Avian reproduction: role of ecology in the evolution of cooperative breeding

A new comparative analysis of the speciose and socially diverse family of African starlings provides evidence that cooperative breeding has evolved in unpredictable, seasonal environments.     

Gynoecium evolution in angiosperms: Monomery,pseudomonomery, and mixomery

The presence of a gynoecium composed of carpels is a key feature of angiosperms. The carpel is often regarded as a homologue of the gymnosperm megasporophyll (that is, an ovule-bearing leaf), but higher complexity of the morphological nature of carpel cannot be ruled out. Angiosperm carpels can fuse to form a syncarpous gynoecium. A syncarpous gynoecium usually includes a well-developed compitum, an area where the pollen tube transmitting tracts of individual carpels unite to enable the transition of pollen tubes from one carpel to another. This phenomenon is a precondition to the emergence of carpel dimorphism manifested as the absence of a functional stigma or fertile ovules in part of the carpels. Pseudomonomery, which is characterized by the presence of a fertile ovule (or ovules) in one carpel only, is a specific case of carpel dimorphism. A pseudomonomerous gynoecium usually has a single plane of symmetry and is likely to share certain features of the regulation of morphogenesis with the monosymmetric perianth and androecium. A genuine monomerous gynoecium consists of a single carpel. Syncarpous gynoecia can be abruptly transformed into monomerous gynoecia in the course of evolution or undergo sterilization and gradual reduction of some carpels. Partial or nearly complete loss of carpel individuality that precludes the assignment of an ovule (or ovules) to an individual carpel is observed in a specific group of gynoecia. We termed this phenomenon mixomery, since it should be distinguished from pseudomonomery.     

A tale of four stories: soil ecology, theory, evolution and the publication system

Background

Soil ecology has produced a huge corpus of results on relations between soil organisms, ecosystem processes controlled by these organisms and links between belowground and aboveground processes. However, some soil scientists think that soil ecology is short of modelling and evolutionary approaches and has developed too independently from general ecology. We have tested quantitatively these hypotheses through a bibliographic study (about 23000 articles) comparing soil ecology journals, generalist ecology journals, evolutionary ecology journals and theoretical ecology journals.

Findings

We have shown that soil ecology is not well represented in generalist ecology journals and that soil ecologists poorly use modelling and evolutionary approaches. Moreover, the articles published by a typical soil ecology journal (Soil Biology and Biochemistry) are cited by and cite low percentages of articles published in generalist ecology journals, evolutionary ecology journals and theoretical ecology journals.

Conclusion

This confirms our hypotheses and suggests that soil ecology would benefit from an effort towards modelling and evolutionary approaches. This effort should promote the building of a general conceptual framework for soil ecology and bridges between soil ecology and general ecology. We give some historical reasons for the parsimonious use of modelling and evolutionary approaches by soil ecologists. We finally suggest that a publication system that classifies journals according to their Impact Factors and their level of generality is probably inadequate to integrate “particularity” (empirical observations) and “generality” (general theories), which is the goal of all natural sciences. Such a system might also be particularly detrimental to the development of a science such as ecology that is intrinsically multidisciplinary.     

Hydrophilous pollination and breeding system evolution in seagrasses: a phylogenetic approach to the evolutionary ecology of the Cymodoceaceae

COX, P. A. & HUMPHRIES, C. J. 1992. Hydrophilous pollination and breeding system evolution in seagrasses: a phylogenetic approach to the evolutionary ecology of the Cymodoceaceae. A phylogenetic analysis of seagrasses of the Cymodoceaceae shows the Cymodoceaceae to be monophyletic and Posidoniaceae to be their sister group. Information on the pollination ecologies and breeding systems of the various genera of the Cymodoceaceae were plotted onto the consensus tree obtained for the group. From this analysis, it is suggested that the clade composed of the Zosteraceae, Posidoniaceae and Cymodoceaceae evolved from a freshwater hydrophilous ancestor that developed submarine pollination and filiform pollen in association with invasion of the marine environment. Dioecism and surface pollination appear to have evolved in the progenitor of the Cymodoceaceae, and hence the seagrasses of the Cymodoceaceae are dioecious due to common descent rather than to convergent evolutionary processes in extant genera.     

Sexual dimorphism in gender plasticity and its consequences for breeding system evolution

Flowering plants are able to develop gametes throughout their lives. As a consequence, environmental conditions can impact this development and alter a plant's functional gender or the degree to which it achieves fitness through male or female function. Two dimorphic breeding systems are widespread among angiosperm families: gynodioecy (hermaphrodites and females) and dioecy (males and females). Gynodioecy can evolve into dioecy, via loss of female function on the hermaphrodites, or it can remain stable. Here I discuss how developmental plasticity of gender can impact the sex ratio of populations and thereby influence the transition of one breeding system into another. I review studies showing that greater plasticity of fruit production by hermaphrodites as compared with females causes sex ratios among populations to vary in response to environmental conditions, with higher female frequency expected in harsh or low-quality sites. I also review how dioecy may evolve in dry sites to avoid inbreeding and any consequent inbreeding depression. Taken together, these studies show the importance of understanding how ecological development affects functional gender and consequently the evolutionary stability or malleability of dimorphic breeding systems.     

The evolution of floral biology in basal angiosperms

In basal angiosperms (including ANITA grade, magnoliids, Choranthaceae, Ceratophyllaceae) almost all bisexual flowers are dichogamous (with male and female functions more or less separated in time), and nearly 100 per cent of those are protogynous (with female function before male function). Movements of floral parts and differential early abscission of stamens in the male phase are variously associated with protogyny. Evolution of synchronous dichogamy based on the day/night rhythm and anthesis lasting 2 days is common. In a few clades in Magnoliales and Laurales heterodichogamy has also evolved. Beetles, flies and thrips are the major pollinators, with various degrees of specialization up to large beetles and special flies in some large-flowered Nymphaeaceae, Magnoliaceae, Annonaceae and Aristolochiaceae. Unusual structural specializations are involved in floral biological adaptations (calyptras, inner staminodes, synandria and food bodies, and secretory structures on tepals, stamens and staminodes). Numerous specializations that are common in monocots and eudicots are absent in basal angiosperms. Several families are poorly known in their floral biology.     

The large genome constraint hypothesis: evolution, ecology and phenotype

BACKGROUND AND AIMS: If large genomes are truly saturated with unnecessary 'junk' DNA, it would seem natural that there would be costs associated ith accumulation and replication of this excess DNA. Here we examine the available evidence to support this hypothesis, which we term the 'large genome constraint'. We examine the large genome constraint at three scales: evolution, ecology, and the plant phenotype. SCOPE: In evolution, we tested the hypothesis that plant lineages with large genomes are diversifying more slowly. We found that genera with large genomes are less likely to be highly specious -- suggesting a large genome constraint on speciation. In ecology, we found that species with large genomes are under-represented in extreme environments -- again suggesting a large genome constraint for the distribution and abundance of species. Ultimately, if these ecological and evolutionary constraints are real, the genome size effect must be expressed in the phenotype and confer selective disadvantages. Therefore, in phenotype, we review data on the physiological correlates of genome size, and present new analyses involving maximum photosynthetic rate and specific leaf area. Most notably, we found that species with large genomes have reduced maximum photosynthetic rates - again suggesting a large genome constraint on plant performance. Finally, we discuss whether these phenotypic correlations may help explain why species with large genomes are trimmed from the evolutionary tree and have restricted ecological distributions. CONCLUSION: Our review tentatively supports the large genome constraint hypothesis.     

The neglected sense-olfaction in primate behavior, ecology, and evolution

This special issue emerged from a symposium held during the 20th Congress of the International Primatological Society in Torino, Italy, in August 2004. The symposium brought together scientists studying several different aspects of olfaction in primates. The topics addressed ranged from the morphology and physiology of the sensory apparatus, the genetics and chemistry of olfactory signals and the use of such signals in primate communication, to a comparative analysis of the role of olfaction in neural evolution. The papers in this issue reflect a surge of interest in diverse aspects of olfaction-an interest that has been stimulated by the more rigorous theoretical approaches and new techniques that have recently become available. This introduction briefly reviews past research on primate olfaction, summarizes the scope of this special issue, and provides a somewhat speculative glimpse of the future.     

The different breeding strategies of penguins: A review

The 18 penguin species are exclusively and widely distributed in the Southern hemisphere, from the Equator to the Antarctic continent, and are thus submitted to various ecological constraints in their reproductive strategy. This results in a high variability in all aspects of the breeding biology of the different species. Although penguins appear primarily adapted for a marine existence, they remain dependent on land for breeding, rearing young, and moulting. Here we describe and compare the breeding cycle of all the penguin species, highlighting the characteristics of each species in terms of breeding range, population status, threats induced by environmental changes, duration of the different phases of the breeding cycle, mate fidelity, body mass, body height, egg mass and duration of egg formation. We also focus on the breeding cycle of the genus Aptenodytes, since it largely differs from the breeding cycle of most of the other penguin species.     

The ecology and evolution of bacteriocins

In this review we focus on the ecological and evolutionary forces that determine the frequency and diversity of colicins inEscherichia coli. To begin, we describe that this killing phenotype is ubiquitous inE. coli, with as many as 50% of the isolates from a population producing colicin toxins, and that each population sampled has its own unique distribution of the more than 20 known colicin types. Next, we explore the dynamics of colicinogeny, which exhibits a typical form of frequency dependence, where the likelihood of successful colicin invasion into a population increases as the initial density of colicinogenic cells increases. We then incorporate thoughts on the evolution of chromosomal resistance to colicins and describe how resistance might influence the dynamics of colicinogen invasion and maintenance and the resulting colicin diversity. The final section deals with a genetic and phylogenetic characterization of colicins and a discussion of the evolutionary mechanisms responsible for generating colicin diversity. In this final section we provide details of the different molecular mechanisms known to play a role in generating colicin diversity, including the two most dominant forces in colincin evolution: recombination and positive, deversifying, selection.     

Primate origins and the evolution of angiosperms

Traditionally, the morphological traits of primates were assumed to be adaptations to an arboreal way of life. However, Cartmill [1972] pointed out that a number of morphological traits characteristic of primates are not found in many other arboreal mammals. He contends that orbital convergence and grasping extremities indicate that the initial divergence of primates involved visual predation on insects in the lower canopy and undergrowth of the tropical forest. However, recent research on nocturnal primates does not support the visually-oriented predation theory. Although insects were most likely important components of the diets of the earliest euprimates, it is argued here that visual predation was not the major impetus for the evolution of the adaptive traits of primates. Recent paleobotanical research has yielded evidence that a major evolutionary event occurred during the Eocene, involving the angiosperms and their dispersal agents. As a result of long-term diffuse coevolutionary interactions with flowering plants, modern primates, bats, and plant-feeding birds all first arose around the Paleocene-Eocene boundary and became the major seed dispersers of modern tropical flora during the Eocene. Thus, it is suggested here that the multitude of resources available on the terminal branches of the newly evolved angiosperm, rain forest trees led to the morphological adaptations of primates of modern aspect.