Biomedical subjects

Roger K Butlin

Publications and source records attributed to Roger K Butlin.

12 recordsLinked to original sources

PubMed2006

Epistatic regulation of behavioural and morphological traits in the zebrafish (Danio rerio).

There is currently a lack of studies examining epistasis in general, and specifically for behavioural traits of evolutionary significance. The advent of more efficient analytical methods for exploring epistasis in QTL studies removes the computational restraint on this type of analysis and suggests that performing further analyses of existing datasets may reveal a more complete picture of the genetic architecture of the traits. Here we report the results from an epistatic QTL analysis of an F2 cross between a wild population and a standard laboratory strain of zebrafish. This further analysis was performed using a simultaneous search to identify epistatically interacting QTL affecting behavioural and morphological traits and uncovered several novel epistatic interactions that reached either genome-wide or suggestive significance levels as determined by a randomisation testing approach. These results provide novel insight into the genetic architecture of the regulation of behavioural as well as morphological phenotypes and call for more studies of epistasis for this group of traits.

Animals↗

PubMed2006

QTL analysis of behavioral and morphological differentiation between wild and laboratory zebrafish (Danio rerio).

The zebrafish is an important model organism for neuro-anatomy and developmental genetics. It also offers opportunities for investigating the functional and evolutionary genetics of behaviour but these have yet to be exploited. The ecology of anti-predator behaviour has been widely studied in fish and has been shown to vary among populations and between wild and domesticated (laboratory) fish. Here, we utilise the strong behavioural differences present between a wild-derived strain of fish from Bangladesh and the laboratory strain AB. In total, 184 F2 fish were generated and tested for shoaling tendency and willingness to approach an unfamiliar object ('boldness'). Our results indicate the existence of QTL for boldness on chromosomes 9 and 16 and suggest another genomic region that influences anti-predator behaviour on chromosome 21. QTL for growth rate, weight and fat content, all of which are elevated in laboratory fish, were detected on chromosome 23. These initial results confirm the potential for QTL mapping of behavioural traits in zebrafish and also for dissecting the consequences of selection during domestication.

Animals↗

PubMed2006

Adaptation to a steep environmental gradient and an associated barrier to gene exchange in Littorina saxatilis.

Steep environmental gradients offer important opportunities to study the interaction between natural selection and gene flow. Allele frequency clines are expected to form at loci under selection, but unlinked neutral alleles may pass easily across these clines unless a generalized barrier evolves. Here we consider the distribution of forms of the intertidal gastropod Littorina saxatilis, analyzing shell shape and amplified fragment length polymorphism (AFLP) loci on two rocky shores in Britain. On the basis of previous work, the AFLP loci were divided into differentiated and undifferentiated groups. On both shores, we have shown a sharp cline in allele frequencies between the two morphs for differentiated AFLP loci. This is coincident with a habitat transition on the shore where the two habitats (cliff and boulder field) are immediately contiguous. The allele frequency clines coincide with a cline in shell morphology. In the middle of the cline, linkage disequilibrium for the differentiated loci rises in accordance with expectation. The clines are extremely narrow relative to dispersal, probably as a result of both strong selection and habitat choice. An increase in F(ST) for undifferentiated AFLPs between morphs, relative to within-morph comparisons, is consistent with there being a general barrier to gene flow across the contact zone. These features are consistent either with an episode of allopatric divergence followed by secondary contact or with primary, nonallopatric divergence. Further data will be needed to distinguish between these alternatives.

Acclimatization↗

PubMed2005

Sex and segregation in temperate bats.

Many temperate insectivorous bats show marked sexual segregation during the summer, but in spectacular, pre-hibernation swarming, gather at caves to mate. In many species, sexual segregation is probably due to a gradient in aerial insect availability that confines females to lower elevations, where high reproductive costs are met by an abundant and reliable food supply. In the hawking and trawling Myotis daubentonii, we show that alongside inter-sexual segregation, there is intra-male segregation and suggest that this results from the exclusion of most males from high-quality habitat. These apparently excluded males suffer reduced foraging efficiency and mating success relative to males that roost with the females in summer. Changes in resources and behaviour at the end of the summer lead to a change in strategy that gives all males a chance to mate during swarming, but this does not overcome the paternity advantage to males that spend the summer with the females.

Animals↗

PubMed2005

Patterns of male sterility in a grasshopper hybrid zone imply accumulation of hybrid incompatibilities without selection.

It is now widely accepted that post-zygotic reproductive isolation is the result of negative epistatic interactions between derived alleles fixed independently at different loci in diverging populations (the Dobzhansky-Muller model). What is less clear is the nature of the loci involved and whether the derived alleles increase in frequency through genetic drift, or as a result of natural or sexual selection. If incompatible alleles are fixed by selection, transient polymorphisms will be rare and clines for these alleles will be steep where divergent populations meet. If they evolve by drift, populations are expected to harbour substantial genetic variation in compatibility and alleles will introgress across hybrid zones once they recombine onto a genetic background with which they are compatible. Here we show that variation in male sterility in a naturally occurring Chorthippus parallelus grasshopper hybrid zone conforms to the neutral expectations. Asymmetrical clines for male sterility have long tails of introgression and populations distant from the zone centre show significant genetic variation for compatibility. Our data contrast with recent observations on 'speciation genes' that have diverged as a result of strong natural selection.

Animals↗

PubMed2005

Recombination and speciation.

Speciation can be viewed as the evolution of restrictions on the freedom of genetic recombination: new combinations of alleles can be generated within species, but alleles from different species cannot be brought together. Recently, there has been increasing realization that the role of chromosomal rearrangements in speciation might be primarily a result of their influence on recombination. I argue that ideas about the role of recombination in speciation should be considered in the context of the variability of recombination rates and patterns more generally and that genic as well as chromosomal causes of restricted recombination should be considered. I review patterns of variation in recombination rates and theoretical progress in understanding the conditions that favour increased or decreased rates. Although progress has been made in understanding conditions that alter overall rates of recombination, widespread variation in patterns of recombination remains largely unexplained. I consider three models for the role of locally restricted recombination in speciation and the evidence currently supporting them.

Adaptation, Biological↗

PubMed2005

Genetic population structure of Natterer's bats explained by mating at swarming sites and philopatry.

During autumn 'swarming', large numbers of temperate bats chase each other in and around underground sites. Swarming has been proposed to be a mating event, allowing interbreeding between bats from otherwise isolated summer colonies. We studied the population structure of the Natterer's bat (Myotis nattereri), a swarming species in northern England, by sampling bats at seven sites in two swarming areas and at 11 summer colonies. Analysis of molecular variance (amova) and genetic assignment analyses showed that the swarming areas (60 km apart) support significantly different populations. A negative correlation was found between the distance of a summer colony from a swarming area and the assignment of bats to that area. High gene diversity was found at all sites (HE = 0.79) suggesting high gene flow. This was supported by a low FST (0.017) among summer colonies and the absence of isolation by distance or substructure among colonies which visit one swarming area. The FST, although low, was significantly different from zero, which could be explained by a combination of female philopatry and male-mediated gene flow through mating at swarming sites with bats from other colonies. Modelling suggested that if effective size of the summer colonies (Ne) was low to moderate (10-30), all mating must occur at the swarming sites to account for the observed FST. If the Ne was higher (50), in addition to random mating during swarming, there may be nonrandom mating at swarming sites or some within-colony mating. Conservation of swarming sites that support potentially large populations is discussed.

Animals↗

PubMed2004

Within- and between-individual sequence variation among ITS1 copies in the meadow grasshopper Chorthippus parallelus indicates frequent intrachromosomal gene conversion.

Sequencing multiple copies of the ITS1 region revealed the coexistence of two or more haplotypes within the genome of Chorthippus parallelus. Using a PCR-RFLP approach, the ITS1 numbers and frequencies of haplotypes present in each of 40 individuals were investigated, revealing a consistent lack of homogeneity. For each individual, the level of intra-individual variation was estimated from a sample of 20 ITS1 copies. The level of differentiation in haplotype frequency among individuals was then estimated by maximum likelihood using models based on the Dirichlet distribution. This confirmed the existence of significant levels of variation among individuals within each population studied. The most likely turnover mechanism that could generate this pattern of variation is gene conversion, operating at the intrachromosomal level. Furthermore, the discovery of linkage disequilibrium among the ITS1 haplotypes of C. parallelus suggests that intrachromosomal gene conversion occurs more frequently than interchromosomal recombination. Subspecies of C. parallelus showed significantly different haplotype distributions following about 0.5 Myr of divergence. With respect to the process of concerted evolution, we show that homogenization of repeats is slow relative to speciation, and the standing variation among individuals is sufficient for selection to operate.

Animals↗

PubMed2004

Habitat fragmentation and biodiversity: testing for the evolutionary effects of refugia.

Concordant areas of endemism among taxa have important implications both for understanding mechanisms of speciation and for framing conservation priorities. Here we discuss the need for careful testing of phylogeographic data for evidence of such concordance, with particular reference to the Indonesian island of Sulawesi. This is because there are good reasons to question whether concordance between taxa is likely to be a common pattern, and because of the serious implications of incorrectly concluding that the biodiversity of a given area can be partitioned in this way.

Biodiversity↗

PubMed2003

Inter and intra-population variation in shoaling and boldness in the zebrafish (Danio rerio).

Population differences in anti-predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish (Danio rerio) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory-raised fish derived from four wild-caught populations. Controlling for differences in rearing environment, significant inter-population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow-sense heritability estimate of 0.40 was obtained, with no apparent dominance effects.

Animals↗

PubMed2002

Low levels of chromosomal differentiation between the grasshoppers Chorthippus brunneus and Chorthippusjacobsi (Orthoptera; Acrididae) in northern Spain.

The grasshopper species Chorthippus brunneus and C. jacobsi (Orthoptera: Acrididae) form a hybrid zone in northern Spain. These species probably diverged while isolated in southern refugia during one of the recent ice ages, and are clearly distinguished by morphology and male calling song. However, in contrast to other Chorthippus taxa that form hybrid zones in Europe, these two species cannot be reliably distinguished on the basis of characteristics of the karyotype such as heterochromatin banding patterns and composition, as revealed by C-banding and fluorochrome staining. Silver staining also reveals the presence of two autosomal nucleolar organiser regions (NORs) in both species. However, differentiation between C. brunneus and C. jacobsi was revealed on the X chromosome using fluorescent in situ hybridisation (FISH). C. brunneus individuals showed additional rDNA sequences on the X chromosome that were not observed in any C. jacobsi individuals. These sequences are not transcribed, indicating either mutational silencing of an ancestral NOR on the X chromosome, or the transposition of non-functional sequences from the autosomes. The implications of these results for the evolution of NOR number in Chorthippus are discussed.

Animals↗

PubMed2002

Mating signal variation and bimodality in a mosaic hybrid zone between Chorthippus grasshopper species.

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are easily distinguished by male calling song and the number of stridulatory pegs on the hind femur, and form a mosaic hybrid zone in northern Spain. In this paper, we fit a two-dimensional cline to variation in male calling song characters, which are of particular interest as they are likely to be involved in mate choice by females. As with variation in peg number, local habitat makes only a small contribution in explaining deviations in mean song score from clinal expectations. However, the fitted width of the cline for song characters is significantly narrower than for peg number, suggesting that mating signals may be associated with reduced hybrid fitness in the field and that recombination rates are sufficient to allow clines for different characters to diverge in width. Despite this, estimates for the overall elevation in linkage disequilibrium at the zone center, based on covariance between peg and song characters, reveal a substantial overrepresentation of parental genotypes at the cline center relative to the expectations of a tension zone of similar width. Examination of covariance at individual sites reveals that this inflated estimate of linkage disequilibrium is caused by several sites where the distribution of phenotypes is effectively bimodal. This substantial variation in linkage disequilibrium at the cline center could result from local variation in the strength of assortative mating or selection against hybrids, or may reflect the long-distance colonization of empty habitat from outside the hybrid zone, which would continually create new contacts between parental genotypes at the cline center. Hybrid zones like this, in which strong linkage disequilibrium occurs in some situations but not in others, are of particular relevance to speciation research and allow investigation of the spread of combinations of alleles through different genetic and ecological backgrounds.

Animals↗