Stimulatory Functions of Male Genitalia in () Alexander and () Doane (Diptera: Tipulidae) and Implications for Theories of Genital Evolution.

Male genitalia have been hypothesized to function as courtship devices during copulation, but it is difficult to use behavioral observations to test this hypothesis because male genitalia are usually hidden inside the female during copulation. In tipuloid flies, however, nearly all of the male's complex genital structures remain outside the female. Copulation behavior and genital morphology in () and .

Genital courtship and female-active roles in mating: sexual selection by mate choice in Caenorhabditis elegans.

A new bridge between studies of sexual selection and the massive literature on Caenorhabditis elegans behaviourand nervous system properties promise to provide important new insights into both fields. This paper shows that mate choice likely occurs in hermaphrodite C. elegans on the basis of stimulation from the male genital spicules, making it possible to apply the toolkit of extensive background knowledge of C.

Complex behavioral plasticity is not reduced in spiderlings with miniature brains.

The brains of smaller animals are smaller than those of their larger relatives, but it is not clear whether their adaptive behavioral flexibility is more limited. Previous interspecific comparisons found that aspects of web construction behavior of very small orb weaving spiders (0.005 mg) were no less precise than those of much larger related orb weavers (30 mg), but the behaviors tested were relatively simple.

Demonstrating sexual selection by cryptic female choice on male genitalia: What is enough?

Rapid divergence in external genital structures occurs in nearly all animal groups that practice internal insemination; explaining this pattern is a major challenge in evolutionary biology. The hypothesis that species-specific differences in male genitalia evolved under sexual selection as courtship devices to influence cryptic female choice (CFC) has been slow to be accepted. Doubts may stem from its radical departure from previous ideas, observational difficulties because crucial events occur hidden within the female's body, and alternative hypotheses involving biologically important phenomena such as speciation, sperm competition, and male-female conflicts of interest.

Why the Static Allometry of Sexually-Selected Traits Is So Variable: The Importance of Function.

Sexually-selected traits often show positive static allometry, with large individuals bearing disproportionately large structures. But many other sexually-selected traits show isometry or even negative allometry, with trait size varying relatively little with body size. We recently proposed that the functions of these traits (as aggressive signals, weapons, courtship signals, and contact courtship devices) determine their allometries.

The allometry of CNS size and consequences of miniaturization in orb-weaving and cleptoparasitic spiders.

Allometric studies of the gross neuroanatomy of adults from nine species of spiders from six web-weaving families (Orbicularia), and nymphs from six of these species, show that very small spiders resemble other small animals in having disproportionately larger central nervous systems (CNSs) relative to body mass when compared with large-bodied forms. Small spiderlings and minute adult spiders have similar relative CNS volumes. The relatively large CNS of a very small spider occupies up to 78% of the cephalothorax volume.

Experiments with genitalia: a commentary.

There has been a recent burst of studies of the function of genitalia, many of which share several important shortcomings. Given that further studies on this topic are likely (there are probably millions of species showing rapid genital divergence), I discuss the studies critically to promote clear formulation of hypotheses and interpretation of results in the future. I also emphasize some possibly important but neglected variables, including female stimulation, phylogenetic contexts, and the behavior of male genitalia, and outline simple techniques that could improve future studies.

Postcopulatory sexual selection: Darwin's omission and its consequences.

In one of his few major oversights, Darwin failed to appreciate that male-male competition and sexual selection can continue even after copulation has begun. The postcopulatory equivalents of both direct male-male battles (sperm competition) and female choice (cryptic female choice) occur within the female's body. Recognition of this hidden, but intense, sexual competition provides new insights into a variety of fields.

Experimental modifications imply a stimulatory function for male tsetse fly genitalia, supporting cryptic female choice theory.

One of the most sweeping of all patterns in morphological evolution is that animal genitalia tend to diverge more rapidly than do other structures. Abundant indirect evidence supports the cryptic female choice (CFC) explanation of this pattern, which supposes that male genitalia often function to court females during copulation; but direct experimental demonstrations of a stimulatory function have been lacking. In this study, we altered the form of two male genital structures that squeeze the female's abdomen rhythmically in Glossina pallidipes flies.

Evolution of genitalia: theories, evidence, and new directions.

Many hypotheses have been proposed to explain why male intromittent genitalia consistently tend to diverge more rapidly than other body traits of the same individuals in a wide range of animal taxa. Currently the two most popular involve sexual selection: sexually antagonistic coevolution (SAC) and cryptic female choice (CFC). A review of the most extensive attempts to discriminate between these two hypotheses indicates that SAC is not likely to have played a major role in explaining this pattern of genital evolution.

Seasonal patterns of parasitism of the tropical spiders Theridion evexum (Araneae, Theridiidae) and Allocyclosa bifurca (Araneae, Araneidae) by the wasps Zatypota petronae and Polysphincta gutfreundi (Hymenoptera, Ichneumonidae).

The rates of parasitism of Theridion evexum by the parasitoid wasp Zatypota petronae, and Allocyclosa bifurca by Polysphincta gutfreundi, were followed for two years. Parasitism of T. evexum was very low (mean 1.

Static allometry and animal genitalia.

A survey of 117 species of arthropods and 17 species of vertebrates showed a strong trend for male genitalia to have relatively low static allometric values. This trend contrasts with the allometry of other structures under sexual selection, which usually show steep allometric slopes. The trend to low allometric genital values is less consistent in mammals than in arthropods.

Fitting together: copulatory linking in some Neotropical Chrysomeloidea.

Copulatory linking of male and female genitalic structures in 11 Neotropical species of Chrysomelidae and one species of Megalopodidae was studied by freezing and then dissecting pairs of beetles in copula. In Megalopus armatus (Megalopodidae) the male has a long endophallus with complex membranous protuberances and a terminal flagellum that probably reaches the spermatheca. In the subfamily Eumolpinae the females have telescoping ovipositors through which the male endophalli pass, reaching to or near the mouth of the spermathecal duct.

Miniaturized orb-weaving spiders: behavioural precision is not limited by small size.

The special problems confronted by very small animals in nervous system design that may impose limitations on their behaviour and evolution are reviewed. Previous attempts to test for such behavioural limitations have suffered from lack of detail in behavioural observations of tiny species and unsatisfactory measurements of their behavioural capacities. This study presents partial solutions to both problems.

Tie them up tight: wrapping by Philoponella vicina spiders breaks, compresses and sometimes kills their prey.

We show that uloborid spiders, which lack the poison glands typical of nearly all other spiders, employ thousands of wrapping movements with their hind legs and up to hundreds of meters of silk line to make a shroud that applies substantial compressive force to their prey. Shrouds sometimes break the prey's legs, buckle its compound eyes inward, or kill it outright. The compressive force apparently results from the summation of small tensions on sticky lines as they are applied to the prey package.

Evolutionary conflicts of interest: are female sexual decisions different?

Analyses of reproductive conflicts of interests have yielded important evolutionary insights in many areas of biology. The usefulness of conflict analyses of traits that have been traditionally interpreted as resulting from female choice is controversial, however. This article explores a possible explanation for why conflicts of interest may be ameliorated in female choice situations.

Rapid divergent evolution of sexual morphology: comparative tests of antagonistic coevolution and traditional female choice.

Male structures specialized to contact females during sexual interactions often diverge relatively rapidly over evolutionary time. Previous explanations for this pattern invoked sexual selection by female choice, but new ideas emphasize possible sexually antagonistic coevolution resulting from male-female conflict over control of fertilization. The two types of selection have often not been carefully distinguished.

Male-female conflict and genitalia: failure to confirm predictions in insects and spiders.

Some recent models suggest a new role for evolutionary arms races between males and females in sexual selection. Female resistance to males is proposed to be driven by the direct advantage to the female of avoiding male-imposed reductions in the number of offspring she can produce, rather than by the indirect advantage of selecting among possible sires for her offspring, as in some traditional models of sexual selection by female choice. This article uses the massive but hitherto under-utilized taxonomic literature on genitalic evolution to test, in a two-step process, whether such new models of arms races between males and females have been responsible for rapid divergent evolution of male genitalia.

The function of female resistance behavior: intromission by male coercion vs. female cooperation in sepsis flies (Diptera: Sepsidae).

Female resistance behavior that occurs prior to intromission does not by itself imply forced copulation. Such behavior may function instead as a test of the male in order to favor some males over others, or to induce the male to desist. Thus, male persistence and forcefullness may sometimes be better described as persuasion rather than coercion.

ONE SIZE FITS ALL? RELATIONSHIPS BETWEEN THE SIZE AND DEGREE OF VARIATION IN GENITALIA AND OTHER BODY PARTS IN TWENTY SPECIES OF INSECTS AND SPIDERS.

Hypotheses regarding the function of elaborate male genitalia were tested in a sample of insects and spiders by comparing their allometric values (slopes in log-log regressions on indicators of body size) with those of other body parts. Male genitalia consistently had lower slopes than other body parts. Perhaps as a consequence of this pattern, genitalic size also tended, though less consistently, to have lower coefficients of variation than did the size of other body parts.

EVIDENCE FOR WIDESPREAD COURTSHIP DURING COPULATION IN 131 SPECIES OF INSECTS AND SPIDERS, AND IMPLICATIONS FOR CRYPTIC FEMALE CHOICE.

Male courtship behavior is generally thought to function prior to copulation, as an inducement to the female to allow the male to copulate with her; this study indicates however, that male courtship during and following copulation ("copulatory courtship") is common in insects and spiders (81% of 131 species in 102 genera and 49 families, mostly Coleoptera, Hemiptera, Diptera, and Araneioidea). Copulatory courtship is apparently evolutionarily labile, as expected if it is under sexual selection; intrageneric variation occurred in all 17 genera in which more than one species was observed. In 81% of 94 species with copulatory courtship, the male abandoned the female soon after copulation ended; thus, copulatory courtship appears not to function generally to induce acceptance of further copulatory attempts.

SPECIES ISOLATION, GENITAL MECHANICS, AND THE EVOLUTION OF SPECIES-SPECIFIC GENITALIA IN THREE SPECIES OF MACRODACTYLUS BEETLES (COLEOPTERA, SCARABEIDAE, MELOLONTHINAE).

The question asked was why male genitalic structures have diverged in three syntopic species of Macrodactylus beetles. Four hypotheses were evaluated: 1. The ways in which male genitalia mesh with internal female structures indicate that selection for species isolation via mechanical exclusion ("lock and key") is unlikely to explain the genitalic differences.

MALE DIMORPHISMS IN BEETLES AND EARWIGS AND THE QUESTION OF DEVELOPMENTAL CONSTRAINTS.

Analysis of 17 species from six families indicates that male dimorphisms in weapon design may be common, at least in homed beetles. This flexibility in developmental programs constitutes evidence against the idea that the forms of these animals' weapons are the result of developmental constraints.