WEIGHT DIFFERENCES BETWEEN Boophilus microplus (IXODOIDEA: IXODIDAE) FROM BRAZIL AND FROM CUBA
DIFERENCIAS DE PESO ENTRE Boophilus microplus (IXODOIDEA:IXODIDAE) DE BRASIL Y DE CUBA
R. de la Vega*, G. Díaz**, A Camejo*, A.H. Fonseca*** and C. Passos Rangel***
*LABIOFAM, Apartado 34, General Peraza, CP-19210, Ciudad Habana, Cuba FAX: (537)334857, E-mail: delavega@infomed.sld.cu; **Departamento Biología Animal y Humana, Facultad de Biología, Universidad de La Habana, E-mail: gdacosta@fbio.uh.cu; ***Universidad Federal Rural de Rio do Janeiro, Seropédica, RJ, Brasil Km 47 Antiga Rodovia Rio-São Paulo, E-mail: adivaldo@ufrrj.br ]]>
ABSTRACT
Weights of engorged females and recently molted adults Boophilus microplus (both females and males) from Cuba and Brazil were compared by means of t-Student tests. It was observed that Brazilian ticks were always significantly heavier than those from Cuba. Some comments about the possible causes, significance of observation and further researches to be performed are offered.
Key words: ticks; weight; Boophilus; Ixodoidea; Ixodidae.
RESUMEN
Se comparó el peso de hembras repletas y adultos recién mudados (hembras y machos) de Boophilus microplus de Cuba y de Brasil mediante pruebas de t de Student. Se observó que las garrapatas de Brasil fueron siempre significativamente más pesadas que las de Cuba. Se comenta sobre las posibles causas y significado de este fenómeno y de las futuras investigaciones a realizar.
Palabras clave: garrapatas; peso; Boophilus; Ixodoidea; Ixodidae.
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INTRODUCTIONEcology has been linked to divergence and speciation, but debates about evolution in sympatry have often eclipsed its importance. Nevertheless, recent studies on diverse taxa have suggested that natural selection caused by shifts in ecology or invasion of novel habitats could develop in extremely rapid rates of evolutionary divergence. Experimental approaches linking rapid ecological divergences are scarce, though recent papers indicate those are the best approaches to be used (7).
In parasites, number of diversifying factors is potentially larger than in free living organisms, because host-parasite coevolution (5). Otherwise, there have been relatively few traditional phylo-geographical studies on non-free living species (1). It was seen that when Boophilus microplus from Australia and from South Africa were crossed, a high degree of infertility and of sterile hybrids were obtained (11). Also, Davey et al. (2) looked for differences in weight on B. microplus ticks from different areas of Mexico and USA, including Puerto Rico, and found that weights of ticks varied with location. In the present paper, it was reported on a weight comparison of recently molted B. microplus (females and males) and engorged females from Cuba and from Brazil.
MATERIALS AND METHODS
Holstein calfs were infested with groups of 10 000 B. microplus larvae. At 13 and 14 days after infestation, nymphs were collected and incubated at 28oC and relative humidity over 80%. Adults were sexed and weighed in an analytical balance (P=0.0001g). Engorged females were taken from the floor of the stable and similarly weighed.
Statistical Analysis._ In each category, mean (m) in grams (g) or in milligrams (mg) and standard deviation (SD) were calculated and any weights not in the interval m ± 2*(SD) were discarded. The m and SD were then recalculated. In all groups, a t-Student test was done. Before mean comparison, a test of variance homogeneity was performed.
RESULTS
Table 1 shows number of ticks utilized within each category and country of the experiment, while Table 2 summarizes the comparative results. ]]>
DISCUSSION
In all categories, Brazilian ticks were heavier than Cuban ones. Geographical isolation could be invoked as a possible explanation of this divergence as ecological conditions of Rio de Janeiro are somewhat different to those of Havana. Otherwise, some authors (4,8) consider that processes of ecological, sexual, and spatial differentiation can interact to create reproductively isolated lineages without geographical isolation. Davey et al. (2) found ovipositional and morphological differences between B. microplus from different sites of the USA-Mexico border and from Puerto Rico. Also, they verified that ticks raised in laboratory were the heaviest and ticks from Puerto Rico the lightest. Besides, these authors encountered morphological differences between males of these sites. However, in a study in USA (9), four natural colonies and four laboratory colonies of B. microplus were subjected to eletrophoretic analysis to determine levels of genetic similarity and genetic variability. Results have shown that high genetic similarity (I=0.984±0.012) and low genetic variability (h=0.092±0.008) exist among these eight populations. Recently (10), in 30 B.microplus strains from different sites of Brazil, Argentina, Colombia, Venezuela and Uruguay, variations were seen in bm86 and bm95 genes that could explain the variable efficiencies of recombinant vaccines derived from the Bm86 and Bm95 proteins in different B. microplus strains.
Otherwise, differences in eggs weight between B. microplus from Brazil and from Cuba also seem to exist according to Labruna et al. (6) report: mean egg weight=0.0050 g and De la Vega (3) results: mean egg weight=0.0044 g. Again, weights from Brazil are higher than those from Cuba. Wilding et al. (12) afirme that speciation requires the acquisition of reproductive isolation, which is still to be proven in the present species from Cuba and from Brazil. Present results could not be interpreted as initial signs of speciation until works about genetic similarity and variability and about sexual behavior and the output of cross-matings of B. microplus of both countries were performed.
ACKNOWLEDGEMENTS
To Mr. Edward Deutsch for the revision of this paper. To Dr. Jorge de la Cruz for his valuable advices.
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(Recibido 20-2-2006; Aceptado 18-3-2006) ]]>