Growth pattern of Carex arenaria (Cyperaceae)

The origin of the orthotropic aerial shoot from the plagiotropic, horizontal rhizome of Carex arenaria L. (Cyperaceae) was studied. A previously proposed adnation or fusion of the first internode of the orthotropic shoot and the fourth internode of the plagiotropic shoot could not be anatomically confirmed. The rhizome branches sympodially and the point of branching results from intercalary meristematic activity in the plagiotropic shoot.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 145–151.     

Phylogeographical patterns and genetic diversity in three species of Eurasian boreal forest beetles

Many species that occur in formerly glaciated areas of Fennoscandia have reached their current ranges from glacial refugial areas in Eurasia. Little is known of the refugia and postglacial colonization routes of insect species that are confined to boreal forests. Here, we investigate the phylogeography of three species of saproxylic beetles distributed across Eurasia: two rare boreal forest specialists, Pytho kolwensis and Pytho abieticola , and a common, less specialized species, Pytho depressus . In all species, there were two well-defined haplotype clades based on 645 bp of cytochrome oxidase subunit I gene sequence. In each species one clade was found only in China. The other clade occurred from China to north-western Europe in both P. kolwensis and P. depressus , but was apparently absent from China in P. abieticola. In spite of common phylogeographical patterns, the distribution of genetic variation differed markedly between the three species. In P. kolwensis , a highly-threatened species in old-growth forests in Fennoscandia, there was an extremely low level of genetic variation throughout Eurasia. One common haplotype, represented by 86% of the samples, dominated in all sampling localities. Levels of genetic variation were higher in both P. abieticola and P. depressus , with 31% and 58%, respectively, of the samples representing a unique haplotype. In each species, relationships between haplotypes were not well resolved, and haplotypes from one sampling locality were generally not clustered in either Neighbour-joining trees or statistical parsimony networks. These patterns in the distribution of genetic variation can be attributed to differences in the species' population sizes, ecologies, glacial refugial areas, and postglacial colonization dynamics.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 267–279.     

Carrion fly community dynamics: patchiness, seasonality and coexistence

ABSTRACT. 1. An outdoor cage experiment was conducted to test the theory that localized interactions facilitate coexistence of species breeding in ephemeral habitats. The same amount of larval resource (50 g of liver) but divided into one, two, four, eight or sixteen pieces was placed into each of fifteen cages once a week from June to September for 4 years.
2. The cage populations were initially mixtures of thirteen species but after 4 years only Lucilia illustris (Meig.), Sarcophaga scoparia Pand. and S.aratrix Pand. remained. Lucilia illustris , by far the most abundant species in the field, predominated in every cage.
3. Sarcophaga went extinct in most cages, but they survived in five cages in which the larval resource was much divided, in agreement with the theoretical prediction.
4. Lucilia silvarum (Meig.) emerged about a week later than L.illustris in early summer; this phenological difference gave rise to a competitive asymmetry between the two species. This difference appears to explain why L.silvarum went extinct in the cages in 3 years, and it may explain why L.silvarum has consistently been less abundant than L.illustris in the natural community.
5. Other differences in phenology, voltinism and rate of development in the flies are described, and such differences are suggested to facilitate regional coexistence of many species in seasonal environments.     

Spatial dynamics of two competing specialist parasitoids in a host metapopulation

1. We investigated spatial dynamics in two specialist larval parasitoids, Cotesia melitaearum and Hyposoter horticola , attacking the Glanville fritillary butterfly, Melitaea cinxia , in Finland.
2. Presence of C. melitaearum in a host larval group significantly reduced the rate of parasitism by H. horticola (18 vs. 33% in groups with and without C. melitaearum ), but there was no significant reverse effect. The parasitism rates at the level of local populations showed a similar trend.
3 Hyposoter horticola females moved frequently among larval groups, whereas C. melitaearum females often spent several days at a single larval group. In agreement with these behavioural observations about movements within populations, H. horticola was found to have a higher colonization rate of host populations than C. melitaearum .
4. At the within-population level, C. melitaearum tended to occupy large larval groups in the centre of the host population, whereas H. horticola parasitized also small and more isolated (peripheral) larval groups, especially in the presence of C. melitaearum . At the metapopulation level, host population size had a significant positive effect on the presence of local populations of both parasitoid species, but isolation had a significant negative effect on the presence of C. melitaearum only.
5. These results suggest that C. melitaearum is a superior competitor, but an inferior disperser to H. horticola , which facilitates the co-existence of the two species both at the level of local populations and at the level of a metapopulation.
6. Data from a 50-patch network showed a decline in the number of host populations from 34 to 13 in 4 years. This decline caused a near-extinction of the superior competitor, but inferior disperser, C. melitaearum , whereas the abundance of the inferior competitor, but superior disperser, H. horticola , remained relatively constant, in agreement with the prediction of a theoretical model.     

Klinokinetic and klinotactic humidity reactions of the beetles Hylobius abietis and Tenebrio molitor

ABSTRACT. The effects of spatially uniform but temporally changing air humidity stimuli on the orientation behaviour of the large pine weevil ( Hylobius abietis L.) and the flour beetle ( Tenebrio molitor L.) were studied in a specially constructed vertical air flow chamber. Moist-acclimatized but hygronegative pine weevils were exposed for 10 s to a moist air stream ( c. 85% R.H.) and then for 10 s to a dry air stream ( c. 50% R.H.). The Tenebrio were divided into two groups acclimatized to moist and dry air respectively. For each group the humidity during the initial 5 s in the air stream was the same as during acclimatization, and then changed to the alternative level. In Hylobius the change from moist to dry air caused a decrease in spatial displacement brought about by a decrease in walking speed and an increase in the amount of turning per unit time. In Tenebrio the change from dry to moist air caused a decrease of walking speed and a turning-back reaction based, presumptively, on idiothetic information about the insect's previous walking direction. The average angle turned during 2 s after the humidity change was 165°. In moist-adapted beetles the dry air stream caused an identical orthokinetic arrestment, but no klinokinetic or klinotactic reaction. Klinokinesis is redefined as a change in the circular variance of turning angles per unit time, which does not change the mean direction (or directions in cases of multimodal distributions) of the circular distribution. Accordingly, klinotaxis consists of a change in the mean directions) of the circular distribution of angular velocities. In both species the turning frequency was more constant than turning per unit distance, suggesting a temporal control in the nervous system of klinokinetic and klinotactic behaviour.     

Arthropod orientation in choice chambers as a Markov chain

ABSTRACT. A Markov model of arthropod locomotor behaviour in choice chambers is presented. In the model, the compartments of the choice chamber and the movements of the animals from one compartment to another are treated as the states and the state transitions of a Markov chain, respectively. The model allows one to calculate the transition probabilities and the equilibrium distribution of animals in a choice chamber from direct measurements of displacement speeds and boundary turning reactions in each compartment. The compartment preferences (i.e. the proportion of time spent in each compartment) in two-compartment choice chambers were found to be strongly correlated with the predictions of the model. Klinokinesis is suggested to have negligible significance in some of the experiments reviewed. An equation is given to evaluate quantitatively the relative strength of kinetic and tactic components in the overall preference in the choice chamber; this assessment has not previously been possible.