[Show abstract][Hide abstract] ABSTRACT: Most organisms represent specialized forms that arose as a result of natural selection and genetic drift to occupy distinct ecological niches. In animals, this process of specialization includes the behaviour of the organisms concerned, honed by locally-induced adaptations to specific host food plants (in herbivores) or prey items (in predators and parasitoids), and possibly reinforced by kairomones, including sex pheromones. The major thrust of evolution is towards ecological specialization as a result of the direct effects of intra- and interspecific competition. Adaptation to new resources lowers such competition and allows survival in new habitats/niches. Other benefits of food resource/habitat switching include ‘enemy free space’. If specialism is the norm for the vast majority of species, what of so-called generalists and generalism, which are widely used terms, but perhaps wrongly so? Does generalism exist or is it a mirage that disappears the closer that it is inspected? We review some of the aspects of specialism and generalism and argue that even apparent generalists are filling distinct ecological niches. Often, generalists are rather specific in terms of food preferences, although they may nevertheless remain opportunistic with an overall broad niche/resource width. When apparent ‘good’ species are examined using molecular (DNA) markers, they are often found to comprise cryptic species. Many generalists may be of this kind. If so, generalism warrants additional investigation to establish its scope and credentials.
Biological Journal of the Linnean Society 01/2011; · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anecdotal evidence has long suggested that the African queen butterfly, Danaus chrysippus (L.), is migratory. More recently, records of rapid and seasonal changes in the frequencies of different colour pattern morphs in Tanzania, Ghana, and Kenya have provided further evidence. This paper demonstrates similarly rapid changes in the frequencies of different mitochondrial haplotypes in Nairobi, Kenya over a two-week period. These changes are correlated with changes in the frequencies of homozygous and hybrid colour forms, and are consistent with colour pattern/haplotype associations that have been observed on a continental scale. We conclude that they can only be explained by migration and that mtDNA analysis can be usefully and generally applied in studies of migratory movement.
[Show abstract][Hide abstract] ABSTRACT: Abstract The lesser wanderer butterfly, Danaus (Anosia) chrysippus petilia (Stoll) (Lepidoptera: Danainae), has been treated as a subspecies for the last 100 years. New mitochondrial DNA sequence data for D. petilia, in conjunction with allozyme, structural, morphometric and pattern characters, constitute a compelling case for its specific rank. The holotype of D. petilia has never been located and, as the type location is uncertain, a neotype is designated. Fresh material was collected and examined for this project. Danaus petilia and D. chrysippus have been separated at Lydekker's Line for an estimated 1.1 million years, and they remain interfertile. However, as an allopatric taxon, diagnosable from D. chrysippus, D. petilia merits specific status under the phylogenetic species concept. The following pairs of D. chrysippus subspecies are considered to be synonyms, the first member of each pair having priority: chrysippus + aegyptius (subspecies), klugii + infumata (hybrid phenotypes) and orientis +liboria (subspecies).
Australian Journal of Entomology 01/2005; 44(1):6 - 14. · 0.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insects are among the greatest pests of agriculture, horticulture and forestry world-wide, inflicting damage and economic costs both directly and by transmitting plant viruses. Many kinds of insects are now resistant or cross-resistant to pesticides. In order to combat these pests, including for purposes of immediate control or to follow movements in order to better understand pest biology, tracking studies are important. In turn, such studies become useful for modelling and forecasting outbreaks. This is especially so for flying insects, which constitute the greatest threat in terms of the dissemination of plant pathogenic viral diseases. Tracking the aerial displacement of small insects over large spatial scales is difficult mainly because of their size. Dilution effects upon take off, together with displacement by air currents, makes the recapture of individuals tagged e.g. by fluorescent or radio-labelling, highly unlikely and hence estimates of flight direction, speed, duration and distance are hampered, more especially over larger distances. This is generally true also for larger insects. Consequently, molecular markers have been employed in attempts to resolve population structure and dynamics by inference from estimates of gene flow. In this article, we describe some of the methodologies devised that have provided invaluable information relating to the movement of small insect pests, particularly aphids, and explain how these techniques can be added to by detail gained from molecular marker studies. We outline a national survey-system that could be managed by specialist centres and involving members of the Public, that would enable invasive pest insect populations to be tracked efficiently. The logistics of such a survey are discussed along with the benefits. Overall, an insect tracking mandate is described that will promote the standardisation of population movement measurements. Adopting this approach should allow more accurate intra- as well as interspecies comparisons.
International Journal of Pest Management 01/2004; 50(4):307-315. · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Artificial cloning and ancient asexuals have impacted upon both scientific and lay thinking in applied and theoretical fields as diverse as medicine and evolution. Hence, this is an opportune time to promote debate and discussion on what maintains a clonal lineage. The genetic fidelity of a clone has been discussed in detail elsewhere [Genet. Res. 79 (2002) 1; Biol. J. Linnean Soc. 79 (2003) 3]. In this paper, we focus on the lineage integrity (=longevity), or physiological lifespan of a clone with respect to senesce in relation to factors controlling telomere functioning. Aspects of cell line research pertinent to eukaryotic clonal lineages are discussed and, in particular, we try to extrapolate aspects of this research and apply it to apomictic (=mitotic) aphid lineages to suggest how they may be maintained. Analogies are made between single cells and individual aphids that senescence through a generation, whilst the respective lineages persist for finite periods, unless that is, compensatory mechanisms have evolved allowing immortality in the one and ancient asexuality in the other. Such comparison may allow fresh insights into the mechanisms of clonal lineage maintenance and evolution. We hypothesise that: (1). the cause of extinction in eukaryotic clonal lineages is due to deleterious effects on key regions of the genome, the chromosomal telomere being one such site; (2). recombination acts as a common mechanism to reset telomere functioning, perhaps more fundamental than its utility to reduce genetic load and maintain adaptability; and (3). ancient lineages persist through time as a function of group-specific compensatory mechanisms that maintain telomere integrity.
Infection Genetics and Evolution 12/2003; 3(4):259-69. · 2.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Molecular clocks based on sequence change in mitochondrial (mt) DNA have been useful for placing molecular phylogenies in their historical context, thereby enhancing evolutionary insight. Nonetheless, despite their importance to phylogeographers, the methodology is controversial. Here we report on two mitochondrial clocks for the butterfly genus Danaus based on sequences from the cytochrome c oxidase subunit I (COI) and small subunit 12S rRNA (12S) genes. Both clocks are, within the context of Danaus, reliable time-keepers, mutually consistent and, respectively, in agreement with a crustacean COI clock and a molluscan 12S clock. Though we have no fossils with which directly to calibrate sequence divergence rates for Danaus, the 12S molluscan and COI crustacean clocks chosen for comparison were calibrated to radiometrically dated geomorphological events. Our results indicate that the Danaus COI clock evolves approximately four times faster than the 12S clock. Differences between rates of sequence change in terminal sister-taxa are small and likelihood ratio tests do not reject a hypothesis that evolution has been clock-like. The species Danaus chrysippus is paraphyletic and, therefore, invalid. Danaus probably split from its sister-genus Tirumala around 4.9 ± 0.3 million years ago in the early Pliocene. Résumé—Les horloges moléculaires basées sur le changement de séquence de l'ADN mitochondrial (mt) ont été utiles pour replacer les phylogénies moléculaires dans leur contexte historique, et ainsi
International Journal of Tropical Insect Science 12/2003; 23(04).
[Show abstract][Hide abstract] ABSTRACT: Subspecies chrysippus, dorippus and alcippus of the butterfly Danaus chrysippus differ at three biallelic colour gene loci. They have partially vicariant distributions, but their ranges overlap over a substantial part of central and East Africa, where hybridism is commonplace. We now report that the West African subspecies alcippus differs from other subspecies, not only in nuclear genotype but also in mitochondrial haplotype in both allopatry and sympatry. The maintenance of concordant nuclear and cytoplasmic genetic differences in sympatry, and in the face of hybridisation, is prima facie evidence for sexual isolation. Other evidence that suggests alcippus may be isolated from chrysippus and dorippus include differences in sex ratio (SR), heterozygote deficiency at one site and deduced differences in patterns of migration. We suggest that, within the hybrid zone, differential infection of subspecies by a male-killing Spiroplasma bacterium causes SR differences that restrict female choice, triggering rounds of heterotypic mating and consequent heterozygote excess that is largely confined to females. The absence of these phenomena from hybrid populations that test negative for Spiroplasma supports the hypothesis. The incomplete sexual isolation and partial vicariance of alcippus suggests that it is a nascent species.
[Show abstract][Hide abstract] ABSTRACT: Populations of clonal organisms are often represented as being evolutionary inert with persistent genetic fidelity. The advent of molecular methods and the corresponding increased genetic resolution of clonal populations forces a reconsideration of this viewpoint. We review molecular data from viruses, prokaryotes and eukaryotes to support the argument that clones possess a highly dynamic and adaptive genome.
Biological Journal of the Linnean Society 01/2003; 79:193–208. · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Elucidation of the genetic variability of a model insect species, the grain aphid, Sitobion avenae (Fabricius), a predominantly asexual herbivore within the temperate agro-ecosystem tested, was initiated using molecular DNA markers (RAPDs). This revealed genetic profiles that appeared related to host adaptation at the specific level amongst the natural populations colonizing different grasses and cereals (Poaceae) within the same geographic location. These profiles were recorded either as 'specialist' genotypes found on specific grasses, or as 'generalist' genotypes colonizing several host types including cultivated cereals or native grasses. These findings are compared with analogous systems found amongst insect species, including at a higher trophic level, i.e. interactions between hymenopterous aphid parasitoids. As the aphids and their respective plant hosts occur in the same geographical region at the same time, this appears to be a rare example of the evolutionary transition leading to sympatric speciation in insects. Hence, this study highlights the importance of understanding not only the demographic parameters to genetic diversity, but also the more intricate correlation of genetic diversity to host types in agricultural environments.
Bulletin of Entomological Research 05/2002; 92(2):159-64. · 1.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Empirical evidence for intraclonal genetic variation is described here for clonal systems using a variety of molecular techniques and implicating a diversity of mechanisms. However, clonal systems are still generally perceived as having strict genetic fidelity. As concepts of genetic variability move from primary sequence data to include epigenetic and structural influences on genetic expression, the ability to detect changes in the genome at short intervals allows precedence to be given to inherent biological variation that is often analytically ignored. Therefore, the advent of powerful molecular techniques, like genome mapping, mean that our concepts of genetic fidelity within eukaryotic clones and the whole philosophy of the 'clone' needs to be re-evaluated and redefined to replace old unproven dogma in this aspect of science.
Genetics Research 03/2002; 79(1):1-9. · 2.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The full complement of known greenbug, Schizaphis graminum (Rondani), biotypes found in the USA were subjected to a molecular phylogenetic analysis based on a 1.2-kb portion of the cytochrome oxidase I mitochondrial gene. In addition to these nine biotypes (B, C, E, F, G, H, I, J and K), a probable isolate of the enigmatic biotype A (NY), a 'new biotype' collected from Elymus canadensis (L.) (CWR), and an isolate from Germany (EUR) were included. Schizaphis rotundiventris (Signoret) was included as an outgroup. Genetic distances among S. graminum biotypes ranged from 0.08% to 6.17% difference in nucleotide substitutions. Neighbour-joining, maximum parsimony and maximum likelihood analyses all produced dendrograms revealing three clades within S. graminum. Clade 1 contained the 'agricultural' biotypes commonly found on sorghum and wheat (C, E, K, I, plus J) and there were few substitutions among these biotypes. Clade 2 contained F, G and NY, and Clade 3 contained B, CWR and EUR, all of which are rarely found on crops. The rarest biotype, H, fell outside the above clades and may represent another Schizaphis species. S. graminum biotypes are a mixture of genotypes belonging to three clades and may have diverged as host-adapted races on wild grasses.
[Show abstract][Hide abstract] ABSTRACT: Tissue from the wing tips of the endangered Apollo butterfly (Parnassius apollo L.) were collected at the end of a breeding season from two sites in Norway: Bandak and Gjendetunga/Bukkelægret about 250 km apart. We investigated the suitability of such non-lethal samples as a source of DNA for studying these populations. Universal mitochondrial DNA (mtDNA) primers were used to amplify DNA from the wing tip extractions. Primers spanning the 12s rRNA region produced 0.35 kb fragments that proved to be invariable in the selected samples when tested for restriction length polymorphisms (RFLPs). These sequences had high homology with analogous mtDNA from other insect sources, e.g. lepidoptera [Spodoptera litura (Fabricius)], and served to authenticate the DNA. Random amplified polymorphic DNA (RAPDs) technology was then used to screen for genetic variability. Of several primers tested, Primer-01 (Operon Kit F) produced a profile that differentiated the population with 88% (P<0.001) efficiency based on multivariate logistic regression analysis of banding profiles. RAPDs were also adapted to develop different molecular marker approaches to screen the samples quickly and cheaply. This work indicates that reliable ‘molecular tags’ can be designed to track demographic populations to study their distribution without endangering the butterfly and highlights the suitability of these markers for use in future population studies.
[Show abstract][Hide abstract] ABSTRACT: The majority of insect species do not show an innate behavioural migration, but rather populations expand into favourabl new habitats or contract away from unfavourable ones by random changes of spatial scale. Over the past 50 years, the scientifi fascination with dramatic long–distance and directed mass migratory events has overshadowed the more universal mode of populatio movement, involving much smaller stochastic displacement during the lifetime of the insects concerned. This may be limitin our understanding of insect population dynamics. In the following synthesis, we provide an overview of how herbivorous insec movement is governed by both abiotic and biotic factors, making these animals essentially ‘slaves of their environment’. N displaced insect or insect population can leave a resource patch, migrate and flourish, leaving descendants, unless suitabl habitat and/or resources are reached during movement. This must have constrained insects over geological time, bringing abou species–specific adaptation in behaviour and movements in relation to their environment at a micro– and macrogeographica scale. With insects that undergo long–range spatial displacements, e.g. aphids and locusts, there is presumably a selectio against movement unless overruled by factors, such as density–dependent triggering, which cause certain genotypes within th population to migrate. However, for most insect species, spatial changes of scale and range expansion are much slower an may occur over a much longer time–scale, and are not innate (nor directed). Ecologists may say that all animals and plant are figuratively speaking ‘slaves of their environments’, in the sense that their distribution is defined by their ecolog and genotype. But in the case of insects, a vast number must perish daily, either out at sea or over other hostile habitats having failed to find suitable resources and/or a habitat on which to feed and reproduce. Since many are blown by the vagarie of the wind, their chances of success are serendipitous in the extreme, especially over large distances. Hence, the strategie adopted by mass migratory species (innate pre–programmed flight behaviour, large population sizes and/or fast reproduction) which improve the chances that some of these individuals will succeed. We also emphasize the dearth of knowledge in the variou interactions of insect movement and their environment, and describe how molecular markers (protein and DNA) may be used t examine the details of spatial scale over which movement occurs in relation to insect ecology and genotype.
Philosophical Transactions of The Royal Society B Biological Sciences 08/1999; 354(1388). · 6.23 Impact Factor