Movement of two grassland butterflies in the same habitat network: the role of adult resources and size of the study area

Abstract. 1.  Movement patterns of two butterfly species (meadow brown Maniola jurtina L. and scarce copper Lycaenae virgaureae L.) were studied in a 172 ha area within a landscape with a high percentage of suitable habitats for mark–release–recapture experiments.
2.  Adult resource density, but not patch size or larval food plant abundance, influenced the numbers and the fractions of residents, emigrants, and immigrants.
3.  Differences between species were observed in movement frequency and maximum distances moved but not in mean distances moved.
4.  The scarce copper showed much greater movement ability than expected from the results of published studies. This is believed to be a result of the comparatively large size of the study area and the high cover of suitable habitat (>50%).
5.  The mean and maximum distances travelled by butterflies reflected differences in the size of the study area.     

Evolution of genetic redundancy for advanced players

An ever expanding database on the sequence organization and repetition of genic and non-genic components of nuclear and organelle genomes reveals that the vast majority of sequences are subject to one or other mechanism of DNA turnover (gene conversion, unequal crossing over, slippage, retrotransposition, transposition and others). Detailed studies, using novel methods of experimental detection and analytical procedures, show that such mechanisms can operate one on top of another and that wide variations in their unit lengths, biases, polarities and rates create bizarre and complex patterns of genetic redundancy. The ability of these mechanisms to operate both within and between chromosomes implies that realistic models of the evolutionary dynamics of redundancy, and of the potential interaction with natural selection in a sexual species, need to consider the diffusion of variant repeats across multiple chromosome lineages, in a population context. Recently, important advances in both experimental and analytical approaches have been made along these lines. There is increasing awareness that genetic redundancy and turnover induces a molecular co-evolution between functionally interacting genetic systems in order to maintain essential functions.     

Experimental simulation of some visual and physical components of a hedge and the effects on butterfly behaviour in an agricultural landscape

Experiments on the corridor function of linear features in real landscapes are difficult and expensive to carry out using the classic replicated and controlled experimental regimes usually required as formal proof of a concept. We describe two experiments using model structures to simulate different attributes of hedges for their potential role in initiating corridor movement.We examined: (i) the visual signal or link provided by flowering plants associated with hedges (represented by a narrow red-and-white builder's warning tape) and (ii) the physical presence of the body of the hedge itself (represented by green horticultural windbreak). Removable, 100 m long, links were created between two habitat patches (Åkerholmer) in an arable field in Vestby, Norway. We recorded the effect of the links on the behaviour of three `species' of the free-flying butterfly community of the study area: the scarce copper (Heodes virgaureae), the heath fritillary (Mellicta athalia) and, as a complex, the high brown (Fabriciana adippe) and niobe fritillaries (F. niobe).The visual link did not elicit a uniform response by the different `species'. Significantly more high brown/niobe fritillaries flew along the visual link than along the control (no link) and mean distances traveled along the tape were significantly longer than for the control. The heath fritillary and scarce copper did not react in this way. The tape had a slight, but statistically significant, barrier effect on the scarce copper but did not act as a barrier to the other species.All three `species' were strongly affected by the presence of the physical link. A significant barrier effect was detected for all three `species' as was a corridor effect with an increased proportion of butterflies moving along the windbreak compared with the control. Mean distances traveled along the windbreak were significantly longer compared with the control, the response being strongest for the scarce copper.The results demonstrated that simple structures could modify the behaviour of species moving through the landscape and that individual species reacted in different ways to the same structure. The experimental approach of using model structures may have promise for modeling aspects of landscape elements in natural situations for a range of species. The results are discussed in relation to butterfly population structure, mate finding, dispersal and corridor design.     

Generation of VNTRs and heteroplasmy by sequence turnover in the mitochondrial control region of two elephant seal species

We describe an unusual repetitive DNA region located in the 3′ end of the light (L)-strand in the mitochondrial control region of two elephant seal species. The array of tandem repeats shows both VNTR (variable-number tandem repeat) and sequence variation and is absent from 12 compared mammalian species, except for the occurrence in the same location of a distinct repetitive region in rabbit mtDNA and a similar repeat in the harbor seal. The sequence composition and arrangement of the repeats differ considerably between the northern elephant seal (Mirounga angustirostris) and the southern species (M. leonina) despite an estimated divergence time of 1 MY (based on an mtDNA-RNA gene and the nonrepetitive control region). Analysis of repeat sequence relationships within and between species indicate that divergence in sequence and structure of repeats has involved both slippagelike and unequal crossingover processes of turnover, generating very high levels of divergence and heteroplasmy. Presented at the NATO Advanced Research Workshop onGenome Organization and Evolution, Spetsai, Greece, 16–22 September 1992     

A covariotide model explains apparent phylogenetic structure of oxygenic photosynthetic lineages

The aims of the work were (1) to develop statistical tests to identify whether substitution takes place under a covariotide model in sequences used for phylogenetic inference and (2) to determine the influence of covariotide substitution on phylogenetic trees inferred for photosynthetic and other organisms. (Covariotide and covarion models are ones in which sites that are variable in some parts of the underlying tree are invariable in others and vice versa.) Two tests were developed. The first was a contingency test, and the second was an inequality test comparing the expected number of variable sites in two groups with the observed number. Application of these tests to 16S rDNA and tufA sequences from a range of nonphotosynthetic prokaryotes and oxygenic photosynthetic prokaryotes and eukaryotes suggests the occurrence of a covariotide mechanism. The degree of support for partitioning of taxa in reconstructed trees involving these organisms was determined in the presence or absence of sites showing particular substitution patterns. This analysis showed that the support for splits between (1) photosynthetic eukaryotes and prokaryotes and (2) photosynthetic and nonphotosynthetic organisms could be accounted for by patterns arising from covariotide substitution. We show that the additional problem of compositional bias in sequence data needs to be considered in the context of patterns of covariotide/covarion substitution. We argue that while covariotide or covarion substitution may give rise to phylogenetically informative patterns in sequence data, this may not always be so.      

Organization and evolutionary progress of a dispersed repetitive family of sequences in widely separated rodent genomes

The genomes of Mus musculus and other rodent species share a long conserved family of sequences that are dispersed and abundant (approx. 20,000 copies), and that have several novel features of organization and evolution. EcoR1 restriction of M. musculus DNA reveals a prominent 1350 bp² set of sequences. Two nonhomologous sequences of 850 and 500 bp, representing almost the total population of the 1350 bp repeats, were used to examine the detailed organization of the dispersed family and its surrounding sequences using a combination of restriction analysis and “Southern” hybridization. The 1350 bp sequence is contained within a longer repeating unit of approximately 3 kb that is dispersed amongst a wide variety of non-homologous and seemingly non-repetitive sequences. At some sites within the 3 kb repeat, considerable sequence heterogeneity has been found between members of the family, such that the family can be divided into largely non-overlapping subsets (or “segments”) according to the positioning of HinIII sites. Underlying the segmental organization there is a low background overlap of each segment with every other. Some but not all members of the family and its variants have been located on the X-chromosome in a Chinese hamster, M. musculus, X chromosome cell line: suggesting a wide genomic dispersion of the family. Homologous repeated sequences to the M. musculus 1350 bp repeat have been identified in species of Mus and Apodemus, with strikingly similar features of organization and dispersion. In M. spretus a 1350 bp sequence is contained within a dispersed repeat of at least 2·9 kb. However, the majority of M. spretus repeats contain an additional restriction site not present in the equivalent M. musculus array, suggesting a mechanism of widespread substitution or “conversion” of one variant by another in each genome. Apodemus sylvaticus possesses two dispersed and homologous families of 1350 bp and 1850 bp repetition, respectively, which contain sequences that have diverged from M. musculus to differing extents. A. mystacinus possesses only one family of dispersed and homologous repeats of 1850 bp. The majority of members within each Apodemus homologous family also contain characteristic variant restriction-site arrangements. The mechanisms underlying the spread of such variants within each array; the generation of segmental patterns; and the evolutionary conservation of this mouse interspersed family (MIF-1) are discussed in relation to the present knowledge of the organization and activity of other dispersed sequence families.     

Effect of host ligation and starvation on the development and emergence of the parasitoid Campoletis sonorensis

The development of some parasitoids is coordinated by their hosts, via endocrine head or thoracic factors. Ligation of these hosts disrupts parasitoid development. To determine if host ligation affects the solitary, larval endoparasitoid Campoletis sonorensis (Cameron) (Ichneumonidae: Hymenoptera), Heliothis virescens (F.) (Noctuidae: Lepidoptera) larvae were parasitized by C. sonorensis and ligated or starved at various times after parasitization. Ligation and starvation increased parasitoid developmental time and the time of ligation or starvation affected parasitoid emergence. However, ligation and starvation had similar effects on parasitoid development and emergence. Based on our data, C. sonorensis development does not appear to be closely coordinated by hormonal factors produced by the host head and/or thorax.

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Résumé Le développement de certains parasitoïdes est coordonné avec celui de leur hôte, via les centres endocrines de la tête et du thorax. La ligature de ces hôtes interrompt le développement du parasitoïde. Pour déterminer si la ligature de l'hôte affecte l'endoparasite larvaire solitaire, C. sonorensis, des chenilles d'Heliothis virescens ont été parasitées par C. sonorensis, et ensuite ligaturées ou mises à jeûner à des temps variables après avoir été parasitées.Tant les chenilles parasitées avec succès que les autres ont présenté une croissance réduite (Fig. 1), mais, 3 jours après avoir été parasitées sans succès l'augmentation de poids a été plus rapide et a pu être distinguée de l'augmentation de poids des chenilles parasitées avec succès. La nymphose des témoins parasités sans succès était retardée par rapport à la nymphose des véritables témoins. La ligature et le jeûne ont eu des effets identiques sur l'émergence des parasitoïdes (Fig. 2), le pourcentage de parasitisme avec succès augmentant avec la durée du délai entre le parasitisme et le traitement (ligature ou jeûne). Les durées de développement des hôtes ligaturés ou mis à jeûner (Fig. 3) étaient toutes significativement plus longues que les durées de développement des témoins. Cependant, les durées de développement des parasitoïdes n'ont pas été modifiées par le traitement des hôtes, le sexe du parasitoïde et le moment du traitement. Le poids des cocons des parasitoïdes (Fig. 4) était lié linéairement avec le jour du traitement, mais sans modification significative par le sexe du parasitoïde ou le traitement de l'hôte.D'après nos travaux, C. sonorensis ne synchronise apparemment pas sa mue et son émergence avec son hôte, H. virescens. La ligature n'empêche pas complètement le développement ou l'émergence de C. sonorensis bien que le pourcentage d'émergence soit réduit par une ligature dans les 7 jours après le parasitisme. De plus, l'effet du jeûne est semblable sur le pourcentage d'émergences. Le pourcentage réduit d'émergence d'hôtes ligaturés ou mis à jeûner était lié significativement avec le moment du traitement, suggérant la responsabilité éventuelle de l'alimentation réduite de l'hôte. Des hôtes parasités ont continué de s'alimenter et de prendre du poids pendant 5 à 7 jours après la ponte, bien que d'une façon bien inférieure aux témoins non parasités, et cette prise d'aliments par l'hôte peut être nécessaire au succès du développement et à la croissance des parasitoïdes. Ligature et jeûne retardent de la mème façon le développement du parasitoïde; ce retard n'est pas lié au moment de la ligature ou du début du jeûne; ainsi, la réduction de la prise d'aliments peut ne pas être la cause première. L'émergence retardée peut être provoquée par un stress général plutôt que par un ou des facteurs céphaliques ou thoraciques spécifiques.