Anders N. Nilsson

The Effect of Geographical Scale of Sampling on DNA Barcoding

Abstract Eight years after DNA barcoding was formally proposed on a large scale, CO1 sequences are rapidly accumulating from around the world. While studies to date have mostly targeted local or regional species assemblages, the recent launch of the global iBOL project (International Barcode of Life), highlights the need to understand the effects of geographical scale on Barcodings goals. Sampling has been central in the debate on DNA Barcoding, but the effect of the geographical scale of sampling has not yet been thoroughly and explicitly tested with empirical data. Here, we present a CO1 data set of aquatic predaceous diving beetles of the tribe Agabini, sampled throughout Europe, and use it to investigate how the geographic scale of sampling affects 1) the estimated intraspecific variation of species, 2) the genetic distance to the most closely related heterospecific, 3) the ratio of intraspecific and interspecific variation, 4) the frequency of taxonomically recognized species found to be monophyletic, and 5) query identification performance based on 6 different species assignment methods. Intraspecific variation was significantly correlated with the geographical scale of sampling (R-square = 0.7), and more than half of the species with 10 or more sampled individuals (N = 29) showed higher intraspecific variation than 1% sequence divergence. In contrast, the distance to the closest heterospecific showed a significant decrease with increasing geographical scale of sampling. The average genetic distance dropped from > 7% for samples within 1 km, to < 3.5% for samples up to > 6000 km apart. Over a third of the species were not monophyletic, and the proportion increased through locally, nationally, regionally, and continentally restricted subsets of the data. The success of identifying queries decreased with increasing spatial scale of sampling; liberal methods declined from 100% to around 90%, whereas strict methods dropped to below 50% at continental scales. The proportion of query identifications considered uncertain (more than one species < 1% distance from query) escalated from zero at local, to 50% at continental scale. Finally, by resampling the most widely sampled species we show that even if samples are collected to maximize the geographical coverage, up to 70 individuals are required to sample 95% of intraspecific variation. The results show that the geographical scale of sampling has a critical impact on the global application of DNA barcoding. Scale-effects result from the relative importance of different processes determining the composition of regional species assemblages (dispersal and ecological assembly) and global clades (demography, speciation, and extinction). The incorporation of geographical information, where available, will be required to obtain identification rates at global scales equivalent to those in regional barcoding studies. Our result hence provides an impetus for both smarter barcoding tools and sprouting national barcoding initiatives—smaller geographical scales deliver higher accuracy.

Assemblages of dytiscid predators and culicid prey in relation to environmental factors in natural and clear-cut boreal swamp forest pools

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Culicidae) were studied during 1987–1988 in 40 small, more or less temporary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and clearing pools were warmer than forest pools. Temperature differences between pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pools had 1–13 species. Ten species occurred in both habitats. A few stenotopic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clearing pools. Five of these were found in the forest pools, of which three had no mosquito larvae. Dytiscid assemblages in both habitats and culicid assemblages in clearing pools showed strong nested patterns.Abundance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area >2 m2 after that the effects of pool area had been accounted for (MANCOVA). In both habitats, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drought frequency of pools had a negative, less significant effect on the biota. In the clearing, the abiotic correlations with abundance were somewhat weakened chiefly by the relatively low abundance values from the largest pool.Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscids were trapped in the larger (1.6 m2), but not in the smaller (0.07 m2) artificial pools, and the immigration rate was markedly higher on clearings than in forest. Dug pools were colonized faster on clearings than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.

Bayesian Tests of Topology Hypotheses with an Example from Diving Beetles

We review Bayesian approaches to model testing in general and to the assessment of topological hypotheses in particular. We show that the standard way of setting up Bayes factor tests of the monophyly of a group, or the placement of a sample sequence in a known reference tree, can be misleading. The reason for this is related to the well-known dependency of Bayes factors on model-specific priors. Specifically, when testing tree hypotheses it is important that each hypothesis is associated with an appropriate tree space in the prior. This can be achieved by using appropriately constrained searches or by filtering trees in the posterior sample, but in a more elaborate way than typically implemented. If it is difficult to find the appropriate tree sets to be contrasted, then the posterior model odds may be more informative than the Bayes factor. We illustrate the recommended techniques using an empirical test case addressing the issue of whether two genera of diving beetles (Coleoptera: Dytiscidae), Suphrodytes and Hydroporus, should be synonymized. Our refined Bayes factor tests, in contrast to standard analyses, show that there is strong support for Suphrodytes nesting inside Hydroporus, and the genera are therefore synonymized. [Bayes factor; Coleoptera; Dytiscidae; marginal likelihood; model testing; posterior odds; reversible-jump MCMC; stepping-stone sampling.]

Abundance and species richness patterns of predaceous diving beetles (Coleoptera, Dytiscidae) in Swedish lakes

Abundance and species richness of dytiscid water beetles were estimated with activity traps in ten lakes each in south, central and north Sweden. Partial least square regression models with two significant components explained 76.5% and 55.8% of the total variance in dytiscid abundance and species richness, respectively. For abundance as well as species richness, component 1 had its highest positive loadings for structural complexity of vegetation and abundance of Asellus and Diptera immatures, and high negative loadings for relative shore depth. Component 2 had its highest positive loadings for fish abundance, number of dipterans in emergence traps and relative shore depth, and high negative loadings for lake area. Both the number of dytiscid individuals and species were higher in the northern lakes than in the two other regions. Smaller species were not more abundant in the traps than larger ones. Species mean abundance was positively correlated with number of lakes occupied.

Phylogeny and historical biogeography of Agabinae diving beetles (Coleoptera) inferred from mitochondrial DNA sequences

The Agabinae, with more than 350 species, is one of the most diverse lineages of diving beetles (Dytiscidae). Using the mitochondrial genes 16S rRNA and cytochrome oxidase I we present a phylogenetic analysis based on 107 species drawn mostly from the four main Holarctic genera. Two of these genera (Ilybius and Ilybiosoma) are consistently recovered as monophyletic with strong support, Platambus is never recovered as monophyletic, and Agabus is found paraphyletic with respect to several of the species groups of Platambus. Basal relationships among the main lineages are poorly defined, although within each of them relationships are in general robust and very consistent across the parameter space, and in agreement with previous morphological analyses. In each of the two most diverse lineages (Ilybius and Agabus including part of Platambus) there is a basal split between Palearctic and Nearctic clades, estimated to have occurred in the late Eocene. The Palearctic clade in turn splits into a Western Palearctic clade and a clade containing mostly Eastern Palearctic species, and assumed to be ancestrally Eastern Palearctic but with numerous transitions to a Holarctic or Nearctic distribution. These results suggest an asymmetry in the colonization routes, as there are very few cases of transcontinental range expansions originating from the Nearctic or the Western Palearctic. According to standard clock estimates, we do not find any transcontinental shift during the Pliocene, but numerous speciation events within each of the continental or subcontinental regions.

A revision of the Agabus chalconatus- and erichsoni-groups (Coleoptera: Dytiscidae), with a proposed phylogeny

Fery, H. & Nilsson, A. N.: A revision of the Agabus chalconatus- and erichsoni-groups (Coleoptera: Dytiscidae), with a proposed phylogeny. Ent. scand. 24: 79-108. Copenhagen, Denmark. April 1993. ISSN 0013-8711. The Holarctic chalconatus- and erichsoni-groups, with 19 and three species respectively, are revised. The following seven new species are described: Agabus balkei from Siberia, Agabus jaechi from Turkey, Agabus larsoni from Canada, Agabus lenkoranensis from Azerbaijan, Agabus pederzanii from Italy, Agabus samokovi from Bulgaria, and Agabus wewalkai from Turkey. Lectotypes are designated for the following nominal species: Dytiscus chalconatus Panzer, 1796, Dytiscus nigroaeneus Marsham, 1802, Colymbetes montanus Stephens, 1828, Agabus neglectus Erichson, 1837, Agabus subtilis Erichson, 1837, Agabus gagates Aube, 1838, Agabus altaicus Gebler, 1848, Agabus erichsoni Gemminger & Harold, 1868, Gaurodytes lutosus Crotch, 1873, Agabus fuscoaenescens Regimbart, 1877, Agabus aenescens Poppius, 1905, Agabus satunini Zaitzev, 1913, and Agabus melanocornis Zimmermann, 1915. The following new synonyms are established: Agabus altaicus Gebler, 1848 = Agabus subtilis Erichson, 1837; Agabus melanocornis Zimmermann, 1915 = Colymbetes montanus Stephens, 1828; Gaurodytes bulgaricus Csiki, 1943 = Dytiscus conspersus Marsham, 1802; Agabus skiathos Hinterseher, 1981 = Agabus pseudoneglectus Franciscolo, 1972; and Agabus maestroae Fresneda & Hernando, 1987 = Agabus albarracinensis Fery, 1986. Agabus aenescens Poppius, 1905, and A. satunini Zaitzev, 1913, are recognized as valid species (sp. rev.). The chalconatus-group is divided into four subgroups and the phylogeny of the group is reconstructed. The relationships of the chalconatus- and erichsoni-groups with other Agabus species-groups and with Ilybius Erichson are discussed.

Larval consumption rates, interspecific predation, and local guild composition of egg-overwintering Agabus (Coleoptera, Dytiscidae) species in vernal ponds

SummaryIn vernal ponds in the boreal region, egg-over-wintering Agabus species form a guild that feeds mainly on larvae and pupae of aedine mosquitoes. The regular co-existence of very similar Agabus species indicates local communities not structured by interspecific competition. However, the lower number of species in local guilds than in the regional species pool poses a problem of limited membership. We suggest that the species of this guild display habitat differences mainly with respect to water temperature, pond size and prey density. In this view, habitat selection reflects body size and thermal growth response of the species, mainly in connection with larval development. We present field data from two northern Swedish vernal ponds. Based on these data, feeding experiments were performed to test the hypothesis outlined above. At a high prey density, larvae of all instars of the larger species A. erichsoni Gemm. & Har. had a significantly higher consumption rate than those of the smaller species A. opacus Aubé. At a low prey density the differences were smaller, and only the third instar larvae differed significantly. At 2° C, larvae of A. opacus had a significantly higher consumption rate than those of A. congener (Thunberg). At 15° C, no significant difference was observed. In studies of within-guild interspecific predation, always the larger larvae consumed the smaller ones. Field data show that egg hatching is spread out in time, and show interspecific differences. Consequently, the effects of unexpected droughts differ with species.

Distribution patterns of freshwater Ostracoda (Crustacea) in the Canary Islands with regards to habitat use and biogeography

In this study biogeographic patterns and habitatrelationships of freshwater Ostracoda wereinvestigated in the Canary Island archipelago. Mostdata were collected from published studies, thoughalso new data from Gran Canaria are presented. In all,22 freshwater species are presently known to theCanaries. Six species, viz. Ilyocypris bradyi,Cypris bispinosa, C. pubera, Herpetocypris chevreuxi, Heterocyprisincongruens, and Sarscypridopsis lanzarotensisare new to Gran Canaria, the first two also being newto the Canaries in general. Testing the influence ofa number of variables on faunal richness indicatedonly a weak association with island area. Distancesbetween islands also proved not significant, and sodid other properties of islands, including age,altitude and precipitation. This was in contrast to acomparison set of data comprising aquatic beetles.Like beetles, however, ostracods did not show a nestedpattern, i.e. faunas of species-poor islands were notsubsets of species-rich island faunas. By having lowendemicity (endemic species lacking in the Canaries),the ostracod fauna resembled island fern floras. Bothgroups of organisms have tiny diaspores (diameter<0.1 mm) and are extensively parthenogeneticsuggesting similar dispersal and founder mechanisms.We identified a pattern (with one exception), wherethose species with distributions extending acrossseveral islands also had wider within-islanddistributions. Many species showed affinities todifferent habitats depending on conductivity of water,altitude and habitat types: whether they werepermanent or temporary, hypogean or epigean, orcharacterized by running or stagnant waters.

A reciassification of the Deronectes-group of genera (Coleoptera: Dytiscidae) based on a phylogenetic study

Within the Hydroporini, the Deronectes-group of genera are characterised by having the mesosternal fork and metasternal keel separated (or secondarily fused), the ventral elytral ridge posteriorly elevated but without ligula, and the male protarsus ventrally without adhesive discs. The genera of the group, viz. Deronectes Sharp, 1882, Stictotarsus Zimmermann, 1919, Scarodytes Gozis, 1914, and Nebrioporus Regimbart, 1906, are reclassified and a hypothesis of their phylogenetic relationships is presented. Karyotypes of 14 European species of Hydroporinae are discussed. Nebrioporus is extended to include most species with parameres with apex hook-like and sclerotised, with Potamonectes Zimmermann, 1921, as a junior synonym, syn. n. Nebrioporus s. str. and Zimmermannius Guignot, 1941 are recognized as subgenera of Nebrioporus. Scarodytes is kept as a separate genus because of its characteristic ventral sculpture and seemingly higher number of autosomes than in Nebrioporus. The species with simple parameres previously placed in Potamonectes are transferred to Stictotarsus together with S. bertrandi (Legros, 1956), previously in Deronectes. Consequently, Trichonectes Guignot, 1941, is a junior subjective synonym of Stictotarsus, syn.n. In an appendix, a check-list is provided for the species of the Deronectes-group. The subgenus Nebrioporus s. str. is divided into three species-groups: the kilimandjarensis-, the abyssinicus-, and the depressus-groups.

An FTIR study of the hydration and molecular ordering at phase transitions in the monooleoylglycerol/water system

Abstract The liquid-crystalline phases of monooleoylglycerol and water have been investigated by FTIR spectroscopy. The use of polarized IR radiation made it possible to obtain the order parameters of transition moments in the lipid molecule. The order parameters as a function of the temperature and water content have been studied for the lamellar liquid-crystalline phase (Lα). The decrease in the ordering of the CO and COCO stretching vibrations in the polar headgroup started earlier than for the CHCH and CH2, stretching vibrations in the acyl chain region at the phase transition between lamellar and non-lamellar structures. The hydration of the ester carbonyl group increased with the water content. The ordering of the acyl chain decreases drastically in the two-phase regions, while it is nearly constant in the Lα phase.