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.
The possibility that environmentally induced phenotypes can be transmitted across generations has intrigued many evolutionary biologists, including myself and many of my collaborators. Such a process could contribute to adaptation, but on a faster timeframe than genetic changes. The conditions under which this sort of process should evolve seem to be relatively limited, though Kathleen provided insight into the kinds of circumstances in which transgenerational plasticity might be expected. I enjoyed this data-packed talk, which also outlined a very thorough experiment examining the effects of immediate and ancestral environments on the developmental transitions of Arabidopsis. The effects of progeny, parent, or grand-parent exposure differed among phenotypes and also depended on the genotype being considered. The study provides evidence that response to prior environments does affect fitness, and that the temporal persistence and environmental stability of these responses has a genetic component. So, the transmission of environmental affects across generations is likely an evolvable trait.
What role does plasticity play in adaptive evolution? One idea, termed “phenotypic accommodation,” is that plasticity mitigates the deleterious effects of new mutations, allowing them to persist in the population long enough to be harnessed by adaptive evolution. Nathan is exploring this idea using field crickets. In this species, male acoustic signals experience opposing selective pressures because song attracts females but also parasitoid flies. A “flatwing” male morph unable to produce song invaded the island of Kauai at the turn of the century, where it has quickly reached fixation. Given the lack of song, how are flatwing males finding females to reproduce? Enter IGEs, Bailey suggested. Using an impressive indoor chamber that simulated natural conditions, his lab has shown that flatwing males move around more throughout development. Flatwing males also increase movement more than normal-winged males do in response to a lack of song in their environment – an IGE that may compensate for inability to attract females. Flatwing males, but not normal-winged males, also differentially expressed many genes between environments with and without song. Based on these observations, Bailey proposed the novel term “plastic drive,” referring to genetic covariance between an adaptive trait and psi (Ψ). He argued that this type of genetic architecture could be important, despite probably being rare; it would allow new mutations under selection to facilitate their own evolution through pleiotropy and/or hitchhiking.
Niels Dingemanse & David Westneat
These co-presenters teamed up to contrast the explanations for the phenotypic similarity between social partners in two different passerines.
Using a long-term dataset on Bavarian great tits, Niels observed that behavioral and morphological traits were correlated among partners, but found no evidence that non-random partner choice or IGEs explain these correlations. Instead, partner similarity appears to result partially from joint reversible plasticity (e.g. partners responding similarly to their shared environment). Observer drift – that is, gradual changes in how observers measures traits over time – was also a major source of apparent similarity between partners. So, partner similarity is not always what it seems!
David presented data on biparental care in sparrows. Partner identity affected feeding rate, and the effect was asymmetrical between the sexes, with males being more sensitive to the identity of their partner. How much care an individual provided was not affected by how much care their partner provided, but IGEs mediated by other traits could be at work.
Niels and David agreed that indirect effects are difficult to identify in both species, and emphasized thinking about indirect effects as a form of plasticity generating within and among-individual variance that can manifest over multiple timescales. To grapple with this, they advised careful and statistically rigorous natural history to tease apart different explanations.
Mothers are pervasive, so we ought to examine how maternal-zygotic interactions affect adaptive evolution. To do this, Michael compared models of the evolution of plasticity in an abiotic environment versus a maternal genetic environment. In both scenarios, natural selection acts on offspring phenotype. In the latter scenario, a change in the environment (as it evolves) and the changing covariance between offspring genotype and the maternal environment also come into play. These additional processes accelerate the rate of evolutionary change. The greater the degree of linkage, the faster evolution proceeded. What I found somewhat surprising was that inbreeding also accelerated evolution but with less linkage (because inbreeding generates increased genetic variation amongmaternal families). Inbreeding was twice as effective as genetic architecture at accelerating evolution. This is noteworthy, as Michael emphasized, given how much emphasis is usually devoted to resolving genetic architecture.
Paternal care is widely observed, and its existence is frequently thought of as a puzzle. Both extra-pair copulations and trade-offs between paternal care and mating opportunities should act as obstacles to evolution of parental care. But, traditional thinking about parental care evolution is rooted in game theory models that assume evolution will optimize mean fitness. Courtney has complimented this literature by using population genetic models to move beyond the assumptions of game theory. Her theory provides counter-intuitive results, including that parental care can evolve relatively easily even when associated with mating costs, and that extra-pair copulations can increasethis parameter space under some conditions. These results are likely to motivate further work to characterize parental care, and wider use of population genetic models that explicitly consider IGEs.
Can IGEs help to explain why there is so much variation in fitness? Nancy is helping to answer this question using an impressive, long-term data set on Florida scrub jays from Archbold field station. As part of her analyses, she partitioned the effects of transmitted and non-transmitted alleles on offspring weight and survival. Nancy plans to use some cool tracking technology to relate IGEs to the social networks of these birds.
Maternal effects are important contributors to phenotypic variation, but the mechanisms involved remain poorly understood. In red deer, maternal immune transfer appears not to affect neonatal survival, and so variation in neonatal survival remains largely unexplained.
Audience effects, whereby the presence of an observer alters behavioral interactions, are widely documented. Does the genotype of the observer matter? Yes, at least in Drosophila simulans. The number of aggressive signals between males depended on the combination of observer sex and genotype.
How does social environment during development affect mating tactics? By rearing sailfin mollies in different social groups, Lange found evidence of both IGEs and non-genetic social effects, on different traits. So, different kinds of social cues may be important for shaping different behaviors.
Reflecting on the day – A common thread running through many of today’s talks was an emphasis on the fact that social interactions can impact phenotype in different ways over multiple timescales. Many of the talks so far have leveraged large-scale, long-term datasets, sophisticated theory, or ambitious experiments to help understand the temporal dynamics of IGEs.
Kathleen Donohue – Environmental effects within and across generations: a case study of phenology in an annual plant
A new faster way to adapt? Environmentally-induced phenotypes can accelerate adaptation to environments.
Which cues are better to predict the environment that exerts the selection? This depends on the mode of temporal environmental variation
Selection on environmental stability depends on how close to the optimum the phenotype is. Can temporal persistence and environmental stability evolve? yes , if there is enough genetic variation for them. This was tested on the Arabidopsis thaliana phenology and life cycle. This plant can exhibit different life cycles which depend on seed germination and flowering time. How do seasonal thermal cues influence life history traits of this plant, specifically germination and flowertime, looking at within-generational plasticity and trans-generational plasticity.
The experiment involved different environment treatments (Cool and Warm) between and within generations to have all possible combinations of environments.
There was no dissipation of the environmental effects, in fact the parent generation had the strongest effect on the response of the present generation, this is in the case of seed germination. In the case of flowering time, there was evidence of dissipation of effects but it is different between genotypes. The strength of the induction is not correlated with the strength of persistence, specifically a genetic association. There is genetic variation in the persistence of the environmental effects, meaning it can evolve. The environmental effects might persist across generations even if the phenotype is not transmitted.
There is less stability in the environmental effects across generations. In the case where the response to the present environment depends on the ancestral environment, there is variation in the way different genotypes responded, in both the case of seed germination and flowering time. In the case of germination time, there was both an antagonizing and reinforcing effect of the prior environment, but not in the case of flowering time which only exhibited reinforcing effects on the phenotype. In terms of fitness, response to prior environments does have influence meaning there is opportunity of evolutionary change.
Responses to ancestral environments appear to have a genetic basis, even if some of the genes don’t seem to respond to both present and ancestral environments.
These questions can be applied on a single individual gene to check for stability of parental effects, consistency in the response to environmental, reinforcement and antagonism.
Conclusion here is that induction, environmental persistence can have a genetic basis and are genetically variable. And response to present and ancestral environments can influence fitness.
Niels Dingemanse/ David Westneat – Adaptive perspectives on indirect effects: why we should consider the hierarchical multilevel structuring of phenotypes
Niels The focus here is on the optimal combinations between social partner phenotypes. The adaptive non-exclusive solutions here are: Non-random assortment, “joint” plasticity, response to partner’s phenotype (response can be to the repeatable and plastic parts of the phenotype). This was tested on the Bavarian great tit species (10 year data). The homologous traits of partners are correlated. Based on variance partitioning model, in both females and males individual identity effects are larger on most phenotypes but no partner identity effects were found. Partitioning sources of partner resemblance (non-random assortment + shared environment effects), using a bivariate mixed effect model. It seems based on results, there is strong environmental correlation between male and female phenotypes. Between the contributors of partner resemblance, results show that observers can have a strong effect on the correlation and there was no evidence of nonrandom assortment.
Dave Biparental care in Sparrows. Sparrows are similar to great tit in some aspects though they do breed more often in a year. There are several types of parental care, plastic to the environment and there are sex differences. How do partners impact each other in parental care? There were strong effects of individual identity on feed rate, however there was individual identity that had effects on the partner’s feeding rate but they were asymmetric. No evidence of an among-interaction due to care behavior between partners. Male and female feed rates are significantly positively correlated at the residual level. There are multiple pathways of social influence on feed rates, potentially there are other traits that are contributing to an interaction effect.
Indirect effects in both species are embedded and difficult to detect. These indirect effects are a form of phenotypic plasticity which have both within and among individual variance and this variance could manifest over different time scales. There is more work to be done on how the interactive effect of a joint phenotype impacts fitness of the individual (i.e. social selection and evolutionary feedbacks)
Nathan Bailey – Plastic Drive: reconsidering the influence of phenotypic plasticity on evolution
The role of plasticity in adaptive evolution and the role of IGE in the rapid adaptive responses in populations. Phenotypic accommodation is defined as adjustment in the phenotype if there is a new variant in the genome that can cause deleterious effects, and this is related to negative pleiotropy. What is the role of IGEs in this accommodation? The study system is the field cricket. This species on a few islands have evolved a male wing that is feminized which cannot make song because the wing is flatter, thus flatwing variant. This variant reached fixation on the island of Kauai, this is difficult to explain since there are costs involved in the loss of song, even if the flatwing protects from parasites. The first test was to see if the silent males just move more frequently in an effort to find mates and results show that there is an influence of the social environment. An interesting point is that the social interaction between two individuals doesn’t just involve the point of contact but even what precedes the actual interaction. It seems that some results show that having the flatwing allele can influence the distance covered by the nymph form of the cricket. So do IGEs play a role in mitigating the negative effect of the adaptive genotype (i.e. flatwing allele)? Is this a covariance between DGE and IGE for the same trait. According to Nathan, it’s more likely to be the covariance between the genetic effect of the trait and the genetic effect of psi, meaning the interaction coefficient. They term this: plastic drive. This is more likely when adaptive traits exert strong negative pleiotropy. Social runaway via IGEs makes social behavior particularly susceptible. This can contribute and even facilitate rapid adaptation.
Kathleen Donohue talked about how parental, or even grandparental, environmental conditions may impact the phenotypes of offspring in Arabidopsis. It was really interesting to see how some past environmental effects were carried over into the subsequent generations. However, the present environmental conditions also played a role by either having an antagonistic effect or allowing phenotypes to be expressed. The genotypes of the offspring also determined how past and present environments impact the phenotypes expressed.
Niels Dingemanse and David Westneat presented a combined talk on parental care and assortative mating in great tits and sparrows. Interestingly, the resemblance in mating partners has been found to be due to some environmental factor instead of assortative mating.
Nathan Bailey presented work on the influence of phenotypic plasticity on evolution. In Hawaii, some male crickets had a mutation that led to flat wings which would prevent predation, but also silenced them. A silenced cricket will not be able to attract a mate which leads to the expectation that, even though the cricket has a higher chance of survival, it will not reproduce. Surprisingly, the mutation prevailed as the crickets adapted by moving around more in order to encounter a mate. Additionally, the nymphs with a mutation would also move around more. I especially enjoyed the description of the room they designed to mimic the natural environment in order to track the movement of the crickets.