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Published on: June 15, 2020
Low temperature reveals genetic variability against male-killing Spiroplasma in Drosophila melanogaster natural
Abstract:
Spiroplasma endosymbionts are maternally inherited microorganisms which infect many arthropod species. In some Drosophila species, it acts as a reproductive manipulator, spreading in populations by killing the sons of infected mothers. Distinct Drosophila melanogaster populations from Brazil exhibit variable male-killing Spiroplasma prevalences. In this study, we investigated the presence of variability for the male-killing phenotype among Drosophila and/or Spiroplasma strains and verified if it correlates with the endosymbiont prevalence in natural populations. For that, we analyzed the male-killing expression when Spiroplasma strains from different populations were transferred to a standard D. melanogaster line (Canton-S) and when a common Spiroplasma strain was transferred to different wild-caught D. melanogaster lines, both at optimal and challenging temperatures for the bacteria. No variation was observed in the male-killing phenotype induced by different Spiroplasma strains. No phenotypic variability among fly lines was detected at optimal temperature (23 °C), as well. Conversely, significant variation in the male-killing expression was revealed among D. melanogaster lines at 18.5 °C, probably caused by imperfect transmission of the endosymbiont. Distinct lines differed in their average sex ratios as well as in the pattern of male-killing expression as the infected females aged. Greater variation occurred among lines from one locality, although there was no clear correlation between the male-killing intensity and the endosymbiont prevalence in each population. Imperfect transmission or male killing may also occur in the field, thus helping to explain the low or intermediate prevalences reported in nature. We discuss the implications of our results for the dynamics of male-killing Spiroplasma in natural populations.
Insights
Male-killing Spiroplasma in Drosophila show temperature-dependent variation in their reproductive manipulation. This variability, linked to imperfect transmission, influences endosymbiont prevalence in natural populations.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genetics
Background:
- Spiroplasma are maternally inherited endosymbionts infecting arthropods.
- In Drosophila, Spiroplasma can manipulate reproduction by killing male offspring, facilitating their spread.
- Brazilian Drosophila melanogaster populations show varying Spiroplasma prevalence.
Purpose of the Study:
- Investigate variability in the male-killing phenotype among different Drosophila and Spiroplasma strains.
- Determine if this variability correlates with Spiroplasma prevalence in natural populations.
- Analyze the impact of temperature on male-killing expression.
Main Methods:
- Transferred Spiroplasma strains from various populations to a standard Drosophila melanogaster line (Canton-S).
- Transferred a common Spiroplasma strain to different wild-caught Drosophila melanogaster lines.
- Assessed male-killing expression at optimal (23 °C) and challenging (18.5 °C) temperatures.
Main Results:
- No variation in male-killing phenotype was observed between different Spiroplasma strains.
- No phenotypic variability was detected among fly lines at 23 °C.
- Significant variation in male-killing expression occurred among D. melanogaster lines at 18.5 °C, linked to imperfect endosymbiont transmission.
- Varied sex ratios and male-killing patterns were observed as infected females aged.
- Greater variation was found among lines from a single locality, but no clear correlation with Spiroplasma prevalence.
Conclusions:
- Temperature influences the expression of the male-killing phenotype in Spiroplasma-infected Drosophila.
- Imperfect Spiroplasma transmission at lower temperatures contributes to variability in male-killing.
- This variability may explain low or intermediate Spiroplasma prevalences observed in natural populations.
- Results provide insights into the population dynamics of male-killing Spiroplasma.
