Paul Van Daele

Identification of sucrose synthase in nonphotosynthetic bacteria and characterization of the recombinant enzymes

Sucrose synthase (SuSy) catalyzes the reversible conversion of sucrose and a nucleoside diphosphate into fructose and nucleotide (NDP)-glucose. To date, only SuSy’s from plants and cyanobacteria, both photosynthetic organisms, have been characterized. Here, four prokaryotic SuSy enzymes from the nonphotosynthetic organisms Nitrosomonas Europaea (SuSyNe), Acidithiobacillus caldus (SuSyAc), Denitrovibrio acetiphilus (SusyDa), and Melioribacter roseus (SuSyMr) were recombinantly expressed in Escherichia coli and thoroughly characterized. The purified enzymes were found to display high-temperature optima (up to 80 °C), high activities (up to 125 U/mg), and high thermostability (up to 15 min at 60 °C). Furthermore, SuSyAc, SuSyNe, and SuSyDa showed a clear preference for ADP as nucleotide, as opposed to plant SuSy’s which prefer UDP. A structural and mutational analysis was performed to elucidate the difference in NDP preference between eukaryotic and prokaryotic SuSy’s. Finally, the physiological relevance of this enzyme specificity is discussed in the context of metabolic pathways and genomic organization.

Does sociality imply a complex vocal communication system? A case study for Fukomys micklemi (Bathyergidae, Rodentia)

African mole-rats (Bathyergidae) display different levels of sociality, ranging from solitary to eusocial. To integrate individuals into a social group, communication is necessary. In this study, we examined vocalizations of a social bathyergid, Fukomys micklemi, in order to investigate the relationship between sociality and communication. Because of its social organization and subterranean lifestyle, we expected this species to have an extensive vocal repertoire. Fifteen different adult specific call-types and four juvenile specific call-types could be recognized, similar to those in other social species. A new call-category, linked to submissive behaviour, is described. These submissive calls were exclusively observed in males, indicating their subordinance. The vocal repertoire of F. micklemi was compared with published results on vocalizations in other subterranean rodents, both in social and solitary species. This comparison confirmed the observation that the vocal repertoire of social species is not only more extensive, but also more diverse than that of solitary species.

A methodological analysis of behavioural observation in social African mole rats (Bathyergidae, Rodentia)

Abstract This study evaluates a number of methodological aspects regarding the recording and analysis of social behaviour in mole rat colonies (Bathyergidae, Rodentia). Behavioural observations were carried out on a colony of wild-caught Fukomys micklemi, in order to define an efficient, standardised method for future research. First, durations of work behaviour were scored and compared with data expressed as frequencies (recording method used in previous research). Second, a comparison was made between a terrarium set-up and a set-up with a perspex tunnel system, including a digging unit. Third, observations were carried out at different times of the day in order to map daily activity patterns. Our results show that the set-up with the tunnel system evokes more work activity and increases behavioural resolution. Using frequencies showed to be a better proxy for activity than the labour-intensive scoring of durations. Interindividual variation in activity patterns over a 24-h period were shown to be highly variable, and the moment of peak activity was not consistent. Observations should thus be carried out randomly during the day to avoid any temporal bias.

Social organization and biting performance in Fukomys mole-rats (Bathyergidae, Rodentia)

A caste system, based on work activity and reproduction, has been proposed in the two African mole-rat species which are generally considered eusocial, Heterocephalus glaber and Fukomys damarensis. Social behaviour in other Fukomys species is key to understanding evolution of sociality within bathyergids, which display a social continuum among species from solitary to eusocial. Furthermore, insight in the social structure of colonies may be instrumental in understanding the observed, extensive intraspecific morphological variation and ultimately help species delimitation. For the first, time social organisation was studied in a colony of wild-caught Fukomys micklemi (Sekute cytotype) from Zambia. Data were collected on work behaviour and analysed against morphological variables and biting performance. Although there was considerable variation in the amount of work performed by each individual, clearly distinguishable castes were not found. Castes might represent an artificial subdivision, which does not necessarily reflect the dynamic changes within a colony. Variation in work may be the result of an ongoing process of continuous change, whereby a colony undergoes a certain evolution that is reflected in developmental patterns of individuals. Ecological factors will undoubtedly play an important role in colony evolution. Consequently, predictions made according to the Aridity Food Distribution Hypothesis should be tested, taking into account the possibility of a dynamic model as described here. The relation between biting performance and behavioural traits was investigated for the first time. Whereas differences in biting performance were strongly correlated with morphological parameters, relation between work and biting performance remains unclear.