in Western Europe. A close relationship between Scandinavian and Western European red deer is most likely. Only individuals from the unenclosed Lindenborg Estate and the enclosed Tofte Skov did not group with any other Danish individuals. As six of seven museum specimens had haplotypes also found in modern Danish samples, current population of red deer in Denmark is genetically close to the original Danish red deer.

The fact that reproductive effort often shows trade-offs with other necessary functions and features of living organisms has been recognized for centuries. Darwin (1872, pg. 142) gives credit to Geoffroy St. Hilaire and Goethe for proposing the law of "Compensation or Balancement of Growth" and ascribes the following quote to Goethe, "In order to spend on one side, nature is forced to economize on the other side." The essence of this law is captured in modern theories and syntheses (Lack, 1947; Cody, 1966; Smith and Fretwell, 1974; Stearns, 1976, 1977, 1992) that emphasize time, energy budgets, and physiological, genetic and phylogenetic associations that govern the form of compensation that results in a trade-off.

The effective population size (Ne), and the ratio between Ne and census population size (N) are often used as measures of population viability. We show that using the harmonic mean of population sizes over time – a common proxy for Ne– has some important evolutionary consequences and implications for conservation management. This stems from the fact that there is no unambiguous relationship between the arithmetic and harmonic means for populations fluctuating in size. As long as the variance of population size increases moderately with increasing arithmetic mean population size, the harmonic mean also increases. However, if the variance of population size increases more rapidly, which existing data often suggest, then the harmonic mean may actually decrease with increasing arithmetic mean. Thus maximizing N may not maximize Ne, but could instead lower the adaptive potential and hence limit the evolutionary response to environmental change. Large census size has the clear advantage of lowering demographic stochasticity, and hence extinction risk, and under certain conditions large census size also minimizes the loss of genetic variation. Consequently, maximising census size has served as a useful dogma in ecology, genetics and conservation. Nonetheless, due to the intricate relationships among Ne, population viability and the properties of population fluctuations, we suggest that this dogma should be taken only as a rule of thumb.

Variation in 19 traits possibly relevant for thermal adaptation was studied in 11 populations of 'Drosophila buzzatii' collected in southeast Australia. Using stepwise multiple regression, the variation was compared to variation in geographic coordinates and to a set of climatic variables estimated for each collection site. For 13 of the traits, a significant part of the variation was explained by climatic variables and/or geographic coordinates, suggesting directional selection for adaptation to the environment in the majority of traits studied. In 10 of the traits, both geographic coordinates and climatic variables explained significant proportions of the variation, with R² ranging from 0.075 to 0.58. Although larvae, pupae and adults of 'D. buzzatii' share a common habitat, the measured traits were not correlated across life stages and gender. Also, there seemed to be special conditions in marginal populations near species borders, giving rise to nonlinear relations with latitude. Climate apparently does influence the adaptive evolution of the traits studied, but they also are affected by other factors that vary with latitude, longitude and distance to coast. These results highlight the complex challenges imposed by the environment on the adaptive process.