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It is shown from the statistical-mechanical overview of Volterra's ecological model how to reckon the fluctuations of collective variables such as the total population of a genus: and that these fluctuations are much decreased (or that the collective populationsteadiness is enhanced) as the speciation is increased. (A niching of species in time, or phase-niching, is entailed here.) Secondly, it is shown how Preston's log-normal distribution describing the species-abundance relationship, as well as a generalization of such distributions, come forth simply and naturally from the statistical-Volterra-dynamics.

The acquisition of reproductive isolation is the most significant event in the speciation process. A knowledge of the nature of the reproductive barriers between species and of the ways in which these barriers evolve is therefore critical to any analysis of speciation mechanisms. The Drosophilidae in the Hawaiian Islands have undergone explosive speciation giving rise to some 650 to 700 endemic species (Carson et al., 1970). In view of the substantial isolation of these oceanic islands from continental land masses, it is believed that the present-day fauna may have been derived from a single successful founder, or perhaps from two separate introductions (Throckmorton, 1966). In spite of their morphological and behavioral diversity, the species constitute a closely knit evolutionary group. The geological recency of the Islands (Macdonald and Abbott, 1970) further implies that evolutionary processes in the group have been exceptionally rapid. All of these features render the Hawaiian Drosophila particularly suitable for studies of the speciation process. Many of the species are very young in evolutionary terms and some may show only partial reproductive isolation, since speciation is most often a slow, continuous process rather than an instantaneous event. Study of the reproductive relationships between such forms should therefore offer the possibility of identifying the primary reproductive barriers formed, thereby obtaining some information on the sequence of events which lead to full speciation. This was the aim of this investigation. Accordingly, it was decided to study a set of homosequential species in the planitibia subgroup of the picture-winged flies. Homosequential species have an identical banding sequence in their polytene salivary gland chromosomes (Carson et al., 1967), and are presumptively very closely related. Furthermore, some homosequential species are, in addition, very recently evolved. Two of the species used in this study are endemic to the island of Hawaii, the youngest in the chain (McDougall, 1964), and must be very recent evolutionary products. This study therefore utilizes species which are judged to be amongst the most closely related and the most recently evolved. The reproductive barriers which isolate them have been analysed initially by the method of interspecific laboratory hybridizations, since this approach has previously proved relatively successful with Hawaiian Drosophila (Yang and Wheeler, 1969). This paper presents the data obtained on their reproductive relationships, and discusses the patterns of species formation which these data suggest.

Evolution consists of changes in the genetic constitution (gene pool) of populations. The process of evolution may be seen in two ways-which have been called anagenesis and cladogenesis (Rensch, 1960). Changes occurring within a given phylogenetic line as time proceeds, are anagenetic evolution. They result in increased adaptation to the environment, and often reflect changes of the physical or biotic conditions of the environments. Cladogenesis occurs when a phylogenetic lineage splits into two or more independently evolving lineages. The great diversity of the living world is the result of cladogenetic evolution, which results in adaptation to a greater variety of niches, or ways of life. Among cladogenetic processes, the most decisive one is speciation, the process by which one species splits into two or more species. Species are groups of populations reproductively isolated from any other such groups. Species are independent evolutionary units. Adaptive changes occurring in an individual or population may be extended to all members of the species by natural selection; however, they cannot be passed on to different species. One of the most important questions in evolutionary genetics is the amount of genetic differentiation occurring in the speciation process. Speciation may occur by a variety of processes. In sexually reproducing organisms speciation most generally occurs according to the model of "geographic speciation." Two main stages may be recognized in this process. First, allopatric populations of the same species become genetically differentiated, mostly as a consequence of their adaptation to different environments. This genetic differentiation can only occur if the populations are geographically separated for some time, and there is no or very little migration between them. The second stage takes place when genetically differentiated populations come into geographic contact. If the gene pools of two populations are sufficiently different, progenies from interpopulational crosses are likely to have less fitness than progenies from intrapopulational crosses. Mating preferences are affected by genes. Alleles that decrease the probability of mating with individuals of a different population will, then, be selected against, while alleles increasing the probability of intrapopulational mating will be favored by natural selection. Eventually, the process may result in two reproductively isolated populations, and thus two different species. The question, "how much genetic differentiation occurs in the process of speciation," must be unfolded into two separate questions concerning the two stages of the process. The first question concerns the genetic differentiation occurring between allopatric populations that are likely to give rise to different species if and when they become, at least partially, sympatric. The second question refers to the amount of genetic differentiation taking place after sympatry, when the populations become reproductively isolated. 1 This is paper number XII in a series: "Enzyme variability in the Drosophila willistoni group." 2 Supported by NSF grant GB32895. 'Present address: Dept. of Biology, Brock University, St. Catherines, Ontario, Canada. 'Address: Department of Zoology, University of Indiana, Bloomington, Indiana.

Ford, J. 1974. Speciation in Australian birds adapted to arid habitats. Emu 74: 161–168.Several stages of speciation can now be identified in some birds occurring mainly in the mulga habitat of the...

The species of the genusVicia are characterized by a significant karyological differentiation in regard to the number and morphology of chromosomes and to the DNA content of the genomes. Some species groups represent descending dysploid series; polyploidy has been found only in few perennial taxa. The species are strongly separated by internal isolation factors, incompatibility and hybrid sterility being the most important ones. InVicia the speciation process is initiated by chromosomal rearrangements as an isolation mechanism, protected by this genetical barrier a divergent evolution of the new derivates may happen, the rate and the scale of it being dependent on the direction and force of the selection pressures. The self-pollination of most of the annual species ofVicia favours this process of quantum speciation even if the other isolation mechanisms are still imperfectly developped in the beginning of the speciation process. By this means a sympatric speciation is also possible, this is supported by distribution patterns of species in some groups of the genus. In this paper the experimental results of karyotype analysis and progeny testing of two lines ofVicia cordata have been discussed, these strains can be used as a model illustrating an initial speciation. The plants of them are very similar in morphological respect, their karyotypes however are clearly differentiated, the differences between them being in the same order as between good species of theVicia sativa complex. TheV. cordata strains are genetically isolated (besides their autogamy) by an incompatibility barrier, the fertility of the heterozygous individuals is however only slightly reduced. One of these strains has a karyotype typically for the speciesV. cordata while the structurally changed one of the second strain results from a chromosomal interchange. It is possible to identify those chromosomes involved in the reciprocal translocation by a comparison of the mitotic complement of both the strains, by the meiotic behaviour of their hybrids and by cytological testing of their progenies. Similar interchanges should be due to the karyotype evolution within theV. sativa complex at all according to the discussed dates. Some of the chromosomes of these taxa however have not been affected by major structural rearrangements, they are forming regular bivalents in the species hybrids indicating thus an high degree of homology. The utilization of interspecific gene transfer by recombination seems therefore possible for breeding purposes. We suppose that quantum speciation with a primary development of internal isolation followed by phylogenetic divergence is an important evolutionary pathway within many mainly annual and autogamous plant groups.

The recent biological definitions of species by Dobzhansky (1941), Mayr (1942), and others have stressed the attainment of reproductive isolation between two populations as the critical step in speciation. As a result, considerable interest has been aroused in the study of sexual isolation at various levels of divergence. The data, which have been accumulating quite rapidly, have been obtained in various ways, but interpretation of these results on a common basis has been rather difficult. It is desirable, therefore, to have some simple means of comparing the results from the different types of mating experiments. If the mating behavior or the degree of sexual isolation between two groups is under study, the mating possibilities are of the following four kinds.

Marine species are liable to dispersion by ocean currents and thus areal gradients of the degree of speciation depend on Coriolis parameters. If Coriolis parameters for past epochs are calculated from these “speciation gradients” some controversial results emerge.

HETEROSIS in maize appears to increase with increased genetic divergence of the parent populations over a rather wide range of diversity (MOLL, SAL- HUANA and ROBINSON 1962). It does not necessarily follow, however, that this relationship will hold throughout the entire ran.ge of diversity in the species. It is widely accepted that cumulative differences between isolated populations may eventually become great enough to cause genic unbalance in population hybrids, which may be manifest by poor F, viability. This is considered to be one of the possible steps toward speciation; and inferiority of interspecific hybrids is not uncommon. In the case of an organism which shows heterosis in crosses between divergent populations, it seems logical to expect that in crosses of extremely di- vergent populations, the expression of heterosis may be limited by unharmonious gene combinations in the F, hybrid. At higher levels of genetic divergence, then, an increase in divergence might be associated with a decrease in heterotic expres- sion. The issue in this report is whether or not heterosis in maize continues to in- crease at higher levels of diversity.

LeQuesne, W. J. (70 Lye Green Road, Chesham, Bucks, England) 1972. Further studies based on the uniquely derived character concept. Syst. Zool., 21:281-288.-A number of methods of selection of characters based on the uniquely derived character concept (LeQuesne, 1969) have been applied to published data on taxa of Orthopteroid insects and also to random data obtained by dealing cards. The latter has been used to verify the essential soundness of the statistical methods. The data on Orthopteroid insects show some uncertainty in the most likely phylogeny among the group, although verifying the existence of some already well-accepted groupings. It is shown that at least 54 out of 80 characters tested are not uniquely derived. Most work employing numerical taxonomic methods has been aimed at establishing phenetic relationships between taxa. Useful as this aim is, I suspect that the main application of numerical methods will in the future become the study of the speciation process and the relative effects of influences such as divergence, convergence, and parallel evolution. In an earlier paper (LeQuesne, 1969) I defined a "uniquely derived character" as one which has evolved only in one direction on a single occasion in the history of the group being studied. This concept produced the logical result that for two independent uniquely derived characters each with two character states, not more than three out of the four possible combinations of character states can be found. Thus, if all four combinations are actually found, one or both of the characters concerned is not uniquely derived. The conicept of the uniquely derived character is one that will, I am sure, help in the study of the speciation process; it is one that has been instinctively assumed by many taxonomists studying evolution and phylogeny. For the work described below, the data of Blackith and Blackith (1968) for higher taxa among the Orthopteroid orders has been carefully studied. For this purpose a number of Fortran programs have been written and run. In this, I am greatly indebted to Mr. J. Bryant, who not only performed much of the programming, but helped considerably in all phases of this work by his interest and valuable suggestions. THE COEFFICIENT OF CHARACTER

One of the most imiportant problems in the study of speciation has been that of the origin of reproductive isolating mechanisms, for it is by the building up of intrinsic barriers which prevent gene exchange between poptilations that we pass from the racial or subspecific to the specific level. Two theories have been proposed to explain how reproductive isolation might arise. The first, favored by Muller (1939, 1942), holds that reproductive isolation is a by-product of genetic divergence. As two subspecies differentiate in geographical isolation, genes which hamper free interbreeding with the other subspecies are incorporated into the genotype in the course of building up adaptive gene complexes. The reproductive isolation may be a pleiotropic effect, or perhaps be a result of change in gene function. The other theory, advanced by Dobzhansky (1940), holds that provided the two subspecies have diverged from one another far enough so that hybrids between them are less well adapted for any available habitat than either parental type, natural selection will act to build up further reproductive isolation, thus preventing the formation of inadaptive hybrids with consequent wastage of reproductive potential and food resources. These two theories are by no mneans mutually exclusive, and indeed both mechanisms in all probability play an imnportant part, perhaps being of greatest importance at dif

1. So far as the population data thus far amassed go, commensal rats in residential habitats are of type II; house mice may be of type I or III in fields but might show type II in residences, and fieral species or subspecies may range from type I to III. Altogether alloresponsive populations seem to be much commoner than the isoresponsive. 2. It is as yet little disclosed to what degree the differentiation of the type is correlated with speciation or subspeciation, even if only a proof that a subspecific population would hold type III as its fixed feature is given. The response types are supposed to be associated with the levels of population shyness. Hence some characters reflected in those may possibly be connected with sexual isolation provoking speciation. 3. Some awkward respects due to the heterogeneous trappability, depending upon the trap-response type, among a mixed population of marked and unmarked animals have been confirmed regarding the methodology for estimating parameters.

In recent years the speciation of parasites as related to their host relationships has presented some of the most interesting and at the same time most difficult problems in the field of parasitology. These problems are by no means of purely academic interest but are of prime importance in connection with the control and prophylaxis of a number of important infections of man and domestic animals.

Evolutionists rarely have the opportunity to analyze and characterize genetically populations of a species which are undergoing speciation. This may be because the final stages of speciation which result in the consolidation of isolating mechanisms are peculiarly rapid (Mayr, 1963). Drosophila paulistorum provides an opportunity for the genetic analysis of the speciation process since it is a superspecies composed of at least six semispecies which show varying degrees of reproductive isolation among themselves (Spassky et al., 1971). D. paulistorum has been the subject of a broad range of investigations many of which have been designed to shed light on the genetics of the speciation process as it has occurred in this superspecies. Dobzhansky and his colleagues (see Dobzhansky and Spassky, 1959 for references) discovered that strains of D. paulistorum from various regions of Central and South America did not always cross easily and in a number of cases when F1 progeny were obtained they were sterile. Systematic collecting throughout much of the northern half of South America and Central America followed by careful testing of all possible combinations of crosses revealed that D. paulistorum consists of a complex of six semispecies. Carmody et al. (1962) showed that there was strong and in some cases complete ethological isolation between the semispecies (see also Ehrman, 1965; Dobzhansky et al., 1969). Were it not for the occasionally fertile backcross male and the existence of the Transitional semispecies, some strains of which are capable of acting as a genetic bridge between two semispecies, this complex of semispecies would rightly be named as six sibling species. Spassky et al. (1971) have reviewed genetic, cytological and biochemical data relating to the relationships between the semispecies of D. paulistorum. Using these data they have attempted to deduce a historical explanation for the present geographical distributions and other relationships between the semispecies. The purpose of the present investigation is to continue this analysis using the data of Richmond (1972) with the goal of clarifying the genetic and evolutionary relationships between the semispecies of D. paulistorum.

The paper deals with the traffic control and job optimization in the marine canal system. The moving of vessels can be described as a set of discrete events and states. Some of these states can be undesirable such as conflicts and deadlocks. It is necessary to apply adequate control policy to avoid deadlocks and blocks the vessels’ moving only in the case of dangerous situation. This paper addresses the use of Petri net as modelling and scheduling tool in this context. To find better solutions the authors propose the integration of Petri net with a genetic algorithm. Also, a matrix based formal method is proposed for analyzing discrete event dynamic system (DEDS). The algorithm is developed to deal with multi-project, multi-constrained scheduling problem with shared resources. It is verified by a computer simulation using MATLAB environment.

Genetic studies were employed to rationalize speciation in the yeast genusMetschnikowia. Using haploid cultures derived parasexually or from isolated single ascospores, hybrids were produced between mostMetschnikowia taxa. The results provided strong evidence for the acceptance ofM. bicuspidata as type of the genus, and enabled clarification of the relationships among the recognized species. Speciation was based primarily on ascus and ascospore morphology, as classification based on physiological properties was shown to be ineffective.Metschnikowia bicuspidata var.californica var. nov. is described, and some possible evolutionary trends are discussed.

1. The primary genetic processes causing evolution in Crepis are gene mutations and structural changes in the chromosomes. 2. The roles of gene mutations are the production of morphological and physiological differentiation within and between species, the accumulation of intra- and interspecific sterility, and possibly the reduction in absolute size of the chromosomes. 3. The roles of chromosome changes are the genesis of intraspecific sterility leading to discontinuity and hence to speciation, and karyotype evolution through reduction in number and symmetry of the chromosomes. 4. The secondary genetic processes involved in the evolution of Crepis are interspecific hybridization, polyploidy and apomixis. 5. The roles of interspecific hybridization are the origin of a small number of new species, especially through amphidiploidy (cf. Babcock and Stebbins, 1938; Stebbins and Babcock, 1939), and the augmentation of karyotype evolution. 6. The roles of polyploidy and apomixis are a small amount of speciation ...

Previous workers have interpreted multivalents present at meiosis in the spermatogenesis of hybrid Triturus as due to translocation heterozygosity. An alternative hypothesis according to which these individuals would be homozygous for reduplicated chromosome ends is put forward here.

RIASSUNTOL'A. delinea l'importanza delle modificazioni cromosomiche del soma nel problema della speciazione delle piante che si riproducono vegetativamente.

The rust fungi are fully parasitic and arose from parasitic ancestors. Heteroecism was evidently universal during their major evolutionary outburst. Thus, the ecology of hosts and parasites was complexly interrelated and profundly influenced the evolution of the rusts. Divergence with their hosts probably has been the chief means of speciation in the rusts. Part of the process, especially in the more advanced groups, has been the initiation of autoecious species on the aecial hosts of parental heteroecious ones. This change may have triggered an evolutionary outburst through partial release from the ecological limits of the heteroecious ancestor. Jumps to hosts of varying taxonomic separation from the ancestral host must have given rise to many species and to some lineages; but few are easily documented. A single example suggests that a hybrid rust may be adapted to a hybrid between its parental hosts; and, if the hybrid host speciates, the rust may do so also.

The cichlid fishes of Africa exhibit two strikingly different patterns of evolution. That members of the genus Tilapia have attained a considerable measure of success by virtue of remaining ecologically generalized while members of the great species flocks which inhabit the major lakes, and which in the majority of cases have been derived from Haplochromis or a Haplochromis-like ancestor, have achieved their success by the diametrically opposite process of super-specialization has already been suggested (Fryer, 1960). The ecological generalization of Tilapia has largely precluded speciation in the great lakes: the diverse super-specializations of many members of the great species flocks have played an important part in their exploitation and sharing of a diversity of habitats and resources and in the ability of many species to co-exist in a single community. During the course of the preparation of a book on these fishes (Fryer and Iles, in press), in which many aspects of their biology will be considered, this difference has been more forcibly brought home to us and we are now able to make a more comprehensive and coherent comparison. As this impinges on several ecological and evolutionary problems related to one of the most spectacular of extant examples of speciation and adaptive radiation it was felt that a brief summary and discussion of certain implications may be of some value.

(1953). Some Speciation Problems in Australian Birds: With Particular Reference to the Relations between Bassian and Eyrean ‘Species-Pairs’. Emu - Austral Ornithology: Vol. 53, No. 2, pp. 131-145.

Facts and theories on the evolution of vocal learning in mammals and birds are reviewed. An attempt is made to articulate principles of general heuristic importance. Different contexts in which vocal learning occurs are evaluated. It is concluded that maximal stimulation of females and benefits accruing from formation of vocal dialects have been selective pressures leading to vocal learning. Correlations between intense speciation and vocal learning, and between long-lasting pair bonds and filial song learning, need further study. In all cases where selective pressures leading to vocal learning have been identified, females are the selective agent. Use of vocal signals to attract females is much rarer in mammals, and this is correlated with a low incidence of vocal learning. The successive steps leading from genetically determined motor ontogenies to vocal learning are discussed.

Speciation requires a change in the controlling factors of one or both of the species concerned, and so involves selective forces which vary with population density. The only good field evidence for such selection is Gershenson's on the hamster. The results of the interaction of selection and controlling factors vary with different systems of control. The mechanisms known to be able to maintain a polymorphism are listed. Many of them involve variable selective coefficients, but only one needs selection varying with population density. The use of polymorphism in detecting competition depends on the way the polymorphism is maintained. When the genetic system is independent of population density the usage is straightforward; when it is not, the results of the correlation analysis may only demonstrate the dependence.