Polyandry and paternity skew in natural and experimental populations of Drosophila serrata

Many species engage in polyandry, resulting in the potential for sexual selection to continue post-copulation through sperm competition and/or cryptic female choice. The relative importance of pre- vs. post-copulatory processes remains unknown for most species despite this information being fundamental for understanding the evolutionary consequences of sexual selection. The Australian fruit fly Drosophila serrata has become a prominent model system for studying precopulatory sexual selection, such as mating preferences and their influence on the evolution of sexually selected traits. Here, we investigated polyandry and the potential for post-copulatory sexual selection in this species using indirect paternity analysis. We genotyped 21 wild-caught and 19 laboratory-reared mothers and their offspring (a total of 787 flies) at six microsatellite loci and found extensive polyandry, with all broods surveyed having at least two sires. Female remating rates were higher than in other Drosophila surveyed to date and no significant differences were found between laboratory and field populations. Additionally, we found evidence for biased sperm usage in several broods of D. serrata . Paternity skew occurred more frequently in broods from the field population than the laboratory one, suggesting differences between the two environments in the level of post-copulatory sexual selection. Our data suggest that D. serrata represents a promising system for studying the interaction between pre- and post-copulatory sexual selection in driving the evolution of sexually selected phenotypes.     

Resource choice in orchard populations of Drosophila

Three capture-recapture experiments were performed on natural populations of Drosophila from orchards in California. Two of the experiments investigated choice between known breeding substrates: oranges v. grapefruits and figs v. peaches. The third involved choice between citrus baits in a citrus orchard and both banana and citrus baits in an adjacent almond orchard. Drosophila pseudoobscura showed no fidelity to the bait or area of initial capture. However, a statistically significant but low level of resource fidelity was displayed by D. melanogaster/D. simulans. An index of differential choice is used to compare our results to those of previous studies. Possible biological bases of choice behaviour are discussed.     

Variability for host preference in insect populations: Mechanistic and evolutionary models

Two models that explain variation in behaviour associated with locating and accepting different habitats (host plants) are described and analyzed. One model describes the dynamics of search-mode ontogeny in Battus philenor butterflies. This model predicts that the proportion of females using either of two search modes at any given time reflects an equilibrium between the rate at which females switch from using a narrow-leaf search mode to using a broad-leaf search mode and the rate at which the opposite switch is made. Preliminary data suggest that the model predicts reasonably well the observed seasonal change in predominant search mode in the field. The second model, really a set of related models, describes the dynamics of genes that influence searching behaviour. Several predictions of these models are: (1) gentic variation for proportional allocation of offspring to different habitats should be more common under soft-selection regimes than under hard-selection regimes. (2) Polyphagy should be more common under soft selection than under hard selection. (3) Whether changes in the relative abundances or relative quality of different habitats lead to evolutionary change in apportionment of offspring to habitats depends in a complex way on mode of population regulation, method of search, type of limitation of fecundity and genetic properties of loci affecting preference. Although the two types of models superficially appear to address different types of behavioural variation, they may be used in a complementary fashion to understand the evolution of habitat selection behaviour.     

The conflict between natural and artificial selection in finite populations

Summary A single locus model of the interaction between natural selection and artificial selection for a quantitative character in a finite population, assuming heterozygote superiority in natural fitness but additive action on the character, has been studied using transition probability matrices.If natural selection is strong enough to create a selection plateau in which genetic variance declines relatively slowly, then the total response to artificial selection prior to the plateau will be much less than that expected in the absence of natural selection, and the half-life of response will be shorter. Such a plateau is likely to have a large proportion, if not all, of the original genetic variance still present. In selection programmes using laboratory animals, it seems likely that the homozygote favoured by artificial selection must be very unfit before such a plateau will occur. A significant decrease in population fitness as a result of artificial selection does not necessarily imply that the metric character is an important adaptive character.These implications of this model of natural selection are very similar to those derived by James (1962) for the optimum model of natural selection. In fact, there seems to be no aspect of the observable response to artificial selection that would enable anyone to distinguish between these two models of natural selection.     

Variation in Drosophila melanogaster central metabolic genes appears driven by natural selection both within and between populations

In this report, we examine the hypothesis that the drivers of latitudinal selection observed in the eastern US Drosophila melanogaster populations are reiterated within seasons in a temperate orchard population in Pennsylvania, USA. Specifically, we ask whether alleles that are apparently favoured in northern populations are also favoured early in the spring, and decrease in frequency from the spring to autumn with the population expansion. We use SNP data collected for 46 metabolic genes and 128 SNPs representing the central metabolic pathway and examine for the aggregate SNP allele frequencies whether the association of allele change with latitude and that with increasing days of spring–autumn season are reversed. Testing by random permutation, we observe a highly significant negative correlation between these associations that is consistent with this expectation. This correlation is stronger when we confine our analysis to only those alleles that show significant latitudinal changes. This pattern is not caused by association with chromosomal inversions. When data are resampled using SNPs for amino acid change the relationship is not significant but is supported when SNPs associated with cis-expression are only considered. Our results suggest that climate factors driving latitudinal molecular variation in a metabolic pathway are related to those operating on a seasonal level within populations.     

黔西北石漠化地区两栖动物多样性及其生境选择

对两栖动物多样性及其生境选择的调查, 可为两栖动物的保护提供基础性资料。我们于2018年9-10月、2019年3-8月对贵州省毕节市撒拉溪石漠化综合治理示范区30个研究样方的两栖动物进行了调查, 共观察到两栖动物5,688只, 隶属2目6科9属10种。采用Shannon-Wiener多样性指数、Margalef丰富度指数、Pielou均匀度指数等分析了不同等级石漠化区域中的两栖动物物种多样性, 采用Sorenson相似性系数、聚类分析等方法分析了群落的相似性与差异性。结果显示: (1)云南小狭口蛙(Glyphoglossus yunnanensis)为优势种, 贵州疣螈(Tylototriton kweichowensis)、红点齿蟾(Oreolalax rhodostigmatus)、中华蟾蜍(Bufo gargarizans)、华西雨蛙(Hyla annectans)和昭觉林蛙(Rana chaochiaoensis)为常见种, 粗皮姬蛙(Microhyla butleri)、沼水蛙(Hylarana guentheri)、筠连臭蛙(Odorrana junlianensis)和威宁蛙(Rana weiningensis)为稀有种。(2)无石漠化区域与潜在石漠化区域两栖动物物种数、个体数以及生境类型较之其他3个等级石漠化区域更为丰富, 多样性指数、丰富度指数以无石漠化区域为最大。(3)无石漠化区域和潜在石漠化区域之间、无石漠化区域和潜在石漠化区域分别与其他3个等级石漠化区域之间表现出较强的差异性。研究表明, 喀斯特地区石漠化导致的生境差异是两栖动物分布差异的重要原因, 加强石漠化的生态治理是喀斯特地区保护两栖动物的重要途径。     

The danger of applying the breeder's equation in observational studies of natural populations

The breeder's equation, which predicts evolutionary change when a phenotypic covariance exists between a heritable trait and fitness, has provided a key conceptual framework for studies of adaptive microevolution in nature. However, its application requires strong assumptions to be made about the causation of fitness variation. In its univariate form, the breeder's equation assumes that the trait of interest is not correlated with other traits having causal effects on fitness. In its multivariate form, the validity of predicted change rests on the assumption that all such correlated traits have been measured and incorporated into the analysis. Here, we (i) highlight why these assumptions are likely to be seriously violated in studies of natural, rather than artificial, selection and (ii) advocate wider use of the Robertson–Price identity as a more robust, and less assumption‐laden, alternative to the breeder's equation for applications in evolutionary ecology.     

A genome scan to detect candidate regions influenced by local natural selection in human populations

As human populations dispersed throughout the world, they were subjected to new selective forces, which must have led to local adaptation via natural selection and hence altered patterns of genetic variation. Yet, there are very few examples known in which such local selection has clearly influenced human genetic variation. A potential approach for detecting local selection is to screen random loci across the genome; those loci that exhibit unusually large genetic distances between human populations are then potential markers of genomic regions under local selection. We investigated this approach by genotyping 332 short tandem repeat (STR) loci in Africans and Europeans and calculating the genetic differentiation for each locus. Patterns of genetic diversity at these loci were consistent with greater variation in Africa and with local selection operating on populations as they moved out of Africa. For 11 loci exhibiting the largest genetic differences, we genotyped an additional STR locus located nearby; the genetic distances for these nearby loci were significantly larger than average. These genomic regions therefore reproducibly exhibit larger genetic distances between populations than the "average" genomic region, consistent with local selection. Our results demonstrate that genome scans are a promising means of identifying candidate regions that have been subjected to local selection.     

Habitat matching: Alternatives and implications to populations and communities

Summary I evaluate habitat matching rules based on ideal distribution models of density-dependent habitat use. Recent approaches and the ideal free continuous input matching rule on which they depend, are restricted to only those habitats that are jointly occupied across the full range of population sizes. These assumptions may often be inappropriate to field applications of habitat matching. I develop alternatives that can be applied to a wide array of ideal forms of habitat selection, including the ideal free, continuous input example. Input matching can be distinguished from assumptions of consumer-resource models and preemptive habitat use by regressions of density between paired habitats (isodars). Isodars for continuous input models should be linear on a logarithmic scale, while those for consumer-resource models should be linear on an arithmetic scale. Pre-emptive isodars can be distinguished from the others by dramatic non-linearities at both low and high densities. Field data on white-footed mice support the consumer-resource theory. Implications of the rules for population regulation and community organization are highlighted by new models that specify how the fitness of pre-emptive habitat selectors should decline with increasing density. Strong non-linearities produced by comparisons between variable and homogeneous habitats produce reversing source-sink population regulation and a new form of cyclical community dynamics. Variable habitats act as a source of emigrants at low density and a sink for immigrants at high density. Subordinate species may occupy only the variable habitat at both low and high density.     

Dispersing brush mice prefer habitat like home

During natal dispersal, young animals leave their natal area and search for a new area to live. In species in which individuals inhabit different types of habitat, experience with a natal habitat may increase the probability that a disperser will select the same type of habitat post-dispersal (natal habitat preference induction or NHPI). Despite considerable interest in the ecological and the evolutionary implications of NHPI, we lack empirical evidence that it occurs in nature. Here we show that dispersing brush mice (Peromyscus boylii) are more likely to search and settle within their natal habitat type than expected based on habitat availability. These results document the occurrence of NHPI in nature and highlight the relevance of experience-generated habitat preferences for ecological and evolutionary processes.     

Nonneutral admixture of immigrant genotypes in African Drosophila melanogaster populations from Zimbabwe

Drosophila melanogaster originated in Africa and colonized the rest of the world only recently (approximately 10,000 to 15,000 years ago). Using 151 microsatellite loci, we investigated patterns of gene flow between African D. melanogaster populations representing presumptive ancestral variation and recently colonized European populations. Although we detected almost no evidence for alleles of non-African ancestry in a rural D. melanogaster population from Zimbabwe, an urban population from Zimbabwe showed evidence for admixture. Interestingly, the degree of admixture differed among chromosomes. X chromosomes of both rural and urban populations showed almost no non-African ancestry, but the third chromosome in the urban population showed up to 70% of non-African alleles. When chromosomes were broken into contingent microsatellite blocks, even higher estimates of admixture and significant heterogeneity in admixture was observed among these blocks. The discrepancy between the X chromosome and the third chromosome is not consistent with a neutral admixture hypothesis. The higher number of European alleles on the third chromosome could be due to stronger selection against foreign alleles on the X chromosome or to more introgression of (beneficial) alleles on the third chromosome.     

Allozyme genotype-environment relationships in natural populations of Drosophila buzzatii

Allozyme frequency data from natural populations of Drosophila buzzatii were analyzed for genotype-environment relationships. Allele frequency and heterozygosity at six loci polymorphic throughout eastern Australia and a number of environmental factors (both means and variabilities) were examined by a variety of multivariate techniques. Significant genotype-environment associations were found for five of the six loci, and after correcting for geographic location significant associations remained for Est-2 and Adh-1 gene frequencies and heterozygosities and for Pgm gene frequencies. The results are discussed in relation to selection and gene flow and provide the basis for laboratory studies to disentangle confounded effects of (1) environmental means and environmental variabilities and (2) allele frequency and heterozygosity, and thus to further test for and determine the nature of any natural selection at particular allozyme loci.This work was supported by a grant from the Australian Research Grants Committee to J. S. F. B.     

Habitat use by sympatric populations of Pseudomys novaehollandiae and Mus domesticus in coastal heathland

Abstract Patterns of habitat use by Pseudomys novaehollandiae and Mus domesticus were investigated on a 6. 8 ha area of coastal heathland, almost five years after it last burned in Myall Lakes National Park. One hundred and fifty-one trap stations were positioned on 17 traplines across a mosaic of interlocking macrohabitats. This pattern was a consequence of the site's topography and to a lesser extent fire history. Multivariate statistical procedures were employed to identify those microhabitat parameters that contribute to both individual species’ habitat use and the partitioning of habitat to reduce competition for space. Trapping results show P. novaehollandiae to be almost three times as abundant as M. domesticus at this time, although M. domesticus does show strong regional, and hence local, fluctuations in abundance over time. Both species exhibit habitat selection (P< 0. 05) with individuals preferring dry, tall closed heath and open heathland habitats. Immature P. novaehollandiae (< 15 g) were found mostly in short dense wet heath and may have been dispersing. Species exhibit high between-habitat overlap using Pianka's formula (0. 88). This overlap is substantially reduced within macrohabitats (0. 28), when trap stations are considered as resource states, suggesting a considerable degree of microhabitat separation at the trap station level. Discriminant function and multiple regression analyses identify microhabitat selection that is not strongly focused, suggesting both species to be spatial generalists. Elevation was selected as the most significant variable in these analyses and represents a soil moisture gradient that determines changes in the floristic and structural components of the biotic environment. No single habitat variable was found to explain within-habitat separation convincingly, however, when a factor analysis of habitat variables was used to produce a reduced three-dimensional factor space the outcome was marked. The 95% confidence envelopes for the distribution of each species show an extremely low overlap in factor space, with a zero overlap in the X-Y plane and less than 1% overlap in theY-Z plane. Differential micro-habitat selection does produce effective habitat partitioning, thus facilitating coexistence of these two species. We suspect this occurs primarily by M. domesticus altering habitat selection. There is evidence to suggest that M. domesticus acts as a fugitive species occupying resource niches left vacant by P. novaehollandiae and other small mammal species coexisting on the study area.     

Contrasting patterns of natural variation in global Drosophila melanogaster populations

Despite the popularity of Drosophila melanogaster in functional and evolutionary genetics, the global pattern of natural variation has not yet been comprehensively described in this species. For the first time, we report a combined survey using neutral microsatellites and mitochondrial sequence variation jointly. Thirty-five populations originating from five continents were compared. In agreement with previous microsatellite studies, sub-Saharan African populations were the most variable ones. Consistent with previous reports of a single 'out of Africa' habitat expansion, we found that non-African populations contained a subset of the African alleles. The pattern of variation detected for the mitochondrial sequences differed substantially. The most divergent haplotypes were detected in the Mediterranean region while Africa harboured most haplotypes, which were all closely related. In the light of the well-established African origin of D. melanogaster, our results cast severe doubts about the suitability of mtDNA for biogeographic inference in this model organism.