Sigrunn Eliassen

Current analyses do not resolve whether extra-pair paternity is male or female driven

Recent studies question the importance of indirect genetic effects in explaining female benefits of extra-pair matings in socially monogamous species. Compiling data on 14 wild bird species, Arnqvist and Kirkpatrick (Am Nat 165:S26–S37, 2005) estimated the average direct cost in terms or reduced parental care to be an order of magnitude larger than the potential effect of genetic benefits. This study has sparked a debate regarding potential confounding factors but no consensus appears to have been reached. Here we focus on the implicit assumption that all individuals face the same selective pressures and argue that this assumption is probably too strong in most cases. Using a theoretical model we show that when the amount of resources that a male provides depends on territory quality, his physical condition or prospects for alternative breeding opportunities, a female may respond to such differences by altering her mating behaviour. Such confounding factors may lead to direct fitness effects that result in negative correlations between paternal care and paternity even if females that produce extra-pair young experience a net benefit. Negative correlations can also result when males forcefully seek copulations and females resist them. We discuss the studies included in the analysis in this light, and conclude that current analyses on the net selective pressures remain uninformative. In addition to considering average effects across individuals and species we suggest giving attention to individual differences and the influence of ecological factors such as territory quality and predation pressures on female mating behaviour.

Quantifying the Adaptive Value of Learning in Foraging Behavior

The value of acquiring environmental information depends on the costs of collecting it and its utility. Foragers that search for patchily distributed resources may use experiences in previous patches to learn the habitat quality and adjust their behavior. We map the ecological landscape for the evolution of learning under a range of conditions, including both spatial and temporal heterogeneity. We compare the learning strategy with genetically fixed patch‐leaving rules and with strategies of foragers that have free and perfect information about their environment. The model reveals that the efficiency of learning is highest when low encounter stochasticity results in reliable estimates of patch quality, when there is no or little temporal change, and when there is little spatial variability. This partially contrasts with the value of learning, which is highest when there is temporal change, because flexible strategies may track the environmental trend, and when there is spatial variability, because there is a need to distinguish between good and bad patches. Learning rules with short‐term memory are beneficial when patch information is accurate and when there is temporal change, whereas learning rules that update slowly are generally more robust to spatial variability.

Evolution of growth in Gulf of St Lawrence cod

Fishing is often size selective such that the likelihood of capture increases with body size. It has therefore been postulated that fishing could favour evolution of slower growth because smaller size would reduce exposure to fishing gear (e.g. [Ricker 1981][1]). A recent study by Swain et al . ([

Effects of the Emotion System on Adaptive Behavior

A central simplifying assumption in evolutionary behavioral ecology has been that optimal behavior is unaffected by genetic or proximate constraints. Observations and experiments show otherwise, so that attention to decision architecture and mechanisms is needed. In psychology, the proximate constraints on decision making and the processes from perception to behavior are collectively described as the emotion system. We specify a model of the emotion system in fish that includes sensory input, neuronal computation, developmental modulation, and a global organismic state and restricts attention during decision making for behavioral outcomes. The model further includes food competition, safety in numbers, and a fluctuating environment. We find that emergent strategies in evolved populations include common emotional appraisal of sensory input related to fear and hunger and also include frequency-dependent rules for behavioral responses. Focused attention is at times more important than spatial behavior for growth and survival. Spatial segregation of the population is driven by personality differences. By coupling proximate and immediate influences on behavior with ultimate fitness consequences through the emotion system, this approach contributes to a unified perspective on the phenotype, by integrating effects of the environment, genetics, development, physiology, behavior, life history, and evolution.

Conditions favouring hard seededness as a dispersal and predator escape strategy

Summery The water-impermeable seed coat of ‘hard’ seeds is commonly considered a dormancy trait. Seed smell is, however, strongly correlated with seed water content, and hard seeds are therefore olfactionally cryptic to foraging rodents. This is the rationale for the crypsis hypothesis, which proposes that the primary functions of hard seeds are to reduce seed predation and promote rodent seed dispersal. We use a mechanistic model to describe seed survival success of plants with different dimorphic soft and hard seed strategies. The model is based on established empirical–ecological relationships of moisture requirements for germination and benefits of seed dispersal, and on experimentally demonstrated relationships between seed volatile emission, predation and predator escape. We find that water-impermeable seed coats can reduce seed predation under a wide range of natural humidity conditions. Plants with rodent dispersed seeds benefit from producing dimorphic soft and hard seeds at ratios where the anti-predator advantages of hard seeds are balanced by the dispersal benefits gained by producing some soft seeds. The seed pathway predicted from the model is similar to those of experimental seed-tracking studies. This validates the relevance and realism of the ecological mechanisms and relationships incorporated in the model. Synthesis. Rodent seed predators are often also important seed dispersers and have the potential to exert strong selective pressures on seeds to evolve methods of avoiding detection, and hard seeds seem to do just that. This work suggests that water-impermeable hard seeds may evolve in the absence of a dormancy function and that optimal seed survival in many environments with rodent seed predators is obtained by plants having a dimorphic soft and hard seed strategy.

Extra-pair mating and evolution of cooperative neighbourhoods.

A striking but unexplained pattern in biology is the promiscuous mating behaviour in socially monogamous species. Although females commonly solicit extra-pair copulations, the adaptive reason has remained elusive. We use evolutionary modelling of breeding ecology to show that females benefit because extra-pair paternity incentivizes males to shift focus from a single brood towards the entire neighbourhood, as they are likely to have offspring there. Male-male cooperation towards public goods and dear enemy effects of reduced territorial aggression evolve from selfish interests, and lead to safer and more productive neighbourhoods. The mechanism provides adaptive explanations for the common empirical observations that females engage in extra-pair copulations, that neighbours dominate as extra-pair sires, and that extra-pair mating correlates with predation mortality and breeding density. The models predict cooperative behaviours at breeding sites where males cooperate more towards public goods than females. Where maternity certainty makes females care for offspring at home, paternity uncertainty and a potential for offspring in several broods make males invest in communal benefits and public goods. The models further predict that benefits of extra-pair mating affect whole nests or neighbourhoods, and that cuckolding males are often cuckolded themselves. Derived from ecological mechanisms, these new perspectives point towards the evolution of sociality in birds, with relevance also for mammals and primates including humans.

Daytime Roosting and Habitat Preference of Capercaillie Tetrao urogallus Males in spring-the Importance of Forest Structure in Relation to anti-predator Behaviour

Radio-equipped adult capercaillie Tetrao urogallus males (N = 10) were tracked during April and May 1996–1997 in a coniferous forest in southeastern Norway, which has been subjected to clear-felling and replanting during the last five decades. With the use of radio-telemetry daytime habitat preference was investigated at two levels of scale: within home range and within forest stands inside home ranges. In addition, roosting habitat preference within stands was investigated by locating heaps of intestinal faeces, henceforth called roosting sites. Within forest stands, forest structure and visibility were measured at roosting sites (N = 94) and at random plots (N = 188). Within home ranges the birds used plantations and old naturally regenerated forest according to availability, and open bogs were avoided. Of the roosting sites, 90% were located underneath the low branches of Norway spruce Picea abies trees. For roosting within old naturally regenerated stands (> 70 years old) males preferred sites with higher tree density, higher vertical and horizontal cover and lower visibility than in the surrounding forest. In young and middle-aged plantations, on the contrary, roosting sites tended to have lower tree density (P = 0.118), but still seemed to have better cover than the surrounding forest (P = 0.117). The forest structure preference of roosting sites was reflected in the use of vegetation types within the old naturally regenerated forest. Because dense cover reduces the probability that the birds are detected by a predator, but at the same time increases the risk of being killed once detected, capercaillie males have to compromise between shelter and outlook. Our data indicate that males prefer good cover at the expense of good overview of the surroundings when selecting roosting sites, and that tree density is usually too dense in younger plantations, probably because outlook is reduced and flying obstructed.

The emotion system promotes diversity and evolvability

Studies on the relationship between the optimal phenotype and its environment have had limited focus on genotype-to-phenotype pathways and their evolutionary consequences. Here, we study how multi-layered trait architecture and its associated constraints prescribe diversity. Using an idealized model of the emotion system in fish, we find that trait architecture yields genetic and phenotypic diversity even in absence of frequency-dependent selection or environmental variation. That is, for a given environment, phenotype frequency distributions are predictable while gene pools are not. The conservation of phenotypic traits among these genetically different populations is due to the multi-layered trait architecture, in which one adaptation at a higher architectural level can be achieved by several different adaptations at a lower level. Our results emphasize the role of convergent evolution and the organismal level of selection. While trait architecture makes individuals more constrained than what has been assumed in optimization theory, the resulting populations are genetically more diverse and adaptable. The emotion system in animals may thus have evolved by natural selection because it simultaneously enhances three important functions, the behavioural robustness of individuals, the evolvability of gene pools and the rate of evolutionary innovation at several architectural levels.

Optimal mate choice patterns in pelagic copepods

The importance of sexual selection for the evolution, dynamics and adaptation of organisms is well known for many species. However, the topic is rarely studied in marine plankton, the basis of the marine food web. Copepods show behaviors that suggest the existence of sexually selected traits, and recent laboratory experiments identified some selected morphological traits. Here, we use a ‘life history-based’ model of sex roles to determine the optimal choosiness behavior of male and female copepods for important copepod traits. Copepod females are predicted to be choosy at population densities typically occurring during the main breeding season, whereas males are not. The main drivers of this pattern are population density and the difference in non-receptive periods between males and females. This suggests that male reproductive traits have evolved mainly due to mate competition. The model can easily be parameterized for other planktonic organisms, and be used to plan experiments about sexual selection.

The crypsis hypothesis explained: a reply to Jayasuriya et al. (2015)

In imbibing seeds, resumption of metabolism leads to the unavoidable release of volatile by-products that are perceived as cues by rodent seed predators. The crypsis hypothesis proposes that the primary function of a water-impermeable, hard seed coat is to reduce rodent seed predation by rendering seeds olfactorily cryptic. In an opinion paper, Jayasuriya et al. (2015) find the crypsis hypothesis unscientific and ‘not consistent with Darwins theory of evolution by natural selection’. It is unfortunate that Jayasuriya et al. (2015) did not appreciate that the crypsis hypothesis offers an alternative explanation for the evolution of water-impermeable seeds: released seed volatiles are cues used by rodents to locate seeds, and variation in seed-coat permeability leading to differences in seed volatile release represents the variable under selection. Furthermore, the sealing of water-impermeable seed coats imposes a cost of increased generation time and, therefore, dormancy-release mechanisms are expected to subsequently evolve in response to local environmental conditions. We also disagree with most other claims by Jayasuriya et al. (2015), who failed to appreciate how species with dimorphic seeds – one morph with permeable and the other with impermeable seed coats – benefit from rodent caching behaviour and population dynamics. We welcome this opportunity to clarify and elaborate on key features and the evolution of water-impermeable seed coats according to the crypsis hypothesis.