2014, Barker, J Stuart F, Thomson, Peter C

Apparent selection affecting starch gel electrophoretic alleles at the 'Esterase-2' locus of 'Drosophila buzzatii' has been detected in laboratory and natural populations. Perturbation-reperturbation of allele frequencies in replicated laboratory populations attempts to test direct selective effects at the locus versus effects of linked loci. Sequential gel electrophoresis has identified more alleles within starch classes, and three of these alleles (within the a, b and c starch alleles) were used in cage population experiments. Allele 'a/1.00/1.00/1.00' was set up in 10 replicate populations with allele 'c/1.00/1.00/1.00', and in an independent 10 replicate populations with allele 'b/0.99/1.01/1.00'. For each set, three reperturbations were done. Replicate populations generally showed similar patterns of allele frequency change and clear directionality: effects of selection, not drift. However, four populations deviated from their replicates, indicating issipation of linkage disequilibrium. Estimates of pre-adult viability in the F2 of pair-wise crosses among 12 sequential gel electrophoretic alleles showed very variable modes of inheritance and relative viability fitnesses. Together with the diversity of patterns of allele frequency change in the cage populations, these results suggest a gene complex, with selection acting on an interacting set of loci which may include 'Esterase'-2.

2006, Wilson, ACC, Sunnucks, P, Bedo, DG, Barker, JSF

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.

2016, Zhang, Yi, Lu, Yongfang, Cuong, Vu Chi, Pham, Lan Doan, Bouahom, Bounthong, Yang, Bingzhuang, Liang, Xianwei, Cai, Zhihua, Vankan, Dianne, Manatchaiworakul, Wallaya, Kowlim, Nonglid, Duangchantrasiri, Somphot, Yindee, Marnoch, Wajjwalku, Worawidh, Colenbrander, Ben, Zhang, Yuan, Beerli, Peter, Lenstra, Johannes A, Barker, J Stuart F, Li, Kuan-Yi, Kuo, Hsiao-Yun, Ju, Yu-Ten, Ye, Shaohui, Faruque, Md Omar, Li, Qiang, Wang, Yachun

The swamp type of the Asian water buffalo is assumed to have been domesticated by about 4000 years BP, following the introduction of rice cultivation. Previous localizations of the domestication site were based on mitochondrial DNA (mtDNA) variation within China, accounting only for the maternal lineage. We carried out a comprehensive sampling of China, Taiwan, Vietnam, Laos, Thailand, Nepal and Bangladesh and sequenced the mtDNA 'Cytochrome b' gene and control region and the Y-chromosomal ZFY, SRY and DBY sequences. Swamp buffalo has a higher diversity of both maternal and paternal lineages than river buffalo, with also a remarkable contrast between a weak phylogeographic structure of river buffalo and a strong geographic differentiation of swamp buffalo. The highest diversity of the swamp buffalo maternal lineages was found in south China and north Indochina on both banks of the Mekong River, while the highest diversity in paternal lineages was in the China/Indochina border region. We propose that domestication in this region was later followed by introgressive capture of wild cows west of the Mekong. Migration to the north followed the Yangtze valley as well as a more eastern route, but also involved translocations of both cows and bulls over large distances with a minor influence of river buffaloes in recent decades. Bayesian analyses of various migration models also supported domestication in the China/Indochina border region. Coalescence analysis yielded consistent estimates for the expansion of the major swamp buffalo haplogroups with a credibility interval of 900 to 3900 years BP. The spatial differentiation of mtDNA and Y-chromosomal haplotype distributions indicates a lack of gene flow between established populations that is unprecedented in livestock.

2004, Bundgaard, J, Barker, JSF, Frydenberg, J, Clarke, AG

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.

2005, Barker, J Stuart F, Krebbs, Robert A, Davies, Hylton Ian

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.

2017, Bundgaard, Jorgen, Barker, J Stuart F

Genetic variation for resistance to heat stress has been found for a number of life-history components in Drosophila species. For male and female fertility (or sterility), stress resistance of the parents is confounded with stress resistance of the haploid gametes. Many genes are known to influence male fertility in 'Drosophila melanogaster'. Some may carry temperature sensitive alleles that reduce fertility through effects on mature sperm when exposed to heat stress. In this study, sperm from each of 320 males were either not heat shocked (control) or exposed to a heat shock (36.9°C for 2 hours) either in the male testes or in the female reproductive tract. We did not detect any temperature sensitive sterility alleles. These results are relevant in relation to haploid gene expression and the findings of considerable amounts of mRNA in mature sperm, potentially important for sperm function and fertilization.

2011, Barker, JSF

Allozyme and microsatellite data from numerous populations of 'Drosophila buzzatii' have been used (i) to determine to what degree Ne varies among generations within populations, and among populations, and (ii) to evaluate the congruence of four temporal and five single-sample estimators of Ne. Effective size of different populations varied over two orders of magnitude, most populations are not temporally stable in genetic composition, and Ne showed large variation over generations in some populations. Short-term Ne estimates from the temporal methods were highly correlated, but the smallest estimates were the most precise for all four methods, and the most consistent across methods. Except for one population, Ne estimates were lower when assuming gene flow than when assuming populations that were closed. However, attempts to jointly estimate Ne and immigration rate were of little value because the source of migrants was unknown. Correlations among the estimates from the single-sample methods generally were not significant although, as for the temporal methods, estimates were most consistent when they were small. These single-sample estimates of current Ne are generally smaller than the short-term temporal estimates. Nevertheless, population genetic variation is not being depleted, presumably because of past or ongoing migration. A clearer picture of current and short-term effective population sizes will only follow with better knowledge of migration rates between populations. Different methods are not necessarily estimating the same Ne, they are subject to different bias, and the biology, demography and history of the population(s) may affect different estimators differently.

2003, Barker, J Stuart F

'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'.

2009, Barker, JSF, Frydenberg, Jane, Gonzalez, Josefa, Davies, Hylton I, Ruiz, Alfredo, Sorensen, Jesper G, Loeschcke, Volker

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).

2002, Wilson, ACC, Sunnucks, P, Barker, JSF

'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.