Peripatric Research Articles

Centrifugal speciation and centres of origin

AbstractAimTo discuss the development and usefulness of the theory of centrifugal speciation and its practical application to the centre of origin hypothesis.LocationThe Indo‐West Pacific Ocean.MethodsUtilization of patterns demonstrating species diversity, generic age, dispersal tracks, phylogenetics, extinction and genetic diversity.ResultsThe centrifugal speciation hypothesis appears to provide a suitable explanation for the way in which centres of origin theoretically operate. Recent information about the centre of origin in the marine East Indies suggests that it is the source of evolutionary radiation for the Indo‐West Pacific. Its mechanism appears to conform to the centrifugal prediction.Main conclusionsThe East Indies Triangle is the origin of a series of dynamic systems that extend across the entire Indo‐West Pacific. These systems are apparently maintained by a continuous outflow from the centre of origin. A series of species replacements from the East Indies over the past 10 million years would create and perpetuate the systems that have been identified.

Review of the dinoflagellate cyst <i>Stephanelytron</i> Sarjeant 1961 emend

Abstract. The stratigraphic distribution of the Late Callovian to Early Oxfordian dinoflagellate cyst Stephanelytron Sarjeant 1961 emend provides new evidence pertaining to its evolution. Middle and Upper Callovian times favoured the development of speciations to a short-ranging Stephanelytron community with corona(s) in ventral–posterior position (Stephanelytron brontes, S. callovianum, S. ceto and S. tabulophorum) from eurytopic species with antapical coronas (S. caytonense, S. membranoidium, S. redcliffense and S. scarburghense). The former group of species (except S. tabulophorum) may represent an example of peripatric speciation from an unfavourable mutation. The reduced stratigraphic range gives the appearance of an endemic population. The genus Lagenadinium Piel, 1985 is a junior synonym of Stephanelytron Sarjeant, 1961. A new emendation of Stephanelytron, two new combinations (S. callovianum and S. membranoidium) and two new species (?S. brontes and S. ceto) are proposed.

Extinction and replacement in the Indo‐West Pacific Ocean

Summary Aim To provide evidence suggesting the existence of a dynamic system of extinction and replacement. Location The Indo‐West Pacific Ocean. Methods Utilization of species distribution patterns produced by detailed systematic works. Results The distribution patterns appear to suggest a sequence of events that is consistent with the centre of origin hypothesis. The East Indies centre is considered to operate according to the centrifugal speciation model. Main conclusions Disjunct patterns appear to have originated in the East Indies and spread out from there. In cases where the vacated area is occupied by a sibling species, competitive (sympatric) speciation may have occurred. Over time the extinction pattern will gradually extend outward until it is played out among small populations far from their centre of origin

COINCIDENT BIOGEOGRAPHIC PATTERNS: INDO-WEST PACIFIC OCEAN.

The majority of tropical marine families demonstrate their greatest concentration of species within the relatively small East Indies Triangle. In every direction, the species diversity decreases with distance from the East Indies. Other patterns suggest that the East Indies is where the average generic age is youngest, where some historical routes of dispersal originate, where the most apomorphic species occur, where genetic diversity is the greatest, and where extinctions are likely to originate. These coincident patterns provide support for the hypothesis that the East Indies has been operating as a center of evolutionary radiation. The driving force for this dynamic system is apparently the predominance of successful speciation involving relatively large populations with higher genetic diversity. This mechanism fits the centrifugal speciation model that was proposed more than 50 years ago.

The Effects of Selection and Bottlenecks on Male Mating Success in Peripheral Isolates

Previous articleNext article No AccessNotes and CommentsThe Effects of Selection and Bottlenecks on Male Mating Success in Peripheral IsolatesArne Ø. Mooers, Howard D. Rundle, Michael C. Whitlock, and Associate Editor: Nicholas BartonArne Ø. Mooers*To whom correspondence should be addressed; e‐mail: [email protected]. Search for more articles by this author , Howard D. Rundle†E‐mail: [email protected]. Search for more articles by this author , Michael C. Whitlock‡E‐mail: [email protected]. Search for more articles by this author , and Associate Editor: Nicholas Barton Search for more articles by this author 1Department of Zoology and Centre for Biodiversity Research, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada; 2Institute for Systematics and Population Biology and Zoological Museum, University of Amsterdam, P.O. Box 94766, Amsterdam 1090GT, The NetherlandsPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 153, Number 4April 1999 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/303186 Views: 80Total views on this site Citations: 24Citations are reported from Crossref HistoryReceived July 10, 1998Accepted November 13, 1998 Keywordsperipheral isolatesinbreedingmate choicemating successgene flowspeciation genetics© 1999 by The University of Chicago.PDF download Crossref reports the following articles citing this article:Elena G. Belkina, Elena B. Naimark, Anastasiya A. Gorshkova, Alexander V. Markov Does adaptation to different diets result in assortative mating? Ambiguous results from experiments on Drosophila, Journal of Evolutionary Biology 31, no.1212 (Oct 2018): 1803–1814.https://doi.org/10.1111/jeb.13375Andrew Z Colvin Peripatric speciation, WikiJournal of Science 1, no.22 (Aug 2018): 008.https://doi.org/10.15347/wjs/2018.008D.R. Matute Founder Speciation, (Jan 2016): 90–96.https://doi.org/10.1016/B978-0-12-800049-6.00078-0Devin Arbuthnott, Howard D. Rundle Misalignment of natural and sexual selection among divergently adapted Drosophila melanogaster populations, Animal Behaviour 87 (Jan 2014): 45–51.https://doi.org/10.1016/j.anbehav.2013.10.005Bianca F. Menezes, Felipe M. Vigoder, Alexandre A. Peixoto, Julien Varaldi, Blanche C. Bitner-Mathé The influence of male wing shape on mating success in Drosophila melanogaster, Animal Behaviour 85, no.66 (Jun 2013): 1217–1223.https://doi.org/10.1016/j.anbehav.2013.03.008Cedric K. W. Tan, Tommaso Pizzari, Stuart Wigby PARENTAL AGE, GAMETIC AGE, AND INBREEDING INTERACT TO MODULATE OFFSPRING VIABILITY IN DROSOPHILA MELANOGASTER, Evolution 99 (May 2013): n/a–n/a.https://doi.org/10.1111/evo.12131Devin Arbuthnott, Howard D. Rundle SEXUAL SELECTION IS INEFFECTUAL OR INHIBITS THE PURGING OF DELETERIOUS MUTATIONS IN DROSOPHILA MELANOGASTER, Evolution 66, no.77 (Feb 2012): 2127–2137.https://doi.org/10.1111/j.1558-5646.2012.01584.xLucia Kwan, Howard D. Rundle ADAPTATION TO DESICCATION FAILS TO GENERATE PRE- AND POSTMATING ISOLATION IN REPLICATE DROSOPHILA MELANOGASTER LABORATORY POPULATIONS, Evolution 64, no.33 (Mar 2010): 710–723.https://doi.org/10.1111/j.1558-5646.2009.00864.xMICHAEL HEADS Inferring biogeographic history from molecular phylogenies, Biological Journal of the Linnean Society 98, no.44 (Nov 2009): 757–774.https://doi.org/10.1111/j.1095-8312.2009.01320.xR. B. STELKENS, O. SEEHAUSEN Phenotypic divergence but not genetic distance predicts assortative mating among species of a cichlid fish radiation, Journal of Evolutionary Biology 22, no.88 (Jul 2009): 1679–1694.https://doi.org/10.1111/j.1420-9101.2009.01777.xAmy G. Vandergast, Andrew J. Bohonak, Stacie A. Hathaway, Joshua Boys, Robert N. Fisher Are hotspots of evolutionary potential adequately protected in southern California?, Biological Conservation 141, no.66 (Jun 2008): 1648–1664.https://doi.org/10.1016/j.biocon.2008.04.009Alan R. Templeton The reality and importance of founder speciation in evolution, BioEssays 30, no.55 (Jan 2008): 470–479.https://doi.org/10.1002/bies.20745Jeremy R. Dettman, Caroline Sirjusingh, Linda M. Kohn, James B. Anderson Incipient speciation by divergent adaptation and antagonistic epistasis in yeast, Nature 447, no.71447144 (May 2007): 585–588.https://doi.org/10.1038/nature05856Lisa M. Meffert, Jennifer L. Regan Reversed selection responses in small populations of the housefly (Musca domestica L.), Genetica 127, no.1-31-3 (May 2006): 1–9.https://doi.org/10.1007/s10709-005-2913-2Timothy H Vines, Dolph Schluter Strong assortative mating between allopatric sticklebacks as a by-product of adaptation to different environments, Proceedings of the Royal Society B: Biological Sciences 273, no.15891589 (Dec 2005): 911–916.https://doi.org/10.1098/rspb.2005.3387A. DRAKE, E. RASHKOVETSKY, H. D. RUNDLE, A. O. MOOERS Variable assortative mating in replicate mating trials using Drosophila melanogaster populations derived from contrasting opposing slopes of 'Evolution Canyon', Israel, Journal of Evolutionary Biology 18, no.44 (Jul 2005): 1123–1129.https://doi.org/10.1111/j.1420-9101.2005.00911.xHoward D. Rundle DIVERGENT ENVIRONMENTS AND POPULATION BOTTLENECKS FAIL TO GENERATE PREMATING ISOLATION IN DROSOPHILA PSEUDOOBSCURA, Evolution 57, no.1111 (Nov 2003): 2557–2565.https://doi.org/10.1111/j.0014-3820.2003.tb01499.xHoward D. Rundle DIVERGENT ENVIRONMENTS AND POPULATION BOTTLENECKS FAIL TO GENERATE PREMATING ISOLATION IN DROSOPHILA PSEUDOOBSCURA, Evolution 57, no.1111 (Jan 2003): 2557.https://doi.org/10.1554/02-717A. Ödeen, A.-B. Florin Sexual selection and peripatric speciation: the Kaneshiro model revisited, Journal of Evolutionary Biology 15, no.22 (Mar 2002): 301–306.https://doi.org/10.1046/j.1420-9101.2002.00378.xA.-B. Florin, A. Odeen Laboratory environments are not conducive for allopatric speciation, Journal of Evolutionary Biology 15, no.11 (Jan 2002): 10–19.https://doi.org/10.1046/j.1420-9101.2002.00356.xPär K Ingvarsson Restoration of genetic variation lost – the genetic rescue hypothesis, Trends in Ecology & Evolution 16, no.22 (Feb 2001): 62–63.https://doi.org/10.1016/S0169-5347(00)02065-6Patrik Nosil, Luke Harmon Niche dimensionality and ecological speciation, (Jan 2001): 127–154.https://doi.org/10.1017/CBO9780511815683.009Menno Schilthuizen Dualism and conflicts in understanding speciation, BioEssays 22, no.1212 (Nov 2000): 1134–1141.https://doi.org/10.1002/1521-1878(200012)22:12<1134::AID-BIES11>3.0.CO;2-5Howard D. Rundle, Arne Ø. Mooers, Michael C. Whitlock EXPERIMENTAL TESTS OF FOUNDER-FLUSH: A REPLY TO TEMPLETON, Evolution 53, no.55 (May 2017): 1632–1633.https://doi.org/10.1111/j.1558-5646.1999.tb05430.x

Rapid parapatric speciation on holey adaptive landscapes.

A classical view of speciation is that reproductive isolation arises as a by-product of genetic divergence. Here, individual-based simulations are used to evaluate whether the mechanisms implied by this view may result in rapid speciation if the only source of genetic divergence are mutation and random genetic drift. Distinctive features of the simulations are the consideration of the complete process of speciation (from initiation until completion), and of a large number of loci, which was only one order of magnitude smaller than that of bacteria. It is demonstrated that rapid speciation on the time-scale of hundreds of generations is plausible without the need for extreme founder events, complete geographic isolation, the existence of distinct adaptive peaks or selection for local adaptation. The plausibility of speciation is enhanced by population subdivision. Simultaneous emergence of more than two new species from a subdivided population is highly probable. Numerical examples relevant to the theory of centrifugal speciation and to the conjectures about the fate of 'ring species' and 'sexual continuums' are presented.

Evolutionary consequences of the latest Paleocene thermal maximum for tropical planktonic foraminifera

Study of planktonic foraminiferal assemblages preserved in the central, equatorial Pacific (ODP Site 865) reveal that genera which inhabited the near-surface, mixed layer diversified during the latest Paleocene thermal maximum (LPTM). This transient diversification gave rise to a suite of short-lived (50 to several 100 ka), distinctive morphotypes ( Morozovella allisonensis sp. nov., M. africana, and Acarinina sibaiyaensis) that are restricted to the LPTM interval. Parallel morphometric and stable isotopic data have been recorded from individual shells of members of the M. velascoensis/ M. allisonensis and A. soldadoensis/ A. sibaiyaensis lineages. The single-specimen isotope data confirm that M. allisonensis and A. sibaiyaensis are indeed stratigraphically restricted to the LPTM carbon isotope excursion; all specimens recorded anomalously low δ 13C values. A stratigraphic succession of single-specimen isotope data from within the δ 13C excursion interval was used to reconstruct the complex population dynamics which mediated the rapid (<10 ka) evolution of the LPTM taxa. These data reveal that local populations of ancestral M. velascoensis temporarily collapsed with the descendant M. allisonensis suddenly originating from a peripherally isolated population. This pattern is most consistent with peripatric speciation. Overall, the evolutionary transition from Acarinina soldadoensis to A. sibaiyaensis is most consistent with sympatric speciation, although certain elements of this transition are suggestive of a parapatric mechanism. We postulate that the rapid evolution of the LPTM taxa A. sibaiyaensis and M. allisonensis was fostered by a deepening of the nutrient-depleted, mixed layer. Alternatively, the LPTM morphotypes M. allisonensis and A. sibaiyaensis may have been extreme ecophenotypic variants arrayed along an intensified ecological gradient. Support for this latter interpretation is derived from the morphometric data which clearly show the morphological intergradation of the LPTM taxa with their respective ancestors. Thus, the morphologic diversification seen during the LPTM may represent failed speciations. Both scenarios invoke a temporary steepening of clinal gradients in response to intensified oligotrophy. The strong size-dependencies displayed by the δ 18O and δ 13C signatures of M. allisonensis and A. sibaiyaensis suggest that photosymbiosis facilitated the evolutionary success of the morozovellids and acarininids during the LPTM.

EXAMINING TWO STANDARD ASSUMPTIONS OF ANCESTRAL RECONSTRUCTIONS: REPEATED LOSS OF DICHROMATISM IN DABBLING DUCKS (ANATINI).

Although phylogenetic reconstruction of ancestral character states is becoming an increasingly common technique for studying evolution, few researchers have assessed the reliability of these reconstructions. Here I test for congruence between a phylogenetic reconstruction and a widely accepted scenario based on independent lines of evidence. I used Livezey's (1991) phylogeny to reconstruct ancestral states of plumage dichromatism in dabbling ducks (Anatini). Character state mapping reconstructs monochromatic ancestors for the genus Anas as well as most of its main clades. This reconstruction differs strongly from the widely accepted scenario of speciation and plumage evolution in the group (e.g., Delacour and Mayr 1945; Sibley 1957). This incongruence may occur because two standard assumptions of character state reconstruction are probably not met in this case. Violating either of these two assumptions would be a source of error sufficient to create misleading reconstructions. The first assumption that probably does not apply to ducks is that terminal taxa, in this case species, are monophyletic. Many of the widespread dichromatic species of ducks may be paraphyletic and ancestral to isolated monochromatic species. Three lines of evidence support this scenario: population-level phylogenies, biogeography, and vestigial plumage patterns. The second assumption that probably does not apply to duck plumage color is that gains and losses of character states are equally likely. Four lines of evidence suggest that dichromatic plumage might be lost more easily than gained: weak female preferences for bright male plumage, biases toward the loss of sexually dichromatic characters, biases toward the loss of complex characters, and repeated loss of dichromatism in other groups of birds. These seven lines of evidence support the accepted scenario that widespread dichromatic species repeatedly budded off isolated monochromatic species. Drift and genetic biases probably caused the easy loss of dichromatism in ducks and other birds during peripatric speciation. In order to recover the accepted scenario using Livezey's tree, losses of dichromatism must be five times more likely than gains. The results of this study caution against the uncritical use of unordered parsimony as the sole criterion for inferring ancestral states. Detailed population-level sampling is needed and altered transformation weighting may be warranted in ducks and in many other groups and character types with similar attributes.

Distribution and deployment ofPresbytis melalophos group in Sumatera, Indonesia

Pelage color and pattern, facial markings, cranial morphology, and vocalization have been studied comparatively in thePresbytis melalophos group in Sumatera. Pelage coloration of fetuses and neonates were described forP. melalophos andP. femoralis. Based on this study, three species —P. thomasi, P. melalophos, andP. femoralis — are recognized. Using field data that have been gathered since 1981, the distribution of these three species has been mapped. The resultant map reveals that no sympatry is known and that rivers form the interspecific boundaries. However, rivers apparently are not barriers to the dispersal of species in this group. Instead, distributions appear to be limited ecologically, by competitive exclusion. Historically, it appears that the ancestral stock initially dispersed throughout this area, then theP. melalophos stock split from theP. thomasi-P. femoralis stock, theP. thomasi stock split from theP. femoralis stock, and, finally, theP. femoralis stock dispersed to eastern Sumatera. It appears unlikely that the centrifugal speciation hypothesis based on the principle of metachromism applies to deployment of theP. melalophos group.

ERNST MAYR AND THE CENTRALITY OF SPECIES.

So much has happened in the last century of our waning millennium that cardinal events of the early years are already enshrined as permanent high points in our culture. In 1904, Anton Chekhov produced Cherry Orchard (and died later that year), James Barrie published Peter Pan, Sigmund Freud wrote Psychopathology of Everyday Life, and Giacomo Puccini's Madama Butterfly received its first performance at La Scala amid a deafening cascade of catcalls (reversed three months later in a second and triumphant showing in Brescia under the baton of Arturo Toscanini). Also in 1904, Henry Adams described the most fantastic American spectacle of the year, the greatest illumination ever attempted with the new-fangled invention of incandescent bulbs: The world has never witnessed so marvelous a phantasm; by night Arabia's crimson sands had never returned a glow half so astonishing, as one wandered among long lines of white palaces, exquisitely lighted by thousands and thousands of electric candles, soft, rich, shadowy, palpable in their sensuous depths. Adams was describing the St. Louis World's Fair, famous for the invention of iced tea, ice cream cones, and the first Olympic Games held in America. Yet, for the illumination provided ever since to our profession of evolutionary biology, Adams might well have been celebrating our cardinal event for that year, the birth on July 5, in Kempten, Germany, of Ernst Mayr. In the three most important of his many sequential and overlapping careers-ornithologist and systematist, evolutionary theorist, and historian of biology-Ernst Mayr has rooted his intellectual vision in defending a rational and tractable science of organic wholeness against a variety of reductionisms and sterile abstractions. I shall devote this tribute to my dear friend and mentor to a discussion of Mayr's key insight on the centrality of species as evolutionary agents, and to the contribution made by this notion to developing theories of macroevolution-a great advance not achieved as simple realization from the void, but from active struggle against previously dominating views of species as arbitrary segments of evolving lineages, and as units too comprehensive, in any case, to act as fundamental agents in sciences committed to reductionistic perspectives. But I wish to record the larger and coordinating role of this integrative organismic worldview as a linchpin of Mayr's scientific life, for this philosophical consistency holds a key to the power of his thought and the extent of his influence. This antireductionism inspired him to become a systematist and field biologist in the first place; it underlies his different (and, I believe, correct) view of the Modem Synthesis as a fusion of laboratory-genetic and field-systematist traditions and not (as so often depicted) as a reduction of descriptive activities in natural history to explanatory models of genetics; it serves as a conceptual basis for all his major ideas in evolutionary theory, including peripatric speciation, genetic revolutions, founder effects, and unity of the genotype; it informs his fundamental vision of the history of biology as a struggle over centuries between the essentialism of Platonic traditions and the rightminded approach that he calls population thinking. centerpiece of Mayr's scientific life, coming between an earlier focus on ornithological field studies and a later dedication to history and philosophy of biological science, rests on his role as a leading architect of one of the half-dozen major scientific achievements in our century: the integration of Mendelian and Darwinian traditions to form for the first time, following factional debate ever since Origin, a unified theory of evolution called the Modem Synthesis. Mayr was, first, a founder of the synthesis in writing a key volume that integrated systematics within the growing concensus (Mayr 1942); then a practical facilitator in helping to organize the Society that publishes this journal and in serving as the first editor of Evolution (see Smocovitis 1994); then, as a grand codifier of the synthesis in writing its most synoptic compendium (Mayr 1963); and, finally, as its primary historian (Mayr and Provine 1980; Mayr 1982). If we consider the synthesis as a fusion of three equally robust disciplines-experimental genetics, genetics, and studies of natural history expressed primarily by systematics (and

The importance of phylogenetic analysis for the assessment of species turnover: a case history of Paleocene mammals in North America

During the latest Cretaceous and the Paleocene in western North America, disappearance rates for mammalian genera track appearance rates, both reaching their peak in the early Paleocene (Puercan) following the extinction of non-avian dinosaurs. Some of the disappearances during this time were pseudoextinctions that resulted when ancestral species disappeared during speciation.Species-level cladistic analyses and a well-constrained biostratigraphic framework are required to study this form of pseudoextinction. Cladistic analyses show that monophyly cannot be established or rejected for some species because these species lack autapomorphies (uniquely derived character states) that unite their constituent members. Such taxa, termed metaspecies, are potential ancestors to species and higher clades with which they share a node in the cladogram.A hypothetical species-level cladistic analysis coupled with three different hypothetical biostratigraphies shows how different models of speciation (bifurcation, budding, or anagenesis) result in very different patterns of true versus pseudoextinction. Depending on the speciation model, true extinction can be overestimated by as much as a factor of four, raising the specter of mass extinction. Species-level studies for three early Tertiary mammalian taxa—taeniodont eutherians, taeniolabidid multituberculates, and periptychid ungulates—use the same procedures. They show that almost 25% of disappearances during the early Paleocene (Puercan) for species in the analysis were pseudoextinctions of metaspecies. Budding and anagenetic-like peripatric speciation, but not bifurcation, are seen in the three examples.Equating disappearance to true extinction can profoundly affect interpretations of faunal turnover, especially during mass extinctions or major faunal reorganizations. Some authors use pseudoextinction to describe the taxonomic rather than evolutionary disappearance of nonmonophyletic groups. Pseudoextinction, as used here refers only to the evolutionary disappearance of metaspecies via speciation. Both usages seem appropriate but should not be confounded.

Marine Regressions and the Evolution of Groundwater Dwelling Amphipods (Crustacea)

The origin of marine lineages of amphipods in continental and insular ground waters is treated, and the im- portance in it of relative sea-level lowering is weighed. Pat- terns of distribution and relationships of Hadzioidea, Salentinellidae, Bogidielloidea and Niphargidae are re- viewed, with emphasis on the evidence for their direct marine origin, and on their dispersal abilities. The process of troglobitization, linked with subterranean evolution, in amphipods is discussed. A two-step model of the evolution of thalassoid lineages is discerned. During the first phase, marine populations colonize crevicular or interstitial habitats. These habitats are physiographically connected with the inland stygohabi- tats, and are characterized by severe ecological conditions. During the second phase, certain lineages overcome the salinity boundary and colonize inland ground waters through active migration or passive isolation, or through a combination of both. Marine regressions seem of little significance in the first evolutionary phase, where they primarily explain the isola- tion in coastal ground waters of marine littoral populations, already adapted to subterranean conditions. Vicariance by marine regressions is considered of relatively great evolu- tionary significance in thalassoid groups of low vagility and dispersal ability. This type of vicariance is followed by peripatric speciation, and a largely polychotomous pattern of descent is predicted.

Chromosomal polymorphisms in subterranean mole rats: origins and evolutionary significance

Two distinct chromosomal polymorphisms, among others, characterize the short (p) and long (qh) arms of chromosome number 1 of the Spalax ehrenbergi complex in Israel. We have studied the geographic distributions of these two polymorphisms in 60 animals belonging to four chromosomal species (2n= 52, 54, 58 and 60). These comprised 15 populations: 12 from continuously distributed populations, two from semi-isolates, and one isolate in the northern Negev Desert. Our results indicate that: (i) the two polymorphisms are widespread not only within populations and species but most strikingly between different bone marrow cells within an individual; this may reflect a diversity generating mechanism; (ii) the two polymorphisms of p and qh, primarily of p, are correlated with climatic factors of water availability and temperature, as well as geographical distances; these correlations are significantly above those expected by chance, (iii) The semi-isolates and the isolate display high levels of polymorphism in both p and qh, but particularly in qh, despite the small size population effects. We suggest that at least the polymorphism in p is involved in the adaptive radiation of mole rats into diverse climatic regimes. Furthermore, we speculate that the forces generating chromosomal polymorphisms relevant to speciation (i.e. Robertsonian mutations), coupled with the evolutionary forces operating in small peripherally isolated populations, may be appropriate for the origin of new chromosomal species through peripatric speciation.

Punctuated equilibrium excused: the original examples fail to support it

The four original stipulations of the definition ofpunctuated equilzbrium (PE; Eldredge & Gould, 1972) are shown to be unsupported, and even contradicted, by the two evidential examples these authors supplied: the trilobite Phacops rana of the Middle Devonian, and the land snail Poectlozonites bermudensis of Late Pleistocene Bermuda. The additional, much-discussed example of Bellamya unicolor and the accompanying suite of molluscan species of Pliocene-Recent African Lake Turkana, studied by Williamson, also fails to exemplify PE. In particular, the data produced for these cases appear to represent counterexamples to Mayr’s paradigm of peripatric speciation, embraced by Eldredge and Gould as the central effective mechanism of PE. The data actually illustrate instead a prevailingly centrifugal pattern of speciation that will accommodate and explain episodic aspects of microevolution in a more realistic way.

Speciation by monobrachial centric fusions

Fixation of centric fusions in natural populations often encounters minimal meiotic problems due to the ability of trivalents to segregate normally; therefore, little sterility barrier is achieved between a founder population and the parental stock. However, a strong sterility barrier can develop between different founder populations fixed for centric fusions that are monobrachially homologous in the resulting biarmed chromosomes (one arm is homologous but the other is nonhomologous). Hybridization through secondary contact then results in complex multivalents, which encounter problems in segregation and produce unbalanced gametes. Speciation mediated by centric fusions is a peripatric speciation model that does not postulate populational phenomena atypical of those characteristic of most mammals. The model appears applicable to a diversity of mammalian taxa such as bats of the Rhogeessa tumida-parvula complex, shrews of the Sorex araneus complex, and rodents of the Mus musculus and Rattus rattus complexes.

EVOLUTION IN PERIPHERAL ISOLATED POPULATIONS: CARPODACUS FINCHES ON THE CALIFORNIA ISLANDS.

The effect of being isolated on an island is seen as an important factor in the evolution of insular populations. An island population may be very different phenetically and genetically from a presumed conspecific population living in a similar environment on the mainland, whereas conspecific populations on a mainland may be very similar to one another even though occurring in widely distant localities and under different ecological conditions (Mayr, 1954). The reason for this is in part that rapid evolution may occur in small peripheral populations (Carson, 1959; Cook, 1961). However, an opposite effect, centrifugal speciation, has also been described wherein peripheral forms of a species may show more primitive traits, not having received the advanced character states which spread from centers where a species is best adapted and where neighboring forms come together and increase genetic heterogeneity (Brown, 195 7). A related problem is that of genetic variation in marginal and peripheral populations. Soule (1973) has reviewed data on reduction in the diversity of coadapted gene combinations in novel environments, the advantages of preserving allelic polymorphism, and the loss of alleles at geographic margins because of genetic drift, and reduced immigration. Recently, the importance of geographic isolation, and especially of populations on the periphery of a species' range, also appears in arguments supporting the view that speciation is primarily by punctuated equilibria (Eldredge and Gould, 1972; Gould and Eldredge, 1977). If our understanding of the way evolution works is correct, there is a great potential for peripherally isolated populations to break from the genetic cohesiveness of the parent species and become genetically independent. A potential for speciation and genetic distinction can be demonstrated when relatively large phenetic differences exist among populations separated by short distances but imposing physical barriers. This situation is often found with populations on fringing islands. The present paper is an analysis of phenetic similarity among populations of the house finch (Carpodacus mexicanus) from the California Islands and the western U.S. (Fig. 1). I want to concentrate on barriers to dispersal and the accumulation of morphological differences among populations. Details of character variation, systematics, and population variability on the islands will be included in later papers (e.g., Power, in press). The house finch is a widespread passerine species of western North America. The genus Carpodacus originated in the Old World; most of the adaptive radiation (about 18 species) has been in Asia. Three species-the house finch (or linnet), purple finch (C. purpureus), and Cassin's.,finch (C. cassini)-are in the New World. Purple and Cassin's finches prefer forested areas, whereas the house finch breeds in desert and scrub vegetation from British Columbia south to central Mexico (Salt, 1952). It is also common in suburbs and around farm buildings, gardens, and orchards. Range expansion into eastern Oregon, eastern Washington, and Oklahoma, and the successful, man-aided establishment of this species in Hawaii (Hirai, 1975) and on the east coast of the U.S. (Gill and Lanyon, 1965) may be due to the presence of human alteration of the habitat, but it also demonstrates the bird's

CHROMOSOMAL EVOLUTION AND THE MODE OF SPECIATION IN THREE SPECIES OF PEROMYSCUS.

The possibility that the Peromyscus maniculatus complex of deer mice arose via the process described as (Brown, 1957) has been discussed by Bowers et al., 1973, Lawlor, 1974, Baker et al., 1975, and Greenbaum et al., 1978. This study was designed to yield additional data on the cytogenetics of three species of this complex in order to evaluate the model as a viable explanation of the evolutionary origin of the complex. Peromyscus melanotis and P. polionotus are believed to be peripheral isolates from the that evolved into the species P. maniculatus (Blair, 1950, Bowers et al., 1973). P. maniculatus is a widespread species occurring in a variety of habitats, whereas P. melanotis is a high montane species found in coniferous forest and P. polionotus is a deep sand species found in grassy fields at lower elevations near sea level (see Hooper, 1968, for general distribution of these three species). It is probable that P. melanotis and P. polionotus are more closely related to P. maniculatus than they are to each other. Based on gross chromosome morphology, the karyotypes of P. polionotus and P. melanotis are more like each other than either is like the karyotypes of P. maniculatus. We have examined the G-banding and C-banding pattern of P. polionotus and compared it to the banding patterns of P. maniculatus and P. melanotis (Greenbaum et al., 1978) to determine whether this similarity in karyotype is reflected in homologous banding patterns or is a product of convergent evolution. If the chromosomal data for the species complex are to fit the centrifugal speciation model then the karyotypes of P. polionotus and P. melanotis must be most like the primitive condition and the karyotype of P. maniculatus must be the most derived. Additionally, the centrifugal speciation model would predict more chromosomal polymorphism and geographic variation in the central stock (P. maniculatus) and less in the peripheral isolates (P. polionotus and P. melanotis). Our study is designed to determine the chromosomal homologies in these species and thereby test the hypothesis that this group is the result of centrifugal speciation.

Morphometrics, Evolution, and Cytotaxonomy of Mainland Bats of the Genus Macrotus (Chiroptera: Phyllostomatidae)

Davis, Brent L., and Robert J. Baker (Dept. Biology, and The Museum, Texas Tech University, Lubbock, Texas) 1974. Morphometrics, Evolution, and Cytotaxonomy of Mainland Bats of the Genus Macrotus (Chiroptera: Phyllostomatidae). Syst. Zool. 23:26-39.-Chromosomal data reveal the existence of two mainland species of Macrotus that are parapatric in distribution. Individuals can be identified to species by both chromosomal features and cranial morphology. A stepwise multiple discriminant analysis and canonical variate analysis show that the two species are morphometrically divergent. The distribution of these two taxa is proof that parapatry occurs in species with high vagility. If chromosomal data had not been available or if chromosomal divergence had not accompanied speciation in Macrotus, this unique pattern of distribution probably would not have been detected. Allopatric, stasipatric, and centrifugal speciation are considered in light of the presently available data for Macrotus. [Macrotus; morphometrics; cytotaxonomy.] Geographic variation in chromosome number is rather uncommon among bats of the family Phyllostomatidae. Of the 77 species of phyllostomatids thus far karyotyped (Baker, 1973), four species show geographic variation-Uroderma bilobatum (Baker et al., 1972), Macrotus waterhousii (Nelson-Rees, et al., 1968), and Micronycteris hirsuta and Vampyressa pusilla (Baker et al., 1973). Chromosomal variation in Macrotus, which previously was thought to have two chromosomal races, is of the Robertsonian type (the fundamental number remains constant but the diploid number varies). The cytotype with a diploid number (2N) of 46 and a fundamental number (FN) of 60 has been reported as having a geographic range from Alamos, Sonora, south through Morelos, and Guerrero (Nelson-Rees et al., 1968). The 2N = 40, FN = 60 cytotype had a known distribution from Carbo, Sonora, north to Arizona and California. Alamos (the most northern published record for the 2N = 46 cytotype) is 335 kilometers south of Carbo (the most southern reported locality of the 2N = 40 cytotype). Variation in diploid number, as understood at the outset of this study, was confined to the subspecies M. w. californicus (Anderson, 1968, 1969; Nelson-Rees, et al., 1968). The primary reason for studying the cytogenetics and morphometrics of Macrotus was to determine the mechanism of evolution and the degree of hybridization between the two cytotypes. Robertsonian variation is the most likely mechanism by which a chromosomal change of this nature could occur (Nelson-Rees et al., 1972). If centric fusions or fissions are the mechanism by which the cytotypes evolved, loss or gain of genetic material probably would have occurred in the heterochromatic region (Jackson, 1971) and a cross between the two cytotypes should be successful, at least on a chromosomal basis of homology. Because of the relative ease with which specimens of Macrotus can be obtained and because the species is chromosomally variable, detailed studies were initiated. Several possibilities are obvious from the outset. First, the two cytotypes could be freely interbreeding. If this were the case, the genetics of the system could be examined by using chromosome number, morphology, and meiotic studies. Second, the two could be sympatric and produce no hybrids. Third, the two could have allopatric distributions. Our studies have revealed a parapatric distribution (as discussed for mammals by Vaughan, 1967) with no phenetic inter-