Songs versus colours versus horns: what explains the diversity of sexually selected traits?

Papers on sexual selection often highlight the incredible diversity of sexually selected traits across animals. Yet, few studies have tried to explain why this diversity evolved. Animals use many different types of traits to attract mates and outcompete rivals, including colours, songs, and horns, but it remains unclear why, for example, some taxa have songs, others have colours, and others horns. Here, we first conduct a systematic survey of the basic diversity and distribution of different types of sexually selected signals and weapons across the animal Tree of Life. Based on this survey, we describe seven major patterns in trait diversity and distributions. We then discuss 10 unanswered questions raised by these patterns, and how they might be addressed. One major pattern is that most types of sexually selected signals and weapons are apparently absent from most animal phyla (88%), in contrast to the conventional wisdom that a diversity of sexually selected traits is present across animals. Furthermore, most trait diversity is clustered in Arthropoda and Chordata, but only within certain clades. Within these clades, many different types of traits have evolved, and many types appear to have evolved repeatedly. By contrast, other major arthropod and chordate clades appear to lack all or most trait types, and similar patterns are repeated at smaller phylogenetic scales (e.g. within insects). Although most research on sexual selection focuses on female choice, we find similar numbers of traits (among sampled species) are involved in male contests (44%) and female choice (55%). Overall, these patterns are largely unexplained and unexplored, as are many other fundamental questions about the evolution of these traits. We suggest that understanding the diversity of sexually selected traits may require a shift towards macroevolutionary studies at relatively deep timescales (e.g. tens to hundreds of millions of years ago).     

Antimicrobial peptides versus parasitic infections?

Reports of antimicrobial peptides generally have evaluations of their antibacterial and antifungal activities. By contrast, little is known of their activities against protozoan and metazoan parasites. In vitro antiparasitic assays suggest that antimicrobial peptides could represent a powerful tool for the development of novel drugs to fight the parasite in the vertebrate host, or to complement current therapeutic strategies.     

Brazilian alcohol: Food versus fuel?

The creation of the ProAlcool (National Alcohol Programme) late in 1975 for the production of fuel alcohol has raised varied criticisms as to the possible consequences for food production in Brazil. This food ‘problem’ in Brazil is embedded in its socio-economic and political system. Agricultural production has kept ahead of population growth, but the main beneficiaries have been commodity export crops; the issue can be identified as ‘commodity export crop production versus crop production for the domestic market’ rather than ‘food versus fuel’. The possible effects of the ProAlcool on food production have been exaggerated and the real implications largely overlooked. The sugar and alcohol sector is today among Brazil's largest industries and, with all its faults, the ProAlcool remains the world's most successful biomass energy programme and as such its importance extends beyond Brazil's national boundaries. Biomass has been demonstrated by a Third World country to be a viable alternative or complement to oil on a national scale. Despite the current (1986) low oil prices an interministerial commission has recently recommended that the ProAlcool programme should be maintained.     

Red deer hunting—commercializing versus availability

Many deer populations in Europe and North America have increased in abundance over the last decades. The increasing populations potentially entail both ecological and economic challenges and opportunities, but in practice we still know little about the extent to which these opportunities are being exploited in different management systems. The Norwegian red deer population has increased in density and expanded rapidly since the 1950s. Traditionally, red deer hunting has been undertaken by the local landowner and his relatives and friends. The present large population raises the question whether attracting other hunters could provide a higher economic return for the landowners and, if so, if they are interested in providing such hunting opportunities. We designed a survey to learn more about the landowners, both with respect to the present level of hunting income as well as economic costs of, for example, forest and agricultural damage; we also sought to understand their interest in increasing their income from red deer hunting and potential obstacles to realizing such an increased economic benefit. The results indicate that landowners on average think that red deer populations on their land result in higher costs than income but are nevertheless satisfied with the way things are. This highlights that increased numbers of deer need not automatically lead to more income for landowners and that the potential for income may be hindered by cultural factors such as reluctance to allow access to non-local hunters.     

Strigolactone versus gibberellin signaling: reemerging concepts?

Main conclusion

In this review, we compare knowledge about the recently discovered strigolactone signaling pathway and the well established gibberellin signaling pathway to identify gaps of knowledge and putative research directions in strigolactone biology. Communication between and inside cells is integral for the vitality of living organisms. Hormonal signaling cascades form a large part of this communication and an understanding of both their complexity and interactive nature is only beginning to emerge. In plants, the strigolactone (SL) signaling pathway is the most recent addition to the classically acting group of hormones and, although fundamental insights have been made, knowledge about the nature and impact of SL signaling is still cursory. This narrow understanding is in spite of the fact that SLs influence a specific spectrum of processes, which includes shoot branching and root system architecture in response, partly, to environmental stimuli. This makes these hormones ideal tools for understanding the coordination of plant growth processes, mechanisms of long-distance communication and developmental plasticity. Here, we summarize current knowledge about SL signaling and employ the well-characterized gibberellin (GA) signaling pathway as a scaffold to highlight emerging features as well as gaps in our knowledge in this context. GA signaling is particularly suitable for this comparison because both signaling cascades share key features of hormone perception and of immediate downstream events. Therefore, our comparative view demonstrates the possible level of complexity and regulatory interfaces of SL signaling.

     

Recognition versus identity — the role of biometrics

The distinction between the recognition of an individual using an automated biometric system and the fundamental notion of their identity is subtle and therefore provokes much debate relating to privacy and other societal issues. This article seeks to clarify some of these issues relating to biometric recognition and identity by providing a framework, and by distinguishing between the technology and societal issues.     

Continu versus discontinu,linéaire versus non linéaire dans l’évolution des espèces

Continuity versus discontinuity, linear versus nonlinear in species evolution. Species evolution is a topic where concepts of continuity and discontinuity have been opposed for two centuries. What is the situation today in biological evolution ? The statistical distribution of appearances and disappearances among rodent species follows power laws, suggesting nonlinearity and fractal structures. Thus, the domain of living beings seems to be extended, through critical physical phenomena, to the analysis of linear versus nonlinear biological phenomena. These observations are consistent with the new scale relativity theory of Nottale, which predicts many domains of resolution in nature separated by scale dependence or scale independence. Despite some scale-dependence particular to various levels of biological organization, the fact that they are also characterized by scale-independence suggests that they could be described by new fundamental laws revealing their potentially fractal and irreversible character. In the proximity of the critical time, specific to each system, the system becomes unstable and fractal, and shows precursor events at an accelerated rate leading up to the critical time. After the critical time, the system shows replicate events, in a decelerating manner. The discontinuous appearance of a number of clades follows a log-periodic law with a middle scale report of 1.73. This law, first applied to earthquakes, stock market crashes, demography, and physical turbulences, and now also being applied with success to macroevolutionary patterns, seems to have a certain universality. To cite this article : J. Chaline, C. R. Palevol 2 (2003).     

Itô versus Stratonovich calculus in random population growth

The context is the general stochastic differential equation (SDE) model dN/dt=N(g(N)+sigmaepsilon(t)) for population growth in a randomly fluctuating environment. Here, N=N(t) is the population size at time t, g(N) is the 'average' per capita growth rate (we work with a general almost arbitrary function g), and sigmaepsilon(t) is the effect of environmental fluctuations (sigma>0, epsilon(t) standard white noise). There are two main stochastic calculus used to interpret the SDE, It? calculus and Stratonovich calculus. They yield different solutions and even qualitatively different predictions (on extinction, for example). So, there is a controversy on which calculus one should use. We will resolve the controversy and show that the real issue is merely semantic. It is due to the informal interpretation of g(x) as being an (unspecified) 'average' per capita growth rate (when population size is x). The implicit assumption usually made in the literature is that the 'average' growth rate is the same for both calculi, when indeed this rate should be defined in terms of the observed process. We prove that, when using It? calculus, g(N) is indeed the arithmetic average growth rate R(a)(x) and, when using Stratonovich calculus, g(N) is indeed the geometric average growth rate R(g)(x). Writing the solutions of the SDE in terms of a well-defined average, R(a)(x) or R(g)(x), instead of an undefined 'average' g(x), we prove that the two calculi yield exactly the same solution. The apparent difference was due to the semantic confusion of taking the informal term 'average growth rate' as meaning the same average.     

Molecules versus morphology? Not for the human cranium

Evolutionary investigations of human crania typically take a limited view of cranial diversity as they discount the possibility that human cranial variation could simply be due to the effects of random genetic drift, gene flow and mutation in favor of natural selection and developmental changes. Natural selection alone cannot explain similarities between patterns of cranial and molecular diversity observed in humans. It appears that the amount of phenotypic variance in the human cranium decreases at the population level as a function of distance from Sub-Saharan Africa much in the same way as observed for human molecular data.     

How Stable Is Stable? Function versus Community Composition

The microbial community dynamics of a functionally stable, well-mixed, methanogenic reactor fed with glucose were analyzed over a 605-day period. The reactor maintained constant pH and chemical oxygen demand removal during this period. Thirty-six rrn clones from each of seven sampling events were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) for the Bacteria and Archaea domains and by sequence analysis of dominant members of the community. Operational taxonomic units (OTUs), distinguished as unique ARDRA patterns, showed reproducible distribution for three sample replicates. The highest diversity was observed in the Bacteria domain. The 16S ribosomal DNA Bacteria clone library contained 75 OTUs, with the dominant OTU accounting for 13% of the total clones, but just 21 Archaea OTUs were found, and the most prominent OTU represented 50% of the clones from the respective library. Succession in methanogenic populations was observed, and two periods were distinguished: in the first, Methanobacterium formicicum was dominant, and in the second, Methanosarcina mazei and a Methanobacterium bryantii-related organism were dominant. Higher variability in Bacteria populations was detected, and the temporal OTU distribution suggested a chaotic pattern. Although dominant OTUs were constantly replaced from one sampling point to the next, phylogenetic analysis indicated that inferred physiologic changes in the community were not as dramatic as were genetic changes. Seven of eight dominant OTUs during the first period clustered with the spirochete group, although a cyclic pattern of substitution occurred among members within this order. A more flexible community structure characterized the second period, since a sequential replacement of a Eubacterium-related organism by an unrelated deep-branched organism and finally by a Propionibacterium-like species was observed. Metabolic differences among the dominant fermenters detected suggest that changes in carbon and electron flow occurred during the stable performance and indicate that an extremely dynamic community can maintain a stable ecosystem function.