Morphometric changes of Triatoma flavida Neiva, 1911 (Hemiptera:Triatominae) in the transition from sylvatic to laboratory conditions

Cambios morfométricos de Triatoma flavida Neiva, 1911 (Hemiptera:Triatominae) que ocurrieron cuando fueron llevados desde su hábitat selvático al laboratorio

Abstracts

The one-generational metric changes occurring in Triatoma flavida (Hemiptera: Triatominae) when carried from its wild habitat (caves) to laboratory, were examined using traditional morphometric techniques. As for other species of Triatoma, Rhodnius or Panstrongylus studied in similar conditions, a significant reduction of head, thorax and wing size was observed. Sexual dimorphism of the wings, while present in the wild sample, was not detected anymore in the laboratory individuals. Biological significance and epidemiological importance are discussed.

Morphometric changes; Sylvatic-laboratory; Triatoma flavida


Fueron examinados los cambios morfométricos que ocurrieron en la primera generación de Triatoma flavida cuando fueron llevados desde su hábitat selvático (cuevas) al laboratorio, mediante el uso de técnicas morfométricas tradicionales. Se observó una reducción significativa del tamaño de la cabeza, tórax y alas, como ocurre en otras especies de Triatoma, Rhodnius o Panstrongylus estudiados en condiciones similares. El dimorfismo sexual de tamaño en las alas, aunque presente en los individuos selváticos, no se detectó en los de laboratorio. La significación biológica y la importancia epidemiológica son discutidas.


BRIEF COMMUNICATION

Morphometric changes of Triatoma flavida Neiva, 1911 (Hemiptera:Triatominae) in the transition from sylvatic to laboratory conditions

Cambios morfométricos de Triatoma flavida Neiva, 1911 (Hemiptera:Triatominae) que ocurrieron cuando fueron llevados desde su hábitat selvático al laboratorio

Jinnay Rodríguez RodríguezI; Omar Fuentes GonzálezI; Jorge Fraga NodarseII; Lianet Monzote FidalgoII; Jean-Pierre DujardinIII

IDepartamento de Control de Vectores, Instituto de Medicina Tropical Pedro Kourí, Autopista Novia del mediodia Km 6, Arroyo Arenas La Lisa, Ciudad Habana, Cuba

IIDepartamento de Parasitología, Instituto de Medicina Tropical Pedro Kourí

IIIUnité Mixte de Recherche (UMR 2724), Institut de Recherches pour le Développement (IRD), Centre National de Recherche Scientifique (CNRS), Montpellier, France

Correspondence to

SUMMARY

The one-generational metric changes occurring in Triatoma flavida (Hemiptera: Triatominae) when carried from its wild habitat (caves) to laboratory, were examined using traditional morphometric techniques. As for other species of Triatoma, Rhodnius or Panstrongylus studied in similar conditions, a significant reduction of head, thorax and wing size was observed. Sexual dimorphism of the wings, while present in the wild sample, was not detected anymore in the laboratory individuals. Biological significance and epidemiological importance are discussed.

Keywords: Morphometric changes; Sylvatic-laboratory; Triatoma flavida.

RESUMEN

Fueron examinados los cambios morfométricos que ocurrieron en la primera generación de Triatoma flavida cuando fueron llevados desde su hábitat selvático (cuevas) al laboratorio, mediante el uso de técnicas morfométricas tradicionales. Se observó una reducción significativa del tamaño de la cabeza, tórax y alas, como ocurre en otras especies de Triatoma, Rhodnius o Panstrongylus estudiados en condiciones similares. El dimorfismo sexual de tamaño en las alas, aunque presente en los individuos selváticos, no se detectó en los de laboratorio. La significación biológica y la importancia epidemiológica son discutidas.

INTRODUCTION

In various species of Triatominae, morphological and genetic changes have been observed associated with their adaptation from sylvatic to domestic or laboratory populations. These changes generally involved genetic drift effects3 together with a reduction in average size and modification of sexual size dimorphism4,6,7. Although these observations are found in various genera (Rhodnius, Triatoma and Panstrongylus), more species have to be analyzed before accepting them as generalities for Triatominae. The idea that such differences observed in laboratory might parallel those between sylvatic and synanthropic populations is another hypothesis6 which can be studied only in species that have natural domestic colonies, like the main vectors of Chagas disease. In the present work, we wished to determine if morphometric changes could be detected in the exclusively sylvatic, Cuban species T. flavida, when adapted to laboratory conditions. This species is endemic in Cuba, it is also the most abundant representative of Triatominae on the island. T. flavida, is a sylvatic species but is reportedly attracted to houses by lights8. In recent years, there have been increasing reports of little-known species of Triatominae establishing domestic colonies, previously considered to be exclusively sylvatic in habitats11. In this regard, our study contributes to the entomological surveillance of a potential vector of Chagas disease.

In 2000, a total of 87 sylvatic specimens of T. flavida (33 fourth instar nymphs, 50 fifth instar nymphs, four adults) were collected in caves of Peninsula de Guanahacabibes, Pinar del Rio (Cuba). These insects were maintained in laboratory conditions at 26 ± 2 °C and 76 ± 2% of relative humidity. Blood meals were offered at intervals of 7-15 days. The original parents (44 females and 37 males) were used for morphometric analysis, together with 21 males and 21 females taken randomly from the F1 generation.

We used a stereoscopic microscope and an ocular micrometer. The measurement of wing and thorax were made with an objective 10X and eyepiece 20X, the head measurements were performed with objective 16 and the same eyepiece, except the PO measurement where we used an objective 25.

Out of 22 characters initially measured according to standard procedures2,4, we retained 15 ones for best accuracy and precision: OE, outer eyes; IE, inner eyes; EO, external ocelli; AO, ante-ocular region; AT, anteclypeus; DE, diameter of eye; PO, post-ocular region; R1 and R2, first and second rostrum segments, respectively; I, width between humerus; J, length of the thorax; H, width at the intersection of the fore and median lobes2 and C, D, E three measurements of the wing4.

Means and standard deviation for each character were reported by sex and biotope (Table 1 for head, Table 2 for thorax and Table 3 for wings), and compared between sexes (Table 4, left part) or ecotopes (Table 4, right part) using HSD of Tukey test13 . Each comparison was tested for final significance using the sequential Bonferroni test as described by SOKAL & ROHLF (1995)12.

In only one generation, size systematically decreased from wild to laboratory specimens for almost all characters (Tables 1, 2, 3), and this reduction was apparently more pronounced in the males (Table 4, right part).

The well known sexual dimorphism of Triatominae (females on average larger than males9) was confirmed for 8 characters in wild specimens while for 3 ones only in laboratory samples (IE, EO, HO). Sexual dimorphism was not present at all for laboratory wings (Table 4, left part).

Biological significance: Head size decreasing in the transition from sylvatic to domestic or laboratory conditions has been demonstrated in other Triatominae species such as Triatoma dimidiata, T. brasiliensis, T. infestans, Rhodnius domesticus, Panstrongylus rufotuberculatus and P. geniculatus1,4,5,6,7,14. It was thus also verified here for T. flavida with a significant decrease in almost all the characters measured in head, thorax and wings.

Various explanations have been suggested to understand this change. For instance, natural selection may favor larger phenotypes in less favorable (more unstable or "sylvatic") habitats, possibly due to a greater capacity to resist temporary food shortages, whereas smaller individuals apparently survive better under laboratory or domestic conditions where food availability is less restricted4,11. DUJARDIN et al. (1999)6 also suggested that the size reduction could reveal the effect of population density on bug size: in laboratory colonies each individual would get less blood because of competition, smaller individuals would survive and the average size decrease. However, other mechanisms, such as inbreeding, different host-feeding patterns and/or developmental times, may also explain these size differences10.

Sexual dimorphism modification appears as a secondary effect of size reduction, as long as this latter occurs at different rates according to sex. When the rate is similar in each sex, no sexual dimorphism modification is expected. For instance no such evidence could be established after five laboratory generations of P. geniculatus7 , although these authors could observe a significant decreasing in head or wing size.

Epidemiological significance: In conclusion, our observations confirmed the previous ones about metric changes in Triatominae in the transition from natural habitat to laboratory conditions of life: size is reduced, sexual dimorphism is affected. As long as these changes could reflect the modifications from sylvatic to domestic conditions of life of any Triatominae, our observations have epidemiological importance. They could provide indeed objective criteria for evaluating the level of adaptation of an insect to domestic structures. In case of complete isolation from sylvatic foci, a well adapted domestic population of Triatominae should have shorter size and modified sexual dimorphism relative to its sylvatic counterpart. No such differences would be detected in case of frequent exchanges with sylvatic foci.

Received: 27 June 2006

Accepted: 11 September 2006

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Publication Dates

  • Publication in this collection
    03 May 2007
  • Date of issue
    Apr 2007

History

  • Received
    27 June 2006
  • Accepted
    11 Sept 2006
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