Rapid speciation and chromosomal evolution in mammals.

Abstract

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and *drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes. Among evolutionary biologists there is a widespread acceptance of the hypothesis that small populations are essential for rapid speciation (1-7). According to this hypothesis, new species may arise from populations initially founded by a small number of individuals isolated on the periphery of the range of the parental species-the founder principle (3-5)-or in small demes maintained by social structuring and ecology (7,8). Widespread also is the idea that small populations are essential for chromosomal evolution, and some authors suggest that the two processes-speciation and chromosomal evolution-may be causally related (7)(8)(9)(10)(11)(12). It is now possible to test these ideas quantitatively because methods have been developed recently for estimating both rates of speciation (13,14) and rates of evolutionary change in gene arrangement (8,15). Unfortunately, few estimates of effective population size are available. Hence, it is not easy to make a direct examination of the relationship between population size and rates of evolution. It is possible, however, to examine quantitatively the relationship between rate of speciation and rate of chromosomal evolution. If both processes are dependent on the occurrence of small demes, the two rates should be correlated. Such a correlation was found in higher plants (14).The present article deals with vertebrates. Rates of chromosomal evolution vary greatly in these animals, being an order of magnitude higher in most mammals than in most other vertebrates (8,15). It was important, therefore, to estimate rates of speciation in a wide variety of vertebrates. The results of such estimates are reported below and compared with the results of an improved method for estimating rate of chromosomal evolution.

Using underdominance to bi-stably transform local populations

“…It has long been recognized that, with underdominance, the probability of fixation of a new, rare mutant is exceedingly small in populations of more than a few individuals (Wright, 1941;Kimura, 1962;Bengtsson and Bodmer, 1976;Lande, 1979). Yet it is clear that mutations, including translocations, with potential underdominant effects accumulate between species and are common even among some closely related species (Bush et al, 1977;White, 1978). Several models have been proposed to try to explain this discrepancy (Bengtsson and Bodmer, 1976;White, 1978;Hedrick, 1981;Walsh, 1982).…”

Multivalents resulting from monobrachial homologies within a hybrid zone in Dichroplus pratensis (Acrididae): meiotic orientation and segregation

“…Chromosomal differences between taxa have long been recognized but the role of chromosomal rearrangements in evolution is controversial. Opinions range from an almost total rejection of any role for the chromosome to the more extreme positions that have been put forward by Matthey, 1966;White, 1968White, , 1969White, , 1970White, , 1973White, , 1975White, , 1978bWhite, , 1982Mayr, 1970Mayr, , 1982Bush, 1975;Bush et al, 1977;Bickham & Baker, 1979;Hewitt, 1979Hewitt, , 1985John, 1981John, , 1983Templeton, 1981;Kirig, 1982Kirig, , 1985Kirig, , 1987Patton & Sherwood, 1983;Reig, 1984;Camacho, 1985;Lande, 1985;Baker & Bickham, 1986;Sites & Moritz, 1987;Bidau, 1988Bidau, , 1990Nachman & Myers, 1989. Some biologists, however, have maintained a judicious and critical view by analysing available data in an impartial way (John, 1981;Patton & Sherwood, 1983;Sites & Moritz, 1987).…”

Геолошка Старост Родова И Варијабилност Броја Хромозома У Кариотиповима Гмизаваца

“…У оквиру анализа система повезују се полни систем, кариотип, величина генома, плоидија и подаци о животном циклусу еукариота: риба, "non-avian" гмизавца, водоземаца и птица; хексапода и арахнида, те ангиосперми (The Tree of Sex Consortium, 2014). Бројна су међусобна повезивања еволуције припадника Animalia, односно Vertebrata са еволуцијом њиховог кариотипа (Chiarelli, Capanna, 1973, Bush, 1975, Bush et al, 1977, Imai et al, 1986, Dawley, Bogart, 1989.…”

“…Подразумјевајући да констатовани бројеви хромозома у кариотипу у гаметогенези бивају преполовљени, без обзира да ли се ради о полиплоидним (триплоидним или тетраплоидним) врстама, онда би се брзина промјене броја хромозома могла свести на такву хаплоидну гарнитуру дијељењем са два, па би за серију родова познате старости те брзине износиле 0,068, 0,352, 0,538, 0,263, 1,562 и просјек 0,557 хромозома хаплоидне гарнитуре на милион година. Ово су веће брзине у односу на оне израчунате у оквиру родова: гмизаваца од 0,0006 до 0,027, просјек 0,009; сисара од 0,000 до 0,609, просјек 0,129 (Bush et al, 1977). Бројеви хромозома у кариотипу, који су присутни у свим категоријама старости 32, 34 и 36, те 50, 52 и 54 одговарали би оптималном нивоу издијељености хромозомског материјала на хромозоме.…”

“…Најтрајнији бројеви хромозома у кариотипу су 32, 34, 36, 50, 52 и 54, пристуни су у по 5 од 6 категорија старости родова. Процјењена просјечна стопа промјене броја хромозома у кариотипу износи 1,114 (хромозома за милион година) међу старосном категоријама родова Горња Креда до Плеистоцен, највећа (3,125. хромозома за милион година) између Плиоцена и Плеистоцена.…”