RANDOM MATING IN THE NORTHERN FLICKER HYBRID ZONE: IMPLICATIONS FOR THE EVOLUTION OF BRIGHT AND CONTRASTING PLUMAGE PATTERNS IN BIRDS

The Red-shafted and Yellow-shafted Flickers hybridize in a narrow zone on the western Great Plains of North America. The two subspecies are markedly different in six plumage traits. Plumage phenotypes were scored for the male and female of 125 mated pairs from the hybrid zone. Correlation analyses revealed no tendency towards pairing of similar phenotypes. A binomial test was performed to determine whether flickers that have parental phenotypes and are presumably immigrants rather than hybrids tend to choose mates similar to themselves. This test again indicated random mating in the hybrid zone. These data complement earlier reports in providing an additional test of alternative hybrid zone theories. Random mating along with evidence of high reproductive success in hybrids suggests that reinforcement of premating reproductive isolation is not occurring and that speciation will not result from the dynamics of the hybrid zone. At least some of the plumage traits seem to be important in the integrated courtship and territorial behaviors of flickers. Since these plumage differences have no significance in mate choice, it is inferred that they evolved in an intrasexual selection context rather than in intersexual or species-recognition contexts. Selection gradients appear to be important in restricting hybridization to a narrow zone. The gradients could result from ecological selection or from sexual selection.     

REPRODUCTIVE BIOLOGY OF TROPICAL LOWLAND RAIN FOREST TREES. I. SEXUAL SYSTEMS AND INCOMPATIBILITY MECHANISMS

Sexual systems of tropical lowland rain forest trees were investigated to estimate the relative proportions of hermaphroditic, monoecious, and dioecious species. Controlled hand pollinations were performed on hermaphroditic species to determine the proportions of self-compatible and self-incompatible species. A total of 333 species was examined; 65.5% species were found to be hermaphroditic, 11.4% monoecious, and 23.1% dioecious. There were no differences between canopy and subcanopy habitats in the distribution of various sexual systems. Out of the 28 species subjected to controlled pollinations, 24 showed the presence of self-incompatibility. The site of the incompatibility barrier in distylous species was either in the stigma or in the style. In most of the monomorphic species, the incompatibility barrier was in the ovary. Although a majority of tree species in the rain forest appear to be obligate outcrossers (xenogamons), the potential for inbreeding due to small effective population size still remains to be explored.     

EMBRYO GROWTH AND SEED SIZE IN RAPHANUS SATIVUS: MATERNAL AND PATERNAL EFFECTS IN VIVO AND IN VITRO

Theories on the evolution of the angiosperm seed disagree as to the effects of different plant tissues on embryo growth. To examine the relative contributions of maternal and paternal genes on embryo growth, we conducted controlled crosses in the greenhouse with wild radish plants (Raphanus sativus), looked for maternal, paternal, and interaction effects on embryo development, and compared the performance of embryos within fruits and in embryo culture. Maternal plant identity affected fruit set, seeds per fruit, embryo developmental stage, and mean seed weight. In embryo culture, maternal effects were found for cotyledon size and embryo weight. Paternal effects were fewer or smaller in magnitude than maternal effects. The identity of the pollen donor affected embryo developmental stage and mean seed weight. In culture, paternal effects were detected for cotyledon size and embryo weight. Our results demonstrate that both maternal and paternal elements affect embryo growth. The fact that maternal effects are greater than paternal effects on embryo development in culture may result from cytoplasmic elements or maternal nuclear genes. Embryo performance in vivo compared to that in vitro varied among maternal plants. The interaction between an embryo and its endosperm and maternal tissues may be either positive or negative, depending upon the maternal plant and the embryo's developmental stage.     

PHYLOGENETIC ANALYSES REVEAL UNEXPECTED PATTERNS IN THE EVOLUTION OF REPRODUCTIVE MODES IN FROGS

Understanding phenotypic diversity requires not only identification of selective factors that favor origins of derived states, but also factors that favor retention of primitive states. Anurans (frogs and toads) exhibit a remarkable diversity of reproductive modes that is unique among terrestrial vertebrates. Here, we analyze the evolution of these modes, using comparative methods on a phylogeny and matched life‐history database of 720 species, including most families and modes. As expected, modes with terrestrial eggs and aquatic larvae often precede direct development (terrestrial egg, no tadpole stage), but surprisingly, direct development evolves directly from aquatic breeding nearly as often. Modes with primitive exotrophic larvae (feeding outside the egg) frequently give rise to direct developers, whereas those with nonfeeding larvae (endotrophic) do not. Similarly, modes with eggs and larvae placed in locations protected from aquatic predators evolve frequently but rarely give rise to direct developers. Thus, frogs frequently bypass many seemingly intermediate stages in the evolution of direct development. We also find significant associations between terrestrial reproduction and reduced clutch size, larger egg size, reduced adult size, parental care, and occurrence in wetter and warmer regions. These associations may help explain the widespread retention of aquatic eggs and larvae, and the overall diversity of anuran reproductive modes.     

LABORATORY EVOLUTION OF LONGEVITY AND REPRODUCTIVE FITNESS COMPONENTS IN MALE FRUIT FLIES: MATING ABILITY

Populations of Drosophila melanogaster that had been selected for divergent rates of senescence were compared with respect to age-specific male mating ability. The competitive mating ability of males from populations with delayed senescence was inferior to that of males from populations with higher rates of senescence when males were young. This relationship was reversed when males were older. For noncompetitive mating ability and for recovery of fertility after an exhaustive mating bout, there was no difference between populations with different rates of senescence when males were young. However when males were older, flies from populations selected for delayed senescence again had superior mating ability. Thus, rates of male reproductive senescence can be altered in predictable ways by natural selection. The results for the competitive mating tests are consistent with the hypothesis that antagonistic gene action between early- and late-life fitness components influences the evolution of senescence in these populations.     

SIGNIFICANT ROLE FOR HISTORICAL EFFECTS IN THE EVOLUTION OF REPRODUCTIVE ISOLATION: EVIDENCE FROM PATTERNS OF INTROGRESSION BETWEEN THE CYPRINID FISHES,LUXILUS CORNUTUS AND LUXILUS CHRYSOCEPHALUS

Samples of Luxilus cornutus, Luxilus chrysocephalus, and their hybrids were collected along hypothesized routes of dispersal from Pleistocene refugia to examine the significance of geographic variation in patterns of introgression between these species. Patterns of allozyme and mitochondrial DNA (mtDNA) variation were generally consistent with those from previous studies. Tests of Hardy-Weinberg equilibrium revealed significant deficiencies of heterozygotes in all samples, indicating some form of reproductive isolation. Mitochondrial DNAs of each species were not equally represented in F₁ hybrids; however, this bias was eliminated when the two largest samples were excluded from the analysis. Backcross hybrids exhibited biased mtDNA introgression, as samples from Lake Erie (eastern) and Lake Michigan (western) drainages showed significant excesses of mtDNAs from L. chrysocephalus and L. cornutus, respectively, relative to frequencies of diagnostic allozyme markers. The extent and direction of allozyme and mtDNA introgression was quantified by calculating isolation index values from morphologically “pure” individuals of each species from each locality. Analysis of variance of these measures identified limited introgression of allozyme variants with no geographic pattern, but significant differences in direction of mtDNA introgression between drainages (i.e., postglacial dispersal route). Association between patterns of mtDNA introgression and dispersal route across the latitudinal width of the contact zone is best explained by genetic divergence during past isolation of ancestral populations from these drainages. These results identify a significant role for historical effects in the evolution of reproductive isolation and the process of speciation.     

THE EVOLUTION OF REPRODUCTIVE EFFORT IN LIZARDS AND SNAKES

Life history theory suggests that the optimal evolved level of reproductive effort (RE) for an organism depends upon the degree to which additional current reproductive investment reduces future reproductive output. Future reproduction can be decreased in two ways, through (i) decreases in the organism's survival rate, and/or (ii) decreases in the organism's growth (and hence subsequent fecundity). The latter tradeoff–that is, the “potential fecundity cost”—should affect the evolution of RE only in species with relatively high survival rate, a relatively high rate of fecundity increase with body size, or a relatively high reproductive frequency per annum. Unless these conditions are met, the probable benefit in future fecundity obtained from decreasing present reproductive output is too low for natural selection to favor any reduction in RE below the maximum physiologically possible. Published data on survival rate, reproductive frequency and relative clutch mass (RCM) suggest that many lizard species fall well below the level at which natural selection can be expected to influence RE through such “potential fecundity” tradeoffs. Hence, the relative allocation of resources between growth and reproduction is unlikely to be directly optimized by natural selection in these animals. Instead, energy allocation should influence the evolution of RE only indirectly, via effects on an organism's probability of survival during reproduction. Survival costs of reproduction may be the most important evolutionary determinants of RE in many reptiles, and information on the nature and extent of such costs is needed before valid measures of reptilian RE can be constructed.     

THE DISPERSAL BARRIER IN THE TROPICAL PACIFIC: IMPLICATIONS FOR MOLLUSCAN SPECIATION AND EXTINCTION

Stretches of deep ocean constitute barriers to the dispersal of many shallow-water marine species in the tropical Pacific. The purpose of this study was to assess the selectivity of these barriers with respect to the habitat characteristics, adult size, and predation-related shell architecture of gastropods, and to explore the implications of this selectivity for macroevolutionary patterns of extinction and speciation. The dispersal barrier between continental islands (represented in my collections by species from eastern Indonesia, the southern Philippines, and the north coast of New Guinea) and the nearby oceanic Palau Islands was studied by evaluating the percentage of each architectural and habitat category that is present on the continental islands but missing in Palau. The barrier is significantly more effective against sand-dwelling species than against rock-dwellers, and among rock-dwellers it is most effective against aperturally unarmored taxa. Barriers between Palau and Guam, Guam and the Hawaiian Islands, and the Line Islands and the tropical Eastern Pacific are generally unselective with respect to substratum type and architecture. The fact that narrow-apertured species are less affected by the barrier between the continental islands and Palau than are other rock-dwelling gastropods is consistent with the interpretation that this group has been unusually resistant to extinction and highly susceptible to founder speciation when oceanic circulation is altered. These patterns of susceptibility and geographical distribution may explain why armored gastropods have increased in numbers relative to unarmored ones in the tropical Pacific during the Cenozoic.     

POLLINATION AND SEED SET IN DIERVILLA LONICERA (CAPRIFOLIACEAE): TEMPORAL PATTERNS OF FLOWER AND OVULE DEPLOYMENT

Ovule development in Diervilla lonicera (Caprifoliaceae) is limited by insufficient pollination early in the blooming period and during extensive rainy periods. Production of flowers is skewed in time; an initial burst of flowering is followed by a long period of sparse flower production. Ovule number per flower increases through the blooming period. I discuss the interactions of fruit and seed set, ovule number, and bumble bee pollinator visitation patterns. When certain flowers have a higher a priori probability of successful pollination, it may be advantageous for plants to put more ovules in those flowers. Selective ovule deployment may be a general adaptive phenomenon that has received little attention.     

REPRODUCTIVE CONFLICT IN BUMBLEBEES AND THE EVOLUTION OF WORKER POLICING

Worker policing (mutual repression of reproduction) in the eusocial Hymenoptera represents a leading example of how coercion can facilitate cooperation. The occurrence of worker policing in “primitively” eusocial species with low mating frequencies, which lack relatedness differences conducive to policing, suggests that separate factors may underlie the origin and maintenance of worker policing. We tested this hypothesis by investigating conflict over male parentage in the primitively eusocial, monandrous bumblebee, Bombus terrestris. Using observations, experiments, and microsatellite genotyping, we found that: (a) worker‐ but not queen‐laid male eggs are nearly all eaten (by queens, reproductive, and nonreproductive workers) soon after being laid, so accounting for low observed frequencies of larval and adult worker‐produced males; (b) queen‐ and worker‐laid male eggs have equal viabilities; (c) workers discriminate between queen‐ and worker‐laid eggs using cues on eggs and egg cells that almost certainly originate from queens. The cooccurrence in B. terrestris of these three key elements of “classical” worker policing as found in the highly eusocial, polyandrous honeybees provides novel support for the hypothesis that worker policing can originate in the absence of relatedness differences maintaining it. Worker policing in B. terrestris almost certainly arose via reproductive competition among workers, that is, as “selfish” policing.     

PATTERNS OF CHARACTER DIVERGENCE AND THE EVOLUTION OF REPRODUCTIVE ECOTYPES OF DALECHAMPIA SCANDENS (EUPHORBIACEAE)

The variation of four floral characters (resin-gland area, gland-stigma distance, gland-anther distance, and anther-stigma distance) was analyzed across 15 populations of Dalechampia scandens occurring sympatrically, in various combinations, with five other congeners. Univariate and multivariate analysis of variance and a posteriori comparison tests indicate that there are significant statistical patterns of character divergence away from sympatric congeners for three of the floral characters. These characters, which on the basis of common garden studies appear to be under genetic control, may not vary independently; i.e., genetic control may be overlapping. The characters appear to be functionally related. Populations of Dalechampia scandens occurring sympatrically with congeners possessing relatively large resin glands, large gland-stigma distances and large anther-stigma distances (e.g., D. dioscoreifolia and D. affinis) have significantly smaller resin glands, gland-stigma distances and anther-stigma distances than do populations occurring sympatrically with congeners with relatively small resin glands, gland-stigma distances, and anther-stigma distances (e.g., D. cissifolia, D. heteromorpha and D. schottii). Populations of D. scandens not sympatric with other Dalechampia species generally have intermediately sized structures. The pattern of bidirectional divergence is consistent with the evolutionary scenario that selection against interspecific pollination has resulted in local ecotypic differentiation and character displacement in populations sympatric with ecologically similar congeners.     

PATTERNS OF LEAF AND FLOWER REMOVAL: THEIR EFFECT ON FRUIT GROWTH IN CHAMAENERION ANGUSTIFOLIUM (FIREWEED)

The response of Chamaenerion angustifolium (fireweed) plants to different patterns of artificial leaf and flower herbivory was examined to determine if the effects of localized herbivory were confined within vertical sectors of the plant. The effect of leaf and flower removal on fruit development was compared for removals within sectors and distributed among sectors. Fruit development did not differ in plants subjected to different patterns of leaf and flower removal. These results suggest that in disturbed plants carbohydrate movement is not confined within vertical sectors.     

THE ROLE OF DEME SIZE,REPRODUCTIVE PATTERNS,AND DISPERSAL IN THE DYNAMICS OF t-LETHAL HAPLOTYPES

The t-lethal haplotypes (t) found in house mouse (Mus musculus) populations are recessive lethals favored by gametic selection whereby male heterozygotes exhibit a non-Mendelian transmission ratio of about 95% t. The expected equilibrium frequency is 0.385; however, empirical values are lower, averaging close to 0.13. We examined the hypothesis that interdemic selection is the cause of the low empirical values by using a deme-structured simulation model that included overlapping generations, a realistic breeding system, differential deme productivity, and a large total population. We found that under some conditions interdemic selection could lower t frequency below 0.13 in the face of immigration rates up to 5%. Low frequencies were correlated with effective deme size (n_e), regardless of whether n_e was changed through changing deme size (n) or through changing the proportion of breeding adults. Earlier workers showed how the first two phases of interdemic selection (random genetic differentiation and mass selection) interacted to reduce the haplotype frequency, but here we show the importance of the third phase (differential productivity of demes) once demes are linked by dispersal. The effect of this phase is not due to the (negative) covariation between deme productivity and haplotype frequency, but occurs when differential deme productivity generates a difference in t frequency between the population of juveniles recruited into their natal deme and the population of juvenile dispersers. This difference was maximized when the average productivity of demes was low, either because few adult females bred at any one time and/or because fecundity was low. Contrary to an earlier prediction, male-biased dispersal also reduced haplotype frequency, and this probably stems from the relative excess of wild-type genotypes among dispersers compared to the deme residents. Another unexpected finding was that the randomly generated excess of heterozygotes (F_IS < 0) found in small demes favored t haplotypes; however, the effect was only seen when the more powerful influence of the third phase of interdemic selection was removed. Simulations of neutral polymorphisms showed that a deme structure giving F_ST ≤ 0.6 is inconsistent with a haplotype frequency below 0.13. Based on current empirical estimates of F_ST (about 0.2), we concluded that immigration rates in the field are too high for interdemic selection alone to cause the observed deficit of lethal haplotypes. One factor that could combine with population structure effects is the observation that the transmission ratio is lowered to around 0.6 in litters produced from postpartum estrus (PPE). Incorporating this factor, we showed that interdemic selection could be effective in lowering the frequency of t below 0.13 when F_ST was above 0.43 even when migration rates were up to 10%. These results suggest that if empirical haplotype and F_ST estimates are accurate, then additional factors such as a lowered fitness of heterozygotes may be involved.     

EVOLUTIONARY IMPLICATIONS OF LEAF RESIN POCKET PATTERNS IN THE TROPICAL TREE HYMENAEA (CAESALPINIOIDEAE: LEGUMINOSAE)

ABSTRACT: Measurement of the size (volume), distribution, and density of resin pockets are compared in margin and center areas of leaves in 11 species (including six varieties of two widespread species) of Hymenaea. Resin composition and yield (mg/g leaf tissue) were analyzed by gas-liquid chromatography. Resin pocket patterns in certain species are highly distinctive; also a relationship seems to exist between patterns of closely related species, with variation having occurred in species or populations of widespread species which have radiated into different kinds of habitats. Thus these patterns may provide useful taxonomic characters, but we suggest that some of the patterns (and thus composition and yield of resin of different portions of the leaf) have evolved under selective pressures of herbivorous insects.     

DEVELOPMENT OF THE SEED AND FRUIT IN RHINANTHUS MAJOR AND R. SEROTINUS

There are seven sessile, campylotropous, discoid ovules in each loculus of the anteroposteriorly flattened bilocular ovary. They are arranged alternately in two rows in each chamber on the axile placenta which is nodular where the ovules are borne. Nucellus degenerates early except at the chalazal end of the curved embryo sac, and the inntermost layer of the integument functions as endothelium. The aggressive, multinucleate micropylar haustorium grows as a tubular body through the micropylar canal and ramifies in the placenta while the two-nucleate chalazal haustorium creates a large space by digesting a good deal of the chalazal tissue. Endosperm is differentiated into three regions: the middle storage, the haustorial micropylar, and the chalazal. Thickness of the integument is considerably added to by the endothelium and by its surrounding meristematic zone of the integument. There are two prominent wings on the dorsal and smaller ones on the lateral faces of the cochlidiospermous seed, its ventral face being occupied by a prominent basal body. A heavily cutinized envelope, formed by the endothelium, surrounds the ovoid storage endosperm. Testa of the seed is mainly composed of the thickened epidermis and the endothelium. The micropylar and the chalazal parts of the endosperm become tanniferous and serve to plug the two ends of the seed. Embryo is straight, and it bears two cotyledons and two plumular leaves.     

西双版纳热带季节雨林6种树种幼树在林下的光合作用

本文研究了西双版纳热带季节６种树种幼树在林下的光合作用。６种树种的叶单位重量面积为１６．０２－２８．６７ｍ＾２．ｋｇ＾－１、光合作用光补偿点为３．８－６．５μｍｏｌ．ｍ＾－２．ｓ－１、光量子产率为０．０１８－０．０４４、最大净光合速率为１．９７－４．７１μｍｏｌＣＯ２．ｍ＾－２．ｓ＾－１ ４６．９９－９２．３３μｍｏｌＣＯ．ｋｇ＾－１．ｓ＾－１（以单位叶干重表示）、暗呼吸速率为０．１５－０．３１μ