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Evolutionary experimentation through hybridization under laboratory condition in Drosophila: evidence for recombinational speciation.

Harini BP, Ramachandra NB - BMC Evol. Biol. (2003)

Bottom Line: Each of these Cytoraces is composed of recombined genomes of the parental races.The results reveal that in most cases, the newly evolved Cytoraces, with different chromosome constitutions, exhibit decreased body size, better fitness and live longer than their parents.Particularly, Cytorace 5, 6 and 8 have evolved with very much higher range values of quantitative traits than the parents and other Cytoraces, which suggests the role of transgressive segregation in the evolution of these Cytoraces.

View Article: PubMed Central - HTML - PubMed

Affiliation: Drosophila stock centre, Department of Studies in Zoology University of Mysore Manasagangotri Mysore-570 006, India. bpharini@hotmail.com

ABSTRACT

Background: Drosophila nasuta nasuta (2n = 8) and Drosophila nasuta albomicans (2n = 6) are a pair of sibling allopatric chromosomal cross-fertile races of the nasuta subgroup of immigrans species group of Drosophila. Interracial hybridization between these two races has given rise to new karyotypic strains called Cytorace 1 and Cytorace 2 (first phase). Further hybridization between Thailand strain of D. n. albomicans and D. n. nasuta of Coorg strain has resulted in the evolution of two more Cytoraces, namely Cytorace 3 and Cytorace 4 (second phase). The third phase Cytoraces (Cytorace 5 to Cytorace 16) have evolved through interracial hybridization among first, second phase Cytoraces along with parental races. Each of these Cytoraces is composed of recombined genomes of the parental races. Here, we have made an attempt to systematically assess the impact of hybridization on karyotypes, morphometric and life history traits in all 16 Cytoraces.

Results: The results reveal that in most cases, the newly evolved Cytoraces, with different chromosome constitutions, exhibit decreased body size, better fitness and live longer than their parents. Particularly, Cytorace 5, 6 and 8 have evolved with very much higher range values of quantitative traits than the parents and other Cytoraces, which suggests the role of transgressive segregation in the evolution of these Cytoraces.

Conclusion: Thus, the rapid divergence recorded in the chromosomes, karyotypes, body size and fitness traits of Cytoraces exhibit the early event of recombinational raciation / speciation in the evolution of the Cytoraces under laboratory conditions.

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Based on the DMR test, 18 members of the nasuta-albomicans complex of Drosophila are constructed into clusters and named in the hierarchical form from the lowest to the highest mean lifetime fecundity (Fig. 5a), ovariole number (Fig. 5b) and lifetime fertility (Fig. 5c). The members belonging to each cluster have insignificant differences. For life time fecundity, six clusters were recognized, of which, cluster 1 to 5 are overlapped with each other, while cluster 6 (C8) is formed as independent cluster. For ovariole number, six clusters were recognised, of which, except cluster 1 (N), all the other clusters from 2 to 6 are overlapped, while cluster 1 is formed as independent cluster. For fertility, cluster 1 (C13) is formed as independent cluster, while cluster 2 to cluster 7 are overlapped with each other.
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Figure 5: Based on the DMR test, 18 members of the nasuta-albomicans complex of Drosophila are constructed into clusters and named in the hierarchical form from the lowest to the highest mean lifetime fecundity (Fig. 5a), ovariole number (Fig. 5b) and lifetime fertility (Fig. 5c). The members belonging to each cluster have insignificant differences. For life time fecundity, six clusters were recognized, of which, cluster 1 to 5 are overlapped with each other, while cluster 6 (C8) is formed as independent cluster. For ovariole number, six clusters were recognised, of which, except cluster 1 (N), all the other clusters from 2 to 6 are overlapped, while cluster 1 is formed as independent cluster. For fertility, cluster 1 (C13) is formed as independent cluster, while cluster 2 to cluster 7 are overlapped with each other.

Mentions: The mean lifetime fecundity, lifetime fertility, ovariole numbers and hatching success in the 18 members of the NAC complex of Drosophila (Table 6) revealed that D. n. nasuta, has decreased lifetime fecundity, lifetime fertility and hatching success than D. n. albomicans as well as most of the Cytoraces. While Cytorace 12 in fecundity and Cytorace 13 in fertility as well as hatching success (Table 6) have reduced values than all other Cytoraces. On the other hand, Cytorace 8 had the highest lifetime fecundity and lifetime fertility, while Cytorace 6 and D. n. albomicans had the highest ovariole number and hatching success respectively (5a-c). The mean lifetime fecundity of the parental races is lower than Cytoraces, however, in Cytoraces, the mean lifetime fecundity extends outside the range of parental races. These observations suggest that, the newly evolved Cytoraces of the third phase have also exhibited the lowest as well as the highest fecundity, indicating the extent of divergence. The results of decreased ovariole number in D. n. nasuta and D. n. albomicans and also first phase Cytoraces (Cytorace 1 and Cytorace 2) suggest that recently evolved Cytoraces are having increased ovariole number than ancestral races (Fig. 5b). The lifetime fertility of all the 16 Cytoraces also extends outside the range of parental races. The percent of hatching success (which was measured by dividing fertility by fecundity values) across the lineages ranges from 60 and 75% with the exception of Cytorace 13 (36%).


Evolutionary experimentation through hybridization under laboratory condition in Drosophila: evidence for recombinational speciation.

Harini BP, Ramachandra NB - BMC Evol. Biol. (2003)

Based on the DMR test, 18 members of the nasuta-albomicans complex of Drosophila are constructed into clusters and named in the hierarchical form from the lowest to the highest mean lifetime fecundity (Fig. 5a), ovariole number (Fig. 5b) and lifetime fertility (Fig. 5c). The members belonging to each cluster have insignificant differences. For life time fecundity, six clusters were recognized, of which, cluster 1 to 5 are overlapped with each other, while cluster 6 (C8) is formed as independent cluster. For ovariole number, six clusters were recognised, of which, except cluster 1 (N), all the other clusters from 2 to 6 are overlapped, while cluster 1 is formed as independent cluster. For fertility, cluster 1 (C13) is formed as independent cluster, while cluster 2 to cluster 7 are overlapped with each other.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC240057&req=5

Figure 5: Based on the DMR test, 18 members of the nasuta-albomicans complex of Drosophila are constructed into clusters and named in the hierarchical form from the lowest to the highest mean lifetime fecundity (Fig. 5a), ovariole number (Fig. 5b) and lifetime fertility (Fig. 5c). The members belonging to each cluster have insignificant differences. For life time fecundity, six clusters were recognized, of which, cluster 1 to 5 are overlapped with each other, while cluster 6 (C8) is formed as independent cluster. For ovariole number, six clusters were recognised, of which, except cluster 1 (N), all the other clusters from 2 to 6 are overlapped, while cluster 1 is formed as independent cluster. For fertility, cluster 1 (C13) is formed as independent cluster, while cluster 2 to cluster 7 are overlapped with each other.
Mentions: The mean lifetime fecundity, lifetime fertility, ovariole numbers and hatching success in the 18 members of the NAC complex of Drosophila (Table 6) revealed that D. n. nasuta, has decreased lifetime fecundity, lifetime fertility and hatching success than D. n. albomicans as well as most of the Cytoraces. While Cytorace 12 in fecundity and Cytorace 13 in fertility as well as hatching success (Table 6) have reduced values than all other Cytoraces. On the other hand, Cytorace 8 had the highest lifetime fecundity and lifetime fertility, while Cytorace 6 and D. n. albomicans had the highest ovariole number and hatching success respectively (5a-c). The mean lifetime fecundity of the parental races is lower than Cytoraces, however, in Cytoraces, the mean lifetime fecundity extends outside the range of parental races. These observations suggest that, the newly evolved Cytoraces of the third phase have also exhibited the lowest as well as the highest fecundity, indicating the extent of divergence. The results of decreased ovariole number in D. n. nasuta and D. n. albomicans and also first phase Cytoraces (Cytorace 1 and Cytorace 2) suggest that recently evolved Cytoraces are having increased ovariole number than ancestral races (Fig. 5b). The lifetime fertility of all the 16 Cytoraces also extends outside the range of parental races. The percent of hatching success (which was measured by dividing fertility by fecundity values) across the lineages ranges from 60 and 75% with the exception of Cytorace 13 (36%).

Bottom Line: Each of these Cytoraces is composed of recombined genomes of the parental races.The results reveal that in most cases, the newly evolved Cytoraces, with different chromosome constitutions, exhibit decreased body size, better fitness and live longer than their parents.Particularly, Cytorace 5, 6 and 8 have evolved with very much higher range values of quantitative traits than the parents and other Cytoraces, which suggests the role of transgressive segregation in the evolution of these Cytoraces.

View Article: PubMed Central - HTML - PubMed

Affiliation: Drosophila stock centre, Department of Studies in Zoology University of Mysore Manasagangotri Mysore-570 006, India. bpharini@hotmail.com

ABSTRACT

Background: Drosophila nasuta nasuta (2n = 8) and Drosophila nasuta albomicans (2n = 6) are a pair of sibling allopatric chromosomal cross-fertile races of the nasuta subgroup of immigrans species group of Drosophila. Interracial hybridization between these two races has given rise to new karyotypic strains called Cytorace 1 and Cytorace 2 (first phase). Further hybridization between Thailand strain of D. n. albomicans and D. n. nasuta of Coorg strain has resulted in the evolution of two more Cytoraces, namely Cytorace 3 and Cytorace 4 (second phase). The third phase Cytoraces (Cytorace 5 to Cytorace 16) have evolved through interracial hybridization among first, second phase Cytoraces along with parental races. Each of these Cytoraces is composed of recombined genomes of the parental races. Here, we have made an attempt to systematically assess the impact of hybridization on karyotypes, morphometric and life history traits in all 16 Cytoraces.

Results: The results reveal that in most cases, the newly evolved Cytoraces, with different chromosome constitutions, exhibit decreased body size, better fitness and live longer than their parents. Particularly, Cytorace 5, 6 and 8 have evolved with very much higher range values of quantitative traits than the parents and other Cytoraces, which suggests the role of transgressive segregation in the evolution of these Cytoraces.

Conclusion: Thus, the rapid divergence recorded in the chromosomes, karyotypes, body size and fitness traits of Cytoraces exhibit the early event of recombinational raciation / speciation in the evolution of the Cytoraces under laboratory conditions.

Show MeSH
Related in: MedlinePlus