Dimorphic Populations Research Articles

ECOLOGICAL DIFFERENTIATION OF COMBINED AND SEPARATE SEXES OFWURMBEA DIOICA(COLCHICACEAE) IN SYMPATRY

The evolution and maintenance of combined vs. separate sexes in flowering plants is influenced by both ecological and genetic factors; variation in resources, partic- ularly moisture availability, is thought to play a role in selection for gender dimorphism in some groups. We investigated the density, distribution, biomass allocation, and physi- ology of sympatric monomorphic (cosexual) and dimorphic (female and male) populations of Wurmbea dioica in relation to soil moisture on the Darling Escarpment in southwestern Australia. Populations with monomorphic vs. dimorphic sexual systems segregated into wet vs. dry microsites, respectively, and biomass allocation patterns and physiological traits reflected differences in water availability, despite similarities in total ramet biomass between the sexual systems. Unisexuals flowered earlier at lower density, and they allocated sig- nificantly more biomass below ground to roots and corms than did cosexuals, which al- located more biomass above ground to leaves, stems, and flowers. Females, males, and cosexuals produced similar numbers of flowers per ramet, but unisexuals produced more ramets than cosexuals, increasing the total number of flowers per genet. Contrary to ex- pectation, cosexuals had significantly higher (more positive) leaf carbon isotope ratios and lower leaf nitrogen content than unisexuals, suggesting that cosexuals are more water-use efficient and have lower rates of photosynthesis per unit leaf mass despite their occurrence in wetter microsites. Cosexuals appear to adjust their stomatal behavior to minimize water loss through transpiration while maintaining high investment in leaves and reproductive structures. Unisexuals apparently maximize the acquisition and storage of both water and nitrogen through increased allocation to roots and corms and enhance the uptake of CO2 by keeping stomata more open. These findings indicate that the two sexual systems have different morphological and physiological features associated with local-scale variation in water availability.

Effects of Population Size and Metapopulation Dynamics on a Mating-System Polymorphism

The evolutionary dynamics of neutral alleles under the Wright–Fisher model are well understood. Similarly, the effect of population turnover on neutral genetic diversity in a metapopulation has attracted recent attention in theoretical studies. Here we present the results of computer simulations of a simple model that considers the effects of finite population size and metapopulation dynamics on a mating-system polymorphism involving selfing and outcrossing morphs. The details of the model are based on empirical data from dimorphic populations of the annual plant Eichhornia paniculata, but the results are also of relevance to species with density-dependent selfing rates in general. In our model, the prior selfing rate is determined by two alleles segregating at a single diploid locus. After prior selfing occurs, some remaining ovules are selfed through competing self-fertilisation in finite populations as a result of random mating among gametes. Fitness differences between the mating-system morphs were determined by inbreeding depression and pollen discounting in a context-dependent manner. Simulation results showed evidence of frequency dependence in the action of pollen discounting and inbreeding depression in finite populations. In particular, as a result of selfing in outcrossers through random mating among gametes, selfers experienced a “fixation bias” through drift, even when the mating-system locus was selectively neutral. In a metapopulation, high colony turnover generally favoured the fixation of the outcrossing morph, because inbreeding depression reduced opportunities for colony establishment by selfers through seed dispersal. Our results thus demonstrate that population size and metapopulation processes can lead to evolutionary dynamics involving pollen and seed dispersal that are not predicted for large populations with stable demography.

Genetic variability in sexually dimorphic and monomorphic populations of Populus euphratica (Salicaceae)

The genetic polymorphism of three populations of the dioecious riparian tree Populus euphratica Oliv. in Israel was examined with isozyme tests. Twelve enzyme systems revealed 20 putative loci, of which 13 were polymorphic. A centrally located population (comprising both females and males) was sampled, as well as two small peripheral and isolated stands: one comprised of only females and one containing males only. Genetic diversity values in P. euphratica were usually lower than those reported in other poplars and other species with similar life-history traits. The highest genetic diversity was found in the central, sexually dimorphic population; however, the sexually monomorphic (unisexual) marginal populations also manifested some genetic diversity, with the lowest values in the male population. Each of the unisexual populations could have originated from very few founder individuals of the same gender. The genetic variability detected in the unisexual populations may reflect somatic mutations accumulated in a vegetatively reproducing lineage over a long time span.

Patterns of Isozyme Diversity and Vegetative Reproduction of Willows in Israel

Isozyme tests were used to examine the genetic structure of six populations ($$n=206$$ individuals) of the two willow species in Israel, Salix alba and Salix acmophylla. The 14 enzymes revealed 23 putative loci, of which 15 were polymorphic. Sexually dimorphic populations (females and males) and monomorphic ones (all female) were tested in these two species, with the following results: (1) The two sexually dimorphic S. alba populations were the most variable in isozymes. (2) The all‐female population of this species had lower genetic diversity. The three tested S. alba populations are part of S. alba's continuous geographical distribution in the Upper Jordan Valley in Israel. Apparently, genetic variability is maintained in this area and, to some degree, also in the all‐female stand. (3) However, the sexually dimorphic S. acmophylla population showed lower isozyme diversity than the S. alba populations, probably because S. acmophylla populations in Israel tend to be smaller and more isolated than those of S. alba. (4) The two all‐female populations of S. acmophylla showed no variability at all; i.e., all 23 loci were monomorphic, indicating that each of these two populations are a single clone. The biased sex ratios, together with the relatively low values of genetic diversity and heterozygosity indicate a possible genetic drift, strong sib‐mating, and vegetative propagation in these willow populations.

Epithelioid trophoblastic tumor: a neoplasm distinct from choriocarcinoma and placental site trophoblastic tumor simulating carcinoma.

This report describes the clinicopathologic and immunohistochemical features of 14 cases of epithelioid trophoblastic tumor (ETT), a distinctive but rare gestational trophoblastic tumor. The patients with this neoplasm were in the reproductive age group and presented with abnormal vaginal bleeding. Although diagnosis was usually associated with a gestational event, the latter was sometimes remote. Two of the 14 patients presented with extrauterine ETT without evidence of prior gestational trophoblastic disease in the uterus. Serum human chorionic gonadotropin levels were elevated in eight of nine patients in whom this information was available. In the uterus, ETT presented as a discrete, hemorrhagic, solid and cystic lesion that was located either in the fundus, lower uterine segment, or endocervix. Microscopically, the tumor was composed of a relatively uniform population of mononucleate intermediate trophoblastic cells forming nests and solid masses. The cells resemble the trophoblastic cells in the chorion laeve, and we have therefore designated them "chorionic-type intermediate trophoblast." Typically, islands of trophoblastic cells were surrounded by extensive necrosis and were associated with a hyaline-like matrix creating a "geographic" pattern that is quite characteristic of this lesion. The mean mitotic count was two mitoses per 10 high-power fields, and the average Ki-67 nuclear labeling index was 18%. Immunohistochemically, all cases were diffusely positive for inhibin-alpha, cytokeratin (AE1/AE3), epithelial membrane antigen, E-cadherin, prolyl 4-hydroxylase, and epidermal growth factor receptor but were only focally immunoreactive for human placental lactogen, human chorionic gonadotropin, PlAP, and Mel-CAM. The monomorphic growth pattern of ETT resembles placental site trophoblastic tumor to a much greater degree than choriocarcinoma which is characterized by a dimorphic population of trophoblast. In contrast to placental site trophoblastic tumor, the cells of ETT are smaller and display less nuclear pleomorphism. In addition, ETT grows in a nodular fashion compared with the infiltrative pattern of placental site trophoblastic tumor. In some of the cases, the trophoblastic cells in ETT replaced the endocervical surface epithelium, giving the appearance that the tumor was derived from the cervix. Moreover, because the associated hyaline-like material in ETT resembles keratin, the tumor can be misinterpreted as a keratinizing squamous cell carcinoma of the cervix. Ten patients underwent total hysterectomy and two had an endometrial curettage only. The two patients who presented with extrauterine ETT underwent small bowel resection and lung resection. Two of 12 patients with ETT in the uterus developed metastasis in the lungs and bone. One of these patients is alive with disease at 43 months and one patient was lost to follow-up after 2 months. One of the two patients who had extrauterine disease died of widespread tumor 36 months after diagnosis. The remainder of the patients are alive and well from 1 to 120 months. In summary, ETT is a rare trophoblastic tumor that simulates carcinoma and can behave in a malignant fashion. It appears to be less aggressive than choriocarcinoma, more closely resembling the behavior of placental site trophoblastic tumor. Based on the morphologic and immunohistochemical features, it appears that ETT develops from neoplastic transformation of chorionic-type intermediate trophoblast.

Variation in oxygen consumption of the western diamondback rattlesnake ( Crotalus atrox ): implications for sexual size dimorphism

Variation in metabolism affects energy budgets of individuals and may serve as a mechanism that influences variation at whole organism or population levels. For example, sex differences in metabolic expenditure may contribute to bioenergetic sources of sexual size dimorphism. We measured oxygen consumption rates of 48 western diamondback rattlesnakes (Crotalus atrox) from a sexually dimorphic population and tested the effects of body mass, body temperature and time of day, in three groups of snakes: males, non-reproductive females, and vitellogenic females. Metabolic rates of male and non-reproductive female C. atrox were similar to rates reported for other rattlesnakes (mass exponents ranging from 0.645–0.670). Oxygen consumption was affected by body mass, body temperature and time of day, and was approximately 1.4 times greater in vitellogenic females than in non-reproductive females. No differences were found between males and non-reproductive females. Accordingly, differences in metabolic rate apparently do not contribute directly to sexual dimorphism in this population. Nevertheless, estimates of size-dependent maintenance expenditure lead us to hypothesize that adult female body size may represent a compromise between selection for increased litter size (accomplished by increasing body size), and selection for increased reproductive frequency (accomplished by decreasing body size, and, therefore inactive maintenance expenditure); this is a mechanistic scenario suggested previously for some endotherms.

Anatomical and neurochemical definition of the nucleus of the stria terminalis in japanese quail (Coturnix japonica)

This study in birds provides anatomical, immunohistochemical, and hodological data on a prosencephalic region in which the nomenclature is still a matter of discussion. In quail, this region is located just dorsal to the anterior commissure and extends from the level of the medial part of the preoptic area at its most rostral end to the caudal aspects of the nucleus preopticus medialis. At this caudal level, it reaches its maximal elongation and extends from the ventral tip of the lateral ventricles to the dorsolateral aspects of the paraventricular nucleus. This area contains aromatase-immunoreactive cells and a sexually dimorphic population of small, vasotocinergic neurons. The Nissl staining of adjacent sections revealed the presence of a cluster of intensely stained cells outlining the same region delineated by the vasotocin-immunoreactive structures. Cytoarchitectonic, immunohistochemical, and in situ hybridization data support the notion that this area is similar and is probably homologous to the medial part of the nucleus of the stria terminalis of the mammalian brain. The present data provide a clear definition of this nucleus in quail: They show for the first time the presence of sexually dimorphic vasotocinergic neurons in this region of the quail brain and provide the first detailed description of this region in an avian species.

Anatomical and neurochemical definition of the nucleus of the stria terminalis in japanese quail (Coturnix japonica)

This study in birds provides anatomical, immunohistochemical, and hodological data on a prosencephalic region in which the nomenclature is still a matter of discussion. In quail, this region is located just dorsal to the anterior commissure and extends from the level of the medial part of the preoptic area at its most rostral end to the caudal aspects of the nucleus preopticus medialis. At this caudal level, it reaches its maximal elongation and extends from the ventral tip of the lateral ventricles to the dorsolateral aspects of the paraventricular nucleus. This area contains aromatase-immunoreactive cells and a sexually dimorphic population of small, vasotocinergic neurons. The Nissl staining of adjacent sections revealed the presence of a cluster of intensely stained cells outlining the same region delineated by the vasotocin-immunoreactive structures. Cytoarchitectonic, immunohistochemical, and in situ hybridization data support the notion that this area is similar and is probably homologous to the medial part of the nucleus of the stria terminalis of the mammalian brain. The present data provide a clear definition of this nucleus in quail: They show for the first time the presence of sexually dimorphic vasotocinergic neurons in this region of the quail brain and provide the first detailed description of this region in an avian species. J. Comp. Neurol. 396:141–157, 1998. © 1998 Wiley-Liss, Inc.

The reproductive ecology of island populations of distylous Menyanthes trifoliata (Menyanthaceae)

Menyanthes trifoliata L. is a distylous, clonal aquatic macrophyte found in shallow bogs and river margins throughout the boreal ecosystem, including the island of Newfoundland. A combination of long-distance dispersal and colonization after deglaciation, and pollen limitation resulting from reduced pollinator diversity and abundance documented on islands, predicts the breakdown of heterostyly to favour the establishment of self-compatible homostyles on islands. To test if self-fertilizing homostyles have been selected, variation in floral characters and compatibility relationships were examined in M. trifoliata populations from the Avalon Peninsula of Newfoundland. Morph ratio and its effect on fruit and seed set were examined in nine populations. Of the seven dimorphic populations, morphs occurred in a 1:1 ratio in four populations and deviated significantly from a 1:1 ratio in three populations. The two populations monomorphic for either pin or thrum morphs set few fruits or seeds (<15%). A strictly reciprocal arrangement of stigma height and anther length was not observed between pin and thrum morphs in the majority of populations studied. Stigma-anther separation showed a bimodal distribution with few intermediate "homostylous" flowers, rather than the discreet bimodal distribution typical of distylous species. Fruit and seed set were high (>60%) in equal morph ratio populations and were not significantly correlated to stigma-anther separation, indicating that there was no selective advantage of being homostylous. All three populations tested were highly self-incompatible, confirming that there has not been a breakdown of heterostyly on the island of Newfoundland. A reduced pollinator fauna typical of island environments may have relaxed stabilizing selection for strict herkogamy between floral morphs, resulting in the observed lack of reciprocity.Key words: Menyanthes trifoliata, distyly, homostyle, reciprocal herkogamy, clonal aquatic macrophyte, island of Newfoundland.

Prevalence of the partial molar phenotype in triploidy of maternal and paternal origin

Triploid partial moles are at risk for trophoblastic neoplasia, yet the prevalence, parent of origin, and evolution of the partial molar phenotype amongst all triploids remains controversial. We determined parental origin by polymerase chain reaction (PCR) analysis, stage of development by gross and histological criteria, and partial molar status according to strict diagnostic criteria for all triploids identified amongst 1,054 consecutively karyotyped spontaneous abortions. Triploidy was detected in 64 of 832 successfully karyotyped specimens. Complete data were collected in 59 cases. Diandric origin was found in 39 specimens, and 20 of these fulfilled all four criteria for partial mole (trophoblast hyperplasia, dimorphic population of large and small villi, villous hydrops greater than 0.5 mm, and irregular villous contour). We separated the 19 diandric triploids not fulfilling all criteria for partial mole into four groups: specimens of early developmental stage, which we believed represented developing (“early”) partial moles (n = 3), cases of late developmental stage, which we believed represented involuting (“ancient”) partial moles (n = 4), cases showing some but not all criteria for partial mole (n = 7), and specimens with few if any criteria suggestive of partial mole (n = 5). In triploids of digynic origin (n = 20), developmental stage was significantly lower, fetal tissue was more frequently identified, and all specimens showed well-preserved fetal red blood cells. Digynic triploids occasionally showed irregular contour, dimorphic villi, and a mild form of trophoblast hyperplasia but never showed hydropic degeneration and were never suspicious for partial mole.

Genetic control of fruit polymorphism in the GenusFedia (Valerianaceae) in the light of dimorphic and trimorphic populations ofF. pallescens

The genusFedia consists of three species (F. cornucopiae, F. graciliflora andF. pallescens) of winter annual herbs, endemic to the western Mediterranean Basin. The deciduous terminal fruits of these taxa are polymorphic in the development of their pericarp and/or calyx, and each population is dimorphic or more rarely trimorphic. The three main fruit types are dispersed in several manners, and are specialized for either epizoochory or myrmecochory. On the basis of our experimental study of dimorphic and trimorphic populations ofF. pallescens subsp.pallescens, a genetic model is presented in order to explain the control of this intrapopulational polymorphism. It is postulated that two diallelic loci are tightly linked on the same chromosome in a functional supergene. One allele of each locus displays a dominance effect in the heterozygous state. Within the four possible homologous allelic segments, only two are present in the dimorphic populations, three in the trimorphic ones, and are otherwise associated in diverse combinations in the remaining taxa of the genus. Similar examples of fruit polymorphism are already documented in the tribeValerianeae, subtribeFediinae. The hypothesis is put forward that this fruit polymorphism is a synapomorphy for the subtribe.

Evolution of the Schistosomes (Digenea: Schistosomatoidea): The Origin of Dioecy and Colonization of the Venous System

Trematodes of the family Schistosomatidae are considered venous system specialists whose sister group is the vascular system generalists (Spirorchidae) of turtles. Colonization of homeotherms by vascular trematodes required precision egg laying near the conduit for egg passage to the external environment and avoidance of pathogenesis that might result in the premature death of the host. Evolution of dioecy from the hermaphroditic condition may have proceeded through androdioecy in which hermaphrodites were specialized for precision egg placement in the vascular system and larger adults became functional males. The evolution of nuclear genes suppressing female function along with cytoplasmic genes suppressing male function could then have resulted in the origin of dioecious, dimorphic populations. Schistosomes compensated for the reduction in potential reproductive partners by (1) increased overdispersion in the vertebrate host, (2) reduced egg hatching time in the external environment, (3) formation of permanent pairs mimicking the hermaphroditic condition, (4) increased longevity in the definitive host, and (5) increased fecundity. Colonization of the venous system was necessitated by (1) evolutionary radiation into terrestrial vertebrates and (2) the increased immunopathology associated with the high, constant body temperature of homeothermic vertebrates. The immune response to spirorchid and schistosome eggs appears to be qualitatively similar in their respective hosts. The arterial dwelling spirorchids release eggs in the direction of blood flow, resulting in a wide dissemination of eggs within the host. The lower body temperature of poikilotherms accompanied by the seasonal nature of the immune response in these hosts would result in a quantitatively reduced pathogenesis. Hosts that did succumb to the infection would most likely die in water, where eggs could be released by predation, scavengers, or decomposition and develop successfully. Colonization of the venous system by schistosomes would require precision egg placement because eggs are released against blood flow. Eggs are sequestered within the portal system of homeotherms, thus restricting egg dispersal and resulting pathogenesis to less sensitive organs. A significant number of eggs may escape into the external environment before a heavily infected host is incapacitated by, or dies from, the infection.

Co-expression of steroid hormone receptors in opioid peptide-containing neurons correlates with patterns of gene expression during the estrous cycle.

The anteroventral periventricular nucleus (AVPV) of the preoptic region represents an essential component of neural pathways regulating gonadotropin secretion, and contains sexually dimorphic populations of neurons that express dynorphin or enkephalin. In the present study we used in situ hybridization to measure prodynorphin (PDYN) and proenkephalin (PENK) mRNA in the AVPV of intact animals killed on each day of the cycle. Levels of PDYN mRNA were lowest in animals killed on the afternoon of proestrus and then increased by over 60% by the morning of the following day. Expression of PENK mRNA was generally stable during the cycle, but a small yet significant reduction was detected on proestrus relative to levels of PENK mRNA in animals killed on the day of diestrus. In addition, we used double in situ hybridization to demonstrate that the majority of PDYN mRNA-containing neurons express both estrogen (50%) and progesterone receptor (85%) mRNAs. Only one quarter of the PENK-containing neurons also co-express estrogen receptor mRNA, and fewer than 10% of the PENK mRNA neurons express PR mRNA. Thus, the differential expression of PDYN and PENK during the cycle generally correlates with distinct differences in the degree of colocalization of ER and PR mRNA in PDYN and PENK mRNA-containing neurons in the AVPV.

Evolutionary consequences of extensive morph loss in tristylous decodon verticillatus (Lythraceae): a shift from tristyly to distyly?

The evolution of distyly from tristyly has occurred repeatedly, especially in the Lythraceae. However, the evolutionary forces involved remain unclear since species exhibiting transitional stages between tristyly and distyly have rarely been studied. The self‐compatible, wetland perennial Decodon verticillatus (Lythraceae) may provide this transitional variation since populations commonly lack style morphs, particularly the mid‐styled (M) morph. In dimorphic populations lacking the M morph, anthers positioned at the mid level in both the long‐ (L) and short‐styled (S) morphs have lost their target stigma, setting the stage for either evolutionary repositioning of mid‐level anthers to increase pollen export to L and S stigmas, or increased variability in mid‐level anther position resulting from relaxed selection. We examined these two hypotheses by comparing floral morphology in eight dimorphic and ten trimorphic populations from throughout the species’ range. We found no evidence that loss of the M morph has led to evolutionary modification of mid‐level stamens. While mid‐level stamens of the S morph were 11.0 ± 4.0% (mean ± 1 SE) longer than those of the L morph in dimorphic populations, divergence in stamen length between morphs occurred to the same extent (10.4 ± 2.0%) in trimorphic populations and cannot be attributed to the absence of the M morph. Analyses of variability using median ratio tests revealed no difference in the variability of mid‐level stamen length between dimorphic and trimorphic populations. Mid‐level stamens were not more variable than long‐ and short‐level stamens within dimorphic populations. The consistent divergence in mid‐level stamens between the L and S morphs may reflect morph‐specific differences in the optimal position of mid‐level anthers for maximizing cross‐pollination and avoiding self‐fertilization.

Hormonal Regulation of CREB Phosphorylation in the Anteroventral Periventricular Nucleus

The anteroventral periventricular nucleus (AVPV) is a nodal point in neural circuits regulating secretion of gonadotropin and contains sexually dimorphic populations of hormonally regulated dopamine-, dynorphin-, and enkephalin-containing neurons. Because the tyrosine hydroxylase (TH), prodynorphin (PDYN), and proenkephalin (PENK) genes contain cAMP response elements that control their expression in their promoters, we used histochemical methods to determine whether ovarian steroids alter expression of the cAMP response element-binding protein (CREB) in the AVPV. Because the ability of CREB to activate transcription depends on phosphorylation at Ser133, we also evaluated the effects of acute steroid treatment on levels of phosphorylated CREB (pCREB) in AVPV neurons by using an antibody that differentiates between CREB and pCREB. Treatment of ovariectomized rats with estradiol treatments caused a significant induction in the number of pCREB-immunoreactive nuclei within 30 min that was maintained for at least 4 hr, but did not alter CREB immunostaining in the AVPV. Pretreatment with the estrogen antagonist Nafoxidine blocked this induction. In contrast, acute administration of progesterone to estrogen-primed animals suppressed and then increased pCREB staining in the ASVPV at 30 and 60 min, respectively; no significant differences between experimental and control animals were apparent by 2 hr after progesterone treatment. Double-labeling experiments showed that pCREB was colocalized with PDYN, PENK, or TH mRNA in the AVPV, suggesting that pCREB may mediate the effect of steroid hormones on gene expression in these neurons.

POPULATION STRUCTURE AND MORPH-SPECIFIC FITNESS DIFFERENCES IN TRISTYLOUS LYTHRUM SALICARIA.

In tristylous plant populations, style-morph frequencies are governed by an interaction between frequency-dependent selection due to disassortative mating and stochastic processes. Provided that there are no inherent fitness differences among morphs, frequency-dependent selection should result in equal morph frequencies at equilibrium. Stochastic models indicate that the short-styled morph has the highest and the long-styled morph the lowest probability of being lost from local populations as a result of random processes. We surveyed the morph composition of 82 populations of the tristylous, self-incompatible herb Lythrum salicaria in two archipelagos, one in central and one in northern Sweden, located close to the range-margin of the species. To examine whether deviations from even morph frequencies can be explained by among-morph differences in reproductive success, we quantified flower and seed production in six and three populations in the northern and southern archipelago, respectively, and we recorded segregation ratios in offspring produced in six trimorphic populations in the northern area. Seed germination and offspring growth were studied in the greenhouse. Ninety percent of the populations in the southern archipelago (N = 31) and 69% of the populations in the northern archipelago (N = 35) were trimorphic; the remaining populations were dimorphic (only populations consisting of at least three flowering plants considered). Dimorphic populations were smaller than trimorphic populations, as predicted by stochastic models. There was a striking difference in the morph composition of L. salicaria populations between the two archipelagos. In the southern archipelago, there was a slight excess of the long-styled morph and a corresponding deficiency of the short-styled morph. In contrast, the northern populations were characterized by a marked deficiency of the mid-styled morph: the average frequency of the mid-styled morph in trimorphic populations was 0.21, and nine of eleven dimorphic populations lacked the mid-styled morph. In both archipelagos, the long-styled morph (the most common morph) produced about 20% fewer seeds per fruit than the other morphs. The long-styled morph also tended to produce fewer seeds per plant. A hand-pollination experiment performed in two of the northern populations indicated that seed production per flower was pollen-limited in the long-styled morph but not in the other two morphs. Seed germination and offspring size after 24 weeks of growth did not differ among morphs. The mid-styled morph tended to have a higher representation in the offspring than in the parental generation in all six trimorphic populations studied further indicating that the deficiency of the mid-styled morph in the northern archipelago does not represent an equilibrium. Taken together, the results do not support the hypothesis that morph-specific differences in reproductive success can account for deviations from even morph frequencies in L. salicaria. It is suggested that among-morph differences in other components of fitness and historical factors may contribute to the current morph structure.

Stamen elongation, pollen size, and siring ability in tristylous elchhornia paniculata (Pontederiaceae)

Selfing variants in tristylous Eichhornia paniculata (Pontederiaceae) possess an elongated, short‐level stamen adjacent to mid‐level stigmas, which causes autonomous selfing. The variants commonly spread in dimorphic, but not trimorphic populations in northeast Brazil. We investigated the effect of stamen elongation on pollen size and siring ability. Competition experiments using controlled hand‐pollination and allozyme markers were used to compare different pollen types. Pollen from the elongated stamen was significantly larger in size than pollen from unmodified short‐level stamens. In mixed pollinations of mid‐level stigmas, pollen from the elongated stamen sired significantly more seed than pollen from unmodified short‐level stamens. Despite these differences, the size and compatibility of pollen from the elongated stamen were more similar to short‐ than mid‐level pollen, indicating that alterations to stamen level were not associated with major changes in pollen characteristics. The results suggest that the advantage of selfing variants in dimorphic populations is mainly due to efficient pollen transfer to mid‐level stigmas rather than increased postpollination siring success of pollen from modified stamens. In addition, the absence of major changes in pollen size and compatibility associated with stamen elongation support other lines of evidence indicating that selfing variants are not the result of recombination in the putative heterostyly supergene.

Hormonal Regulation of Opioid Peptide Neurons in the Anteroventral Periventricular Nucleus

Steroid hormones provide a means of coordinating the activity of widespread neural systems that mediate endocrine, autonomic, and somatomotor aspects of reproductive processes that are essential for the propagation of mammalian species. Because these processes are quite different in each sex, the neural pathways that control them are also sexually differentiated. The anteroventral periventricular nucleus (AVPV) of the preoptic region occupies a nodal point in sexually dimorphic forebrain circuits and appears to play a critical role in regulating gonadotropin secretion. The AVPV contains sexually dimorphic populations of opioid peptide containing neurons that display different patterns of development and are differentially regulated in adult animals by gonadal steroids. Moreover, estrogen (ER) and progesterone (PR) receptors are expressed in AVPV neurons in a transmitter-specific way, and the expression of these nuclear transacting factors is differentially regulated by sex steroids. Thus, neurons in the AVPV show distinct patterns of hormonal regulation of gene expression, and distinct hormone receptor profiles.

Tristyly, self-compatibility and floral variation in Decodon verticillatus (Lythraceae)

Abstract Heterostyly typically involves reciprocal polymorphism in stamen and style lengths, physiological self- and intramorph-incompatibility, and a set of associated polymorphisms of pollen and stigma characters. This study examined floral morphology and compatibility relationships in the monotypic, herbaceous perennial Decodon verticillatus (Lythraceae). There have been conflicting reports on the occurrence of tristyly in the species, probably because of frequent loss of style morphs from populations in parts of the species' range. Floral morphology was examined using material collected from natural populations throughout the range. Detailed floral measurements revealed discrete trimorphism in style length and anther positioning in three populations. Data from two dimorphic populations showed similar patterns of floral polymorphism, except that both were missing the mid-styled morph. In one dimorphic population, there was evidence for modification in the length of mid-level stamens. Measurements in three populations indicated pronounced floral variability, including high frequencies of modified phenotypes with reduced stigma anther separation. Pollen size was only weakly differentiated among anther levels, and there were no differences in pollen production among anther levels or morphs. In contrast, stigma size and papilla length showed a strong negative correlation with style length; a pattern opposite to most heterostylous species. Experimental crosses performed under glasshouse conditions on plants from two populations showed a high degree of both self- and intramorph-compatibility. A comparative analysis of floral morphology showed that D. verticillatus is not unusual in terms of the precision and reciprocity of organ positioning compared with 13 other tristylous species.

Tristyly, self-compatibility and floral variation in Decodon verticillatus (Lythraceae)

Heterostyly typically involves reciprocal polymorphism in stamen and style lengths, physiological self- and intramorph-incompatibility, and a set of associated polymorphisms of pollen and stigma characters. This study examined floral morphology and compatibility relationships in the monotypic, herbaceous perennial Decodon verticillatus (Lythraceae). There have been conflicting reports on the occurrence of tristyly in the species, probably because of frequent loss of style morphs from populations in parts of the species' range. Floral morphology was examined using material collected from natural populations throughout the range. Detailed floral measurements revealed discrete trimorphism in style length and anther positioning in three populations. Data from two dimorphic populations showed similar patterns of floral polymorphism, except that both were missing the mid-styled morph. In one dimorphic population, there was evidence for modification in the length of mid-level stamens. Measurements in three populations indicated pronounced floral variability, including high frequencies of modified phenotypes with reduced stigma anther separation. Pollen size was only weakly differentiated among anther levels, and there were no differences in pollen production among anther levels or morphs. In contrast, stigma size and papilla length showed a strong negative correlation with style length; a pattern opposite to most heterostylous species. Experimental crosses performed under glasshouse conditions on plants from two populations showed a high degree of both self- and intramorph-compatibility. A comparative analysis of floral morphology showed that D. verticillatus is not unusual in terms of the precision and reciprocity of organ positioning compared with 13 other tristylous species.