DOCSLIB.ORG

Inviability and Sperm Motility Between Drosophila Simulans and D

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Inviability and Sperm Motility Between Drosophila Simulans and D Heredity 78 (1997)354—362 Received/8 December 1995 Genetic basis of sperm and testis length differences and epistatic effect on hybrid inviability and sperm motility between Drosophila simulans and D. secheiia DOMINIQUE JOLY*t, CLAUDE BAZINt, LING-WEN ZENG & RAMA S. SINGH tLaboratofre Populations, Genétique et Evolution, CNRS 91198 Gifsur Yvette Cedex, France, lDepartment of Ecology and Evolution, 1101 E. 57th St., The University of Chicago, Chicago, IL 60637, USA and §Department of Biology, MacMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1 Resultsare reported from a genetic study of hybrid inviability and three 'fertilization traits' (sperm motility and length, and testis size) that affect hybrid sterility between the sibling species Drosophila simulans and D. sechellia. The main findings are as follows. (i) For sperm length there was a dominant effect of the D. simulans genome over that of D. sechellia, and the Y chromosome of D. sechellia in the background of D. simulans reduced the sperm length. (ii) In contrast, testis length, in spite of its generally high correlation with sperm length, showed an additive effect. (iii) We found a strong asymmetric incompatibility between the D. sechellia X chromosome and D. simulans autosomes: D. sechellia X chromosome with D. simulans auto- somes, but not the reverse, showed a significant reduction in testis length as well as in hybrid inviability compared to the parental species. (iv) Between the two autosomes, chromosome 3 had a greater effect on these traits than chromosome 2, and there was additionally an epistatic effect between these chromosomes with respect to their parental vs. recombinant status: recombinant chromosomes 2 and 3, together, had lower viability than any other combination. (v) The testis size in the backcross generation was greater than the parental species, suggesting that some modifier genes are being released from their species-specific genetic control. (vi) The species-specific homogeneity of the genome was important for all three traits—offspring viability, hybrid male fertility and testis length. These results are discussed with respect to the role of sexual selection and genetic divergence during speciation. Keywords:Drosophila,epistatic effect, speciation, species differences, sperm length, testis length. Introduction Zouros et al., 1988; Zeng & Singh, 1993a,b, 1995). Previous studies have generally focused on hybrid Thegenetic mechanisms of species formation is one male sterility and relatively little attention has been of the most challenging problems in evolutionaty paid to hybrid inviability; this approach was intended biology and we have seen the resurgence of a to identify genes affecting hybrid sterility. Species renewed interest in these mechanisms (see Orr, differ in more than reproductive isolation, so a 1991; Coyne, 1992; Pantazidis et a!., 1993). One way broader approach, including all traits affecting to approach this problem is to study the genetic reproduction, is required. This report combines the basis of reproductive isolation between related two approaches. Sperm length is an excellent trait species and this has currently become the favoured for studying species differences as it is species- experimental approach (Dobzhansky, 1936; Zouros, specific and is the most rapidly evolving trait in 1981; Wu & Beckenbach, 1983; Coyne, 1984, 1985, insects (Joly et al., 1989, 1991). Drosophila species 1993; Coyne & Kreitman, 1986; Orr, 1987, 1989; are good candidates on which to perform such an investigation because they encompass the extreme *Correspondence E-mail: joly@sunbge,bge.cnrs-gif.fr range of sperm length variation in all invertebrates, 354 1997The Genetical Society of Great Britain. GENETICS OF SPECIATION 355 ranging from 33 em in D. subobscura (Joly et al., was not successful. All stocks and crosses were 1989) to nearly 6 cm in D. bifurca (Joly et a!., 1995). reared in 8-dram vials on banana medium at This study reports the genetic analysis of hybrid 21—23°C. inviability and three strongly related fertilization traits, sperm length and motility and testis size, in Y chromosome introgression the sibling species D. simulans and D. sechellia from Interspecific the melanogaster complex. These species are closely Toexamine the effect of the Y chromosome on related (Coyne, 1984; Lachaise et a!., 1986). Their sperm length between D. simulans and D. sechellia, chromosomes are entirely homosequential and we introgressed the Y chromosome of D. sechellia crosses (D. simulans female by D. sechellia males) into the background of D. simulans. The method can be easily made giving fertile, hybrid females and used is the same as described in Zeng & Singh sterile, hybrid males (Lemeunier & Ashburner, (1993b). F hybrid females were backcrossed to 1984). Drosophila sechellia sperm length has strongly males of D. sechellia and the resulting backcross diverged from that of the mauritiana-simulans pair, males were crossed to D. simulans females. The being almost one and a half times as long as that of males produced in this cross, which carried the Y D. simulans (1.6 and 1.2 mm, respectively; Joly, chromosome of D. sechellia, were then crossed to D. 1987). simulans females repeatedly to replace other The results show interesting differences in the chromosomes by those of D. simulans. effects of sex chromosomes, autosomes and their interactions on hybrid inviability and sterility, sperm Testisdissection, s/ide preparation and sperm length and motility and testis size. length measurement Brokensperm are indistinguishable from intact Materialand methods sperm, so it is problematic to measure individual sperm longer than 1 mm directly. Instead, the length Species stocks, genetic markers and crossing of bundles of fully elongated mature cysts were scheme measured in the testis. Sperm and mature cysts of AD.simulansstrain homozygous for a recessive one species have similar lengths and the latter could mutant marker on each of the five major chromo- be identified as a fully elongated cyst by the charac- some arms, and a D. sechellia strain (Robertson) teristic aspects of the extremities (one is occupied by were supplied courtesy of Dr Jerry Coyne. The five the sperm head which begins to spread and the mutant markers are forked-2 on the X chromosome other by what will form the waste bag at the sperm individualization stage). This method allows rapid (f2:1-60),net and plum on the second chromosome (nt: 11-2, 2L; pm: 11-103, 2R), and scarlet and ebony measurement of large numbers of samples. Pure- on the third chromosome (st: 111-44, 3L; e: 111-71, species males and backcross males with different 3R). The tiny fourth chromosome was not studied phenotypes were dissected in saline solution because no marker was available. The crossing (Ringer) on microscope slides using a pair of forceps scheme is the same as used by Dobzhansky (1937) and a dissecting needle. Testes were separated from and others (Coyne, 1985; Coyne & Kreitman, 1986; seminal vesicles and the rest of the male reproduc- Orr, 1989). Females of the marker strain were tive tract. Cysts were spread out of the testes, and crossed to D. sechellia males and the F1 hybrid separated from each other by using a very fine females were backcrossed to D. simulans (f2;ntpm; needle. The slides with the cysts or the testis (only St e) males producing offspring with different one testis per male) were allowed to dry at room combinations of D. simulans and D. sechellia temperature, fixed with 95 per cent ethanol for 4 chromosomes. The identity of these chromosomes or mm, dried again, and then stained with 2 per cent chromosomal regions was read from the individual's aceto-orcein solution. They were finally washed with phenotype. By examining a trait of each backcross distilled water, dried and sealed with permanent phenotype, one can determine the effect of each mounting medium. chromosomal combination on that trait. We exam- The cyst and testis length measurements were ined four different traits between species or between aided by using the public domain program NIH species and their hybrids: sperm and testis lengths, IMAGE. This program (written by W. Rasband at the hybrid male sperm motility, and viability of back- US National Institutes of Health) can be obtained cross offsprings. The reciprocal F1 (the cross through anonymous ftp from zippy.nimh.nih.gov and between D. sechellia females and D. simulans males) runs on a Macintosh computer which was connected The Genetical Society of Great Britain, Heredily, 78, 354—362. 356 D. JOLY ETAL. to a dissecting microscope through a video camera Viability effects (Hitachi, model VK-C150). Because previous studies have shown little interindividual variation (Joly, TheX chromosomal effect on hybrid viability can be 1987), 50 cysts for one male from each parental determined by comparing the same autosomal geno- species and F1 hybrids were measured. In the back- types segregating with the D. simulans or D. sechellia cross progeny, 15 cysts per male and 25 males per X chromosome. In this experiment the Y chromo- phenotype were analysed. In the following sections, some comes from D. simulans. In Table 1 we can see the measures are called sperm length but are made that the X chromosomes, regardless of their origin on the cyst. The mean testis length was based on the (from D. sechellia or D. simulans), have no effect mean of 25 independent testes for each phenotype. when autosomes were heterozygous (1/2 D. sechellia and 1/2 D. simulans, 617 and 608, respectively). On the contrary, when autosomes were homozygous Results from D. simulans (iv' pm; st e) the X chromosome of D. sechellia had a significant reduction in the F1male hybrids between D. simulans females and D. number of progeny (440) compared to the X sechellia are perfectly viable but sterile. To inves- chromosome of D. simulans progeny (626). tigate the autosomal or sex chromosomal contribu- The viability of males from the 16 backcross tion to male viability and sterility we have analysed phenotypes having the X chromosome from D.
Load more

Recommended publications
  • Reproductive Mode and Speciation: the Viviparity-Driven Conflict Liypothesis David W
    Hypothesis Reproductive mode and speciation: the viviparity-driven conflict liypothesis David W. Zeh* and Jeanne A. Zeh Summary in the speciation process.*^"®' With patterns in nature (see In birds and frogs, species pairs retain the capacity to below) exhibiting profound between-lineage differences in produce viable hybrids for tens of millions of years, an order of magnitude longer than mammals. What the relative rates at which pre- and postzygotic isolation accounts for these differences in relative rates of pre- evolve,*^~^°' a unifying theory of speciation has remained and postzygotic isolation? We propose that reproduc- elusive. Here, we present a new hypothesis to account for the tive mode is a critically important but previously over- extreme disparity that exists between lineages in patterns of looked factor in the speciation process. Viviparity speciation. This viviparity-driven conflict hypothesis proposes creates a post-fertilization arena for genomic conflicts absent in egg-laying species. With viviparity, conflict that the reproductive stage at which divergence occurs most can arise between: mothers and embryos; sibling rapidly between populations is strongly influenced by the embryos in the womb, and maternal and paternal degree to which embryonic development involves physiolo- genomes within individual embryos. Such intra- and gical interactions between mother and embryo. After briefly intergenomic conflicts result in perpetual antagonistic reviewing between-lineage differences in patterns of specia- coevolution, thereby accelerating interpopulation post- zygotic isolation. In addition, by generating intrapopula- tion, we develop the hypothesis that postzygotic isolation tion genetic incompatibility, viviparity-driven conflict should evolve more rapidly in viviparous animals than in favors polyandry and limits the potential for precopula- oviparous species, because development of the embryo tory divergence.
    [Show full text]
  • Coupling, Reinforcement, and Speciation Roger Butlin, Carole Smadja
    Coupling, Reinforcement, and Speciation Roger Butlin, Carole Smadja To cite this version: Roger Butlin, Carole Smadja. Coupling, Reinforcement, and Speciation. American Naturalist, Uni- versity of Chicago Press, 2018, 191 (2), pp.155-172. 10.1086/695136. hal-01945350 HAL Id: hal-01945350 https://hal.archives-ouvertes.fr/hal-01945350 Submitted on 5 Dec 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License vol. 191, no. 2 the american naturalist february 2018 Synthesis Coupling, Reinforcement, and Speciation Roger K. Butlin1,2,* and Carole M. Smadja1,3 1. Stellenbosch Institute for Advanced Study, Wallenberg Research Centre at Stellenbosch University, Stellenbosch 7600, South Africa; 2. Department of Animal and Plant Sciences, The University of Sheffield, Sheffield S10 2TN, United Kingdom; and Department of Marine Sciences, University of Gothenburg, Tjärnö SE-45296 Strömstad, Sweden; 3. Institut des Sciences de l’Evolution, Unité Mixte de Recherche 5554 (Centre National de la Recherche Scientifique–Institut de Recherche pour le Développement–École pratique des hautes études), Université de Montpellier, 34095 Montpellier, France Submitted March 15, 2017; Accepted August 28, 2017; Electronically published December 15, 2017 abstract: During the process of speciation, populations may di- Introduction verge for traits and at their underlying loci that contribute barriers Understanding how reproductive isolation evolves is key fl to gene ow.
    [Show full text]
  • Speciation Through Evolution of Sex-Linked Genes
    Heredity (2009) 102, 4–15 & 2009 Macmillan Publishers Limited All rights reserved 0018-067X/09 $32.00 www.nature.com/hdy SHORT REVIEW Speciation through evolution of sex-linked genes A Qvarnstro¨m and RI Bailey Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Norbyva¨gen, Uppsala, Sweden Identification of genes involved in reproductive isolation expectation but mainly in female-heterogametic taxa. By opens novel ways to investigate links between stages of the contrast, there is clear evidence for both strong X- and speciation process. Are the genes coding for ecological Z-linkage of hybrid sterility and inviability at later stages of adaptations and sexual isolation the same that eventually speciation. Hence genes coding for sexual isolation traits are lead to hybrid sterility and inviability? We review the role of more likely to eventually cause hybrid sterility when they are sex-linked genes at different stages of speciation based on sex-linked. We conclude that the link between sexual four main differences between sex chromosomes and isolation and evolution of hybrid sterility is more intuitive in autosomes; (1) relative speed of evolution, (2) non-random male-heterogametic taxa because recessive sexually antag- accumulation of genes, (3) exposure of incompatible onistic genes are expected to quickly accumulate on the recessive genes in hybrids and (4) recombination rate. At X-chromosome. However, the broader range of sexual traits early stages of population divergence ecological differences that are expected to accumulate on the Z-chromosome may appear mainly determined by autosomal genes, but fast- facilitate adaptive speciation in female-heterogametic spe- evolving sex-linked genes are likely to play an important role cies by allowing male signals and female preferences to for the evolution of sexual isolation by coding for traits with remain in linkage disequilibrium despite periods of gene flow.
    [Show full text]
  • The Genetic Basis of Reproductive Isolation: Insights from Drosophila
    Colloquium The genetic basis of reproductive isolation: Insights from Drosophila H. Allen Orr* Department of Biology, University of Rochester, Rochester, NY 14627 Recent studies of the genetics of speciation in Drosophila have number of new and careful studies of the biogeography, ecology, focused on two problems: (i) identifying and characterizing the and genetics of speciation, and we now understand a good deal genes that cause reproductive isolation, and (ii) determining the about the evolution of reproductive isolation (3). We can, for evolutionary forces that drove the divergence of these ‘‘speciation instance, describe the rate at which this reproductive isolation genes.’’ Here, I review this work. I conclude that speciation genes evolves (Fig. 1), and the ecological factors that drive speciation, correspond to ordinary loci having normal functions within species. at least in some cases (6). We can also point to plausible examples These genes fall into several functional classes, although a role in in which the process of reinforcement may have completed transcriptional regulation could prove particularly common. More speciation (3, 7, 8). Finally, we know a fair amount about the important, speciation genes are typically very rapidly evolving, and number and location of the genes that cause reproductive this divergence is often driven by positive Darwinian selection. isolation (at least in its postzygotic form), and the causes of Finally, I review recent work in Drosophila pseudoobscura on the patterns like Haldane’s rule (3, 9, 10). possible role of meiotic drive in the evolution of the genes that Given this progress, it is natural to ask: What now are the cause postzygotic isolation.
    [Show full text]
  • Inviability of Intergeneric Hybrids Involving Triticum Monococcum and T
    INVIABILITY OF INTERGENERIC HYBRIDS INVOLVING TRITICUM MONOCOCCUM AND T. AEGILOPOIDES’ E. R. SEARS U. S. Department of Agriculture, Columbia, Missouri Received July 26, 1943 INTRODUCTION ITH the development in recent years of colchicine techniques and other wreliable methods for doubling chromosome number in plants, interspecific and intergent -ic hybrids which formerly could not be maintained because of their sterility’can now easily be rendered fertile and true-breeding, The ready source of essehtially new species thereby made available is rather strictly lim- ited, however, by the failure of many crosses between reasonably close rela- tives to yield viable hybrids. Noteworthy progress has recently been made toward extending the limits of crossability. The discovery by LAIBACH(1925) that the embryos of certain inviable hybrid seeds can be dissected out and grown on artificial media, coupled with the recent development by VAN OVERBEEK,CONKLIN, and BLAKESLEE(1942) of methods for culturing extremely young embryos, should permit many otherwise impossible crosses to be made. Certain other devices, notably the style-shortening technique of MANGELSDORFand REEVES(1931) and the mixed pollinations of BEASLEY(1940), have served in special instances to make possible the production of hybrids. An important barrier to hybridization which cannot be overcome by any of the foregoing methods is the lethality of hybrid seedlings. In the genus Crepis, BABCOCKand NAVASHIN(1930) reported that 19 out of 103 interspecif- ic hybrids were abnormal or weak, in most cases dying before reaching the flowering stage; and EAST(1935a) found 14 inviable types in 77 hybrid com- binations in Nicotiana. The very early stage at which,some hybrid seedlings die makes it probable that there are numerous comparable instances where the embryo dies before maturity of the seed.
    [Show full text]
  • Mechanisms of Speciation
    International Journal of Evolutionary Biology Mechanisms of Speciation Guest Editors: Kyoichi Sawamura, Chau-Ti Ting, Artyom Kopp, and Leonie C. Moyle Mechanisms of Speciation International Journal of Evolutionary Biology Mechanisms of Speciation Guest Editors: Kyoichi Sawamura, Chau-Ti Ting, Artyom Kopp, and Leonie C. Moyle Copyright © 2012 Hindawi Publishing Corporation. All rights reserved. This is a special issue published in “International Journal of Evolutionary Biology.” All articles are open access articles distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Editorial Board Giacomo Bernardi, USA Kazuho Ikeo, Japan Jeffrey R. Powell, USA Terr y Burke, UK Yoh Iwasa, Japan Hudson Kern Reeve, USA Ignacio Doadrio, Spain Henrik J. Jensen, UK Y. Satta, Japan Simon Easteal, Australia Amitabh Joshi, India Koji Tamura, Japan Santiago F. Elena, Spain Hirohisa Kishino, Japan Yoshio Tateno, Japan Renato Fani, Italy A. Moya, Spain E. N. Trifonov, Israel Dmitry A. Filatov, UK G. Pesole, Italy Eske Willerslev, Denmark F. Gonza’lez-Candelas, Spain I. Popescu, USA Shozo Yokoyama, USA D. Graur, USA David Posada, Spain Contents Mechanisms of Speciation, Kyoichi Sawamura, Chau-Ti Ting, Artyom Kopp, and Leonie C. Moyle Volume 2012, Article ID 820358, 2 pages Cuticular Hydrocarbon Content that Affects Male Mate Preference of Drosophila melanogaster from West Africa, Aya Takahashi, Nao Fujiwara-Tsujii, Ryohei Yamaoka, Masanobu Itoh, Mamiko Ozaki, and Toshiyuki Takano-Shimizu Volume 2012, Article ID 278903, 10 pages Evolutionary Implications of Mechanistic Models of TE-Mediated Hybrid Incompatibility, Dean M. Castillo and Leonie C. Moyle Volume 2012, Article ID 698198, 12 pages DNA Barcoding and Molecular Phylogeny of Drosophila lini and Its Sibling Species, Yi-Feng Li, Shuo-Yang Wen, Kuniko Kawai, Jian-Jun Gao, Yao-Guang Hu, Ryoko Segawa, and Masanori J.
    [Show full text]
  • A Single Pleiotropic Locus Influences the Rate of Hybridization Between Two Sibling Species of Lygaeus Bugs
    Received: 7 April 2020 | Accepted: 8 September 2020 DOI: 10.1002/ece3.6853 ORIGINAL RESEARCH A single pleiotropic locus influences the rate of hybridization between two sibling species of Lygaeus bugs Vicki L. Balfour | Daniella Black | David M. Shuker School of Biology, University of St Andrews, St Andrews, UK Abstract The evolution of reproductive isolation lies at the heart of understanding the pro- Correspondence Vicki L. Balfour, School of Biology, Harold cess of speciation. Of particular interest is the relationship between pre- and postzy- Mitchell Building, University of St Andrews, gotic reproductive isolation, and the genetic architecture of traits that contribute to St Andrews, KY16 9TH, UK. Email: [email protected] one or both forms of reproductive isolation. The sibling species of seed bug Lygaeus equestris and L. simulans show a classic pattern of asymmetric prezygotic reproduc- tive isolation, with female L. equestris hybridizing with male L. simulans, but with no hybridization in the reciprocal direction. We have recently described a mutant pale color form of L. simulans, that inherits as a single Mendelian locus and is pleiotropic for a number of other life history and behavioral traits. Here, we tested whether this locus also influences pre- and postzygotic reproductive isolation. Two sets of experimental crosses revealed that behavioral isolation varied with mutant versus wild-type phenotype for male L. simulans, with the pale form less successful at mat- ing with female L. equestris. In terms of trying to assess postzygotic isolation, levels of hybrid offspring production were uniformly low across the experiments. However, we did obtain, for the first time, hybrid offspring from a pairing between a female L.
    [Show full text]
  • Duke University Dissertation Template
    Parental Conflict, Parent of Origin Effects, and the Evolution of Hybrid Seed Failure in Mimulus by Jennifer M. Coughlan Department of Biology Duke University Date:_______________________ Approved: ___________________________ John Willis, PhD, Supervisor ___________________________ Kathleen Donohue, PhD ___________________________ Mark Rausher, PhD ___________________________ Mohamed Noor, PhD ___________________________ Thomas Mitchell-Olds Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biology in the Graduate School of Duke University 2018 i v ABSTRACT Parental Conflict, Parent of Origin Effects, and the Evolution of Hybrid Seed Failure in Mimulus by Jennifer M. Coughlan Department of Biology Duke University Date:_______________________ Approved: ___________________________ John Willis, PhD, Supervisor ___________________________ Kathleen Donohue, PhD ___________________________ Mark Rausher, PhD ___________________________ Mohamed Noor, PhD ___________________________ Thomas Mitchell-Olds An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biology in the Graduate School of Duke University 2018 i v Copyright by Jennifer M. Coughlan 2018 Abstract The earth is home to roughly 9 million eukaryotic species. The formation and maintenance of this diversity requires the accumulation of barriers to reproduction. One of the most common post-zygotic barriers in plants is hybrid seed inviability (HSI). Despite its commonality, we know relatively little about the genetic mechanisms and evolutionary forces which are responsible for this barrier, particularly in naturally co- occurring species. Here I tested the role of parental conflict in HSI between co-occurring monkey flowers in the M. guttatus species complex. I assessed the strength and directionality of HSI within and between phenotypically described perennial variants of the M.
    [Show full text]
  • Lack of Intrinsic Postzygotic Isolation in Haplodiploid Male Hybrids Despite High Genetic Distance
    bioRxiv preprint doi: https://doi.org/10.1101/2020.01.08.898957; this version posted January 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. Lack of intrinsic postzygotic isolation in haplodiploid male hybrids despite high genetic distance 1 1 2 1 Emily E. Bendall , Kayla M. Mattingly , Amanda J. Moehring , Catherine R. Linnen 1University of Kentucky, Department of Biology, Lexington, KY 40506, USA 2Western University, Department of Biology, London, Ontario, Canada Abstract Evolutionary biologists have long been interested in understanding the mechanisms underlying Haldane’s rule. The explanatory theories of dominance and faster-X, which are based on recessive alleles being expressed in the heterogametic sex, have been proposed as common mechanisms. These mechanisms predict that greater hemizygosity leads to both faster evolution and greater expression of intrinsic postzygotic isolation. Under these mechanisms, haplodiploids should evolve and express intrinsic postzygotic isolation faster than diploids because the entire genome is analogous to a sex chromosome. Here, we measure sterility and inviability in hybrids between Neodiprion pinetum and N. lecontei, a pair of haplodiplopids that differ morphologically, behaviorally, and genetically. We compare the observed isolation to that expected from published estimates of isolation in diploids at comparable levels of genetic divergence. We find that both male and female hybrids are viable and fertile, which is less isolation than expected. We then discuss several potential explanations for this surprising lack of isolation, including alternative mechanisms for Haldane’s rule and a frequently overlooked quirk of haplodiploid genetics that may slow the emergence of complete intrinsic postzygotic isolation in hybrid males.
    [Show full text]
  • Evolution 2 Speciation
    Evolution 2 Evolution Speciation • The evolution of life is directly connected to the evolution of earth. • Evidence: – Fossils –Geology – Biogeography • Similarities in rock types • Glaciation • Fossil distributions Plate tectonics Plate tectonics Alfred Wegener (1880-1930) His theory was based on several 1915 – he suggested that 300 observations: mya all of the continents 1. The fit of the continents. formed a supercontinent that 2. Similarity of rock types across he called “Pangea”. Atlantic. 3. Glacial “tracks”. 4. Fossil distributions. Plate Tectonics Plate Tectonics Continental Margins 1 Plate Tectonics Plate Continental Margins Tectonics Near perfect fit when continents are joined by continental margins. South America Africa Plate Tectonics Plate Tectonics Glacial striations reveal ancient continental connections. Matching rock assemblages across the Atlantic Ocean. Plate Tectonics Plate Tectonics Glacial striations reveal ancient continental connections. Glacial Striations 2 Plate Tectonics Plate Tectonics Glacial Striations Glacial Striations Plate Tectonics Plate tectonics New evidence supporting Overlapping Fossil Wegener: assemblages 1. Sea floor spreading 2. Magnetic sea floor patterns 3. Sea floor age patterns Plate Tectonics Plate Tectonics Evidence of sea floor spreading The planet experience periodic reversals in the poles. Rock reflect direction of magnetism when they are created. Sea floor reveals a mirror image of rock magnetism. 3 Plate Tectonics Plate Tectonics Evidence of sea floor spreading Sea floor spreading The planet experience Age of seafloor N . A periodic reversals in the increases at m Europe a e n ri poles. equal rates i ca h India relative to C Rock reflect direction of oceanic rifts. Africa magnetism when they The oldest sea are created.
    [Show full text]
  • Postzygotic Isolation and Haldane's Rule in a Grasshopper
    Heredity 69 (1992) 527—538 Received 3 March 1992 Genetical Society of Great Britain Postzygotic isolation and Haldane's rule in a grasshopper S. R. VIRDEE & G. M. HEWITT School of Biological Sciences, University of East Angila, Norwich NR4 7TJ, UK. Hybrid dysfunction was examined in reciprocal F1 and backcross hybrids between parapatric subspecies of the meadow grasshopper Chorthippus parallelus. Haldane's rule applies and dysfunction is restricted to the XO males which are sterile. The degree of disruption differs between reciprocal F1s. Males whose mothers were C. p. parallelus have poorer testes, a consequence of either the parallelus X chromosome, which carries a nucleolar organizer region (NOR), or a cytoplasmic factor. There is considerable variation in phenotype amongst F1 families when compared to parental families, which reflects hybrid breakdown. Sterility is probably caused by det- rimental epistatic interactions between the single X and the mixed autosomes. Significant differences in testis morphology and survivorship among backcrosses could be attri- buted to cytoplasmically transmitted factors. An interaction between the cytoplasm and the region of the X chromosome carrying the NOR accounts for variation among backcross individuals. There is no incompatibility between the X and autosomes in backcrosses. This raises questions about the mechanism underlying sterility in the F1. Hybrid dysfunction in this species appears to be polygenically determined. These data emphasize the importance of cytoplasmic influences, as well as the role of the X chromosome, in postzygotic isolation. Keywords: hybridzone, nucleolar organizerregion, postzygotic isolation, sex chromosomes, sterility, testis dysfunction. Templeton, 1984; Barton & Charlesworth, 1984). For Introduction example, divergence at many loci, each of small effect, Reproductiveisolation can arise in a number of ways.
    [Show full text]
  • The Evolutionary Genetics of Plant Hybrid Incompatibilities Lila Fishman and Andrea L
    Contents 1. INTRODUCTION . 708 2. GENIC INCOMPATIBILITIES. 708 2.1. The Dobzhansky-Muller Model: An Epistatic Solution to the Puzzle of Unfit Hybrids. 708 2.2. Nuclear Genic Incompatibilities. 711 2.3. Cytonuclear Incompatibilities . 717 3. CHROMOSOMAL REARRANGEMENTS—THE ONCE AND FUTURE KINGS OF PLANT REPRODUCTIVE ISOLATION? . 722 3.1. Inversions: Common Suppression of Recombination Without Direct Fertility Costs? . 723 3.2. Crossing the Valley of Low Fitness to Speciation: The Enduring Mystery ofUnderdominantTranslocations............................................ 723 1. INTRODUCTION Hybrid incompatibilities, here defined as genic and structural interactions between divergent genomes resulting in the reduced fitness of interspecific or interpopulation hybrids, are a long- standing puzzle in evolutionary biology. How does bringing together two perfectly functional genetic programs in a hybrid somehow result in reproductive failure or death? Why, given natural selection as a major force in species divergence, do such deleterious incompatibilities evolve? When and where do hybrid incompatibilities act as barriers to gene flow during divergence and as direct contributors to speciation? While these questions transcend (eukaryotic) taxon, the answers de- pend in large part on the reproductive and developmental biology of a given organism. That is, how plant hybrids fall apart reflects how plants are put together. Thus, the study of plant hybrid incom- patibilities touches many fields in plant biology, from molecular biology to the ecology of species interactions. Our goal here is to summarize recent work on the full breadth of plant hybrid incom- patibilities from an evolutionary genetic perspective. This perspective necessarily includes both molecular mechanisms and potential speciation consequences (see the sidebar titled The Question of Consequences), but our primary focus is on recent progress toward understanding how and why incompatibilities evolve and on what they tell us about evolutionary processes within plant species.
    [Show full text]