Diffusion-driven period-doubling bifurcations

Discrete-time growth-dispersal models readily exhibit diffusive instability. In some instances, this diffusive instability parallels that found in continuous-time reaction-diffusion equations. However, if a sufficiently eruptive prey is held in check by a predator, predator overdispersal may also lead to one or a series of diffusion-driven period-doubling bifurcations. Quite common discrete-time predator-prey models exhibit this new brand of diffusive instability.     

Speciation and development

Understanding general principles about the origin of species remains one of the foundational challenges in evolutionary biology. The genomic divergence between groups of individuals can spawn hybrid inviability and hybrid sterility, which presents a tantalizing developmental problem. Divergent developmental programs may yield either conserved or divergent phenotypes relative to ancestral traits, both of which can be responsible for reproductive isolation during the speciation process. The genetic mechanisms of developmental evolution involve cis- and trans-acting gene regulatory change, protein–protein interactions, genetic network structures, dosage, and epigenetic regulation, all of which also have roots in population genetic and molecular evolutionary processes. Toward the goal of demystifying Darwin's “mystery of mysteries,” this review integrates microevolutionary concepts of genetic change with principles of organismal development, establishing explicit links between population genetic process and developmental mechanisms in the production of macroevolutionary pattern. This integration aims to establish a more unified view of speciation that binds process and mechanism.     

Speciation and legislation

Abstract

The chemical speciation of milks containing trace levels of aluminium defies experimental analysis because of the extremely low concentrations and labile equilibria present. Nevertheless, atomic absorption spectrophotometry data in combination with precisely determined formation constants have been used to construct speciation models simulated using the ECCLES computer program and the Cardiff thermodynamic database.

Formation constants for the Al³⁺-citrate, -succinate, -picolinate, and -malate systems are reported for 37°C and I = 150 mmol dm^?3. Total aluminium concentrations in a range of commercially available bovine milks are given.

In general, the major aluminium species present are charged citrate complexes which present little or no apparent threat to a healthy human as such complexes will not be absorbed through the intestinal walls. However, the importance of phosphate binding is revealed and further studies recommended.     

Speciation and Changing Environment

The current genetical theories regarding the effects of environmentalchanges in shaping new species are first reviewed briefly; Matthew'sconcept based upon paleontological and zoogeographic data isthen compared and found in accord with the genetical set. Thistheory proposes that changing climates, whether of an annualor long-term nature, induce speciation. Accordingly the northtemperate continental land-masses are viewed as the main arenasof vertebrate evolution, especially temperate Eurasia. A morerecent concept from biogeographic sources, that of Darlington,proves discordant to all the foregoing but agrees more closelywith observed facts of recent distribution and the geologicrecord. Its major premises are that speciation proceeds mostrapidly under tropical conditions and in regions of vast extent;hence, the Old World tropics are pointed to as the principaltheater of speciation. These two zoogeographic concepts arethen harmonized by showing that, during the period in whichmost of the evolution of the vertebrate taxa occurred, the tropicalbelts were much more extensive than at present and includedwhat are now north temperate regions. The genetic theories areshown to be especially valuable in elucidating the changes involvedin the life cycle of a species rather than the effects of majorclimatic changes.     

Speciation and Sexual Conflict

We review mathematical models that explicitly consider the dynamics of evolutionary change driven by sexual conflict over mating rate when males are selected for increasing mating success whereas females are selected to restrict mating rate. These models focus on a pair of traits each of which is controlled by a separate set of genes expressed in one sex only. The traits control the probability of mating and/or fertilization. Overall, there are at least six different dynamic regimes observed in models of sexual conflict: (1) continuous coevolutionary chase between the sexes (which can result in allopatric speciation as a byproduct), (2) evolution towards an equilibrium, (3) cyclic evolution, (4) evolution towards a line of equilibria with subsequent random drift along this line, (5) Buridan’s Ass regime involving extensive diversification in female alleles without comparable diversification in male alleles, and (6) extensive diversification in both male and female alleles (which can result in sympatric speciation). Mathematical models also show that different dynamic regimes can be observed with the same set of parameter values but under different initial conditions. It is also possible that the same population switches from one regime to another as a result of stochastic perturbations due to, say, random genetic drift. Moreover, different sets of loci controlling mating and fertilization in the same species can follow different dynamic regimes. We attempt to make some generalizations and identify important directions for theoretical and empirical work.     

Speciation genes

Until recently, the genes that cause reproductive isolation remained black boxes. Consequently, evolutionary biologists were unable to answer several questions about the identities and characteristics of "speciation genes". Over the past few years, however, evolutionary geneticists have finally succeeded in isolating several such genes, providing our first glimpse at factors that are thought to be representative of those underlying the origin of species. Evolutionary analysis of these genes suggests that speciation results from positive Darwinian selection within species. Molecular evolutionary study of the genes causing reproductive isolation may represent an important new phase in the study of speciation.     

Nonsymmetrical bifurcations in arterial branching

The results of optimality studies of the branching angles of arterial bifurcations are extended to nonsymmetrical bifurcations. Predicted nonsymmetrical bifurcations are found to be not unlike those observed in the cardiovascular system.     

Selfish Genes and Plant Speciation

A key to understand the process of speciation is to uncover the genetic basis of hybrid incompatibilities. Selfish genetic elements (SGEs), DNA sequences that can spread in a population despite being associated with a fitness cost to the individual organism, make up the largest component in many plant genomes, but their role in the genetics of speciation has long been controversial. However, the realization that many organisms have evolved a variety of suppressor mechanisms that reduce the deleterious effects of SGEs has spurred renewed interest in their importance for speciation. The relationship between SGEs and their suppressors often results in strong selection on at least two interacting loci and this arms race therefore creates a situation where SGEs may give rise to hybrid dysgenesis due to Bateson–Dobzhansky–Muller incompatibilities (BDMIs). Here, I argue that examples of SGEs underlying BDMIs may be particularly common among plants compared to other taxa and that a focus on loci involved in genetic conflicts may be especially useful for workers interested in the genetics of plant speciation. I first discuss why the frequent mating system shifts and hybridization events in plants make for a specifically dynamic relationship between SGEs and plant host genomes. I then review some recent empirical observations consistent with SGE-induced speciation in plants. Lastly, I suggest some future directions to test fully the utility of this perspective.     

Phylogeny and Speciation of Felids

The phylogeny of the Felidae is reconstructed using a total evidence approach combining sequences from 12S rRNA, 16S rRNA, NADH-5, and cytochrome b genes with morphological and karyological characters. The 1504-character data set generated two equally parsimonious trees (CI = 0.413, 1795 steps) of which a strict consensus revealed one polytomy in the placement of the bay cat group. The tree supports several traditional groupings such as the genera Panthera and Lynx and the ocelot group of small South American felids, and it provides additional resolution of relationships within and among the major felid lineages. Combining phylogenetic, distributional, and ecological data indicates that vicariant speciation has played a relatively minor role in the diversification of the felids (approximately 26% of events), while sympatric speciation has been more important than expected on theoretical grounds (approximately 51.8% of events), although postspeciation dispersal may have blurred the boundaries between sympatric, parapatric, and peripheral isolate modes. An examination of ecological changes on the felid tree shows repeated patterns of resource partitioning in time (activity patterns), space (preferred habitat type), and food (as measured by body size) among closely related species. The rapid diversification of the cats thus appears to have been associated more with ecological than with geological separation.     

Speciation centres and sustainable development

Biodiversity can be regarded as the result of the dynamic processes starting with speciation and ending with species extinction. Speciation urges populations of organisms within an already‐existing species to change as a consequence of ecological change. It can occur everywhere as the selective pressures causing it are randomly distributed ( Dobzhansky et al., 1977 , p. 4); hence, a need to promote a development policy that does not endanger these natural processes. This conservation concept addresses a global ecological policy and is different from the more classical concept of conservation based on the promotion of natural parks to preserve rare species and their direct habitats. The latter concept has the disadvantage to lead to the protection of limited surfaces, which cannot harbour most of speciation centres and leaves the rest of the world unprotected. Examples will illustrate the dangers faced by continental and insular speciation centres.     

Speciation and Bursts of Evolution

A longstanding debate in evolutionary biology concerns whether species diverge gradually through time or by rapid punctuational bursts at the time of speciation. The theory of punctuated equilibrium states that evolutionary change is characterised by short periods of rapid evolution followed by longer periods of stasis in which no change occurs. Despite years of work seeking evidence for punctuational change in the fossil record, the theory remains contentious. Further there is little consensus as to the size of the contribution of punctuational changes to overall evolutionary divergence. Here we review recent developments which show that punctuational evolution is common and widespread in gene sequence data.