Herbert G. Baker

SELF-COMPATIBILITY AND ESTABLISHMENT AFTER ‘“LONG-DISTANCE” DISPERSAL

lophaga and by the absence, also as primary infestants, of Anoplura. 8. The absence of Anoplura as primary infestants of South American land mammals seems to show that the sucking lice, as a group, originated at the earliest during the very late Mesozoic, if not at the beginning of the Tertiary. The reasons for this inference are: a) If sucking lice existed before the Pliocene in South America, they must have suffered complete extinction. This is hard to believe, especially because autochton rodents have proved very suitable hosts for cricetine-born Anoplura. As a matter of fact, the exchange of parasites has been much more intense in the cricetinehystricomorph direction than otherwise. b) If sucking lice existed in North America during the Paleocene, it is hard to believe they did not follow the heavy wave of immigration which entered South America at the time. c) Absence of sucking lice in North America at the Mesozoic-Tertiary boundary could only beexplained by either non-existence of the group or a very restricted distribution. This because the early Tertiary was a time of intensive faunal movements in Holarctica. d) If the Anoplura at that time had a restricted distribution, this should be due to very young age of the group, as they have proved very aggressive and succesful in colonizing empty ecological niches. 9. The possibility of detecting secondary infestations implies the possibility of evaluating evolutionary rates, as we are in a position to assign maximum lengths to the processes of divergence. Further knowledge of faunal movements inside South America will enhance the precision of such estimates. 10. We believe it would be rewarding to apply the methods outlined above to the fauna of other areas, especially the Oriental region and Africa. Otherwise, similar methods might be used for other couples of host-parasite groups, provided adequate taxonomic knowledge is available. Acknowledgments. The authors are indebted to a great many friends for help in preparing the paper of which this is an extract; these friends are listed in the article in Revista Brasileira de Entomologia. At the present time the authors wish to state their gratitude to the Editor of EVOLUTION for this opportunity of presenting their data to a much wider public than it would be possible otherwise.

Evolution in the Tropics

The substance of this article was delivered as the Presidential Address to the Society for the Study of Evolution, December 30, 1969, in Boston, Massachusetts. Attention is drawn to evolutionary studies in the tropics which appear to be advancing the subject significantly. Then, detailed attention is given to the possible evolutionary bases of the most striking biological characteristic of the tropics: the extraordinary floristic and faunistic diversity of tropical ecosystems. Because most contributions to the discussion of this topic have come from zoologists, the emphasis here is placed on botanical aspects. It is concluded that each of several potential explanations for the diversity may be valid and that a great need for the future is synthesis rather than arbitration between theories. THERE ARE MANY reasons why, as we come to the end of the 1960s, we should pay attention to what is happening in the study of evolution in the tropics. After many years of neglect, the tropics are getting more study by ecologists-and where the ecologists find their stimulation and their information there is also material for evolutionists, provided that we are still interested, as they are, in adaptation. Despite recent claims by molecular biologists (e.g., King and Jukes 1969, Wilson and Sarich 1969) for nonselective biochemical evolution, I believe that adaptation, maintained by natural selection, is still the cornerstone of the evolutionary edifice-and the tropics provide superb opportunities for studying multifarious examples of adaptation in action. Quite recently there have been important advances, with evolutionary significance, in several areas of tropical biology, and I should like to draw attention to some of them. For example, one of the most exciting developments in plant physiology in the last few years has been the demonstration that there are at least two biochemical pathways along which photosynthesis by flowering plants may proceed. The conventional or Calvin pathway (Calvin and Bassham 1962) involves phosphorylated chemical compounds with three carbon atoms while the more recently discovered pathway (Hatch and Slack 1966) involves four-carbon, dicarboxylic acids as early products of photosynthesis. Plants using the four-carbon pathway can fix carbon dioxide at rates up to twice that of those using the conventional mechanism, at least partly because they waste nothing in photorespiration. Correspondingly, their carbon dioxide compensation points (the level of CO2 in the atmosphere at which respiration just balances photosynthesis) are extremely low. Furthermore, they have peculiarities in the bundle sheaths of the leaves (Laetsch 1968) by which they may be recognized, as well as leaf structures which reduce gaseous exchange. Accumulation of carbon dioxide is facilitated under certain dark circumstances and, because C4 photosynthesis is not inhibited by accumulating oxygen during illumination (Olle Bjorkman, pers. comm.), their photosynthetic rates continue to increase as light intensities up to the maximum experienced in daylight are reached. Photosynthesis also continues even when dissolved carbon dioxide concentrations in the cells are reduced to low levels

Comparative phenological studies of treelet and shrub species in tropical wet and dry forests in the lowlands of Costa Rica.

SUMMARY (1) During 1970-73, marked individuals of 154 treelet and shrub species at a Wet forest site and 95 species at a Dry forest site in Costa Rica were observed regularly at 4- to 6-week intervals for changes in leafing, flowering and fruiting. (2) All the shrubs in the Wet forest were evergreen. New leaves were produced continually throughout the year by half the species, although this behaviour was more pronounced in species of secondary forest (87%0). For the community as a whole, leaf production was equable throughout the year. (3) About half of the treelets and shrubs in the Dry forest were deciduous. Hill forest treelets and shrubs produced most leaves at the beginning of the wet season, Riparian forest treelets and shrubs had a peak in leaf production near the end of the wet season, and leafing of species of secondary forest was continuous throughout the wet season. Most treelets and shrubs were bare or dormant during the dry season. Leaf loss was greatest during February. (4) There were no consistent peaks of flowering for treelet and shrub species in the Wet forest, but flowering levels tended to be greatest in the first half of each year. (4) Continuous flowering was rare among Wet forest treelets and shrubs, being characteristic of only a few species of secondary forest. Most Wet forest treelets and shrubs (64%) had several flowering episodes each year, with the episodes separated by 3-5-month intervals. Species with only a single brief synchronous flowering period were rare. (6) By contrast, flowering amongst Dry forest treelets and shrubs showed a pronounced seasonal pattern. The Hill forest treelet and shrub community had a sharp peak of flowering at the beginning of the wet season, while, in contrast, the Riparian forest treelet and shrub community had its major flowering at the end of the wet season. Most Dry forest species flowered synchronously once or twice each year. (7) There was a weak tendency for maximum fruiting of Wet forest shrubs in the second half of each year. A short period of fruit maturation (4 months) was shown by most Wet forest treelets and shrubs, although one species had a fruit maturation time of 27 months. Ten species of Wet forest treelets and shrubs flowered at least once during the study, but failed to produce fruit.

On the calculation of sugar concentration in flower nectar

SummaryThere are several sources of potential error in calculating the concentration or energy value of floral nectar. Errors resulting from confusing data become substantial with increasing concentration. The different methods of expressing sugar concentration are here clarified, and the correct methods of converting from one to the other are provided. Refractometers in use in field studies usually read on a weight per total weight basis; this is recommended as the mode of statement. The perils of oversimplifying conversions from this mode, as is often done, are pointed out.

Rainfall as a factor in the release, timing, and synchronization of anthesis by tropical trees and shrubs

Although a number of studies have described seasonality of flowering by tropical plants (most often trees) either at the species or community level, for tropicalplants there have been few studies treating the induction of reproductive structures, their ensuing development, or the triggering of anthesis (opening of the flower). In this paper we present data which demonstrates that rainfall, either directly or indirectly, is an important timing and spacing mechanism for the flowering of at least some tropical plants. We also attempt to relate this phenomenon to some prior relevant studies on flowering in the tropics.

The predictive value of nectar chemistry to the recognition of pollinator types.

ABSTRACT The analysis of “nectar sugar ratios” shows a close relationship between the sucrose/(glucose + fructose) ratio and the type of pollinator that visits the flowers. When taken in conjunction with the morphology of the flowers and inflorescence, these ratios can be good predictors of the pollinators. Predictions are made for Erythrina crista-galli (Fabaceae), where its hexose-dominated nectar suggests passerine-bird pollination in contrast to species which are hummingbird-pollinated. Similarly, the genus Puya (Bromeliaceae) contains species with abundant sucrose in the nectar (hummingbird-pollinated species) and species with abundant hexose belonging to the massive monocarpie subgenus Puya. In P. raimondii, the hexose-dominated nectar and the inflorescence morphology suggest that it will be passerine-bird pollinated in the high Andes where it is native. Luehea speciosa (Tiliaceae), in the American tropics, has hexose-rich nectar and we predicted that it would be bat-pollinated. No bats were seen to...

Evolutionary Significance of Polyploidy in the Pteridophyta

Polyploidy occurs in the heterosporous and homosporous Pteridophyta, but with a much higher frequency in the latter. Ninety-six percent of the homosporous Pteridophyta show a gametic chromosome number greater than 27, whereas 90 percent of the heterosporous ones possess a gametic chromosome number less than 28. Ultrafrequent establishment of poly- ploidy in the homosporous Pteridophy- ta appears to be necessary to create and maintain genetic variation in the face of the homozygotizing effects of habitual self-fertilization in the monoe- cious gametophytes of these plants.

Bat Activity and Pollination of Bauhinia Pauletia: Plant-Pollinator Coevolution

The relationship between the pollination biology of a tropical plant, Bauhinia pauletia, and the foraging strategies of the nectarivorous bats visiting it was studied. At least two bat species are pollen vectors, Plyllostomus discolor and Glossophaga soricina. Artibeus jamaicensis and Sturnira lilium were also captured near Bauhinia flowers. Larger bats (P. discolor) drain flowers of nectar and forage in groups, while smaller bats (G. soricina) make brief visits and forage independently. These foraging strategies should optimize energetic gain for the bats and promote outcrossing for the plant. Bauhinia pauletia is self-compatible, but is found where conditions favor outcrossing. Andromonoecism (the presence of hermaphrodite and male flowers) in this species appears to be an adaptation to pollination by large pollinators that also promotes outcrossing.

The Occurrence and Significance of Amino Acids in Floral Nectar

Approximately 1 500 angiosperm species, in previous papers, have been sampled for the assessment of the amino acids (a. a.) in their nectar. We reaffirm that the findings provide statistically significant data linking differences in the concentration with pollinator type. Flowers that are pollinated by animals that have alternative sources of protein-building a. a.’s show lower a. a. concentration than those that are not. There is a tendency for woody plant nectar a. a.’s to be less concentrated than those of herbaceous plants, but there can be “phylogenetic constraints” which may reduce the correlations of a. a. concentration with pollinator type and with life form. The individual a. a.’s form complements which are qualitatively extremely constant within species. Proline is a normal constituent of many nectars and does not necessarily indicate contamination of the nectar by pollen. Criticism of our findings byGottsberger & al. (1984) is answered by reference to our previous publications and those of other workers, and to the presentation of data from California native species, not published previously. All previous postulates are borne out by these new data with the exception of positive correlations of a. a. concentration with “primitive” and “advanced” floral characteristics taken one at a time, which appear to be inconsistent and are affected strongly by the nature of the family in which they occur. Summary data are provided for families and genera which indicate that high or low a. a. concentration can typify certain families and genera of both relatively “primitive” and relatively “advanced” nature. Needs for future research on an ecosystem basis are quoted.

Reproductive biology of some Costa Rican Cordia species (Boraginaceae).

Reproductive features of eight Cordia species (Boraginaceae) from the seasonally dry Pacific slope of Costa Rica are described. Components of the floral, pollinatory, breeding, and seed-dispersal systems of each species are interactive. Two sets of syndromes are recognized: one consisting of floral, pollinatory, and breeding-system traits; the other composed of growth form, habitat preferences, and seed-dispersal traits. Within the genus, in the Neotropics, there has been a radiation from an ancestor presumably characterized by a basic chromosome number of 8, heterostyly, and fleshy fruitedness. Within the separate lines that have diverged in respect of the second syndrome, episodes of polyploidization have occurred as well as chromosomal loss (aneuploidy). Homostyly and dioecism have appeared several times in Cordia, in different lines. Comparisons with the reproductive characteristics shown by Cordia species in two other neotropical communities reveal no contradictions to the generalizations drawn from the Pacific slope results. As PART OF AN EFFORT to understand the evolutionary changes and selective pressures that have brought about the kinds of reproductive adaptations which are to be seen in tropical forests, we have subjected the genus Cordia to an intensive investigation. The eight species of Cordia in the seasonally dry Pacific lowlands of Guanacaste Province, Costa Rica, were chosen for investigation (table 1). Cordia contains a number of common species that present a wide array of breeding systems, ranging from homostyly to heterostyly and dioccy, including flower morphs adapted for varied pollinatory assemblages, and utilizing both wind and animal seed dispersal. Our objective is to quantify, as far as possible, the critical aspects of phenology, floral and pollination biology, breeding system, and seed-dispersal strategy of different Cordia species, to attempt to discern correlations between these features, to interpret their ecological importance, and finally to point out evolutionary shifts which appear to have taken place as well as the selective pressures which may have produced them. DISTRIBUTION Gentry and Janos (1974) have summarized the Central American distribution of Cordia, and additional information is to be found in the work of Johnston (1949a,b, 1950). All eight Guanacaste Cordia species are widespread through most of Central America, presumably at drier sites (with the exception of C. alliodora which occurs up to 1000 meters and is found on the wet Atlantic slope as well). The distribution of Cordia alliodora and C. gerascmnthas extends northward into Mexico, while Cordia inermis and C. pringlei extend southward to northern South America. Most of the species also occur on several islands in the Caribbean.