scholarly journals The role of pseudo-overdominance in maintaining inbreeding depression

2021 ◽  
Author(s):  
Diala Abu Awad ◽  
Donald M Waller
Keyword(s):  
Inbreeding Depression ◽  
Mating Systems ◽  
Balancing Selection ◽  
Background Selection ◽  
Recessive Mutations ◽  
Tight Linkage ◽  
Classical Models ◽  
Inbred Populations ◽  
Selective Effects

Classical models ignoring linkage predict that deleterious recessive mutations purge or fix within inbred populations, yet these often retain moderate to high segregating load. True overdominance generates balancing selection that sustains inbreeding depression even in inbred populations but is rare. In contrast, arrays of mildly deleterious recessives linked in repulsion may occur commonly enough to generate pseudo-overdominance and sustain segregating load. We used simulations to explore how long pseudo-overdominant regions (POD's) persist following their creation via hybridization between populations fixed for alternative mutations at linked loci. Balancing haplotype loads, tight linkage, and moderate to strong cumulative selective effects serve to maintain POD's, suggesting that POD's may most often arise and persist in low recombination regions (e.g., inversions). Selection and drift unbalance the load, eventually eliminating POD's, but this process is very slow when pseudo-overdominance is strong. Background selection across the genome accelerates the loss of weak POD's but reinforces strong POD's in inbred populations by disfavoring homozygotes. Further modeling and studies of POD dynamics within populations could help us understand how POD's affect persistence of the load and how inbred mating systems evolve.

scholarly journals Why do Inbreeding Depression and Load Resist Both Purging and Fixation?

2020 ◽  
Author(s):  
Donald Waller
Keyword(s):  
Inbreeding Depression ◽  
Empirical Studies ◽  
Intermediate Frequency ◽  
Comparative Genomic ◽  
Background Selection ◽  
Recessive Mutations ◽  
Genomic Analyses ◽  
Genetic Signatures ◽  
Inbred Populations ◽  
Sufficient Strength

Upon inbreeding, the architecture of the inbreeding load shifts as selection purges strongly deleterious recessive mutations and drift fixes many milder ones. Most small inbred populations show limited genetic variation while crosses between such populations commonly express pronounced heterosis, confirming fixation. In contrast, purging appears to be limited in that inbred populations often retain substantial inbreeding depression. In addition we have the enigma Darwin noted: purely selfing taxa are unknown. Because both purging and fixation reduce inbreeding depression and load, another mechanism must exist to sustain these. Background selection and the associations that develop among alleles in small inbred populations will shift the architecture of the load potentially creating blocks of recessive mutations linked in repulsion. This would generate pseudo-overdominance that could sustain these “PODs” and inbreeding load. Recombination and crosses between lineages could erode PODs. Crosses between populations fixed for different mutations would generate high pseudo-overdominance, enhancing heterosis and potentially POD formation. New recessive mutations arising within PODs would reinforce overdominance. PODs should generate clear genetic signatures including genomic hotspots of heterozygosity and linkage disequilibrium containing alleles at intermediate frequency generating segregating load. Results from several simulation and empirical studies match these predictions. Further simulations and comparative genomic analyses are needed to rigorously test whether PODs exist in sufficient strength and number to generate persistent inbreeding depression and load in inbred lineages.

scholarly journals Evidence for an epigenetic role in inbreeding depression

2012 ◽  
Vol 8 (5) ◽  
pp. 798-801 ◽  
Author(s):  
Philippine Vergeer ◽  
Niels (C. A. M.) Wagemaker ◽  
N. Joop Ouborg
Keyword(s):  
Inbreeding Depression ◽  
Evolutionary Biology ◽  
Quantitative Traits ◽  
Mating Systems ◽  
Epigenetic Variation ◽  
Perennial Plant ◽  
Fitness Effects ◽  
Demethylation Agent ◽  
Epigenetic Processes

Inbreeding depression (i.e. negative fitness effects of inbreeding) is central in evolutionary biology, affecting numerous aspects of population dynamics and demography, such as the evolution of mating systems, dispersal behaviour and the genetics of quantitative traits. Inbreeding depression is commonly observed in animals and plants. Here, we demonstrate that, in addition to genetic processes, epigenetic processes may play an important role in causing inbreeding effects. We compared epigenetic markers of outbred and inbred offspring of the perennial plant Scabiosa columbaria and found that inbreeding increases DNA methylation. Moreover, we found that inbreeding depression disappears when epigenetic variation is modified by treatment with a demethylation agent, linking inbreeding depression firmly to epigenetic variation. Our results suggest an as yet unknown mechanism for inbreeding effects and demonstrate the importance of evaluating the role of epigenetic processes in inbreeding depression.

scholarly journals Genetic sex determination and sex-specific lifespan in tetrapods – evidence of a toxic Y effect

2020 ◽  
Author(s):  
Zahida Sultanova ◽  
Philip A. Downing ◽  
Pau Carazo
Keyword(s):  
Sex Chromosomes ◽  
Alternative Hypothesis ◽  
Z Chromosome ◽  
W Chromosome ◽  
Deleterious Mutations ◽  
Recessive Mutations ◽  
Y Chromosomes ◽  
Heterogametic Sex ◽  
Taxonomic Patterns

ABSTRACTSex-specific lifespans are ubiquitous across the tree of life and exhibit broad taxonomic patterns that remain a puzzle, such as males living longer than females in birds and vice versa in mammals. The prevailing “unguarded-X” hypothesis (UXh) explains this by differential expression of recessive mutations in the X/Z chromosome of the heterogametic sex (e.g., females in birds and males in mammals), but has only received indirect support to date. An alternative hypothesis is that the accumulation of deleterious mutations and repetitive elements on the Y/W chromosome might lower the survival of the heterogametic sex (“toxic Y” hypothesis). Here, we report lower survival of the heterogametic relative to the homogametic sex across 138 species of birds, mammals, reptiles and amphibians, as expected if sex chromosomes shape sex-specific lifespans. We then analysed bird and mammal karyotypes and found that the relative sizes of the X and Z chromosomes are not associated with sex-specific lifespans, contrary to UXh predictions. In contrast, we found that Y size correlates negatively with male survival in mammals, where toxic Y effects are expected to be particularly strong. This suggests that small Y chromosomes benefit male lifespans. Our results confirm the role of sex chromosomes in explaining sex differences in lifespan, but indicate that, at least in mammals, this is better explained by “toxic Y” rather than UXh effects.

scholarly journals Maternal effects alter the severity of inbreeding depression in the offspring

2016 ◽  
Vol 283 (1838) ◽  
pp. 20161023 ◽  
Author(s):  
Natalie Pilakouta ◽  
Per T. Smiseth
Keyword(s):  
Maternal Effects ◽  
Inbreeding Depression ◽  
Potential Role ◽  
Causal Effect ◽  
Natural Populations ◽  
Larval Survival ◽  
Burying Beetle ◽  
Nicrophorus Vespilloides ◽  
Selection For

A maternal effect is a causal influence of the maternal phenotype on the offspring phenotype over and above any direct effects of genes. There is abundant evidence that maternal effects can have a major impact on offspring fitness. Yet, no previous study has investigated the potential role of maternal effects in influencing the severity of inbreeding depression in the offspring. Inbreeding depression is a reduction in the fitness of inbred offspring relative to outbred offspring. Here, we tested whether maternal effects due to body size alter the magnitude of inbreeding depression in the burying beetle Nicrophorus vespilloides . We found that inbreeding depression in larval survival was more severe for offspring of large females than offspring of small females. This might be due to differences in how small and large females invest in an inbred brood because of their different prospects for future breeding opportunities. To our knowledge, this is the first evidence for a causal effect of the maternal phenotype on the severity of inbreeding depression in the offspring. In natural populations that are subject to inbreeding, maternal effects may drive variation in inbreeding depression and therefore contribute to variation in the strength and direction of selection for inbreeding avoidance.

A genetic view on the role of prolonged drought stress and mating systems on post-drought recovery, persistence and drought memory of orchardgrass (Dactylis glomerata L.)

Euphytica ◽  
2020 ◽  
Vol 216 (6) ◽  
Author(s):  
Fatemeh Saeidnia ◽  
Mohammad Mahdi Majidi ◽  
Aghafakhr Mirlohi ◽  
Soheila Spanani ◽  
Zohreh Karami ◽  
...  
Keyword(s):  
Drought Stress ◽  
Mating Systems ◽  
Dactylis Glomerata ◽  
Prolonged Drought ◽  
Drought Recovery ◽  
Dactylis Glomerata L

scholarly journals No evidence for an adaptive role of early molt into breeding plumage in a female fairy wren

2019 ◽  
Vol 31 (2) ◽  
pp. 411-420
Author(s):  
Sergio Nolazco ◽  
Michelle L Hall ◽  
Sjouke A Kingma ◽  
Kaspar Delhey ◽  
Anne Peters
Keyword(s):  
Mating Systems ◽  
Reproductive Effort ◽  
Adaptive Function ◽  
Female Ornamentation ◽  
Extrapair Mating ◽  
Study Results ◽  
Selection For ◽  
Breeding Plumage ◽  
Adaptive Role

Abstract The evolution of ornaments as sexually selected signals is well understood in males, but female ornamentation remains understudied. Fairy wrens offer an excellent model system, given their complex social structure and mating systems, and the diversity of female ornamentation. We investigated whether early molt into ornamental breeding plumage plays an adaptive role in females of the monogamous purple-crowned fairy wren Malurus coronatus, the only fairy wren known to have female seasonal plumage. Using 6 years of monitoring, we found that the timing of female molt was similar to males, but there was no evidence for assortative mating. Like males (previous study), older and dominant individuals acquired their breeding plumage earlier; however, in contrast to males, early molt did not seem to be costly since unfavorable environmental conditions or previous reproductive effort did not delay molt. Early female molt was not associated with any indicator of reproductive quality nor did it attract additional offspring care by their partners. We also found no association between early molt and the likelihood of acquiring a dominant (breeding) position or with the presence or proximity to same-sex rivals. Our study results, which are similar to previous findings in conspecific males, suggest that directional selection for early molt might be relaxed in this species, in contrast to other genetically polygamous fairy wrens in which early molt predicts extrapair mating success in males. However, the finding that molt timing is status dependent raises the possibility that other attributes of the ornament may fulfill an adaptive function in females.

scholarly journals Beyond sex allocation: the role of mating systems in sexual selection in parasitoid wasps

2014 ◽  
Vol 90 (2) ◽  
pp. 599-627 ◽  
Author(s):  
Rebecca A. Boulton ◽  
Laura A. Collins ◽  
David M. Shuker
Keyword(s):  
Sexual Selection ◽  
Sex Allocation ◽  
Mating Systems ◽  
Parasitoid Wasps
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