Uniparental Species Research Articles

Sexual size dimorphism in shorebirds, gulls, and alcids: the influence of sexual and natural selection.

Charadrii (shorebirds, gulls, and alcids) have an unusual diversity in their sexual size dimorphism, ranging from monomorphism to either male-biased or female-biased dimorphism. We use comparative analyses to investigate whether this variation relates to sexual selection through competition for mates or natural selection through different use of resources by males and females. As predicted by sexual selection theory, we found that in taxa with socially polygynous mating systems, males were relatively larger than females compared with less polygynous species. Furthermore, evolution toward socially polyandrous mating systems was correlated with decreases in relative male size. These patterns depend on the kinds of courtship displays performed by males. In taxa with acrobatic flight displays, males are relatively smaller than in taxa in which courtship involves simple flights or displays from the ground. This result remains significant when the relationship with mating system is controlled statistically, thereby explaining the enigma of why males are often smaller than females in socially monogamous species. We did not find evidence that evolutionary changes in sexual dimorphism relate to niche division on the breeding grounds. In particular, biparental species did not have greater dimorphism in bill lengths than uniparental species, contrary to the hypothesis that selection for ecological divergence on the breeding grounds has been important as a general explanation for patterns of bill dimorphism. Taken together, these results strongly suggest that sexual selection has had a major influence on sexual size dimorphism in Charadrii, whereas divergence in the use of feeding resources while breeding was not supported by our analyses.

SEXUAL SIZE DIMORPHISM IN SHOREBIRDS, GULLS, AND ALCIDS: THE INFLUENCE OF SEXUAL AND NATURAL SELECTION

Charadrii (shorebirds, gulls, and alcids) have an unusual diversity in their sexual size dimorphism, ranging from monomorphism to either male-biased or female-biased dimorphism. We use comparative analyses to investigate whether this variation relates to sexual selection through competition for mates or natural selection through different use of resources by males and females. As predicted by sexual selection theory, we found that in taxa with socially polygynous mating systems, males were relatively larger than females compared with less polygynous species. Furthermore, evolution toward socially polyandrous mating systems was correlated with decreases in relative male size. These patterns depend on the kinds of courtship displays performed by males. In taxa with acrobatic flight displays, males are relatively smaller than in taxa in which courtship involves simple flights or displays from the ground. This result remains significant when the relationship with mating system is controlled statistically, thereby explaining the enigma of why males are often smaller than females in socially monogamous species. We did not find evidence that evolutionary changes in sexual dimorphism relate to niche division on the breeding grounds. In particular, biparental species did not have greater dimorphism in bill lengths than uniparental species, contrary to the hypothesis that selection for ecological divergence on the breeding grounds has been important as a general explanation for patterns of bill dimorphism. Taken together, these results strongly suggest that sexual selection has had a major influence on sexual size dimorphism in Charadrii, whereas divergence in the use of feeding resources while breeding was not supported by our analyses.Corresponding Editor: E. Ketterson

Genetic diversity in thelytokous oribatid mites (Acari; Acariformes: Desmonomata)

The oribatid mite taxon Desmonomata contains the largest known grouping of animals which reproduce by thelytokous parthenogenesis. Considering long-standing views on the fate of thelytokous lineages, their apparent radiation is a paradox, made even more interesting by a general lack of life-history characteristics normally ascribed to thelytokous animals. In addition, existing hypotheses suggest that at least one large sexual mite taxon, the Astigmata, had its origins in this asexual radiation. Electrophoretic data imply that there is no meiotic recombination in most of the species studied, and that rare males are nonfunctional. Compared with one of the sexual species, there is relatively low genetic diversity among the thelytokes, but no case was a population comprised of only one clone. Unlike most other uniparental species, these mites have no close sexual relatives, which means that asexuality is not recent and genetic variability may have arisen since the loss of sex.

Strategies of mass change in breeding birds

Birds experience strikingly different patterns of mass change during breeding. In some species with uniparental incubation, the incubating parents (mostly females) lose mass and attain their lowest point when the chicks hatch (Incubatory mass loss strategy = IML). In species with shared incubation, or with intense incubation feeding, the incubating parents maintain or increase in body mass without reducing attentiveness levels (Incubatory mass constancy = IMC). In other species, uniparental incubation with IMC is associated with reduced levels of attentiveness. The mobilization of fat stores or its preservation are involved in the two strategies. IML leads to mass increases after hatching of the young, while the opposite is true for IMC. The non-incubating sex in uniparental species does not experience significant mass changes during breeding. Fasting endurance, predation risk and mode of development are proposed as the main selective factors determining strategy. Latitude, climate, diet and food availability interact with the main factors. From a revision of the literature we can deduce that IML is mainly found among large birds with precocial development, while IMC is typical of smaller species with altricial development. Proportional mass losses are positively correlated with body mass in IML-species, as well as in precocial species, where body mass explains more than 70% of the variation in proportional mass change. Incubation periods increase with body mass in uniparental IMC-species, but not in IML-species. IML is thus associated to fast embryonic growth in large species. Successful raising of highly-dependent young in altricial and semialtricial species apparently depends on one of the parents retaining reserves until hatching. Subsequent mass losses may be necessary to maintain the brooding parent through a period when nestlings require heat, insulation and food. Patterns of mass change are not mere consequences of reproductive stress but the outcome of adaptive compromises between different selective factors and constitute an important aspect of the breeding biology and life history of birds.

Biosystematic studies onAphytis in India—A promising area of research

Species of the genusAphytis Howard (Hymenoptera, Chalcidoidea, Aphelinidae) develop as primary ectoparasites of armoured scale insects (Homoptera, Coccoidea and Diaspididae) and are the most important natural enemies of this group of pests. Several species have been successfully employed in the biological control of important armoured scale insect pests in different parts of the world. In spite of the importance ofAphytis, very little is known about the species occurring in India, a promising area for additional and important species. In the past although taxonomists have made significant contributions to our knowledge of Indian Chalcidoidea, the genusAphytis has largely been neglected because the identification of the species in this group is extremely difficult for want of readily recognizable morphological criteria and due to the common occurrence of sibling and uniparental species. The recognition of sibling species and different biological races is often important in biological control. Hence there is a need in India to initiate studies onAphytis to establish the identity of cryptic species and to recognize biological races and other infra-specific entities exhibiting morphological and biological differences, with special attention to those parasitic on armoured scale insects on economically important plants. These studies would pave the way for biological control strategies for pest species in India and elsewhere and also for those which may eventually attain pest status due to changing ecosystems.

Seasonal Distribution of Trichogramma (Hymenoptera: Trichogrammatidae) Species Associated with a Maryland Soybean Field

Heliothis virescens (F.) egg cloths were used to sample Trichogramma populations in a 450-m2 soybean plot and an adjoining 450-m2 plot of natural, weedy vegetation during 1981 and 1982. Fourteen biparental and one uniparental species were collected, including, in descending order of abundance, T. pretiosum Riley, T. minutum Riley, T. exiguum Pinto and Platner, T. retorridum (Girault), T. marylandense Thorpe, T. parkeri Nagarkatti, and T. nubilale Ertle and Davis. Cross-mating tests determined the existence of a Trichogramma population that is morphologically indistinguishable but reproductively isolated from T. pretiosum . Collections of this new population were only 5% as frequent as those of T. pretiosum . The seasonal distributions of the species are described, and a method for screening field collections of Trichogramma for sibling and cryptic species is presented.

SYSTEMATICS OF THE TRICHADENOTECNUM ALEXANDERAE SPECIES COMPLEX (PSOCOPTERA: PSOCIDAE) BASED ON AN INVESTIGATION OF MODES OF REPRODUCTION AND MORPHOLOGY

AbstractTrichadenotecnum alexanderae Sommerman is shown to represent one biparental (= euphrasic) species capable of facultative parthenogenesis (thelytoky) and three uniparental (= obligatorily parthenogenetic) sibling species, as determined by tests for mating, life history observations, and morphological analysis of specimens over the geographic range of the species complex. The name T. alexanderae is restricted to the biparental species because the holotype is a male. The three uniparental species are here named and described as T. castum n. sp., T. merum n. sp., and T. innuptum n. sp. The female of T. alexanderae is redescribed to allow its separation from the three uniparental species. A key to females of the species complex is supplied. All three uniparental species were derived from the biparental ancestor of T. alexanderae. Most collections of populations represented only by females consist of one or more uniparental species. Facultative parthenogenesis is shown to maintain a population of T. alexanderae through one generation only. The biparental species is found not to be restricted geographically to a relictual or peripheral range within the species complex, but to occupy a rather wide, north-temperate distribution across eastern North America.

A biosystematic study ofAspidiotus neriiBouché (Homoptera: Diaspididae), with the description of one new species

Summary Uniparental (UP) and biparental (BP) populations of the oleander or ivy scale, Aspidiotus nerii Bouche, were reared under similar conditions. Development of the UP population was always slower than that of the BP scales. UP females usually produced less than half the number of progeny the BP females had, and the patterns of development and oviposition were quite dissimilar. The shield of UP females was slightly, but consistently, darker than that of BP females, and the latter never colonized Pittosporum undulation, the only host-plant on which UP population occur in Israel. These criteria are used to describe the uniparental population as Aspidiotus paranerii Gerson sp. nov. and to differentiate it from A. nerii. As the biology of A. paranerii clearly differs from that of a Californian uniparental sibling species of A. nerii, it is argued that the latter may have a series of such parthenogenetic relatives.

Biological Control of the Tomato Fruitworm, Cabbage Looper, and Hornworms on Processing Tomatoes in Southern California, Using Mass Releases of Trichogramma pretiosum123

Parasitization of eggs of the tomato fruitworm, Heliothis zea (Boddie), the cabbage looper, Trichopilusia ni (Hübner), and horn worms (primarily the tobacco hornworm, Manduca sexta (Johannson)), was studied on tomato foliage in Orange County, Calif., in 1966 and 1967. Mass releases of Trichogramma for biological control of these pests on processing tomatoes were assessed, using a uniparental species in 1968 and the native T. pretiosum Riley in 1969. Parasitization of tomato fruit worm, cabbage looper, and horn worm eggs averaged 55.7, 53.4, and 49.5%, respectively, for the June-August survey period in 1966 and 51.4, 24.6, and 41.9% for the August-October period in 1967. T. pretiosum was the only parasite reared from the eggs. In 1966 and 1967, 12.7 and 11.9%, respectively, of the tomatoes were in of the jured by the tomato fruit worm. Parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs in 1968 averaged 81.2, 58.7, and 76.8%, respectively, in the release field compared to 74.9, 42.1, and 81.4% in the control. Most of the egg parasitization in both fields was by T. pretiosum. Of 13,136 and 14,810 fruit examined in the release and control fields, respectively, in 1968, 1.6 and 2.9% were injured by the tomato fruit worm. In 1969, parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs averaged 64.4, 39.0, and 57.7%, respectively, in the release field compared with 42.4, 9.9, and 45.2% in the control. Parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs was about 5, 7, and 10 times higher, respectively, in the release field than that in the control for the first 6 weeks. Of 8454 and 7714 fruit examined in 1969 in the release and control fields, respectively, 2.1 and 7.2% were injured by the tomato fruit worm.

Variation in Three Sympatric Sibling Species of Whiptail Lizards, Genus Cnemidophorus

Specific relationships are augmented for three sibling species of the sexlineatus group of the genus Cnemidophorus (C. inornatus: bi- parental, C. uniparens: uniparental, and C. velox: uniparental) by analy- ses of variation in sympatric populations. Sympatric contacts total seven for C. inornatus and C. uniparens in Arizona, Chihuahua, and New Mexico, one for C. uniparens and C. velox in central Arizona, and one for C. inor- natus-C.uniparens- C. velox in central New Mexico. These contacts occur inecotonal habitats between desert-grassland (C. uniparens), plains grass- land (C. inornatus), and pinyon-juniper woodland (C. velox). Variation in tax o n o m i c characters an a 1 y z e d by standard statistical methods for single frequency distributions indicates that C. inornatus gen- erally has lower values for scales around mid-body (SAB), scales between the paravertebral light stripes (SPV), higher SPV/SAB x 100 and lower numbers of femoral pores (FP) than C. uniparens. Cnemidophorus velox, on the other hand, has higher values for SAB, SPV, and SPV/SAB x 100 than does C. uniparens. Of the three species, C. velox tends to have the lowest values for interlabial scales (ILS) and the highest ones for preanal scales (PAS), whereas both C. inornatus and C. uniparens resemble each other in these characters. Samples of both uniparental species tend to be less vari- able than those of C. uniparens. Where sympatric, C. uniparens and C. velox are quite distinct in color pattern, with C. uniparens having essentially six stripes and C. velox, seven. Cnemidophorus inornatus most commonly has seven stripes, but both six and eight-striped individuals also occur. In features of scutellation, C. inornatus is the most distinct with granu- lar postantebrachial and mesoptychial scales. The postantebrachials and mesoptychials of C. velox are essentially intermediate between those of C. inornatus and C. uniparens, but more closely resemble the enlarged, angu- lar scales of C. uniparens. No males identified conclusively as C. uniparens or C. velox were found, althoughthree male specimens similar to C. uniparens were obtained. These specimens and an associated female were taken from areas of sympatry, and may well represent hybrids between C. uniparens and C. inornatus. As yet,

Ecological Relationships of Two Species of the Lizard Genus Cnemidophorus in the Santa Rita Mountains of Arizona

Ecological relationships of locally sympatric populations of the southern whiptail (Cnemidophorus tigris gracilis Baird and Girard), and the Chihuahua whiptail (Cnemidophorus exsanguis Lowe) on the Santa Rita Experimental Range, Arizona, were studied intermittently in 1962 and for their entire period of activity in 1963. Although analysis of stomach contents (consisting largely of termites) and daily activity pattern reveal little divergence between the two species, differences in foraging behavior may reflect differences in the kinds of food resources being exploited. Cnemidophorus exsanguis is an all-female species and has a clutch size half again as great as that of C. tigris. The indications are that competition does occur. About 20%o of the species belonging to the lizard genus Cnemidophorus (whiptail lizards) are uniparental, males being either unknown or extremely rare (Maslin, 1962, 1966). Three of the five species groups recognized within the genus include uniparental species, there being one such species for both the TESSELATUS and DEPPEI groups, and several in the SEXLINEATUS group. With the exception of Cnemidophorus cozumelus, which occurs on the Yucatan Peninsula of Mexico (and nearby islands), all of the uniparental species are restricted to an area from western Colorado and southeastern Utah to north-central Mexico, and from central Arizona to, western Texas. Few previous studies have been concerned with the ecology of the uniparental whiptails, possibly because of the uncertainty evident in the literature as to how uniparental species should be treated taxonomically (see, e.g., Maslin, 1966). Only M'ilstead (1953) has reported a comprehensive ecological study involving both unisexual and bisexual species of Cnemidophorus exsanguis. My paper reports such a study carried out with Cnemidophorus exsanguis Lowe (uniparental) and C. tigris gracilis Baird and Girard (bisexual). DISTRIBUTION AND HABITAT The overall geographic ranges of Cnemidophorus tigris gracilis and C. exsanguis overlap widely. Cnernidophorus tigris gracilis occurs in northeastern Sonora and northwestem Chihuahua, Mexico, in southwestern New Mexico (excluding the extreme southwestern corner of the state) and south-central and southeastern Arizona (excluding the extreme southeastern comer). Cnemidophorus exsanguis occupies about the same geographic range, but occurs more extensively in New Mexico than C. tigris gracilis (Stebbins, 1966). The study reported herein was carried out in the Santa Rita Mountains of southern Ari1 Present address: Museum of Natural History, University of Kansas, Lawrence 66044.

The Bisexuality of Uniparental Hymenoptera, a Function of the Environment

REPRODUCTION in the Hymenoptera is characterized by the production of uniparental apomictic2 individuals. The normal male, always uniparental, is haploid. The female, either uniparental or biparental, is diploid. In a uniparental species, the progeny of unmated females are usually females; in a biparental species, usually males. There is, however, in many if not all hymienopterous species, a capacity to produce both sexes uniparentally (amphitoky). This uniparental bisexuality, as recorded for a number of hymenopterous species, appears to be an effect of environmental factors. The purpose of this paper is to present evidence supporting the thesis that the sexuality of a uniparental population is an expression of the type of germinal tissue in the preceding generation, the type being determined by environmental conditions. The observations forming the basis of this study were made during the mass propagation of beneficial insects at the University of California Citrus Experiment Station, Riverside, California.