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Spatial swarm segregation and reproductive isolation between the molecular forms of Anopheles gambiae.

Diabaté A, Dao A, Yaro AS, Adamou A, Gonzalez R, Manoukis NC, Traoré SF, Gwadz RW, Lehmann T - Proc. Biol. Sci. (2009)

Bottom Line: We found evidence of clustering of swarms composed of individuals of a single molecular form within the village.We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali.However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.

ABSTRACT
Anopheles gambiae, the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.

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(a) Spatial segregation of swarms of the molecular forms (shaded ovals) and indoor composition of the molecular forms collected in the vicinity of the swarms (vertical bars) in 2006. With the exceptions of swarms 0, 11, 16 and 18, all swarms were sampled more than once (2–8 evenings) at the same site. Swarm sizes ranged from 5 to 74. (b) Spatial segregation of swarms of the molecular forms (shaded ovals) in 2007. Locations of swarms 1, 11, 15, 16 and 18 are seen on the map, but these swarms were not sampled in 2007. Swarm 33 and swarm 14 are mixed swarms respectively of the M form and An. arabiensis, and of the S and M forms.
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RSPB20091167F1: (a) Spatial segregation of swarms of the molecular forms (shaded ovals) and indoor composition of the molecular forms collected in the vicinity of the swarms (vertical bars) in 2006. With the exceptions of swarms 0, 11, 16 and 18, all swarms were sampled more than once (2–8 evenings) at the same site. Swarm sizes ranged from 5 to 74. (b) Spatial segregation of swarms of the molecular forms (shaded ovals) in 2007. Locations of swarms 1, 11, 15, 16 and 18 are seen on the map, but these swarms were not sampled in 2007. Swarm 33 and swarm 14 are mixed swarms respectively of the M form and An. arabiensis, and of the S and M forms.

Mentions: Swarms were sampled when swarm size was near its peak, between 10 and 20 min after sunset. Swarms usually appeared in the same location every evening. In 2006, identification of 901 males from 47 swarms revealed complete swarm segregation, with every swarm being composed exclusively of either M or S males (figure 1a). Three swarms (swarms 1, 2 and 17; figure 1a) were sampled three times in the same evening (2 min apart) to assess temporal change in male composition. Overall, 29, 23 and 74 specimens, respectively, were sampled from these swarms (sample size range per time point 2–30), and composition remained 100 per cent of the S form. The composition of all swarm sites sampled at different dates remained unchanged except for one swarm (swarm 17), which consisted exclusively of S males on four evenings (sample size range: 23–74 specimens), but consisted of M males on one evening (sample size, 13 specimens; figure 1a).


Spatial swarm segregation and reproductive isolation between the molecular forms of Anopheles gambiae.

Diabaté A, Dao A, Yaro AS, Adamou A, Gonzalez R, Manoukis NC, Traoré SF, Gwadz RW, Lehmann T - Proc. Biol. Sci. (2009)

(a) Spatial segregation of swarms of the molecular forms (shaded ovals) and indoor composition of the molecular forms collected in the vicinity of the swarms (vertical bars) in 2006. With the exceptions of swarms 0, 11, 16 and 18, all swarms were sampled more than once (2–8 evenings) at the same site. Swarm sizes ranged from 5 to 74. (b) Spatial segregation of swarms of the molecular forms (shaded ovals) in 2007. Locations of swarms 1, 11, 15, 16 and 18 are seen on the map, but these swarms were not sampled in 2007. Swarm 33 and swarm 14 are mixed swarms respectively of the M form and An. arabiensis, and of the S and M forms.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2821344&req=5

RSPB20091167F1: (a) Spatial segregation of swarms of the molecular forms (shaded ovals) and indoor composition of the molecular forms collected in the vicinity of the swarms (vertical bars) in 2006. With the exceptions of swarms 0, 11, 16 and 18, all swarms were sampled more than once (2–8 evenings) at the same site. Swarm sizes ranged from 5 to 74. (b) Spatial segregation of swarms of the molecular forms (shaded ovals) in 2007. Locations of swarms 1, 11, 15, 16 and 18 are seen on the map, but these swarms were not sampled in 2007. Swarm 33 and swarm 14 are mixed swarms respectively of the M form and An. arabiensis, and of the S and M forms.
Mentions: Swarms were sampled when swarm size was near its peak, between 10 and 20 min after sunset. Swarms usually appeared in the same location every evening. In 2006, identification of 901 males from 47 swarms revealed complete swarm segregation, with every swarm being composed exclusively of either M or S males (figure 1a). Three swarms (swarms 1, 2 and 17; figure 1a) were sampled three times in the same evening (2 min apart) to assess temporal change in male composition. Overall, 29, 23 and 74 specimens, respectively, were sampled from these swarms (sample size range per time point 2–30), and composition remained 100 per cent of the S form. The composition of all swarm sites sampled at different dates remained unchanged except for one swarm (swarm 17), which consisted exclusively of S males on four evenings (sample size range: 23–74 specimens), but consisted of M males on one evening (sample size, 13 specimens; figure 1a).

Bottom Line: We found evidence of clustering of swarms composed of individuals of a single molecular form within the village.We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali.However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.

ABSTRACT
Anopheles gambiae, the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.

Show MeSH
Related in: MedlinePlus