Genetic conflict outweighs heterogametic incompatibility in the mouse hybrid zone?

<p>Abstract</p> <p>Background</p> <p>The <it>Mus musculus musculus/M. m. domesticus </it>contact zone in Europe is characterised by sharp frequency discontinuities for sex chromosome markers at the centre of wider clines in allozyme frequencies.</p> <p>Results</p> <p>We identify a triangular area (approximately 330 km²) where the <it>musculus </it>Y chromosome introgresses across this front for up to 22 km into <it>domesticus </it>territory. Introgression of the Y chromosome is accompanied by a perturbation of the census sex ratio: the sex ratio is significantly female biased in <it>musculus </it>localities and <it>domesticus </it>localities lacking Y chromosome introgression. In contrast, where the <it>musculus </it>Y is detected in <it>domesticus </it>localities, the sex ratio is close to parity, and significantly different from both classes of female biased localities. The geographic position of an abrupt cline in an X chromosome marker, and autosomal clines centred on the same position, seem unaffected by the <it>musculus </it>Y introgression.</p> <p>Conclusion</p> <p>We conclude that sex ratio distortion is playing a role in the geographic separation of speciation genes in this section of the mouse hybrid zone. We suggest that clines for genes involved in sex-ratio distortion have escaped from the centre of the mouse hybrid zone, causing a decay in the barrier to gene flow between the two house mouse taxa.</p

Testing parasite 'intimacy': the whipworm Trichuris muris in the European house mouse hybrid zone.

Host-parasite interaction studies across hybrid zones often focus on host genetic variation, treating parasites as homogeneous. 'Intimately' associated hosts and parasites might be expected to show similar patterns of genetic structure. In the literature, factors such as no intermediate host and no free-living stage have been proposed as 'intimacy' factors likely constraining parasites to closely follow the evolutionary history of their hosts. To test whether the whipworm, Trichuris muris, is intimately associated with its house mouse host, we studied its population genetics across the European house mouse hybrid zone (HMHZ) which has a strong central barrier to gene flow between mouse taxa. T. muris has a direct life cycle and nonmobile free stage: if these traits constrain the parasite to an intimate association with its host we expect a geographic break in the parasite genetic structure across the HMHZ. We genotyped 205 worms from 56 localities across the HMHZ and additionally T. muris collected from sympatric woodmice (Apodemus spp.) and allopatric murine species, using mt-COX1, ITS1-5.8S-ITS2 rDNA and 10 microsatellites. We show four haplogroups of mt-COX1 and three clear ITS1-5.8S-ITS2 clades in the HMHZ suggesting a complex demographic/phylogeographic history. Microsatellites show strong structure between groups of localities. However, no marker type shows a break across the HMHZ. Whipworms from Apodemus in the HMHZ cluster, and share mitochondrial haplotypes, with those from house mice. We conclude Trichuris should not be regarded as an 'intimate' parasite of the house mouse: while its life history might suggest intimacy, passage through alternate hosts is sufficiently common to erase signal of genetic structure associated with any particular host taxon

Coupling between tolerance and resistance for two related Eimeria parasite species

Resistance (host capacity to reduce parasite burden) and tolerance (host capacity to reduce impact on its health for a given parasite burden) manifest two different lines of defense. Tolerance can be independent from resistance, traded off against it, or the two can be positively correlated because of redundancy in underlying (immune) processes. We here tested whether this coupling between tolerance and resistance could differ upon infection with closely related parasite species. We tested this in experimental infections with two parasite species of the genus Eimeria. We measured proxies for resistance (the (inverse of) number of parasite transmission stages (oocysts) per gram of feces at the day of maximal shedding) and tolerance (the slope of maximum relative weight loss compared to day of infection on number of oocysts per gram of feces at the day of maximal shedding for each host strain) in four inbred mouse strains and four groups of F1 hybrids belonging to two mouse subspecies, Mus musculus domesticus and Mus musculus musculus. We found a negative correlation between resistance and tolerance against Eimeria falciformis, while the two are uncoupled against Eimeria ferrisi. We conclude that resistance and tolerance against the first parasite species might be traded off, but evolve more independently in different mouse genotypes against the latter. We argue that evolution of the host immune defenses can be studied largely irrespective of parasite isolates if resistance-tolerance coupling is absent or weak (E. ferrisi) but host-parasite coevolution is more likely observable and best studied in a system with negatively correlated tolerance and resistance (E. falciformis)

Large-scale genetic analysis reveals mammalian mtDNA heteroplasmy dynamics and variance increase through lifetimes and generations

Vital mitochondrial DNA (mtDNA) populations exist in cells and may consist of heteroplasmic mixtures of mtDNA types. The evolution of these heteroplasmic populations through development, ageing, and generations is central to genetic diseases, but is poorly understood in mammals. Here we dissect these population dynamics using a dataset of unprecedented size and temporal span, comprising 1947 single-cell oocyte and 899 somatic measurements of heteroplasmy change throughout lifetimes and generations in two genetically distinct mouse models. We provide a novel and detailed quantitative characterisation of the linear increase in heteroplasmy variance throughout mammalian life courses in oocytes and pups. We find that differences in mean heteroplasmy are induced between generations, and the heteroplasmy of germline and somatic precursors diverge early in development, with a haplotype-specific direction of segregation. We develop stochastic theory predicting the implications of these dynamics for ageing and disease manifestation and discuss its application to human mtDNA dynamics.</p

Intensity of infection with intracellular Eimeria spp. and pinworms is reduced in hybrid mice compared to parental subspecies

Genetic diversity in animal immune systems is usually beneficial. In hybrid recombinants, this is less clear, as the immune system could also be impacted by genetic conflicts. In the European house mouse hybrid zone, the long‐standing impression that hybrid mice are more highly parasitized and less fit than parentals persists despite the findings of recent studies. Working across a novel transect, we assessed infections by intracellular protozoans, Eimeria spp., and infections by extracellular macroparasites, pinworms. For Eimeria, we found lower intensities in hybrid hosts than in parental mice but no evidence of lowered probability of infection or increased mortality in the centre of the hybrid zone. This means ecological factors are very unlikely to be responsible for the reduced load of infected hybrids. Focusing on parasite intensity (load in infected hosts), we also corroborated reduced pinworm loads reported for hybrid mice in previous studies. We conclude that intensity of diverse parasites, including the previously unstudied Eimeria, is reduced in hybrid mice compared to parental subspecies. We suggest caution in extrapolating this to differences in hybrid host fitness in the absence of, for example, evidence for a link between parasitemia and health.Peer Reviewe

Spatiotemporal patterns of egg laying in the common cuckoo

Understanding egg-laying behaviour of brood parasites in space and time can improve our knowledge of interactions between hosts and parasites. However, no studies have combined information on the laying activity of an obligate brood parasite with detailed information on the distribution of host nests within an area and time period. Here, we used molecular methods and analysis of egg phenotypes to determine maternal identity of common cuckoo, Cuculus canorus, eggs and chicks found in the nests of four species of Acrocephalus warblers in consecutive years. The median size of a cuckoo female laying area (calculated as a minimum convex polygon) was correlated negatively with the density of host nests and positively with the number of eggs assigned to a particular female. Cuckoo female laying areas overlapped to a large extent and their size and location did not change between years. Cuckoo females preferentially parasitized host nests located close to their previously parasitized nests and were mostly host specific except for two that parasitized two host species. Future studies should focus on sympatric host and parasite communities with variable densities across different brood-parasitic systems to investigate how population density of hosts affects fitness and evolution of brood parasites. For instance, it remains unknown whether female parasites moving to new sites need to meet a threshold density of a potential host. In addition, young females may be more limited in their egg laying, particularly with respect to the activity of other parasites and hosts, than older females

Data from: Phenotypic resources immortalized in a panel of wild-derived strains of five species of house mice

&lt;p&gt;The house mouse, &lt;em&gt;Mus musculus&lt;/em&gt;, is a widely used animal model in biomedical research, with classical laboratory strains (CLS) being the most frequently employed. However, the limited genetic variability in CLS hinders their applicability in evolutionary studies. Wild-derived strains (WDS), on the other hand, provide a suitable resource for such investigations. To assess the proportion of variation added by wild progenitors, we estimated phenotypic variation in 84 WDS representing 5 species (&lt;em&gt;M. musculus&lt;/em&gt;, &lt;em&gt;M. spretus&lt;/em&gt;, &lt;em&gt;M. spicilegus&lt;/em&gt;, &lt;em&gt;M. macedonicus&lt;/em&gt;, &lt;em&gt;M. caroli&lt;/em&gt;), 3 subspecies (&lt;em&gt;M. m. musculus&lt;/em&gt;, &lt;em&gt;M. m. domesticus&lt;/em&gt;, &lt;em&gt;M. m. castaneus&lt;/em&gt;), and compared it with 5 CLS. The spectrum of WDS captures long-term mouse evolution, estimated to be over 5 million years ago since the split of &lt;em&gt;M. caroli&lt;/em&gt; from the remaining mouse species. All mice are housed in a conventional breeding facility (without a nanofilter barrier or specific-pathogen free condition) at the Institute of Vertebrate Biology, Czech Academy of Sciences, in Studenec. They are maintained under standard conditions: light/dark regime of 14/10 hours, temperatures of 23 ± 1 °C during summer (April-September) and 22 ± 1 °C during winter (October-March), respectively, and relative humidity within 40-70 %. Mice have access to food pellets and tap water &lt;em&gt;ad libitum&lt;/em&gt;. Further data on this mouse repository and WDS can be obtained at &lt;a href="https://housemice.cz/en/strains/"&gt;https://housemice.cz/en/strains/&lt;/a&gt;.&lt;/p&gt; &lt;p&gt;Morphological traits were measured in 4335 mice and include body weight, spleen weight, body length, tail length, weight of both ovaries, sperm count, the weight of testes, left epididymis, and seminal vesicles. Reproductive ability was estimated in 87 WDS and 8 CLS. This dataset was obtained from 90,077 offspring born to 8,298 mothers in 17,049 litters recorded in Studenec studbooks between 2000 and 2023. Reproductive performance was characterized by litter size, newborn mortality (calculated as the proportion of stillborn or cannibalized mice across all litters), and the number of generations produced per year. We also estimated the time since a WDS was established from wild progenitors until completing 20 generations of strict brother-sister mating, i.e., the generation at which a strain of mice can be considered inbred.&lt;/p&gt; &lt;p&gt;Although CLS resemble &lt;em&gt;M. m. domesticus&lt;/em&gt; and&lt;em&gt; M. m. musculus &lt;/em&gt;WDS, they differ from them in 8 and 11 out of 15 phenotypic traits, respectively. The data suggest that WDS can be a useful tool in evolutionary studies, providing a basis for comparative analyses with other mammal taxa, particularly classical laboratory mice. The detected stunning phenotypic variation supplemented by genetic variation have great potential for medical applications.&lt;/p&gt;&lt;p&gt;Funding provided by: Czech Science Foundation&lt;br&gt;Crossref Funder Registry ID: https://ror.org/01pv73b02&lt;br&gt;Award Number: 21-28491S&lt;/p&gt;&lt;p&gt;Funding provided by: Czech Academy of Sciences&lt;br&gt;Crossref Funder Registry ID: https://ror.org/053avzc18&lt;br&gt;Award Number: &lt;/p&gt;&lt;p&gt;Funding provided by: Czech Science Foundation&lt;br&gt;Crossref Funder Registry ID: https://ror.org/01pv73b02&lt;br&gt;Award Number: 19-19056S&lt;/p&gt;&lt;p&gt;The measures presented in four csv files were obtained from fresh mice immediately after sacrifice, and the units of variables are specified as millimeters (mm) for length measures and grams for mass measures.&lt;/p&gt

The Spread of an Advantageous Allele Across a Barrier: The Effects of Random Drift and Selection Against Heterozygotes

A local barrier to gene flow will delay the spread of an advantageous allele. Exact calculations for the deterministic case show that an allele that is favorable when rare is delayed very little even by a strong barrier: its spread is slowed by a time proportional to log((B/σ)√2S)/S, where B is the barrier strength, σ the dispersal range, and fitnesses are 1:1 + S:1 + 2S. However,when there is selection against heterozygotes, such that the allele cannot increase from low frequency, a barrier can cause a much greater delay. If gene flow is reduced below a critical value, spread is entirely prevented. Stochastic simulations show that with additive selection, random drift slows down the spread of the allele, below the deterministic speed of σ√2S. The delay to the advance of an advantageous allele caused by a strong barrier can be substantially increased by random drift and increases with B/(2Sρσ2) in a one-dimensional habitat of density ρ. However, with selection against heterozygotes, drift can facilitate the spread and can free an allele that would otherwise be trapped indefinitely by a strong barrier. We discuss the implications of these results for the evolution of chromosome rearrangements.</jats:p

The house mouse chromosomal hybrid zone in Valtellina (SO): a summary of past and present research

&lt;strong&gt;Abstract&lt;/strong&gt; Karyotypic variation due to the centric (Robertsonian: Rb) fusion of chromosomes is a widespread phenomenon among small mammal species. In 1993, we described a house mouse chromosomal hybrid zone in Upper Valtellina (SO). Here, we found mice with 32 different karyotypes, including the standard, or all-acrocentric race (2n=40), four Rb races (2n=22-26) and 27 hybrid types (2n=23-39). This hybrid zone presents a unique opportunity to study the role of Rb fusions and races in speciation. We have been studying this dynamic hybrid system using a wide variety of techniques: karyology, histology, breeding, mark-recapture and DNA sequencing. All four Rb races appear to be closely related, but 40AA has probably been introduced recently into the valley. However, the fertility of laboratory-reared hybrids between several of these races (24UV, 26POS, 40AA) are lower than expected compared to homozygotes and previous studies. Effective subpopulation size and migration rates within and between villages are also relatively low. We discuss the use of these parameters to study the process of speciation in ongoing computer simulations