Intraspecific resource competition as a cause of sympatric speciation

Journal Article[In most models of speciation], the fitness value of an animal is determined by the genotype it has, and the habitat in which it lives. In a more realistic model it should also depend on how much necessary resource is available for the animal and the competition from other genotypes for this resource. Models can be constructed which take into account such competition between genotypes. In a special case one can find the exact conditions for the stable coexistence of two incipient species, which have some degree of gene flow between them but also slightly different resource utilization distributions. An interesting property of this class of models is that they show how sympatric speciation can occur in a species where all animals live in the same habitat and under the same fitness regime, but differ, due to their genetic constitution, in their resource utilization

Conditional relatedness, recombination, and the chromosome numbers of insects

Book ChapterIf two polymorphic loci are out of phase equilibrium, a homozygote at one of these loci is more highly related to its kin, at the other locus, than is an equivalent heterozygote. As a result, selection can favor (1) phenotypic responses to relative heterozygosity, and (2) increased recombination between the loci inducing these responses. Selection is expected to have these consequences only to the extent that kin strongly affect each other's fitnesses. The chromosome numbers of social insects appear to be higher, on average, than those of allied solitary species, which is consistent with this model on the assumption that chromosome numbers are selected in part for their effects on recombination

Evidence for a cryptic species complex in the ant parasitoid Apocephalus paraponerae (Diptera: Phoridae)

Journal ArticleCryptic species complexes occur in many taxa, in particular in the insect order Diptera. Here we describe a possible new cryptic species complex in the family Phoridae. Three lines of evidence suggest that Apocephalus paraponerae, an ant parasitoid, is actually a complex of at least four genetically distinct but morphologically almost indistinguishable populations attacking at least three different ant hosts. First, the host-location cues used by A. paraponerae to locate two of the host species differ. Second, A. paraponerae attracted to these two ant host species differ consistently in average hind femur length and costal vein length, two measures of body size. Finally, mtDNA sequence comparisons of individuals from a variety of locations and host ant species indicate high sequence divergence between populations and low sequence divergence within populations. We discuss aspects of host location behaviour that may be important in cryptic species formation, and we speculate that many such cryptic complexes may exist in this family and others with similar mechanisms of host location and exploitation

Models of sex ratio evolution

Journal ArticleOur understanding of sex ratio evolution depends strongly on models that identify: (1) constraints on the production of male and female offspring, and (2) fitness consequences entailed by the production of different attainable brood sex ratios. Verbal and mathematical arguments by, among others, Darwin, Dusing, Fisher, and Shaw and Mohler established the fundamental principle that members of the minority sex tend to have higher fitness than members of the majority sex. They also outlined how various ecological, demographic and genetic variables might affect the details of sex-allocation strategies by modifying both the constraints and the fitness functions. Modern sex-allocation research is devoted largely to the exploration of such effects, which connect sex ratios to many other aspects of the biologies of many species

Parasites and sex

Book ChapterParasites of many kinds have long been recognized as important regulators of population size (e.g., May, 1983b), but only during the last decade or two have they been widely viewed as the protagonists in fast-paced (and long-running) evolutionary thrillers involving subtle features of the biochemistry, anatomy, and behavior of their hosts. On this view, their power as agents of evolution derives from their ubiquity and from the great amounts of mortality they can cause (which are also the properties that make them effective agents of population regulation) and, just as importantly, from their imperfect (but improvable) abilities to defeat the imperfect (but improvable) defenses of their hosts. Thus each party is expected to experience the other as a changeable (and generally worsening) part of its environment

Biological richness of deserts

Book ChapterA desert is "waterless," "treeless," "barren," "remote," "uninteresting," and "presumably uninhabited," according to the authoritative Oxford English Dictionary. The word is derived from deserere, a Latin verb meaning "to leave." In English, to desert is still to "abandon," "forsake," or "fail." Because language shapes perception, emptiness tends to figure prominently in one's first (and possibly lasting) impression of any place referred to as a desert. What should be there (water, trees) is absent. What is there is useless and dull. "Normal" plants and animals may once have lived there, but if so, they found the place inhospitable and eventually departed, leaving behind an impoverished residue of twisted, spiny losers

Ideas in ecology

Journal ArticleThe word "ecology" means different things to different people. For example, during the last 25 years or so the word has been used to label attitudes, life-styles, consumer goods, political parties, and college courses. In the 1960s one university renamed its "Home Economics" course "Home Ecology." (But our own biology department reacted to the growing visibility of its conventional "Ecology" course by renaming it "Population Biology.") It is often said that Thoreau coined the word "ecology." He certainly ought to have done so, given the Rousseauesque yearnings that surround the word, and this may be why the myth lives on, even though it stems from a 1958 misreading of the word "geology" as "ecology" in one of his letters (James 1985). The German biologist Haeckel was actually the first to use the word "Oecologie," in 1866

Sexual dimorphism in the Hymenoptera

Journal ArticleSpectacular sex differences of many kinds occur abundantly among the wasps, bees and ants that make up the insect order Hymenoptera. In some cases these differences are so extreme that males and females of the same species have been classified in different genera for decades, until a chance observation of mating, or emergence from a single nest, establishes their identity. Even where the sexes are similar in morphology they lead very different lives. The hard-working females hunt for prey or other larval provisions, and in many taxa they carry these provisions back to a nest that they have constructed to protect their offspring. The males, by contrast, lead short lives (sometimes nasty and brutish), devoted to the single purpose of inseminating females. Countless variations on this theme have evolved during the long and successful history of the order, and other features of hymenopteran biology have allowed these sex differences of ecology to be translated into equally striking sex differences of behavior, morphology and physiology