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Postmating Reproductive isolation between strains of Drosophila willistoni

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ABSTRACT

Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.

No MeSH data available.


Haplotype network of D. willistoni stocks from multiple localities. The identity of the strains as Northern vs. Southern subspecies is color coded as in Figure 1. Mutations are shown as hatch marks along connecting lines. The black circles represent missing intermediate haplotypes. Strains with the same haplotype are grouped together with the size of the circle being proportional to the number of strains belonging to a haplotype. The identity of the different strains sequenced is abbreviated as in Figure 1. Drosophila strains sequenced but not phenotypically assayed are identified as follows: Brazil (B1 to B15 = haplotypes 1 to 15);38 Nicaragua (N00); El Salvador (ES01); Florida (F02); México (M03, M15, M28, M31); Guadeloupe (G20, G25); Guana (GU21, GU26, GU27); Uruguay (U17). The names of the strains sharing the most common haplotype are boxed.
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f0003: Haplotype network of D. willistoni stocks from multiple localities. The identity of the strains as Northern vs. Southern subspecies is color coded as in Figure 1. Mutations are shown as hatch marks along connecting lines. The black circles represent missing intermediate haplotypes. Strains with the same haplotype are grouped together with the size of the circle being proportional to the number of strains belonging to a haplotype. The identity of the different strains sequenced is abbreviated as in Figure 1. Drosophila strains sequenced but not phenotypically assayed are identified as follows: Brazil (B1 to B15 = haplotypes 1 to 15);38 Nicaragua (N00); El Salvador (ES01); Florida (F02); México (M03, M15, M28, M31); Guadeloupe (G20, G25); Guana (GU21, GU26, GU27); Uruguay (U17). The names of the strains sharing the most common haplotype are boxed.

Mentions: The mitochondrial cytochrome oxidase gene (mtCOI) is a commonly used genetic marker for barcoding of animal species. To assess whether this universally used barcode gene could be useful to genetically fingerprint the Northern and Southern subspecies, we performed a sequence analysis of an approximately 650¬†bp region of 20 southern and 15 northern strains. Overall, we found limited genetic differentiation between strains, with genetic distance estimates ranging from 0 to 0.009. The Southern subspecies (Segregating site, S = 21; ŌÄ = 0.0045) is more polymorphic than the Northern subspecies (S = 8, ŌÄ = 0.0018) and it shows richer haplotype diversity (Hd = 0.984 and 0.571 respectively) (Fig.¬†2). A haplotype network analyses shows a cluster of 13 strains sharing the same haplotype. This cluster is composed mainly (10) of Northern subspecies strains and all Caribbean strains except for the southernmost island of Grenada. However, mtCOI haplotypes do not show an obvious separation of Northern and Southern subspecies (Fig.¬†3). The intermingling of Northern and Southern haplotypes is reflected by estimates of genetic differentiation. Estimates of genetic differentiation can be sensitive to sample size, haplotype diversity and sequence length. We used Hudson's nearest-neighbor statistic (Snn) to measure genetic differentiation between Northern and Southern subspecies, as this statistic is less sensitive to populations' diversity. We found no evidence of genetic differentiation between subspecies (Snn = 0.528; P = 0.232).Figure 2.


Postmating Reproductive isolation between strains of Drosophila willistoni
Haplotype network of D. willistoni stocks from multiple localities. The identity of the strains as Northern vs. Southern subspecies is color coded as in Figure 1. Mutations are shown as hatch marks along connecting lines. The black circles represent missing intermediate haplotypes. Strains with the same haplotype are grouped together with the size of the circle being proportional to the number of strains belonging to a haplotype. The identity of the different strains sequenced is abbreviated as in Figure 1. Drosophila strains sequenced but not phenotypically assayed are identified as follows: Brazil (B1 to B15 = haplotypes 1 to 15);38 Nicaragua (N00); El Salvador (ES01); Florida (F02); México (M03, M15, M28, M31); Guadeloupe (G20, G25); Guana (GU21, GU26, GU27); Uruguay (U17). The names of the strains sharing the most common haplotype are boxed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036932&req=5

f0003: Haplotype network of D. willistoni stocks from multiple localities. The identity of the strains as Northern vs. Southern subspecies is color coded as in Figure 1. Mutations are shown as hatch marks along connecting lines. The black circles represent missing intermediate haplotypes. Strains with the same haplotype are grouped together with the size of the circle being proportional to the number of strains belonging to a haplotype. The identity of the different strains sequenced is abbreviated as in Figure 1. Drosophila strains sequenced but not phenotypically assayed are identified as follows: Brazil (B1 to B15 = haplotypes 1 to 15);38 Nicaragua (N00); El Salvador (ES01); Florida (F02); México (M03, M15, M28, M31); Guadeloupe (G20, G25); Guana (GU21, GU26, GU27); Uruguay (U17). The names of the strains sharing the most common haplotype are boxed.
Mentions: The mitochondrial cytochrome oxidase gene (mtCOI) is a commonly used genetic marker for barcoding of animal species. To assess whether this universally used barcode gene could be useful to genetically fingerprint the Northern and Southern subspecies, we performed a sequence analysis of an approximately 650¬†bp region of 20 southern and 15 northern strains. Overall, we found limited genetic differentiation between strains, with genetic distance estimates ranging from 0 to 0.009. The Southern subspecies (Segregating site, S = 21; ŌÄ = 0.0045) is more polymorphic than the Northern subspecies (S = 8, ŌÄ = 0.0018) and it shows richer haplotype diversity (Hd = 0.984 and 0.571 respectively) (Fig.¬†2). A haplotype network analyses shows a cluster of 13 strains sharing the same haplotype. This cluster is composed mainly (10) of Northern subspecies strains and all Caribbean strains except for the southernmost island of Grenada. However, mtCOI haplotypes do not show an obvious separation of Northern and Southern subspecies (Fig.¬†3). The intermingling of Northern and Southern haplotypes is reflected by estimates of genetic differentiation. Estimates of genetic differentiation can be sensitive to sample size, haplotype diversity and sequence length. We used Hudson's nearest-neighbor statistic (Snn) to measure genetic differentiation between Northern and Southern subspecies, as this statistic is less sensitive to populations' diversity. We found no evidence of genetic differentiation between subspecies (Snn = 0.528; P = 0.232).Figure 2.

View Article: PubMed Central - PubMed

ABSTRACT

Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.

No MeSH data available.