CULTURE STUDIES ON THE RELATIONSHIP BETWEEN SCHIZYMENIA AND HAEMATOCELIS (GIGARTINALES,RHODOPHYCEAE) FROM THE PACIFIC COAST OF NORTH AMERICA1

Carpospores from Schizymenia pacifica (Kylin) Kylin (Gymnophlaeaceae) from California formed crusts anatomically identical to Haematocelis rubens J. Agardh (Cruoriaceae). Tetraspores of H. rubens from Monterey, California, and Baja California, Mexico, germinated to form basal discs from which arose upright multiaxial blades with a filamentous medulla and cortical gland cells. Pro-carps and spermatangia were present on the same blades; subsequently, cystocarps characteristic of Schizymenia pacifica developed. Re-examination of herbarium specimens suggests that the foliose tetrasporangial phases previously reported as S. pacifica are referable to Halymenia, Dilsea, Cryptonemia, or Turnerella. Schizymenia pacifica (type locality: San Juan Islands, Washington) thus is considered to be the gametophyte in the life history of Haematocelis rubens (type locality: Brest, France), which has also been reported to be the tetrasporophyte of S. dubyi (Chauvin ex Duby) J. Agardh (type locality: Cherbourg, France). Atlantic and Pacific gametophytes and tetrasporophytes are anatomically very similar, suggesting that only one species is involved, but critical studies must be made before a decision on this taxonomic question can be reached. Haematocelis zonalis Dawson et Neushul (type locality: Anacapa Island, California) is considered to be a growth form of the tetrasporangial phase of S. pacifica.     

ORGANIZATION OF PREDATOR-PREY COMMUNITIES AS AN EVOLUTIONARY GAME

We consider a simple predator-prey model of coevolution. By allowing coevolution both within and between trophic levels the model breaks the traditional dichotomy between coevolution among competitors and coevolution between a prey and its predator. By allowing the diversity of prey and predator species to emerge as a property of the evolutionarily stable strategies (ESS), the model breaks another constraint of most approaches to coevolution that consider as fixed the number of coevolving species. The number of species comprising the ESS is influenced by a parameter that determines the predator's niche breadth. Depending upon the parameter's value the ESS may contain: 1) one prey and one predator species, 2) two prey and one predator, 3) two prey and two predators, 4) three prey and two predators, 5) three prey and three predators, etc. Evolutionarily, these different ESSs all emerge from the same model. Ecologically, however, these ESSs result in very different patterns of community organization. In some communities the predator species are ecologically keystone in that their removal results in extinctions among the prey species. In others, the removal of a predator species has no significant impact on the prey community. These varied ecological roles for the predator species contrasts sharply with the essential evolutionary role of the predators in promoting prey species diversity. The ghost of predation past in which a predator's insignificant ecological role obscures its essential evolutionary role may be a frequent property of communities of predator and prey.     

ARE PARALLEL MORPHOLOGIES OF CAVE ORGANISMS THE RESULT OF SIMILAR SELECTION PRESSURES?

The amphipod Gammarus minus is present in both caves and springs, with cave populations showing elaborated (size and antennae) and reduced (eye) characters relative to spring populations. Earlier studies have shown that cave populations resulted from independent invasions of hydrologically isolated subterranean drainages and that there is genetic variation for both elaborated and reduced characters. In this study we tested the hypothesis that a similar pattern of selection on isolated cave populations is responsible for the parallel evolution of cave morphologies. We used variation in mating success and fecundity to test for the presence of directional selection on eye, antennal, and body size characters in a set of cave and spring populations during a series of seasonal cross-sectional samplings. We found significant directional selection for smaller eyes in caves and larger eyes in springs, which supports the hypothesis that selection is responsible for reduced eye size in cave populations. We also found selection for larger body and antennal size in cave populations, which is consistent with the hypothesis that parallel patterns of selection in caves are responsible for the elaboration of body and antennal size. However, we found selection for larger body and antennal size in spring populations that is not consistent with the observed divergence of spring and cave populations. We suggest that unmeasured components of viability selection could be more important in springs than in caves and may act against the selection for larger size found in spring populations.     

THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.     

Regional Comparison of the Shapes of Later Acheulean Handaxes

This article documents an unexpected regional difference in the shapes of later Acheulean hand-axes. Almost 1,200 handaxes from 17 sites located in Europe, East Africa, India, and the Near East were measured using a polar coordinate technique and compared using discriminant analysis and analysis of variance. One group of handaxes, those from Israel, clearly stood apart. The reasons for this distinction are unclear but may relate to raw material, time, or, perhaps, cultural tradition.     

NATURAL SELECTION ON BILL CHARACTERS IN THE TWO BILL MORPHS OF THE AFRICAN FINCH PYRENESTES OSTRINUS

Evidence for natural selection on seven bill and body characters is examined in the two bill morphs of the African estrildid finch Pyrenestes ostrinus. Two regression methods are used in examining natural selection in association with survivorship: a parametric (Lande and Arnold, 1983) and a non-parametric (Schluter, 1988) method. Selection was estimated in adult males, females and juveniles over a four-year period in a population in south-central Cameroon. Selection was common among groups but patterns differed and depended on the method used in detecting selection. The non-parametric method revealed evidence for disruptive selection occurring on bill width and is explained within the context of known feeding efficiencies and the hardness of important seeds in finch diets. Directional selection was common on bill characters in all groups, but infrequent on other characters. There was no evidence of selection on generalized size or shape characters. Selection on bill characters was common across groups despite low annual variation in rainfall. This contrasts with studies of Galápagos finches in which selection is frequently associated with dramatic changes in food supply caused by high variance in annual rainfall. Patterns of selection on bill traits in P. ostrinus also differ from those in song sparrows and Galápagos finches by exhibiting evidence for natural selection on all bill dimensions.