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G M Hewitt

Publications and source records attributed to G M Hewitt.

At least 37 records · Page 2Linked to original sources
PubMed2000

Extensive homoplasy, nonstepwise mutations, and shared ancestral polymorphism at a complex microsatellite locus in Lake Malawi cichlids.

Recent studies have suggested that size homoplasy is a prevalent feature of microsatellites and is expected to increase with time of divergence among populations and taxa. In this study, we performed sequence analysis of alleles from a complex microsatellite locus (Pzeb4, initially isolated from Pseudotropheus (Maylandia) zebra) from 1 midwater-feeding and 10 rock-dwelling cichlid fish species from Lake Malawi, East Africa, to investigate how widespread size homoplasy is among closely related taxa at this locus. All cichlid fishes endemic to this lake are believed to have originated within the last 700,000 years, and some species may be less than 200 years old. The number of eletromorphs found per species varied from 3 to 13. Sequence analysis of 95 cloned Pzeb4 PCR products (representing 18 electromorphs) revealed 13 new alleles. Ten of the 13 electromorphs (77%) were found to show size homoplasy due to either single nucleotide substitutions/indels or large indels. To investigate how well this locus fits the single-step mutation model (SMM), the minimum number of mutations required to explain the length differences between pairs of alleles was plotted against their size differences. Of the 300 comparisons, 166 (55.3%) corresponded to SMM expectations and 86 (28.7%) required a smaller number of mutations, and for 48 (16.0%) pairwise comparisons, a larger number of mutations were required to explain the length differences as compared with SMM expectations. Finally, a large deletion in the microsatellite sequence observed in the three rock-dwelling species Pseudotropheus lucerna, Pseudotropheus (Tropheops) 'band,' and Pseudotropheus (Tropheops) 'rust' and the midwater-feeding species Copadichromis sp. is believed to represent a shared ancestral polymorphism.

Africa↗
PubMed2000

Colonization and diversification of the species Brachyderes rugatus (Coleoptera) on the Canary Islands: evidence from mitochondrial DNA COII gene sequences.

The genus Brachyderes Schönherr (Coleoptera: Curculionidae) is represented by the species B. rugatus Wollaston on the Canary Islands, with one subspecies on each of the islands of Gran Canaria, Tenerife, La Palma, and El Hierro. These four subspecies are associated with the endemic pine tree Pinus canariensis, and their distributions are broadly coincident. Eighty-eight individual Canarian Brachyderes, sampled from across the distributions of each subspecies, have been sequenced for 570 bp of the mitochondrial DNA (mtDNA) cytochrome oxidase II gene (COII). No mitotypes are shared among islands. Both maximum-likelihood and distance-based phylogenetic analyses have shown that: Tenerife is composed of a single monophyletic clade of mitotypes, El Hierro is composed of a single monophyletic clade occurring within a larger clade comprising all the La Palma mitotypes, and the mitotypes of these three islands form a monophyletic group distinct from Gran Canaria. New methods for estimating divergence times without the assumption of rate constancy have been used to reconstruct the direction and approximate timing of colonizations among the islands. Colonization has occurred from older to progressionally younger islands, and these colonizations are estimated to have occurred less than 2.6 million years ago, although the timing of the initial colonization of the archipelago is not discernable. New methods for the estimation of diversification rates that use branching times as the analyzed variable have been applied to each island fauna. Hypothesized effects of different levels of recent volcanism among islands were not apparent. All islands exhibit a gradually decreasing rate of genetic diversification that is marked by periodic sudden changes in rate.

Animals↗
PubMed2000

Interpreting colonization of the Calathus (Coleoptera: Carabidae) on the Canary Islands and Madeira through the application of the parametric bootstrap.

The Canary Islands have proven to be an interesting archipelago for the phylogeographic study of colonization and diversification with a number of recent studies reporting evolutionary patterns and processes across a diversity of floral and faunal groups. The Canary Islands differ from the Hawaiian and Galapagos Islands by their close proximity to a continental land mass, being 110 km from the northwestern coast of Africa. This close proximity to a continent obviously increases the potential for colonization, and it can be expected that at the level of the genus some groups will be the result of more than one colonization. In this study we investigate the phylogeography of a group of carabid beetles from the genus Calathus on the Canary Islands and Madeira, located 450 km to the north of the Canaries and 650 km from the continent. The Calathus are well represented on these islands with a total of 29 species, and on the continent there are many more. Mitochondrial cytochrome oxidase I and II sequence data has been used to identify the phylogenetic relationships among the island species and a selection of continental species. Specific hypotheses of monophyly for the island fauna are tested with parametric bootstrap analysis. Data suggest that the Canary Islands have been colonized three times and Madeira twice. Four of these colonizations are of continental origin, but it is possible that one Madeiran clade may be monophyletic with a Canarian clade. The Calathus faunas of Tenerife and Madeira are recent in origin, similar to patterns previously reported for La Gomera, El Hierro, and Gran Canaria.

Animals↗
PubMed1999

MtDNA phylogeography and recent intra-island diversification among Canary Island Calathus beetles.

The genus Calathus Bonelli comprises 24 species on the Canary Islands. Sequences of 927 and 687 bp of the mitochondrial cytochrome oxidase I and II genes, respectively, as well as the intervening tRNA leu gene in 21 of the 24 species, have identified three genetically divergent and unequivocally monophyletic groupings. A phylogeographic analysis is presented for the major monophyletic group comprising all the species of Gran Canaria, La Gomera, and El Hierro, and two Tenerifean species. A distance-based phylogenetic analysis and maximum parsimony analysis have clearly shown that this clade is composed of four distinct lineages. DNA sequence data suggest a recent origin for this clade and that lineages have not evolved at the same rate. Compared with diversification patterns observed in other Coleoptera on the Canary Islands, diversification has been recent relative to the time of colonization within the islands of Gran Canaria and La Gomera. Calathus diversification on La Gomera has been greater than on Gran Canaria. The influences of geological and ecological history are discussed in relation to Calathus diversification.

Animals↗
PubMed1999

Fine-scale genetic structuring in a natural population of European wild rabbits (Oryctolagus cuniculus).

The genetic structure of a free-living tagged population of European wild rabbits (Oryctolagus cuniculus) was investigated for two consecutive years (1990 and 1991) using 10 polymorphic microsatellite loci. A specific social behaviour, the formation of stable breeding groups, influenced the genetic structure of the population. These breeding groups were shown to constitute genetically differentiated units with low levels of gene flow between them. The average relatedness among members of a social group was higher than within the population as a whole. As a result of female philopatry coupled with male-biased natal dispersal, the relatedness of females was higher than that of males, both within social groups and in the whole population. Furthermore, the average relatedness of females within groups was twice the relatedness of females between groups. This study reveals marked fine-scale, intrapopulation genetic structure, which is attributable to the social behaviour of the European wild rabbit.

Age Factors↗
PubMed1999

Macrogeographical population differentiation in oceanic environments: a case study of European hake (Merluccius merluccius), a commercially important fish.

Polymorphism at six microsatellite loci was used to study genetic variability and population structure in six geographically distant natural populations of European hake (Merluccius merluccius L.). Four hundred and eighty-three individuals were sampled from Trondheimsfjord in Norway, the Celtic Sea, the southern Bay of Biscay, Faro off Portugal, the Mediterranean Sea north of the coast of Tunisia and the Adriatic Sea. Population subdivision was found between Mediterranean and Atlantic samples, theta = 0.029 (P < 0. 001). No substructuring was found between samples within the Mediterranean Sea, theta = 0.003 and RST = 0.007 (P > 0.05). The Atlantic population structure appears to be more complex than previously suggested by the placement of stock boundaries by the International Council for the Exploration of the Seas (ICES). Analyses based on various models of microsatellite evolution all suggest that differentiation exists between Bay of Biscay and Portugese samples, theta = 0.013 (P < 0.001), RST = 0.036 (P < 0. 001) which are currently managed as one stock. By contrast, fixation indices indicated no differentiation between southern Bay of Biscay samples and Celtic Sea samples, theta = 0.003 (P = 0.02), phiST = 0. 007 (P = 0.10) which are managed as separate stocks. These results suggest that if the observed trends are stable through time, current management policy of European hake may need revision.

Animals↗
PubMed1998

The phylogeography of the darkling beetle, Hegeter politus, in the eastern Canary Islands.

We investigated the phylogeography of Hegeter politus, a saprophagous, flightless darkling beetle endemic to the eastern Canary Islands, using a fragment of the mitochondrial COI gene. Distance and parsimony based gene trees of the mitotypes identified revealed a striking association between mitotype clades and sampling locations. The branching order of the clades suggested that the colonization of the islands by Hegeter politus proceeded from the southern part of Fuerteventura in a north-northeast direction to Lanzarote and the smaller islands. Based on this, a colonization scenario compatible with the reported geological ages and volcanisms of the various parts of the islands has been proposed. The high divergence of the beetles collected from the extreme south of Fuerteventura (the Jandía peninsula) from all other samples has led us to propose that they may be from a new species that has not been described previously. The ecological isolation of Jandía from the rest of Fuerteventura by the sand dunes that cover its narrow isthmus in the north, and the existence of many plant and animal endemisms unique to Jandía, lend supportive evidence to our proposal. The similarities between the evolution of island endemics in the Hawaiian and Canary archipelagos have been discussed. We conclude that many endemics in the Canary archipelago, like the Hawaiian Islands, are most likely to have originated from post-colonization differentiation and divergence.

Animals↗
PubMed1998

mtDNA phylogeography and postglacial patterns of subdivision in the meadow grasshopper Chorthippus parallelus.

A 300 bp portion of the mitochondrial cytochrome oxidase subunit I (COI) gene was used to investigate the intraspecific genetic structure of the European meadow grasshopper Chorthippus parallelus. Levels of genetic subdivision between geographical regions in Europe were assessed using the KST statistic and revealed patterns indicative of the postglacial history of this organism. Northern European populations are shown to share a very recent common ancestor with, and hence originate from, a Balkan expansion. Genetic distances between these areas and both southern Italy and central Spain are shown to be approximately equal, even though only the Spanish form is recognized as a distinct subspecies. Distance estimates indicate that the common ancestor of the two subspecies lived more than one glacial cycle ago, and the refugial populations have probably been diverging in isolation for five or six glacial cycles (approximately equal to 550,000 years). Comparisons are made to the analysis of a similar data set using an anonymous nuclear DNA marker (Cooper et al., 1995). Although the structure revealed is generally very similar, differences in the location of transition zones between different genetic forms of C. parallelus may reflect the different historical assortment of these molecules.

Animals↗
PubMed1998

Chloroplast DNA recognizes three refugial sources of European oaks and suggests independent eastern and western immigrations to Finland.

Refugial differentiation and routes of postglacial migration are major determinants of the patterns of geographical variation we see in natural populations today. We used patterns of chloroplast DNA (cpDNA) variation to investigate the postglacial colonization history of the European oak species Quercus robur and Q. petraea. By sequencing two cpDNA segments using universal primers, we revealed four polymorphic sites which identify four cytotypes with characteristic geographical distributions. Of these, the principal eastern, central and western cytotypes divide the range into three longitudinal zones, each extending from the south to the north of Europe. This corroborates the idea that the postglacial colonization started from three distinct southerly refugia. The fourth cytotype, restricted to East Anglia, was probably derived from the western type postglacially. As a special problem, we addressed the controversial origin of Q. robur at its northern limits in south-western Finland, where it currently occupies a narrow coastal zone disjunct from the remaining oak range. Using a PCR-RFLP assay that discriminates the eastern cytotype, a contact zone of two cytotypes was identified in the region of the Salpausselkä ridges. This suggests that the marginal northern occurrence was independently colonized both from the east and from the west, across the Baltic Sea.

Chloroplasts↗
PubMed1998

The chromosomes of Diprion pini and D. similis (Hymenoptera: Diprionidae): implications for karyotype evolution.

Earlier cytological investigations characterize the family Diprionidae with a modal chromosome number of seven. This study shows that Diprion pini and D. similis have 14 acrocentric chromosomes (n = 14 for haploid males and 2n = 28 for diploid females). In D. pini, rRNA genes are located on the satellite and the round short arm of the chromosome carrying this segment. We studied six populations with no evidence of chromosomal polymorphism at the species level. Our results disagree with those published previously and reopen the question of karyotype evolution. Chromosome morphology, ISH and C-banding results support the hypothesis of chromosome number doubling by centric fission and not by polyploidization, followed by the growth of short arms by means of pericentromeric DNA amplification.

Animals↗
PubMed1998

Mitochondrial DNA phylogeography of European hedgehogs.

European hedgehog populations belonging to Erinaceus europaeus and E. concolor have been investigated by mitochondrial DNA analysis. A 383 bp fragment of the cytochrome b gene has been sequenced and maximum parsimony and neighbour-joining trees of Tamura-Nei genetic distance values have been constructed. Similar topologies have been produced by both methods, showing a deep divergence between E. europaeus and E. concolor and a further subdivision of each species into a western and an eastern clade. A comparison with previously published allozyme data is made, and concordant and discordant patterns are discussed. The influence of Pleistocene glaciations on the observed pattern of divergence is inferred.

Animals↗
PubMed1997

The phylogenetic relationships of seven European Ips (Scolytidae, Ipinae) species.

In Central Europe seven lps species are characterized by differences in morphology, structure of galleries, host specificity and aggressiveness. These species were analysed by allozyme markers and by sequencing 567 bp of the mitochondrial cytochrome oxidase I gene, in order to define their phylogenetic relationships. Orthotomicus erosus and Tomicus minor were taken as outgroup species. The data revealed high inter-specific and low intra-specific sequence divergence. Plotting the observed sequence divergence caused by transversions (Tv) and transitions (Ts) and the level of saturation for Ts and Tv of each codon position showed that the third positions were highly saturated by multiple substitutions. Maximum parsimony analysis produced two groups: (1) I. typographus, I. cembrae, I. amitinus, I. duplicatus and I. acuminatus; (2) I. mannsfeldi, I. sexdentatus and the two outgroups. In all analyses the species of the first cluster were put together and I. typographus and I. cembrae, and I. mannsfeldi and O. erosus emerged as sister pairs. The data do not support a common ancestor for the seven European lps species. The eight-spined bark beetles (except I. mannsfeldi) and I. acuminatus formed a monophyletic group. The close relationship of I. mannsfeldi and O. erosus supports the latter belonging to the genus lps as proposed by Wood (1982) and Escherich (1923). However, more genetic markers and more species of the genera Orthotomicus and Pityokteines have to be analysed to resolve the phylogenetic positions of I. sexdentatus I. mannsfeldi within the tribe lpinl.

Amylases↗
PubMed1997

Polymorphic microsatellite loci in the European rabbit (Oryctolagus cuniculus) are also amplified in other lagomorph species.

Six polymorphic microsatellite markers developed for the European wild rabbit (Oryctolagus cuniculus) were amplified with 20 other species of lagomorphs, representing both commercially important species and species important from a conservation perspective. Successful amplification of a number of these loci has provided an important set of new molecular markers for this mammalian order.

Alleles↗
PubMed1997

Assessment of the universality and utility of a set of conserved mitochondrial COI primers in insects.

A set of mitochondrial COI primers has been studied by genomic PCR and many primer combinations shown to work universally well across Insecta. They are able to amplify various amplicons with different variability which enables the selection of a particular amplicon as a suitable DNA marker for a project. The potential usefulness of different amplicons is examined, with analysis on published study cases employing these regions. With respect to their variability, amplicons UEA5/UEA6, UEA7/UEA8 and UEA5/UEA8 could be useful for low- to mid-level phylogenetic analysis, i.e. from species, genus to perhaps family level depending on taxa involved. UEA5/UEA6 will be too conserved for intraspecific studies. Amplicons UEA3/UEA4 and UEA9/UEA10 would be better suited to low-level phylogenetic investigations, such a analysis of relationships among closely related species and population genetic studies. However, these guidelines should not be over-generalized for the reasons given. Amplification conditions of various primer combinations, and general problems in the use of conserved PCR primers are discussed.

Conserved Sequence↗