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Seasonal abundance and sexual variation in morphometric traits of Oxelytrum discicolle (Brulle, 1840) (Coleoptera: Silphidae) in a Brazilian Atlantic Forest

Abundância sazonal e variação morfométrica nos caracteres sexuais de Oxelytrum discicolle (Brulle, 1840) (Coleoptera: Silphidae) em uma floresta Atlântica brasileira

Abstracts

A total of 293 specimens of Oxelytrum discicolle were sampled weekly over a period of two years using a black light trap. The study took place in an Atlantic Forest reserve located near Viçosa city, Minas Gerais State, Brazil. The period of peak abundance of O. discicolle occurred during the wet season between the months of October and March. Statistical analysis showed that the abundance of individuals was significantly and positively correlated with temperature, but not with rainfall or relative humidity. Of 28 morphological measurements taken on each collected specimen, seven were found to be sexually dimorphic; however, neither morphology nor the degree of sexual dimorphism varied significantly among seasons.

Oxelytrum discicolle; population dynamic; sexual dimorphism; Minas Gerais


Um total de 293 espécimes de Oxelytrum discicolle foram amostrados semanalmente num período de dois anos usando uma armadilha tipo "black light". O estudo foi feito em uma reserva de Mata Atlântica localizada próximo à cidade de Viçosa, Minas Gerais, Brasil. O período de pico de abundância de O. discicolle ocorreu durante a estação úmida, entre os meses de outubro e março. A análise estatística mostrou que a abundância dos indivíduos foi significantemente e positivamente correlacionada com a temperatura, mas não com a precipitação e umidade relativa. De 28 características morfológicas tomadas em cada espécime coletado, sete foram encontradas sexualmente dimórficas, entretanto, nem morfologia nem o grau de dimorfismo sexual variaram significantemente entre as estações.

Oxelytrum discicolle; dinâmica populacional; dimorfismo sexual; Minas Gerais


ARTICLES

Seasonal abundance and sexual variation in morphometric traits of Oxelytrum discicolle (Brulle, 1840) (Coleoptera: Silphidae) in a Brazilian Atlantic Forest

Abundância sazonal e variação morfométrica nos caracteres sexuais de Oxelytrum discicolle (Brulle, 1840) (Coleoptera: Silphidae) em uma floresta Atlântica brasileira

Paulo Sérgio Fiuza FerreiraI,II; Evaldo Martins PiresI, Raul Narciso Carvalho GuedesI, Márcio MendesIII; Lívia Aguiar CoelhoIII

IMuseu de Entomologia, Departamento de Biologia Animal, Universidade Federal de Viçosa, 36571-000 Viçosa, Minas Gerais, Brazil

IIAuthor Correspondent: (pfiuza@ufv.br)

IIIMuseu de História Natural, Universidade do Vale do Rio Doce (UNIVALE), 35030-390 Governador Valadares, Minas Gerais, Brasil

ABSTRACT

A total of 293 specimens of Oxelytrum discicolle were sampled weekly over a period of two years using a black light trap. The study took place in an Atlantic Forest reserve located near Viçosa city, Minas Gerais State, Brazil. The period of peak abundance of O. discicolle occurred during the wet season between the months of October and March. Statistical analysis showed that the abundance of individuals was significantly and positively correlated with temperature, but not with rainfall or relative humidity. Of 28 morphological measurements taken on each collected specimen, seven were found to be sexually dimorphic; however, neither morphology nor the degree of sexual dimorphism varied significantly among seasons.

Key words: Oxelytrum discicolle, population dynamic, sexual dimorphism, Minas Gerais

RESUMO

Um total de 293 espécimes de Oxelytrum discicolle foram amostrados semanalmente num período de dois anos usando uma armadilha tipo "black light". O estudo foi feito em uma reserva de Mata Atlântica localizada próximo à cidade de Viçosa, Minas Gerais, Brasil. O período de pico de abundância de O. discicolle ocorreu durante a estação úmida, entre os meses de outubro e março. A análise estatística mostrou que a abundância dos indivíduos foi significantemente e positivamente correlacionada com a temperatura, mas não com a precipitação e umidade relativa. De 28 características morfológicas tomadas em cada espécime coletado, sete foram encontradas sexualmente dimórficas, entretanto, nem morfologia nem o grau de dimorfismo sexual variaram significantemente entre as estações.

Palavras-chave:Oxelytrum discicolle, dinâmica populacional, dimorfismo sexual, Minas Gerais

Introduction

The Silphidae (carrion beetles or burying beetles) are a distinct group living on dead vertebrate remains from the early decay to the late dry stage. There are conflicting descriptions of the food habits of silphids. Reed (1958) states that the immatures feed on the carrion and infrequently on maggots, while adults fed almost always on maggots. Payne and Crossley (1966) found adult silphids feeding only on maggots and did not mention immature food habits. Oliveira-Costa (2003) states silphids predators and Carvalho & Linhares (2001) assert the carrion beetles are both predators and saprophagous.

The biological, systematic and ecological studies of carrion beetles of Brazil are very few. In a majority of papers the species of burying beetles are cited in inventories of collected insects. Outside Brazil, there is more information about silphid ecology (Anderson 1982, Wilson et al. 1984), physiology (Ements & Zhulidov 1982, Wilson & Knollenberg 1984), biology (Ements & Zhulidov 1982, Peck & Anderson 1982, Prins 1984) and systematic (Kryzhanouskii & Sabiroba 1981, Schawaller 1977). According Costa (2000) the world fauna of carrion beetles is represented by 14 genera and 175 species. Neotropical Region has nine genera and 82 species. South America has six genera and 24 species, and one genus and three species in Brazil according Peck & Anderson, (1982), and two genera and five species according Costa (2000). The major ecological role of the silphids is their living intimately with the decomposition process of vertebrate carcasses. Jointly with the flies and other beetles they are of major importance in studies of Forensic entomology (Catt & Haskell 1990).

The objectives of this manuscript are to contribute to knowledge of Neotropical Silphidae in regard to the abundance of adults of Oxyelytrum discicolle under the influence of climate in dry and wet seasons; to evaluate if there are any morphological traits in different dry and wet seasons and between sex. Furthermore, the results will yield information for to researchers in Forensic entomology in Brazilian Atlantic Forest.

Material and Methods

The research took place on the natural reserve of Atlantic Forest set at municipality of Viçosa, State of Minas Gerais, Brazil, called Bacia do Córrego do Paraíso (coordinates: 20º45'16,5" S and 42º51'53,2" W). The sample method employed a black light trap (Ferreira & Martins 1982). The light trap was operated once a week during the period of 6:00 PM to 6:00 AM. The weather data were taken from Meteorological Station of Universidade Federal de Viçosa.

The sampling period was between August 1981 to July 1983. Specimens were identified at Identification Center for Fitophagous Insects (CIIF), Universidade Federal do Paraná (UFPR).

A total of 293 individuals of Oxelytrum discicolle was used in this study (170 female and 123 males).

The quantitative characters are based on measurements of 28 morphological features. They were made using an ocular micrometer Wild (10X) in a Wild M 5 microscope at various objective magnifications. The measurements of morphological structures were taken in millimeters and the values were computed for use in the general analysis. Figure 2 show exactly how the quantitative measurements were made: body length (Figure 2-1) = Ó head length, with length of the pronotum and elytron length, maximum body width (Figure 2-2), head length (Figure 2-3), head width (Figure 2-4 frons width (Figure 2-5), distance between antennal insection (Figure 2-6), length of the antennae (Figure 2-7), length of the antennal club (Figure 2-8), length of scape (Figure 2-9), length of 2nd and 3rd antennal segments (Figure 2-10), length of compound eye (Figure 2-11), width of compound eye (Figure 2-12), width of the pronotum base (Figure 2-13), median pronotum length (Figure 2-14), maximum pronotum width (Figure 2-15), scutellum length (Figure 2-16), width of the scutellum base (Figure 2-17), elytron length (Figure 2-18), maximum elytron width (Figure 2-19), length of the anterior femur (Figure 2-20), length of the anterior tibia (Figure 2-21), length of the anterior tarsi (Figure 2-22), length of the median femur (Figure 2-23), length of the median tibia (Figure 2-24), length of the median tarsi (Figure 2-25), length of the posterior femur (Figure 2-26), length of the posterior tibia (Figure 2-27), and length of the posterior tarsi (Figure 2-28).


Two statistical analyses were employed: correlation analysis (PROC CORRE: SAS Institute, 2001) and two-way multivariate analysis of variance using the procedure PROC GLM with the MANOVA statement from SAS (SAS Institute 2001).

The influence of the weather parameters of rainfall, temperature and relative humidity on the abundance of O. discicolle was tested using correlation analysis (PROC CORR; SAS Institute 2001). The full set of morphometric data was subjected to a two-way multivariate analysis of variance with season and sex as independent variables using the procedure PROC GLM with the MANOVA statement from SAS (SAS Institute 2001). Subsequent two-way univariate analyses of variance (PROC GLM; SAS Institute 2001) were carried out for each individual morphological trait complementing the multivariate analysis to recognize the traits that were indeed different between sex and/or season.

Results

A total of 293 specimens (170 females and 123 males) of Oxelytrum discicolle were collected throughout the sampling period (August 1981 to July 1983) and this species showed seasonal peaks of abundance during the wet season, between the months of October to March (Figure 1). However, there was no difference between the female/male rates (± 1.4:1.0, respectively). The abundance of this species was only significantly and positively correlated with temperature (p < 0.05).This fact suggests the temperature as the main factor to the fly activities of O. discicolle (Table 1).


The two-way multivariate analysis of variance for the 28 morphometric traits assessed (Figure 2) indicated significant effect of sex (p < 0.05), while season showed only marginally significant effect (p = 0.05) (Table 2). The interaction between sex and season was not significant (Table 2) and therefore was not further considered. The two-way univariate analyses of variance carried out for each individual trait indicated significant differences for seven morphological traits between the 28 assessed (Table 3). Among these seven traits, there were significant differences only between sex (Table 3).

Body and elytron length, length of the antennae and of the 2nd and 3rd antennal segments, maximum pronotum width and length of the median tibia and posterior tarsi were the traits showing significant differences between sexes (Table 3). Body and elytron length as well as length of the median tibia were longer for females, while length of antenna and of the 2nd and 3rd antennal segments, pronotum width and length of the posterior tarsi were longer in males (Table 4).

Discussion

The analysis of the 28 morphometric traits between sexes and seasons (0.05 at 5%) showed no significance. On the other hand, among opposite sexes was significant and related to sexual dimorphism (0,007 to 5.0%). The females showed to be larger than males by their body and elytra length. In general the larger length of the females is associated with reproductive features (Renthal et al., 2003). The males present larger antenna which appear to support larger number of receptor sensila that increases, among other functions, its capacity to locate the females for mating (Chapman, 1998). Other characteristics found in the males were the largest width of the pronotum and posterior tarsi as well as the smaller length of the medium tibia. The meaning of these differences is not clear, but represent expressions of sexual dimorphism. Temperature was the only influence in the distribution of adults seasonal activity. The analysis between individuals of the same sex in different seasons showed no significance. The few individuals that appeared in the dry season appear to have had a delay in their development. This probable problem was not reflected in the 28 morphometric traits. The abundance of O. discicolle in the time of higher temperature or the wet season means the reproductive period of the species in the Atlantic forest is between October to March.

Date Received 08/01/2005

Revised 02/28/2006

Accepted 05/11/2006

ISSN 1676-0611

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Publication Dates

  • Publication in this collection
    12 Dec 2006
  • Date of issue
    2006

History

  • Reviewed
    28 Feb 2006
  • Received
    08 Jan 2005
  • Accepted
    05 Nov 2006
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