Sex chromosomes and mating‐type chromosomes can display large genomic regions without recombination. Recombination suppression often extended stepwise with time away from the sex‐ or ...mating‐type‐determining genes, generating evolutionary strata of differentiation between alternative sex or mating‐type chromosomes. In anther‐smut fungi of the Microbotryum genus, recombination suppression evolved repeatedly, linking the two mating‐type loci and extended multiple times in regions distal to the mating‐type genes. Here, we obtained high‐quality genome assemblies of alternative mating types for four Microbotryum fungi. We found an additional event of independent chromosomal rearrangements bringing the two mating‐type loci on the same chromosome followed by recombination suppression linking them. We also found, in a new clade analysed here, that recombination suppression between the two mating‐type loci occurred in several steps, with first an ancestral recombination suppression between one of the mating‐type locus and its centromere; later, completion of recombination suppression up to the second mating‐type locus occurred independently in three species. The estimated dates of recombination suppression between the mating‐type loci ranged from 0.15 to 3.58 million years ago. In total, this makes at least nine independent events of linkage between the mating‐type loci across the Microbotryum genus. Several mating‐type locus linkage events occurred through the same types of chromosomal rearrangements, where similar chromosome fissions at centromeres represent convergence in the genomic changes leading to the phenotypic convergence. These findings further highlight Microbotryum fungi as excellent models to study the evolution of recombination suppression.
Multiple events of recombination suppression in homologous mating‐type chromosomes.
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2.
Assortative Mating in Animals Jiang, Yuexin; Bolnick, Daniel I.; Kirkpatrick, Mark
The American naturalist,
06/2013, Volume:
181, Issue:
6
Journal Article
Peer reviewed
Open access
Assortative mating occurs when there is a correlation (positive or negative) between male and female phenotypes or genotypes across mated pairs. To determine the typical strength and direction of ...assortative mating in animals, we carried out a meta-analysis of published measures of assortative mating for a variety of phenotypic and genotypic traits in a diverse set of animal taxa. We focused on the strength of assortment within populations, excluding reproductively isolated populations and species. We collected 1,116 published correlations between mated pairs from 254 species (360 unique species-trait combinations) in five phyla. The mean correlation between mates was 0.28, showing an overall tendency toward positive assortative mating within populations. Although 19% of the correlations were negative, simulations suggest that these could represent type I error and that negative assortative mating may be rare. We also find significant differences in the strength of assortment among major taxonomic groups and among trait categories. We discuss various possible reasons for the evolution of assortative mating and its implications for speciation.
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The mode in which sexual organisms choose mates is a key evolutionary process, as it can have a profound impact on fitness and speciation. One way to study mate choice in the wild is by measuring ...trait correlation between mates. Positive assortative mating is inferred when individuals of a mating pair display traits that are more similar than those expected under random mating while negative assortative mating is the opposite. A recent review of 1134 trait correlations found that positive estimates of assortative mating were more frequent and larger in magnitude than negative estimates. Here, we describe the scale-of-choice effect (SCE), which occurs when mate choice exists at a smaller scale than that of the investigator's sampling, while simultaneously the trait is heterogeneously distributed at the true scale-of-choice. We demonstrate the SCE by Monte Carlo simulations and estimate it in two organisms showing positive (Littorina saxatilis) and negative (L. fabalis) assortative mating. Our results show that both positive and negative estimates are biased by the SCE by different magnitudes, typically toward positive values. Therefore, the low frequency of negative assortative mating observed in the literature may be due to the SCE's impact on correlation estimates, which demands new experimental evaluation.
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The large body of theory on speciation with gene flow has brought to light fundamental differences in the effects of two types of mating rules on speciation: preference/trait rules, in which ...divergence in both (female) preferences and (male) mating traits is necessary for assortment, and matching rules, in which individuals mate with like individuals on the basis of the presence of traits or alleles that they have in common. These rules can emerge from a variety of behavioral or other mechanisms in ways that are not always obvious. We discuss the theoretical properties of both types of rules and explain why speciation is generally thought to be more likely under matching rather than preference/trait rules. We furthermore discuss whether specific assortative mating mechanisms fall under a preference/trait or matching rule, present empirical evidence for these mechanisms, and propose empirical tests that could distinguish between them. The synthesis of the theoretical literature on these assortative mating rules with empirical studies of the mechanisms by which they act can provide important insights into the occurrence of speciation with gene flow. Finally, by providing a clear framework we hope to inspire greater alignment in the ways that both theoreticians and empiricists study mating rules and how these rules affect speciation through maintaining or eroding barriers to gene flow among closely related species or populations.
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Partial prezygotic isolation is often viewed as more important than partial postzygotic isolation (low fitness of hybrids) early in the process of speciation. I simulate secondary contact between two ...populations (species) to examine effects of assortative mating and low hybrid fitness in preventing blending. A small reduction in hybrid fitness (e.g., by 10%) produces a narrower hybrid zone than a strong but imperfect mating preference (e.g., 10 times stronger preference for conspecific over heterospecific mates). In the latter case, rare F1 hybrids find each other attractive (due to assortative mating), leading to the buildup of a continuum of intermediates. The weakness of assortative mating compared with reduced fitness of hybrids in preventing blending is robust to varying genetic bases of these traits. Assortative mating is most powerful in limiting blending when it is encoded by a single locus or is essentially complete, or when there is a large mate search cost. In these cases assortative mating is likely to cause hybrids to have low fitness, due to frequency-dependent mating disadvantage of individuals of rare mating types. These results prompt a questioning of the concept of partial prezygotic isolation, since it is not very isolating unless there is also postzygotic isolation.
Age shapes fundamental processes related to behaviour, survival and reproduction, where age influences reproductive success, non‐random mating with respect to age can magnify or mitigate such ...effects. Consequently, the correlation in partners' age across a population may influence its productivity. Despite widespread evidence for age‐assortative mating, little is known about what drives this assortment and its variation. Specifically, the relative importance of active (same‐age mate preference) and passive processes (assortment as a consequence of other spatial or temporal effects) in driving age assortment is not well understood.
In this paper, we compare breeding data from a great tit and mute swan population (51‐ and 31‐year datasets, respectively) to tease apart the contributions of pair retention, cohort age structure and active age‐related mate selection to age assortment in species with contrasting life histories.
Both species show age‐assortative mating and variable assortment between years. However, we demonstrate that the drivers of age assortment differ between the species, as expected from their life histories and resultant demographic differences. In great tits, pair fidelity has a weak effect on age‐assortative mating through pair retention; variation in age assortment is primarily driven by fluctuations in age structure from variable juvenile recruitment. Age‐assortative mating is, therefore, largely passive, with no evidence consistent with active age‐related mate selection. In mute swans, age assortment is partly explained by pair retention, but not population age structure, and evidence exists for active age‐assortative pairing.
This difference is likely to result from shorter life‐spans in great tits compared with mute swans, leading to fundamental differences in their population age structure, whereby a larger proportion of great tit populations consist of a single age cohort. In mute swans, age‐assortative pairing through mate selection may also be driven by greater age‐dependent variation in fitness.
The study highlights the importance of considering how different life histories and demographic differences arising from these affect population processes that appear congruent across species. We suggest that future research should focus on uncovering the proximate mechanisms that lead to variation in active age‐assortative mate selection (as seen in mute swans); and the consequences of variation in age structure on the ecological and social functioning of wild populations.
Age‐assortative mating in animals is widespread, but the underlying causes are often looked past. Using two species at either end of the fast–slow continuum of life history, it is revealed that the mechanisms underpinning age assortment are distinct despite generating similar patterns, driven by demographic differences in the populations.
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Seminal fluid proteins (SFPs) produced in reproductive tract tissues of male insects and transferred to females during mating induce numerous physiological and behavioral postmating changes in ...females. These changes include decreasing receptivity to remating; affecting sperm storage parameters; increasing egg production; and modulating sperm competition, feeding behaviors, and mating plug formation. In addition, SFPs also have antimicrobial functions and induce expression of antimicrobial peptides in at least some insects. Here, we review recent identification of insect SFPs and discuss the multiple roles these proteins play in the postmating processes of female insects.
Bateman's classic paper on fly mating systems inspired quantitative study of sexual selection but also resulted in much debate and confusion. Here, I consider the meaning of Bateman's principles in ...the context of selection theory. Success in precopulatory sexual selection can be quantified as a “mating differential,” which is the covariance between trait values and relative mating success. The mating differential is converted into a selection differential by the Bateman gradient, which is the least squares regression of relative reproductive success on relative mating success. Hence, a complete understanding of precopulatory sexual selection requires knowledge of two equally important aspects of mating patterns: the mating differential, which requires a focus on mechanisms generating covariance between trait values and mating success, and the Bateman gradient, which requires knowledge of the genetic mating system. An upper limit on the magnitude of the selection differential on any sexually selected trait is given by the product of the standard deviation in relative mating success and the Bateman gradient. This latter view of the maximum selection differential provides a clearer focus on the important aspects of precopulatory sexual selection than other methods and therefore should be an important part of future studies of sexual selection.
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In this innovative celebration of diversity and affirmation of individuality in animals and humans, Joan Roughgarden challenges accepted wisdom about gender identity and sexual orientation. A ...distinguished evolutionary biologist, Roughgarden takes on the medical establishment, the Bible, social science--and even Darwin himself. She leads the reader through a fascinating discussion of diversity in gender and sexuality among fish, reptiles, amphibians, birds, and mammals, including primates. Evolution's Rainbow explains how this diversity develops from the action of genes and hormones and how people come to differ from each other in all aspects of body and behavior. Roughgarden reconstructs primary science in light of feminist, gay, and transgender criticism and redefines our understanding of sex, gender, and sexuality. Witty, playful, and daring, this book will revolutionize our understanding of sexuality. Roughgarden argues that principal elements of Darwinian sexual selection theory are false and suggests a new theory that emphasizes social inclusion and control of access to resources and mating opportunity. She disputes a range of scientific and medical concepts, including Wilson's genetic determinism of behavior, evolutionary psychology, the existence of a gay gene, the role of parenting in determining gender identity, and Dawkins's "selfish gene" as the driver of natural selection. She dares social science to respect the agency and rationality of diverse people; shows that many cultures across the world and throughout history accommodate people we label today as lesbian, gay, and transgendered; and calls on the Christian religion to acknowledge the Bible's many passages endorsing diversity in gender and sexuality. Evolution's Rainbow concludes with bold recommendations for improving education in biology, psychology, and medicine; for
democratizing genetic engineering and medical practice; and for building a public monument to affirm diversity as one of our nation's defining principles.
Six llamas and 6 alpacas were mated to vasectomized males; ovulation and corpus luteum formation followed. Progesterone in blood was elevated from day 5 and reached maximum concentrations of 10–20 ...nmol/1 on day 7–8. A rapid decline in progesterone levels occurred on day 9–10 in connection with repeated surge releases of prostaglandin F
2α
. Oestradiol-17β levels were > 100–200 pmol/1 during oestrus when the animals were mated. These high levels might have been caused by coital stimulation. A temporary increase was detected in connection with the rise in progesterone levels in the early luteal phase. With this exception levels of oestradiol stayed low, 20–40 pmol/1 during the luteal phase but rose in most animals after luteolysis to 40–60 pmol/1.
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