No abstract

RNA molecules and in particular the nuclear SSU RNA play an important role in molecular systematics. With the advent of increasingly parameterized substitution models in systematic research, the incorporation of secondary-structure information became a realistic option compensating interdependence of character variation. As a prerequisite, consensus structures of eukaryotic SSU RNA molecules have become available through extensive comparative analyses and crystallographic studies. Despite extensive research in hexapod phylogenetics, consensus SSU RNA secondary structures focusing on hexapods have not yet been explored. In this study, we compiled a representative hexapod SSU data set of 261 sequences and inferred a specific consensus SSU secondary-structure model. Our search for conserved structural motives relied on a combined approach of thermodynamic and covariation analyses. The hexapod consensus-structure model deviates from the canonical eukaryotic model in a number of helices. Additionally, in several helices the hexapod sequences did not support a single consensus structure. We provide consensus structures of these sections of single less-inclusive taxa, thus facilitating the adaptation of the consensus hexapod model to less-inclusive phylogenetic questions. The secondary-structure catalog will foster the application of RNA structure models in phylogenetic analyses using the SSU rRNA molecule, and it will improve the realism of substitution models and the reliability of reconstructions based on rRNA sequences.

The population size of the solitary digger bee Andrena vaga was documented using mark‐recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly‐Seber model for open populations with time‐dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark‐recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark‐recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.

We studied the differentiation of North American squash bee (Apidae: Apiformes) populations by using geometric wing morphometry to evaluate hypotheses for the origin and possible expansion route of bees after the dispersal of their Cucurbita floral hosts. Two hypotheses consider the possible impact of early human cultures on the distribution of this mutualistic species complex: 1) the geographic range of the bees naturally expanded after the hypsithermal range expansion of the wild buffalo gourd, Cucurbita foetidissima Kunth; or 2) the bees shifted to mesophytic gourds of the C. pepo group at the Mexican Gulf coast and tracked the cultivation and/or trade by early human hunter-gatherer societies in the context of fishing technology along stream valleys to northeastern America. We morphometrically measured 228 specimens of Peponapis pruinosa (Say) collected at 15 sites between Mississippi and Ontario, Canada. Twenty-three landmarks were taken from the right forewings. The resulting measurements were analyzed by multivariate statistics. Our results support the first hypothesis of a western origin of North American squash bee populations and a mainly natural range expansion during the hypsithermal range expansion of the buffalo gourd.

Die Sammelstrategie der beiden endogäischen, oligolektischen syntop und synchron auftretenden Wildbienenarten Panurgus calcaratus (Scopoli, 1763) und Dasypoda hirtipes (Fabricius, 1793) wurden im Naturschutzgebiet Wahner Heide (Rheinland, BRD) untersucht. Saisonale und diurnale Rhythmik sowie die Sammelstrategien beider Arten wurden erfaßt, um eventuell bestehende Trennungsmechanismen oder Nischendiffenzierung aufzudecken. Neben dem Verproviantierungsverhalten der Bienen wurde die Oligolektie durch Pollenentnahme von Weibchen und durch Beobachtung an den Pollenquellen überprüft. Beide Arten nutzen ausschließlich gelbe, photonastische, zungenblütige Asteraceae als Pollenquellen, präferieren sandige Flächen mit geringer Vegetation als Nistplatz und sind von Anfang Juli bis Ende August aktiv. Eine Spezialisierung innerhalb der Oligolektie auf einzelne Arten zungenblütiger Asteraceae konnte nicht erkannt werden. Dasypoda hirtipes wies eine allgemein längere diurnale Aktivität auf und war zudem auch bei geringeren Temperaturen noch aktiv. Die Pollensammelaktivitäten werden bei beiden Arten maßgeblich von den photonastischen Pollenquellen limitiert. Desweiteren ist die Bienenaktivität von klimatischen Faktoren wie Lichtintensität, Bewölkung und Lufttemperatur abhängig. Artspezifische diurnale und saisonale Verhaltensweisen und Aktivitätsrhythmen werden im Hinblick auf Körpergröße und -farbe, Hitzeabsorptions- und Reflektions-Fähigkeit, Überhitzungsgefahr sowie Effekte der Ekto- und Heterothermie auf den Wärmehaushalt diskutiert. Jede Art verfolgt eine eigene Sammelstrategie, welche hauptsächlich durch ultimative Faktoren wie die Physiologie der jeweiligen Bienenart beeinflußt und zugleich limitiert wird. Weder Nistplatzangebot noch die Ressourcen Pollen oder Nektar sind im Untersuchungsgebiet begrenzt, so daß keine Evidenz für Konkurrenz zwischen den beiden Arten besteht.StichwörterInterspecific competition, oligolecty, optimal foraging strategies, photonasty, resource partitioning, separation mechanisms.