Meet the bloggers:
Mitchel Daniel is a postdoctoral fellow at Florida State University. He is an evolutionary and behavioral ecologist, and is especially interested in sexual selection, kin selection, and kin recognition. Follow Mitchel’s work @MitchelJDaniel.
Walid Mawass is an evolutionary geneticist, currently a PhD candidate at the Université du Québec à Trois-Rivières, studying the evolution of life histories in French-Canadian historical populations using quantitative genetic and genomic approaches. Walid is interested in evolutionary genetics theory in general, with a current focus on contemporary evolution in natural populations and the role of interactions between environment and genetics on evolutionary trajectories. Follow Walid’s work @MawassWalid.
Sabrina Heiser is a PhD Candidate in Dr. Charles D. Amsler’s lab at the University of Alabama at Birmingham. Her research focuses on the factors driving the geographic distribution of chemical defenses in a red seaweed. For her sample and data collection, she gets to go and SCUBA dive in Antarctica. She received her B.Sc. in Marine Biology from Plymouth University (UK) and is originally from Germany. Follow her adventures on her website.
Competition is fundamental to adaptive evolution, and is rife with DGEs and IGEs. These genetic effects are usually combined additively in models, but is it important to consider non-additivity? Alistair presented a series of hypothetical and empirical examples that drove home the importance of non-additivities in contest competition, including GxG interactions – that is, genetic variance in psi. One way to think about GxG interactions is as the place were IGEs meet GxE interactions. GxG interactions probably play an important role in the evolution of social plasticity, but not much empirical work has explored this yet.
When genetic variance in fitness exists, fitness tends to evolve upwards; but, it can’t increase forever because of limited resources. Given resource limitation, genes that help individuals to acquire resources will deprive others of those resources. This (approximately) zero-sum game should result in negative correlations between DGEs and IGEs. To test this idea, Andrew made use of a very cool natural experiment provided by the Kluane red squirrel and the white spruce cones on which they feed. White spruce exhibit mast years in which cones are plentiful, and non-mast years in which this food source is scarce. During non-mast years, there was a negative relationship between an individual squirrel’s survival and the survival of others in their neighborhood; this relationship disappeared during mast years. Similar patterns were also present for annual reproductive success. Thus, IGEs on fitness may constrain evolution – depending on resource availability.
GxG and GxE interactions are complicated and difficult to predict. There are soooooo many gene interactions to test. How, then, can we study epistasis? One way is to focus on a subset of these interactions: mitochondrial and nuclear interactions. By looking at this across multiple environments, we can start to understand GxGxE. In Drosophila, patterns of epistasis were affected by diet, with greater amounts of protein reducing epistasis. Gene expression data showed that more overlap than expected by chance between GxG and GxE genes, so these two types of interactions are not independent. I liked David’s suggestion to think of GxG interactions as one gene altering the cellular environment of another gene – visualizing the genome as part of the cellular environment in this way is an interesting perspective to take.
Sara Raj Pant
Extrapair reproduction (EPR) is widespread. It is easy to imagine why males engage in EPR, but explaining female EPR is more challenging. One adaptive hypothesis for this behavior is that females gain additive genetic benefits through EPR by mating with males that have “good genes”. A requirement for the “good genes” hypothesis to work is high heritability of EPR. Sara has tested this assumption by applying a quantitative genetics approach to the Seychelles warbler. A quantitative genetics approach revealed that EPR has significant but relatively low repeatability and heritability. Consequently, EPR is unlikely to evolve via additive genetic benefits. Other processes that do not require high heritability are worth exploring. These results were interesting, and line up with literature on many other organisms suggesting that additive genetic benefits often cannot explain mating preferences.
Are groups more than just the sum of their genes? Justin helped to address this question by examining how the genetic composition of pharaoh ant groups affects collective behavior. His experiment made use of 36 colonies (an impressive sample size for a eusocial study system) complete with a pedigree for between colony relatedness (also a useful rarity). He observed the collective behavior of mixed groups of ants, each containing individuals from different pairs of colonies. These genetic combinations affected aggression and exploratory behavior in unpredictable ways; any one colony had disparate effects on the behavior of the mixed group depending on which colony it was mixed with! This suggests substantial GxG epistasis, meaning that non-additive genetic effects are important to consider when trying to predict group behavior. There was also evidence that relatedness matters, as less aggression was observed when the relatedness between colonies was higher.
Why is there so much genetic variation in ecologically-relevant traits despite erosive processes? One possible explanation is a rare male mating advantage. Rare male advantage can arise from females preferring to mate with males that have rare or novel traits. Does male-male competition also contribute? Rare male advantage could result from males competing more intensely with similar rivals. Contrary to this idea, Alexa observed that male guppies direct more competition towards rivals with color patterns dissimilar to their own. This should erode variation, and could potentially interfere with female preference for rare or novel-looking males.
The Mexican tetra has a surface form and a derived cave form, making it a great system for studying evolutionary transitions. Mateo exposed surface form fish to complete darkness to mimic the cave environment, and found 356 differentially expressed genes. About half of these genes differed in expression in the same direction found when comparing the surface and cave forms, possibly indicating adaptive plasticity. In the future, Mateo will explore the molecular mechanisms controlling this plasticity.
Alastair Wilson – DGExIGE Genetics of animal contest: from DGE+IGE to DGExIGE
A quantitative genetic view into animal contests. It is important to gain insight from other disciplines and their models of the reality of a certain phenomenon. In this case, this concerns the role of IGEs in animal contests. There has been a lot of focus on the cooperation and altruism side of interaction between individuals, though competition is as interesting. Animal contests are in fact simple, where from a dyadic contest there is a winner and loser, where the winner acquires resources and this positively affects their fitness through their growth and life history. In this context, we can envisage DGE on the contest behavior and the opponent’s genotype leading to IGEs on the same behavior. Wilson used a variance partitioning model that includes IGEs of the opponent on the focal individual’s phenotype. Empirical results based on deer mice showed additive genetic variance in contest behaviors. In the red deer, results did show positive selection on contest winning. Evolutionary dynamics depend on both DGE and IGE. IGEs can constrain or facilitate evolutionary change. There are results that show that the role of IGE in resource-acquisition traits can constrain evolutionary change by limiting the amount of additive genetic variance available to selection.
Cooperative antipredator behavior in a fission-fusion society of guppies. In this type of society, we can observe predator inspection, long term affiliations between individuals, and cooperation between non-relatives is more prevalent. There is already evidence for IGEs influencing cooperative behavior in inbred strains, especially in the case of shoaling. In the case of wild guppies, what kind of interacting phenotypes and IGEs can we observe? First, the interaction coefficient psi was measured through 4 sequential interactions with 2 patterns for both females and males. Results show that psi in fact varies with sex, predation regime, and river of origin of wild guppies. Interestingly, the partner’s mean distance to the predator was the most influential aspect of partner behavior on focal individuals’ behavior. Based on the trials, it seems that some fish may reverse their response to similar partner behavior. This might suggest that the fish can respond differently to different aspects of the partner’s phenotype. Moreover, psi can vary in direction as well across some populations. These results point to the possibility of DGExIGE at play here. So the interest here is to see how individuals can vary in their influence on the focal individual. Additionally, responsiveness of the focal individual might vary as well to the same IGE from the same social partner. The focus is on the physiological underpinnings of the variation in both responsiveness and influence. A useful element of fish biology is that they broadcast their physiological state through hormones secreted through their gills and pheromones that can cause partners to change behavior. Experiments did show that in inbred strains do differ in the chemical environment they provide to their social partners. Next, an experiment was conducted to see if it is possible to use endocrine disrupting compounds to change guppy physiology of the social partner and consequently modulate the behavior of the focal fish. Results indeed show that altering partner phenotype through these compounds also changes focal behavior. Another aspect is sensitivity to visual and chemical partner signals could influence cooperation between partners through modulating the cues of cooperation. Based on the results, fish which were more acute to visual cues were more cooperative and exhibited more anti-predator behavior. Hence, what mechanisms underlie responsiveness, for example, hormones can trigger gene expression to make more hormone receptors and thus lead to behavioral changes. An experiment on different inbred strains did show more expression of hormonal receptors in more responsive strains. Experimental results reveal that short term manipulation of estrogen receptors can change visual acuity in guppies, and this is the case in both males and females. This result however is against what was expected. Additionally, manipulating estrogen receptors expression can influence shoaling. Though there is still lack of evidence for how visual acuity is affected by estrogen receptors expression, there is enough empirical evidence showing the sequence of processes that can underlie the interaction between the social partner and the focal individual leading to cooperation.
Andrew McAdam presented his research on annual fitness in red squirrels. Most red squirrels do not disperse far, and social interactions may indirectly impact their fitness. He looked at this in terms of food availability in mast years compared to non-mast years. In non-mast years, the fitness, measured in survival and reproduction, was negatively impacted by the fitness of others. Whereas in mast years this was not the case which allows potential genetic variation in fitness to not be constrained as such by indirect genetic effects through social interactions.
David Rand talked about his work on gene by gene by environment interactions in the model system Drosophila. Genotype by environment interactions can be good or bad, depending on the conditions of the environment as the environment can directly impact cells and gene performance. The question is how gene – gene interactions (epistasis) are impacted by environmental conditions. It appeared that many epistatic interactions were also impacted by the environment.
The work of Bronwyn Bleakley is looking at how guppy phenotypes interact in nature. Fish are known to chemically broadcast their physiological state through hormones such as estrogen. Estrogen signaling influences the ability of guppies to see. Her work has shown that this further impacts the cooperative antipredator behavior which means that estrogen signaling can have a direct as well as potentially indirect genetic effect.
Justin Walsh’s work focused on the collective behavior of ant groups and to which degree it is impacted by genotypes. Very impressively, the lab he was working in allowed him to use ants for which the pedigree up to the F14 generation was known. He compared homogenous and mixed genotype groups and found evidence for genotype x genotype epistasis. Overall, it appeared that more related individuals were less aggressive towards each other. It was also interesting to hear that in nature, sometimes colonies combine, making this a feasible scenario.