ENDOMORPHIC AND ECTOMORPHIC CHARACTERS IN PELECYPHORA AND ENCEPHALOCARPUS

Boke , Norman H. (U. Oklahoma, Norman.) Endomorphic and ectomorphic characters in Pelecyphora and Encephalocarpus. Amer. Jour. Bot. 46(3) : 197-209. Illus. 1959.—Outstanding ectomorphic characters of Pelecyphora valdeziana include its small size; pectinate, hairy spines; broad, truncate, floral buds; dehiscent, berry-like fruits; and black, tuberculate seeds. The leaves are vestigial, and although the areole meristem originates on the adaxial face of the tubercle primordium, it is soon elevated to the summit by intercalary growth. The first primordium of the single, elliptical series of spines is initiated immediately in front of the rudimentary leaf. Others form in acropetal sequence on either side of the areole meristem. The last ones form across the areole, leaving a meristem, which may be floral or vegetative, on the anterior side. Whether areoles of P. valdeziana can be considered dimorphic is doubtful. However, they approach the type of dimorphism found in Epithelantha. Pelecyphora aselliformis has acuminate floral buds; dry, papery fruits; and brown, curved, reticulate seeds. The leaves are reduced almost to extinction. The areole meristem becomes separated into spiniferous and axial portions early in ontogeny, but the 2 parts remain connected by a band of trichomes, which probably represents a vestigial groove. The axial meristem may be reproductive or vegetative. The sequence of spine initiation in P. aselliformis is unusual in that it begins at the anterior side of the spiniferous meristem and proceeds toward the posterior side. Areoles in this species are clearly dimorphic, much as in the mammillarias, but the vestigial groove is reminiscent of Coryphantha and related genera. Although adult specimens of Encephalocarpus strobiliformis bear scale-like tubercles, which are very different from the laterally compressed tubercles of P. aselliformis, their flowers, fruits, and seeds are almost identical. The two species share the same type of areole dimorphism, including the vestigial groove. Tubercles on seedlings and young branches of E. strobiliformis are prismatic rather than scale-like. Since they tend to be laterally compressed at the summit and bear elliptical areoles with many more spines than the adult, they resemble seedling tubercles of P. aselliformis. Tubercles on adult specimens likewise resemble each other in the structure of the epidermis and hypodermis. It does not seem possible that P. valdeziana can be retained in the genus Pelecyphora. If seed structure has any systematic value, the species belongs in or near the genus Thelocactus, to which it was assigned by Bravo. Pelecyphora aselliformis and Encephalocarpus strobiliformis, on the other hand, share so many important characters that they could well be considered cogeneric. Both seed structure and the rudimentary grooves on the tubercles suggest that their affinities may lie with certain coryphanthas or mammillarias rather than with Ariocarpus and Epithelantha.     

STRUCTURE AND DEVELOPMENT OF THE SHOOT IN DOLICOTHELE

Boke , Norman H. (U. Oklahoma, Norman.) Structure and development of the shoot in Dolicothele. Amer. Jour. Bot. 48(4): 316–321. Illus. 1961.—A study of 2 species of Dolicothele reveals that although they have dimorphic areoles and a pattern of spine development similar to those of certain mammillarias, they share a significant number of ectomorphic and endomorphic characters with coryphanthas of the “vivipara group.” These include a tendency toward a cespitose habit; relatively large flowers; green fruits; pitted seeds; medullary vascular systems; forking of the main tubercle traces in the bases of the tubercles; lack of mucilage cells; thin-walled epidermis and hypodermis, both devoid of crystals; and large, druse-like crystalline aggregates in older parts of the pith and cortex. The evidence suggests that Coryphantha vivipara and closely allied species are the nearest extant relatives of Dolicothele. It would, therefore, seem inconsistent to return Dolicothele to Mammillaria unless an author's viewpoint were so conservative that he was willing also to return most, if not all, coryphanthas and escobarias to that genus.     

ANATOMY AND DEVELOPMENT IN SOLISIA

Boke , Norman H. (U. Oklahoma, Norman.) Anatomy and development in Solisia. Amer. Jour. Bot. 47(1): 59—65. Illus. 1960.–The genus Solisia contains a single species of small cacti which resemble certain mammillarias in having: pink, lateral flowers; milky juice; and dimorphic areoles. Adult specimens have elongate spiniferous areoles with an unusual sequence of spine initiation. The first four or five primordia appear at the posterior end of the areole meristem; the next are initiated near its center, after which initiation proceeds both acropetally and basipetally until the single, elliptical series of primordia is complete. A similar pattern of spine initiation occurs in Pelecyphora aselliformis, but this species differs markedly from S. pectinata in other respects. In seedlings of S. pectinata the areoles are broadly elliptical and spine initiation is strictly acropetal, a situation found in certain species of Mammillaria. Seeds of S. pectinata are black with a large hilum and a small perisperm. Since the perisperm has apparently been overlooked, it appears that only the black seed coat and relatively large hilum keep the species out of Mammillaria. If Buxbaum's postulates concerning the value of seed structure in tracing phylogeny in the Cactaceae are valid, S. pectinata must have diverged from the main line of evolution somewhere below Neobesseya. In that event, the species probably merits generic rank; otherwise, it seems preferable to return it to Mammillaria.     

Independent evolution of sexual dimorphism and female‐limited mimicry in swallowtail butterflies (Papilio dardanus and Papilio phorcas)

Several species of swallowtail butterflies (genus Papilio) are Batesian mimics that express multiple mimetic female forms, while the males are monomorphic and nonmimetic. The evolution of such sex‐limited mimicry may involve sexual dimorphism arising first and mimicry subsequently. Such a stepwise scenario through a nonmimetic, sexually dimorphic stage has been proposed for two closely related sexually dimorphic species: Papilio phorcas, a nonmimetic species with two female forms, and Papilio dardanus, a female‐limited polymorphic mimetic species. Their close relationship indicates that female‐limited polymorphism could be a shared derived character of the two species. Here, we present a phylogenomic analysis of the dardanus group using 3964 nuclear loci and whole mitochondrial genomes, showing that they are not sister species and thus that the sexually dimorphic state has arisen independently in the two species. Nonhomology of the female polymorphism in both species is supported by population genetic analysis of engrailed, the presumed mimicry switch locus in P. dardanus. McDonald–Kreitman tests performed on SNPs in engrailed showed the signature of balancing selection in a polymorphic population of P. dardanus, but not in monomorphic populations, nor in the nonmimetic P. phorcas. Hence, the wing polymorphism does not balance polymorphisms in engrailed in P. phorcas. Equally, unlike in P. dardanus, none of the SNPs in P. phorcas engrailed were associated with either female morph. We conclude that sexual dimorphism due to female polymorphism evolved independently in both species from monomorphic, nonmimetic states. While sexual selection may drive male–female dimorphism in nonmimetic species, in mimetic Papilios, natural selection for protection from predators in females is an alternative route to sexual dimorphism.     

WHY SHOULD LEK-BREEDERS BE MONOMORPHIC?

Approximately one-quarter of all lek-breeding bird species are sexually monomorphic. Understanding the significance, if any, of this exception to the usual correlation between sexual selection and dimorphism requires detailed data on the mating systems of both monomorphic and dimorphic species. The capuchinbird (Perissocephalus tricolor) is a sexually monomorphic, lek-breeding member of the cotinga family. I studied the social and sexual behavior of this species, and compared it with the Guianan cock-of-the-rock (Rupicola rupicola), a dimorphic, lekking member of the same family. Male–male competition in capuchinbirds involved direct contests for dominance, rather than territorial displays as in classic lek species. In each year, one dominant individual was able to control the most desired display site on the 8-male lek, and was the only male that copulated. In contrast to dimorphic lek birds, female as well as male capuchinbirds engaged in frequent and intense aggression at the lek, and both males and females engaged in sexual mimicry. I suggest that plumage monomorphism in lek birds has evolved as a result of social competition affecting both sexes. This hypothesis accounts for the exaggerated plumage characters shared by males and females in capuchinbirds and a number of other monomorphic lek birds. The evolution of plumage can best be analyzed as an arms race, in which the balance of selective forces acting on each sex can produce a variety of equilibrium states, ranging from sexual indistinguishability to extreme dimorphism.     

The dorsal tail tubercle of Mertensiella caucasica and M. luschani (Amphibia: Salamandridae)

Males of the two species of Mertensiella (M. caucasica and M. luschani) possess a tubercle projecting from the skin of the dorsal tail base, the single morphological character that defines the genus. The dorsal tail tubercle functions during courtship, and its role is similar in both species. The tubercle is inserted into the cloaca of the female during ventral amplexus, shortly before the male deposits a spermatophore. Histological examination, however, revealed that the dorsal tubercles differ structurally between the two species. In M. caucasica, the tubercle consists primarily of elongate mucous glands, with granular glands occurring only at the base. Both mucous and granular glands of the tubercle are larger than those in typical skin. Unlike typical skin, however, mucous glands are larger than granular glands. In M. luschani, mucous glands and granular glands occur throughout the tubercle, and the granular glands are larger than the mucous glands, although both types are larger than those in typical skin. The dorsal tubercles of M. caucasica and M. luschani may not be homologous structures and may have resulted from convergent evolution. J Morphol 232:93–105, 1997. © 1997 Wiley-Liss, Inc.     

Sexual dimorphism in proconsul

One of the more important sources of variability in primate species is sexual dimorphism. Most Primates heavier than five kilos bodyweight are sexually dimorphic, both in body size and in shape of certain hard tissues. Despite these facts, most of the fossil Primates from East African Miocene deposits were originally perceived as being monomorphic, a perception which has propogated through the literature. Re-examination ofProconsul from various sites in Western Kenya results in the view that it was as dimorphic in its splanchonocranium and in bodyweight as chimpanzees and gorillas. The clearest evidence comes from Rusing Island, where adequate samples are known of two morphs, traditionally identified as two species, but more likely to represent two sexes of a single species,P. nyanzae. Co-occurrence of the two morphs is 100% at the various Rusinga sites. Less complete samples have been collected from the Tinderet sites os Koru and Songhor, yet what is available shows that similar patterns of dimorphism characterise the speciesP. africanus andP. major, and that the co-occurrence of the two morphs in each species is 100%. The identification of fossils taking into consideration the role of sexual dimorphism clarifies many of the old debates in which individual specimens frequently shifted between different species, mainly on the basis of metric rather than morphologic evidence. Consequently, the distribution of the species ofProconsul is rather different after accounting for dimorphism, than it was before.     

TRAPPING AND RINGING OF EGYPTIAN GEESE AND AFRICAN SHELDUCK AT VOGELVLEI,CAPE

Many small plovers Charadrius spp. have sexually monomorphic plumage and cryptic sexual size dimorphism. The objective of our study was to assess the variation in body sizes between male and female plovers breeding in Madagascar. We collected blood samples and data on adult body sizes of four small plovers (Madagascar Plover Charadrius thoracicus, Kittlitz's Plover C. pecuarius, White-fronted Plover C. marginatus and Three-banded Plover C. tricollaris), and used molecular genetic markers to sex the adults. We found significant differences in body size among the four species, and between sexes. Furthermore, individuals from the southern ecoregion tended to be larger than in the western ecoregion. The Madagascar Plover's body size was significantly more dimorphic than the Kittlitz's and White-fronted Plovers. Breeding Malagasy plovers' show significant sexual size dimorphism (SSD): Madagascar Plover females were heavier and had longer wings than males, whereas the males had longer tarsi; in White-fronted Plover only wing length was different between the sexes. Taken together, our work reports SSD in small African plovers that exhibit monomorphic plumage, and we propose that SSD may be more common than currently acknowledged; we term this 'cryptic sexual size dimorphism'. Our results also suggest sexual selection and/or natural selection exert different pressures on body size in different Malagasy plover species.     

Geographical variation in egg size dimorphism in rockhopper penguins

All crested penguins present a unique reversed hatching asynchrony: the larger second-laid egg (B-egg) hatches before the smaller first-laid egg (A-egg). Although both eggs often hatch, the A-chick generally dies of starvation within days after hatching. However, within rockhopper penguins, the population at the Falkland Islands is unique in that some birds manage to raise both chicks. Although it has been suggested that the egg size dimorphism between A- and B-eggs may explain how long both eggs and chicks survive, this hypothesis has never been explicitly tested. We expect that both eggs are retained longer in the less dimorphic clutches than in the more dimorphic ones. In this paper, we have compiled egg measurements for three rockhopper penguin species (Eudyptes chrysocome, E. filholi and E. moseleyi) in order to compare the intra-clutch egg size dimorphism among these species. Furthermore, we have collected new data to compare egg size dimorphism between two populations of E. chrysocome (Falkland Islands versus Staten Island). A-egg volumes are more variable between species and populations than B-egg volumes. E. chrysocome and especially the population from the Falkland Islands produces the largest A-eggs and the least dimorphic eggs. Nevertheless, as differences in A-egg volumes between species and between the populations of Falkland Islands and Staten Island are stronger and more significant than differences in egg dimorphism, we suggest that A-egg volume, more than egg dimorphism, could be one of the factors influencing the prevalence of twins. A large A-egg and/or reduced egg dimorphism is probably necessary to enable rockhopper penguins to raise two chicks, but other reasons may also be involved which enable them to keep both eggs and chicks.     

Quantitative survey of sieve tube distribution in foliar terminal veins of ten dicot species

Quantitative data on sieve tubes in foliar terminal veins (vein endings) were added to the meager published information from only five dicot species. Correlations with other minor vein configurations were also explored. Leaf samples from ten species of dicots (Oxalis nelsonii, O. pes-capri, O. rubra, O. stricta [Oxalidaceae], Caesalpinia pulcherrima. Glycine max, Trifolium repens [Leguminosae], Ampelamus albidus [Asclepidaceae], Eupatorium rugosum [Asteraceae], and Polygonum convolvulus [Polygonaceae]) were selected for two quantitative procedures: 1) a survey of the arrangement of terminal veins and distribution of sieve tubes in terminal veins in 100 areoles per species using stained leaf clearings; and 2) a search for correlations of sieve tube distribution with number and branching patterns of terminal veins, and with sizes of areoles using image analysis. Two Oxalis species (O. pes-capri and O. stricta) had the smallest areoles and virtually no sieve tubes in any terminal vein. Polygonum convolvulus, at the other extreme, had sieve tubes extending to the tips of most terminal veins. The other species had various intermediate sieve tube configurations. The data indicate that species with few or no sieve tubes associated with their terminal veins, regardless of the number of terminal veins per areole, have smaller areoles. These results may have implications regarding the entry of leaf photosynthates into the vascular system.     

Differential polymorphism in cutaneous glands of archaic Leiopelma species

Endemic New Zealand frogs of the genus Leiopelma are from a basal lineage of extant anurans that release defensive secretions onto their skin when disturbed. Here, we characterize the gross anatomy and microscopic structure of the skin of L. archeyi, L. hochstetteri, and L. pakeka using stereoscopic, light and transmission electron microscopy. The terrestrial L. archeyi and L. pakeka possess dimorphic granular glands, categorized as type I and II, based on their frequency and morphological traits, whereas the semi‐aquatic L. hochstetteri lacks type I glands. This is the first report of differential dimorphism in anurans of the same genus. This dimorphism could be interpreted as an adaptation to different physiological or ecological needs of these species. However, species within this ancient genus share similar general gland morphology with other anurans, namely, a secretory unit containing storage granules ensheathed by myoepithelial cells. Type I glands are ellipsoid, large and contain a homogeneous mass of electron‐dense granules (1.8 ± 0.08 μm in diameter). Type II glands are round and contain larger heterogeneous granules (4.06 ± 0.16 μm) of varying densities. Exposure to noradrenaline causes the contraction of myoepithelial cells, resulting in bulk discharge of type I glands through the epidermal duct onto the skin surface. Differential release of secretions from dimorphic glands may be indicative of their functional specialisation in antipredatory or regulative roles. Mass spectrometric techniques were used to de novo sequence peptides present in the skin secretions of Leiopelma species. A total of 30 previously undescribed peptides from Leiopelma species were fully or partially sequenced. These peptides exhibited no similarity to any known compounds. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Cotyledon areoles in Bobgunnia (Fabaceae: Swartzieae)

Cotyledon areoles, a seed character unique to papilionoid legumes, are reported for the first time in the legume tribe Swartzieae, an anomalous group sometimes considered to be intermediate between subfamilies Caesalpinioideae and Papilionoideae. Bobgunnia madagascariensis has a linear, slightly branched cotyledon areole on the abaxial surface of each cotyledon. Previous reports of other papilionoid seed features in this species are confirmed and extended. These highly distinctive papilionoid seed structures, and recent reports from floral ontogeny and molecular systematics which show Bobgunnia to be closely related to Swartzia and several other genera of Swartzieae, add further evidence to assertions that Swartzia seed structures are derived by simplification from a papilionoid seed, and not by retention of less specialized caesalpinioid seed features. The function and evolutionary advantage of cotyledon areoles are unknown and need investigation. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 287–291.     

Diversity of sexual dimorphism in electrocommunication signals and its androgen regulation in a genus of electric fish, Apteronotus

Gymnotiform electric fish emit an electric organ discharge that, in several species, is sexually dimorphic and functions in gender recognition. In addition, some species produce frequency modulations of the electric organ discharge, known as chirps, that are displayed during aggression and courtship. We report that two congeneric species (Apteronotus leptorhynchus and A. albifrons) differ in the expression of sexual dimorphism in these signals. In A. leptorhynchus, males chirp more than females, but in A. albifrons chirping is monomorphic. The gonadosomatic index and plasma levels of 11-ketotestosterone were equivalent in both species, suggesting that they were in similar reproductive condition. Corresponding to this difference in dimorphism, A. leptorhynchus increases chirping in response to androgens, but chirping in A. albifrons is insensitive to implants of testosterone, dihydrotestosterone or 11-ketotestosterone. Species also differ in the sexual dimorphism and androgen sensitivity of electric organ discharge frequency. In A. leptorhynchus, males discharge at higher frequencies than females, and androgens increase electric organ discharge frequency. In A.␣albifrons, males discharge at lower frequencies than females, and androgens decrease electric organ discharge frequency. Thus, in both chirping and electric organ discharge frequency, evolutionary changes in the presence or direction of sexual dimorphism have been accompanied and perhaps caused by changes in the androgen regulation of the electric organ discharge. Accepted: 18 February 1998     

Mixed evidence for the erosion of intertactical genetic correlations through intralocus tactical conflict

Alternative reproductive tactics, whereby members of the same sex use different tactics to secure matings, are often associated with conditional intrasexual dimorphisms. Given the different selective pressures on males adopting each mating tactic, intrasexual dimorphism is more likely to arise if phenotypes are genetically uncoupled and free to evolve towards their phenotypic optima. However, in this context, genetic correlations between male morphs could result in intralocus tactical conflict (ITC). We investigated the genetic architecture of male dimorphism in bulb mites (Rhizoglyphus echinopus) and earwigs (Forficula auricularia). We used half‐sibling breeding designs to assess the heritability and intra/intersexual genetic correlations of dimorphic and monomorphic traits in each species. We found two contrasting patterns; F. auricularia exhibited low intrasexual genetic correlations for the dimorphic trait, suggesting that the ITC is moving towards a resolution. Meanwhile, R. echinopus exhibited high and significant intrasexual genetic correlations for most traits, suggesting that morphs in the bulb mite may be limited in evolving to their optima. This also shows that intrasexual dimorphisms can evolve despite strong genetic constraints, contrary to current predictions. We discuss the implications of this genetic constraint and emphasize the potential importance of ITC for our understanding of intrasexual dimorphisms.     

Disassortative mating prevails in style‐dimorphic Narcissus papyraceus despite low reciprocity and compatibility of morphs

Evolution to reduce inbreeding can favor disassortative (intermorph) over assortative (intramorph) mating in hermaphroditic sexually polymorphic plant species. Heterostyly enhances disassortative pollination through reciprocal placement of stigmas and anthers of morphs and appropriate pollinators. Stylar dimorphism in which there is not reciprocal anther placement may compromise disassortative mating, particularly when there is not intramorph incompatibility. Variable rates of disassortative mating along with differential female fecundity or siring success among floral morphs could lead to variation in morph ratio. We investigated mating patterns, female fecundity, and siring success of style‐length morphs in Narcissus papyraceus, a self‐incompatible but morph‐compatible species with dimorphic (long‐ and short‐styled) and monomorphic (long‐styled) populations in central and north regions of its range, respectively. We established experimental populations in both regions and exposed them to ambient pollinators. Using paternity analysis, we found similar siring success of morphs and high disassortative mating in most populations. Female fecundity of morphs was similar in all populations. Although these results could not completely explain the loss of dimorphism in the species’ northern range, they provided evidence for the evolutionary stability of stylar dimorphism in N. papyraceus in at least some populations. Our findings support the hypothesis that prevailing intermorph mating is key for the maintenance of stylar dimorphism.     

Degrees of sexual dimorphism in Cebus and other new world monkeys

Sexual dimorphism in primate species expresses the effects of phylogeny, life history, behavior, and ontogeny. The causes and implications of sexual dimorphism have been studied in several different primates using a variety of morphological databases such as body weight, canine length, and coat color and ornamentation. In addition to these different patterns of dimorphism, the degree to which a species is dimorphic results from a variety of possible causes. In this study we test the general hypothesis that a species highly dimorphic for one size-based index of dimorphism will be equally dimorphic (relative to other species) for other size-based indices. Specifically, the degree and pattern of sexual dimorphism in Cebus and several other New World monkey species is measured using craniometric data as a substitute for the troublesome range of variation in body weight estimates. In general, the rank ordering of species for dimorphism ratios differs considerably across neural vs. non-neural functional domains of the cranium. The relative degree of sexual dimorphism in different functional regions of the cranium is affected by the independent action of natural selection on those regions. Regions of the cranium upon which natural selection is presumed to have acted within a species show greater degrees of dimorphism than do the same regions in closely related taxa. Within Cebus, C. apella is consistently more dimorphic than other Cebus species for facial measurements, but not for neural or body weight measurements. The pattern in C. apella indicates no single best measurement of the degree of dimorphism in a species; rather, the relative degree of dimorphism applies only to the region being measured and may be enhanced by other selective pressures on morphology. Am J Phys Anthropol 107:243–256, 1998. © 1998 Wiley-Liss, Inc.     

Environmental stress and the evolution of dioecy: Wurmbea dioica (Colchicaceae) in Western Australia

Stressful ecological conditions have been implicated in the evolution of separate sexes in plants. Gender dimorphic species are often found in drier habitats than their sexually monomorphic relatives, and gynodioecious populations appear closer to a dioecious state as resources, particularly water, become limiting. This pattern could result if dry conditions decrease the relative seed fitness of cosexual plants, allowing female plants to become established in monomorphic populations. We studied geographical variation in gender expression and biomass allocation among 12 monomorphic and dimorphic populations of Wurmbea dioica along a latitudinal precipitation gradient in southwestern Australia to provide insight into mechanisms by which aridity might favor transitions between sexual systems. Plants in monomorphic and dimorphic populations exhibited contrasting gender expression and patterns of biomass allocation in areas with different levels of precipitation. Among dimorphic populations, lower precipitation was associated with a higher frequency of female plants, and reduced allocation to female function by hermaphrodites during flowering. In contrast, stress conditions had no effect on female allocation at flowering in monomorphic populations. Across latitudes, unisexuals and cosexuals exhibited consistent differences in above ground traits, with cosexuals having larger leaves, taller stems and larger flowers. Although all plants were smaller under drier conditions, cosexuals decreased above ground allocation to vegetative and reproductive structures with decreasing latitude. In contrast, unisexuals increased allocation to reproduction in drier areas at the expense of below ground size. Aridity was associated with reduced flower size among all gender classes, but not with changes in flower number. These data do not support the hypothesis that resource limitation of female allocation in cosexual populations favors the establishment of gender dimorphism in W. dioica. Alternative hypotheses, involving higher selfing rates and enhanced survival of unisexuals relative to cosexuals under resource-limited conditions, are discussed as possible explanations for the origin of dioecy in W. dioica. This revised version was published online in August 2006 with corrections to the Cover Date.