versión impresa ISSN 0101-8175
Rev. Bras. Zool. v.23 n.4 Curitiba dic. 2006
Analysis of the geographical variation of elytral color polymorphisms in three species of soldier beetles, Chauliognathus Hentz (Cantharidae) in southern Brazil
Análise da variação geográfica no polimorfismo de coloração dos élitros em três espécies de Chauliognathus, Hentz (Cantharidae) no Sul do Brasil
Vilmar Machado; Victor H. Valiati
Laboratório de Biologia Molecular, Universidade do Vale do Rio dos Sinos. Caixa Postal 275, 93022-000 São Leopoldo, Rio Grande do Sul, Brasil
In the present report, we investigate polymorphism in three of the Brazilian species of Chauliognathus Hentz, 1930 (Coleoptera, Cantharidae), by analyzing the geographical color pattern variation of the elytra in C. flavipes, C. fallax and C. octomaculatus. These species belong to the mullerian complex called the "yellow-black". They are usually found in clusters on their host plants at various locations and present similarities in the external body morphology and in the color pattern of the elytra and the pronotum. Chauliognathus flavipes is the most common species with eight phenotypic classes followed by of C. fallax and C. octomaculatus with six and two phenotypic classes respectively. The analyses indicate a statistically significant difference in the frequencies of colour patterns of the three species over the entire area sampled. In general, the significant differences were observed between the regions of the State of Rio Grande do Sul (p < 0.05) but were not found within the individual regions except in the case of the Metropolitan region. That region and its three microregions demonstrated a positive co-relationship between an increase in altitude and the occurrence of diversity in C. flavipes and C. fallax (r = 0.860, p < 0.01; r = 0.974, p < 0.01, respectively).
Key words: Coleoptera; mullerian mimicry; aposematism.
No presente estudo investigamos o polimorfismo em três espécies de Chauliognathus Hentz, 1930 (Coleoptera, Cantharidae), analisando a variação geográfica no padrão de coloração dos élitros em C. flavipes, C. fallax e C. octomaculatus. Estas espécies pertencem ao complexo mülleriano chamado "amarelo-preto". São encontradas formando grandes agregados sobre as plantas que utilizam como substratos de alimentação e apresentam semelhança morfológica e para a coloração dos élitros e pronoto. Chauliognathus flavipes é a espécie mais freqüente e apresenta o maior número de padrões fenotípicos (8) seguidos de C. fallax e C. octomaculatus com seis e dois padrões respectivamente. Diferenças significativas nas freqüências dos padrões de coloração nas três espécies foram detectadas ao longo da área analisada. Em geral, as diferenças foram observadas entre as regiões do Estado do Rio Grande do Sul (p < 0,05), mas não dentro das regiões, exceto para a região Metropolitana. Nas três microregiões que formam a região Metropolitana encontrou-se uma correlação positiva entre o aumento da altitude e a diversidade em C. flavipes e C. fallax (r = 0,860, p < 0,01; r = 0,974, p < 0,01, respectivamente).
Palavras-chave: Coleoptera; mimetismo mülleriano; aposematismo.
Species that exhibit visible polymorphisms are ideal for studying the micro-evolutionary forces that maintain genetic variation in nature. The colour is one of the few phenotypic characters that vary in discrete classes, and this suggests a character with a simple genetic base that is thus easily applied in classical genetic work (see for example, EKENDALL & JOHANNESSON 1997, HOFFMAN & BLOUIN 2000), and classical studies with Biston betularia Linnaeus, 1758 (KETTLWELL 1961) and Cepaea sp. (JONES et al. 1977).
A fuller understanding of how colour polymorphisms in natural populations are maintained is fundamental in evolutionary biology. Considerable indirect evidence and some concrete proof indicates that the variation may be sustained through selective predation by hunting predators who use colour vision to locate their prey (SILLÉN -TULBERG & BRYANT 1983, ENDLER 1988, WHITELEY & OWEN 1997, MALLET & JORON 1999).
The existence of color polymorphisms and the factors that maintain this polymorphism in Müllerian mimetic organisms have generated much debate and renewed the interest in mimicry (MACDOUGALL & DAWKINS 1998, JORON & MALLET 1998, MALLET & JORON 1999, JORON 2005). In this kind of mimetism, the monomorphism is thought to evolve due to stabilization selection on the color pattern on aposematic species.
Many coleopteran species exhibit striking elytra colour polymorphisms and so provide an excellent system to study questions about the evolution and maintenance of polymorphisms (KEARNS et al. 1990, BERNSTEIN & BERNSTEIN 1998, MACHADO & ARAÚJO 1999, MACHADO et al. 2004).
The genus Chauliognathus Hentz, 1930 occurs in Australia, South and North America and runs to more than 250 species, most of them occurring in Neotropical regions. Despite its diversity and ready availability for sampling, there are few studies about the biology of these species. In Brazil, DELKESKAMP (1939) described nearly 100 species that can be collected between october and march (Spring and Autumn in the Southern Hemisphere).
In the present report, we investigate the geographical variation in the frequencies of the coloration patterns by analysing the colour pattern variation of the elytra in three Brazilian species to improve our understanding of the evolutionary dynamics of colour polymorphisms in the Chauliognathus beetle. The species analysed are part of the "yellow-black" complex described by MACHADO et al. (2001). They present similarities in the external body morphology and in the colour pattern of the elytra and the pronotum. They are usually found in clusters on their host plants at various locations in the southern regions of Brazil. The study of the occurrence and maintenance of the variations of colour patterns in Chauliognathus is an alternative approach to the models used in similar investigations of butterfly species (MACH