Runaway evolution from male-male competition

Wondrously elaborate weapons and displays that appear to be counter to ecological optima are widespread features of male contests for mates across the animal kingdom. To understand how such diverse traits evolve, here we develop a quantitative genetic model of sexual selection for a male signaling trait that mediates aggression in male‐male contests and show that an honest indicator of aggression can generate selection on itself by altering the social environment. This can cause selection to accelerate as the trait is elaborated, leading to runaway evolution. Thus, an evolving source of selection provided by the social environment is the fundamental unifying feature of runaway sexual selection driven by either male‐male competition or female mate choice. However, a key difference is that runaway driven by male‐male competition requires signal honesty. Our model identifies simple conditions that provide clear, testable predictions for empirical studies using standard quantitative genetic methods.

Mite load predicts the quality of sexual color and locomotor performance in a sexually dichromatic lizard

Since Darwin, the maintenance of bright sexual colors has recurrently been linked to mate preference. However, the mechanisms underpinning such preferences for bright colors would not be resolved for another century. Likely, the idea of selection for colors that could decrease the chances of survival (e.g., flashy colors that can inadvertently attract predators) was perceived as counterintuitive. It is now widely accepted that these extreme colors often communicate to mates the ability to survive despite a "handicap" and act as honest signals of individual quality when they are correlated with the quality of other traits that are directly linked to individual fitness. Sexual colors in males are frequently perceived as indicators of infection resistance, in particular. Still, there remains considerable discord among studies attempting to parse the relationships between the variables associating sexual color and infection resistance, such as habitat type and body size. This discord may arise from complex interactions between these variables. Here, we ask if sexual color in male Florida scrub lizards (Sceloporus woodi) is an honest signal of resistance to chigger mite infection. To this end, we use linear modeling to explore relationships between mite load, different components of sexual color, ecological performance, body size, and habitat type. Our data show that that the brightness of sexual color in scrub lizards is negatively associated with the interaction between mite load and body size, and scrub lizards suffer decreased endurance capacity with increases in mite load. Our data also indicate that mite load, performance, and sexual color in male scrub lizards can vary between habitat types. Collectively, these results suggest that sexual color in scrub lizards is an honest indicator of individual quality and further underscore the importance of considering multiple factors when testing hypotheses related to the maintenance of sexual color.

Are body size and volatile blends honest signals in orchid bees?

Secondary sexual traits may convey reliable information about males’ ability to resist pathogens and that females may prefer those traits because their genes for resistance would be passed on to their offspring. In many insect species, large males have high mating success and can canalize more resources to the immune function than smaller males. In other species, males use pheromones to identify and attract conspecific mates, and thus, they might function as an honest indicator of a male's condition. The males of orchid bees do not produce pheromones. They collect and store flower volatiles, which are mixed with the volatile blends from other sources, like fungi, sap and resins. These blends are displayed as perfumes during the courtship. In this study, we explored the relationship between inter‐individual variation in body size and blend composition with the males’ phenoloxidase (PO) content in Euglossa imperialis. PO content is a common measure of insect immune response because melanine, its derived molecule, encapsulates parasites and pathogens. Body size and blend composition were related to bees’ phenolic PO content. The inter‐individual variation in body size and tibial contents could indicate differences among males in their skills to gain access to some compounds. The females may evaluate their potential mates through these compounds because some of them are reliable indicators of the males’ capacity to resist infections and parasites.

Kin Discrimination in Protists: From Many Cells to Single Cells and Backwards

During four decades (1960-1990s), the conceptualization and experimental design of studies in kin recognition relied on work with multicellular eukaryotes, particularly Unikonta (including invertebrates and vertebrates) and some Bikonta (including plants). This pioneering research had an animal behavior approach. During the 2000s, work on taxa-, clone- and kin-discrimination and recognition in protists produced genetic and molecular evidence that unicellular organisms (e.g. Saccharomyces, Dictyostelium, Polysphondylium, Tetrahymena, Entamoeba and Plasmodium) could distinguish between same (self or clone) and different (diverse clones), as well as among conspecifics of close or distant genetic relatedness. Here, we discuss some of the research on the genetics of kin discrimination/recognition and highlight the scientific progress made by switching emphasis from investigating multicellular to unicellular systems (and backwards). We document how studies with protists are helping us to understand the microscopic, cellular origins and evolution of the mechanisms of kin discrimination/recognition and their significance for the advent of multicellularity. We emphasize that because protists are among the most ancient organisms on Earth, belong to multiple taxonomic groups and occupy all environments, they can be central to reexamining traditional hypotheses in the field of kin recognition, reformulating concepts, and generating new knowledge.

Individual differences affect honest signalling in a songbird

Research in the past decade has established the existence of consistent individual differences or 'personality' in animals and their important role in many aspects of animal behaviour. At the same time, research on honest signalling of aggression has revealed that while some of the putative aggression signals are reliable, they are only imperfectly so. This study asks whether a significant portion of the variance in the aggression-signal regression may be explained by individual differences in signalling strategies. Using the well-studied aggressive signalling system of song sparrows (Melospiza melodia), we carried out repeated assays to measure both aggressive behaviours and aggressive signalling of territorial males. Through these assays, we found that aggressive behaviours and aggressive signalling were both highly repeatable, and moreover that aggressive behaviours in 2009-2010 predicted whether the birds would attack a taxidermic mount over a year later. Most significantly, we found that residual variation in signalling behaviours, after controlling for aggressive behaviour, was individually consistent, suggesting there may be a second personality trait determining the level of aggressive signalling. We term this potential personality trait 'communicativeness' and discuss these results in the context of honest signalling theories and recent findings reporting prevalence of 'under-signalling'.

The evolution of honest queen pheromones in insect societies

Social insect workers are often capable of reproduction, but will not do so in the presence of a fertile queen. In large societies, queens are expected to produce a pheromone that honestly signals her dominance and/or fertility, to which workers respond by suppressing the development of their ovaries and by preventing other workers from reproducing (worker policing). However, what maintains the honesty of such queen pheromones is still under discussion. The explanation that an honest queen signal evolves simply because it serves the interest of all colony members does not seem to hold, since it is undermined by the fitness benefits of direct reproduction of workers at the individual level. A better explanation may be found in the idea that queen pheromones are difficult to produce for subordinate individuals, either because policing workers attack them, or because queen pheromones are intrinsically costly chemicals. Here, I discuss some of the arguments for and against these hypotheses and the evolutionary scenarios that each would lead to.