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An ancient mitochondrial polymorphism in Adalis bipunctata linked to a sex-ratio-distorting bacterium.

ABSTRACT: Sex-ratio-distorting microbes are common parasites of arthropods. Although the reasons they have invaded and spread though populations are well understood, their subsequent dynamics within those populations are virtually unknown. We have found that different strains of a male-killing Rickettsia bacterium infecting the beetle Adalia bipunctata are associated with distinct mitochondrial haplotypes, which is expected as both the mitochondria and the bacteria are maternally transmitted. These mitochondrial haplotypes shared a common ancestor >2 million years ago, and their overall diversity is significantly greater than expected under neutrality from comparisons with a nuclear gene. Furthermore, a variety of statistical tests show strong deviations from neutrality in mitochondrial but not in nuclear genes. We therefore conclude that natural selection is probably maintaining a polymorphism of different Rickettsia strains in this species. Despite the age of the different mitochondrial haplotypes, there is very little genetic diversity within them. Furthermore, there is considerable variation in mitochondrial haplotype and bacterial strain frequency between populations, despite it being thought that this species has fairly low levels of population structure. We conclude that the fitness of these male killers may be negatively frequency dependent or different strains may be favored in different populations. These hypotheses await experimental confirmation.

SUBMITTER: Jiggins FM

PROVIDER: S-EPMC1456815 | biostudies-literature | 2005 Nov

REPOSITORIES: biostudies-literature

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An ancient mitochondrial polymorphism in Adalis bipunctata linked to a sex-ratio-distorting bacterium.

Jiggins Francis M FM Tinsley Matthew C MC

Genetics 20050803 3

Sex-ratio-distorting microbes are common parasites of arthropods. Although the reasons they have invaded and spread though populations are well understood, their subsequent dynamics within those populations are virtually unknown. We have found that different strains of a male-killing Rickettsia bacterium infecting the beetle Adalia bipunctata are associated with distinct mitochondrial haplotypes, which is expected as both the mitochondria and the bacteria are maternally transmitted. These mitoch ...[more]

PMID: 16079227

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Project description:Patterns of mtDNA variation within a species reflect long-term population structure, but may also be influenced by maternally inherited endosymbionts, such as Wolbachia. These bacteria often alter host reproductive biology and can drive particular mtDNA haplotypes through populations. We investigated the impacts of Wolbachia infection and geography on mtDNA variation in the diamondback moth, a major global pest whose geographic distribution reflects both natural processes and transport via human agricultural activities.The mtDNA phylogeny of 95 individuals sampled from 10 countries on four continents revealed two major clades. One contained only Wolbachia-infected individuals from Malaysia and Kenya, while the other contained only uninfected individuals, from all countries including Malaysia and Kenya. Within the uninfected group was a further clade containing all individuals from Australasia and displaying very limited sequence variation. In contrast, a biparental nuclear gene phylogeny did not have infected and uninfected clades, supporting the notion that maternally-inherited Wolbachia are responsible for the mtDNA pattern. Only about 5% (15/306) of our global sample of individuals was infected with the plutWB1 isolate and even within infected local populations, many insects were uninfected. Comparisons of infected and uninfected isofemale lines revealed that plutWB1 is associated with sex ratio distortion. Uninfected lines have a 1:1 sex ratio, while infected ones show a 2:1 female bias.The main correlate of mtDNA variation in P. xylostella is presence or absence of the plutWB1 infection. This is associated with substantial sex ratio distortion and the underlying mechanisms deserve further study. In contrast, geographic origin is a poor predictor of moth mtDNA sequences, reflecting human activity in moving the insects around the globe. The exception is a clade of Australasian individuals, which may reflect a bottleneck during their recent introduction to this region.

Project description:There is evidence of offspring sex ratio adjustment in a range of species, but the potential mechanisms remain largely unknown. Elevated maternal corticosterone (CORT) is associated with factors that can favour brood sex ratio adjustment, such as reduced maternal condition, food availability and partner attractiveness. Therefore, the steroid hormone has been suggested to play a key role in sex ratio manipulation. However, despite correlative and causal evidence CORT is linked to sex ratio manipulation in some avian species, the timing of adjustment varies between studies. Consequently, whether CORT is consistently involved in sex-ratio adjustment, and how the hormone acts as a mechanism for this adjustment remains unclear. Here we measured maternal baseline CORT and body condition in free-living blue tits (Cyanistes caeruleus) over three years and related these factors to brood sex ratio and nestling quality. In addition, a non-invasive technique was employed to experimentally elevate maternal CORT during egg laying, and its effects upon sex ratio and nestling quality were measured. We found that maternal CORT was not correlated with brood sex ratio, but mothers with elevated CORT fledged lighter offspring. Also, experimental elevation of maternal CORT did not influence brood sex ratio or nestling quality. In one year, mothers in superior body condition produced male biased broods, and maternal condition was positively correlated with both nestling mass and growth rate in all years. Unlike previous studies maternal condition was not correlated with maternal CORT. This study provides evidence that maternal condition is linked to brood sex ratio manipulation in blue tits. However, maternal baseline CORT may not be the mechanistic link between the maternal condition and sex ratio adjustment. Overall, this study serves to highlight the complexity of sex ratio adjustment in birds and the difficulties associated with identifying sex biasing mechanisms.

Dataset Information

An ancient mitochondrial polymorphism in Adalis bipunctata linked to a sex-ratio-distorting bacterium.

Publications

An ancient mitochondrial polymorphism in Adalis bipunctata linked to a sex-ratio-distorting bacterium.

Similar Datasets

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