African dung beetle Onthophagus gazella Fabricius (Coleoptera: Scarabaeidae) esterase isozymes

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Abstract

African beetles Onthophagus gazella from both sexes were analyzed by electrophoresis for an investigation of esterase isozymes using alpha-naphthyl propionate and methylumbelliferyl propionate as substrates. Only one of the esterases (Est. 6) reacted with one of the substrates (alpha-naphthyl propionate). Six areas of activity were found, two of them being polymorphic (Est. 3 and Est. 4). For presence of Est. 3, 337 individuals were analyzed, including descendants of 32 controlled crossings: two alleles were identified, whose frequencies are Est. 3A = 0.447 and Est. 3B = 0.553. The population is in equilibrium for this locus (qui-square = 4.18; 0.2 > P > 0.1). For Est. 4, 338 individuals, descendants of 32 controlled crossings, were analysed. In this case, three alleles were identified whose frequencies are: Est. 4A = 0.277; Est. 4B = 0.661; and Est. 4C = 0.062. The population is not in equilibrium for this locus (qui-square = 40.259; p < 0.001). Two esterases were detected only in the pupal stage and another one in larvae. Of the 23 loci analyzed in these insects up to now, 3 are polymorphic (13%), which indicates very low variability in the population here studied.

Translated abstract

Foram analisados adultos de ambos os sexos do besouro africano Onthophagus gazella por eletroforese, para investigação de isozimas de esterases, utilizando como substratos alfa-naftil propionato e metil umbeliferil propionato. Somente uma das esterases (Est. 6) reagiu apenas com um dos substratos (alfa-naftil propionato). Foram encontradas seis regiões de atividades diferentes, sendo duas polimórficas (Est. 3 e Est. 4). Na região de Est. 3, foram analisados 337 indivíduos, incluindo descendentes de 32 cruzamentos controlados, e identificados 2 alelos, cujas freqüências são: Est. 3A = 0,447 e Est. 3B = 0,553. A população está em equilíbrio para esse loco (qui-quadrado = 4,18; 0,2 > p > 0,1). Na região de Est. 4, foram analisados 338 indivíduos, incluindo descendentes de 32 cruzamentos controlados, e identificados 3 alelos, cujas freqüências são: Est. 4A = 0,277; Est. 4B = 0,661; e Est. 4C = 0,062. A população não está em equilíbrio para esse loco (qui-quadrado = 40, 259; p < 0,001). Foram detectadas duas regiões de esterases características da fase de pupa e uma região que aparece somente na larva. Do total de 23 locos amostrados até o momento nesses insetos, 3 são polimórficos (13%), o que indica variabilidade genética muito baixa na população estudada.

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Most cited references 23

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Evolutionary genetics of Drosophila esterases.

J Oakeshott, E. van Papenrecht, T M Boyce … (1993)

Over 30 carboxylester hydrolases have been identified in D. melanogaster. Most are classified as acetyl, carboxyl or cholinesterases. Sequence similarities among most of the carboxyl and all the cholinesterases so far characterised from D. melanogaster and other eukaryotes justify recognition of a carboxyl/cholinesterase multigene family. This family shows minimal sequence similarities with other esterases but crystallographic data for a few non-drosophilid enzymes show that the family shares a distinctive overall structure with some other carboxyl and aryl esterases, so they are all put in one superfamily of/beta hydrolases. Fifteen esterase genes have been mapped in D. melanogaster and twelve are clustered at two chromosomal sites. The constitution of each cluster varies across Drosophila species but two carboxyl esterases in one cluster are sufficiently conserved that their homologues can be identified among enzymes conferring insecticide resistance in other Diptera. Sequence differences between two other esterases, the EST6 carboxyl esterase and acetylcholinesterase, have been interpreted against the consensus super-secondary structure for the carboxyl/cholinesterase multigene family; their sequence differences are widely dispersed across the structure and include substantial divergence in substrate binding sites and the active site gorge. This also applies when EST6 is compared across species where differences in its expression indicate a difference in function. However, comparisons within and among species where EST6 expression is conserved show that many aspects of the predicted super-secondary structure are tightly conserved. Two notable exceptions are a pair of polymorphisms in the substrate binding site of the enzyme in D. melanogaster. These polymorphisms are associated with differences in substrate interactions in vitro and demographic data indicate that the alternative forms are not selectively equivalent in vivo.